阅读说明：本技术 一种电化学检测用途微弱信号采样电路 (Weak signal sampling circuit for electrochemical detection ) 是由 余箫 胡佳薇 何佳艳 文薏凯 傅力 朱蕲 陆潇晓 于 2020-06-10 设计创作，主要内容包括：本发明公开一种电化学检测用途微弱信号采样电路。本发明在外部工作电极电路接口W无电流输入时,场效应管Q1处于静态,内阻较小；当接口W有电流输入时,场效应管栅极G与源极S极加上正向电压,由P沟道结型场效应管的特性可知此时内阻非常大,漏源极电流基本为0,对工作电极电路输入信号没影响,微弱电流信号直接经过放大器OPA1放大。信号经过OPA1后再经过二级放大器OPA2放大达到理想的电压信号,总的放大倍数为两级放大倍数的乘积。(The invention discloses a weak signal sampling circuit for electrochemical detection. According to the invention, when no current is input into the external working electrode circuit interface W, the field effect transistor Q1 is in a static state, and the internal resistance is small; when current is input into the interface W, forward voltage is applied to the grid G and the source S of the field effect transistor, the internal resistance is very high at the moment according to the characteristic of the P-channel junction type field effect transistor, the drain-source current is basically 0, the input signal of the working electrode circuit is not influenced, and the weak current signal is directly amplified through the amplifier OPA 1. The signal is amplified by a two-stage amplifier OPA2 after passing through an OPA1 to reach an ideal voltage signal, and the total amplification factor is the product of two-stage amplification factors.)

1. A weak signal sampling circuit for electrochemical detection is characterized by comprising a connecting port W with an external working electrode circuit, a connecting port Ref with an external reference electrode circuit, a field effect tube Q1, an amplifier OPA1-OPA3, resistors R1-R6 and a capacitor C2; the connection port W is connected with the source S of the field effect transistor Q1, the negative input end of the amplifier OPA1 and one end of the resistor R3, and the interface Ref is connected with the drain D of the field effect transistor Q1, the positive input end of the amplifier OPA1, the negative input end of the amplifier OPA3 and the output end of the amplifier OPA 3; the base electrode of the field effect transistor Q1 is connected with an external control end; the positive input end of the amplifier OPA3 is connected with one end of the resistor R1 and one end of the resistor R2; the output end of the amplifier OPA1 is connected with one end of the resistor R3 and the positive input end of the amplifier OPA 2; the negative input end of the amplifier OPA2 is connected with one end of the resistor R4 and one end of the resistor R5; the output end of the amplifier OPA2 is connected with the other end of the resistor R5, one end of the capacitor C2 and one end of the resistor R6 to serve as the output end; the other end of the resistor R1 is connected with VDD, and the other end of the resistor R2, the other end of the resistor R6 and the other end of the capacitor C2 are grounded; the power supply terminals VDD of the amplifier OPA1, the amplifier OPA2, and the amplifier OPA3 are grounded.

2. The weak signal sampling circuit for electrochemical detection as claimed in claim 1, wherein said field effect transistor Q1 is a P-channel junction field effect transistor.

Technical Field

The invention belongs to the technical field of analog circuits, relates to a weak signal sampling circuit for electrochemical detection, and particularly relates to a front-end analog sensing circuit for an electrochemical workstation.

Background

With the rapid development of modern society science and technology, people have higher and higher requirements on the precision of electrochemical analytical instruments, and the instrument products cannot acquire weak analog signals in real time by using a sensing circuit. In a modern high-precision electrochemical workstation, analog quantity acquired by a sensing circuit is very weak, and the analog quantity can be transmitted to a microprocessor for logic processing and feedback to a user only by further carrying out amplification, filtering and other processing through a sensing circuit interface circuit. However, the weak signal current generated by the electrochemical reaction is in milliampere (mA), microampere (uA) and nanoamp (nA), and the current signal is amplified for further processing.

In order to detect weak signals, a current signal is converted into a voltage signal, and then the voltage signal is amplified. Although the voltage signal is easy to amplify, the voltage signal is easily interfered by the conversion resistor and the outside. In order to increase the amplification factor, the resistance of the feedback resistor needs to be increased. The larger the resistance is, the larger the noise is, and when the feedback resistance is too large, the circuit can generate self-excitation, and signals are easily interfered, so that the design difficulty of the circuit is increased.

Disclosure of Invention

The invention aims to provide a weak signal sampling circuit for electrochemical detection aiming at the defects of the prior art, and the weak current signal is prevented from being influenced by the precision and the temperature of resistance during I/V conversion.

