CN112653406A - Biopotential amplifier and physiological signal measurement system - Google Patents
Biopotential amplifier and physiological signal measurement system Download PDFInfo
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Abstract
The present invention relates to a biopotential amplifier including an open-loop amplification circuit and a closed-loop amplification circuit, and a physiological signal measurement system. The input end of the open-loop amplifying circuit is used for receiving the biopotential to be amplified, and the output end of the open-loop amplifying circuit is connected with the input end of the closed-loop amplifying circuit; the open-loop amplifying circuit is used for amplifying the biopotential to be amplified to obtain amplified biopotential; the closed-loop amplifying circuit is used for amplifying the amplified biopotential and correcting the gain of the closed-loop amplifying circuit through feedback. The biopotential amplifier provided by the invention amplifies biopotential to be amplified through the open-loop amplification circuit and the closed-loop amplification circuit, and the closed-loop amplification circuit corrects the gain of the closed-loop amplification circuit through feedback, so that the biopotential amplifier maintains stable output biopotential through constant stable gain to enlarge the linear output range, and the amplification performance of the biopotential amplifier can be improved.
Description
Technical Field
The invention relates to the technical field of integrated circuits, in particular to a biopotential amplifier and a physiological signal measuring system.
Background
Currently, due to diversified demands for high-quality medical technologies, there is an increasing market demand for physiological measurement systems such as electrocardiographic measurement systems, electroencephalographs, and blood pressure measurement systems. The core component in a physiological measurement system is a physiological signal amplifier, the performance of which determines the performance of the entire measurement system.
In the conventional technology, the amplification performance of the physiological signal amplifier is low.
Disclosure of Invention
In view of the above, it is necessary to provide a biopotential amplifier and a physiological signal measuring system.
In one aspect, an embodiment of the present application provides a biopotential amplifier, including: the system comprises an open-loop amplifying circuit and a closed-loop amplifying circuit, wherein the input end of the open-loop amplifying circuit is used for receiving the biopotential to be amplified, and the output end of the open-loop amplifying circuit is connected with the input end of the closed-loop amplifying circuit;
the open-loop amplifying circuit is used for amplifying the biopotential to be amplified to obtain amplified biopotential;
the closed-loop amplifying circuit is used for amplifying the amplified biopotential and correcting the gain of the closed-loop amplifying circuit through feedback.
In one embodiment, a closed loop amplification circuit includes:
the input end of the gain switch unit is connected with the output end of the open-loop amplification circuit;
the input end of the amplifying unit is connected with the output end of the gain switch unit, the output end of the amplifying unit is connected with the control end of the gain switch unit, and the biopotential output by the amplifying unit is used for controlling the on-off of the gain switch unit so as to correct the gain of the closed-loop amplifying circuit.
In one embodiment, the gain switching unit includes:
the first end of the first gain switch is connected with the first output end of the open-loop amplification circuit, the second end of the first gain switch is connected with the first input end of the amplification unit, and the third end of the first gain switch is connected with the output end of the amplification unit;
and a first end of the second gain switch is connected with a second output end of the open-loop amplification circuit, a second end of the second gain switch is connected with a second input end of the amplification unit, and a third end of the second gain switch is connected with an output end of the amplification unit.
In one embodiment, the first gain switch comprises:
the source electrode of the first field effect transistor is connected with the first input end of the amplifying unit, the grid electrode of the first field effect transistor is connected with the output end of the amplifying unit, and the drain electrode of the first field effect transistor is connected with the first output end of the open-loop amplifying circuit;
and the resistor R1 is connected in parallel between the drain and the source of the first field effect transistor.
