Heart sound and coronary murmur detection device and detection method

Abstract

The present invention discloses a heart sound and coronary artery murmur detection device, comprising: a pickup placed at the projection positions of the coronary arteries on the body surface, the projection positions including the positions near the sternal body in the third intercostal space on the left side of the human body, the positions near the sternal body in the fourth intercostal space, the positions near the sternal body in the third intercostal space on the right side of the human body, and the positions near the sternal body in the fourth intercostal space, the pickup being used for collecting a first sound signal; a filter amplification circuit, the input end of which is connected to the output end of the pickup, and which is used for extracting and amplifying the coronary artery murmur signal to form a first coronary artery murmur signal. By using the above device to synchronously collect the first sound signals at multiple positions, it is ensured that the murmurs in the complete cardiac coronary artery region are effectively captured; by extracting and processing the coronary artery murmur signal through the filter amplification circuit, it is convenient to realize the early screening of coronary heart disease according to the coronary artery murmur signal. The present invention also discloses a heart sound and coronary artery murmur detection method.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and particularly to a device and a method for detecting heart sounds and coronary murmurs. Background Art

[0002] According to the "Report on Cardiovascular Health and Diseases in China 2022", currently, the mortality rate of cardiovascular diseases ranks first among various diseases both in rural and urban areas and has become the leading cause of death among urban and rural residents. Coronary heart disease is the main cause of death among cardiovascular diseases. It is estimated that the current number of cardiovascular disease patients is 330 million, among which the number of coronary heart disease patients is 11.39 million, ranking second only to hypertension and stroke.

[0003] However, all the above-mentioned coronary heart disease assessment methods require large medical devices and well-trained operators, so they are mainly concentrated in large hospitals and the examination costs are expensive. For most patients, they will only go to the hospital for medical treatment when they first experience severe chest pain symptoms. Even worse, some patients will have a myocardial infarction when they first experience severe chest pain, missing the best intervention time for treatment means. Therefore, a large number of potential coronary heart disease patients need a non-invasive, affordable and easy-to-operate early screening device for coronary heart disease.

[0004] Heart sound is a physiological sound signal containing rich information that can be obtained from the human body, reflecting the movement status of the myocardium, valves and blood vessels. The main body of the heart is composed of myocardium, which is overall conical and is an important organ that promotes the blood circulation of the whole body. A cycle of heart activity is called a cardiac cycle, which includes one contraction and one relaxation. Heart sound is the sound generated when the heart beats and is a mechanical vibration generated by the closure of heart valves, myocardial contraction, blood hitting the blood vessel wall and the ventricular wall. The heart beat sound of a normal person is clear and regular; while the heart beat of a person with heart disease may not follow the normal rhythm or contain murmurs.

[0005] However, the existing technologies focus on obtaining the overall signals of heart sounds and murmurs and analyzing the overall signals. That is to say, the existing technologies do not extract the murmur signals from the overall signals and analyze the murmur signals. In other words, the existing technologies only focus on the overall signals, especially the heart sound signals in the overall signals, and do not focus on the murmur signals. For example, Chinese Utility Model Patent CN210383921U discloses a heart sound detection device and its detection system. The heart sound detection device includes: a pickup, which is used to collect the heart sound signals at the heart or the sound signals at the carotid artery after closely attaching to the skin of the subject; a microcontroller, which is electrically connected to the pickup and receives the signal output of the pickup. A short-range wireless communication module, which is electrically connected to the microcontroller and wirelessly transmits the detection data output via the microcontroller. A power supply, which is configured to supply power to the pickup, the microcontroller, and the short-range wireless communication module. This heart sound detection device can be widely used at an acceptable price and does not require professional equipment. As long as a mobile terminal that is readily available, such as a mobile phone or a tablet computer, is used, the detection of heart sound signals can be achieved to solve the problems of inconvenient use, insufficient functions of the detection device, and high cost existing in the existing heart sound detection devices for the diagnosis and evaluation of coronary artery diseases.

[0006] Furthermore, the existing technologies also disclose technical solutions for obtaining the overall signals of heart sounds and murmurs and analyzing the heart based on the murmur signals. However, the murmurs obtained in the existing technologies are mostly the murmurs of heart valves, and heart valve diseases are analyzed based on the murmurs of heart valves. For example, Chinese Invention Patent Authorization CN116019480B discloses a method and device for identifying tricuspid stenosis by fusing the temporal characteristics of heart sound and electrocardiogram signals. According to the phonocardiogram and electrocardiogram collected from the detected person, heart valve diseases are determined by analyzing the murmurs that appear in the systolic or diastolic phase of the heart sound signals. Another example is Chinese Invention Patent Authorization CN102283670B, which discloses a method and device for quantitative analysis of heart sound signals. This method for quantitative analysis of heart sound signals collects the heart sound signals of the aortic valve, pulmonary valve, mitral valve, and tricuspid valve, respectively extracts the characteristic parameters in the collected heart sound signals, and calculates the heart sound energy in different periods. According to the percentage of the heart sound energy in each period in the entire cycle, the heart sound intensity, the time and intensity of the murmur appearance can be determined, and thus the quantitative analysis of the heart sound signals can be simply and conveniently realized, providing diagnostic parameters for the diagnosis of common cardiovascular diseases in clinical practice.

[0007] Coronary murmur signals are essentially sound signals generated when turbulent blood flow passes through narrowed coronary arteries. The vibration generated by the turbulent flow hitting the blood vessel wall is transmitted to the body surface through the cardiothoracic conduction system. Since coronary murmur signals are attenuated by chest muscles and adipose tissue after generation and are also easily interfered by murmurs from other organs in the thoracic and abdominal cavities, their intensity is extremely weak compared to normal heart sounds. Due to the very weak coronary murmur, it is difficult to collect. In the existing technology, there is a lack of devices or methods for collecting heart sound signals and coronary murmur signals, processing and accurately analyzing the coronary murmur signals to analyze coronary artery lesions. Summary of the Invention

[0008] The purpose of the present invention is to provide a device and method for collecting heart sound signals and coronary murmur signals, processing and analyzing the coronary murmur signals to analyze coronary artery lesions.

[0009] In a first aspect, the heart sound and coronary murmur detection device provided by the present invention can collect heart sound signals and weak coronary murmur signals, extract the coronary murmur signals, and perform processing such as amplification and filtering on the coronary murmur signals. Based on the processed coronary murmur signals, early screening of coronary heart disease is realized.

[0010] To solve the above technical problems, an embodiment of the present invention discloses a heart sound and coronary murmur detection device, including: a pickup, which is placed at the projection position of the coronary artery on the body surface. The projection positions include: the position near the sternal body in the third intercostal space on the left side of the human body and the position near the sternal body in the fourth intercostal space, as well as the position near the sternal body in the third intercostal space on the right side of the human body and the position near the sternal body in the fourth intercostal space. The pickup is used to collect a first sound signal, and the first sound signal includes a heart sound signal and a coronary murmur signal; a filter amplification circuit, the input end of the filter amplification circuit is connected to the output end of the pickup, and the filter amplification circuit is used to extract the coronary murmur signal and amplify the coronary murmur signal to form a first coronary murmur signal.

[0011] By adopting the above technical solution, by setting a highly sensitive pickup at the projection position of the coronary artery on the body surface, synchronous collection of heart sound signals and weak coronary murmur signals at multiple positions of the human body is realized, ensuring effective capture of murmurs in the complete coronary artery region of the heart; through the filter amplification circuit, extraction and processing of the coronary murmur signal are realized, facilitating early screening of coronary heart disease based on the processed coronary murmur signal.

[0012] According to another specific embodiment of the present invention, the pickup includes at least one of an electret microphone, a piezoelectric accelerometer, and a piezoelectric sensor, or the filter amplification circuit includes an active filter and an operational amplifier, wherein the active filter can further be a Sallen-Key filter.

[0013] According to another specific embodiment of the present invention, the first sound signal is an alternating current signal, and the heart sound and coronary murmur detection device includes an AC coupling circuit. The input end of the AC coupling circuit is connected to the output end of the pickup, and the AC coupling circuit is used to remove the DC component in the first sound signal to form a second sound signal.

[0014] According to another specific embodiment of the present invention, the heart sound and coronary murmur detection device includes a fixed gain adjustment circuit. The input end of the fixed gain adjustment circuit is connected to the output end of the AC coupling circuit, and the fixed gain adjustment circuit is used to amplify the second sound signal to form a third sound signal; the output end of the fixed gain adjustment circuit is connected to the input end of the filter amplification circuit. Alternatively, the heart sound and coronary murmur detection device includes an automatic gain adjustment circuit. The input end of the automatic gain adjustment circuit is connected to the output end of the filter amplification circuit, and the automatic gain adjustment circuit is used to receive the first coronary murmur signal output from the output end of the filter amplification circuit and adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal.

[0015] According to another specific embodiment of the present invention, the heart sound and coronary murmur detection device includes an overload detection module. The input end of the overload detection module is connected to the output end of the automatic gain adjustment circuit, and the overload detection module is used to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain adjustment circuit exceeds a preset voltage threshold: if the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, the output end of the overload detection module outputs an overload signal; if the peak value of the voltage of the second coronary murmur signal does not exceed the preset voltage threshold, the output end of the overload detection module outputs an un-overload signal. Alternatively, there is an analog-to-digital conversion circuit. The input end of the analog-to-digital conversion circuit is connected to the output end of the automatic gain adjustment circuit, and the analog-to-digital conversion circuit is used to receive the second coronary murmur signal output from the output end of the automatic gain adjustment circuit and convert the second coronary murmur signal into a digital signal.

[0016] According to another specific embodiment of the present invention, the heart sound and coronary murmur detection device includes a microelectronic control circuit. The input end of the microelectronic control circuit is connected to the output end of the overload detection module, and the microelectronic control circuit is used to receive the overload signal output from the output end of the overload detection module; the output end of the microelectronic control circuit is connected to the input end of the automatic gain adjustment circuit, and the microelectronic control circuit is used to control the automatic gain adjustment circuit to execute receiving the first coronary murmur signal output from the output end of the filter amplification circuit and adjusting the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal according to the overload signal; the input end of the microelectronic control circuit is further connected to the output end of the analog-to-digital conversion circuit, and the microelectronic control circuit is used to receive the digital signal output from the output end of the analog-to-digital conversion circuit.

[0017] According to another specific embodiment of the present invention, the heart sound and coronary murmur detection device includes a PCB. The PCB includes a power layer and a ground layer. The PCB is provided with a first copper cladding cutting area that is not connected to the power layer and the ground layer. The PCB includes an analog signal area and a digital signal area, and the analog signal area and the digital signal area are grounded at a single point. Preferably, the analog signal area includes a microphone, an AC coupling circuit, a fixed gain adjustment circuit, a filter amplification circuit, and an automatic gain adjustment circuit connected in sequence. Preferably, the digital signal area includes an overload detection module, an analog-to-digital conversion circuit, and a microelectronic control circuit. Preferably, the first copper cladding cutting area is provided between the analog signal area and the digital signal area, so that electrical isolation is achieved between the analog signal area and the digital signal area. The heart sound and coronary murmur detection device includes a power supply circuit, and the first copper cladding cutting area does not affect the connection between the analog signal area and the power supply circuit, nor does it affect the connection between the digital signal area and the power supply circuit. Or, the filter amplification circuit includes an operational amplifier. The PCB is provided with a second copper cladding cutting area that is not connected to the power layer and the ground layer, and the second copper cladding cutting area is provided below the output pin, the non-inverting input pin, and the inverting input pin of the operational amplifier.

[0018] According to another specific embodiment of the present invention, the Sallen-Key filter includes a first capacitor. Preferably, the first capacitor is an NPO type capacitor.

[0019] According to another specific embodiment of the present invention, the AC coupling circuit includes a second capacitor. Preferably, the second capacitor is an NPO type capacitor.

