An instrument amplifier for bioelectrical signals

Abstract

The present invention discloses an instrument amplifier for bioelectric signals, including a signal input module, which amplifies the received bioelectric signal and performs impedance matching, and then outputs a low-impedance signal; a charge transfer module, which restores the waveform of the amplified low-impedance signal after low-pass high-frequency clutter removal, and outputs a low-pass frequency point signal; and a signal module, which is used to provide a signal source to the charge transfer module for charge transfer output. By using the charge transfer principle, a circuit with a high common mode ratio can be constructed using an ordinary operational amplifier, thereby making the present invention easier to implement in practical applications while reducing the number of components, reducing the volume of the application circuit, reducing the application cost, and expanding the advantages of single operational amplifier application in the instrument circuit space.

Description

Technical Field

[0001] The invention relates to the technical field of biomedical electronics, and in particular to an instrument amplifier for bioelectric signals. Background Art

[0002] At present, electrocardiogram monitoring system, electroencephalogram monitoring system and neural signal recording system are a research hotspot in the field of biomedical electronics at home and abroad. The recording research of electrocardiogram signals, electroencephalogram signals and neural signals has a wide range of application value. Among them, electrocardiogram signals are of great significance for detecting physiological and pathological changes of the heart. Electroencephalogram signals and neural signals are of high value for detecting and diagnosing neurological diseases such as epilepsy. Their research progress is of great significance for future neural prostheses and the cure of neurological diseases. For electronic systems that record and detect the above-mentioned biological signals, high-performance instrumentation amplifiers are a crucial module.

[0003] The frequency band of bioelectric signals is relatively low, generally below 10kHz, and the amplitude of the signal is weak, generally between a few microvolts and a few millivolts. For example, EEG signals are generally distributed between 0.5Hz and 100Hz, and the amplitude is generally between 1μV and 100μV; ECG signals are generally distributed between 0.5Hz and 500Hz, and the amplitude is between 1μV and 500μV; neural signals are generally divided into action potential signals and local potential signals, with frequencies between 200Hz and 10kHz and 0.1Hz to 200Hz, respectively, and the amplitude is generally between hundreds of microvolts and several millivolts. At the same time, in the recording system of EEG, ECG, and neural signals, the electrodes used to detect signals will have an output impedance of up to thousands of ohms due to the attachment of surrounding neurons or cells. Due to the characteristics of bioelectric signals, instrument amplifiers used for biosignals are required to have low noise, high common-mode rejection ratio, high input impedance, and high amplification factor.

[0004] There are two types of commonly used instrument amplifier circuits: the first is an ordinary three-op-amp structure, which is characterized by a simple structure and easy application; the second is a chopper op-amp structure, which is characterized by a complex structure but better noise and common mode than the ordinary three-op-amp structure.

[0005] However, the existing low-noise and high-common-mode instruments with ordinary three-op-amp structures are relatively expensive, mainly because the matching resistance requirements of the third pole are relatively high and difficult to match; at the same time, the chopper op-amp structure uses more analog switches, the circuits are complex, and it is difficult to integrate, making it difficult to implement in applications.

[0006] Therefore, there is an urgent need to invent an instrument amplifier that can use the charge transfer principle to build a circuit with a higher common mode ratio using an ordinary operational amplifier, while reducing the number of components, making it easier to implement in practical applications, reducing the size of the application circuit, reducing the application cost, and expanding the application of single operational amplifiers in the instrument circuit space to produce instrument amplifiers for bioelectric signals. Summary of the invention

[0007] The purpose of the present invention is to provide an instrument amplifier for bioelectric signals, which uses the charge transfer principle to realize a method in which an ordinary operational amplifier can build a circuit with a higher common mode ratio, thereby reducing the number of components while being easier to implement in practical applications. It has the advantages of reducing the volume of application circuits, reducing application costs, expanding the application space of single operational amplifiers for instrument circuits, and solving the problems in the prior art.

