CN110138346B - Capacitive coupling type chopper instrument amplifier capable of improving noise performance - Google Patents

Capacitive coupling type chopper instrument amplifier capable of improving noise performance Download PDF

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CN110138346B
CN110138346B CN201910411904.6A CN201910411904A CN110138346B CN 110138346 B CN110138346 B CN 110138346B CN 201910411904 A CN201910411904 A CN 201910411904A CN 110138346 B CN110138346 B CN 110138346B
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input
offset cancellation
circuit
capacitor
operational amplifier
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CN110138346A (en
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穆庚
吕良剑
叶大蔚
史传进
张怡云
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Fudan University
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Fudan University
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/189—High frequency amplifiers, e.g. radio frequency amplifiers
    • H03F3/19—High frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only
    • H03F3/195—High frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only in integrated circuits
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
    • H03F3/45928—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit
    • H03F3/45932—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit by using feedback means
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/372—Noise reduction and elimination in amplifier

Abstract

The invention provides a capacitance coupling type chopping instrument amplifier for improving noise performance, which combines an input chopping circuit, an operational amplifier circuit, a pseudo-resistance biasing circuit, an electrode offset cancellation loop and a digital electrode offset cancellation module, so that the original electrode offset cancellation loop can adopt smaller offset cancellation capacitors and also can keep equivalent input offset cancellation capacity and system pole positions of a circuit system, the pole design pressure of an electrode offset cancellation loop integrator is weakened, and the smaller offset cancellation capacitors greatly attenuate the system equivalent input reference noise of the electrode offset cancellation loop, thereby improving the noise performance of the circuit.

Description

Capacitive coupling type chopper instrument amplifier capable of improving noise performance
Technical Field
The invention relates to the technical field of analog circuit signal processing, in particular to a capacitive coupling type chopper instrument amplifier for improving noise performance.
Background
Instrumentation amplifiers have long been an extremely important part of the bioelectronic readout circuitry. As shown in fig. 1, since the biological signal is in a frequency band ranging from about several millihertz to about several hundreds, several kilohertz, and its amplitude value is as small as several microvolts. Therefore, circuit design on a conventional CMOS process is required to eliminate 1/f noise at its inherent low frequency while keeping the thermal noise of the entire circuit at a low level.
However, because of the demand for wearable bioelectrics, it is not possible for an instrumentation amplifier to reduce thermal noise directly by increasing power consumption or to reduce 1/f noise by increasing area. The high power consumption can increase the current consumption of the circuit, and the period of one-time wearable record of the wearable equipment is reduced; the large area increases the design cost of the chip, and this approach is also limited by the design of noise. Among the noise canceling methods, the chopping (chopping) technique is a continuous method that does not cause noise folding and thus increases the noise floor, and is therefore widely used in bioelectronic read circuits.
Among various applications of chopping technology, a capacitive coupling type chopping instrumentation amplifier is proved to be an instrumentation amplifier structure which is very suitable for low-power-consumption design. In order to ensure that the amplifier amplifies the biological signal while suppressing the dc offset of the electrode, the system requires a very low frequency (on the order of a few millihertz or slightly larger) high pass pole, and such high pass pole and electrode dc offset cancellation capability is accomplished by an electrode offset cancellation (DSL) loop. However, the low high-pass pole of the system increases the design difficulty of the electrode offset cancellation loop, and the requirement of the instrumentation amplifier on low power consumption can cause the noise of the electrode offset cancellation loop to influence the noise performance of the system.