[0020] In a second aspect, an embodiment of the present invention discloses a method for detecting heart sounds and coronary murmurs. Detection is performed using the heart sound and coronary murmur detection device in any of the embodiments in the first aspect described above, and includes: using a microphone, placing the microphone at the projection positions of the coronary arteries on the body surface, and the projection positions include: the position near the sternal body in the third intercostal space on the left side of the human body and the fourth intercostal space near the sternal body, as well as the position near the sternal body in the third intercostal space on the right side of the human body and the fourth intercostal space near the sternal body. Using the microphone to collect the first sound signals at the position near the sternal body in the third intercostal space on the left side of the human body and the fourth intercostal space near the sternal body, as well as the position near the sternal body in the third intercostal space on the right side of the human body and the fourth intercostal space near the sternal body. The first sound signals include heart sound signals and coronary murmur signals. Using the filter amplification circuit to extract the coronary murmur signals and amplify the coronary murmur signals to form the first coronary murmur signals.

[0021] By adopting the above technical solution, synchronous acquisition of heart sound signals and weak coronary artery murmur signals at multiple positions of the human body is achieved, ensuring effective capture of murmurs in the coronary artery region of the complete heart; through the filter amplification circuit, extraction and processing of the coronary artery murmur signals are realized, facilitating early screening of coronary heart disease based on the processed coronary artery murmur signals.

[0022] According to another specific embodiment of the present invention, the heart sound and coronary artery murmur detection method further includes: removing the DC component in the first sound signal by using an AC coupling circuit to form a second sound signal.

[0023] According to another specific embodiment of the present invention, the heart sound and coronary artery murmur detection method further includes: amplifying the second sound signal by using a fixed gain adjustment circuit to form a third sound signal.

[0024] According to another specific embodiment of the present invention, the heart sound and coronary artery murmur detection method further includes: adjusting the voltage value of the first coronary artery murmur signal to a preset voltage range by using an automatic gain adjustment circuit to form a second coronary artery murmur signal.

[0025] According to another specific embodiment of the present invention, the heart sound and coronary artery murmur detection method further includes: using an overload detection module to detect whether the peak value of the voltage of the second coronary artery murmur signal output by the automatic gain adjustment circuit exceeds a preset voltage threshold: if the peak value of the voltage of the second coronary artery murmur signal exceeds the preset voltage threshold, an overload signal is output through the overload detection module; if the peak value of the voltage of the second coronary artery murmur signal does not exceed the preset voltage threshold, an underload signal is output through the overload detection module.

[0026] According to another specific embodiment of the present invention, the heart sound and coronary artery murmur detection method further includes: if the peak value of the voltage of the second coronary artery murmur signal exceeds the preset voltage threshold, an overload signal is output through the overload detection module, and the steps of adjusting the voltage value of the first coronary artery murmur signal to a preset voltage range by using the automatic gain adjustment circuit to form a second coronary artery murmur signal; using the overload detection module to detect whether the peak value of the voltage of the second coronary artery murmur signal output by the automatic gain adjustment circuit exceeds the preset voltage threshold are repeated until an underload signal is output through the overload detection module, and an analog-to-digital conversion circuit receives the second coronary artery murmur signal output from the output end of the automatic gain adjustment circuit and converts the second coronary artery murmur signal into a digital signal.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The heart sound and coronary murmur detection device provided by the present invention realizes the synchronous acquisition of heart sound signals and weak coronary murmur signals at multiple positions of the human body by setting a highly sensitive pickup at the projection position of the coronary artery on the body surface, ensuring the effective capture of the murmur in the complete cardiac coronary region. That is to say, the heart sound and coronary murmur detection device provided by the present invention can collect coronary murmurs with high acquisition difficulty and weak sound signals. The heart sound and coronary murmur detection device provided by the present invention realizes the extraction and processing of coronary murmur signals through a filter amplification circuit, facilitating the early screening of coronary heart disease based on the processed coronary murmur signals.

[0029] 2. When the heart sound and coronary murmur detection device provided by the present invention collects heart sound and coronary murmur signals, it suppresses the noise in the sound signal conditioning channel or other hardware such as the power supply circuit and PCB layout; it suppresses the signal distortion in the sound signal conditioning channel or other hardware such as the PCB layout, solves the noise problem and signal distortion problem in the process of collecting and processing heart sound and coronary murmur signals, extracts accurate coronary murmurs and analyzes them, and processes and accurately analyzes the coronary murmur signals to analyze coronary artery lesions.

[0030] 3. The heart sound and coronary murmur detection device provided by the present invention selects at least one of an electret microphone, a piezoelectric accelerometer, and a piezoelectric sensor as the pickup, which can collect weak coronary murmurs and ensure the accuracy and sensitivity of coronary murmur collection;

[0031] The heart sound and coronary murmur detection device provided by the present invention sets up an AC coupling circuit to remove the DC component in the first sound signal, namely the heart sound and coronary murmur signal, to form a second sound signal;

[0032] The heart sound and coronary murmur detection device provided by the present invention sets up a fixed gain adjustment circuit and an automatic gain adjustment circuit, which can adjust the individual differences of heart sounds and coronary murmurs, improving the universality and applicability of the device;

[0033] The heart sound and coronary murmur detection device provided by the present invention sets up a fixed gain adjustment circuit and a filter amplification circuit to achieve secondary amplification of the coronary murmur signal;

[0034] The heart sound and coronary murmur detection device provided by the present invention sets up an overload detection module to detect whether the second coronary murmur signal output by the automatic gain adjustment circuit is the target coronary murmur signal.

[0035] 4. The heart sound and coronary artery murmur detection method provided by the present invention realizes the synchronous acquisition of heart sound signals and weak coronary artery murmur signals at multiple positions of the human body, ensuring the effective capture of murmurs in the complete coronary artery region of the heart; through the filter amplification circuit, the extraction and processing of coronary artery murmur signals are realized, which is convenient for the early screening of coronary heart disease according to the processed coronary artery murmur signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 An image showing the normal heart sound signal in the embodiment of the present invention;

[0037] Figure 2 A schematic diagram showing the modules of the heart sound and coronary artery murmur detection device in the embodiment of the present invention;

[0038] Figure 3 A diagram showing the acquisition positions of heart sounds and valve murmurs in the prior art;

[0039] Figure 4 A cross-sectional anatomical structure diagram showing the boundary of human lung segments in the embodiment of the present invention;

[0040] Figure 5 A frequency response curve showing the signal conditioning channel in the embodiment of the present invention;

[0041] Figure 6a A diagram showing the aluminum electrolytic capacitor in the embodiment of the present invention;

[0042] Figure 6b A diagram showing the tantalum electrolytic capacitor in the embodiment of the present invention;

[0043] Figure 6c A diagram showing the multilayer ceramic capacitor in the embodiment of the present invention;

[0044] Figure 7 A schematic diagram showing the power supply circuit in the embodiment of the present invention;

[0045] Figure 8 A diagram showing the power quality test results of the output of the 23VLDO power supply chip in the embodiment of the present invention;

[0046] Figure 9 A diagram showing the power quality test results of the output of the 5VLDO power supply chip in the embodiment of the present invention;

[0047] Figure 10 A block diagram showing the PCB layout structure in the embodiment of the present invention;

[0048] Figure 11 A curve showing the change of the capacitance value of capacitors with three material temperature characteristics with the DC voltage, with the same nominal capacitance value and the same rated voltage, in the embodiment of the present invention;

[0049] Figure 12Shows the schematic diagram of PCB layout in the embodiment of the present invention;

[0050] Figure 13 Shows the flow of the central heart sound and coronary murmur detection method in the embodiment of the present invention Figure 1 ;

[0051] Figure 14 Shows the flow of the central heart sound and coronary murmur detection method in the embodiment of the present invention Figure 2 ;

[0052] Figure 15 Shows the schematic diagram of the structure of the electronic device in the embodiment of the present invention. Detailed implementation manners

[0053] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention will be introduced in conjunction with preferred embodiments, this does not mean that the features of this invention are limited to this implementation manner. On the contrary, the purpose of introducing the invention in conjunction with the implementation manner is to cover other alternatives or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, many specific details will be included in the following description. The present invention can also be implemented without using these details. In addition, in order to avoid confusing or obscuring the key points of the present invention, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0054] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0055] The terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0056] In the description of this embodiment, it should also be noted that unless otherwise clearly specified and limited, the terms "set", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this embodiment can be understood according to specific situations.

[0057] To make the purpose, technical solutions and advantages of the present invention clearer, the implementation manners of the present invention will be further described in detail below with reference to the drawings.

[0058] Heart sound is a physiological sound signal containing rich information that can be obtained from the human body, reflecting the movement status of the myocardium, valves, and blood vessels. The main body of the heart is composed of myocardium, which is overall conical in shape and is an important organ for promoting the blood circulation of the whole body. A cycle of heart activity is called a cardiac cycle, which includes one contraction and one relaxation. Heart sound is the sound generated during heartbeats, which is the mechanical vibration produced by the closure of heart valves, myocardial contraction, blood hitting the blood vessel walls and ventricular walls. The heartbeats of normal people are clear and regular; while the heartbeats of people with heart diseases may not follow the normal rhythm or contain murmurs. The frequency of normal heart sound is less than 150 Hz.

[0059] Reference Figure 1 , normal heart sounds are generally divided into four types in the time domain, namely:

[0060] (1) The first heart sound (D1), which appears at the beginning of the cardiac systolic phase, mainly includes the vibrations caused by the rapid flowing blood hitting the atrioventricular valves and ventricular walls during ventricular contraction, the vibrations caused by the sudden closure of the atrioventricular valves, and the vibrations caused by the blood ejected from the left ventricle hitting the blood vessel walls of the aorta and pulmonary artery. The duration of the first heart sound is generally longer, about 0.15 s, and the frequency is mainly distributed in the mid-low frequency band, about 50 - 100 Hz.

[0061] (2) The second heart sound (D2), which appears at the beginning of the cardiac diastolic phase, is the sound generated by the rapid closure of the aortic valve and pulmonary valve, resulting in the reflected blood flow hitting the blood vessel walls of the two major arteries and the ventricular walls. The duration of the second heart sound is generally shorter, usually 0.08 s, and it is distributed in the high, mid, and low frequency bands, about 10 - 400 Hz.

[0062] (3) The third heart sound appears after the second heart sound (D2), which is the vibration generated by the blood in the pulmonary veins and atria entering the ventricles and hitting the ventricular walls after the opening of the atrioventricular valves. The third heart sound can be heard on the body surface of most teenagers using a stethoscope. The third heart sound usually appears 0.1 - 0.2 s after the second heart sound (D2), and the duration is only about 0.05 s, and the frequency is distributed in the low frequency band, about 20 - 70 Hz.

[0063] (4) The fourth heart sound appears before the first heart sound (D1), which is the vibration caused by the atrial contraction during diastole, resulting in the rapid filling of blood in the ventricles, and hardly appears in adults. Its frequency is mainly concentrated in the low frequency band, about 20 - 70 Hz.

[0064] Abnormalities in the condition of heart activity can be reflected by changes in heart sounds. When blood passes through partially blocked or compressed coronary blood vessels, its velocity increases. When the blood flows over the curved surface caused by plaques in the lumen, a normal stress perpendicular to the surface generated by fluid elasticity will be produced. This normal stress will be converted into a pressure gradient perpendicular to the curved surface, thereby forming a mechanical energy gradient perpendicular to the surface, triggering the blood to change from laminar flow to turbulent flow. The chaotic turbulent flow impacts the arterial wall, generating additional murmurs.

[0065] Essentially, the coronary murmur signal is the turbulent flow generated when blood flows through the stenotic coronary artery. The vibration generated by the turbulent flow impacting the blood vessel wall is transmitted to the body surface through the cardiothoracic conduction system to generate a sound signal.

[0066] Medical theory proves that coronary blood flow reaches its maximum value in the early diastolic phase of the cardiac cycle and then gradually decreases. During this period, the heart activity pauses and the myocardium relaxes. Therefore, from the time domain perspective, coronary murmurs are most prominent in the diastolic phase, facilitating the detection of coronary murmur signals. Coronary murmurs also differ in frequency from normal heart sounds, mainly concentrated in the relatively high-frequency band, usually appearing at a frequency of 200 - 800 Hz.

