A capacitively coupled instrumentation amplifier and a method for acquiring biological signals

Abstract

This invention relates to instrumentation amplifiers and biosignal acquisition methods, specifically to a capacitively coupled instrumentation amplifier and biosignal acquisition method. It solves the technical problems of poor accuracy and integrity of biosignals acquired by existing instrumentation amplifiers, as well as their large area. This invention employs an input impedance enhancement circuit to increase the input impedance, resulting in more complete biosignals. It also uses a transimpedance matching enhancement circuit to increase the matching degree between the output signal of the feedback loop and the differential output signal. Simultaneously, by reducing the feedback capacitor to increase the closed-loop gain and lower the requirement for the input capacitor, it not only reduces the area but also increases the input impedance, improving the accuracy and integrity of the acquired biosignals. The second-order DC electrode offset cancellation circuit uses a second-order low-pass filter to narrow the transition band, more effectively separating the DC electrode offset signal from the biosignal, eliminating the DC electrode offset problem during biosignal acquisition, and making the acquired biosignals more accurate.

Description

Technical Field

[0001] This invention relates to an instrumentation amplifier and a method for acquiring biological signals, specifically to a capacitively coupled instrumentation amplifier and a method for acquiring biological signals. Background Technology

[0002] Wearable medical devices have attracted researchers' attention due to their ability to monitor users' physiological data in real time and non-invasively. Wearable medical devices require the acquisition of biosignals before auxiliary judgment; the acquisition of biosignals is typically achieved by an instrumentation amplifier. The instrumentation amplifier needs to acquire and preliminarily process micro-amplitude, low-frequency biosignals; therefore, its performance has a significant impact on the accuracy and completeness of the acquired biosignals. Furthermore, as a wearable medical device, the instrumentation amplifier needs to have a sufficiently small area.

[0003] Because biosignals are relatively weak, a high closed-loop gain is required from the instrumentation amplifier. Therefore, in existing technologies, instrumentation amplifiers typically achieve high closed-loop gain by increasing the input capacitance. However, this increases the amplifier's area and decreases its input impedance, resulting in poor accuracy and integrity of the acquired biosignals. Furthermore, due to DC electrode misalignment during biosignal acquisition, existing capacitively coupled instrumentation amplifiers typically use a DC electrode misalignment cancellation loop (DSL) composed of a first-order filter to eliminate DC electrode misalignment (e.g., ...). Figure 1 As shown in the diagram, however, after passing the cutoff frequency, the signal attenuation rate of the first-order filter is 20 dB / dec (meaning it attenuates at a rate of 20 dB per decade), resulting in incomplete elimination of DC electrode offset. This also leads to poor accuracy and integrity of the acquired biological signals. Furthermore, biological signals have low-frequency characteristics, requiring the first-order filter to have a small cutoff frequency. This results in large resistance and capacitance in the DC electrode offset elimination circuit, and also increases the area of ​​the capacitively coupled instrumentation amplifier. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of poor accuracy and integrity of biological signals acquired by existing instrumentation amplifiers, as well as large area acquisition, and to provide a capacitively coupled instrumentation amplifier and a biological signal acquisition method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A capacitively coupled instrumentation amplifier is characterized by comprising, in sequence, an input chopper unit, an input signal storage unit, a first fully differential amplifier, a chopper output unit, and a second fully differential amplifier, as well as a second-order DC electrode offset cancellation circuit, a feedback chopper modulation unit, an input impedance boosting circuit, and a transimpedance matching enhancement circuit.

[0007] The input terminal of the input chopper unit serves as the input terminal of the instrumentation amplifier, used to receive the differential input signal V. in The output of the second fully differential amplifier serves as the output of the instrumentation amplifier, used to output the differential output signal V. out ;

[0008] The output of the second fully differential amplifier is connected to the input of the feedback chopper modulation unit and the input of the second-order DC electrode offset cancellation circuit, respectively. The output of the feedback chopper modulation unit is connected to the input of the input impedance boosting circuit and the input of the transimpedance matching enhancement circuit, respectively. The output of the input impedance boosting circuit is connected to the input of the input signal storage unit. The outputs of the transimpedance matching enhancement circuit and the second-order DC electrode offset cancellation circuit are connected to the input of the first fully differential amplifier, respectively.

[0009] The feedback chopper modulation unit, the second-order DC electrode offset elimination circuit, the input impedance enhancement circuit, and the transimpedance matching enhancement circuit constitute the feedback circuit.

[0010] The feedback chopper modulation unit is used to modulate the differential output signal V. out The frequency of the output differential feedback chopper signal V out_ch ;

[0011] The input impedance boosting circuit employs a positive feedback loop to modulate the differential feedback chopper signal V. out_ch This causes the input signal storage unit to have no current input, thereby increasing the input impedance;

[0012] The transimpedance matching enhancement circuit is used to enable differential feedback chopping signal V through capacitive cross-coupling. out_ch With differential output signal V out match;

[0013] The second-order DC electrode offset cancellation circuit includes a second-order low-pass filter composed of an integrator, used to separate and cancel the differential input signal V. in DC electrode misalignment signal V EOS This reduces electrode mismatch during biosignal acquisition.

[0014] Furthermore, the feedback chopper modulation unit includes a feedback chopper modulator CH. fb The transimpedance matching enhancement circuit includes a feedback capacitor C. A1 Feedback capacitor C A2 Feedback capacitor C A3 Feedback capacitor C B1 Feedback capacitor C B2 and feedback capacitor C B3 ;

[0015] The feedback chopper modulator CH fb The first and second input terminals are connected to the positive and negative output terminals of the second fully differential amplifier, respectively, and the feedback chopper modulator CH... fb The first output terminal is connected to the feedback capacitor C. B3 One end, feedback capacitor C A2 One end is connected to the first input terminal of the input impedance boosting circuit, and the feedback chopper modulator CH is connected. fb The second output terminal is connected to the feedback capacitor C respectively. B2 One end, feedback capacitor C A3 One end of the circuit is connected to the second input terminal of the input impedance boosting circuit;

[0016] The feedback capacitor C B3 The other end, feedback capacitor C B2 The other end is connected to the feedback capacitor C B1 One end is connected to the feedback capacitor C. B1 The other end is connected to the non-inverting input of the first fully differential amplifier;

[0017] The feedback capacitor C A2 The other end, feedback capacitor C A3 The other end is connected to the feedback capacitor C A1 One end is connected to the feedback capacitor C. A1 The other end is connected to the inverting input of the first fully differential amplifier.

