A T-type resistor network transimpedance amplifier circuit with automatic voltage compensation

Abstract

The present invention discloses a voltage automatic compensation T-type resistor network transimpedance amplifier circuit, the amplifier circuit includes: a transimpedance input circuit, a voltage follower circuit, a voltage gain circuit, and a compensation voltage adjustment network circuit. Compared with the prior art, the present invention adopts a T-type resistor network to realize the ultra-large resistance feedback resistor in the transimpedance amplifier, abandoning the expensive, high installation and maintenance cost and large resistance resistor with large error; the voltage automatic compensation circuit is adopted to overcome the large offset voltage error introduced by the T-type resistor network, and the error generated by the bias current passing through the large feedback resistor is also eliminated, so that one network solves two problems; the circuit is completely completed by hardware, compared with collecting the output voltage and then adjusting the offset voltage by software, the circuit structure is simpler, the zero adjustment is faster, the error is smaller, and the accuracy of weak current measurement is greatly improved.

Description

Technical Field

[0001] The invention relates to the field of general weak signal measurement electronic technology, and in particular to a voltage automatic compensation T-type resistor network transimpedance amplifier circuit. Background Art

[0002] In the field of general weak signal measurement electronic technology, current measurement of fA to pA usually uses an inverting amplifier circuit to convert current into voltage. Since the current is very small, the feedback resistor needs to reach the T-ohm level. Such a large resistor mainly brings two problems. On the one hand, the bias current of the operational amplifier forms a voltage drop on the feedback resistor, which causes deviation in the output voltage. On the other hand, many resistors of the T-ohm level require vacuum tube packaging, which is expensive and has high requirements for use. The T-type resistor network uses low-resistance resistors to achieve large feedback resistors, which can be used to replace a single resistor. However, compared with a single large resistor, the offset voltage in the T-type resistor network structure has a huge impact, which often causes the measurement circuit to directly enter the saturation state, seriously affecting the accuracy of the measurement results. Summary of the invention

[0003] The present invention aims to provide a T-type resistor network transimpedance amplifier circuit with automatic voltage compensation, so that the circuit can automatically adjust the compensation voltage at the in-phase end according to the output voltage to achieve precise zero adjustment, so as to achieve the technical effect of weak current measurement sensitivity and dynamic range requirements.

[0004] The technical solution of the present invention is achieved in this way:

[0005] A voltage automatic compensation T-type resistor network transimpedance amplifier circuit, the amplifier circuit comprising:

[0006] A transimpedance input circuit, the transimpedance input circuit comprising a low bias current operational amplifier A1 and a T-type resistor network, the T-type resistor network forming a feedback resistor connected between the inverting input terminal and the output of the low bias current operational amplifier, and the non-inverting input terminal of the low bias current operational amplifier A1 connected to a voltage-controlled current source through a resistor R4;

[0007] A voltage follower circuit, the voltage follower circuit comprising an operational amplifier A2, the operational amplifier A2 having a common-phase input terminal connected to an output terminal of a low bias current operational amplifier A1, and the output terminal of the operational amplifier A2 connected to a voltage gain circuit via a resistor R1;

[0008] A voltage gain circuit, wherein the voltage gain circuit comprises an operational amplifier A3, wherein the inverting input terminal of the operational amplifier A3 is connected to a resistor R1, and a resistor R2 and a low-pass filter capacitor C1 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier A3, and the output terminal of the operational amplifier A3 is connected to a compensation voltage regulation network circuit via a switch K;

[0009] A compensation voltage regulation network circuit, the compensation voltage regulation network circuit includes a resistor R3, an inverting integration circuit and a voltage-controlled current source, the inverting integration circuit includes an operational amplifier A4 and an integration capacitor C2, wherein one end of the integration capacitor C2 is connected to the output end of the operational amplifier A4, and the other end is connected to the inverting input end of the operational amplifier A4, one end of the resistor R3 is connected to the switch K, and the other end is connected to the inverting input end of the operational amplifier A4, and the output end of the operational amplifier A4 is also connected to the voltage-controlled current source;

[0010] The non-inverting input terminal of the operational amplifier A3 and the non-inverting input terminal of the operational amplifier A4 are both grounded.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The voltage-automatic-compensated T-type resistor network transimpedance amplifier circuit of the present invention adopts a T-type resistor network to realize an ultra-large-resistance feedback resistor in a transimpedance amplifier, thereby eliminating large-resistance resistors that are expensive, have high installation and maintenance costs, and have large errors; the voltage-automatic compensation circuit is adopted to overcome the large offset voltage error introduced by the T-type resistor network, and the error generated by the bias current passing through the large feedback resistor is also eliminated, so that one network solves two problems; the circuit is completely completed by hardware, and compared with collecting the output voltage and then adjusting the offset voltage by software, the circuit structure is simpler, the zero adjustment is faster, the error is smaller, and the accuracy of weak current measurement is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of a T-type resistor network transimpedance amplifier circuit for automatic voltage compensation according to the present invention.