Disclosure of Invention
The invention aims to provide a capacitive coupling type chopping instrument amplifier capable of improving noise performance, which combines an input chopping circuit, an operational amplifier circuit, a pseudo-resistor bias circuit, an electrode offset cancellation loop and a digital electrode offset cancellation module, so that the original electrode offset cancellation loop can adopt a smaller offset cancellation capacitor and also can keep equivalent input offset cancellation capacity and system pole position of a circuit system, the pole design pressure of an integrator in the electrode offset cancellation loop is weakened, and the smaller offset cancellation capacitor greatly attenuates the system equivalent input reference noise of the electrode offset cancellation loop, thereby improving the noise performance of the circuit.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a capacitively coupled chopper instrumentation amplifier comprising:
the input chopper circuit modulates an original input signal into an original high-frequency signal and couples the original high-frequency signal to the input end of an operational amplifier circuit; the operational amplification circuit is used for amplifying the high-frequency input signal entering the operational amplification circuit and outputting an output signal;
the pseudo resistance bias circuit is connected with the input end of the operational amplification circuit and provides input common mode bias voltage for the operational amplification circuit;
the input end of the electrode offset cancellation loop is connected with the output end of the operational amplification circuit, the output end of the electrode offset cancellation loop is connected with the input end of the operational amplification circuit and used for canceling the electrode direct-current offset voltage of the input signal, the electrode offset cancellation loop comprises an integrator, and the integrator outputs the voltage after integrating the output signal;
the negative feedback circuit is used for providing negative feedback regulation for the operational amplification circuit, the input end of the negative feedback circuit is connected with the output end of the operational amplification circuit, the output end of the negative feedback circuit is connected with the input end of the operational amplification circuit, and the negative feedback circuit modulates an output signal into a high-frequency signal and feeds the high-frequency signal back to the input end of the operational amplification circuit to serve as a high-frequency input signal of the operational amplification circuit;
and the input end of the digital electrode offset elimination module is connected with the output end of the integrator of the electrode offset elimination loop, and the output end of the digital electrode offset elimination module is connected with the operational amplifier input end of the operational amplification circuit.
Preferably, the digital electrode offset cancellation module comprises:
the input end of the logic control module is connected with the output end of the integrator in the electrode offset cancellation loop;
a first digital module chopping modulator, an input end of which is connected with an output end of the logic control module, wherein the logic control module outputs a control signal to the first digital module chopping modulator;
a first adjustable offset canceling capacitor, an input end of which is connected to an output end of the first digital module chopping modulator, and an output end of the first adjustable offset canceling capacitor is connected to a positive input end of the operational amplifier circuit;
a second adjustable offset canceling capacitor, an input end of which is connected to the other output end of the first digital module chopping modulator, and an output end of the second adjustable offset canceling capacitor is connected to a negative input end of the operational amplifier circuit;
the logic control module adjusts the capacitance of the first adjustable offset cancellation capacitor and the capacitance of the second adjustable offset cancellation capacitor, and also adjusts the capacitance of the first digital module chopping modulator and the passing voltage polarity thereof to cancel the input direct current offset voltage.
Preferably, the first adjustable offset canceling capacitor and the second adjustable offset canceling capacitor are in an initial state of a ground state, the integrator outputs a voltage to the logic control module, and the logic control module determines whether an absolute value of the integrator output voltage exceeds an initially set constant value;
if the voltage is less than the constant value, the logic control module does not perform any adjustment action on the first adjustable offset cancellation capacitor and the second adjustable offset cancellation capacitor;
and if the voltage exceeds the constant value, the logic control module judges whether the voltage is positive or negative, and then controls and adjusts the connection state of the first adjustable offset cancellation capacitor and the second adjustable offset cancellation capacitor and the capacitance value of the first adjustable offset cancellation capacitor and the second adjustable offset cancellation capacitor.
Preferably, when the voltage is positive, the first adjustable offset canceling capacitor is connected to ground, and the second adjustable offset canceling capacitor is connected to a power supply;
when the voltage is negative, the first adjustable offset canceling capacitor is connected to a power supply, and the second adjustable offset canceling capacitor is connected to the ground.
Preferably, the input chopper circuit includes:
the biological signal is connected with the input end of the input chopping modulator, and the input chopping modulator outputs a high-frequency signal;
a first input coupling capacitor, an input end of which is connected with an output end of the input chopping modulator, and an output end of which is connected with an input end of the operational amplification circuit;
a second input coupling capacitor, an input end of which is connected with the other output end of the input chopping modulator, and an output end of which is connected with the input end of the operational amplification circuit;
the first input coupling capacitor and the second input coupling capacitor couple the high-frequency signal output by the input chopping modulator to the negative input end and the positive input end of the operational amplifier circuit respectively.
Preferably, the operational amplifier circuit includes:
the positive input end and the negative input end of the first-stage operational amplifier are connected with the pseudo-resistance biasing circuit, and the output end of the first-stage operational amplifier is connected with the input end of an operational amplifier circuit chopping modulator;
the positive input end and the negative input end of the second-stage operational amplifier are connected with the output end of the chopping modulator of the operational amplifier circuit, and the output end of the second-stage operational amplifier outputs an output signal;
the positive input end and the negative input end of the second-stage operational amplifier are respectively connected with a first Miller compensation capacitor and a second Miller compensation capacitor in parallel.