[0008] To achieve the above-mentioned object, the present invention provides the following technical solutions: an instrument amplifier for bioelectric signals, comprising a signal input module 1, wherein the signal input module 1 amplifies the bioelectric signal received by the signal input module 1 and performs impedance matching to output a low-impedance signal;

[0009] A charge transfer module 2, wherein the charge transfer module 2 performs waveform restoration on the amplified low impedance signal after low-pass high-frequency clutter removal, and outputs a low-pass frequency point signal;

[0010] The signal module 3 is used to provide a signal source to the charge transfer module 2 for charge transfer output.

[0011] As an improvement of the instrument amplifier for bioelectric signals described in the present invention, the signal input module 1 includes an RC filtering circuit composed of a resistor R1, a capacitor C4, a resistor R8, and a capacitor C7, and an amplification circuit composed of a first operational amplifier U2A, a second operational amplifier U2B, a resistor R4, and a resistor R6, wherein the first end of the resistor R1 and the first end of the resistor R8 are respectively connected to the bioelectric signal, the second end of the resistor R1 is respectively connected to the first end of the capacitor C4 and the same-direction input end of the first operational amplifier U2A, and the second end of the resistor R8 is respectively connected to the first end of the capacitor C7 and the second operational amplifier U2A. The same-direction input terminal of the amplifier U2B, the second end of the capacitor C4 and the second end of the capacitor C7 are grounded respectively, the reverse input terminal of the first operational amplifier U2A is connected in series with the resistor R5 and then connected to the reverse input terminal of the second operational amplifier U2B, the first end of the resistor R4 is connected to the reverse input terminal of the first operational amplifier U2A, and the second end is connected to the output terminal of the first operational amplifier U2A, the first end of the resistor R6 is connected to the reverse input terminal of the second operational amplifier U2B, and the second end is connected to the output terminal of the second operational amplifier U2B, which are used to amplify the bioelectric signal, perform impedance matching, and output a low-impedance signal.

[0012] As an improvement to the instrument amplifier for bioelectric signals described in the present invention, the charge transfer module 2 includes a primary low-pass filter circuit composed of a resistor R2, a capacitor C5 and a resistor R9 for removing irrelevant high-frequency signals, a charge and discharge circuit composed of a resistor R3, a resistor R10, a single-pole double-throw analog switch Q1, a single-pole double-throw analog switch Q2, and a capacitor C6, and a secondary low-pass filter circuit composed of a resistor R7 and a capacitor C8, wherein the first end of the resistor R2 and the first end of the resistor R9 are respectively connected to the output end of the first operational amplifier U2A and the output end of the second operational amplifier U2B, the second end of the resistor R2 and the second end of the resistor R9 are respectively connected to the first end and the second end of the capacitor C5, and the second end of the resistor R2 is connected in series with the resistor R3 and then connected to the single-pole double-throw analog switch Q 1, the second end of the resistor R9 is connected in series with the resistor R10 and then connected to the normally open pin 6 of the single-pole double-throw analog switch Q2, the pin 1 of the single-pole double-throw analog switch Q1 is connected to the pin 1 of the single-pole double-throw analog switch Q2, the pin 2 of the single-pole double-throw analog switch Q1 is connected to VCC, the pin 3 of the single-pole double-throw analog switch Q1 is grounded, the normally closed pin 5 of the single-pole double-throw analog switch Q1 is connected to the first end of the capacitor C6, the second end of the capacitor C6 is connected to the normally closed pin 4 of the single-pole double-throw analog switch Q2, the pin 2 of the single-pole double-throw analog switch Q2 is connected to VCC, the pin 3 of the single-pole double-throw analog switch Q2 is grounded, the normally closed pin 4 of the single-pole double-throw analog switch Q2 is connected in series with the first end of the resistor R7 and then outputs a low-pass frequency point signal, the first end of the capacitor C8 is connected to the second end of the resistor R7, and the second end of the capacitor C8 is grounded.