[0014] In the figure: a transimpedance input circuit 100, a voltage follower circuit 200, a voltage gain circuit 300, and a compensation voltage regulation network circuit 400. DETAILED DESCRIPTION

[0015] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0016] like Figure 1 As shown, a voltage automatic compensation T-type resistor network transimpedance amplifier circuit of the present invention comprises:

[0017] A transimpedance input circuit 100, wherein the transimpedance input circuit 100 comprises a low bias current operational amplifier A1 and a T-type resistor network, wherein a typical bias current value is from several fA to several tens of fA, wherein the T-type resistor network constitutes a feedback resistor connected between an inverting input terminal and an output of the low bias current operational amplifier, and a non-inverting input terminal of the low bias current operational amplifier A1 is connected to a voltage-controlled current source through a resistor R4;

[0018] A voltage follower circuit 200, wherein the voltage follower circuit 200 comprises an operational amplifier A2, wherein a non-inverting input terminal of the operational amplifier A2 is connected to an output terminal of a low bias current operational amplifier A1, and an output terminal of the operational amplifier A2 is connected to a voltage gain circuit via a resistor R1;

[0019] A voltage gain circuit 300, wherein the voltage gain circuit 300 comprises an operational amplifier A3, wherein the inverting input terminal of the operational amplifier A3 is connected to a resistor R1, and a resistor R2 and a low-pass filter capacitor C1 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier A3, and the output terminal of the operational amplifier A3 is connected to a compensation voltage regulation network circuit via a switch K;

[0020] A compensation voltage regulation network circuit 400, wherein the compensation voltage regulation network circuit 400 includes a resistor R3, an inverting integration circuit and a voltage-controlled current source, wherein the inverting integration circuit includes an operational amplifier A4 and an integration capacitor C2, wherein one end of the integration capacitor C2 is connected to the output end of the operational amplifier A4, and the other end is connected to the inverting input end of the operational amplifier A4, one end of the resistor R3 is connected to the switch K, and the other end is connected to the inverting input end of the operational amplifier A4, and the output end of the operational amplifier A4 is also connected to the voltage-controlled current source;

[0021] The non-inverting input terminal of the operational amplifier A3 and the non-inverting input terminal of the operational amplifier A4 are both grounded.

[0022] The present invention is further described as follows based on the above circuit structure:

[0023] Among them, the low bias current operational amplifier A1 is referred to as A1, the operational amplifier A2 is referred to as A2, the operational amplifier A3 is referred to as A3, and the operational amplifier A4 is referred to as A4.

[0024] Ra, Rb and Rc form a T-type resistor network, and the output voltage V1 of A1 can be expressed as:

[0025]

[0026]

[0027] Among them, V′ os is the offset voltage of operational amplifier A1 itself, I b is the bias current of A1 and I is the input current.

[0028] In the circuit zeroing mode, there is no current input to the circuit input, and switch K is closed. The voltage V os There are several situations:

[0029] when

[0030] V os >Ib R a -V′ os

[0031] V3 is positive, and the current flows to the capacitor C2 through the resistor R3. The Vc potential increases in the reverse direction, the output current of the voltage-controlled current source increases in the reverse direction, and Vos decreases, thereby reducing V3.

[0032] Likewise, when

[0033] V os <I b R a -V' os

[0034] V3 is negative, and the current flows out of the capacitor C2 through the resistor R3. The Vc potential decreases in the reverse direction, the output current of the voltage-controlled current source decreases in the reverse direction, and Vos increases, thereby increasing V3.

[0035] when

[0036] V os =I b R a -V' os

[0037] Then the output voltage V3 of A3 is 0, no current flows through the resistor R3, the voltage on the capacitor C2 remains unchanged, and V3 remains unchanged at 0.

[0038] In the zero adjustment mode, V3 maintains 0 potential in a steady state, so zero adjustment can be achieved.