[0018] Furthermore, the second-order DC electrode offset cancellation circuit includes a second-order low-pass filter and a chopper modulator CH. p Capacitor C C3 and capacitor C D3 ;

[0019] The second-order low-pass filter includes an integrator LNA3 and an adjustable pseudo-resistor R. C1 Adjustable pseudo resistor R C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 Capacitor C C1 Capacitor C C2 Capacitor C D1 and capacitor C D2 ;

[0020] The adjustable pseudo-resistor R C1 One end is connected to the positive output terminal of the second fully differential amplifier, and the other end is connected to capacitor C. C1 One end, adjustable pseudo resistor R C2 One end, adjustable pseudo resistor R C3One end is connected; adjustable pseudo resistor R C2 The other end is connected to the inverting input of integrator LNA3 and capacitor C, respectively. C2 One end is connected to an adjustable pseudo resistor R. C3 The other end, capacitor C C2 The other end, the positive output of integrator LNA3, is connected to chopper modulator CH. p The first input terminal is connected to capacitor C. C1 The other end is grounded;

[0021] The adjustable pseudo-resistor R D1 One end is connected to the negative output terminal of the second fully differential amplifier, and the other end is connected to capacitor C. D1 One end, adjustable pseudo resistor R D2 One end, adjustable pseudo resistor R D3 One end is connected; adjustable pseudo resistor R D2 The other end is connected to the non-inverting input of integrator LNA3 and capacitor C, respectively. D2 One end is connected to an adjustable pseudo resistor R. D3 The other end, capacitor C D2 The other end, the negative output of integrator LNA3, is connected to chopper modulator CH. p The second input terminal is connected to capacitor C. D1 The other end is grounded;

[0022] The chopper modulator CH p The first output terminal and capacitor C C3 One end is connected to capacitor C C3 The other end is connected to the inverting input of the first fully differential amplifier; the chopper modulator CH p The second output terminal and capacitor C D3 One end is connected to capacitor C D3 The other end is connected to the non-inverting input of the first fully differential amplifier.

[0023] Furthermore, the input impedance boosting circuit includes a capacitor C. pf1 and capacitor C pf2 ;

[0024] The capacitor C pf1 One end is connected to the feedback chopper modulator CH fb The first output terminal is connected, and the other end is connected to one input terminal of the input signal storage unit;

[0025] The capacitor C pf2 One end is connected to the feedback chopper modulator CH fb The second output terminal is connected, and the other end is connected to the other input terminal of the input signal storage unit.

[0026] Furthermore, the input chopper unit includes an input chopper modulator CH. in The input signal storage unit includes an input capacitor C. in1 and input capacitor C in2 The first fully differential amplifier includes a fully differential amplifier LNA1, and the chopper output unit includes an output chopper modulator CH. out The second fully differential amplifier includes a fully differential amplifier LNA2 and a Miller compensation capacitor C. m1 and Miller compensation capacitor C m2 ;

[0027] The input chopper modulator CH in The first and second input terminals serve as the input terminals of the instrumentation amplifier, used to receive the differential input signal V. in Input chopper modulator CH in The first output terminal is connected to the input capacitor C. in1 One end, capacitor C pf2 The other end is connected, and the second output terminal is connected to the input capacitor C. in2 One end, capacitor C pf1 The other end is connected; input capacitor C in1 The other end is connected to capacitor C. C3 The other end, feedback capacitor C A1 The other end is connected to the inverting input of the fully differential amplifier LNA1; the input capacitor C in2 The other end is connected to capacitor C. D3 The other end, feedback capacitor C B1 The other end is connected to the non-inverting input of the fully differential amplifier LNA1;

[0028] The positive output terminal of the fully differential amplifier LNA1 is connected to the output chopper modulator CH. out The first input terminal is connected, and the negative output terminal is connected to the output chopper modulator CH. out The second input terminal is connected; the output chopper modulator CH out The first output terminal is connected to the inverting input terminal of the fully differential amplifier LNA2 and the Miller compensation capacitor C, respectively. m1 One end is connected, and the second output end is connected to the non-inverting input of the fully differential amplifier LNA2 and the Miller compensation capacitor C, respectively. m2 One end is connected;

[0029] The positive output terminal of the fully differential amplifier LNA2 is connected to the Miller compensation capacitor C. m1 At the other end, the feedback chopper modulator CH fb First input terminal, adjustable pseudo resistor R C1 One end is connected, and the negative output terminal is connected to the Miller compensation capacitor C. m2At the other end, the feedback chopper modulator CH fb The second input terminal, the adjustable pseudo resistor R D1 One end is connected; the positive and negative output terminals of the fully differential amplifier LNA2 serve as the output terminals of the instrumentation amplifier, used to output the differential output signal V. out .

[0030] Furthermore, it also includes a common-mode circuit, which includes a resistor R. b1 and resistance R b2 ;

[0031] The resistor R b1 One end is connected to the inverting input of the fully differential amplifier LNA1, and resistor R b1 The other end is connected to the common-mode voltage V. cm ;

[0032] The resistor R b2 One end is connected to the non-inverting input of the fully differential amplifier LNA1, and resistor R b2 The other end is connected to the common-mode voltage V. cm .

[0033] Furthermore, the feedback capacitor C A2 The capacitance value is equal to the feedback capacitance C. B3 The capacitance value, feedback capacitor C B2 The capacitance value is equal to the feedback capacitance C. A3 The capacitance value.

[0034] Furthermore, the input chopper modulator CH in Including switches S1, S2, S3, and S4;

[0035] One end of switch S1 is connected to one end of switch S2, serving as the input chopper modulator CH. in The first input terminal; one end of switch S3 is connected to one end of switch S4, serving as the input chopper modulator CH. in The second input terminal;

[0036] The other end of switch S1 is connected to the other end of switch S3, serving as the input chopper modulator CH. in The first output terminal; the other end of switch S2 is connected to the other end of switch S4, serving as the input chopper modulator CH. in The second output terminal;

[0037] The clock input terminal of switch S1 is connected to the clock input terminal of switch S4, serving as the input chopper modulator CH. in The first clock input terminal; the clock input terminal of switch S2 is connected to the clock input terminal of switch S3, serving as the input chopper modulator CH.in The second clock input; input chopper modulator CH in The first clock input terminal and the second clock input terminal are used to input clock signals;

[0038] The output chopper modulator CH out Feedback chopper modulator CH fb and chopper modulator CH p Structure and Input Chopper Modulator CH in The structures are the same.

[0039] Furthermore, the adjustable pseudo-resistance R C1 It includes adjustable voltage source V1, adjustable voltage source V2, transistor M1, and transistor M2;

[0040] The positive terminal of the adjustable voltage source V1 is connected to the drain of transistor M1 and the source of transistor M2, serving as an adjustable pseudo-resistor R. C1 One end; the negative terminal of the adjustable voltage source V1 is connected to the gate of transistor M1;

[0041] The positive terminal of the adjustable voltage source V2 is connected to the drain of transistor M2 and the source of transistor M1, serving as an adjustable pseudo-resistor R. C1 At the other end, the negative terminal of the adjustable voltage source V2 is connected to the gate of transistor M2;

[0042] The adjustable pseudo-resistor R C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 With adjustable pseudo resistor R C1 The structures are the same.

[0043] This invention also provides a method for acquiring biological signals, employing the aforementioned capacitively coupled instrumentation amplifier, characterized by the following steps:

[0044] Step 1: Collect biological signals and use them as differential input signals V in Input to the input chopper unit;

[0045] Step 2: Input chopper unit to differential input signal V in The input chopping signal V is obtained by chopping. in_ch Then it is transmitted to the input signal storage unit;

[0046] Step 3: The input signal storage unit stores the input chopper signal V. in_ch And transmit it to the first fully differential amplifier;

[0047] Step 4: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially chop the input signal V. in_ch The differential output signal V is obtained by performing a single amplification, chopping, and a second amplification. out Then, they are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset elimination circuit, respectively.

[0048] Step 5: Separate and modulate the differential output signal V of the second-order DC electrode offset elimination circuit. out The DC electrode misalignment signal in the signal is reversed to obtain the DC feedback signal -V. EOS DC feedback signal -V EOS With input chopper signal V in_ch The input chopping signal V is superimposed at the input of the first fully differential amplifier to cancel it out. in_ch The DC electrode misalignment signal in the signal is used to obtain the biological input chopper signal V. ein_ch ;

[0049] Simultaneously, the feedback chopper modulation unit modulates the differential output signal V out Chopping is performed to obtain the differential feedback chopping signal V. out_ch Then, they are transmitted to the input impedance boosting circuit and the transimpedance matching enhancement circuit, respectively.

