Biological filter circuit capable of shortening stabilization time

Abstract

The invention discloses a biological filter circuit capable of shortening stabilization time, and belongs to the field of signal filter circuits. The biological filter circuit provided by the invention is composed of a detection circuit, a time delay circuit, a selection circuit and an analog filter. According to the circuit, two filters which can be switched to work and are different in cut-off frequency are arranged in an analog filter, through cooperation of a detection circuit, a time delay circuit and a selection circuit, when signal input is detected, the filter with the high cut-off frequency is used for rapidly stabilizing signals, and after the filters are stabilized, the filter is switched to the filter with the low cut-off frequency through a switch; and the cut-off frequency is shifted to a frequency interval suitable for detecting the biological signal, so that the stable reaching time of the filter is shortened. The biological filter circuit has a good noise suppression effect on biological signals.

Description

Technical Field

[0001] The invention belongs to the field of signal filtering circuits, and in particular relates to a biological filter circuit capable of shortening stabilization time. Background Art

[0002] The biofilter circuit is a circuit used to filter and reduce noise of biological signals. It can effectively extract and process various weak signals collected from organisms, which constitute the main components of biological signals. In addition to the well-known electromyographic signals (EMG), biological signals also cover a wealth of physiological activity information, such as subtle fluctuations in pulse, dynamic changes in joint movements, and plantar pressure distribution. These signals provide valuable data for understanding and evaluating human health status, movement patterns, and physiological responses.

[0003] Biosignal processing technology has been deeply integrated into modern medical equipment and daily health monitoring equipment, and its application range is wide and diverse. In the field of telemedicine, through precise biosignal processing, doctors can remotely monitor patients' physiological indicators and make timely medical judgments; physiological signal monitoring systems are commonly found in gyms, rehabilitation centers and home health monitoring, helping users understand their physical condition in real time; motion status tracking devices use biosignals to analyze users' motion patterns and optimize training plans; and somatosensory gaming devices interpret biosignals to achieve natural interaction between players and the gaming environment, enhancing the authenticity and interactivity of the entertainment experience.

[0004] However, biological signals directly obtained from sensors are often accompanied by various environmental noises and electronic equipment interference. If these noises are not processed, they will seriously affect the accuracy and reliability of the signal. Therefore, filters, as a key link in signal processing, play a vital role. A notable feature of biological signals is that their frequencies are generally low, which requires analog filters to operate at lower cutoff frequencies to ensure that the authenticity and integrity of the signal are not destroyed by high-frequency noise. However, the use of low cutoff frequencies brings a significant problem, that is, the filter's settling time is significantly increased. Settling time refers to the time it takes from the analog filter input signal to the filter working in a stable state. The working characteristics of the analog filter commonly used in electronic technology are determined by the resistance R and capacitance C in the circuit. Its cutoff frequency f can be obtained by the formula f=1 / 2πRC, and the corresponding time constant τ=RC. It can be seen that it takes longer for the analog filter to reach a stable state when working at a low cutoff frequency.

[0005] This means that in bio-signal monitoring scenarios that require a quick response, such as pulse wave detection, bio-signal-based somatosensory gaming scenarios, and any other applications with strict real-time requirements, traditional low-cutoff frequency filters may not be able to quickly reach a stable state, thereby delaying the extraction of key information and affecting the accuracy and timeliness of monitoring.

[0006] In view of the above problems, it is urgent to design a biological filter circuit that can accelerate the filter to reach a stable state and is suitable for biological signal processing. Summary of the invention

[0007] The purpose of the present invention is to solve the problem that the stabilization time of the low cut-off frequency filter in the existing biological filter circuit is too long, and to provide a biological filter circuit with shortened stabilization time.