[0067] The technical problem existing in the prior art is that since the coronary murmur signal will be attenuated by the chest muscles and adipose tissue after being generated, and is also easily interfered by the murmurs from other organs in the thoracic and abdominal cavities, its intensity is very weak compared to normal heart sounds. Therefore, it is difficult to collect coronary murmurs. Even if coronary murmurs are collected, due to the noise influence and signal distortion influence of the sound signal conditioning channel or other hardware in the existing heart sound collection device, it is also difficult to extract and analyze coronary murmurs. Thus, there is a lack of a device or method in the prior art for collecting heart sound signals and coronary murmur signals, and processing and accurately analyzing the coronary murmur signals to analyze coronary artery lesions.

[0068] Reference Figure 2 Therefore, in the first aspect, the present invention provides a heart sound and coronary murmur detection device 1, including a pickup 11 and a filter amplification circuit 14.

[0069] Among them, the pickup 11 is placed at the projection position of the coronary artery on the body surface. The projection positions include: the position near the sternal body in the third intercostal space on the left side of the human body and the fourth intercostal space near the sternal body, as well as the position near the sternal body in the third intercostal space on the right side of the human body and the fourth intercostal space near the sternal body. The pickup 11 is used to collect the first sound signal, and the first sound signal includes a heart sound signal and a coronary murmur signal.

[0070] In this embodiment, the pickup 11 is placed at the projection position of the coronary artery on the body surface, and the projection position includes the position within 1 cm from the left margin of the sternal body in the third intercostal space on the left side of the human body, the position within 1 cm from the left margin of the sternal body in the fourth intercostal space on the left side of the human body, the position within 1 cm from the right margin of the sternal body in the third intercostal space on the right side of the human body, and the position within 1 cm from the right margin of the sternal body in the fourth intercostal space on the right side of the human body.

[0071] The input end of the filter amplification circuit 14 is connected to the output end of the pickup 11. The filter amplification circuit 14 is used to extract the coronary murmur signal and amplify the coronary murmur signal to form the first coronary murmur signal.

[0072] Most traditional heart sound auscultations use traditional stethoscopes. Now, there are also devices such as sensors used to collect heart sounds or collect heart sounds and valvular murmurs. Refer to Figure 3 , traditional heart sound auscultation is divided into multiple auscultation areas, mainly focusing on the valve structures within and between each chamber of the heart. The multiple auscultation areas are respectively the mitral valve auscultation area (such as the M position shown in Figure 3 ), the tricuspid valve auscultation area (such as the T position shown in Figure 3 ), the aortic valve auscultation area (such as the A position shown in Figure 3 ), the second aortic valve auscultation area (such as the E position shown in Figure 3 ), and the pulmonary valve auscultation area (such as the P position shown in Figure 3 ), a total of five auscultation areas. After using devices such as sensors to collect heart sounds and valvular murmurs, it is mainly used for the analysis of valvular lesions.

[0073] The coronary murmur signal is essentially the sound signal generated by the turbulent flow of blood through the stenotic coronary artery, where the turbulent flow impacts the blood vessel wall. Therefore, in order to collect accurate coronary murmur signals, the placement position of the sensor mainly focuses on the projection position of the coronary artery of interest on the body surface.

[0074] Figure 4 Shows the cross-sectional anatomical structure diagram of the human lung segment boundary. 1Z is the first rib on the left side of the human body, 1Y is the first rib on the right side of the human body, 2Z is the second rib on the left side of the human body, 2Y is the second rib on the right side of the human body, 3Z is the third rib on the left side of the human body, 3Y is the third rib on the right side of the human body, 4Z is the fourth rib on the left side of the human body, 4Y is the fourth rib on the right side of the human body, 5Z is the fifth rib on the left side of the human body, and 5Y is the fifth rib on the right side of the human body. X 1 、X 2 、X 3 、X 4 are pickups (i.e., sound sensors), and the position where X is located is the position corresponding to the center of the sensor.

[0075] At the boundary position of the lung segments, the right coronary artery and the left coronary artery (anterior descending branch) run on the surface of the heart, that is, at the position closest to the body surface. Their corresponding surface projections are at the positions of the left and right fourth intercostal spaces of the human body close to the body of the sternum. Considering the differences in human anatomical structures and minimizing the signal attenuation caused by the ribs as much as possible, the heart sound and coronary artery murmur detection device 1 sets the placement positions of the pickups 11 to the positions of the left third intercostal space of the human body close to the body of the sternum, the left fourth intercostal space of the human body close to the body of the sternum, the right third intercostal space of the human body close to the body of the sternum, and the right fourth intercostal space of the human body close to the body of the sternum.

[0076] It should be noted that the position of the left third intercostal space of the human body close to the body of the sternum specifically refers to the gap between the left third rib 3Z and the left fourth rib 4Z of the human body, that is, Figure 4 the gap where the pickup X shown in 1 is located. The position of the left fourth intercostal space of the human body close to the body of the sternum specifically refers to the gap between the left fourth rib 4Z and the left fifth rib 5Z of the human body, that is, Figure 4 the gap where the pickup X shown in 3 is located. The position of the right third intercostal space of the human body close to the body of the sternum specifically refers to the gap between the right third rib 3Y and the right fourth rib 4Y of the human body, that is, Figure 4 the gap where the pickup X shown in 3 is located. The position of the right fourth intercostal space of the human body close to the body of the sternum specifically refers to the gap between the right fourth rib 4Y and the right fifth rib 5Y of the human body, that is, Figure 4 the gap where the pickup X shown in 4 is located.

[0077] Exemplarily, referring to Figure 4 , the pickup X 1 is set at a position within 1 cm from the left edge of the body of the sternum in the gap of the left third rib 3Z of the human body, the pickup X 3 is set at a position within 1 cm from the left edge of the body of the sternum in the gap of the left fourth rib 4Z of the human body, the pickup X 2 is set at a position within 1 cm from the left edge of the body of the sternum in the gap of the right third rib 3Y of the human body, and the pickup X 4 is set at a position within 1 cm from the left edge of the body of the sternum in the gap of the right fourth rib 4Y of the human body.

[0078] By adopting the above technical solution, by setting the highly sensitive pickup 11 at the surface projection position of the coronary artery on the body surface, the synchronous acquisition of heart sound signals and weak coronary artery murmur signals at multiple positions of the human body is realized, ensuring the effective capture of the murmur in the coronary artery region of the complete heart.

[0079] In this embodiment, a filter amplification circuit 14 is provided, which is used to extract and amplify the coronary artery murmur signal from the sound signal output from the output end of the pickup 11 and attenuate the heart sound signal, facilitating the early screening of coronary heart disease based on the processed coronary artery murmur signal.

[0080] In some possible embodiments provided by the present invention, the pickup 11 includes at least one of an electret microphone, a piezoelectric accelerometer, and a piezoelectric sensor.

[0081] The pickup 11, that is, the sensor, includes types such as a microphone and an accelerometer.

[0082] A microphone is an electroacoustic transducer that can convert sound waves into electrical signals. A microphone, also known as a microphone, is divided into various types according to its sensor technology and characteristics. For example, dynamic microphones, condenser microphones, electret microphones, and diaphragm microphones, etc.

[0083] The performance indicators of a microphone include signal-to-noise ratio (SNR), sensitivity, acoustic overload point (AOP), and frequency response. These indicators determine the applicability of the microphone in different application scenarios. For example, the higher the signal-to-noise ratio, the lower the noise generated by the microphone while receiving the sound signal; the higher the sensitivity, the stronger the response of the microphone to sound; the higher the acoustic overload point, the greater the sound pressure level that the microphone can withstand; the wider the frequency response, the wider the range of sound frequencies that the microphone can capture.

[0084] In this embodiment, the signal-to-noise ratio is calculated based on a reference sound level of 1 Pascal, and the standard is the 1 kHz sound pressure level (SPL) of 94 dB at the microphone diaphragm. The same acoustic reference level is also used to evaluate the sensitivity, that is, the output amplitude of the microphone signal when the microphone diaphragm is exposed to the standard sound pressure level. The AOP is the sound pressure level value when the harmonic distortion in the signal is equal to 10%. If the SPL value is higher than the AOP, the harmonic distortion will be higher than 10%. When selecting a microphone, the most suitable model should be determined according to the actual application requirements and budget.

[0085] Table 1 shows the main performance comparison between an electret microphone and high-performance analog MEMS microphones and high-performance digital MEMS microphones of STMicroelectronics.

[0086] Table 1

[0087]

[0088] Among them, the electret microphone is a sensor based on the capacitance principle and works using the permanent charge characteristics of the electret material. When sound waves reach the microphone, the internal diaphragm vibrates, thereby changing the capacitance between the electret material and the diaphragm. Since the electret material has a permanent charge, this capacitance change induces a corresponding charge change on the fixed electrode. Through the built-in field-effect transistor, these charge changes are converted into voltage signals, thus outputting audio signals. The electret microphone has the characteristics of high sensitivity, good stability, and low cost, and is widely used in various audio acquisition and communication devices.

[0089] An analog Micro-Electro-Mechanical Systems (MEMS) microphone is a microphone manufactured using MEMS technology. MEMS technology is a technology that combines microelectronics and micro-mechanical engineering, which allows the fabrication of very small mechanical structures on a silicon wafer, and these structures can respond to sound waves and convert them into electrical signals. The working principle of an analog MEMS microphone is based on the vibration caused by sound waves. When sound waves enter the microphone, they cause the vibration of the MEMS diaphragm. The vibration of the diaphragm is converted into an electrical signal through a capacitive sensor (usually a change in capacitance). This electrical signal is analog because it contains the original sound signal and noise. Analog MEMS microphones usually need to be used with an analog-to-digital converter (ADC) to convert the analog signal into a digital signal for further processing or transmission. This conversion process helps to improve the signal quality and allows for more complex signal processing, such as noise suppression and gain control.

[0090] A digital MEMS microphone is a microphone manufactured using MEMS technology. Similar to analog MEMS microphones, it converts sound energy into an electrical signal through the vibration of the MEMS diaphragm caused by sound waves. However, the digital MEMS microphone has a built-in ADC, which means it can directly convert the electrical signal into a digital signal, usually stored in the form of a sampling rate and bit depth (such as 16 bits or 24 bits). This design allows the digital MEMS microphone to be directly connected to a digital audio interface or a digital signal processor (DSP), simplifying the signal processing and transmission process.

[0091] According to Table 1, the electret microphone has the highest signal-to-noise ratio, that is, the lower the noise generated by the electret microphone while receiving the sound signal. The signal-to-noise ratios of the analog MEMS microphone and the digital MEMS microphone are the same and both are lower than that of the electret microphone, that is, the noise generated by the analog MEMS microphone and the digital MEMS microphone while receiving the sound signal is the same and both are higher than the noise generated by the electret microphone while receiving the sound signal. The analog MEMS microphone has the highest sensitivity, followed by the electret microphone, and the digital MEMS microphone has the lowest sensitivity. That is, the analog MEMS microphone has the strongest response to sound, followed by the electret microphone, and the digital MEMS microphone has the weakest response to sound. The electret microphone has the highest acoustic overload point, followed by the analog MEMS microphone, and the digital MEMS microphone has the lowest acoustic overload point, which means that the electret microphone can withstand the largest sound pressure level, followed by the analog MEMS microphone, and the digital MEMS microphone can withstand the smallest sound pressure level. The electret microphone has the largest frequency response range, followed by the analog MEMS microphone, and the digital MEMS microphone has the smallest frequency response range.