[0013] As an improvement to the instrument amplifier for bioelectric signals described in the present invention, the signal module 3 includes a signal source circuit composed of a chip U1, a capacitor C1, a capacitor C2 and a capacitor C3, wherein pin 5 of the chip U1 is connected to pin 1 of a single-pole double-throw analog switch Q1 for oscillation signal output, pin 4 of the chip U1 is grounded, pin 5 and pin 3 of the chip U1 are respectively connected to the first end and the second end of capacitor C1, pin 1 of the chip U1 is grounded, the first end of the capacitor C2 is connected to pin 1 of the chip U1, the second end of the capacitor C2 is grounded, the first end of the capacitor C3 is connected to pin 2 of the chip U1, the second end is grounded, and pin 2 of the chip U1 is grounded, which is used for the negative power supply driving capability of the charge pump and the oscillation signal output, thereby realizing fast switching of the single-pole double-throw analog switch Q1 and the single-pole double-throw analog switch Q2 between normally open and normally closed.

[0014] As an improvement to the instrument amplifier for bioelectric signals described in the present invention, the gain coefficients of the first operational amplifier U2A and the second operational amplifier U2B are: GAIN=1+(R4+R7) / R6.

[0015] As an improvement to the instrument amplifier for bioelectric signals described in the present invention, the two ends of the capacitor C5 in the primary low-pass filter circuit are low-pass frequency points, and the output voltage of the resistance and capacitance values ​​at both ends is calculated as follows:

[0016] Uo=Ui / [(2*Pi*f*R*C)^2+1]^0.5, where:

[0017] Uo is the output voltage; Ui is the input voltage; Pi is the pi; f is the signal frequency.

[0018] As an improvement to the instrument amplifier for bioelectric signals described in the present invention, the chip U1 is of the SGM3204 type.

[0019] As a second aspect of the present invention, the instrument amplifier for bioelectric signals is used in the field of biomedical electronic technology.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The charge transfer principle is used to realize a method in which a circuit with a high common mode ratio can be constructed using an ordinary operational amplifier, thereby reducing the number of components and making the present invention easier to implement in practical applications, thereby reducing the volume of the application circuit, reducing the application cost, and expanding the application space of a single operational amplifier in instrument circuits;

[0022] 2. This circuit uses a charge pump circuit close to 1MHZ, and the theoretical value of the acquisition bandwidth is 0-100KHZ, which greatly meets the needs of ordinary bioelectric acquisition, and achieves a very small noise level by adopting high-frequency chopping. At the same time, it reduces the number of original parts, is easier to implement in practical applications, reduces the size of the application circuit, and has lower costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an example diagram of the output waveform of the original bioelectric signal after charge transfer in an embodiment of the present invention.

[0024] Figure 2 The figure is a schematic diagram of the circuit principle of an instrument amplifier for bioelectric signals in one embodiment of the present invention.

[0025] Figure 3 The figure is a schematic diagram of the bioelectric signal transmission process in one embodiment of the present invention.

[0026] Figure 4 Schematic diagram of the effect of high common mode ratio of the bioelectric signal instrument amplifier in one embodiment of the present invention.

[0027] Notes in the figure: 1-signal input module, 2-charge transfer module, 3-signal module. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0030] As an embodiment of the present invention, an instrument amplifier for bioelectric signals, such as Figure 1-3 As shown, it includes a signal input module 1, which amplifies the received bioelectric signal and performs impedance matching to output a low-impedance signal;

[0031] Charge transfer module 2, which performs waveform restoration on the amplified low impedance signal after low-pass high-frequency clutter removal, and outputs a low-pass frequency point signal;

[0032] Signal module 3, signal module 3 is used to provide a signal source to the charge transfer module 2 for charge transfer output, and realizes a method in which a common operational amplifier can build a circuit with a higher common mode ratio through the charge transfer principle, thereby making the present invention easier to implement in practical applications while reducing the number of components, reducing the volume of the application circuit, reducing the application cost, and expanding the advantages of single operational amplifier application in instrument circuit space.