[0008] The specific technical solutions adopted by the present invention are as follows:

[0009] A biological filter circuit for shortening stabilization time, comprising a detection circuit, a delay circuit, a selection circuit and an analog filter;

[0010] The analog filter comprises a first filter and a second filter which can switch between the two filters, and the cut-off frequency of the second filter is higher than the cut-off frequency of the first filter;

[0011] The detection circuit is used to detect the input voltage signal at the biological signal source, and compare whether the input voltage signal is higher than the first threshold voltage, if so, continuously output the first high level, otherwise no output;

[0012] The delay circuit is used to convert the first high level output by the detection circuit into a current to charge the capacitor, thereby gradually increasing the capacitor voltage of the capacitor;

[0013] The selection circuit is used to detect the capacitor voltage of the capacitor and compare whether the capacitor voltage is higher than the second threshold voltage. If so, the second high level is output, otherwise no output is output; the selection circuit is also used to output a mode switching signal for the analog filter according to the first high level and the second high level. In the initial state where there is no biological signal source input voltage signal, the default working mode is the high-frequency filtering mode in which the second filter is in a working state. When the first high level and the second high level are detected to exist at the same time, the working mode of the analog filter is switched from the high-frequency filtering mode to the low-frequency filtering mode in which the first filter is in a working state. When it is detected that the first high level disappears, the capacitor voltage of the capacitor is set to zero, and the analog filter is switched from the low-frequency filtering mode back to the high-frequency filtering mode.

[0014] Preferably, the analog filter is composed of two switchable filter circuits cascaded;

[0015] The first switchable filter circuit is composed of a first capacitor, a second capacitor, a first resistor, a second resistor, a sixth resistor, an eighth resistor, a first switch, a third switch and a first comparator, wherein the signal input end thereof is divided into three paths after passing through the first capacitor, the first path is connected to the positive input end of the first comparator after passing through the second capacitor, the second path is connected to the negative input end of the first comparator after passing through the second resistor, and the third path is connected to the negative input end of the first comparator and the output end of the first comparator after passing through the first switch and the sixth resistor; one end of the first resistor is grounded, and the other end is connected to the positive input end of the first comparator; one end of the eighth resistor is grounded, and the other end is connected to the positive input end of the first comparator after passing through the third switch;

[0016] The circuit structure of the second switchable filter circuit is exactly the same as that of the first switchable filter circuit;

[0017] And the four switches in the two switchable filter circuits are all synchronously controlled to open and close by the switching signal output by the selection circuit; when the four switches are disconnected at the same time, a first filter is formed, and the analog filter enters the low-frequency filtering mode; when the four switches are turned on at the same time, a second filter is formed, and the analog filter enters the high-frequency filtering mode.

[0018] Preferably, the detection circuit includes a first voltage source and a third comparator, the positive input terminal of the third comparator is connected to the biological signal source, the negative input terminal is connected to the first voltage source, and the output terminal is connected to the selection circuit and the delay circuit. When the input voltage signal of the biological signal source is higher than the first threshold voltage provided by the first voltage source, the third comparator outputs a first high level.

[0019] Preferably, the delay circuit comprises a tenth resistor and a fifth capacitor, one end of the tenth resistor is connected to the output end of the third comparator, the other end is connected to the charging end of the fifth capacitor, and the other end of the fifth capacitor is grounded.

[0020] Preferably, the selection circuit includes a second voltage source, a fourth comparator, a transistor, a fifth resistor and an RS trigger, wherein the negative input terminal of the fourth comparator is connected to the charging terminal of the fifth capacitor, the positive input terminal of the fourth comparator is connected to the second voltage source, and the output terminal of the fourth comparator and the output terminal of the third comparator are respectively connected to the two input terminals of the RS trigger; the output terminal of the RS trigger is connected to the base of the transistor after passing through the fifth resistor, and the collector and emitter of the transistor are respectively connected to the two ends of the fifth capacitor, and the output terminal of the RS trigger is also connected to and controls the four switches in the two switchable filter circuits; when the capacitor voltage of the fifth capacitor is higher than the second threshold voltage provided by the second voltage source, the fourth comparator outputs the second high level; when the first high level and the second high level are input into the RS trigger at the same time, the RS trigger controls the four switches in the two switchable filter circuits to be all disconnected, and when the input voltage signal of the biological signal source stops inputting or is lower than the first threshold voltage provided by the first voltage source, the third comparator no longer outputs the first high level, and the RS trigger controls the four switches in the two switchable filter circuits to be all turned on.

[0021] Preferably, in the detection circuit, the first threshold voltage provided by the first voltage source is adjustable to change the starting detection position of the signal.

[0022] Preferably, in the delay circuit and selection circuit, the resistance of the tenth resistor and / or the capacitance of the fifth capacitor and / or the second threshold voltage provided by the second voltage source can be adjusted to control the delay time required for the analog filter to switch from the high-frequency filtering mode to the low-frequency filtering mode.