Preferably, the electrode offset cancellation loop comprises:
the positive input end and the negative input end of the integrator are connected with the output end of the operational amplification circuit;
the output end of the integrator is connected with the input end of an electrode offset elimination loop chopping modulator, and the integrator integrates the output signal and outputs voltage;
the input end of the first electrode offset cancellation loop offset cancellation capacitor is connected with one output end of the electrode offset cancellation loop chopping modulator, and the output end of the first electrode offset cancellation loop offset cancellation capacitor is connected with the input end of the operational amplification circuit;
a second electrode offset cancellation loop offset cancellation capacitor, an input end of which is connected with the other output end of the electrode offset cancellation loop chopping modulator, and an output end of the second electrode offset cancellation loop offset cancellation capacitor is connected with an input end of the operational amplification circuit;
the first electrode offset cancellation loop offset cancellation capacitor and the second electrode offset cancellation loop offset cancellation capacitor couple signals output by the electrode offset cancellation loop chopping modulator to a negative input end and a positive input end of the operational amplification circuit respectively.
Preferably, the negative feedback circuit comprises:
the negative feedback circuit chopping modulator is connected with the output signal and modulates the output signal into a high-frequency signal for output;
the input end of the first negative feedback coupling capacitor is connected with one output end of the negative feedback circuit chopping modulator, and the output end of the first negative feedback coupling capacitor is connected with the input end of the operational amplification circuit; the input end of the second negative feedback coupling capacitor is connected with the other output end of the negative feedback circuit chopping modulator, and the output end of the second negative feedback coupling capacitor is connected with the input end of the operational amplification circuit;
the first negative feedback coupling capacitor and the second negative feedback coupling capacitor couple the high-frequency signal to a positive input end and a negative input end of the operational amplifier circuit respectively.
Compared with the prior art, the invention has the following advantages:
(1) the input chopper circuit, the operational amplifier circuit, the electrode offset cancellation loop, the digital electrode offset cancellation module and the like are combined, so that the original electrode offset cancellation loop can adopt smaller offset cancellation capacitors and also can keep the equivalent input offset cancellation capability and system pole position of a circuit system, and the pole design pressure of the electrode offset cancellation loop integrator is weakened;
(2) due to the introduction of the digital electrode offset elimination module, a small offset elimination capacitor can be kept in the electrode offset elimination loop, so that the system equivalent input reference noise of the electrode offset elimination loop is greatly attenuated, and the noise performance of the circuit is improved.
Drawings
FIG. 1 is a schematic diagram of the electrodes of the present invention converting biological signals into electrical signals for amplification by an instrumentation amplifier;
fig. 2 is a schematic diagram of a circuit structure of the capacitive coupling type chopper instrument amplifier of the invention.
Detailed Description
The present invention will now be further described by way of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings.
The input signal of the analog front end is generally generated by an electrode connected with a body, however, a direct current offset voltage with the amplitude of 50mV exists between the electrodes, so a loop is needed to reduce the influence of the direct current offset voltage, otherwise, the gain of the analog front end of dozens to one hundred times is saturated due to the large electrode offset. An electrode offset cancellation loop is a loop that attenuates this effect. As shown in FIG. 1, the electrode of the present invention converts biological signals into electrical signals, and the electrical signals are amplified by an instrumentation amplifier.
As shown in fig. 2, a schematic diagram of a circuit structure of a capacitive coupling type chopper instrument amplifier of the present invention includes an input chopper circuit 1, an operational amplifier circuit 2, a pseudo-resistor bias circuit 3, an electrode offset cancellation loop 4, a negative feedback circuit 5, and a digital electrode offset cancellation module 6, wherein:
input chopper circuit 1 for inputting original biological signal VinModulating the signal into an original high-frequency signal, and coupling the original high-frequency signal to the input end of the operational amplification circuit 2;
an operational amplifier circuit 2 for amplifying the high frequency input signal entering the operational amplifier circuit 2 and outputting an output signal Vout；
The pseudo resistance bias circuit 3 is connected with the input end of the operational amplification circuit 2 and is used for providing input common mode bias voltage for the operational amplification circuit 2;
an input end of the electrode offset cancellation loop 4 is connected to an output end of the operational amplifier circuit 2, an output end of the electrode offset cancellation loop 4 is connected to an input end of the operational amplifier circuit 2 and used for canceling the electrode direct-current offset voltage of the input signal, the electrode offset cancellation loop 4 includes an integrator G, and the integrator G integrates the high-frequency signal and outputs an integrated voltage signal VDSL_out；
Providing a negative feedback regulation negative feedback circuit 5 for the operational amplification circuit 2, wherein the input end of the negative feedback regulation negative feedback circuit 5 is connected with the output end of the operational amplification circuit 2, the output end of the negative feedback regulation negative feedback circuit 5 is connected with the input end of the operational amplification circuit 2, and the negative feedback regulation negative feedback circuit 5 outputs a signal VoutModulating the signal into a high-frequency signal, and feeding the high-frequency signal back to the input end of the operational amplification circuit 2 to be used as a high-frequency input signal of the operational amplification circuit 2;
the input end of the digital electrode offset cancellation module 6 is connected with the output end of the integrator G of the electrode offset cancellation loop 4, the output end of the digital electrode offset cancellation module 6 is connected with the operational amplifier input end of the operational amplifier circuit 2, and the digital electrode offset cancellation module 6 is used for reducing the offset cancellation capacitance in the electrode offset cancellation loop 4, so that the pole design pressure of the integrator G is reduced, and the noise influence of the electrode offset cancellation loop 4 on a system is reduced.