In one embodiment, the amplifying unit includes:
the grid electrode of the second field effect transistor is connected with the second end of the first gain switch, and the source electrode of the second field effect transistor is used for being connected with a power supply;
the drain electrode of the third field effect transistor is connected with the drain electrode of the second field effect transistor, the grid electrode of the third field effect transistor is connected with the second end of the second gain switch, and the source electrode of the third field effect transistor is grounded;
a first end of the resistor R2, a first end of the resistor R2 is connected with a grid electrode of the second field effect transistor, and a second end of the resistor R2 is connected with a third end of the first gain switch;
and a first end of the resistor R3, a first end of the resistor R3 and a gate of the third field effect transistor are connected, and a second end of the resistor R3 and a third end of the second gain switch are connected.
In one embodiment, the method further comprises the following steps:
the input end of the first voltage buffer is connected with the first output end of the open-loop amplifying circuit, and the output end of the first voltage buffer is connected with the first end of the first gain switch;
and the input end of the second voltage buffer is connected with the second output end of the open-loop amplifying circuit, and the output end of the second voltage buffer is connected with the first end of the second gain switch.
In one embodiment, the method further comprises the following steps:
and the third voltage buffer is connected with the output end of the closed-loop amplifying circuit.
In one embodiment, the method further comprises the following steps:
and the high-pass filter is connected with the input end of the open-loop amplifying circuit and is used for filtering the biopotential to be amplified.
In one embodiment, the open-loop amplifier circuit is an open-loop rail-to-rail differential amplifier circuit.
In another aspect, an embodiment of the present application further provides a physiological signal measuring system, including:
the biopotential amplifier provided in the above embodiment;
the skin electrode is connected with the input end of the biopotential amplifier;
the input end of the filter is connected with the output end of the biopotential amplifier;
and the analog-to-digital converter is connected with the output end of the filter.
A biopotential amplifier includes an open-loop amplification circuit and a closed-loop amplification circuit. The input end of the open-loop amplifying circuit is used for receiving the biopotential to be amplified, and the output end of the open-loop amplifying circuit is connected with the input end of the closed-loop amplifying circuit. The open-loop amplifying circuit is used for amplifying the biopotential to be amplified to obtain amplified biopotential; the closed-loop amplifying circuit is used for amplifying the amplified biopotential and correcting the gain of the closed-loop amplifying circuit through feedback. The biopotential amplifier provided by the embodiment of the application amplifies biopotential to be amplified through the open-loop amplification circuit and the closed-loop amplification circuit, and the closed-loop amplification circuit corrects the gain of the closed-loop amplification circuit through feedback, so that the biopotential amplifier maintains stable output biopotential through constant stable gain to enlarge the linear output range, a higher dynamic measurement range can be obtained, and the amplification performance of the biopotential amplifier can be improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the description of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a physiological signal measuring system according to an embodiment of the present application;
FIG. 2 is a schematic structural diagram of a biopotential amplifier provided in an embodiment of the present application;
fig. 3 is a schematic structural diagram of an open-loop amplifying circuit according to an embodiment of the present application;
FIG. 4 is a schematic structural diagram of a biopotential amplifier provided in an embodiment of the present application;
FIG. 5 is a schematic structural diagram of a biopotential amplifier provided in an embodiment of the present application;
FIG. 6 is a schematic diagram of a voltage buffer according to an embodiment of the present application;
fig. 7 is a schematic structural diagram of a biopotential amplifier according to an embodiment of the present application.
Description of reference numerals:
10. a biopotential amplifier; 20. a physiological signal measurement system; 21. a skin electrode; 22. a filter; 23. an analog-to-digital converter; 100. an open-loop amplification circuit; 110. a first differential pair of field effect transistors; 120. a second differential pair of field effect transistors; 200. a closed loop amplification circuit; 210. a gain switching unit; 211. a first gain switch; 212. a second gain switch; 201. a first field effect transistor; 220. an amplifying unit; 221. a second field effect transistor; 222. a third field effect transistor; 300. a first voltage buffer; 400. a second voltage buffer; 500. a third voltage buffer; 600. a high pass filter.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
The following describes the technical solutions of the present application and how to solve the technical problems with the technical solutions of the present application in detail with specific embodiments. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.
