Small current measuring device

Abstract

The utility model belongs to the technical field of small current measurement, and particularly relates to a transimpedance amplification circuit which comprises a feedback resistor, an anti-interference circuit and a signal following circuit, the anti-interference circuit is connected with the signal following circuit, one end of the feedback circuit is connected with one end of the anti-interference circuit, and the other end of the feedback circuit is connected with one end of the signal following circuit; the ADC conversion circuit is connected with the signal following circuit, and the processing circuit is connected with the ADC conversion circuit. According to the device, a negative feedback loop is formed through the feedback resistor, the anti-interference circuit and the signal following circuit, due to the effect of the negative feedback loop, the change of feedback current causes the adjustment of output voltage, and the output voltage tends to the input current, so that the input current is converted into the output voltage; and the amplification factor is relatively high and the imbalance is relatively low.

Description

Technical Field

[0001] This application relates to the field of low current measurement technology, and particularly to low current measurement devices. Background Technology

[0002] In related technologies, the measurement method for small currents usually adopts the resistance measurement method. However, the resistance measurement method is easily limited by the size, accuracy and noise level of the resistor itself, and its measurement accuracy cannot be guaranteed.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] In view of at least one of the above technical problems, this application provides a small current measuring device.

[0005] This application provides a small current measuring device, comprising:

[0006] The transimpedance amplifier circuit includes: a feedback resistor, an anti-interference circuit, and a signal follower circuit. The anti-interference circuit is connected to the signal follower circuit. One end of the feedback resistor is connected to one end of the anti-interference circuit, and the other end of the feedback resistor is connected to one end of the signal follower circuit.

[0007] The ADC conversion circuit is connected to the signal follower circuit.

[0008] The processing circuit is connected to the ADC conversion circuit.

[0009] One of the above technical solutions has at least one of the following advantages or beneficial effects: This device forms a negative feedback loop through a feedback resistor, an anti-interference circuit, and a signal follower circuit. Due to the effect of this negative feedback loop, the change in feedback current will lead to the adjustment of the output voltage, so that the output voltage tends to the input current. In this way, the input current is converted into the output voltage, and it has a high amplification factor and a low offset.

[0010] In one possible implementation, the anti-interference circuit includes: a first operational amplifier, a fourth resistor, and a fourth capacitor. The first input terminal of the first operational amplifier is connected to the feedback resistor, the second input terminal of the first operational amplifier is grounded, the output terminal of the first operational amplifier is connected to the signal follower circuit through the fourth resistor, and the fourth capacitor is connected between the output terminal of the first operational amplifier and the second input terminal of the first operational amplifier.

[0011] In one possible implementation, the first operational amplifier is a self-stabilizing zero operational amplifier.

[0012] In one possible implementation, the signal follower circuit includes: a second operational amplifier, a third operational amplifier, and a fifth resistor. The second input terminal of the second operational amplifier is connected to an anti-interference circuit, the first input terminal of the second operational amplifier is grounded, the output terminal of the second operational amplifier is connected to the first input terminal of the third operational amplifier through the fifth resistor, and the output terminal of the third operational amplifier is connected to a feedback resistor.

[0013] In one possible implementation, the signal follower circuit includes: a second capacitor, one end of which is connected to the second input terminal of the second operational amplifier and one end of the feedback resistor, and the other end of which is connected to the output terminal of the third operational amplifier and the other end of the feedback resistor.

[0014] In one possible implementation, a third capacitor is provided between one end of the second capacitor and the second input terminal of the second operational amplifier.

[0015] In one possible implementation, the second and third operational amplifiers are JFET-type input operational amplifiers.

[0016] The present application will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic block diagram of the small current measuring device provided in the embodiments of this application;

[0019] Figure 2 A schematic block diagram of the transimpedance amplifier circuit provided in the embodiments of this application;

[0020] Figure 3 A circuit diagram of a transimpedance amplifier circuit provided in an embodiment of this application; Detailed Implementation

[0021] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0022] like Figures 1 to 3 As shown, this embodiment provides a small current measuring device, including: a transimpedance amplifier circuit 100, an ADC conversion circuit 200, and a processing circuit 300.

