A transimpedance stage circuit and a micro-current excitation and detection circuit using the same

Abstract

The present invention discloses a transimpedance stage circuit, which includes a transimpedance stage, an inverting amplifier, and a non-inverting amplifier; the transimpedance stage is used to convert a micro-current signal generated under an excitation voltage into a voltage signal; the inverting amplifier is used to amplify and invert the voltage signal output by the transimpedance stage, and the output voltage is denoted as V outP ; the non-inverting amplifier is used to amplify and output the voltage signal output by the transimpedance stage in the same phase, and the output voltage is denoted as V outN ; the present invention also discloses a micro-current excitation and detection circuit, which includes a transimpedance stage circuit, a filtering circuit, and an output driving circuit; the transimpedance stage circuit is used to convert a micro-current signal into a voltage signal; the filtering circuit is used to filter out the noise in the voltage signal output by the transimpedance stage circuit; the output driving circuit is used to enhance the voltage signal output by the filtering circuit for use by the subsequent circuit; the present invention has the advantages of high conversion gain, low noise, large dynamic range, and the output signal being independent of the magnitude of the input excitation voltage signal, etc.

Description

Technical Field

[0001] The present invention belongs to the fields of analog integrated circuits and biomedical engineering, and particularly relates to a transimpedance stage circuit and a micro-current excitation and detection circuit applying the circuit. Background Art

[0002] With the rapid development of integrated circuits, the demand for micro-current excitation and detection has become increasingly urgent. For example, in the field of biomedical engineering, biological cells are stimulated with voltage signals, and the micro-currents generated by the biological cells are detected, and then the cell characteristics are studied.

[0003] Since the current signals generated by biological cells are very weak, as low as the nanoampere (10 -9 ampere) level. In order to detect micro-currents, some solutions adopt the current amplification scheme. Usually, current amplification is achieved through the current mirror method. For example, a current amplifier is used. However, when a conventional current amplifier performs such weak current mirror amplification, the mirror error is large. Moreover, the traditional current amplifier has a large noise, which will seriously deteriorate the signal-to-noise ratio of the detection. There are also some solutions that use a transimpedance amplifier to convert the micro-current signal into a voltage signal. However, the transimpedance amplifier either cannot superimpose the excitation voltage signal at the same time, or there is an excitation voltage signal component in the final output, and the excitation voltage signal component is usually not desired in the micro-current detection system. The reason is that the voltage signal used to stimulate biological cells will vary with the type of cells, and this varying excitation voltage is not the signal to be detected and should not appear in the final output, and it is difficult for the traditional current detection circuit to eliminate this excitation signal.

[0004] Since different detection systems have different requirements for the detection current accuracy and detection range, it is often difficult for general circuits to achieve both a large detection range and high precision at the same time.

[0005] Therefore, the micro-current excitation and detection circuit needs to have characteristics such as high conversion gain, low noise, large dynamic range, and the output signal being independent of the magnitude of the input excitation voltage signal. Summary of the Invention

[0006] Object of the Invention: To solve the problems existing in the existing micro-current excitation and detection circuits, such as large noise, small detection range, low detection accuracy, and the existence of excitation voltage signal components in the output signal, the present invention proposes a transimpedance stage circuit and a micro-current excitation and detection circuit applying the circuit.

[0007] Technical solution: A transimpedance stage circuit includes a transimpedance stage, an inverting amplifier, and a non-inverting amplifier; the transimpedance stage is used to convert a micro-current signal generated under an excitation voltage into a voltage signal; it is composed of a first operational amplifier and a first resistor, the excitation voltage is input to the positive input terminal of the first operational amplifier, the micro-current generated under the excitation voltage is input to the negative input terminal of the first operational amplifier, and the first resistor serves as the negative feedback of the first operational amplifier; the inverting amplifier is used to amplify and invert the voltage signal output by the transimpedance stage, and the output voltage is denoted as V outP ; it is composed of a second operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor; the output signal of the first operational amplifier is connected to the negative input terminal of the second operational amplifier through the sixth resistor; the excitation voltage is connected to the positive input terminal of the second operational amplifier through the eighth resistor; the common-mode voltage is connected to the positive input terminal of the second operational amplifier through the ninth resistor; the seventh resistor serves as the negative feedback of the second operational amplifier; the non-inverting amplifier is used to amplify and output the voltage signal output by the transimpedance stage in the same phase, and the output voltage is denoted as V outN ; it is composed of a third operational amplifier, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; the output signal of the first operational amplifier is input to the positive input terminal of the third operational amplifier through the fourth resistor; the common-mode voltage is connected to the positive input terminal of the third operational amplifier through the fifth resistor; the excitation voltage is connected to the negative input terminal of the third operational amplifier through the second resistor; the third resistor serves as the negative feedback of the third operational amplifier;