The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. The term "connected" and "coupled" when used in this application, unless otherwise indicated, includes both direct and indirect connections (couplings). In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present application and for simplicity in description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be considered as limiting the present application.
In this application, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through intervening media. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
Referring to fig. 1, the biopotential amplifier 10 provided herein is applied to a physiological signal measurement system 20, which includes skin electrodes 21, a filter 22, and an analog-to-digital converter 23. The first end of the skin electrode 21 is used for connecting the skin of the patient, and the second end of the skin electrode 21 is connected with the input end of the biopotential amplifier 10. The first end of the skin electrode 21 typically has two electrodes. The filter 22 is connected between the biopotential amplifier 10 and the analog-to-digital converter 23. The filter 22 is used for filtering the signal amplified by the biopotential amplifier 10, so as to filter the noise in the biopotential amplified by the biopotential amplifier 10, and make the biopotential obtained by the biopotential amplifier more accurate. The analog-to-digital converter 23 is used for converting the analog signal filtered by the filter 22 into a digital signal for subsequent display and the like. The present embodiment does not set any limitation to the kind, structure, and the like of the skin electrode 21, the filter 22, and the analog-to-digital sensor 23 as long as the functions thereof can be achieved.
Referring to fig. 2, an embodiment of the present application provides a biopotential amplifier 10 including an open-loop amplifier circuit 100 and a closed-loop amplifier circuit 200. The open-loop amplification circuit 100 includes an input and an output, and the closed-loop amplification circuit 200 also includes an input and an output. In use, the skin electrode 21 is disposed on the skin of a patient, the input terminal of the open-loop amplification circuit 100 receives the biopotential to be amplified, and the open-loop amplification circuit 100 is configured to amplify the biopotential to be amplified to obtain the amplified biopotential. The output of the open-loop amplifier circuit 100 is connected to the input of the closed-loop amplifier circuit 200. The closed-loop amplification circuit 200 is used to amplify the amplified biopotential and to modify the gain of the closed-loop amplification circuit 200 by feedback.
The open-loop amplification circuit 100 is a non-loop amplification circuit without a feedback circuit, and the open-loop amplification circuit 100 has a high input impedance, so that the open-loop gain of the open-loop amplification circuit 100 is large, that is, the open-loop amplification circuit 100 has a good amplification effect on the biopotential to be amplified. The closed-loop amplifier circuit 200 is a loop amplifier circuit including a feedback loop. When the difference between the biopotentials to be amplified passing through the two electrodes of the skin electrode 21 is large, the gain of the closed-loop amplification circuit 200 is small, and the gain of the closed-loop amplification circuit 200 can be corrected through a feedback loop, so that the gain is not reduced, and the amplification effect of the biopotential amplifier 10 on the biopotentials to be amplified can be ensured. The specific circuit structures of the closed-loop amplification circuit 100 and the closed-loop amplification circuit 200 are not limited in this embodiment as long as the functions thereof can be realized.
The biopotential amplifier 10 provided by the embodiment of the present application includes an open-loop amplification circuit 100 and a closed-loop amplification circuit 200. The input end of the open-loop amplifying circuit 100 is used for receiving the biopotential to be amplified, and the output end of the open-loop amplifying circuit 100 is connected with the input end of the closed-loop amplifying circuit 200. The open-loop amplification circuit 100 is used for amplifying the biopotential to be amplified to obtain an amplified biopotential; the closed-loop amplification circuit 200 is used to amplify the amplified biopotential and to modify the gain of the closed-loop amplification circuit 200 by feedback. The biopotential amplifier 10 provided in the embodiment of the present application amplifies the to-be-amplified potential through the open-loop amplification circuit 100 and the closed-loop amplification circuit 200, and the closed-loop amplification circuit 200 corrects the gain of the closed-loop amplification circuit 200 through feedback, so that the biopotential amplifier 10 maintains stable output biopotential through constant stable gain to expand the linear output range, and thus a higher dynamic measurement range can be obtained, and the amplification performance of the biopotential amplifier 10 can be improved. The biopotential amplifier 10 can maintain a relatively high common mode rejection ratio and power supply rejection ratio, and use feedback in the closed loop amplification circuit 200 enables the biopotential amplifier 10 to have low power consumption.