[0023] Preferably, in the analog filter, the cutoff frequency of the second filter is at least one order of magnitude higher than the cutoff frequency of the first filter, and the cutoff frequency of the first filter is 50 mHz to 100 mHz.

[0024] Preferably, the biological signal source is a pulse signal sensor.

[0025] Preferably, the pulse signal sensor is a piezoresistive flexible film sensor.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a biological filter circuit composed of a detection circuit, a delay circuit, a selection circuit and an analog filter. The circuit sets two filters that can switch between working but have different cutoff frequencies in the analog filter. Through the cooperation of the detection circuit, the delay circuit and the selection circuit, when a signal input is detected, a filter with a high cutoff frequency is used to quickly stabilize the signal. After the filter is stabilized, a switch is used to switch to a filter with a low cutoff frequency, and the cutoff frequency is moved to a frequency range suitable for detecting biological signals, thereby shortening the time it takes for the filter to reach stability. Simulation results show that the biological filter circuit of the present invention has a good suppression effect on pulse wave components below 0.05 Hz. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a circuit module composition of a biological filter circuit for shortening the stabilization time;

[0029] Figure 2 A specific implementation circuit diagram of a biological filter circuit for shortening the stabilization time;

[0030] Figure 3 is the pulse signal originally input in the embodiment of the present invention;

[0031] Figure 4 The figure is the filtering result of the pulse signal by the biological filter circuit and the traditional active high-pass filter in the embodiment of the present invention;

[0032] Figure 5 This is a pulse signal collected using the biological filter circuit of this embodiment. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0034] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for the purpose of distinguishing descriptions, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0035] The present invention provides a biological filter circuit with shortened stabilization time, which is used to accelerate the filter to reach a stable working state without affecting its signal detection function and shorten its stabilization time. Figure 1 As shown, in a preferred embodiment of the present invention, the biological filter circuit for shortening the stabilization time includes a detection circuit, a delay circuit, a selection circuit and an analog filter, which is connected to the biological signal source when in use to collect the voltage signal detected by the biological signal source. The principle of shortening the stabilization time of the biological filter circuit is that a first filter and a second filter that can switch to work but have different cutoff frequencies are set in the analog filter, the second filter is a high cutoff frequency filter, and the first filter is a low cutoff frequency filter. The working state of the two filters in the analog filter is switched by the detection circuit, the delay circuit and the selection circuit. When the signal of the biological signal source enters the filter circuit, it is first quickly stabilized by the second filter with a higher cutoff frequency in the analog filter. At the same time, the detection circuit detects that the signal input is started by the delay circuit. After waiting for a short period of time (the waiting time is recorded as the delay time), the selector switches the working path of the analog filter to the first filter. At this time, the cutoff frequency moves to the low-frequency position, and the analog filter is in a stable working state suitable for detecting biological signals.

[0036] The following is the above Figure 1 The specific working modes and mutual coordination relationships of each circuit module in the biological filter circuit for shortening the stabilization time are described in detail.

[0037] In the biological filter circuit of the present invention, the above-mentioned analog filter has a first filter and a second filter that can switch between working modes, and the cutoff frequency of the second filter is higher than the cutoff frequency of the first filter. In the initial state where there is no biological signal source input voltage signal, the default working mode is that the second filter is in working state. Since the cutoff frequency of the second filter is higher than the cutoff frequency of the first filter, and the first filter and the second filter are selected to work, there are actually two different modes in the entire analog filter. The default working mode is a high cutoff frequency mode that can promote signal stability, and the other mode when the first filter is working is a low cutoff frequency mode suitable for detecting biological signals. The high cutoff frequency mode is only suitable for quickly stabilizing the signal in a short time of the input signal, and it is necessary to understand the switch back to the low cutoff frequency mode after the delay time is reached. Therefore, the switching of different filtering modes in the analog filter needs to rely on the cooperation of the detection circuit, the delay circuit, and the selection circuit.

[0038] In the biological filter circuit of the present invention, the detection circuit is used to detect the input voltage signal at the biological signal source and compare whether the input voltage signal is higher than the first threshold voltage. If so, the first high level is continuously output, otherwise no output is performed.