[0050] Step 6: The input impedance boosting circuit applies a differential feedback chopping signal V. out_ch Modulation is performed so that the output current of the input impedance boosting circuit is equal to the input current of the input signal storage unit, but with opposite polarities, so that the two cancel each other out, resulting in no current input to the input signal storage unit.

[0051] Meanwhile, the transimpedance matching enhancement circuit enhances the differential feedback chopper signal V. out_ch Capacitor cross-coupling is performed to enable differential feedback chopper signal V out_ch The values ​​of the positive and negative electrodes are equal, and then this is compared with the biological input chopper signal V. ein_ch The differential feedback signal V is obtained by superimposing the signals at the input of the first fully differential amplifier. fb And transmit it to the first fully differential amplifier;

[0052] Step 7: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially process the differential feedback signal V. fb The differential output signal V is obtained and output by performing a single amplification, chopping, and a second amplification. out Then, the signals are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset elimination circuit, respectively, and the process returns to step 5 until the acquisition of biological signals is completed.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. The present invention provides a capacitively coupled instrumentation amplifier, which uses an input impedance enhancement circuit to increase the input impedance, making the acquired biological signals more complete; uses a transimpedance matching enhancement circuit to improve the matching degree between the output signal of the feedback circuit and the differential output signal; and uses a second-order DC electrode offset elimination circuit to eliminate the DC electrode offset problem in the biological signal acquisition process, making the acquired biological signals more accurate.

[0055] 2. The present invention provides a capacitively coupled instrumentation amplifier, in which the transimpedance matching enhancement circuit increases the closed-loop gain by reducing the feedback capacitor and reduces the requirement for the input capacitor. This can increase the input impedance while reducing the area, thereby improving the accuracy and integrity of the acquired biological signals.

[0056] 3. The present invention provides a capacitively coupled instrumentation amplifier, wherein the second-order DC electrode offset cancellation circuit adopts a second-order low-pass filter composed of an integrator, which has a narrower transition band and can more effectively separate the DC electrode offset signal and the biological signal, thereby further improving the integrity and accuracy of the acquired biological signal. At the same time, an adjustable pseudo-resistor is used to reduce the requirements for capacitors, thereby reducing the area of ​​the second-order low-pass filter.

[0057] 4. The present invention provides a capacitively coupled instrumentation amplifier, wherein the feedback capacitor C in the transimpedance matching enhancement circuit is... A2 The capacitance value is equal to the feedback capacitance C. B3 The capacitance value, feedback capacitor C B2 The capacitance value is equal to the feedback capacitance C. A3 The capacitance value is adjusted to make the gains of the positive and negative feedback loops of the differential output signal equal, thereby ensuring good matching between the output of the feedback loop and the differential output signal. Attached Figure Description

[0058] Figure 1 The circuit schematic of an existing capacitively coupled instrumentation amplifier;

[0059] Figure 2 This is a schematic diagram of the capacitively coupled instrumentation amplifier of the present invention.

[0060] Figure 3 This is a circuit schematic diagram of an embodiment of the capacitively coupled instrumentation amplifier of the present invention;

[0061] Figure 4 The input chopper modulator CH is shown in the embodiment of the capacitively coupled instrumentation amplifier of the present invention. in The circuit schematic;

[0062] Figure 5 The adjustable pseudo-resistor R in the embodiment of the capacitively coupled instrumentation amplifier of the present invention C1 The circuit schematic. Detailed Implementation

[0063] The present invention provides a capacitively coupled instrumentation amplifier and a biosignal acquisition method in further detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0064] A type of capacitively coupled instrumentation amplifier, such as Figure 2 As shown, it includes an input chopper unit, an input signal storage unit, a first fully differential amplifier, a chopper output unit, and a second fully differential amplifier connected in sequence, as well as a common-mode circuit, a feedback chopper modulation unit, and a second-order DC servo loop (abbreviated as 2). nd The input chopper unit comprises an input impedance enhancement circuit (IIEC) and a matched transimpedance boosting loop (MTBL). The input terminal of the input chopper unit serves as the input terminal of the instrumentation amplifier, used to receive the differential input signal V. in The output of the second fully differential amplifier serves as the output of the instrumentation amplifier, used to output the differential output signal V. out The feedback loop consists of a feedback chopper modulation unit, a second-order DC electrode offset elimination circuit, an input impedance enhancement circuit, and a transimpedance matching enhancement circuit.

[0065] like Figure 3 As shown, the input chopper unit includes an input chopper modulator CH. in The input signal storage unit includes an input capacitor C. in1 and input capacitor C in2 The first fully differential amplifier includes a fully differential amplifier LNA1, and the chopper output unit includes an output chopper modulator CH. out The second fully differential amplifier includes a fully differential amplifier LNA2 and a Miller compensation capacitor C. m1 and Miller compensation capacitor C m2 The common-mode circuit includes resistor R. b1 and resistance R b2 The feedback chopper modulation unit includes a feedback chopper modulator CH. fb The input impedance boosting circuit includes capacitor C. pf1 and capacitor C pf2 The transimpedance matching enhancement circuit includes a feedback capacitor C. A1 Feedback capacitor C A2 Feedback capacitor CA3 Feedback capacitor C B1 Feedback capacitor C B2 and feedback capacitor C B3 The second-order DC electrode offset cancellation circuit includes a second-order low-pass filter and a chopper modulator CH. p Capacitor C C3 and capacitor C D3 The second-order low-pass filter includes an integrator LNA3 and an adjustable pseudo-resistor R. C1 Adjustable pseudo resistor R C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 Capacitor C C1 Capacitor C C2 Capacitor C D1 and capacitor C D2 .

[0066] Input chopper modulator CH in The first and second input terminals serve as the input terminals of the instrumentation amplifier, used to receive the differential input signal V. in Chopper modulator CH in The first output terminal and the input capacitor C in1 One end is connected, and the second output end is connected to the input capacitor C. in2 One end is connected; input capacitor C in1 The other end is connected to the inverting input of the fully differential amplifier LNA1, and the input capacitor C in2 The other end is connected to the non-inverting input of the fully differential amplifier LNA1.

[0067] The positive output terminal of the fully differential amplifier LNA1 is connected to the output chopper modulator CH. out The first input terminal is connected, and the negative output terminal is connected to the output chopper modulator CH. out Connect the second input terminal. Output chopper modulator CH out The first output terminal is connected to the inverting input terminal of the fully differential amplifier LNA2 and the Miller compensation capacitor C. m1 One end is connected, and the second output end is connected to the non-inverting input of the fully differential amplifier LNA2 and the Miller compensation capacitor C. m2 One end is connected.

[0068] The positive output terminal of the fully differential amplifier LNA2 is connected to the Miller compensation capacitor C. m1 At the other end, the feedback chopper modulator CH fb First input terminal, adjustable pseudo resistor R C1 One end is connected, and the negative output terminal of the fully differential amplifier LNA2 is connected to the Miller compensation capacitor C.m2 At the other end, the feedback chopper modulator CH fb The second input terminal, the adjustable pseudo resistor R D1 One end is connected. The positive and negative output terminals of the fully differential amplifier LNA2 serve as the output terminals of the instrumentation amplifier, used to output the differential output signal V. out .