Referring to fig. 3, in one embodiment, the open-loop amplifier circuit 100 is an open-loop rail-to-rail differential amplifier circuit. The circuit includes a first differential pair of fets 110 and a second differential pair of fets 120. The first fet differential pair 110 includes an nfet T1, an nfet T2, a pfet T3, a pfet T4, and a first current source. The grid electrode of the N-type field effect transistor T1 is connected with the first electrode of the skin electrode 21, the source electrode of the N-type field effect transistor T1 is connected with the first current source, and the drain electrode of the N-type field effect transistor T1 is connected with the grid electrode of the P-type field effect transistor T3. The drain of the PFET T3 is connected to the source, and the source of the PFET T3 is connected to the source of the PFET T4. The grid electrode of the N-type field effect transistor T2 is connected with the second electrode of the skin electrode 21, the source electrode of the N-type field effect transistor T2 is connected with a current source, and the drain electrode of the N-type field effect transistor T2 is connected with the drain electrode of the P-type field effect transistor T4. The gate of PFET T4 is connected to the gate of PFET T3.
The second fet differential pair 120 includes a pfet T5, a pfet T6, an nfet T7, an nfet T8, and a second current source. The grid of the PFET T5 is connected to the first electrode of the skin electrode 21, the source of the PFET T5 is connected to the second current source, and the drain of the PFET T5 is connected to the drain of the NFET T7. The grid electrode of the P-type field effect transistor T6 is connected with the second electrode of the skin electrode 21, the source electrode of the P-type field effect transistor T6 is connected with the source electrode of the P-type field effect transistor T5, and the drain electrode of the P-type field effect transistor T6 is connected with the drain electrode of the N-type field effect transistor T8. The gate and the drain of the NFET T7 are connected, and the source of the NFET T7 is connected to the source of the NFET T8. The gate of NFET T8 is connected to the gate of NFET T7.
In the embodiment of the present application, the rail-to-rail differential amplifier circuit can realize the rail-to-rail of the input biopotential to be amplified and the output amplified biopotential range of the open-loop amplifier circuit 100, that is, the swing of the output amplified biopotential is close to the ground and the power supply voltage. In other words, the use of the open-loop rail-to-rail differential amplifier circuit can increase the output range of the open-loop amplifier circuit 100, thereby increasing the output range of the biopotential amplifier 10 and thus increasing the amplification performance of the biopotential amplifier 10.
Referring to fig. 4, in one embodiment, the closed-loop amplifying circuit 200 includes a gain switching unit 210 and an amplifying unit 220. The gain switching unit 210 includes an input terminal, an output terminal, and a control terminal, and the amplifying unit 220 also includes an input terminal and an output terminal. An input terminal of the gain switching unit 210 is connected to an output terminal of the open-loop amplification circuit 100 as an input terminal of the closed-loop amplification circuit 200. The output terminal of the amplifying unit 220 serves as the output terminal of the closed-loop amplifying circuit 200, and outputs the final amplified biopotential. An output terminal of the amplifying unit 220 is connected to a control terminal of the gain switching unit 210. The biopotential output from the output terminal of the amplifying unit 220 is used to control the on/off of the gain switching unit 210 to modify the gain of the closed-loop amplifying circuit 200. The output end of the amplifying unit 220 is connected to the control end of the gain switch unit 210, so that the gain switch unit 210 and the amplifying unit 220 form a feedback loop, and the on/off of the gain switch unit 210 is controlled by the biopotential output by the output end of the amplifying unit 220, so as to achieve the purpose of correcting the gain of the closed-loop amplifying circuit 200. In other words, the on/off of the gain switch unit 210 is controlled by the biopotential output from the output terminal of the amplifying unit 220, so that the decrease of the gain of the closed-loop amplifying circuit 200 can be compensated, and the amplification factor of the biopotential to be amplified by the biopotential amplifier 10, that is, the amplification performance of the biopotential amplifier 10 can be improved.