Wherein, the digital electrode offset cancellation module 6 comprises:
logic control module, input of whichThe end of the integrator is connected with the output end of the integrator G in the electrode offset cancellation loop 4, and the integrator G outputs a signal VoutOutput voltage V after integrationDSL_out；
First digital module chopping modulator CHDhpThe input end of the logic control module is connected with the output end of the logic control module, and the logic control module outputs a control signal to the first digital module chopping modulator CHDhp；
First tunable offset canceling capacitor CDhp1Having an input terminal connected to said first digital block chopping modulator CHDhpIs connected to the first adjustable offset canceling capacitor CDhp1An output end and a first-stage operational amplifier G of the operational amplification circuitm1Are connected with the positive input end of the main body;
second tunable offset canceling capacitor CDhp2Having an input terminal connected to said first digital block chopping modulator CHDhpIs connected to the other output terminal of the second tunable offset canceling capacitor CDhp2An output end and a first-stage operational amplifier G of the operational amplification circuitm1Is connected with the negative input end of the power supply;
the logic control module adjusts the first adjustable offset cancellation capacitor CDhp1And said second adjustable offset canceling capacitor CDhp2Also adjusts the first digital module chopping modulator CHDhpThe input direct current offset voltage is eliminated according to the size of the capacitor and the polarity of the passing voltage.
The input chopper circuit 1 includes:
input chopping modulator CHinSaid biosignal VinAnd said input chopping modulator CHinIs connected to the input terminal of the said input chopping modulator CHinOutputting a high-frequency signal;
first input coupling capacitor Cin1Input terminal thereof and said input chopping modulator CHinAn output terminal connected to the first input coupling capacitor Cin1The output end is connected with the negative input end of the operational amplification circuit 2;
second input coupling capacitor Cin2Input terminal thereof and said input chopping modulator CHinThe other output end is connected with the second input coupling capacitor Cin2The output end is connected with the positive input end of the operational amplifier circuit; the first input coupling capacitor Cin1And said second input coupling capacitance Cin2The input chopping modulator CHinThe output high-frequency signal is respectively coupled to the negative input end and the positive input end of the operational amplifier circuit 2.
The operational amplifier circuit 2 includes:
first stage operational amplifier Gm1A positive input terminal thereof connected to the pseudo-resistor bias circuit 3 and the second input coupling capacitor Cin2Connected, the first stage operational amplifier Gm1The negative input end, the pseudo resistance biasing circuit 3 and the first input coupling capacitor Cin1Output terminal connected, the first stage operational amplifier Gm1Output terminal and an operational amplifier circuit chopper modulator CHoutThe input ends of the two-way valve are connected;
second stage operational amplifier Gm2The positive and negative input ends of which are connected with the chopping modulator CH of the operational amplifier circuitoutIs connected to the output terminal of the second stage operational amplifier Gm2The output end outputs an output signal Vout(ii) a The second stage operational amplifier Gm2The positive and negative input terminals of the first transistor are respectively connected in parallel with a first Miller compensation capacitor Cm1And a second Miller compensation capacitor Cm2。
The pseudo resistance bias circuit 3 is a pair of resistors and includes a first resistor Rb1And a second resistor Rb2. The first resistor Rb1And the first stage operational amplifier Gm1Is connected to the negative input terminal of the first resistor R, the second resistor Rb2And the first stage operational amplifier Gm1Is connected with the positive input end of the transformer.