[0008] The transfer function of the transimpedance stage circuit is expressed as:

[0009]

[0010] In the formula, R f is the resistance value of the first resistor; the resistance values of the third resistor, the fifth resistor, the seventh resistor, and the ninth resistor are the same, and are all denoted as R; the resistance values of the second resistor, the fourth resistor, the sixth resistor, and the eighth resistor are the same, and are all denoted as R';

[0011] By adjusting R f and the ratio of R / R', the gain of the transimpedance stage circuit is changed.

[0012] The present invention also discloses a micro-current excitation and detection circuit, including a transimpedance stage circuit, a filtering circuit, and an output driving circuit; the transimpedance stage circuit is used to convert a micro-current signal into a voltage signal; this transimpedance stage circuit is the transimpedance stage circuit disclosed above; the filtering circuit is used to filter out the noise in the voltage signal output by the transimpedance stage circuit; the output driving circuit is used to enhance the voltage signal output by the filtering circuit for use by the subsequent circuit.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention solves the problem of difficult micro-current detection;

[0015] 2. The excitation voltage of the present invention can be adjusted within a wide range, and is suitable for the stimulation of various different cells and the detection of their micro-currents, but is not limited to this application;

[0016] 3. The output voltage of the present invention does not contain an excitation voltage component;

[0017] 4. The present invention has a high signal-to-noise ratio and strong circuit driving ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic block diagram of the micro-current excitation and detection circuit of the present invention;

[0019] Figure 2 is a circuit diagram of the transimpedance stage of the present invention;

[0020] Figure 3 is a simulation result of the relationship between the typical output voltage and the detected current of the present invention;

[0021] Figure 4 is a typical first-order RC filter circuit;

[0022] Figure 5 is a typical source follower output driving circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

[0024] As Figure 1 shown, the micro-current excitation and detection circuit of the present invention mainly consists of a transimpedance stage circuit 100, a filter circuit 200, and an output driving circuit 300. Among them, the transimpedance stage circuit 100 is used to convert the micro-current signal into a voltage signal; the filter circuit 200 is used to filter out high-frequency noise; the output driving circuit 300 is used to enhance the driving ability of the signal for use by the subsequent circuit, and the subsequent circuit includes but is not limited to an analog-to-digital converter (ADC) or a driving amplifier, etc. The circuit of the present invention can detect currents as low as the nanoampere (10 -9 ampere) level and can achieve a signal-to-noise ratio of up to 30 dB. At the same time, the final output signal of the present invention does not contain an excitation voltage signal component.

[0025] The core module of the micro-current excitation and detection circuit is the transimpedance stage circuit 100. The transimpedance stage circuit of the present invention is as Figure 2As shown, it mainly includes a first operational amplifier OPA1, a first resistor Rf, a second operational amplifier OPA2, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a third operational amplifier OPA3, a second resistor R2, a third resistor R3, a fourth resistor R4, and a fifth resistor R5.

[0026] Among them, a transimpedance stage 101 is formed by the first operational amplifier OPA1 and the first resistor Rf; the circuit connection relationship is: the excitation voltage Vscan is input to the positive input terminal of the first operational amplifier OPA1, and the micro-current I in generated under the excitation voltage is input to the negative input terminal of the first operational amplifier OPA1. One end of the first resistor Rf is connected to the negative input terminal of the first operational amplifier OPA1, and the other end is connected to the output terminal of the first operational amplifier OPA1. The first resistor Rf serves as the negative feedback of the first operational amplifier OPA1.