With continued reference to fig. 4, in one embodiment, the gain switch unit 210 includes a first gain switch 211 and a second gain switch 212. The first gain switch 211 includes a first terminal, a second terminal, and a third terminal. A first terminal of the first gain switch 211 is connected to a first output terminal of the open-loop amplifier circuit 100, a second terminal of the first gain switch 211 is connected to a first input terminal of the amplifier unit 220, and a third terminal of the first gain switch 211 is connected to an output terminal of the amplifier unit 220. The second gain switch 212 also includes a first terminal, a second terminal, and a third terminal. A first terminal of the second gain switch 212 is connected to the second output terminal of the open-loop amplifier circuit 100, a second terminal of the second gain switch 212 is connected to the second input terminal of the amplifying unit 220, and a third terminal of the second gain switch 212 is connected to the output terminal of the amplifying unit 220.
A first terminal of the first gain switch 211 and a first terminal of the second gain switch 212 are commonly connected as an input terminal of the gain switch unit 210 to an output terminal of the open-loop amplification circuit 100. A second terminal of the first gain switch 211 and a second terminal of the second gain switch 212 are connected to the amplifying unit 220 as an output terminal of the gain switching unit 210. The third terminal of the first gain switch 211 and the third terminal of the second gain switch 212 are both control terminals of the gain switch unit 210.
With continued reference to fig. 4, in one embodiment, the first gain switch 211 includes a first fet 201 and a resistor R1. The source of the first field effect transistor 201 is connected to the first input terminal of the amplifying unit 220, the gate of the first field effect transistor 201 is connected to the output terminal of the amplifying unit 220, and the drain of the first field effect transistor 201 is connected to the first output terminal of the open-loop amplifying circuit 100. The resistor R1 is connected in parallel between the drain and the source of the first fet 201. The resistor R1 is used to protect the first fet 201 and ensure the normal operation of the first fet 201. The source of the first field effect transistor 201 is connected to the first input terminal of the amplifying unit 220 as the second terminal of the first gain switch 211, the gate of the first field effect transistor 201 is connected to the output terminal of the amplifying unit 220 as the third terminal of the first gain switch 211, and the drain of the first field effect transistor 201 is connected to the first output terminal of the switching amplifying circuit 100 as the first terminal of the first gain switch 211.
The circuit structure of the second gain switch 212 is the same as that of the first gain switch 211, and is not described herein again.
With continued reference to fig. 4, in one embodiment, the amplifying unit 220 includes a second fet 221, a third fet 222, a resistor R2, and a resistor R3. The gate of the second fet 221 is connected to the second terminal of the first gain switch 211, and the source of the second fet 221 is used for connection to a power supply. The drain of the third fet 222 is connected to the drain of the second fet 221, the gate of the third fet 222 is connected to the second terminal of the second gain switch 212, and the source of the third fet 222 is grounded. The gate of the second fet 221 is connected to the second terminal of the first gain switch 211 as the first input terminal of the amplifying unit 220, the gate of the third fet 222 is connected to the second terminal of the second gain switch 212 as the second input terminal of the amplifying unit 220, and the drain of the second fet 221 and the drain of the third fet 222 are both used as the output terminals of the amplifying unit 220. A first terminal of the resistor R2 is connected to the gate of the second fet 221, and a second terminal of the resistor R2 is connected to the third terminal of the first gain switch 211. A first terminal of the resistor R3 is connected to the gate of the third fet 222, and a second terminal of the resistor R3 is connected to the third terminal of the second gain switch 212. The resistor R2 and the resistor R3 are used for protecting the amplifying circuit.