[0039] In the biological filter circuit of the present invention, the delay circuit is used to convert the first high level output by the detection circuit into a current to charge the capacitor, thereby gradually increasing the capacitor voltage of the capacitor.

[0040] In the biological filter circuit of the present invention, the selection circuit is used to detect the capacitor voltage of the capacitor and compare whether the capacitor voltage is higher than the second threshold voltage. If so, the second high level is output, otherwise no output is output. The selection circuit is also used to output a mode switching signal for the analog filter according to the first high level and the second high level. The specific switching logic is: in the initial state without the input voltage signal of the biological signal source, the default working mode is the high-frequency filtering mode in which the second filter is in the working state. When the first high level and the second high level are detected to exist at the same time, the working mode of the analog filter is switched from the high-frequency filtering mode to the low-frequency filtering mode in which the first filter is in the working state. When the disappearance of the first high level is detected, the capacitor voltage of the capacitor is set to zero to facilitate the capacitor to recharge, and the analog filter is switched from the low-frequency filtering mode back to the high-frequency filtering mode.

[0041] In the present invention, the specific circuit designs of the detection circuit, delay circuit, selection circuit and analog filter can be adjusted according to actual needs.

[0042] In the embodiment of the present invention, the first filter and the second filter in the analog filter are not independent filters. The second filter needs to achieve the purpose of mode switchability by adding controllable switches and resistors and reusing the circuit structure of the first filter. In order to match this specific analog filter, the present invention also designs a specific detection circuit, delay circuit and selection circuit. Figure 1 The specific structure of each circuit module in the biological filter circuit shown in the embodiment of the present invention is described in detail.

[0043] like Figure 2As shown, the specific circuit forms of the detection circuit, delay circuit, selection circuit and analog filter in the embodiment of the present invention are shown. The electronic components in the circuit include the first capacitor C1, the second capacitor C2, the third capacitor C3, the fourth capacitor C4, the fifth capacitor C5, the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, the tenth resistor R10, the first comparator U1, the second comparator U2, the third comparator U3, the fourth comparator U4, the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the first voltage source V1, the second voltage source V2, and the transistor Q1. The input voltage signal of the biological signal source is recorded as SIGNAL. The device forms of the first comparator U1, the second comparator U2, the third comparator U3, and the fourth comparator U4 are all operational amplifiers.

[0044] In an embodiment of the present invention, the analog filter is composed of two switchable filter circuits in cascade. The first switchable filter circuit is composed of a first capacitor C1, a second capacitor C2, a first resistor R1, a second resistor R2, a sixth resistor R6, an eighth resistor R8, a first switch S1, a third switch S3 and a first comparator U1, wherein the signal input end thereof is divided into three paths after passing through the first capacitor C1, the first path is connected to the positive input end of the first comparator U1 after passing through the second capacitor C2, the second path is connected to the negative input end of the first comparator U1 after passing through the second resistor R2, and the third path is connected to the negative input end of the first comparator U1 and the output end of the first comparator U1 after passing through the first switch S1 and the sixth resistor R6; one end of the first resistor R1 is grounded, and the other end is connected to the positive input end of the first comparator U1; one end of the eighth resistor R8 is grounded, and the other end is connected to the positive input end of the first comparator U1 after passing through the third switch S3.

[0045] The circuit structure of the second switchable filter circuit is exactly the same as that of the first switchable filter circuit. Specifically, the second switchable filter circuit is composed of a third capacitor C3, a fourth capacitor C4, a third resistor R3, a fourth resistor R4, a seventh resistor R7, a ninth resistor R9, a second switch S2, a fourth switch S4 and a second comparator U2. Its signal input end is divided into three paths after passing through the third capacitor C3. The first path is connected to the positive input end of the second comparator U2 after passing through the fourth capacitor C4, the second path is connected to the negative input end of the second comparator U2 after passing through the fourth resistor R4, and the third path is connected to the negative input end of the second comparator U2 and the output end of the second comparator U2 after passing through the second switch S2 and the seventh resistor R7; one end of the third resistor R3 is grounded, and the other end is connected to the positive input end of the second comparator U2; one end of the ninth resistor R9 is grounded, and the other end is connected to the positive input end of the second comparator U2 after passing through the fourth switch S4.