[0027] Among them, an inverting amplifier 102 is formed by the second operational amplifier OPA2, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, and the ninth resistor R9; the circuit connection relationship is: one end of the sixth resistor R6 is connected to the output terminal of the first operational amplifier OPA1, and the other end is connected to the negative input terminal of the second operational amplifier OPA2. And the other end of the sixth resistor R6 is connected to one end of the seventh resistor R7, and the other end of the seventh resistor R7 is connected to the output terminal of the second operational amplifier OPA2. The seventh resistor R7 serves as the negative feedback of the second operational amplifier OPA2. The excitation voltage Vscan is connected to the positive input terminal of the second operational amplifier OPA2 through the eighth resistor R8, and the common-mode voltage Vcm is connected to the positive input terminal of the second operational amplifier OPA2 through the ninth resistor R9. The output voltage of the second operational amplifier OPA2 is denoted as V outP .

[0028] Among them, a non-inverting amplifier 103 is formed by the third operational amplifier OPA3, the second resistor R2, the third resistor R3, the fourth resistor R4, and the fifth resistor R5; the circuit connection relationship is: the output signal of the first operational amplifier OPA1 is input to the positive input terminal of the third operational amplifier OPA3 through the fourth resistor R4, the common-mode voltage Vcm is connected to the positive input terminal of the third operational amplifier OPA3 through the second resistor, the excitation voltage Vscan is connected to the negative input terminal of the third operational amplifier OPA3 through the second resistor R2. One end of the third resistor R3 is connected to the negative input terminal of the third operational amplifier OPA3, and the other end is connected to the output terminal of the third operational amplifier OPA3. The third resistor R3 serves as the negative feedback of the third operational amplifier OPA3. The output voltage of the third operational amplifier OPA3 is denoted as V outN .

[0029] The micro-current I generated under the excitation voltage inAfter flowing through the transimpedance stage 101, the inverting amplifier 102, and the non-inverting amplifier 103, a differential output voltage is obtained: V outP and V outN .

[0030] The transfer function of the transimpedance stage circuit is as follows:

[0031]

[0032] In the formula, R f is the resistance value of the first resistor; the resistance values of the third resistor R3, the fifth resistor R5, the seventh resistor R7, and the ninth resistor R9 are the same, all denoted as R; the resistance values of the second resistor R2, the fourth resistor R4, the sixth resistor R6, and the eighth resistor R8 are the same, all denoted as R'.

[0033] Figure 3 The typical simulation results of the present invention are given. As can be seen from the figure, within the current input range of ±200 nA, whether it is the positive terminal output V outP , the negative terminal output V outN , or the final output Vo, all show a first-order linear relationship with the input current.

[0034] It can be seen from the above formula that by adjusting R f and the ratio of R / R', the gain of the transimpedance stage can be changed. Moreover, it can be seen from the transfer function that the output V o of the transimpedance stage is independent of the excitation voltage Vscan. Because the common-mode terminals of the non-inverting amplifier and the inverting amplifier are also applied with the excitation voltage Vscan, this circuit cancels out the excitation voltage Vscan component output by the transimpedance stage 101 at the input end, so the excitation voltage Vscan will not appear at the final output end.

[0035] The first resistor Rf, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, and the ninth resistor R9 can maintain a fixed resistance value or can be variable resistors.

[0036] By setting the resistance value of the first resistor Rf to a relatively large value, setting the resistance values of the third resistor R3, the fifth resistor R5, the seventh resistor R7, and the ninth resistor R9 to relatively large values, and setting the resistance values of the second resistor R2, the fourth resistor R4, the sixth resistor R6, and the eighth resistor R8 to relatively small values, small currents with high precision can be detected, such as the current of DNA base pairing during biological DNA synthesis sequencing, and the detection of single or several electrode currents, etc.

[0037] By setting the resistance value of the first resistor Rf to a relatively small value, setting the resistance values of the third resistor R3, the fifth resistor R5, the seventh resistor R7, and the ninth resistor R9 to relatively small values, and setting the resistance values of the second resistor R2, the fourth resistor R4, the sixth resistor R6, and the eighth resistor R8 to relatively large values, high-precision large currents can be detected, such as the current in the chronoamperometric measurement of the DNA molecule concentration in a solution, and the current detection when thousands of electrodes are simultaneously used, and other such situations.