In the embodiment of the present application, a compact amplifying unit 220 can be formed by connecting the second fet 221 and the third fet 222 in series, so that the area of the biopotential amplifier 10 can be reduced.
Referring to fig. 5, in one embodiment, the biopotential amplifier 10 further includes a first voltage buffer 300 and a second voltage buffer 400. An input terminal of the first voltage buffer 300 is connected to a first output terminal of the open-loop amplifying circuit 100, and an output terminal of the first voltage buffer 300 is connected to a first terminal of the first gain switch 211. The input terminal of the second voltage buffer 400 is connected to the second output terminal of the open-loop amplifier circuit 100, and the output terminal of the second voltage buffer 400 is connected to the first terminal of the second gain switch 212. The first voltage buffer 300 can prevent reduction of the amplified biopotential input to the first gain switch 211 from the first output terminal of the split-loop amplification circuit 100 when the input impedance of the first gain switch 211 is not high. Similarly, the second voltage buffer 400 can prevent the amplified biopotential input from the second output terminal of the split-loop amplifier circuit 100 to the second gain switch 212 from being reduced when the input impedance of the second gain switch 212 is not high. In summary, using the first voltage buffer 300 and the second voltage buffer 400 can prevent the reduction of the amplified biopotential output from the open-loop amplification circuit 100 when the input impedance of the closed-loop amplification circuit 200 is not high, thereby allowing the biopotential amplifier 10 to expand the linear output range by maintaining a stable output with a constant amplification gain. The first voltage buffer 300 and the second voltage buffer 400 may have the same or different structures, and the present embodiment does not limit the structures of the first voltage buffer 300 and the second voltage buffer 400, as long as the functions thereof can be achieved.
With continued reference to fig. 5, in one embodiment, the biopotential amplifier 10 further includes a third voltage buffer 500. The third voltage buffer 500 is connected to an output terminal of the closed-loop amplification circuit 200. The third voltage buffer 500 is connected to the output end of the closed-loop amplifying circuit 200, so that the feedback resistor with a smaller resistance value is used in the closed-loop amplifying circuit 200 to achieve the purpose that the influence of the change of the external resistance on the closed-loop gain of the closed-loop amplifying circuit 200 is smaller, and further, the amplifying performance of the biopotential amplifier 10 can be improved.
In a specific embodiment, the first voltage buffer 300, the second voltage buffer 400, and the third voltage buffer 500 have the same circuit structure, and are all rail-to-rail voltage buffers as shown in fig. 6.
Referring to fig. 7, in one embodiment, biopotential amplifier 10 further includes a high pass filter 600. The high-pass filter 600 is connected to the input of the open-loop amplifier circuit 100 for filtering the biopotential to be amplified. The use of the high-pass filter 600 can filter out the dc offset in the biopotential to be amplified, thereby enabling the amplification performance of the biopotential amplifier 10 to be improved. The present embodiment does not set any limitation to the specific circuit structure of the high-pass filter 600 as long as the function thereof can be achieved.
The principle of the biopotential amplifier 10 is explained in detail with reference to fig. 7:
suppose that the voltages of the two electrodes of the skin electrode 21 are V, respectivelyin+And Vin. Output voltage V of open-loop amplifier circuit 1001And V3An intermediate supply voltage. At Vin+And Vin-The closed-loop gain of the closed-loop amplifier circuit 200 is not reduced significantly when the difference therebetween is small. At this time, the first gain switch 211 and the second gain switch 212 do not operate. Output voltage V of open-loop amplifier circuit 1001And V3Can be expressed as: v1＝-A1n·(Vin+-Vin-)，V3＝-A1p·(Vin+-Vin-) Wherein A is1nAnd A1pIs the open loop gain of the open loop amplification circuit 100.