[0046] In the above analog filter, the four switches in the two switchable filter circuits, namely the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4, are all synchronously controlled to open and close by the switching signal output by the above selection circuit. When the four switches are disconnected at the same time, a first filter composed of capacitors C1, C2, C3, C4 and resistors R1, R2, R3, R4 and U1, U2 is formed, so that the analog filter enters the above low-frequency filtering mode. When the four switches are turned on at the same time (i.e., the switches are closed), a second filter is formed by further combining switches S1, S2, S3, S4 and resistors R6, R7, R8, R9 on the basis of the first filter, so that the analog filter enters the above high-frequency filtering mode.

[0047] In an embodiment of the present invention, the detection circuit includes a first voltage source V1 and a third comparator U3, wherein the positive input terminal of the third comparator U3 is connected to the biological signal source, and the input voltage signal received from the biological signal source is recorded as SIGNAL; the negative input terminal of the third comparator U3 is connected to the first voltage source V1, and the first voltage source V1 provides a first threshold voltage; the output terminal of the third comparator U3 is connected to the selection circuit and the delay circuit. The third comparator U3 can determine the corresponding output based on the input voltage signal SIGNAL and the first threshold voltage. When the input voltage signal SIGNAL of the biological signal source is higher than the first threshold voltage provided by the first voltage source V1, the third comparator U3 outputs a first high level VCMP, otherwise no output.

[0048] In an embodiment of the present invention, the delay circuit includes a tenth resistor R10 and a fifth capacitor C5, one end of the tenth resistor R10 is connected to the output end of the third comparator U3, one of the two plates of the fifth capacitor C5 is required to be used as a charging end, the other end of the tenth resistor R10 is connected to the charging end of the fifth capacitor C5, and the other end of the fifth capacitor C5 is grounded. When the third comparator U3 in the detection circuit outputs the first high level VCMP, the first high level VCMP is converted into a current through the tenth resistor R10 and charges the fifth capacitor C5, gradually increasing the capacitor voltage VCMPDLY of the fifth capacitor C5.

[0049] In an embodiment of the present invention, the selection circuit includes a second voltage source V2, a fourth comparator U4, a transistor Q1, a fifth resistor R5 and an RS trigger A1. The negative input terminal of the fourth comparator U4 is connected to the charging terminal of the fifth capacitor C5, and is used to input the capacitor voltage VCMPDLY of the fifth capacitor C5; the positive input terminal of the fourth comparator U4 is connected to the second voltage source V2, and is used to input the second threshold voltage provided by the second voltage source V2, so that the fourth comparator U4 can compare the relative height between the capacitor voltage VCMPDLY of the fifth capacitor C5 and the second threshold voltage provided by the second voltage source V2, and then output the second high level VCMPTO when the capacitor voltage VCMPDLY of the fifth capacitor C5 is higher than the second threshold voltage provided by the second voltage source V2. The output terminal of the fourth comparator U4 and the output terminal of the third comparator U3 are respectively connected to the two input terminals of the RS trigger A1, wherein the output terminal of the fourth comparator U4 is connected to the S terminal of the RS trigger A1, and the output terminal of the third comparator U3 is connected to the R terminal of the RS trigger A1. The output end of the RS trigger A1 is connected to the base of the transistor Q1 through the fifth resistor R5, and the collector and emitter of the transistor Q1 are respectively connected to the two ends of the fifth capacitor C5. At the same time, in order to realize the working mode switching of the above-mentioned analog filter, the output end of the RS trigger A1 also needs to connect and control the four switches in the two switchable filter circuits. Based on this selection circuit, the selection and switching logic for the working mode of the analog filter is as follows: when the capacitor voltage VCMPDLY of the fifth capacitor C5 is higher than the second threshold voltage provided by the second voltage source V2, the fourth comparator U4 outputs the second high level VCMPTO; when the first high level VCMP and the second high level VCMPTO are simultaneously input into the RS trigger A1, it indicates that the input signal SIGNAL has been detected and the delay time has been reached, and the RS trigger A1 outputs the control signal HPFBYP to control the four switches in the two switchable filter circuits to be all disconnected, and the first filter starts working and enters the low-frequency filtering mode; when the input voltage signal SIGNAL of the biological signal source stops inputting or is lower than the first threshold voltage provided by the first voltage source V1, the third comparator U3 no longer outputs the first high level VCMP, and the RS trigger A1 controls the four switches in the two switchable filter circuits to be all turned on, and the second filter starts working and enters the high-frequency filtering mode.