[0069] Feedback chopper modulator CH fb The first output terminal is connected to the feedback capacitor C. B3 One end, feedback capacitor C A2 One end, capacitor C pf1 One end is connected to the feedback chopper modulator CH. fb The second output terminal is connected to the feedback capacitor C respectively. B2 One end, feedback capacitor C A3 One end, capacitor C pf2 One end is connected. Capacitor C pf2 The other end is connected to the input capacitor C in1 One end is connected to capacitor C pf1 The other end is connected to the input capacitor C in2 One end is connected. Feedback capacitor C B3 The other end, feedback capacitor C B2 The other end is connected to the feedback capacitor C B1 One end is connected to the feedback capacitor C. B1 The other end is connected to resistor R respectively b2 One end is connected to the non-inverting input of the fully differential amplifier LNA1. Feedback capacitor C A2 The other end, feedback capacitor C A3 The other end is connected to the feedback capacitor C A1 One end is connected to the feedback capacitor C. A1 The other end is connected to resistor R respectively b1 One end of the resistor is connected to the inverting input of the fully differential amplifier LNA1. b1 The other end and resistor R b2 The other end is connected to the common-mode voltage V. cm .

[0070] Adjustable pseudo resistor R C1 The other end is connected to capacitor C. C1 One end, adjustable pseudo resistor R C2 One end, adjustable pseudo resistor R C3 One end is connected. Adjustable pseudo-resistor R C2 The other end is connected to the inverting input of integrator LNA3 and capacitor C, respectively. C2 One end is connected to an adjustable pseudo resistor R. C3 The other end, capacitor C C2The other end, the positive output of integrator LNA3, is connected to chopper modulator CH. p The first input terminal is connected to capacitor C. C1 The other end is grounded.

[0071] Adjustable pseudo resistor R D1 The other end is connected to capacitor C. D1 One end, adjustable pseudo resistor R D2 One end, adjustable pseudo resistor R D3 One end is connected. Adjustable pseudo-resistor R D2 The other end is connected to the non-inverting input of integrator LNA3 and capacitor C, respectively. D2 One end is connected to an adjustable pseudo resistor R. D3 The other end, capacitor C D2 The other end, the negative output of integrator LNA3, is connected to chopper modulator CH. p The second input terminal is connected to capacitor C. D1 The other end is grounded.

[0072] chopper modulator CH p The first output terminal and capacitor C C3 One end is connected to capacitor C C3 The other end is connected to the inverting input of the fully differential amplifier LNA1. Chopper modulator CH p The second output terminal and capacitor C D3 One end is connected to capacitor C D3 The other end is connected to the non-inverting input of the fully differential amplifier LNA1.

[0073] A chopper modulator is used to increase / decrease the frequency of a signal. For example... Figure 4 As shown, the input chopper modulator CH in It includes switches S1, S2, S3, and S4. One end of switch S1 is connected to one end of switch S2, serving as the input chopper modulator CH. in The first input terminal; one end of switch S3 is connected to one end of switch S4, serving as the input chopper modulator CH. in The second input terminal. The other end of switch S1 is connected to the other end of switch S3, serving as the input chopper modulator CH. in The first output terminal. The other end of switch S2 is connected to the other end of switch S4, serving as the input chopper modulator CH. in The second output terminal. The clock input terminal of switch S1 is connected to the clock input terminal of switch S4, serving as the input chopper modulator CH. in The first clock input terminal. The clock input terminal of switch S2 is connected to the clock input terminal of switch S3, serving as the input chopper modulator CH. in The second clock input. Input chopper modulator CHin The first clock input is used to input the clock signal CLK, and the second clock input is used to input the clock signal CLKB. The output chopper modulator CH... out Feedback chopper modulator CH fb and chopper modulator CH p Structure and Input Chopper Modulator CH in The structures are the same.

[0074] For the input chopper modulator CH in and output chopper modulator CH out When the clock signal CLK is high, the differential input signal V in The positive terminal is connected to the non-inverting input of the fully differential amplifier LNA1, and the differential input signal V... in The negative terminal is connected to the inverting input of the fully differential amplifier LNA1; the negative output terminal of the fully differential amplifier LNA2 outputs the differential output signal V. out The negative terminal of the fully differential amplifier LNA2 outputs a differential output signal V. out The positive terminal. When the clock signal CLKB is high, the differential input signal V... in The positive terminal is connected to the inverting input terminal of the fully differential amplifier LNA1, and the differential input signal V in The negative terminal is connected to the non-inverting input of the fully differential amplifier LNA1; the negative output terminal of the fully differential amplifier LNA2 outputs the differential output signal V. out The positive terminal of the fully differential amplifier LNA2 outputs a differential output signal V. out The negative terminal. Through the above steps, the positive and negative terminals are interchanged, thereby generating a square wave signal.

[0075] In this embodiment, the input chopper unit is used to process the differential input signal V. in The signal is chopped to increase its frequency to the chopping frequency, thus obtaining the input chopped signal V. in_ch The input signal storage unit is used to store the input chopper signal V. in_ch Stored in the input capacitance C in1 and input capacitor C in2 In the middle, the first and second fully differential amplifiers are used to amplify the input chopped signal V. in_ch Generate differential output signal V out The chopper output unit is used to chop the output signal of the first fully differential amplifier again, reducing its signal frequency to the fundamental frequency. The common-mode circuit is used to adjust the common-mode voltage of the feedback signals from the first and second fully differential amplifiers to a preset common-mode voltage V. cm The feedback chopper modulation unit is used to modulate the differential output signal V. out The frequency is used to obtain the differential feedback chopper signal V.out_ch .

[0076] The transimpedance matching enhancement circuit achieves the preset closed-loop gain by reducing the feedback capacitance of the feedback loop. This is achieved by canceling a portion of the current before the feedback loop reaches the virtual point, which reduces the area of ​​the first and second fully differential amplifiers. Furthermore, through capacitive cross-coupling, it enhances the differential feedback chopping signal V. out_ch The positive and negative terminals are related to the differential output signal V. out The positive and negative terminals are matched. The transimpedance matching enhancement circuit is connected between the input of the fully differential amplifier LNA1 and the feedback chopper modulator CH. fb Between the outputs, through Figure 3 Points A and B in the diagram partially cancel out the current to increase impedance. Specifically, this is manifested in the feedback capacitor C. A1 and differential feedback chopper signal V out_ch Add a feedback capacitor C between them A2 Feedback capacitor C A3 In the feedback capacitor C B1 and differential feedback chopper signal V out_ch Add a feedback capacitor C between them B2 Feedback capacitor C B3 At this point, on the circuit containing point A:

[0077]

[0078] Among them, V A Let C be the voltage at point A. A1 C A2 C A3 The feedback capacitors C are respectively A1 Feedback capacitor C A2 Feedback capacitor C A3 The capacitance value, C in1 For the input capacitor C in1 The capacitance value, For differential input signal V in The input voltage, V out+ The differential output signal V out The positive output voltage, V out- The differential output signal V out The negative output voltage.

[0079] Then, the gain GainA of the loop containing point A. closed-loop for:

[0080]

[0081] in, The differential output signal V out The output voltage.

[0082] In the circuit containing point B:

[0083]

[0084] Among them, V B Let C be the voltage at point B. B1 C B2 C B3 The feedback capacitors C are respectively B1 Feedback capacitor C B2 Feedback capacitor C B3 The capacitance value, C in2 For the input capacitor C in2 The capacitance value.