Suppose node voltage V2And V4For the common mode voltage of the closed-loop amplifying circuit 200, the node voltage V2And V4Can be expressed as:
wherein, VoutIs the output voltage of the closed loop amplifier circuit 200.
Assuming that the gain of the third voltage buffer 500 is 1, the output voltage V isoutCan be expressed as: vout＝-gm11(ro11||ro12)·V2-gm12(ro11||ro12)·V4Wherein g ism11Is the conductance, g, of the second field effect transistor 221m12Is the conductance of the third FET 222, ro11Is the output resistance, r, of the second FET 221o12Is the output resistance of the third fet 222. According to the symmetrical design of the closed-loop amplifying circuit 200, gm11And gm12Equal, at this time, the open loop gain A of the closed loop amplifier circuit2Can be expressed as:
due to the symmetrical feedback design, V2And V4May be considered equal. Assuming that the output resistance of the third voltage buffer 500 is much smaller than the resistances of the resistor R1 and the resistor R3, the gain V of the biopotential amplifier 10out/(Vin+-Vin-) Can be expressed as:
suppose A1＝A1n＝A1pThe resistances of the resistor R1 and the resistor R3 are much smaller than the resistances of the resistor R2 and the resistor R4, and the gain A of the biopotential amplifier 10outCan be simplified as follows: a. theov＝A1·A2,c1Wherein A is2,c1Is the closed loop gain of the closed loop amplifying circuit, A2,c1＝Vout/V1＝Vout/V3And, furthermore,
if A2》1，AovCan be simplified to only A1And (R2| | R4)/(R1| | | R3).
At Vin+And VinWhen the difference between the two is large, the output voltage V of 10 of the biopotential amplifieroutA change occurs such that the first gain switch 211 and the second gain switch 212 start to operate, and at this time, the gain of the closed-loop amplification circuit 200 can be expressed as:
wherein, R1 ═ R (R1| | | R)ON,T9),R3'＝(R3||RON,T10) Where T9 represents the fet in the first gain switch 211 and T10 represents the fet in the second gain switch 212. When A isoutClose to ground, T9 will be off (R)ON,T9Infinity), when AoutIs close to VDDWhen, T10Will be turned off (R)ON,T10∞) therefore, R1 'and R3' will compensate for a2The overall gain is reduced.
In this example, for A2For each 10dB reduction, Aov drops by 5dB without the gain switch cell 210 and A with the gain switch cell 210ovThe drop is 2.3dB, which indicates that the gain switch unit 210 can be added to make the biopotential amplifier 10 obtain a wider linear output range.
In a specific embodiment, A1＝35dB、A2The current source of the open-loop rail-to-rail differential amplifier circuit is 0.7 μ a, and the resistance in the amplifier unit 220 is the n-well diffusion resistance, 30 dB. The biopotential amplifier 10 has a supply voltage of 3.3V and an area of 0.063mm2. When the output range of the biopotential amplifier 10 is 0.15V to 3.12V, the stable voltage gain is 46.3dB, the input amplitude is 15mVpp, and the total harmonic distortion is 0.04%.
Referring to fig. 1, an embodiment of the present application further provides a physiological signal measuring system 20 including the biopotential amplifier 10, the skin electrodes 21, the filter 22 and the analog-to-digital converter 23 provided in the above embodiment. The skin electrodes 21 are connected to the input of the biopotential amplifier 10, the input of the filter 22 is connected to the output of the biopotential amplifier 10, and the analog-to-digital converter 23 is connected to the output of the filter 22. For a detailed description of the skin electrodes 21, the filter 22 and the analog-to-digital converter 23, reference is made to the above description, which is not repeated here. Since the physiological signal measuring system 20 includes the biopotential amplifier 10, the physiological signal measuring system 20 has all the structures and advantages of the biopotential amplifier 10, which will not be described in detail herein.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A biopotential amplifier, comprising: the system comprises an open-loop amplifying circuit and a closed-loop amplifying circuit, wherein the input end of the open-loop amplifying circuit is used for receiving a biological potential to be amplified, and the output end of the open-loop amplifying circuit is connected with the input end of the closed-loop amplifying circuit;
the open-loop amplifying circuit is used for amplifying the biological potential to be amplified to obtain amplified biological potential;
the closed-loop amplifying circuit is used for amplifying the amplified biopotential and correcting the gain of the closed-loop amplifying circuit through feedback.