[0050] Therefore, in the above Figure 2 The biofilter circuit with shortened stabilization time shown in the figure can adjust the overall biofilter performance parameters by adjusting the parameters of multiple components, which can be divided into the following three aspects:

[0051] 1) In the detection circuit, the first threshold voltage provided by the first voltage source V1 is adjustable to change the starting detection position of the signal SIGNAL.

[0052] 2) In the delay circuit and the selection circuit, one or more of the resistance of the tenth resistor R10, the capacitance of the fifth capacitor C5, and the second threshold voltage provided by the second voltage source V2 can be adjusted to control the delay time required for the analog filter to switch from the high-frequency filtering mode to the low-frequency filtering mode.

[0053] 3) In the analog filter, the cutoff frequency of the second filter and the cutoff frequency of the first filter are adjustable to change the filtering performance of the two filtering modes. Preferably, the cutoff frequency of the second filter is at least one order of magnitude higher than the cutoff frequency of the first filter, and the cutoff frequency of the first filter is 50 mHz to 100 mHz.

[0054] When in use, the above-mentioned biological filter circuit can be connected to a biological signal source to quickly and stably filter and collect the signal SIGNAL generated by the biological signal source. Figure 2 The overall working principle of the biological filter circuit with shortened stabilization time shown is as follows: when there is no signal SIGNAL input, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are in a closed state, and the analog filter works in the high-frequency filtering mode of the second filter; when there is a signal SIGNAL input, the third comparator U3 in the detection circuit compares the input signal with the first threshold voltage provided by the first voltage source V1, and when the DC component of the input signal is greater than the first threshold voltage provided by the first voltage source V1, the third comparator U3 stably outputs the first high level, so that the delay circuit converts the first high level output by the detection circuit into a current to charge the fifth capacitor C5 through the tenth resistor R10, and the voltage VCMPDLY at one end node of the fifth capacitor C5 gradually increases. When VCMPDLY is greater than the second threshold voltage provided by the second voltage source V2, the fourth comparator U4 outputs a second high level, and the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are disconnected through the RS trigger A1, and the analog filter switches from the second filter operation to the first filter operation, and the cut-off frequency becomes lower, thereby formally starting to collect biological signals; when the signal SIGNAL stops input or is lower than the first threshold voltage provided by the first voltage source V1, the RS trigger A1 turns on the transistor Q1, and the fifth capacitor C5 discharges through the transistor Q1 to reduce the voltage VCMPDLY. When it is lower than the second threshold voltage provided by the second voltage source V2, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are closed again, the transistor Q1 automatically returns to the disconnected state, and the voltage of the fifth capacitor C5 is reset to zero, and the analog filter switches from the first filter operation state to the second filter operation state, waiting for the next valid biological signal input.

[0055] The above-mentioned biological filter circuit is particularly suitable for collecting pulse wave signals, that is, the biological signal source is a pulse signal sensor, and the pulse signal sensor can be a piezoresistive flexible film sensor or other forms of sensors. The filtering stabilization effect of the biological filter circuit is demonstrated below through a specific embodiment.

[0056] Example

[0057] In this embodiment, the biological signal is a pulse signal. The human heart rate generally ranges from 30 to 210 beats per minute, and the pulse is mainly determined by the heartbeat, so the frequency of the pulse signal is 0.5 to 3.5 Hz. The pulse formation mechanism and the position of the artery determine that the pulse signal is very weak, and it is often interfered with by noise, drift and abnormal values ​​during the acquisition process. These interferences seriously affect the accuracy of the collected signal and must be filtered out. When collecting pulse signals, there are mainly three types of myoelectric noise, baseline drift, and power frequency interference.