[0085] Then, the gain GainB of the loop containing point B. closed-loop for:

[0086]

[0087] To ensure good matching between the feedback loop and the differential signal output, the output of the loop at point A must be equal to the output of the loop at point B; that is, the gains of the loops at points A and B must be equal. Therefore, in this embodiment, C... A2 = C B3 C B2 = C A3 .

[0088] like Figure 1 In the existing capacitively coupled instrumentation amplifier shown, the feedback loop consists of feedback capacitors C5 and C6, and chopper modulator Ch3. The overall closed-loop gain of amplifiers GM1 and GM2 is Gain. closed-loop for:

[0089]

[0090] Among them, C 1,2 C is the capacitance value of input capacitor C1 or input capacitor C2. 5,6 This refers to the capacitance value of either feedback capacitor C5 or feedback capacitor C6.

[0091] Given a closed-loop gain of 200, let C 5,6 =0.1 pF, then C 1,2 =20 pF.

[0092] In this embodiment, taking the loop containing point B as an example, let C... A2 = C B3 =0.8C A1, B1 C B2 = C A3 =1.2CA1, B1 Feedback capacitor C A1 Or feedback capacitor C B1 capacitance value C A1,B1 =0.1pF, then under the same closed-loop gain, the input capacitor C in1 Or input capacitor C in2 capacitance value C in1,2 =2.67pF, and Figure 1 Compared to existing capacitively coupled instrumentation amplifiers, this embodiment reduces the input capacitance by 17.33 pF under the same closed-loop gain and feedback capacitance value.

[0093] In this embodiment, the input impedance boosting circuit adopts a positive feedback loop to modulate the differential feedback chopper signal V. out_ch This prevents current from entering the input signal storage unit, thereby increasing the input impedance. Before adding the input impedance boosting circuit, the input impedance... for:

[0094]

[0095] Among them, f hp This is the chopping frequency.

[0096] As can be seen, the input impedance is inversely proportional to the chopping frequency, which is typically on the order of kHz, much higher than the frequency of the input signal. To improve the input impedance, this embodiment adds an input impedance boosting circuit to the feedback loop, making the input capacitor C... in1 and input capacitor C in2 No current flows into the input terminal, i.e., through capacitor C. pf1 or capacitor C pf2 Current I pf1,2 Equal to through the input capacitor C in1 Or input capacitor C in2 Current I in1,2 Theoretically, the input impedance can be made infinite, that is:

[0097]

[0098]

[0099] in, C in1,2 Input capacitor C in1 Or input capacitor C in2 The capacitance value, C pf1,2 For capacitor C pf1 or capacitor C pf2 The capacitance value, Gain closed-loop This represents the amplifier's closed-loop gain.

[0100] At this time, the input impedance for:

[0101]

[0102] In this embodiment, the input impedance of the capacitively coupled instrumentation amplifier increases by (Gain) compared to before the input impedance boosting circuit was added. closed-loop -1) times.

[0103] like Figure 1 In the existing capacitively coupled instrumentation amplifier shown, its input impedance boosting circuit consists of capacitor C. 11 Capacitor C 12 It consists of a chopper modulator Ch4, whose input impedance is... for:

[0104]

[0105] Among them, C 11,12 For capacitor C 11 or capacitor C 12 The capacitance value.

[0106] Given a closed-loop gain of 200 and a feedback capacitor C 5,6 When =0.1pF, such as Figure 1 The input capacitor C of the existing capacitively coupled instrumentation amplifier shown is... 1,2 =20pF, while the input capacitance C in this embodiment is... in1,2 =2.67pF, therefore, the input impedance of the capacitively coupled instrumentation amplifier in this embodiment is... Figure 1 It is 7.49 times that of the existing capacitively coupled instrumentation amplifier shown.

[0107] There is a DC electrode mismatch signal V between the biological signal and the electrode. EOS This signal will be superimposed on the differential input signal V. in The frequencies of both are fed into the input chopper modulator CH. in and output chopper modulator CH out Adjusted twice, the frequency of amplifier noise and other non-ideal factors is processed by the output chopper modulator CH. out Adjust once. Differential input signal V in DC electrode offset signal V EOS The frequency is modulated twice by chopping, resulting in a low-frequency signal at the output, which cannot be directly filtered out by a filter. Therefore, in this embodiment, a second-order DC electrode offset cancellation circuit is set at the rear end of the fully differential amplifier LNA2 to integrate the DC electrode offset signal output by the fully differential amplifier LNA2 and then feed it back to the input of the fully differential amplifier LNA1 to obtain the DC feedback signal -V. EOSUsing the input chopping signal V in_ch With DC feedback signal -V EOS Superposition, thereby eliminating the differential input signal V in DC electrode misalignment signal V EOS .

[0108] In this embodiment, the differential input signal V in The frequency of the amplifier is modulated to the fundamental frequency through even-order frequency modulation; the frequency of non-ideal factors such as amplifier noise is modulated to the chopping frequency through odd-order frequency modulation. The second-order low-pass filter in the second-order DC electrode offset elimination circuit is used to filter out non-ideal factors such as amplifier noise, thereby improving the performance of the fully differential amplifiers LNA1 and LNA2.

[0109] like Figure 1 The DC electrode offset circuit in the existing capacitively coupled instrumentation amplifier shown includes capacitors C9 and C1. 10 A first-order filter consisting of resistors R3 and R4 and integrator GM3, along with chopper modulator Ch5 and coupling capacitors C7 and C8, and the cutoff frequency f of integrator GM3. GM3 for:

[0110]

[0111] Among them, C 9,10 For capacitor C9 or capacitor C 10 The capacitance value, R 3,4 This refers to the resistance value of resistor R3 or resistor R4.

[0112] In this embodiment, the signal attenuation rate after the cutoff frequency of the second-order low-pass filter is as follows: Figure 1 The first-order filter in the existing capacitively coupled instrumentation amplifier shown is twice that of the first-order filter.

[0113] Set the cutoff frequency to 10Hz, such as Figure 1 In the existing capacitively coupled instrumentation amplifier shown, R 3,4 =10GΩ, C 9,10 =1.59pF. In this embodiment, capacitor C C1 or capacitor C D1 The capacitance value C1 and the capacitance C C2 or capacitor C D2 The capacitance value C2 is the same, and the adjustable pseudo resistor R C2 Or adjustable pseudo resistor R D2 The resistance value R2 and the adjustable pseudo-resistance R C3 Or adjustable pseudo resistor R D3 The resistance values ​​R3 are equal, i.e., C1=C2, R2=R3, where R2=R3=10GΩ, therefore C1=C2=1.59pF. (This is similar to...) Figure 1 Compared to the existing capacitively coupled instrumentation amplifier shown, this embodiment adds only four 10GΩ adjustable pseudo-resistors and two 1.59pF capacitors at the same cutoff frequency, resulting in a total area increase of 0.003348mm². 2 Compared to, Figure 1 The existing capacitively coupled instrumentation amplifier shown in this embodiment has a slightly increased area of ​​the second-order low-pass filter, but the transition band of the second-order low-pass filter is narrower, which can better separate biological signals from DC electrode misalignment signals.

[0114] The second-order DC electrode offset cancellation circuit uses a second-order low-pass filter composed of an integrator to extract the differential output signal V. out The DC electrode offset signal is then passed through a chopper modulator CH. p and capacitor C C3 Capacitor C D3 Coupled to the input of the fully differential amplifier LNA1, the input chopped signal V is realized. in_ch The offset signal of the DC electrode is canceled. This embodiment uses a second-order low-pass filter to narrow the transition band, which can more effectively separate the differential output signal V. out The DC electrode offset signal and biological signal are combined, and an adjustable pseudo-resistor is used to reduce the requirement for capacitors, thereby reducing the area of ​​the second-order low-pass filter.