The electrode offset cancellation loop 4 includes:
an integrator G having an input terminal connected to the second stage operational amplifier G of the operational amplifier circuit 2m2The output ends of the two-way valve are connected; the output end of the integrator G is connected with an electrode offset elimination loop chopped-wave modulator CHhpInput deviceEnd of said integrator G for said output signal VoutOutput voltage V after integrationDSL_out；
First electrode offset cancellation loop offset cancellation capacitor Chp1The input end of the chopper modulator CH is the electrode offset elimination loophpAn output terminal, the first electrode offset cancellation loop offset cancellation capacitor Chp1The output end of the operational amplifier circuit 2 is connected with a first-stage operational amplifier G of the operational amplifier circuitm1Is connected with the negative input end of the power supply;
second electrode offset cancellation loop offset cancellation capacitor Chp2The input end of the chopper modulator CH is the electrode offset elimination loophpAnother output terminal, the second electrode offset cancellation loop offset cancellation capacitor Chp2An output end and a first-stage operational amplifier G of the operational amplification circuit 2m1Are connected with the positive input end of the main body; the first electrode offset cancellation loop offset cancellation capacitor Chp1And said second electrode offset cancellation loop offset cancellation capacitor Chp2A loop chopping modulator CH for eliminating the electrode offsethpThe output signals are respectively coupled to the negative input end and the positive input end of the operational amplifier circuit 2.
The negative feedback circuit 5 includes:
negative feedback circuit chopping modulator CHfbSaid output signal VoutAnd said negative feedback circuit chopping modulator CHfbIs connected to the output signal VoutModulating the signal into a high-frequency signal and outputting the signal;
first negative feedback coupling capacitor Cfb1The input end of which is connected with the negative feedback circuit chopping modulator CHfbAn output terminal connected to the first negative feedback coupling capacitor Cfb1An output end and a first-stage operational amplifier G of the operational amplification circuit 2m1Are connected with the positive input end of the main body;
second negative feedback coupling capacitor Cfb2The input end of which is connected with the negative feedback circuit chopping modulator CHfbThe other output end is connected with the second negative feedback coupling capacitor Cfb2An output end and a first-stage operational amplifier G of the operational amplification circuit 2m1Is connected with the negative input end of the power supply; the first negative feedback coupling capacitor Cfb1And said second negative feedback coupling capacitor Cfb2The high-frequency signals are coupled to the positive input end and the negative input end of the operational amplifier circuit 2 respectively.
During operation, the integrator G outputs a voltage VDSL_outTo the logic control module, the logic control module firstly judges the voltage V output by the integrator GDSL_outWhether the absolute value of (V) exceeds a constant value (which is designed according to the needs of the designer), e.g. to determine the voltage VDSL_outWhether the first offset is larger than 0.5VDD or not, if the absolute value is larger than 0.5VDD, the logic control module simultaneously adjusts and increases the first adjustable offset cancellation capacitor CDhp1And said second tunable offset canceling capacitor CDhp2The capacitance value of (2). If the voltage is less than 0.5VDD, the logic control module does not adjust the first adjustable offset cancellation capacitor CDhp1And a second adjustable offset canceling capacitor CDhp2Is used to perform any adjustment actions.
Secondly, if the voltage V is judgedDSL_outIs less than 0.5VDD, the tunable offset cancellation capacitor C is not activatedDhpAny operation is performed; if the voltage V is judgedDSL_outAbsolute value over 0.5VDD, and voltage VDSL_outIs judged to control the adjustable offset eliminating capacitor CDhpOf (c) is used. When the voltage V isDSL_outWhen the first adjustable offset cancellation capacitor C is in positiveDhp1To ground, the second adjustable offset canceling capacitor CDhp2Is connected to a power supply; when the voltage V isDSL_outWhen the voltage is negative, the first adjustable offset eliminating capacitor CDhp1Connected to a power supply, the second adjustable offset canceling capacitor CDhp2To ground.
Wherein the first adjustable offset canceling capacitor CDhp1And said second tunable offset canceling capacitor CDhp2The tunable capacitor array is controlled by a switch, and has various specific implementation methods and forms, which are commonly used in the field of integrated circuits and are not described herein again, so that the tunable capacitor array is replaced by the tunable capacitor for description. Default first tunableOffset canceling capacitor CDhp1And said second tunable offset canceling capacitor CDhp2All are connected to the ground, and the adjustable offset cancellation capacitor C is only judged after the logic control module judges the output voltage of the integrator GDhpControl to determine the adjustable offset cancellation capacitor CDhpIs continuously connected with the ground or selectively connected with the power supply, and determines the adjustable offset cancellation capacitor CDhpThe value of the capacitance of (a) is changed or kept unchanged.