[0092] In this embodiment, considering the relatively weak characteristics of the coronary murmur to be collected, when the heart sound and coronary murmur detection device 1 selects the microphone, that is, the pickup 11, it is hoped to collect more coronary murmur signals so as to extract more and more accurate coronary murmur signals subsequently. Therefore, the heart sound and coronary murmur detection device 1 selects the electret microphone with the highest signal-to-noise ratio and the largest frequency response range as the microphone. At the same time, the electret microphone has a high sensitivity, especially a higher sensitivity in the high-frequency band, and has a stronger ability to capture coronary murmur signals. It should be noted here that the frequency of the heart sound signal is less than 150 Hz, and the frequency of the coronary murmur signal is mainly concentrated in the relatively high-frequency band, and usually appears at a frequency of 200 - 800 Hz. Moreover, the electret microphone has the characteristics of a larger sound pressure level that it can withstand and good stability.

[0093] An accelerometer is a mechanical energy - electrical energy transducer that can convert shock, vibration, and mechanical waves into electrical signals. According to the working principle, accelerometers can be divided into three types: piezoelectric accelerometers, piezoresistive accelerometers, and capacitive MEMS accelerometers. Among them, the piezoresistive accelerometer has too low sensitivity and is usually used for impact tests of vehicles; the capacitive MEMS accelerometer has a small frequency response range and is usually used for low-frequency acceleration detection in fields such as airbags and mobile devices. The piezoelectric accelerometer works based on the piezoelectric effect principle, and the internal piezoelectric material generates a charge signal proportional to the acceleration when subjected to an external acceleration, so it is most suitable for collecting vibration signals.

[0094] The performance indicators of accelerometers usually include: sensitivity, frequency response, acceleration range of response, noise density, etc. The sensitivity of an accelerometer refers to its sensitivity to changes in acceleration. The higher the sensitivity, the more sensitive the accelerometer is to changes in acceleration. Frequency response describes the response ability of an accelerometer at different frequencies. An ideal accelerometer should maintain a flat response throughout the operating frequency range. However, in reality, an accelerometer may experience resonance or cut-off at certain frequencies. The acceleration range of response is the maximum and minimum acceleration values that an accelerometer can measure. Usually, the design of an accelerometer takes into account the maximum acceleration it can withstand to prevent damage. Noise density is the ratio of the noise voltage output by an accelerometer to the frequency within a certain frequency range. A lower noise density means that the accelerometer can provide a more accurate signal during measurement.

[0095] Table 2 shows the performance comparison of the selected piezoelectric accelerometer with that of capacitive MEMS accelerometers and piezoresistive accelerometers.

[0096] Table 2

[0097]

[0098] Among them, the piezoelectric accelerometer works based on the piezoelectric effect principle. The internal piezoelectric material generates a charge signal proportional to the acceleration when subjected to external acceleration. Through a built-in charge amplifier, these charges are converted into voltage signals, thus providing high-precision acceleration measurement results.

[0099] The capacitive MEMS accelerometer is a sensor that uses capacitance changes to detect acceleration. The capacitive MEMS accelerometer usually consists of a movable cantilever beam (or mass block) and a fixed electrode. The root of the cantilever beam is fixed to the sensor housing, and the end of the beam is a movable mass block. When the sensor is subjected to acceleration, the mass block moves relative to the fixed electrode, thus changing the capacitance value between the two. The change in capacitance is proportional to the acceleration. The built-in detection circuit of the sensor measures the change in capacitance and converts it into an electrical signal. After further processing, the acceleration value can be obtained.

[0100] The piezoresistive accelerometer is a sensor that uses the piezoresistive effect to measure acceleration. The piezoresistive effect is a physical phenomenon in which the resistance value of certain materials changes when subjected to mechanical stress. The working principle of the piezoresistive accelerometer is based on this effect. By converting mechanical stress (i.e., acceleration) into a change in resistance value, the measurement of acceleration is achieved.

[0101] According to Table 2, the capacitive MEMS accelerometer with the model number 4221MF has the highest sensitivity, which is significantly higher than that of the piezoelectric accelerometer and piezoresistive accelerometer with the model number 4507 - B - 002. That is, the capacitive MEMS accelerometer is more sensitive to acceleration changes. The piezoelectric accelerometer has the highest frequency response, which is significantly higher than that of the capacitive MEMS accelerometer and piezoresistive accelerometer. That is, the piezoelectric accelerometer has a significantly higher response ability at frequencies from 0.4 to 6000 Hz than the other two. The piezoelectric accelerometer has the lowest noise density, which means that the piezoelectric accelerometer can provide a more accurate signal during measurement.

[0102] In this embodiment, in the application of heart sound and coronary murmur acquisition, the piezoelectric accelerometer converts the acceleration signal of chest wall vibration into an electrical signal. Its advantages are that its sensor size is small and its weight is light, which is beneficial to good attachment to the chest wall. At the same time, the piezoelectric accelerometer has high sensitivity and a wide frequency response range, and is suitable for applications such as structural health monitoring and mechanical vibration monitoring.

[0103] Piezoelectric sensors are a direct method of converting mechanical energy into electrical energy, and can convert mechanical vibrations caused by sound waves into electrical signals. Piezoelectric sensors can be divided into four types according to their materials: piezoelectric ceramics, piezoelectric single crystals, piezoelectric polymers, and piezoelectric nanocomposites. Piezoelectric ceramics play a crucial role in modern technology due to their excellent electrical, piezoelectric, and dielectric properties, but their brittleness makes them prone to cracking under a relatively large strain. Among them, lead zirconate titanate is the most commonly used piezoelectric ceramic; the main properties of piezoelectric single crystals are similar to those of piezoelectric ceramics, being hard and brittle while having a large piezoelectric coefficient; piezoelectric polymer materials have a lightweight structure, are easy to manufacture, and have excellent flexibility. These characteristics make them very suitable for integration into compliant and flexible wearable devices; composite materials and nanocomposites are used to adjust and enhance the properties of various piezoelectric materials, and these materials represent the combined advantages of ceramics and polymers and are suitable for various applications, namely energy harvesting, sensing, and actuation, etc.

[0104] Piezoelectric sensors do not require additional power supply, so these devices are lightweight, cost - effective, and easy to manufacture, which is very attractive for wearable applications. Wearable piezoelectric energy harvesters can effectively collect various forms of mechanical energy through the piezoelectric effect, providing a multi - functional solution for powering electronic devices. The key parameters of piezoelectric sensors include: sensitivity, frequency response, noise level, etc. Considering the relatively weak characteristics of coronary murmurs, a piezoelectric ceramic sensor with the highest piezoelectric coefficient was selected.

[0105] In summary, in this embodiment, the pickup 11 includes at least one of an electret microphone, a piezoelectric accelerometer, and a piezoelectric sensor.

[0106] In some possible embodiments provided by the present invention, the pickup 11 includes two types, namely an electret microphone and a piezoelectric accelerometer. There are 4 pickups 11, among which 2 are electret microphones, namely the first electret microphone and the second electret microphone; 2 are piezoelectric accelerometers, namely the first piezoelectric accelerometer and the second piezoelectric accelerometer. As Figure 4 shown, the first electret microphone X 1 is placed at a position 1 cm to the left of the left edge of the sternal body between the third rib 3Z and the fourth rib 4Z on the left side of the human body, and the second electret microphone X 2 is placed at a position 1 cm to the right of the right edge of the sternal body between the third rib 3Y and the fourth rib 4Y on the right side of the human body; the first piezoelectric accelerometer X 3 is placed at a position 1 cm to the left of the left edge of the sternal body between the fourth rib 4Z and the fifth rib 5Z on the left side of the human body, and the second piezoelectric accelerometer X 4 is placed at a position 1 cm to the right of the right edge of the sternal body between the fourth rib 4Y and the fifth rib 5Y on the right side of the human body.

[0107] By adopting the above technical solution, by arranging 4 highly sensitive pickups 11 at the projection positions of the coronary arteries on the body surface, the synchronous acquisition of heart sound signals and weak coronary artery murmur signals at multiple positions of the human body is realized, ensuring the effective capture of the murmur in the complete cardiac coronary artery region.

[0108] In some possible embodiments provided by the present invention, in combination with Figure 2 , the filter amplification circuit 14 includes an active filter and an operational amplifier. An active filter is a filter circuit implemented using active components (such as transistors, operational amplifiers, etc.). Compared with passive filters (composed only of resistors, capacitors, and inductors), active filters can provide more flexible designs, higher input impedances, lower output impedances, and better noise performance

[0109] In some possible embodiments, the active filter is a Sallen-Key filter. The filter types can be divided into two types: filters built with discrete components and integrated filters. The cut-off frequencies and orders covered by integrated filters cannot meet our requirements for high-pass filters in the low-frequency band. Therefore, it is chosen to build the filter using discrete components by ourselves. The filter structure built with discrete components is divided into two structures: Sallen-Key and MFB (Multiple Feedback, which is a multiple feedback structure). After actual testing, the roll-off and passband performance of the MFB type filter is not as good as that of the Sallen-Key structure filter obtained through simulation and parameter calculation. Therefore, the Sallen-Key filter is chosen in this embodiment.

[0110] In some possible embodiments, the operational amplifier is a non-inverting amplifier. That is, an active filter with a multi-stage Sallen-Key structure and a non-inverting amplifier form a filter amplification circuit 14. The filter amplification circuit is, in the order of signal input, a fourth-order high-pass filter, a non-inverting amplifier with a gain of 10, a second-order low-pass filter, and a non-inverting amplifier with a gain of 5. The overall bandwidth of the filter amplification circuit is 200 - 2000 Hz, and the total gain is 50 times.

[0111] With the above technical solution, the filter amplification circuit 14 extracts and amplifies the coronary murmur signal from the sound signal output from the pickup 11, and attenuates the heart sound signal, facilitating the early screening of coronary heart disease based on the processed coronary murmur signal.

[0112] In some possible embodiments provided by the present invention, the first sound signal, that is, the heart sound and the coronary murmur signal, is an AC signal. Referring to Figure 2 , the heart sound and coronary murmur detection device 1 includes an AC coupling circuit 12. The input end of the AC coupling circuit 12 is connected to the output end of the pickup 11. The AC coupling circuit 12 is used to remove the DC component in the first sound signal to form a second sound signal. That is, the AC coupling circuit 12 allows the AC signal to pass through and blocks the DC component.

[0113] In this embodiment, the first sound signal output from the pickup 11 first passes through the AC coupling circuit 12 to remove the DC part in the first sound signal. The AC coupling circuit 12 consists of a simple RC network, and its cut-off frequency is as shown in Formula 1:

[0114]

[0115] In the formula, R and C are the resistance value and capacitance value of the RC network respectively. According to the requirements of the capacitance material and the signal bandwidth, the heart sound and coronary murmur detection device 1 finally sets the cut-off frequency of the AC coupling to 33.9 Hz. After actual testing, the attenuation of the AC coupling structure within the signal passband is within ±0.1 dB, and the frequency response curve is as shown by the curve Ch2 in Figure 5 .

[0116] Referring to Figure 2 , the frequency response curve of the second sound signal output after passing through the filter amplification circuit 14 after removing the DC component by the AC coupling circuit 12 is as shown by the curve Ch1 in Figure 5 . The filter amplification circuit 14 realizes the extraction and amplification of the coronary murmur in the second sound signal and the attenuation of the heart sound signal.

[0117] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes a fixed gain adjustment circuit 13. The input end of the fixed gain adjustment circuit 13 is connected to the output end of the AC coupling circuit 12. The fixed gain adjustment circuit 13 is used to amplify the second sound signal to form a third sound signal. The output end of the fixed gain adjustment circuit 13 is connected to the input end of the filter amplification circuit 14.

[0118] The fixed gain adjustment circuit is used to provide a constant signal amplification factor, that is, gain.