[0115] like Figure 3 As shown, the input of the second-order low-pass filter is V. i The output terminal is V o V i First, it passes through the adjustable pseudo resistor R. C1 Adjustable pseudo resistor R D1 In the adjustable pseudo-resistance R C2 With adjustable pseudo resistor R C1 Between, adjustable pseudo-resistance R D2 With adjustable pseudo resistor R D1 They pass through capacitor C respectively C1 Capacitor C D1 Capacitor C C1 Capacitor C D1 One end is connected to the circuit (point V1), and the other end is grounded. Adjustable pseudo-resistor R. C2 Adjustable pseudo resistor R D2 Connect the input terminal of the integrator LNA3, and the capacitor C C2 Capacitor C D2 Connected to the input terminals (V) of the integrator LNA3 respectively. X (point) and adjustable pseudo-resistance R C2 Adjustable pseudo resistor R D2 Between, the adjustable pseudo-resistance R C3Adjustable pseudo resistor R D3 Connected to the output of integrator LNA3 and adjustable pseudo-resistor R C1 Adjustable pseudo resistor R D1 Between. Then we have:

[0116]

[0117] Where V1 is the voltage at point V1, and R2 is the adjustable pseudo-resistance R C2 Or adjustable pseudo resistor R D2 The resistance value, V X For V X Voltage at point, V o V is the output terminal of a second-order low-pass filter. o The voltage is s, the complex frequency is , and C2 is the capacitance C. C2 or capacitor C D2 The capacitance value.

[0118] Because the integrator LNA3 has a virtual short and virtual open circuit, V X =0, then:

[0119]

[0120] At point V1, according to Kirchhoff's current law, we can obtain:

[0121]

[0122]

[0123] Among them, V i V is the input terminal of a second-order low-pass filter. i The voltage value, R1 is an adjustable pseudo-resistor R C1 Or adjustable pseudo resistor R D1 The resistance value, R3 is an adjustable pseudo-resistor R C3 Or adjustable pseudo resistor R D3 The resistance value, C1 is the capacitance C C1 or capacitor C D1 The capacitance value.

[0124] The transfer function H(s) of the second-order low-pass filter is:

[0125]

[0126] Where K is the DC gain of the integrator LNA3, ω0 is the cutoff angular frequency of the second-order low-pass filter, and Q is the quality factor.

[0127] Therefore, the cutoff angular frequency ω0 of the second-order low-pass filter can be obtained as:

[0128]

[0129] The cutoff frequency of a second-order low-pass filter for:

[0130]

[0131] The second-order DC electrode offset cancellation circuit separates the DC electrode offset signal from the biological signal. Since the biological signal is a micro-amplitude signal, a second-order low-pass filter with an extremely low cutoff frequency is required to filter out the biological signal, which requires a large capacitor and resistor.

[0132] In this embodiment, an adjustable pseudo-resistor (PR) is used to increase the resistance value to the GΩ (gigaohm) level, thereby reducing the requirement for capacitors and thus reducing the area of ​​the second-order low-pass filter. For example... Figure 5 As shown, the adjustable pseudo-resistor R used in this embodiment C1 This includes adjustable voltage source V1, adjustable voltage source V2, transistor M1, and transistor M2. The positive terminal of adjustable voltage source V1 is connected to the drain of transistor M1 and the source of transistor M2, serving as an adjustable pseudo-resistor R. C1 One end of the adjustable voltage source V1 is connected to the gate of transistor M1. The positive terminal of the adjustable voltage source V2 is connected to the drain of transistor M2 and the source of transistor M1, serving as an adjustable pseudo-resistor R. C1 At the other end, the negative terminal of the adjustable voltage source V2 is connected to the gate of transistor M2. The adjustable dummy resistor R... C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 With adjustable pseudo resistor R C1 The structures are the same.

[0133] Transistors M1 and M2 are operating in the subthreshold region, with drain-source current I... SD for:

[0134]

[0135]

[0136] Among them, I SD0 V is the reference value for the subthreshold drain-source current. SG V is the gate-source voltage. SD V is the drain-source voltage. th Where is the thermal voltage, n is the subthreshold slope factor, µ is the carrier mobility, and C is the thermal voltage. ox Here, V represents the gate oxide capacitance per unit area, W is the transistor width, L is the transistor length, and V... TThis is the threshold voltage.

[0137] Then the resistance of transistor M1 and transistor M2 for:

[0138]

[0139] Where V1 is the voltage value of the adjustable voltage source V1.

[0140] Substitute I SD0 We can obtain:

[0141]

[0142] The adjustable pseudo resistor R C1 The total resistance is:

[0143]

[0144] Therefore, the adjustable pseudo-resistance R can be adjusted by adjusting the voltage value of the adjustable voltage source V1. C1 The resistance value.

[0145] The working principle of the capacitively coupled instrumentation amplifier provided in this embodiment is as follows: Input chopper modulator CH in The differential input signal V in chopper generates input chopper signal V in_ch And by the input capacitor C in1 Input capacitor C in2 Storage. A second-order low-pass filter extracts the differential output signal V. out DC electrode offset signal in the chopper modulator CH p and capacitor C C3 Capacitor C D3 By coupling and modulating it, a DC feedback signal -V is obtained. OS DC feedback signal -V OS With input chopper signal V in_ch The input chopper signal V is superimposed at the input of the fully differential amplifier LNA1 to cancel it out. in_ch The DC electrode misalignment signal in the signal is used to obtain the biological input chopper signal V. ein_ch The feedback capacitor C in the feedback loop A1 Feedback capacitor C A2 Feedback capacitor C A3 Feedback capacitor C B1 Feedback capacitor C B2 Feedback capacitor C B3 With input capacitor C in1 Input capacitor C in2 Connected in series with the input chopper modulator CH in With feedback chopper modulator CH fbBetween, the feedback chopper modulator CH fb The differential output signal V out Chopper generates differential feedback chopper signal V out_ch Input capacitor C in1 Input capacitor C in2 With feedback capacitor C A1 Feedback capacitor C A2 Feedback capacitor C A3 Feedback capacitor C B1 Feedback capacitor C B2 Feedback capacitor C B3 The differential feedback chopper signal V is divided by capacitor voltage division. out_ch With biological input chopper signal V ein_ch The differential feedback signal V is formed by superposition. fb The fully differential amplifiers LNA1 and LNA2 will output the differential feedback signal V. fb Amplification is performed, and the output is passed through the chopper modulator CH. out Chopper generates differential output signal V out .

[0146] This embodiment also provides a biosignal acquisition method, which uses the above-mentioned capacitively coupled instrumentation amplifier and includes the following steps:

[0147] Step 1: Collect biological signals and use them as differential input signals V in Input to the input chopper unit.

[0148] Step 2: Input chopper unit to differential input signal V in The input chopping signal V is obtained by chopping. in_ch Then it is transmitted to the input signal storage unit.

[0149] Step 3: The input signal storage unit stores the input chopper signal V. in_ch It is then transmitted to the first fully differential amplifier.

[0150] Step 4: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially chop the input signal V. in_ch The differential output signal V is obtained by performing a single amplification, chopping, and a second amplification. out Then, they are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset cancellation circuit, respectively.