The two steps are completed after a plurality of periods after the chip is started, and then the logic control module does not output the control signal and adjust the capacitor.
Generally, the noise and poles of the integrator G equivalent to the input noise and system poles of the system can be expressed as equation (1).
Figure BDA0002063074050000091
Here, DSLnoise is output noise of the integrator G in the electrode offset canceling loop, and DSLpole is a unit gain frequency of the integrator G in the electrode offset canceling loop.
In this embodiment, to detect ECG signals from 0.05Hz to 250Hz, the system pole must be less than 0.05Hz, since the system pole is subject to
Figure BDA0002063074050000092
The effect is that the poles of the integrator must meet
Figure BDA0002063074050000093
Figure BDA0002063074050000094
Figure BDA0002063074050000095
The calculation of the value of (a) can be accomplished as follows: assuming a 50mV detuning of the electrodes and a 1V output amplitude value at the integrator G, then this is required
Figure BDA0002063074050000096
In order to meet the high signal amplification capability of the system, e.g. 100 times, i.e.
Figure BDA0002063074050000097
Based on the above relationship, we can obtain
Figure BDA0002063074050000098
For the
Figure BDA0002063074050000099
In other words, the pole of the electrode offset cancellation loop 4 integrator G must be designed at 0.01Hz, which greatly increases the design difficulty. According to theoretical analysis, the noise equivalent of integrator G is input to the system
Figure BDA00020630740500000910
That is, at this typical value the integrator G output noise is equivalent to the noise at the system input after its attenuation 1/20. However, for low power designs, the high output noise of integrator G, 1/20 times the attenuation factor, is not sufficient. The above pole and noise correspond to the system in numerical relationship as shown in equation (2):
Figure BDA00020630740500000911
in order to reduce the pole design pressure of the electrode offset cancellation loop 4 and the noise impact on the system, the offset cancellation capability is also kept constant, reducing ChpThe original 1/5 value is obtained, and a new proportional relation can be obtained. The capacitive coupling type chopping instrument amplifier containing the digital electrode offset elimination module 6 can achieve the effect.
The logic control module detects the output V of the integrator GDSL_outFurther controlling the adjustable offset cancellation capacitor CDhpAnd the first digital module chopping modulator CHDhpThe polarity of the input voltage generates a feedback current to eliminate the input electrode offset.
Figure BDA0002063074050000101
Due to original ChpThe attenuation is its value of 1/5, as shown in equation (2),
Figure BDA0002063074050000102
and the pole of the integrator G in the electrode offset cancellation loop 4 can be designed to be 0.05Hz when the pole is reduced to 1, namely the requirement of the system pole of 0.05Hz can be met. Therefore, the pole of the integrator G in the electrode offset elimination loop 4 is consistent with the pole of the system in size, and the design pressure is reduced; and the noise becomes 1/100 original, making the effect of integrator G noise on the system almost negligible. But at this time, the offset voltage elimination capability is reduced to 1/5, that is, the offset voltage elimination capability can only eliminate the electrode offset with the amplitude of 10mV at most, and in order to eliminate the electrode offset with the amplitude of 50mV, the digital electrode offset elimination module 6 in the invention eliminates the residual electrode offset with the amplitude of 40mV, so that the whole system can eliminate the offset with the amplitude of 50 mV. Thus, according to the analysis, CDhpThe ratio of the maximum adjustable range to the feedback capacitance is
Figure BDA0002063074050000103
From the above, the adjustable offset canceling capacitor C is provided with the digital electrode offset canceling module 6DhpElectrode offset elimination loop offset elimination capacitor C in original electrode offset elimination loop 4 is distributedhpThe 4/5 electrode is detuned so that the original ChpThe attenuation is its 1/5 value, so overall the total offset cancellation capacitance is unchanged, except that its original 1/5 is retained at the integrator G output in the original electrode offset cancellation loop, and its 4/5 is at the digital offset cancellation loop 6 output.