[0039] When the potential of V3 is 0, the voltage-controlled current source has a fixed output and is disconnected from A4. At the same time, switch K is grounded, zero adjustment is completed, and the circuit enters the measurement mode. The output potential V3 of A3 is proportional to the input current.

[0040] Based on the circuit structure and working principle of the present invention, it can be seen that a T-type resistor network is used to implement an ultra-large resistance feedback resistor in a transimpedance amplifier, thereby abandoning a large resistance resistor that is expensive, has high installation and maintenance costs, and has large errors; an automatic voltage compensation circuit is used to overcome the large offset voltage error introduced by the T-type resistor network, and at the same time, the error caused by the bias current passing through the large feedback resistor is also eliminated, so that one network solves two problems; the circuit is completely completed by hardware, and compared with collecting the output voltage and then adjusting the offset voltage by software, the circuit structure is simpler, the zero adjustment is faster, the error is smaller, and the accuracy of weak current measurement is greatly improved.

Claims

1. A T-type resistor network transimpedance amplifier circuit with automatic voltage compensation, characterized in that: The amplifying circuit comprises: A transimpedance input circuit, the transimpedance input circuit comprising a low bias current operational amplifier A1 and a T-type resistor network, the T-type resistor network forming a feedback resistor connected between the inverting input terminal and the output of the low bias current operational amplifier, and the non-inverting input terminal of the low bias current operational amplifier A1 connected to a voltage-controlled current source through a resistor R4; A voltage follower circuit, the voltage follower circuit comprising an operational amplifier A2, the operational amplifier A2 having a common-phase input terminal connected to an output terminal of a low bias current operational amplifier A1, and the output terminal of the operational amplifier A2 connected to a voltage gain circuit via a resistor R1; A voltage gain circuit, wherein the voltage gain circuit comprises an operational amplifier A3, wherein the inverting input terminal of the operational amplifier A3 is connected to a resistor R1, and a resistor R2 and a low-pass filter capacitor C1 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier A3, and the output terminal of the operational amplifier A3 is connected to a compensation voltage regulation network circuit via a switch K; A compensation voltage regulation network circuit, the compensation voltage regulation network circuit includes a resistor R3, an inverting integration circuit and a voltage-controlled current source, the inverting integration circuit includes an operational amplifier A4 and an integration capacitor C2, wherein one end of the integration capacitor C2 is connected to the output end of the operational amplifier A4, and the other end is connected to the inverting input end of the operational amplifier A4, one end of the resistor R3 is connected to the switch K, and the other end is connected to the inverting input end of the operational amplifier A4, and the output end of the operational amplifier A4 is also connected to the voltage-controlled current source; The non-inverting input terminal of the operational amplifier A3 and the non-inverting input terminal of the operational amplifier A4 are both grounded. Among them, the low bias current operational amplifier A1 is referred to as A1, the operational amplifier A2 is referred to as A2, the operational amplifier A3 is referred to as A3, and the operational amplifier A4 is referred to as A4. Ra, Rb and Rc form a T-type resistor network, and the output voltage V1 of A1 can be expressed as: Among them, V′ os is the offset voltage of operational amplifier A1 itself, I b is the bias current of A1, I is the input current, In the circuit zeroing mode, there is no current input to the circuit input, and the switch K is closed. The voltage V os There are several situations: when V os >I b R a -V′ os , V3 is positive, and the current flows to the capacitor C2 through the resistor R3. The Vc potential increases in the reverse direction, the output current of the voltage-controlled current source increases in the reverse direction, and Vos decreases, thereby reducing V3. Likewise, when V os <I b R a -V′ os , V3 is negative, and the current flows out of the capacitor C2 through the resistor R3. The Vc potential decreases in the reverse direction, the output current of the voltage-controlled current source decreases in the reverse direction, and Vos increases, thereby increasing V3. when V os =I b R a -V′ os , Then the output voltage V3 of A3 is 0, no current flows through the resistor R3, the voltage on the capacitor C2 remains unchanged, and V3 remains unchanged at 0. In zero adjustment mode, V3 maintains 0 potential in a steady state, so zero adjustment can be achieved. When the potential of V3 is 0, the voltage-controlled current source has a fixed output and is disconnected from A4. At the same time, switch K is grounded, zero adjustment is completed, and the circuit enters the measurement mode. The output potential V3 of A3 is proportional to the input current.

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