[0033] In one embodiment of the present invention, the signal input module 1 includes an RC filtering circuit composed of a resistor R1, a capacitor C4, a resistor R8, and a capacitor C7, and an amplifying circuit composed of a first operational amplifier U2A, a second operational amplifier U2B, a resistor R4, and a resistor R6, wherein the first end of the resistor R1 and the first end of the resistor R8 are respectively connected to the bioelectric signals IN1 and IN2, the second end of the resistor R1 is respectively connected to the first end of the capacitor C4 and the same-direction input end of the first operational amplifier U2A, the second end of the resistor R8 is respectively connected to the first end of the capacitor C7 and the same-direction input end of the second operational amplifier U2B, the second end of the capacitor C4 and the second end of the capacitor C7 are respectively grounded, and the reverse input end of the first operational amplifier U2A is connected to the reverse input end of the first operational amplifier U2A. The first end of the resistor R4 is connected to the reverse input terminal of the first operational amplifier U2A, and the second end is connected to the output terminal of the first operational amplifier U2A. The first end of the resistor R6 is connected to the reverse input terminal of the second operational amplifier U2B, and the second end is connected to the output terminal of the second operational amplifier U2B. The IN1 and IN2 bioelectric signals pass through the RC filtering circuit composed of resistor R1, capacitor C4, resistor R8, and capacitor C7 to the first operational amplifier U2A and the second operational amplifier U2B for amplification, and the amplification factor is: GAIN=1+(R4+R7) / R6, which is used to amplify weak bioelectric signals, perform impedance matching, and output a lower output impedance.

[0034] In one embodiment of the present invention, the charge transfer module 2 includes a primary low-pass filter circuit composed of a resistor R2, a capacitor C5 and a resistor R9 for removing irrelevant high-frequency signals, a charge and discharge circuit composed of a resistor R3, a resistor R10, a single-pole double-throw analog switch Q1, a single-pole double-throw analog switch Q2 and a capacitor C6, and a secondary low-pass filter circuit composed of a resistor R7 and a capacitor C8, wherein a first end of the resistor R2 and a first end of the resistor R9 are respectively connected to an output end of a first operational amplifier U2A and an output end of a second operational amplifier U2B, and a second end of the resistor R2 and a The second end of the resistor R9 is connected to the first end and the second end of the capacitor C5 respectively, the second end of the resistor R2 is connected in series with the resistor R3 and then connected to the normally open pin 6 of the single-pole double-throw analog switch Q1, the second end of the resistor R9 is connected in series with the resistor R10 and then connected to the normally open pin 6 of the single-pole double-throw analog switch Q2, the pin 1 of the single-pole double-throw analog switch Q1 is connected to the pin 1 of the single-pole double-throw analog switch Q2, the pin 2 of the single-pole double-throw analog switch Q1 is connected to VCC, the pin 3 of the single-pole double-throw analog switch Q1 is grounded, the normally closed pin 5 of the single-pole double-throw analog switch Q1 is connected to the first end of the capacitor C6, and the second end of the capacitor C6 is connected to Connect to the normally closed pin 4 of the single-pole double-throw analog switch Q2, the pin 2 of the single-pole double-throw analog switch Q2 is connected to VCC, the pin 3 of the single-pole double-throw analog switch Q2 is grounded, the normally closed pin 4 of the single-pole double-throw analog switch Q2 is connected in series with the first end of the resistor R7 to output a low-pass frequency signal, the first end of the capacitor C8 is connected to the second end of the resistor R7, the second end of the capacitor C8 is grounded, the signal amplified by the first operational amplifier U2A and the second operational amplifier U2B passes through a low-pass filter circuit composed of resistor R2, resistor R5 and capacitor C9 to remove unused high-frequency signals, and the resistance and capacitance values ​​here are customized as low-pass Frequency point, at this time, the output voltage of the resistance and capacitance values ​​at both ends of capacitor C5 is calculated as: Uo=Ui / [(2*Pi*f*R*C)^2+1]^0.5, where: Uo is the output voltage; Ui is the input voltage; Pi is the pi; f is the signal frequency. This circuit uses a charge pump circuit close to 1MHZ, and the theoretical value of the acquisition bandwidth is 0-100KHZ, which greatly meets the needs of ordinary bioelectric acquisition, and achieves a very small noise level by adopting high-frequency chopping. At the same time, it reduces the number of original parts, makes it easier to implement practical applications, reduces the volume of application circuits, and has lower costs.