In summary, the input chopper circuit 1, the operational amplifier circuit 2, the pseudo-resistance bias circuit 3, the electrode offset cancellation loop 4 and the digital electrode offset cancellation module 6 are combined together, so that the original electrode offset cancellation loop 4 can adopt a smaller offset cancellation capacitor and also can keep the input offset cancellation capacity and the system pole position equivalent to those of a circuit system, the pole design pressure of an integrator G in the electrode offset cancellation loop 4 is weakened, and the smaller offset cancellation capacitor greatly attenuates the system equivalent input reference noise of the electrode offset cancellation loop 4, thereby improving the noise performance of the circuit.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (7)

1. A capacitively coupled chopper instrumentation amplifier comprising:
an input chopper circuit (1) for receiving an original input signal (V)in) Modulating the signal into an original high-frequency signal, and coupling the original high-frequency signal to an input end of an operational amplification circuit (2); the operational amplifier circuit (2) is used for amplifying a high-frequency input signal entering the operational amplifier circuit (2) and outputting an output signal (V)out)；
The pseudo resistance bias circuit (3) is connected with the input end of the operational amplification circuit (2) and provides input common mode bias voltage for the operational amplification circuit (2);
an electrode offset cancellation loop (4), the input end of which is connected with the output end of the operational amplification circuit (2), the output end of the electrode offset cancellation loop (4) is connected with the input end of the operational amplification circuit (2) and is used for canceling the original input signal (V)in) The electrode offset cancellation loop (4) comprises an integrator (G) for said output signal (V)out) Output voltage V after integrationDSL_out；
A negative feedback circuit (5) for providing negative feedback regulation for the operational amplification circuit (2), the input end of the negative feedback circuit and the operational amplification circuit (2)) The output end of the negative feedback circuit (5) is connected with the input end of the operational amplification circuit (2), and the negative feedback circuit (5) outputs a signal (V)out) Modulating the signal into a high-frequency signal, and feeding the high-frequency signal back to the input end of the operational amplification circuit (2) to be used as a high-frequency input signal of the operational amplification circuit (2);
the digital electrode offset cancellation module (6) is used for reducing the size of an offset cancellation capacitor in the electrode offset cancellation loop (4), the input end of the digital electrode offset cancellation module is connected with the output end of an integrator (G) of the electrode offset cancellation loop (4), and the output end of the digital electrode offset cancellation module (6) is connected with the operational amplifier input end of the operational amplification circuit (2);
the digital electrode offset cancellation module (6) comprises:
the input end of the logic control module is connected with the output end of the integrator (G) in the electrode offset cancellation loop (4);
first digital module chopping modulator (CH)Dhp) An input terminal of which is connected to an output terminal of said logic control module, said logic control module outputting a control signal to said first digital module chopping modulator (CH)Dhp)；
First tunable offset canceling capacitor (C)Dhp1) Having an input connected to said first digital block chopping modulator (CH)Dhp) Is connected to an output terminal of said first tunable offset cancellation capacitor (C)Dhp1) The output end is connected with the positive input end of the operational amplification circuit (2);
second tunable offset cancel capacitor (C)Dhp2) Having an input connected to said first digital block chopping modulator (CH)Dhp) Is connected to the other output terminal of the first tunable offset cancellation capacitor (C)Dhp2) The output end of the operational amplifier circuit is connected with the negative input end of the operational amplifier circuit (2);
the logic control module adjusts the first adjustable offset cancellation capacitance (C)Dhp1) And said second adjustable offset canceling capacitor (C)Dhp2) Also adjusts the first digital block chopping modulator (CH)Dhp) The input direct current offset voltage is eliminated according to the size of the capacitor and the polarity of the passing voltage.
2. The capacitively coupled chopper instrumentation amplifier of claim 1,
said first tunable offset canceling capacitor (C)Dhp1) And said second adjustable offset canceling capacitor (C)Dhp2) The initial state is a grounding state, and the integrator (G) outputs a voltage VDSL_outTo the logic control module, the logic control module judges the voltage VDSL_outWhether the absolute value of (a) exceeds an initially set constant value;
if the voltage V isDSL_outLess than said constant value, said logic control module does not apply said first adjustable offset cancellation capacitance (C)Dhp1) And said second adjustable offset canceling capacitor (C)Dhp2) Performing any adjustment actions;
if the voltage V isDSL_outWhen the constant value is exceeded, the logic control module judges the voltage VDSL_outTo control and adjust said first adjustable offset cancellation capacitance (C)Dhp1) And said second adjustable offset canceling capacitor (C)Dhp2) And its capacitance magnitude.