[0119] In this embodiment, the fixed gain adjustment circuit 13 is composed of an instrumentation amplifier. Due to the limitation of the amplitude of the original heart sound signal, the amplification factor for the coronary murmur signal may not be sufficient. Moreover, the load-carrying capacity of some operational amplifiers used for pre-amplification is relatively low. Therefore, it is necessary to select a suitable operational amplifier separately for the second-stage amplification of the coronary murmur signal. Furthermore, the internal noise of the heart sound signal and the coronary murmur signal will also be amplified during the signal amplification process. Therefore, a low-noise operational amplifier needs to be selected for the second-stage amplification part. In order to eliminate this part of the noise, it is necessary to set a filter and select appropriate filter and parameters. That is to say, in this embodiment, the heart sound and coronary murmur detection device 1 realizes the first-stage amplification of the coronary murmur signal through the fixed gain circuit 13, and the filter amplification circuit 14 performs the second-stage amplification on the first-stage amplified coronary murmur signal.

[0120] In this embodiment, the selected model of the instrumentation amplifier is LT6370, which is a gain-programmable and high-precision instrumentation amplifier. Its main features include low input offset voltage, low drift, high common-mode rejection ratio, and high gain accuracy. Its gain range can be set from 1 to 1000 times by only one external resistor. These features make LT6370 suitable for various precision signal amplification and measurement applications.

[0121] In some other possible embodiments, exemplarily, the instrumentation amplifier can also select at least one of models such as INA126, AD620, ZJA3600, etc. The above are only examples of the selected models of the instrumentation amplifier. The present invention does not limit the specific models of the instrumentation amplifier. As long as these models of instrumentation amplifiers can achieve the first-stage amplification of the coronary murmur signal and adjust the coronary murmur signal to the target voltage range.

[0122] The operational amplifier of the filter amplification circuit 14 of the heart sound and coronary murmur detection device 1 selects the ADA4522 series, which provides multiple packages of single-channel, dual-channel, and four-channel, and has Characterized by low input voltage noise and low power consumption, it has a ground detection input and a rail-to-rail output function, with advantages such as a wide operating voltage and temperature range, high open-loop gain, and extremely low DC and AC errors. It is very suitable for amplifying very small input signals and accurately reproducing larger signals in various applications.

[0123] In some other possible embodiments, by way of example, the operational amplifier of the filter amplification circuit 14 can be selected from at least one of the models such as OPA182, LT1008, OPZ302, etc. The above are only examples of the selection of the operational amplifier, and the present invention does not limit the specific model of the operational amplifier, as long as the operational amplifiers of these models can perform the second-stage amplification on the coronary murmur signal after the first-stage amplification.

[0124] Reference Figure 2 , in this embodiment, the second sound signal after removing the DC component by the AC coupling circuit 12 provides a bias current path through the 2.5V reference voltage source 28, and then enters the fixed gain adjustment module 13 composed of an instrumentation amplifier in a single-ended input configuration, and its gain is controlled by an external resistor. Resistors with different resistance values correspond to different gains. Different resistors are selected by the connected multi-position slide switch or rotary switch to switch the gain between ×1 / ×2 / ×5 / ×10 / ×20, that is, to switch the gain between 1-fold gain, 2-fold gain, 5-fold gain, 10-fold gain, and 20-fold gain.

[0125] Table 3 shows the correspondence between the resistance value and the gain, that is, the instrumentation amplifier R G and the gain relationship comparison table.

[0126] Table 3

[0127]

[0128] By way of example, for instance, when the resistance value with a standard of 1% is 1.27 kΩ, the gain is 20.06; another example is that when the resistance value with a standard of 1% is 121 kΩ, the gain is 201.

[0129] Continue to refer to Figure 2 , in some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes an automatic gain adjustment circuit 15. The input end of the automatic gain adjustment circuit 15 is connected to the output end of the filter amplification circuit 14. The automatic gain adjustment circuit 15 is used to receive the first coronary murmur signal output from the output end of the filter amplification circuit 14 and adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal.

[0130] Continue to refer to Figure 2, in some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes an overload detection module 16. The input end of the overload detection module 16 is connected to the output end of the automatic gain adjustment circuit 15. The overload detection module 16 is used to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain adjustment circuit 15 exceeds a preset voltage threshold: if the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, the output end of the overload detection module 16 outputs an overload signal; if the peak value of the voltage of the second coronary murmur signal does not exceed the preset voltage threshold, the output end of the overload detection module 16 outputs an underload signal.

[0131] In the prior art, since the coronary murmur signal is attenuated by chest muscles and adipose tissues after being generated, and is also easily interfered by the murmurs of other organs in the chest and abdominal cavities, its intensity is very weak compared with normal heart sounds. And the signal conditioning channel will introduce noise, and there is also noise in the quantization of the analog-to-digital converter (i.e., ADC). The noise introduced by the signal conditioning channel may come from the components used in the signal conditioning channel, unreasonable design of the PCB, crosstalk between channels, spatial electromagnetic interference, etc. The quantization noise of the ADC comes from the quantization error generated when the analog signal is converted into a digital signal. It is a uniformly distributed random noise that determines the effective number of bits of the ADC. When the quantization noise is larger, the signal-to-noise ratio is lower, and the effective number of bits of the ADC is also smaller.

[0132] The existing sound signal acquisition system has poor noise removal performance, cannot capture more coronary murmur signals, is affected by noise interference during the analysis and processing of coronary murmur signals, cannot accurately analyze coronary murmur signals, and thus cannot accurately analyze coronary lesions.

[0133] I. Noise suppression in the signal conditioning channel 01

[0134] Reference Figure 2 , for this reason, in some possible embodiments provided by the present invention, a signal conditioning channel 01 composed of a pickup 11, an AC coupling circuit 12, a fixed gain adjustment circuit 13, a filter amplification circuit 14, and an automatic gain adjustment module 15 is disclosed.

[0135] The noise generated by signal conditioning channel 01 affects the processes of collecting, extracting, and processing coronary murmur signals. Specifically, the internal noise of signal conditioning channel 01 can be defined as the interference voltage and current signals generated by all resistors and semiconductor devices in the circuits included in the signal conditioning channel. There are mainly two sources of the noise of the signal conditioning channel discussed in this patent, namely, the inherent input voltage noise of the operational amplifier and the Johnson noise of the external circuit resistors. Among them, the external circuit resistors refer to the resistors for providing complex impedance, feedback resistors that constitute the Sallen-Key filter structure, as well as the feedback resistors and gain resistors for providing gain that constitute the non-inverting amplifier structure. When there are multiple noise sources in the circuit, the total root mean square noise generated is equal to the square root of the sum of the squares of the root mean square noise of each noise source, as shown in Equation 2:

[0136]

[0137] The Johnson noise of the resistor comes from the thermal agitation of electrons inside the resistor. This thermal agitation causes the movement of charges, thereby generating a noise voltage. The calculation of the Johnson noise is shown in Equation 3:

[0138]

[0139] In the formula, k is the Boltzmann constant and k = 1.374×10 -23 K / °K; R is the resistance value; T is the thermodynamic temperature (unit: K); B is the bandwidth for measuring the thermal noise of the resistor.

[0140] Therefore, the thermal noise of the resistor can be reduced by reducing the resistance value used, reducing the device temperature, and reducing the measurement bandwidth.

[0141] The inherent input voltage noise of the operational amplifier can be divided into two parts according to the frequency distribution characteristics. One part is the pink noise that dominates in the low-frequency region, and the other part is the white noise that dominates in the high-frequency region. The frequencies equal on the spectra of the pink noise and the white noise are defined as the noise corner frequency f nc . Therefore, when describing the total noise of the operational amplifier, the noise needs to be divided into two parts, namely, pink noise and white noise, and then the total voltage noise is obtained according to the root mean square addition rule of Equation 2.

[0142] In summary, for the noise generated in signal conditioning channel 01 that affects the processes of collecting, extracting, and processing coronary murmur signals, the thermal noise of the resistor is reduced by reducing the resistance value used, reducing the device temperature, and reducing the measurement bandwidth, and the appropriate selection of the instrumentation amplifier and the operational amplifier is carried out, realizing the noise suppression in the signal conditioning channel.

[0143] As described above, there is quantization noise in an analog-to-digital converter (i.e., ADC) in the prior art. By setting an anti-aliasing filter at the front stage of the analog-to-digital converter (i.e., ADC) and making a reasonable ADC selection, the quantization noise of the ADC can be reduced.

[0144] Since there are large differences in the basic heart sound levels among different patients, and the amplitude of the coronary murmur is much weaker than that of the basic heart sound. Therefore, when the heart sound and coronary murmur detection device 1 collects signals, it is necessary to adjust the gain of signal conditioning for the collection processes of different patients. The heart sound and coronary murmur detection device 1 makes the signal swing as close as possible to within 80% of the ADC range through two adjustable gain methods, namely a fixed gain adjustment circuit and an automatic gain adjustment circuit. The design of these two adjustable gain methods can make the best use of the quantization range of the ADC and achieve the highest quantization accuracy.

[0145] Exemplarily, the selected ADC has a range of 5V. 80% of the range of this selected ADC is 0 - 4V. The coronary murmur signal collected by the pickup 11 is 0.4V. After passing through the two adjustable gain methods of the fixed gain adjustment circuit 13 and the automatic gain adjustment circuit 15, the voltage value of the obtained coronary murmur signal should be within the range of 0 - 4V, that is, within 80% of the ADC range, so as to maximize the use of the sampling accuracy. Maximizing the use of the sampling accuracy means that after amplifying the coronary murmur signal (small signal) to 0 - 4V, it is easier to capture more points with smaller fluctuations, that is, the ability to capture weak signals is stronger, more information of the coronary murmur signal is collected, and more accurate results can be obtained based on a larger data volume. The design of the two adjustable gain methods can best restore the captured coronary murmur signal and has the highest quantization accuracy.

[0146] Among them, the anti-aliasing filter is a low-pass filter, and its main function is to filter out frequency components higher than half of the sampling frequency before signal sampling to prevent signal aliasing. Aliasing refers to the "shift" of frequency components higher than half of the sampling rate to the useful frequency band, and this phenomenon is usually harmful. Therefore, an anti-aliasing filter needs to be used before the analog-to-digital converter (ADC) to filter out these frequency components.

[0147] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes an analog-to-digital conversion circuit 17. The input end of the analog-to-digital conversion circuit 17 is connected to the output end of the automatic gain adjustment circuit 15. The analog-to-digital conversion circuit 17 is used to receive the second coronary murmur signal output from the output end of the automatic gain adjustment circuit 15 and convert the second coronary murmur signal into a digital signal.

[0148] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes a microelectronic control circuit 18. The input end of the microelectronic control circuit 18 is connected to the output end of the overload detection module 17. The microelectronic control circuit 18 is configured to receive the overload signal output from the output end of the overload detection module 17. The output end of the microelectronic control circuit 18 is connected to the input end of the automatic gain adjustment circuit 15. The microelectronic control circuit 18 is configured to control the automatic gain adjustment circuit 15 to receive the first coronary murmur signal output from the output end of the receiving filter amplification circuit 14 and adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal. The input end of the microelectronic control circuit 18 is further connected to the output end of the analog-to-digital conversion circuit 17. The microelectronic control circuit 18 is configured to receive the digital signal output from the output end of the analog-to-digital conversion circuit 17.

[0149] II. Noise Suppression in the Power Supply Circuit

[0150] With the continuous improvement of the integration degree of integrated circuits, the use of low-voltage power supplies has increased significantly. In addition, the versatility of integrated circuits has led to an increase in power consumption and current consumption. When designing a power supply, in addition to indicators such as input and output voltages, output power, and power conversion efficiency, in a high-precision signal acquisition system, such as the heart sound and coronary murmur detection device 1 proposed in this application, attention also needs to be paid to the noise of the power supply.

[0151] The noise of the power supply generally includes two parts. One is the power supply ripple with a relatively fixed frequency, which is related to the power supply switching frequency or the power supply input frequency. The other part is the noise with an unfixed frequency, which is related to the electrical appliances. The ripple and noise of the power supply affect the signal quality on the signal conditioning channel by powering the analog devices. Excessive power supply ripple and noise will be loaded on the signal, resulting in noise with the same frequency as the power supply ripple on the signal.