[0151] Step 5: Separate and modulate the differential output signal V of the second-order DC electrode offset elimination circuit. out The DC electrode misalignment signal in the signal is reversed to obtain the DC feedback signal -V. EOS DC feedback signal -V EOS With input chopper signal Vin_ch The input chopping signal V is superimposed at the input of the first fully differential amplifier to cancel it out. in_ch The DC electrode misalignment signal in the signal is used to obtain the biological input chopper signal V. ein_ch ;

[0152] Simultaneously, the feedback chopper modulation unit modulates the differential output signal V out Chopping is performed to obtain the differential feedback chopping signal V. out_ch Then, it is transmitted to the input impedance boosting circuit and the transimpedance matching enhancement circuit, respectively.

[0153] Step 6: The input impedance boosting circuit applies a differential feedback chopping signal V. out_ch Modulation is performed so that the output current of the input impedance boosting circuit is equal to the input current of the input signal storage unit, but with opposite polarities, so that the two cancel each other out, resulting in no current input to the input signal storage unit.

[0154] Meanwhile, the transimpedance matching enhancement circuit enhances the differential feedback chopper signal V. out_ch Capacitor cross-coupling is performed to enable differential feedback chopper signal V out_ch The values ​​of the positive and negative electrodes are equal, and then this is compared with the biological input chopper signal V. ein_ch The differential feedback signal V is obtained by superimposing the signals at the input of the first fully differential amplifier. fb And transmit it to the first fully differential amplifier.

[0155] Step 7: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially process the differential feedback signal V. fb The differential output signal V is obtained and output by performing a single amplification, chopping, and a second amplification. out Then, the signals are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset elimination circuit, respectively, and the process returns to step 5 until the acquisition of biological signals is completed.

Claims

1. A capacitively coupled instrumentation amplifier, characterized in that: It includes an input chopper unit, an input signal storage unit, a first fully differential amplifier, a chopper output unit and a second fully differential amplifier connected in sequence, as well as a second-order DC electrode offset cancellation circuit, a feedback chopper modulation unit, an input impedance boosting circuit and a transimpedance matching enhancement circuit; The input terminal of the input chopper unit serves as the input terminal of the instrumentation amplifier, used to receive differential input signals. V in The output of the second fully differential amplifier serves as the output of the instrumentation amplifier, used to output differential output signals. V out ; The output of the second fully differential amplifier is connected to the input of the feedback chopper modulation unit and the input of the second-order DC electrode offset cancellation circuit, respectively. The output of the feedback chopper modulation unit is connected to the input of the input impedance boosting circuit and the input of the transimpedance matching enhancement circuit, respectively. The output of the input impedance boosting circuit is connected to the input of the input signal storage unit. The outputs of the transimpedance matching enhancement circuit and the second-order DC electrode offset cancellation circuit are connected to the input of the first fully differential amplifier, respectively. The feedback chopper modulation unit, the second-order DC electrode offset elimination circuit, the input impedance enhancement circuit, and the transimpedance matching enhancement circuit constitute the feedback circuit. The feedback chopper modulation unit is used to modulate the differential output signal. V out The frequency of the output differential feedback chopper signal. V out_ch ; The input impedance boosting circuit employs a positive feedback loop to modulate the differential feedback chopper signal. V out_ch This causes the input signal storage unit to have no current input, thereby increasing the input impedance; The transimpedance matching enhancement circuit is used to enable differential feedback chopping signals through capacitive cross-coupling. V out_ch With differential output signal V out match; The second-order DC electrode offset cancellation circuit includes a second-order low-pass filter composed of an integrator, used to separate and cancel the differential input signal. V in DC electrode misalignment signal V EOS This reduces electrode mismatch during biosignal acquisition.

2. The capacitively coupled instrumentation amplifier according to claim 1, characterized in that: The feedback chopper modulation unit includes a feedback chopper modulator. CH fb The transimpedance matching enhancement circuit includes a feedback capacitor. C A1 Feedback capacitor C A2 Feedback capacitor C A3 Feedback capacitor C B1 Feedback capacitor C B2 and feedback capacitor C B3 ; The feedback chopper modulator CH fb The first and second input terminals are connected to the positive and negative output terminals of the second fully differential amplifier, respectively, for the feedback chopper modulator. CH fb The first output terminal is connected to the feedback capacitor. C B3 One end, feedback capacitor C A2 One end is connected to the first input terminal of the input impedance boosting circuit, and the feedback chopper modulator is connected. CH fb The second output terminal is connected to the feedback capacitor. C B2 One end, feedback capacitor C A3 One end of the circuit is connected to the second input terminal of the input impedance boosting circuit; The feedback capacitor C B3 The other end, feedback capacitor C B2 The other end is connected to the feedback capacitor C B1 One end is connected to the feedback capacitor. C B1 The other end is connected to the non-inverting input of the first fully differential amplifier; The feedback capacitor C A2 The other end, feedback capacitor C A3 The other end is connected to the feedback capacitor C A1 One end is connected to the feedback capacitor. C A1 The other end is connected to the inverting input of the first fully differential amplifier.

3. A capacitively coupled instrumentation amplifier according to claim 2, characterized in that: The second-order DC electrode offset cancellation circuit includes a second-order low-pass filter and a chopper modulator. CH p ,capacitance C C3 and capacitor C D3 ; The second-order low-pass filter includes an integrator LNA3 and an adjustable pseudo-resistor. R C1 Adjustable pseudo resistor R C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 ,capacitance C C1 ,capacitance C C2 ,capacitance C D1 and capacitor C D2 ; The adjustable pseudo resistor R C1 One end is connected to the positive output terminal of the second fully differential amplifier, and the other end is connected to the capacitor. C C1 One end, adjustable pseudo resistor R C2 One end, adjustable pseudo resistor R C3 One end is connected; adjustable pseudo resistor R C2 The other end is connected to the inverting input of the integrator LNA3 and the capacitor, respectively. C C2 One end is connected to an adjustable pseudo resistor. R C3 The other end, capacitor C C2 The other end, the positive output of integrator LNA3, is connected to the chopper modulator. CH p The first input terminal is connected to the capacitor. C C1 The other end is grounded; The adjustable pseudo resistor R D1 One end is connected to the negative output terminal of the second fully differential amplifier, and the other end is connected to the capacitor. C D1 One end, adjustable pseudo resistor R D2 One end, adjustable pseudo resistor R D3 One end is connected; adjustable pseudo resistor R D2 The other end is connected to the non-inverting input of the integrator LNA3 and the capacitor, respectively. C D2 One end is connected to an adjustable pseudo resistor. R D3 The other end, capacitor C D2 The other end, the negative output of integrator LNA3, is connected to the chopper modulator. CH p The second input terminal is connected to the capacitor. C D1 The other end is grounded; The chopper modulator CH p The first output terminal and capacitor C C3 One end is connected to the capacitor. C C3 The other end is connected to the inverting input of the first fully differential amplifier; chopper modulator CH p The second output terminal and capacitor C D3 One end is connected to the capacitor. C D3 The other end is connected to the non-inverting input of the first fully differential amplifier.

4. A capacitively coupled instrumentation amplifier according to claim 3, characterized in that: The input impedance boosting circuit includes a capacitor. C pf1 and capacitor C pf2 ; The capacitor C pf1 One end is connected to the feedback chopper modulator CH fb The first output terminal is connected, and the other end is connected to one input terminal of the input signal storage unit; The capacitor C pf2 One end is connected to the feedback chopper modulator CH fb The second output terminal is connected, and the other end is connected to the other input terminal of the input signal storage unit.