3. The capacitively coupled chopper instrumentation amplifier of claim 2,
when the voltage V isDSL_outTo be positive, the first adjustable offset canceling capacitor (C)Dhp1) To ground, the second adjustable offset canceling capacitor (C)Dhp2) Is connected to a power supply;
when the voltage V isDSL_outWhen negative, the first adjustable offset canceling capacitor (C)Dhp1) Connected to a power supply, said second adjustable offset canceling capacitor (C)Dhp2) To ground.
4. The capacitively coupled chopper instrumentation amplifier of claim 1, wherein the input chopper circuit (1) comprises:
input chopping modulator (CH)in) Said original input signal (V)in) Andsaid input chopping modulator (CH)in) Said input chopping modulator (CH)in) Outputting a high-frequency signal;
first input coupling capacitance (C)in1) Its input terminal and said input chopping modulator (CH)in) An output terminal connected to the first input coupling capacitor (C)in1) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
second input coupling capacitance (C)in2) Its input terminal and said input chopping modulator (CH)in) Another output terminal connected to the second input coupling capacitor (C)in2) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
the first input coupling capacitance (C)in1) And said second input coupling capacitance (C)in2) Chopping the input to a modulator (CH)in) The output high-frequency signals are respectively coupled to the negative input end and the positive input end of the operational amplification circuit (2).
5. The capacitively coupled chopper instrumentation amplifier of claim 1, wherein the operational amplifier circuit (2) comprises:
first stage operational amplifier (G)m1) The positive and negative input terminals of which are connected to the pseudo-resistance bias circuit (3), the first stage operational amplifier (G)m1) Output terminal and an operational amplifier circuit chopper modulator (CH)out) The input ends of the two-way valve are connected;
second stage operational amplifier (G)m2) With positive and negative input terminals and the chopping modulator (CH) of the operational amplifier circuitout) Is connected to the output of the second stage operational amplifier (G)m2) Output end outputs output signal (V)out)；
The second stage operational amplifier (G)m2) The positive and negative input terminals of the first transistor are respectively connected in parallel with a first Miller compensation capacitor (C)m1) And a second Miller compensation capacitor (C)m2)。
6. The capacitively coupled chopper instrumentation amplifier of claim 1, wherein the electrode offset cancellation loop (4) comprises:
the positive input end and the negative input end of the integrator (G) are connected with the output end of the operational amplification circuit (2);
the output end of the integrator (G) is connected with an electrode offset elimination loop chopped-wave modulator (CH)hp) An input, the integrator (G) couples the output signal (V)out) Output voltage V after integrationDSL_out；
First electrode offset cancellation loop offset cancellation capacitor (C)hp1) Loop chopping modulator (CH) with input terminal for canceling offset of said electrodeshp) An output terminal connected to the first electrode offset cancellation loop offset cancellation capacitor (C)hp1) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
second electrode offset cancellation loop offset cancellation capacitor (C)hp2) Loop chopping modulator (CH) with input terminal for canceling offset of said electrodeshp) The other output end is connected with the second electrode offset cancellation loop offset cancellation capacitor (C)hp2) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
said first electrode offset cancellation loop offset cancellation capacitor (C)hp1) And said second electrode offset cancellation loop offset cancellation capacitance (C)hp2) A chopping modulator (CH) for eliminating the electrode offset loophp) The output signals are respectively coupled to the negative input end and the positive input end of the operational amplification circuit (2).
7. The capacitively coupled chopper instrumentation amplifier of claim 1, wherein the negative feedback circuit (5) comprises:
negative feedback circuit chopping modulator (CH)fb) Said output signal (V)out) And said negative feedback circuit chopping modulator (CH)fb) Is connected to the input of the output signal (V)out) Modulating the signal into a high-frequency signal and outputting the signal;
first negative feedback coupling capacitor (C)fb1) The input end of which is connected to the negative feedback circuit chopping modulator (CH)fb) An output terminal is connected, theFirst negative feedback coupling capacitor (C)fb1) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
second negative feedback coupling capacitor (C)fb2) The input end of which is connected to the negative feedback circuit chopping modulator (CH)fb) The other output terminal is connected with the second negative feedback coupling capacitor (C)fb2) The output end of the operational amplifier circuit (2) is connected with the input end of the operational amplifier circuit;
the first negative feedback coupling capacitor (C)fb1) And said second negative feedback coupling capacitance (C)fb2) And respectively coupling the high-frequency signals to a positive input end and a negative input end of the operational amplification circuit (2).
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