[0023] The transimpedance amplifier circuit 100 is used to convert the input current into the output voltage when the input current flows in, due to the negative feedback effect. This achieves a high amplification factor and a low offset.

[0024] The ADC conversion circuit 200 features low noise characteristics and maintains excellent performance in high-signal-quality conversion. This ADC conversion circuit 200 has a maximum channel scan rate of 50 kSPS and provides a fast response time.

[0025] The processing circuit 300 includes an FPGA and an MCU. The combination of the ADC conversion circuit 200 and the FPGA not only improves the speed and efficiency of data processing, but also accelerates the processing speed of the MCU by transmitting signals between the FPGA and the MCU through the SPI data transmission bus, thereby greatly improving the measurement speed.

[0026] The input current enters the transimpedance amplifier circuit 100, which converts the input current into an output voltage. The voltage then enters the ADC conversion circuit 200 for analog-to-digital conversion. The signal is then sent to the processing circuit 300 for digital signal processing, and finally the measured current value is displayed on the screen.

[0027] The circuit structure of the small current measuring device is described below.

[0028] The transimpedance amplifier circuit 100 includes: a feedback resistor R3, an anti-interference circuit 110, and a signal follower circuit 120. The anti-interference circuit 110 is connected to the signal follower circuit 120. One end of the feedback resistor is connected to one end of the anti-interference circuit 110, and the other end of the feedback resistor is connected to one end of the signal follower circuit 120. An ADC conversion circuit 200 is connected to the signal follower circuit 120, and a processing circuit 300 is connected to the ADC conversion circuit 200. This device forms a negative feedback loop through the feedback resistor R3, the anti-interference circuit 110, and the signal follower circuit 120. Due to the effect of this negative feedback loop, changes in the feedback current will lead to adjustments in the output voltage, causing the output voltage to tend towards the input current. In this way, the input current is converted into the output voltage, and it has a high amplification factor and low offset.

[0029] like Figures 1 to 3As shown, in some embodiments, the anti-interference circuit 110 includes: a first operational amplifier U1, a fourth resistor R4 and a fourth capacitor C4. The first input terminal of the first operational amplifier U1 is connected to the feedback resistor R3, the second input terminal of the first operational amplifier U1 is grounded, the output terminal of the first operational amplifier U1 is connected to the signal follower circuit 120 through the fourth resistor R4, and the fourth capacitor C4 is connected between the output terminal of the first operational amplifier U1 and the second input terminal of the first operational amplifier U1.

[0030] The first operational amplifier U1 is a self-stabilized zero-point operational amplifier with rail-to-rail output swing and low noise characteristics. It has extremely low offset, drift, and bias current, an offset voltage of only 3μV, an offset drift of 0.01μV / ℃, and a noise of 1.2μV peak-to-peak (0.1Hz to 10Hz). It can eliminate interference from the input terminal.

[0031] Since small current signals are easily affected by interference, the fourth capacitor C4 can be used to adjust the circuit gain and change the circuit's frequency response. The fourth resistor R4 can improve the stability of small current signals.

[0032] like Figures 1 to 3 As shown, in some embodiments, the signal follower circuit 120 includes: a second operational amplifier U2, a third operational amplifier U3 and a fifth resistor R5. The second input terminal of the second operational amplifier U2 is connected to the anti-interference circuit 110, the first input terminal of the second operational amplifier U2 is grounded, the output terminal of the second operational amplifier U2 is connected to the first input terminal of the third operational amplifier U3 through the fifth resistor R5, and the output terminal of the third operational amplifier U3 is connected to the feedback resistor R3.

[0033] The second operational amplifier U2 and the third operational amplifier U3 are JFET-type input operational amplifiers. The JFET input design features low input bias and offset current, low offset voltage temperature coefficient, low harmonic distortion, and low noise.