5. A capacitively coupled instrumentation amplifier according to claim 4, characterized in that: The input chopper unit includes an input chopper modulator. CH in The input signal storage unit includes an input capacitor. C in1 and input capacitance C in2 The first fully differential amplifier includes a fully differential amplifier LNA1, and the chopper output unit includes an output chopper modulator. CH out The second fully differential amplifier includes a fully differential amplifier LNA2 and a Miller compensation capacitor. C m1 and Miller compensation capacitor C m2 ; The input chopper modulator CH in The first and second input terminals serve as the input terminals of the instrumentation amplifier, used to receive differential input signals. V in Input chopper modulator CH in The first output terminal is connected to the input capacitor respectively. C in1 One end of the capacitor C pf2 The other end is connected, and the second output terminal is connected to the input capacitor. C in2 One end of the capacitor C pf1 The other end is connected; input capacitor C in1 The other end is connected to the capacitor. C C3 The other end, feedback capacitor C A1 The other end is connected to the inverting input of the fully differential amplifier LNA1; input capacitor C in2 The other end is connected to the capacitor. C D3 The other end, feedback capacitor C B1 The other end is connected to the non-inverting input of the fully differential amplifier LNA1; The positive output terminal of the fully differential amplifier LNA1 is connected to the output chopper modulator. CH out The first input terminal is connected, and the negative output terminal is connected to the output chopper modulator. CH out The second input terminal is connected; the output chopper modulator. CH out The first output terminal is connected to the inverting input terminal of the fully differential amplifier LNA2 and the Miller compensation capacitor, respectively. C m1 One end is connected, and the second output end is connected to the non-inverting input of the fully differential amplifier LNA2 and the Miller compensation capacitor, respectively. C m2 One end is connected; The positive output terminal of the fully differential amplifier LNA2 is connected to the Miller compensation capacitor. C m1 The other end, feedback chopper modulator CH fb First input terminal, adjustable pseudo resistor R C1 One end is connected, and the negative output end is connected to the Miller compensation capacitor. C m2 The other end, feedback chopper modulator CH fb Second input terminal, adjustable pseudo resistor R D1 One end is connected; the positive and negative output terminals of the fully differential amplifier LNA2 serve as the output terminals of the instrumentation amplifier, used to output differential output signals. V out .

6. A capacitively coupled instrumentation amplifier according to claim 5, characterized in that: It also includes common-mode circuitry, which includes resistors. R b1 and resistance R b2 ; The resistor R b1 One end is connected to the inverting input of the fully differential amplifier LNA1, and the resistor... R b1 The other end is connected to the common-mode voltage. V cm ; The resistor R b2 One end is connected to the non-inverting input of the fully differential amplifier LNA1, and the resistor... R b2 The other end is connected to the common-mode voltage. V cm .

7. A capacitively coupled instrumentation amplifier according to claim 6, characterized in that: The feedback capacitor C A2 The capacitance value is equal to the feedback capacitor. C B3 The capacitance value, feedback capacitor C B2 The capacitance value is equal to the feedback capacitor. C A3 The capacitance value.

8. A capacitively coupled instrumentation amplifier according to claim 7, characterized in that: The input chopper modulator CH in Including switches S1, S2, S3, and S4; One end of switch S1 is connected to one end of switch S2, serving as an input chopper modulator. CH in The first input terminal; one end of switch S3 is connected to one end of switch S4, serving as the input chopper modulator. CH in The second input terminal; The other end of switch S1 is connected to the other end of switch S3, serving as an input chopper modulator. CH in The first output terminal; the other end of switch S2 is connected to the other end of switch S4, serving as the input chopper modulator. CH in The second output terminal; The clock input terminal of switch S1 is connected to the clock input terminal of switch S4, serving as an input chopper modulator. CH in The first clock input terminal; the clock input terminal of switch S2 is connected to the clock input terminal of switch S3, serving as an input chopper modulator. CH in Second clock input; input chopper modulator CH in The first clock input terminal and the second clock input terminal are used to input clock signals; The output chopper modulator CH out Feedback chopper modulator CH fb and chopper modulator CH p Structure and input chopper modulator CH in The structures are the same.

9. A capacitively coupled instrumentation amplifier according to claim 8, characterized in that: The adjustable pseudo resistor R C1 Including adjustable voltage sources V 1. Adjustable voltage source V 2. Transistor M 1 and transistor M 2; The adjustable voltage source V 1's positive terminal and transistor M 1. Drain of transistor M The source connection of 2 acts as an adjustable pseudo-resistor. R C1 One end; adjustable voltage source V The negative terminal of 1 and the transistor M 1 gate connection; The adjustable voltage source V 2's positive terminal and transistor M 2 drain, transistor M The source connection of 1 acts as an adjustable pseudo-resistor. R C1 At the other end, an adjustable voltage source V The negative electrode of 2 and the transistor M 2 gate connection; The adjustable pseudo resistor R C2 Adjustable pseudo resistor R C3 Adjustable pseudo resistor R D1 Adjustable pseudo resistor R D2 Adjustable pseudo resistor R D3 With adjustable pseudo resistor R C1 The structures are the same.

10. A method for acquiring biological signals, employing a capacitively coupled instrumentation amplifier as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Acquire biological signals and use them as differential input signals V in Input to the input chopper unit; Step 2: Input chopper unit to differential input signal V in Chopping is performed to obtain the input chopped signal. V in_ch Then it is transmitted to the input signal storage unit; Step 3: The input signal storage unit stores the input chopper signal. V in_ch And transmit it to the first fully differential amplifier; Step 4: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially chop the input signal. V in_ch The differential output signal is obtained by performing a single amplification, chopping, and a second amplification. V out Then, they are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset elimination circuit, respectively. Step 5: Separate and modulate the differential output signal of the second-order DC electrode offset elimination circuit. V out The DC electrode misalignment signal is reversed to obtain a DC feedback signal. V EOS DC feedback signal - V EOS With input chopper signal V in_ch The input chopping signal is superimposed at the input of the first fully differential amplifier to cancel it out. V in_ch The DC electrode misalignment signal in the signal is used to obtain the biological input chopper signal. V ein_ch ; Simultaneously, the feedback chopper modulation unit modulates the differential output signal. V out Chopping is performed to obtain a differential feedback chopping signal. V out_ch Then, they are transmitted to the input impedance boosting circuit and the transimpedance matching enhancement circuit, respectively. Step 6: Input impedance boosting circuit chopping the differential feedback signal V out_ch Modulation is performed so that the output current of the input impedance boosting circuit is equal to the input current of the input signal storage unit, but with opposite polarities, so that the two cancel each other out, resulting in no current input to the input signal storage unit. Meanwhile, the transimpedance matching enhancement circuit enhances the differential feedback chopper signal. V out_ch Capacitor cross-coupling is performed to enable differential feedback chopper signal. V out_ch The values ​​of the positive and negative electrodes are equal, and then this is compared with the biological input chopper signal. V ein_ch The differential feedback signal is obtained by superimposing the signals at the input of the first fully differential amplifier. V fb And transmit it to the first fully differential amplifier; Step 7: The first fully differential amplifier, the chopper output unit, and the second fully differential amplifier sequentially process the differential feedback signal. V fb The differential output signal is obtained and output by performing a first amplification, chopping, and second amplification. V out Then, the signals are transmitted to the feedback chopper modulation unit and the second-order DC electrode offset elimination circuit, respectively, and the process returns to step 5 until the acquisition of biological signals is completed.

Images