[0058] In this embodiment, the biological signal source is a pulse signal sensor in the form of a piezoresistive flexible film, model RP_C76LT_LF2 ​​sensor, and the main noise in the signal is a baseline drift with a very low frequency. The cutoff frequency of the first filter is 100mHz, and the cutoff frequency of the second filter is 1.9 Hz. The device parameters are C1 capacitance of 10 uF, C2 capacitance of 10 uF, R1 resistance of 412 kΩ, R2 resistance of 60.4 kΩ, C3 capacitance of 10 uF, C4 capacitance of 10 uF, R3 resistance of 174 kΩ, R4 resistance of 147 kΩ, and R6, R7, R8, and R9 resistance of 20 kΩ; comparators U1 and U2 form an active filter circuit with the above resistors and capacitors, and operational amplifier AD712 is selected; comparators U3 and U4 use LT1017. In the delay circuit, the delay time is adjusted by changing the resistance and capacitance. In this embodiment, the device parameters are as follows: R10 resistance is 1 MΩ, C5 capacitance is 10 uF, Q1 uses transistor 2N3906, and R5 resistance is 220 Ohm. In addition, the power supply voltages are VDD +5V, VEE -5V, Vdigital +5V, and V1 and V2 are 1V and 2V respectively.

[0059] To verify the effectiveness of the design, the unprocessed pulse signal data collected by the RP_C76LT_LF2 ​​sensor was imported into the power electronics simulation tool LTspice as a signal source, and filter simulation was performed on the biological filter circuit of this embodiment (denoted as sig_fir_sw) and the traditional active high-pass filter (denoted as Sig_fil, that is, only the first filter circuit is used in the analog filter, and the second filter circuit is not set). The simulation results are shown in the figure. Figure 3 and Figure 4 As shown in the figure, the horizontal axis is time and the vertical axis is voltage value. Figure 3 The input pulse signal V(signal) is 15 seconds long. Figure 4 The blue curve V(sig_fil_sw) represents the filtered signal obtained by the biological filter circuit sig_fil_sw of this embodiment and the traditional active high-pass filter sig_fil, and the red curve V(sig_fil) represents the filtered signal obtained by the traditional active high-pass filter sig_fil. It can be observed that the time for the filter provided in this embodiment to reach a stable working state is greatly shortened. Figure 5 The pulse signal collected by the biofilter circuit of this embodiment is demonstrated, indicating that the circuit can effectively collect stable pulse signals.

[0060] The above-described embodiments are only some preferred implementations of the present invention, but are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A biological filter circuit with shortened stabilization time, characterized in that: It includes detection circuit, delay circuit, selection circuit and analog filter; The analog filter comprises a first filter and a second filter which can switch between the two filters, and the cut-off frequency of the second filter is higher than the cut-off frequency of the first filter; The detection circuit is used to detect the input voltage signal at the biological signal source, and compare whether the input voltage signal is higher than the first threshold voltage, if so, continuously output the first high level, otherwise no output; The delay circuit is used to convert the first high level output by the detection circuit into a current to charge the capacitor, thereby gradually increasing the capacitor voltage of the capacitor; The selection circuit is used to detect the capacitor voltage of the capacitor and compare whether the capacitor voltage is higher than the second threshold voltage. If so, the second high level is output, otherwise no output is output; the selection circuit is also used to output a mode switching signal for the analog filter according to the first high level and the second high level. In the initial state where there is no biological signal source input voltage signal, the default working mode is the high-frequency filtering mode in which the second filter is in a working state. When the first high level and the second high level are detected to exist at the same time, the working mode of the analog filter is switched from the high-frequency filtering mode to the low-frequency filtering mode in which the first filter is in a working state. When it is detected that the first high level disappears, the capacitor voltage of the capacitor is set to zero, and the analog filter is switched from the low-frequency filtering mode back to the high-frequency filtering mode.