[0034] like Figures 1 to 3 As shown, in some embodiments, the signal follower circuit 120 includes a second capacitor C2, one end of which is connected to the second input terminal of the second operational amplifier U2 and one end of the feedback resistor R3, and the other end of which is connected to the output terminal of the third operational amplifier U3 and the other end of the feedback resistor R3. The second capacitor C2 and the feedback resistor R3 form a low-pass filter, limiting the bandwidth of the circuit and reducing the broadband noise of the output.

[0035] like Figures 1 to 3As shown, in some embodiments, a third capacitor C3 is provided between one end of the second capacitor C2 and the second input terminal of the second operational amplifier U2. In actual circuits, the parasitic capacitance generated in the circuit will interact with the feedback resistor R3, forming unnecessary poles and zeros in the loop gain response of the amplifier. Through the third capacitor C3, the circuit can reach steady state when measuring small currents.

[0036] The working process of this device is as follows: When the input current enters the transimpedance amplifier circuit 100, it is converted into a corresponding output voltage through the feedback resistor R3. The first operational amplifier U1, the second operational amplifier U2, the third operational amplifier U3, the fourth resistor R4, the fifth resistor R5, and the feedback resistor R3 form a negative feedback loop. In this negative feedback loop, the change in the feedback current will adjust the output voltage, making it tend towards the input current, thereby realizing the conversion from input current to output voltage.

[0037] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0038] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0039] The above are merely preferred embodiments of this application and do not constitute any limitation on this application. Any person skilled in the art can make many possible variations and modifications to the technical solution of this application, or modify it into equivalent embodiments, without departing from the scope of the technical solution of this application. Therefore, all equivalent changes made based on the shape, structure, and principle of this application without departing from the content of the technical solution of this application should be covered within the protection scope of this application.

Claims

1. A small current measuring device, characterized in that, include: A transimpedance amplifier circuit includes: a feedback resistor, an anti-interference circuit, and a signal follower circuit. The anti-interference circuit is connected to the signal follower circuit. One end of the feedback resistor is connected to one end of the anti-interference circuit, and the other end of the feedback resistor is connected to one end of the signal follower circuit. The ADC conversion circuit is connected to the signal follower circuit. The processing circuit is connected to the ADC conversion circuit.

2. The small current measuring device according to claim 1, characterized in that, The anti-interference circuit includes: a first operational amplifier, a fourth resistor, and a fourth capacitor. The first input terminal of the first operational amplifier is connected to the feedback resistor, the second input terminal of the first operational amplifier is grounded, the output terminal of the first operational amplifier is connected to the signal follower circuit through the fourth resistor, and the fourth capacitor is connected between the output terminal of the first operational amplifier and the second input terminal of the first operational amplifier.

3. The small current measuring device according to claim 2, characterized in that, The first operational amplifier is a self-stabilized zero operational amplifier.

4. The small current measuring device according to claim 1, characterized in that, The signal follower circuit includes a second operational amplifier, a third operational amplifier, and a fifth resistor. The second input terminal of the second operational amplifier is connected to the anti-interference circuit. The first input terminal of the second operational amplifier is grounded. The output terminal of the second operational amplifier is connected to the first input terminal of the third operational amplifier through the fifth resistor. The output terminal of the third operational amplifier is connected to the feedback resistor.

5. The small current measuring device according to claim 4, characterized in that, The signal follower circuit includes: a second capacitor, one end of which is connected to the second input terminal of the second operational amplifier and one end of the feedback resistor, and the other end of which is connected to the output terminal of the third operational amplifier and the other end of the feedback resistor.

6. The small current measuring device according to claim 5, characterized in that, A third capacitor is provided between one end of the second capacitor and the second input terminal of the second operational amplifier.

7. The small current measuring device according to claim 4, characterized in that, The second and third operational amplifiers are JFET type input operational amplifiers.

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