[0035] In one embodiment of the present invention, the low-pass bioelectric signal is charged and discharged by the resistor R3 and the resistor R10 through the normally open pins of the single-pole double-throw analog switch Q1 and the single-pole double-throw analog switch Q2 to charge and discharge the capacitor C6. After the charge is discharged, the capacitor C6 is then charged and discharged by the normally closed pins of the single-pole double-throw analog switch Q1 and the single-pole double-throw analog switch Q2 to charge and discharge the resistor R7 and the capacitor C8. The secondary low-pass filter circuit composed of the resistor R7 and the capacitor C8 filters out unnecessary high-frequency noise and restores the original bioelectric signal waveform. In one embodiment of the present invention, the oscillation signal is selected to be 10 times the signal acquisition frequency. This circuit uses a charge pump circuit close to 1MHZ, and the theoretical value of the acquisition bandwidth is 0HZ-100K, which greatly meets the needs of ordinary bioelectric acquisition.

[0036] In one embodiment of the present invention, the signal module 3 includes a signal source circuit composed of a chip U1, a capacitor C1, a capacitor C2 and a capacitor C3, wherein the chip U1 is of the SGM3204 type, wherein the pin 5 of the chip U1 is connected to the pin 1 of the single-pole double-throw analog switch Q1 for outputting an oscillation signal, the pin 4 of the chip U1 is grounded, the pin 5 and the pin 3 of the chip U1 are respectively connected to the first end and the second end of the capacitor C1, the pin 1 of the chip U1 is grounded, the first end of the capacitor C2 is connected to the pin 1 of the chip U1, the second end of the capacitor C2 is grounded, the first end of the capacitor C3 is connected to the pin 2 of the chip U1, the second end is grounded, and the pin 2 of the chip U1 is grounded, which is used for the negative power supply driving capability and oscillation signal output of the charge pump, and realizes fast switching of the single-pole double-throw analog switch Q1 and the single-pole double-throw analog switch Q2 between normally open and normally closed.

[0037] As an embodiment of the present invention, Figure 4 As shown, the main factors affecting the ordinary three op amps are:

[0038] In the formula, CMR is the common mode rejection of the instrument amplifier. It can be seen from the formula that the errors of the resistors R1 and R2 seriously affect the common mode rejection ratio. For example, the resistors R1, R2, R3 and R4 have the same value. If there is a 0.1% error in the ratio of the resistors R1 to R2, the CMR of the instrument amplifier will be greatly reduced from the ideal level to the 66dB level. The circuit of the present invention adopts a similar three-op amp structure design, and uses a chopper circuit to replace the three-op amp rear-stage op amp circuit, which eliminates the disadvantage of low common mode ratio caused by rear-stage resistor matching, and provides a novel instrument amplifier structure.

[0039] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention, and any figure marks in the claims should not be regarded as limiting the claims involved.