In order to solve the above-mentioned technical problem, the present invention provides a weak signal sampling circuit for electrochemical detection, comprising: the circuit comprises a connecting port W with an external working electrode circuit, a connecting port Ref with an external reference electrode circuit, a field effect tube Q1, an amplifier OPA1-OPA3, resistors R1-R6 and a capacitor C2; the connector W is connected with the source S of the field-effect transistor Q1, the negative input end of the amplifier OPA1 and one end of the resistor R3, and the connector Ref is connected with the drain D of the field-effect transistor Q1, the positive input end of the amplifier OPA1, the negative input end of the amplifier OPA3 and the output end of the amplifier OPA 3; the grid of the field effect transistor Q1 is connected with an external control end; the positive input end of the amplifier OPA3 is connected with one end of the resistor R1 and one end of the resistor R2; the output end of the amplifier OPA1 is connected with one end of the resistor R3 and the positive input end of the amplifier OPA 2; the negative input end of the amplifier OPA2 is connected with one end of the resistor R4 and one end of the resistor R5; the output end of the amplifier OPA2 is connected with the other end of the resistor R5, one end of the capacitor C2 and one end of the resistor R6 to serve as the output end; the other end of the resistor R1 is connected with VDD, and the other end of the resistor R2, the other end of the resistor R6 and the other end of the capacitor C2 are grounded; the power supply terminals VDD of the amplifier OPA1, the amplifier OPA2 and the amplifier OPA3 are connected, and the grounding terminal is grounded;

preferably, the field effect transistor Q1 is a P-channel junction field effect transistor.

The invention has the beneficial effects that: the invention directly amplifies current signals, reduces I/V conversion, avoids the influence of the precision and temperature of the resistor during I/V conversion, and simultaneously, the circuit adopts two-stage amplification, and the amplification factor of each stage is relatively reduced, thus avoiding the amplification of interference signals by the preamplifier and reducing the noise interference of the amplifier caused by overlarge feedback resistor.

Drawings

Fig. 1 is a circuit diagram of a weak signal sampling circuit for electrochemical detection.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Fig. 1 is a weak signal sampling circuit for electrochemical detection, which includes a connection port W to an external working electrode circuit, a connection port Ref to an external reference electrode circuit, a field effect transistor Q1, an amplifier OPA1, an amplifier OPA2, and an amplifier OPA 3; the connection port W is connected with the source S of the field effect transistor Q1 and the negative input end of the amplifier OPA1, the connection port Ref is connected with the drain D of the field effect transistor Q1 and the positive input end of the amplifier OPA1, and the connection port Ref is also connected with the negative input end and the output end of the amplifier OPA3 respectively; the amplifier OPA1 is connected in series with the amplifier OPA2, and the amplifier OPA1 and the amplifier OPA2 constitute a two-stage amplification circuit. The negative input terminal and the output terminal of the amplifier OPA1 are connected in parallel with a resistor R3, and the negative input terminal and the output terminal of the amplifier OPA2 are connected in parallel with a resistor R5.

The output end of the amplifier OPA2 is connected to the ground terminal through a resistor R6, the resistor R6 is connected in parallel with a capacitor C2, and the positive input end of the amplifier OPA3 is connected to the power terminal through a resistor R1 and to the ground terminal through a resistor R2. The field effect transistor Q1 is a P-channel junction field effect transistor. The amplifier OPA3 is a voltage follower, and since the input resistance of the voltage follower is large, the influence of the input pole on the output pole is small, and the reference voltage of the preamplifier OPA1 can be unified by the voltage follower in the circuit. When no current is input into the external working electrode circuit interface W, the field effect tube Q1 is in a static state, and the internal resistance is small; when current is input into the interface W, forward voltage is applied to the grid G and the source S of the field effect transistor, the internal resistance is very high at the moment according to the characteristic of the P-channel junction type field effect transistor, the drain-source current is basically 0, the input signal of the working electrode circuit is not influenced, and the weak current signal is directly amplified through the amplifier OPA 1. The weak current does not need I/V conversion, so that the influence of the precision and resistance value of the resistor on a conversion circuit along with the temperature change is avoided. The current signal preamplifier OPA1 sets the amplification factor as the case may be. The amplification factor of the stage is not too high, and the stage is too high and is easy to amplify weaker noise. The signal is amplified by a two-stage amplifier OPA2 after passing through OPA1 to reach the ideal voltage signal, and the total amplification factor is the product of two-stage amplification factors (OPA1 × OPA 2).