2. The biopotential amplifier of claim 1 wherein said closed loop amplification circuit comprises:
the input end of the gain switch unit is connected with the output end of the open-loop amplification circuit;
the input end of the amplifying unit is connected with the output end of the gain switch unit, the output end of the amplifying unit is connected with the control end of the gain switch unit, and the biopotential output by the amplifying unit is used for controlling the on-off of the gain switch unit so as to correct the gain of the closed-loop amplifying circuit.
3. The biopotential amplifier of claim 2, wherein said gain switching unit comprises:
a first end of the first gain switch is connected with a first output end of the open-loop amplification circuit, a second end of the first gain switch is connected with a first input end of the amplification unit, and a third end of the first gain switch is connected with an output end of the amplification unit;
and a first end of the second gain switch is connected with a second output end of the open-loop amplification circuit, a second end of the second gain switch is connected with a second input end of the amplification unit, and a third end of the second gain switch is connected with an output end of the amplification unit.
4. The biopotential amplifier of claim 3 wherein said first gain switch comprises:
a source electrode of the first field effect transistor is connected with a first input end of the amplifying unit, a grid electrode of the first field effect transistor is connected with an output end of the amplifying unit, and a drain electrode of the first field effect transistor is connected with a first output end of the open-loop amplifying circuit;
and the resistor R1 is connected in parallel between the drain and the source of the first field effect transistor.
5. The biopotential amplifier of claim 3, wherein said amplification unit comprises:
a grid electrode of the second field effect transistor is connected with the second end of the first gain switch, and a source electrode of the second field effect transistor is used for being connected with a power supply;
a drain electrode of the third field effect transistor is connected with a drain electrode of the second field effect transistor, a grid electrode of the third field effect transistor is connected with the second end of the second gain switch, and a source electrode of the third field effect transistor is grounded;
a resistor R2, a first terminal of the resistor R2 is connected with the gate of the second FET, and a second terminal of the resistor R2 is connected with the third terminal of the first gain switch;
a resistor R3, a first terminal of the resistor R3 is connected to the gate of the third FET, and a second terminal of the resistor R3 is connected to the third terminal of the second gain switch.
6. The biopotential amplifier of claim 3, further comprising:
a first voltage buffer, an input terminal of which is connected to a first output terminal of the open-loop amplification circuit, and an output terminal of which is connected to a first terminal of the first gain switch;
and the input end of the second voltage buffer is connected with the second output end of the open-loop amplifying circuit, and the output end of the second voltage buffer is connected with the first end of the second gain switch.
7. The biopotential amplifier of claim 1, further comprising:
and the third voltage buffer is connected with the output end of the closed-loop amplifying circuit.
8. The biopotential amplifier of claim 1, further comprising:
and the high-pass filter is connected with the input end of the open-loop amplifying circuit and is used for filtering the biological potential to be amplified.
9. The biopotential amplifier of claim 1 wherein said open loop amplification circuit is an open loop rail-to-rail differential amplification circuit.
10. A physiological signal measurement system, comprising:
the biopotential amplifier of any one of claims 1-9;
the skin electrode is connected with the input end of the biopotential amplifier;
the input end of the filter is connected with the output end of the biopotential amplifier;
and the analog-to-digital converter is connected with the output end of the filter.
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