[0040] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An instrument amplifier for bioelectric signals, comprising: A signal input module (1), wherein the signal input module (1) amplifies the received bioelectric signal and performs impedance matching to output a low-impedance signal; A charge transfer module (2), wherein the charge transfer module (2) performs waveform restoration on the amplified low-impedance signal after low-pass high-frequency clutter removal, and outputs a low-pass frequency point signal; A signal module (3), the signal module (3) being used to provide a signal source to the charge transfer module (2) for charge transfer output; The signal input module (1) comprises an RC filter circuit composed of a resistor R1, a capacitor C4, a resistor R8, and a capacitor C7, and an amplifier circuit composed of a first operational amplifier U2A, a second operational amplifier U2B, a resistor R4, a resistor R5, and a resistor R6, and is characterized in that: The charge transfer module (2) comprises a primary low-pass filter circuit composed of a resistor R2, a capacitor C5 and a resistor R9 for removing irrelevant high-frequency signals, a charge and discharge circuit composed of a resistor R3, a resistor R10, a single-pole double-throw analog switch Q1, a single-pole double-throw analog switch Q2 and a capacitor C6, and a secondary low-pass filter circuit composed of a resistor R7 and a capacitor C8, wherein a first end of the resistor R2 and a first end of the resistor R9 are respectively connected to an output end of a first operational amplifier U2A and an output end of a second operational amplifier U2B, a second end of the resistor R2 and a second end of the resistor R9 are respectively connected to a first end and a second end of the capacitor C5, a second end of the resistor R2 is connected in series with a resistor R3 and then connected to a normally open pin 6 of the single-pole double-throw analog switch Q1, and the resistor R The second end of 9 is connected in series with resistor R10 and then connected to the normally open pin 6 of the single-pole double-throw analog switch Q2. The pin 1 of the single-pole double-throw analog switch Q1 is connected to the pin 1 of the single-pole double-throw analog switch Q2. The pin 2 of the single-pole double-throw analog switch Q1 is connected to VCC. The pin 3 of the single-pole double-throw analog switch Q1 is grounded. The normally closed pin 5 of the single-pole double-throw analog switch Q1 is connected to the first end of the capacitor C6. The second end of the capacitor C6 is connected to the normally closed pin 4 of the single-pole double-throw analog switch Q2. The pin 2 of the single-pole double-throw analog switch Q2 is connected to VCC. The pin 3 of the single-pole double-throw analog switch Q2 is grounded. The normally closed pin 4 of the single-pole double-throw analog switch Q2 is connected in series with the first end of the resistor R7 and then outputs a low-pass frequency point signal. The first end of the capacitor C8 is connected to the second end of the resistor R7, and the second end of the capacitor C8 is grounded.

2. The instrument amplifier for bioelectric signals according to claim 1, characterized in that: The signal module (3) comprises a signal source circuit composed of a chip U1, a capacitor C1, a capacitor C2 and a capacitor C3, wherein the pin 5 of the chip U1 is connected to the pin 1 of the single-pole double-throw analog switch Q1 for outputting an oscillating signal, the pin 4 of the chip U1 is grounded, the pin 5 and the pin 3 of the chip U1 are respectively connected to the first end and the second end of the capacitor C1, the pin 1 of the chip U1 is grounded, the first end of the capacitor C2 is connected to the pin 1 of the chip U1, the second end of the capacitor C2 is grounded, the first end of the capacitor C3 is connected to the pin 2 of the chip U1, the second end is grounded, the pin 2 of the chip U1 is grounded, and the negative power supply driving capability of the charge pump and the output of the oscillating signal are used to realize fast switching between normally open and normally closed of the single-pole double-throw analog switch Q1 and the single-pole double-throw analog switch Q2.

3. The instrument amplifier for bioelectric signals according to claim 1, characterized in that: The gain factors of the first operational amplifier U2A and the second operational amplifier U2B are both: GAIN=1+(R4+R7) / R6.

4. The instrument amplifier for bioelectric signals according to claim 2, characterized in that: The two ends of the capacitor C5 in the primary low-pass filter circuit are low-pass frequency points, and the output voltage of the resistance and capacitance values ​​at both ends is calculated as follows: Uo=Ui / [(2*Pi*f*R*C)^2+1]^0.5, In the formula: Uo is the output voltage; Ui is the input voltage; Pi is the pi; f is the signal frequency.

5. The instrument amplifier for bioelectric signals according to claim 2, characterized in that: The chip U1 is of SGM3204 type.

6. Application of an instrument amplifier for bioelectric signals according to any one of claims 1 to 5 in the field of biomedical electronic technology.

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