2. The biofilter circuit with shortened stabilization time as claimed in claim 1, characterized in that: The analog filter is composed of two switchable filter circuits cascaded; The first switchable filter circuit is composed of a first capacitor (C1), a second capacitor (C2), a first resistor (R1), a second resistor (R2), a sixth resistor (R6), an eighth resistor (R8), a first switch (S1), a third switch (S3) and a first comparator (U1). The signal input end thereof is divided into three paths after passing through the first capacitor (C1), the first path is connected to the positive input end of the first comparator (U1) after passing through the second capacitor (C2), the second path is connected to the negative input end of the first comparator (U1) after passing through the second resistor (R2), and the third path is connected to the negative input end of the first comparator (U1) and the output end of the first comparator (U1) after passing through the first switch (S1) and the sixth resistor (R6); one end of the first resistor (R1) is grounded, and the other end is connected to the positive input end of the first comparator (U1); one end of the eighth resistor (R8) is grounded, and the other end is connected to the positive input end of the first comparator (U1) after passing through the third switch (S3); The circuit structure of the second switchable filter circuit is exactly the same as that of the first switchable filter circuit; And the four switches in the two switchable filter circuits are all synchronously controlled to open and close by the switching signal output by the selection circuit; when the four switches are disconnected at the same time, a first filter is formed, and the analog filter enters the low-frequency filtering mode; when the four switches are turned on at the same time, a second filter is formed, and the analog filter enters the high-frequency filtering mode.

3. The biofilter circuit with shortened stabilization time as claimed in claim 2, characterized in that: The detection circuit comprises a first voltage source (V1) and a third comparator (U3), wherein the positive input terminal of the third comparator (U3) is connected to the biological signal source, the negative input terminal is connected to the first voltage source (V1), and the output terminal is connected to the selection circuit and the delay circuit; when the input voltage signal of the biological signal source is higher than a first threshold voltage provided by the first voltage source (V1), the third comparator (U3) outputs a first high level.

4. The biofilter circuit with shortened stabilization time as claimed in claim 3, characterized in that: The delay circuit comprises a tenth resistor (R10) and a fifth capacitor (C5), one end of the tenth resistor (R10) is connected to the output end of the third comparator (U3), the other end is connected to the charging end of the fifth capacitor (C5), and the other end of the fifth capacitor (C5) is grounded.

5. The biofilter circuit for shortening the stabilization time as claimed in claim 4, characterized in that: The selection circuit comprises a second voltage source (V2), a fourth comparator (U4), a transistor (Q1), a fifth resistor (R5) and an RS trigger (A1), wherein the negative input end of the fourth comparator (U4) is connected to the charging end of the fifth capacitor (C5), the positive input end of the fourth comparator (U4) is connected to the second voltage source (V2), the output end of the fourth comparator (U4) and the output end of the third comparator (U3) are respectively connected to the two input ends of the RS trigger (A1); the output end of the RS trigger (A1) is connected to the base of the transistor (Q1) through the fifth resistor (R5), the collector and emitter of the transistor (Q1) are respectively connected to the two ends of the fifth capacitor (C5), and the RS trigger The output end of (A1) is also connected to and controls four switches in two switchable filter circuits; when the capacitor voltage of the fifth capacitor (C5) is higher than the second threshold voltage provided by the second voltage source (V2), the fourth comparator (U4) outputs a second high level; when the first high level and the second high level are simultaneously input into the RS trigger (A1), the RS trigger (A1) controls all four switches in the two switchable filter circuits to be disconnected; when the input voltage signal of the biological signal source stops being input or is lower than the first threshold voltage provided by the first voltage source (V1), the third comparator (U3) no longer outputs the first high level, and the RS trigger (A1) controls all four switches in the two switchable filter circuits to be turned on.

6. The biofilter circuit with shortened stabilization time as claimed in claim 5, characterized in that: In the detection circuit, the first threshold voltage provided by the first voltage source (V1) is adjustable to change the starting detection position of the signal.

7. The biofilter circuit with shortened stabilization time as claimed in claim 5, characterized in that: In the delay circuit and the selection circuit, the resistance of the tenth resistor (R10) and / or the capacitance of the fifth capacitor (C5) and / or the second threshold voltage provided by the second voltage source (V2) can be adjusted to control the delay time required for the analog filter to switch from the high-frequency filtering mode to the low-frequency filtering mode.

8. The biofilter circuit with shortened stabilization time as claimed in claim 5, characterized in that: In the analog filter, the cutoff frequency of the second filter is at least one order of magnitude higher than the cutoff frequency of the first filter, and the cutoff frequency of the first filter is 50 mHz to 100 mHz.

9. The biofilter circuit with shortened stabilization time as claimed in claim 1, characterized in that: The biological signal source is a pulse signal sensor.

10. The biofilter circuit with shortened stabilization time as claimed in claim 9, characterized in that: The pulse signal sensor adopts a piezoresistive flexible film sensor.

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