[0152] Traditional power supply design methods use aluminum electrolytic capacitors and tantalum electrolytic capacitors with large capacitance values as output filter capacitors. However, these electrolytic capacitors are relatively large in volume, so it is difficult to reduce the space requirements. In addition, electrolytic capacitors also have the disadvantages of high self-heating and high ripple voltage due to the ripple current ΔI. The service life of the capacitor is affected by temperature. Generally speaking, according to the "half-life rule", for every increase in the operating temperature, the product life will be reduced by half. This means that the high self-heating value caused by the ripple current will shorten the life of the capacitor. The relationship between the ripple current and the heat generation is expressed by Formula 4, and the relationship between the ripple current and the ripple voltage is expressed by Formula 5:

[0153] Self Heating Rate: P = ESR × ΔI 2 Formula 4

[0154] Among them, Self heating rate: P represents the heating power, ESR represents the equivalent series resistance of the capacitor, and △I represents the ripple current.

[0155]

[0156] Among them, Ripple Voltage: △V represents the ripple voltage, ESR represents the equivalent series resistance of the capacitor, C0 represents the capacitance value of the capacitor, and f sw represents the switching frequency of the power supply chip.

[0157] The capacitance value of the output filter capacitor is usually selected according to the switching frequency of the chip. The capacitance value of the output filter capacitor and the switching frequency of the chip are relatively fixed with the determination of the power supply demand and the selection of the power supply chip. For capacitors of the same size, there will be a large difference in ESR for capacitors of different materials.

[0158] Exemplarily, taking the 47uF output filter capacitor with the same capacitance value as an example, when f sw is 300kHz, as Figure 6a shown, the typical size of the aluminum electrolytic capacitor is and the typical ESR is 650mΩ. As Figure 6b shown, the typical size of the tantalum electrolytic capacitor is 3.5mm×2.8mm×1.9mm, and the typical ESR is 100mΩ. As Figure 6c shown, the typical size of the multilayer ceramic capacitor (MLCC) is 3.2mm×2.5mm×2.5mm, and the typical ESR is 2mΩ. According to Formula 5, at this time, as Figure 6a shown, the peak-to-peak value of the ripple voltage of the aluminum electrolytic capacitor is 75mV, as Figure 6b shown, the peak-to-peak value of the ripple voltage of the tantalum electrolytic capacitor is 20mV, as Figure 6c shown, the peak-to-peak value of the ripple voltage of the multilayer ceramic capacitor (MLCC) is 4mV.

[0159] Therefore, an MLCC is used as the output filter capacitor of the power supply chip in the heart sound and coronary murmur detection device 1. That is, in some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes a power supply circuit, the power supply circuit includes a power supply chip, and the output filter capacitor of the power supply chip is a multilayer ceramic capacitor.

[0160] Refer to Figure 7 , a 10uF multilayer ceramic capacitor (MLCC) is used at the output positions of the 24V Boost power supply chip 21 and the 23V LDO power supply chip 22, and a 2.2uF multilayer ceramic capacitor (MLCC) is used at the output positions of the 7V Boost power supply chip 24, the 5V LDO power supply chip 25, and the 3.3V LDO power supply chip 26.

[0161] Reference Figure 7 and Figure 8 as Figure 8 The test results shown indicate that at the output of the 23V LDO power supply chip 22 for power supply to the pickup 11, the power supply ripple is less than 4mVpp.

[0162] Reference Figure 7 and in combination with Figure 2 as Figure 9 The test results shown indicate that at the output of the 5V LDO power supply chip 25 for power supply to some circuits (fixed gain adjustment circuit 13, filter amplification circuit 14, and automatic gain adjustment circuit 15) in the signal conditioning channel 01, the power supply ripple is less than 4mVpp.

[0163] By adopting the above technical solution, by selecting multilayer ceramic capacitors for the output filter capacitors in the power supply circuit, noise suppression in the power supply circuit is achieved.

[0164] III. Noise Suppression in PCB Layout

[0165] Regarding the noise introduced due to unreasonable design of the PCB, crosstalk between channels, and spatial electromagnetic interference, etc., the heart sound and coronary murmur detection device 1 provided by the present invention reduces the noise introduced by components, the PCB, and crosstalk through optimizing the circuit layout design. Also, by setting shielding covers, the noise introduced by spatial electromagnetic interference can be reduced.

[0166] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection device 1 includes a PCB, the PCB includes a power supply layer and a grounding layer, the grounding layer includes a first grounding layer and a second grounding layer, and the first grounding layer, the power supply layer, and the second grounding layer are overlapped and arranged from top to bottom.

[0167] Exemplarily, the power supply layer is located at the fourth layer in the PCB stacking structure, the upper layer (i.e., the third layer) of the power supply layer is the first grounding layer, and the distance between the power supply layer and the first grounding layer is 0.55mm. The lower layer (i.e., the fifth layer) of the power supply layer is the second grounding layer, and the distance between the power supply layer and the second grounding layer is 0.0994mm.

[0168] By adopting the above technical solution, through reasonably arranging the board layer structure, that is, for the coronary murmur detection device 1 with a multilayer board, using a dedicated power supply layer and ground layer, reducing the impedance and potential difference between the power supply layer and the ground layer, thereby reducing noise and interference, and achieving noise suppression for the heart sound and coronary murmur detection device 1.

[0169] In some possible embodiments provided by the present invention, the PCB includes an analog signal area and a digital signal area, and the analog signal area and the digital signal area are grounded at a single point. Among them, the analog signal area includes a signal conditioning channel 01, and the signal conditioning channel 01 is sequentially connected to a pickup 11, an AC coupling circuit 12, a fixed gain adjustment circuit 13, a filter amplification circuit 14, and an automatic gain adjustment circuit 15; the digital signal area includes an overload detection module 16, an analog-to-digital conversion circuit 17, and a microelectronic control circuit 18.

[0170] In this embodiment, referring to Figure 10 , the PCB includes an analog signal area and a digital signal area.

[0171] Among them, the analog signal area includes a signal conditioning channel 01. In this embodiment, there are 4 signal conditioning channels 01, namely signal conditioning channel one 011, signal conditioning channel two 012, signal conditioning channel three 013, and signal conditioning channel four 014. Among them, each signal conditioning channel further includes, as Figure 2 shown, a sequentially connected pickup 11, an AC coupling circuit 12, a fixed gain adjustment circuit 13, a filter amplification circuit 14, and an automatic gain adjustment circuit 15.

[0172] The digital signal area includes an analog-to-digital conversion circuit 17 and a microelectronic control circuit 18. The analog-to-digital conversion circuit 17 is also the analog-to-digital converter ADC and its peripheral devices; the microelectronic control circuit 18 is also the microcontroller unit MCU and its peripheral devices.

[0173] In this embodiment, the analog signal area and the digital signal area are grounded at a single point. That is, the ground wires of the analog signal area and the digital signal area are both connected to the same reference point, rather than multiple different ground points. The purpose of this grounding method is to reduce the ground loop and lower the electromagnetic interference.

[0174] By adopting the above technical solution, by separating the analog signal area and the digital signal area on the PCB, and grounding at a single point between the analog signal area and the digital signal area to reduce noise coupling, the noise suppression of the heart sound and coronary murmur detection device 1 is further realized.

[0175] Referring to Figure 10 , in some possible embodiments provided by the present invention, the PCB further includes a power supply circuit 20. The power supply circuit 20 is respectively connected to the analog signal area and the digital signal area for supplying power to the analog signal area and the digital signal area; the power supply circuit 20 includes decoupling capacitors (not shown in the figure), and the decoupling capacitors are arranged near the pins of the power supply chip.

[0176] It should be noted that the positions and quantities of the grounding pins of the power supply chip are related to the model of the power supply chip, and the positions and quantities of the grounding pins of different models of power supply chips are different. However, the decoupling capacitors need to be placed near the grounding pins of the power supply chip.

[0177] Adopting the above technical solution, the decoupling capacitors are arranged as close as possible to the pin positions of the power integrated circuit, reducing the loop area of the transient current, optimizing the power distribution, and achieving noise suppression for the heart sound and coronary murmur detection device 1.

[0178] The power supply circuit 20 includes a sensor power supply module 25 as shown in Figure 2 When the microphone is a microphone or an accelerometer, the sensor power supply module 25 is the IEPE power supply 23 in Figure 7 .

[0179] Refer to Figure 10 . In some possible embodiments provided by the present invention, the PCB is provided with a first copper cladding cutting area Q1, and the first copper cladding cutting area Q1 is not connected to the power layer and the grounding layer; the first copper cladding cutting area Q1 is arranged between the analog signal area and the digital signal area, so that electrical isolation is achieved between the analog signal area and the digital signal area; the first copper cladding cutting area Q1 does not affect the connection between the analog signal area and the power supply circuit 20, nor does it affect the connection between the digital signal area and the power supply circuit 20.

[0180] In this embodiment, the first copper cladding cutting area Q1 is not connected to the power layer and the grounding layer, that is, the first copper cladding cutting area Q1 is not energized, and there is no current passing through this area. That is to say, the first copper cladding cutting area Q1 has no mechanical connection and electrical connection with other components on the PCB.

[0181] As shown in Figure 10 , the first copper cladding cutting area Q1 is arranged between the signal conditioning channels (signal conditioning channel one 011, signal conditioning channel two 012, signal conditioning channel three 013, and signal conditioning channel four 014) and the analog-to-digital conversion circuit 17.

[0182] Continuing to refer to Figure 10 , the heart sound and coronary murmur detection device 1 includes an analog signal area, and the analog signal area includes 4 signal conditioning channels (signal conditioning channel one 011, signal conditioning channel two 012, signal conditioning channel three 013, and signal conditioning channel four 014). Refer to Figure 2 and in combination with Figure 10 , where each signal conditioning channel includes a pickup 11, an AC coupling circuit 12, a fixed gain adjustment circuit 13, a filter amplification circuit 14, and an automatic gain adjustment circuit 15 connected in sequence.

[0183] The heart sound and coronary murmur detection device 1 includes a power supply circuit 20. The arrow connected to the power supply circuit 20 indicates the path through which the heart sound and coronary murmur detection device 1 is input by an external power supply, processed by the power supply circuit 20 of the heart sound and coronary murmur detection device 1, and then supplies power to each part of the heart sound and coronary murmur detection device 1.

[0184] In this embodiment, the external power supply is a lithium battery, and a power supply chip is used to reasonably supply power to other devices, such as performing step-up and step-down voltage processing on the voltage and outputting a voltage adapted to each device.

[0185] The heart sound and coronary murmur detection device 1 further includes a digital signal area, and the digital signal area includes an analog-to-digital conversion circuit 17 and a microelectronic control circuit 18. Among them, the analog-to-digital conversion circuit 17 includes an analog-to-digital converter ADC and peripheral devices; the microelectronic control circuit 18 includes a microcontroller unit MCU and peripheral devices.

[0186] The dotted line and arrow connected to the signal conditioning channel represent the return current path of each device in the analog signal circuit. That is, the return current path in the analog signal circuit includes the return current path F1 connected to the signal conditioning channel 011, the return current path F2 connected to the signal conditioning channel 012, the return current path F3 connected to the signal conditioning channel 013, and the return current path F4 connected to the signal conditioning channel 014.

[0187] The dotted line and arrow connected to the analog-to-digital conversion circuit 17 and the microelectronic control circuit 18 represent the return current path of the digital signal circuit. That is, the return current path of the digital signal circuit includes the return current path F5 connected to the analog-to-digital conversion circuit 17 and the return current path F6 connected to the microelectronic control circuit 18.

[0188] The first copper-clad cutting area Q1 is the cutting area of the copper plane, and the copper-clad connection of each layer of the ground plane and the power plane is not included in the cutting area. The return current path D1 is the return current path of the digital signal circuit blocked by the first copper-clad cutting area Q1.