[0038] The filtering circuit 200 of the present invention can be a first-order RC filtering circuit, or other higher-order filtering circuits. Filtering circuits of this kind or other equivalent circuits for filtering out noise are all within the protection scope of the present invention. Figure 4 A typical first-order RC filtering circuit is given.

[0039] The output driving circuit 300 of the present invention can provide a relatively strong driving ability. Since the filtering circuit needs to achieve good filtering characteristics, the resistance values of the resistors in the filtering circuit will be very large, which limits the driving ability of the driving circuit. Therefore, an additional stage of driving is required to improve the driving ability of the current detection circuit. The driving circuit can be a simple source / emitter follower, or a unity-gain buffer or a buffer with gain based on an operational amplifier. The above buffer structures are all within the protection scope of this patent. Figure 5 A circuit diagram of an output driving circuit using a source follower with a PMOS transistor as the core device is given.

Claims

1. A transimpedance stage circuit, characterized in that: It includes a transimpedance stage, an inverting amplifier, and a non-inverting amplifier; The transimpedance stage is used to convert the micro-current signal generated under the excitation voltage into a voltage signal; it is composed of a first operational amplifier and a first resistor. The excitation voltage is input to the positive input terminal of the first operational amplifier, and the micro-current generated under the excitation voltage is input to the negative input terminal of the first operational amplifier. The first resistor serves as the negative feedback of the first operational amplifier; The inverting amplifier is used to amplify and invert the voltage signal output by the transimpedance stage, and the output voltage is denoted as V outP ; it is composed of a second operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor; the output signal of the first operational amplifier is connected to the negative input terminal of the second operational amplifier through the sixth resistor; the excitation voltage is connected to the positive input terminal of the second operational amplifier through the eighth resistor; the common-mode voltage is connected to the positive input terminal of the second operational amplifier through the ninth resistor; the seventh resistor serves as the negative feedback of the second operational amplifier; The in-phase amplifier is used to amplify the voltage signal output by the transimpedance stage and output it in phase. The output voltage is denoted as V outN ; It is composed of a third operational amplifier, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; the output signal of the first operational amplifier is input to the positive input terminal of the third operational amplifier through the fourth resistor; the common-mode voltage is connected to the positive input terminal of the third operational amplifier through the fifth resistor; the excitation voltage is connected to the negative input terminal of the third operational amplifier through the second resistor; the third resistor serves as the negative feedback of the third operational amplifier; The transfer function of the transimpedance stage circuit is expressed as: wherein, R f is the resistance value of the first resistor; The resistance values of the third resistor, the fifth resistor, the seventh resistor, and the ninth resistor are the same, all denoted as R; the resistance values of the second resistor, the fourth resistor, the sixth resistor, and the eighth resistor are the same, all denoted as R′, and V o represents the output of the transimpedance stage circuit; By adjusting R f and the ratio of R / R′, the gain of the transimpedance stage circuit is changed.

2. The transimpedance stage circuit according to claim 1, characterized in that: The resistance values of the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor, the eighth resistor, and the ninth resistor are fixed resistance values.

3. The transimpedance stage circuit according to claim 1, characterized in that: The first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor, the eighth resistor, and the ninth resistor are all variable resistors.

4. A microcurrent excitation and detection circuit, characterized in that: It includes a transimpedance stage circuit, a filtering circuit, and an output driving circuit; The transimpedance stage circuit is used to convert the micro-current signal into a voltage signal; this transimpedance stage circuit is a transimpedance stage circuit described in any one of claims 1 to 3; The filtering circuit is used to filter out the noise in the voltage signal output by the transimpedance stage circuit; The output driving circuit is used to enhance the voltage signal output by the filtering circuit for use by the subsequent circuit.

5. The microcurrent excitation and detection circuit according to claim 4, characterized in that: The filtering circuit is a first-order RC filtering circuit.

6. The microcurrent excitation and detection circuit according to claim 4, characterized in that: The filtering circuit is a high-order filtering circuit.

7. The microcurrent excitation and detection circuit according to claim 4, characterized in that: The output driving circuit is a source or emitter follower circuit.

8. The microcurrent excitation and detection circuit according to claim 4, characterized in that: The output driving circuit is an op-amp-based unity-gain buffer circuit.

9. The microcurrent excitation and detection circuit according to claim 4, characterized in that: The output driving circuit is a buffer circuit with gain.

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