[0189] Since the return current always returns to the power supply along the path of the lowest impedance, if the return current of the digital signal circuit is not blocked by the first copper-clad cutting area Q1, the return current path D1 will pass through the ground plane on the analog signal circuit, and the reference voltage of the analog device with this part of the ground plane as the reference will be interfered, thus generating digital noise. The first copper-clad cutting area Q1 can force the return current of this part to bypass the analog signal area, that is, below the signal conditioning path, and then return to the negative power supply. The separation of the return current in space can reduce noise coupling.

[0190] Adopting the above technical solution, when arranging the PCB of the heart sound and coronary murmur detection device 1, the return currents of various parts of the circuit (such as signal conditioning channel one 011, signal conditioning channel two 012, signal conditioning channel three 013, signal conditioning channel four 014, analog-to-digital conversion circuit 17, and microelectronic control circuit 18) are fully considered. The return currents of each part are managed by arranging the positions of each part and cutting the copper plane, reducing the noise caused by the coupling of return currents. The noise suppression of the heart sound and coronary murmur detection device 1 is achieved by managing the return currents.

[0191] In summary, the heart sound and coronary murmur detection device 1 mainly suppresses the noise in the acquisition system from three aspects, namely, noise suppression of the signal conditioning channel, noise suppression of the power supply circuit, and noise suppression of the PCB layout, ensuring the signal-to-noise ratio of the acquired coronary murmur signal.

[0192] In the prior art, in the process of collecting, extracting, and processing coronary murmur signals in the sound signal acquisition system, there are not only noise problems but also signal distortion problems. During the transmission or processing of the signal, due to various factors, the signal quality deteriorates or the signal shape changes, resulting in the problem of signal distortion. The existing sound signal acquisition systems perform poorly in noise removal and signal distortion, unable to capture more coronary murmur signals. During the analysis and processing of coronary murmur signals, they are affected by noise interference and signal distortion, unable to accurately analyze coronary murmur signals, and thus unable to accurately analyze coronary lesions.

[0193] Signal distortion is divided into two types: linear distortion and nonlinear distortion. Linear distortion refers to the change in the amplitude or phase of the signal during transmission due to the imperfect linear characteristics of the device or circuit, but no new frequency components are generated, so the impact on the signal is relatively small. Nonlinear distortion refers to the generation of new frequency components during signal transmission due to the nonlinear characteristics of the device or circuit, resulting in changes in the amplitude, phase, or shape of the signal. Harmonic distortion in nonlinear distortion means that in the spectrum, in addition to the fundamental wave of the signal, there are also some second, third, and higher-order harmonics of the fundamental wave. These harmonics will cause distortion of the amplifier output signal, thus affecting the quality of the output signal of the amplifier circuit.

[0194] The heart sound and coronary murmur detection device provided by the present invention addresses the signal distortion problem from two aspects: distortion suppression in the signal conditioning channel and distortion suppression in the PCB layout, ensuring the integrity of the signal.

[0195] I. Distortion Suppression in the Signal Conditioning Channel

[0196] In a complete signal conditioning channel, capacitors are mainly applied in the AC coupling circuit 12 at the front end of the signal conditioning channel and the active filter with a Sallen-Key structure in the filter amplification circuit 14. The Sallen-Key filter is an active filter circuit constructed using operational amplifiers, resistors, and capacitors. The basic structure of the filter includes an operational amplifier, two resistors, and two capacitors. Its principle is based on the feedback network, and the cut-off frequency and quality factor of the filter are set by adjusting the values of the resistors and capacitors. Due to its simplicity and flexibility, it is widely used in electronic circuit design.

[0197] Among them, the quality factor is a parameter describing the performance of devices such as filters and resonant circuits. It measures the degree of deviation of the circuit from the ideal response in the resonant state, that is, the quality or purity of the circuit. The higher the quality factor, the closer the response of the circuit to the ideal state at a specific frequency, the smaller the response to other frequencies, and the better the performance of the circuit.

[0198] For multilayer ceramic capacitors MLCC, especially capacitors of the high dielectric constant series (such as X5R and X7R characteristics), special attention should be paid to the fact that their capacitance may be different from the nominal value under DC voltage, and this property is called the DC bias characteristic. The higher the capacitance value of the capacitor, the more obvious its DC bias characteristic. For example, for a capacitor with a nominal value of 47uF - 6.3V - X5R, at a voltage of 6.3V, its actual capacitance may be only about 15% of the nominal value. While for a capacitor with a nominal value of 100nF - 6.3V - X5R, at the same voltage, the capacitance is approximately 75% of its nominal value.

[0199] In addition, the material characteristics of the capacitor also have a significant impact on its DC bias characteristic. Figure 11 Shows the capacitance change curves of three capacitors with the same nominal capacitance value and the same rated voltage with respect to the DC voltage. They are NPO-type capacitors, Y5V capacitors, and X7R capacitors respectively.

[0200] Among them, the NPO-type capacitor is a type of multilayer ceramic capacitor (MLCC), which is usually used in applications such as decoupling, filtering, and signal coupling in electronic circuits. The Y5V capacitor is a ceramic capacitor, which has a very high dielectric coefficient, which enables a relatively large capacitance to be manufactured in a smaller physical size. This makes the Y5V capacitor suitable for applications with low requirements for capacitance and loss at a relatively low cost. The X7R capacitor is a ceramic capacitor, which is classified as a temperature-stable capacitor and is characterized by a relatively large dielectric constant.

[0201] Reference Figure 11, the NPO capacitor has the best DC bias characteristics, and its capacitance value changes the least as the voltage increases. The DC bias characteristics of the X7R capacitor are slightly inferior to those of the NPO capacitor. The Y5V capacitor has the worst DC bias characteristics, and when the DC voltage approaches the rated voltage, its capacitance value is only 20% of the nominal value. However, due to physical size and material limitations, the maximum capacitance value of the NPO capacitor is only 0.1 uF. Therefore, when using the NPO capacitor, it is necessary to pay attention to whether its capacitance value meets the requirements for processing low-frequency signals.

[0202] According to the above analysis, in some possible embodiments provided by the present invention, the Sallen-Key filter includes a first capacitor, and the first capacitor is an NPO-type capacitor.

[0203] In some possible embodiments provided by the present invention, the AC coupling circuit 12 includes a second capacitor, and the second capacitor is an NPO-type capacitor.

[0204] Adopting the above technical solution, the AC coupling circuit 12 and the Sallen-Key active filter of the heart sound and coronary murmur detection device 1 both use NPO-type capacitors, providing the best temperature characteristics and DC bias characteristics, and also reducing the harmonic distortion of the signal.

[0205] II. Distortion suppression in PCB layout

[0206] The methods for suppressing signal distortion through PCB layout mainly include suppressing the parasitic parameters and stray parameters of circuits and components. Specifically, among many parasitic parameters and stray parameters, the most concerned in a low-frequency signal acquisition system such as the heart sound and coronary murmur detection device 1 is the stray capacitance on the transmission path. The stray capacitance may slow down the signal speed by increasing the energy loss during transmission; it may cause additional zeros to appear in the amplifier circuit such as the filter amplification circuit 14, resulting in oscillations in the output of the operational amplifier; it may jointly form additional poles with the internal resistance and capacitive load of the amplifier, leading to instability in the amplifier output. Therefore, minimizing the stray capacitance will improve the stability of the amplifier output, reduce the leakage on the signal transmission path, and ensure low distortion of the signal.

[0207] Figure 12 Shows a PCB layout scheme used for a filter with a Sallen-Key structure formed by an operational amplifier and its surrounding devices.

[0208] Reference Figure 2 and Figure 12 , the heart sound and coronary murmur detection device 1 provided by the present invention includes a filter amplification circuit 14, and the filter amplification circuit includes an operational amplifier. The heart sound and coronary murmur detection device 1 further includes a PCB, the PCB includes a power layer and a ground layer, and the PCB is provided with a second copper cladding cutting area Q2 (such as Figure 12As shown, the second copper cladding cutting area Q2 is not connected to the power layer and the ground layer. The second copper cladding cutting area Q2 is disposed below the output pin 6, the non-inverting input pin 3, and the inverting input pin 2 of the operational amplifier U6.

[0209] Reference Figure 12 , in this embodiment, U6 is the low-noise operational amplifier ADA4522 used. The shaded wireframe represents the area where the copper plane is cut, removing the copper cladding connection of the ground plane and the power plane, that is, the second copper cladding cutting area Q2. The way of cutting the copper plane below and around the output pin 6, the non-inverting input pin 3, and the inverting input pin 2 of the operational amplifier U6 reduces the stray capacitance at these important nodes. This method greatly increases the distance between the plates that may form a capacitance with the pins of the operational amplifier U6, thereby reducing the stray capacitance to a range that will not affect the stability of the operational amplifier U6.

[0210] Second, reference Figure 13 And in combination with Figure 2 , the embodiment of the present invention discloses a method for detecting heart sounds and coronary murmurs, which is detected by using the heart sound and coronary murmur detection device 1 in any one of the foregoing first aspects, including:

[0211] S1: Place the pickup 11 at the projection positions of the coronary arteries on the body surface. The projection positions include: the positions of the third intercostal space near the sternal body and the fourth intercostal space near the sternal body on the left side of the human body, and the positions of the third intercostal space near the sternal body and the fourth intercostal space near the sternal body on the right side of the human body (the projection positions are as Figure 4 shown). Use the pickup 11 to collect the first sound signals at the positions of the third intercostal space near the sternal body and the fourth intercostal space near the sternal body on the left side of the human body, and the positions of the third intercostal space near the sternal body and the fourth intercostal space near the sternal body on the right side of the human body. The first sound signals include heart sound signals and coronary murmur signals.

[0212] S0: Use the filter amplification circuit 14 to extract the coronary murmur signal and amplify the coronary murmur signal to form the first coronary murmur signal.

[0213] By adopting the above technical solution, the synchronous acquisition of heart sound signals and weak coronary murmur signals at multiple positions of the human body is realized, ensuring the effective capture of the murmur in the complete cardiac coronary region; through the filter amplification circuit 14, the extraction and processing of the coronary murmur signal are realized, facilitating the early screening of coronary heart disease according to the processed coronary murmur signal.

[0214] Reference Figure 14, in some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes: S2: removing the DC component in the first sound signal by using an AC coupling circuit 12 to form a second sound signal.

[0215] After step S2, the purity and accuracy of the signal are improved, ensuring that the DC component in the first sound signal will not have an adverse impact on the signal processing and analysis.

[0216] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes: S3: amplifying the second sound signal by using a fixed gain adjustment circuit 13 to form a third sound signal.

[0217] That is, after S2: removing the DC component in the first sound signal by using an AC coupling circuit 12 to form a second sound signal, the heart sound and coronary murmur detection method further includes: S3: amplifying the second sound signal by using a fixed gain adjustment circuit 13 to form a third sound signal.

[0218] Step S3 is the first-stage amplification of the second sound signal, improving the intensity, quality and system performance of the second sound signal, enabling it to meet the requirements of subsequent signal processing or transmission.

[0219] In some possible embodiments provided by the present invention, in the heart sound and coronary murmur detection method, S0: extracting the coronary murmur signal by using a filter amplification circuit 14 and amplifying the coronary murmur signal to form a first coronary murmur signal. Specifically, it is step S4: extracting the coronary murmur signal from the third sound signal by using a filter amplification circuit 14 and amplifying the coronary murmur signal to form a first coronary murmur signal.

[0220] That is, after step S3, the heart sound and coronary murmur detection method further includes step S4: extracting the coronary murmur signal from the third sound signal by using a filter amplification circuit 14 and amplifying the coronary murmur signal to form a first coronary murmur signal.

[0221] Step S4 realizes the extraction and amplification of the coronary murmur signal, which is the second-stage amplification of the sound signal, further improving the intensity, quality and system performance of the coronary murmur signal, enabling it to meet the requirements of subsequent signal processing or transmission.

[0222] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes: S5: adjusting the voltage value of the first coronary murmur signal to a preset voltage range by using an automatic gain adjustment circuit 15 to form a second coronary murmur signal.

[0223] That is, after step S4, the heart sound and coronary murmur detection method further includes: S5: Using the automatic gain adjustment circuit 15 to adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal.

[0224] The heart sound and coronary murmur detection method makes the signal swing as close as possible to within 80% of the ADC range through two adjustable gain methods: fixed gain adjustment and automatic gain adjustment. The design of these two adjustable gain methods can make the best use of the quantization range of the ADC and achieve the highest quantization accuracy.

[0225] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes:

[0226] S6: Using the overload detection module 16 to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain adjustment circuit 15 exceeds a preset voltage threshold:

[0227] S61: If the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, output an overload signal through the overload detection module 16;

[0228] S62: If the peak value of the voltage of the second coronary murmur signal does not exceed the preset voltage threshold, output an underload signal through the overload detection module 16.

[0229] That is, after step S5, the heart sound and coronary murmur detection method further includes S6, S61, and S62.

[0230] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes: S7: Using the analog-to-digital conversion circuit 17 to receive the second coronary murmur signal output from the automatic gain adjustment circuit 15 and convert the second coronary murmur signal into a digital signal.

[0231] In some possible embodiments provided by the present invention, the heart sound and coronary murmur detection method further includes: S61: If the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, output an overload signal through the overload detection module 16, and then, repeat the execution of:

[0232] Step S5: Using the automatic gain adjustment circuit 15 to adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal;

[0233] S6: Using the overload detection module 16 to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain adjustment circuit 15 exceeds a preset voltage threshold;

[0234] Until step S62 is executed: Output an underload signal through the overload detection module 16.

[0235] Step S7: Use the analog-to-digital conversion circuit 17 to receive the second coronary murmur signal output from the automatic gain adjustment circuit 15, and convert the second coronary murmur signal into a digital signal.

[0236] With the above solution, the second coronary murmur signal is adjusted by the detection feedback method and the automatic gain adjustment method to meet the requirement that the peak value of the voltage does not exceed the preset voltage threshold. The second coronary murmur signal is the coronary murmur signal after acquisition, noise removal, filtering, amplification, and gain, which ensures the effective and accurate processing of the murmur in the complete coronary region of the heart, facilitating the early screening of coronary heart disease based on the second coronary murmur signal.

[0237] In a third aspect, referring to Figure 15 , the present invention provides an electronic device 2, including a memory 201, a processor 202, and a computer program stored in the memory 201 and executable on the processor 202. When the processor 202 executes the computer program, it implements the heart sound and coronary murmur detection method in any implementation manner of the foregoing second aspect. Among them, the memory 201 may include, for example, a system memory, a fixed non-volatile storage medium, etc. The system memory stores, for example, an operating system, application programs, a boot loader, and other programs.

[0238] In this embodiment, the electronic device realizes the synchronous acquisition of heart sound signals and weak coronary murmur signals at multiple positions of the human body, ensuring the effective capture of the murmur in the complete coronary region of the heart; the extraction and processing of the coronary murmur signal are realized through the filter amplification circuit.

[0239] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, it implements the heart sound and coronary murmur detection method in any implementation manner of the foregoing second aspect.

[0240] With the above technical solution, the computer-readable storage medium realizes the synchronous acquisition of heart sound signals and weak coronary murmur signals at multiple positions of the human body, ensuring the effective capture of the murmur in the complete coronary region of the heart; the extraction and processing of the coronary murmur signal are realized through the filter amplification circuit.

[0241] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can adopt the form of a computer program product implemented on one or more computer-usable non-transitory storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0242] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to produce a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices generate means for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0243] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0244] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0245] Although the present invention has been illustrated and described with reference to certain preferred embodiments of the present invention, those of ordinary skill in the art should understand that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. Those skilled in the art can make various changes in form and detail, including making several simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A heart sound and coronary murmur detection device, characterized in that, Comprising: A pickup, which is placed at the projection position of the coronary artery on the body surface. The projection positions include: the position near the sternal body in the third intercostal space on the left side of the human body, the position near the sternal body in the fourth intercostal space, the position near the sternal body in the third intercostal space on the right side of the human body, and the position near the sternal body in the fourth intercostal space. The pickup is used to collect a first sound signal, and the first sound signal includes a heart sound signal and a coronary artery murmur signal; A filter amplification circuit, which includes a Sallen-Key filter and an operational amplifier. The input end of the filter amplification circuit is connected to the output end of the pickup. The filter amplification circuit is used to extract the coronary artery murmur signal and amplify the coronary artery murmur signal to form a first coronary artery murmur signal. Among them, the filter amplification circuit is, in the order of signal input, a fourth-order high-pass filter, a first non-inverting amplifier, a second-order low-pass filter, and a second non-inverting amplifier.

2. The heart sound and coronary murmur detection device according to claim 1, characterized in that, The pickup includes at least one of an electret microphone, a piezoelectric accelerometer, and a piezoelectric sensor.

3. The heart sound and coronary murmur detection device according to claim 1, characterized in that, The first sound signal is an alternating current signal. The heart sound and coronary artery murmur detection device includes an AC coupling circuit. The input end of the AC coupling circuit is connected to the output end of the pickup. The AC coupling circuit is used to remove the DC component in the first sound signal to form a second sound signal.

4. The heart sound and coronary murmur detection device according to claim 1, characterized in that, Comprising: A fixed gain adjustment circuit, the input end of which is connected to the output end of the AC coupling circuit. The fixed gain adjustment circuit is used to amplify the second sound signal to form a third sound signal, and the output end of the fixed gain adjustment circuit is connected to the input end of the filter amplification circuit; An automatic gain adjustment circuit, the input end of which is connected to the output end of the filter amplification circuit. The automatic gain adjustment circuit is used to receive the first coronary artery murmur signal output from the output end of the filter amplification circuit and adjust the voltage value of the first coronary artery murmur signal to a preset voltage range to form a second coronary artery murmur signal.

5. The heart sound and coronary murmur detection device according to claim 1, characterized in that, Comprising: An overload detection module, the input end of which is connected to the output end of the automatic gain adjustment circuit. The overload detection module is used to detect whether the peak value of the voltage of the second coronary artery murmur signal output by the automatic gain adjustment circuit exceeds a preset voltage threshold: If the peak value of the voltage of the second coronary artery murmur signal exceeds the preset voltage threshold, the output end of the overload detection module outputs an overload signal; If the peak value of the voltage of the second coronary artery murmur signal does not exceed the preset voltage threshold, the output end of the overload detection module outputs an underload signal; An analog-to-digital conversion circuit, the input end of which is connected to the output end of the automatic gain adjustment circuit. The analog-to-digital conversion circuit is used to receive the second coronary artery murmur signal output from the output end of the automatic gain adjustment circuit and convert the second coronary artery murmur signal into a digital signal.

6. The heart sound and coronary murmur detection device according to claim 1, characterized in that, Comprising a microelectronic control circuit, the input end of which is connected to the output end of the overload detection module. The microelectronic control circuit is used to receive the overload signal output from the output end of the overload detection module; The output end of the microelectronic control circuit is connected to the input end of the automatic gain adjustment circuit. The microelectronic control circuit is used to control the automatic gain adjustment circuit to receive the first coronary murmur signal output from the output end of the filter amplification circuit according to the overload signal, and adjust the voltage value of the first coronary murmur signal to a preset voltage range to form a second coronary murmur signal. The input end of the microelectronic control circuit is further connected to the output end of the analog-to-digital conversion circuit. The microelectronic control circuit is used to receive the digital signal output from the output end of the analog-to-digital conversion circuit.

7. The heart sound and coronary murmur detection device according to claim 1, characterized in that, It includes a PCB. The PCB includes a power layer and a ground layer. The PCB is provided with a first copper cladding cutting area that is not connected to the power layer and the ground layer. The PCB includes an analog signal area and a digital signal area, and the analog signal area and the digital signal area are grounded at a single point. The heart sound and coronary murmur detection device includes a power supply circuit. The first copper cladding cutting area does not affect the connection between the analog signal area and the power supply circuit, nor does it affect the connection between the digital signal area and the power supply circuit. The filter amplification circuit includes an operational amplifier. The PCB is provided with a second copper cladding cutting area that is not connected to the power layer and the ground layer. The second copper cladding cutting area is located below the output pin, non-inverting input pin, and inverting input pin of the operational amplifier.

8. The heart sound and coronary murmur detection device according to claim 7, characterized in that, The analog signal area includes a signal conditioning channel. The signal conditioning channel includes the pickup, AC coupling circuit, fixed gain adjustment circuit, the filter amplification circuit, and the automatic gain adjustment circuit connected in sequence; and / or, the digital signal area includes an analog-to-digital conversion circuit and a microelectronic control circuit; and / or, the first copper cladding cutting area is located between the analog signal area and the digital signal area, so that the analog signal area and the digital signal area are electrically isolated.

9. The heart sound and coronary murmur detection device according to claim 2, wherein The Sallen-Key filter includes a first capacitor.

10. The heart sound and coronary murmur detection device according to claim 9, characterized in that, The first capacitor is an NPO type capacitor.

11. The heart sound and coronary murmur detection device according to claim 3, characterized in that, The AC coupling circuit includes a second capacitor.

12. The heart sound and coronary murmur detection device according to claim 11, characterized in that, The second capacitor is an NPO type capacitor.

13. A method for detecting heart sounds and coronary murmurs, characterized in that, Performing detection using the heart sound and coronary murmur detection device according to any one of claims 1 to 12 includes: Placing the pickup at the projection positions of the coronary arteries on the body surface. The projection positions include: the positions near the sternal body in the third intercostal space on the left side of the human body and the fourth intercostal space near the sternal body, as well as the positions near the sternal body in the third intercostal space on the right side of the human body and the fourth intercostal space near the sternal body. Using the pickup to collect the first sound signals at the positions near the sternal body in the third intercostal space on the left side of the human body and the fourth intercostal space near the sternal body, as well as the positions near the sternal body in the third intercostal space on the right side of the human body and the fourth intercostal space near the sternal body. The first sound signals include heart sound signals and coronary murmur signals. Extract the coronary murmur signal using the filtering and amplifying circuit, and amplify the coronary murmur signal to form a first coronary murmur signal. Among them, the filtering and amplifying circuit includes a Sallen-Key filter and an operational amplifier, and the filtering and amplifying circuit is a 4th-order high-pass filter, a first non-inverting amplifier, a 2nd-order low-pass filter, and a second non-inverting amplifier in the order of signal input.

14. The heart sound and coronary murmur detection method according to claim 13, characterized in that, It further includes: Remove the DC component in the first sound signal using an AC coupling circuit to form a second sound signal.

15. The heart sound and coronary murmur detection method according to claim 14, wherein The method further includes: amplify the second sound signal using a fixed gain adjustment circuit to form a third sound signal.

16. The heart sound and coronary murmur detection method according to claim 15, characterized in that, It further includes: adjust the voltage value of the first coronary murmur signal to a preset voltage range using an automatic gain control circuit to form a second coronary murmur signal.

17. The heart sound and coronary murmur detection method according to claim 16, wherein It further includes: Use an overload detection module to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain control circuit exceeds a preset voltage threshold: If the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, output an overload signal through the overload detection module; If the peak value of the voltage of the second coronary murmur signal does not exceed the preset voltage threshold, output an underload signal through the overload detection module.

18. The heart sound and coronary murmur detection method according to claim 17, characterized in that, It further includes: If the peak value of the voltage of the second coronary murmur signal exceeds the preset voltage threshold, output an overload signal through the overload detection module, and repeat the operation of adjusting the voltage value of the first coronary murmur signal to a preset voltage range using the automatic gain control circuit to form a second coronary murmur signal; Use the overload detection module to detect whether the peak value of the voltage of the second coronary murmur signal output by the automatic gain control circuit exceeds a preset voltage threshold until an underload signal is output through the overload detection module, and use an analog-to-digital conversion circuit to receive the second coronary murmur signal output from the output terminal of the automatic gain control circuit and convert the second coronary murmur signal into a digital signal.

Images