A high-stability active feedback charge amplification circuit

Abstract

The utility model discloses a kind of high-stability active feedback charge amplification circuit, it is related to charge amplification technical field, including charge amplification circuit, double operational amplifier active feedback circuit and double pole compensation circuit.Charge amplification circuit converts the charge signal output by piezoelectric sensor into voltage signal, double operational amplifier active feedback circuit replaces the direct current passage of large feedback resistance by two small resistors, to reduce output offset voltage, double pole compensation circuit compensates phase margin by increasing two poles, increase phase margin to improve system stability.The utility model increases system phase margin by double pole compensation, effectively avoid the overshoot or oscillation of signal when measuring, and by double operational amplifier active feedback replaces feedback resistance direct current passage, improve the measurement accuracy of charge amplification circuit under quasi-static, make charge amplification circuit have better adaptability in multiple application scenarios, greatly save cost.

Description

Technical Field

[0001] This utility model relates to the field of charge amplifier technology, specifically to a highly stable active feedback charge amplifier circuit. Background Technology

[0002] A cylinder pressure sensor can be considered equivalent to a high-impedance charge source that outputs a weak signal. Since the charge is too small to be measured directly, a charge amplifier circuit is needed to amplify it, converting the charge into a voltage for other instruments to analyze and process. A traditional charge amplifier circuit consists of an operational amplifier and a negative feedback network composed of a feedback capacitor and a feedback resistor. The charge amplifier circuit is an integrator circuit that integrates the input current over time. Its output voltage is proportional to the integral value of the input current or the amount of input charge. The feedback resistor dissipates the energy stored in the feedback capacitor; therefore, the charge amplifier circuit is also called a self-zeroing amplifier circuit or a lossy integrator circuit.

[0003] To achieve good low-frequency characteristics in the charge amplifier circuit, when the feedback capacitor value is in the picofarad to nanofarad range, a very large feedback resistor is required, with a resistance ranging from hundreds of megohms to gigahertz. Due to the presence of input bias current in the operational amplifier circuit, a large output offset voltage will be generated when this current flows through the very large feedback resistor. Furthermore, since the charge amplifier circuit is a deep negative feedback system, a very large feedback resistor will make the entire system extremely unstable; when the system phase lags by 360°, the charge amplifier circuit will oscillate. Utility Model Content

[0004] This invention provides a highly stable active feedback charge amplifier circuit to address the above-mentioned issues, thereby solving the problems of overshoot or oscillation during measurement and decreased measurement accuracy due to output offset voltage during quasi-static measurement.

[0005] Specifically, this utility model provides a high-stability active feedback charge amplifier circuit, which includes: a charge amplifier circuit, a dual-pole compensation circuit, and a dual operational amplifier active feedback circuit.

[0006] The bipolar compensation circuit includes a capacitor C. a Input resistance R of the compensation circuit in The first resistor R in the compensation circuit a The second resistor R in the compensation circuit b ;

[0007] Input resistance R of the compensation circuit in Capacitor C a and the first resistor R of the compensation circuit a The input resistance R of the compensation circuit is connected in series. inAs the input terminal for receiving charge signals, the first resistor R of the compensation circuit a One end serves as the voltage output terminal; the second resistor R in the compensation circuit b One end is connected to the voltage output terminal, and the other end is grounded;

[0008] The charge amplification circuit is used to amplify the charge signal output by the piezoelectric sensor into a voltage signal, and includes a first operational amplifier U1 and a feedback resistor R. f Feedback capacitor C f ;

[0009] The inverting input of the first operational amplifier U1 is connected to the first resistor R of the compensation circuit. a The output of the first operational amplifier U1 is connected to a capacitor C. a and the first resistor R of the compensation circuit a The positive input terminal is grounded; the feedback resistor R f and feedback capacitor C f All are related to capacitor C a and the first resistor R of the compensation circuit a in parallel;

[0010] The dual operational amplifier active feedback circuit and feedback capacitor C f Parallel connection is used to shift the overall phase forward through double-pole compensation, thereby increasing the system's phase margin and improving system stability.

[0011] Furthermore, the dual operational amplifier active feedback circuit includes a second operational amplifier U2, a third operational amplifier U3, a first feedback circuit resistor R1, and a second feedback circuit resistor R2;

[0012] One end of the first resistor R1 in the feedback circuit is connected to the voltage output terminal, and the other end is connected to the positive input terminal of the second operational amplifier U2. The inverting input terminal of the second operational amplifier U2 is connected to its output terminal. The output terminal of the second operational amplifier U2 is connected to the positive input terminal of the third operational amplifier U3. The inverting input terminal of the third operational amplifier U3 is connected to its output terminal. The output terminal of the third operational amplifier U3 is connected to the second resistor R2 in the feedback circuit. The other end of the second resistor R2 is connected to the feedback capacitor C. f .

[0013] Furthermore, the first operational amplifier U1, the second operational amplifier U2, and the third operational amplifier U3 have the same specifications.

[0014] Furthermore, the feedback capacitor C f 1000pF, feedback resistor R f The input resistance R of the compensation circuit is 500MΩ. in 10kΩ, capacitor C aThe first resistor R of the compensation circuit is 20pF. a The second resistor R in the compensation circuit is 1kΩ. b The resistance is 47Ω, the first resistor R1 in the feedback circuit is 2.6MΩ, and the second resistor R2 in the feedback circuit is 2.6MΩ.

[0015] The beneficial effects achieved by this utility model are:

[0016] The present invention provides a high-stability active feedback charge amplifier circuit, comprising: a charge amplifier circuit (1), a dual-pole compensation circuit (2), and a dual operational amplifier active feedback circuit (3). The charge amplifier circuit (1) is used to amplify the charge signal output by the piezoelectric sensor into a voltage signal. The dual-pole compensation circuit (2) is used to increase the phase margin of the system. The dual operational amplifier active feedback circuit (3) is used to replace the DC path of the feedback resistor. The dual-pole compensation effectively avoids overshoot or oscillation of the signal during measurement by increasing the phase margin of the system. The active feedback of the dual operational amplifier replaces the DC path of the feedback resistor, thereby improving the measurement accuracy of the charge amplifier circuit under quasi-static conditions and making the charge amplifier circuit more adaptable to various application scenarios. Attached Figure Description

[0017] Figure 1 This is the circuit schematic diagram of this utility model;

[0018] Figure 2 This is a schematic diagram of a traditional charge amplifier circuit.

[0019] Figure 3 Bode plot of a traditional charge amplifier circuit;

[0020] Figure 4 This is the Bode diagram of the circuit of this utility model. Detailed Implementation

[0021] The technical solution of this utility model will be described in more detail below with reference to the accompanying drawings. This utility model includes, but is not limited to, the following embodiments.

[0022] Figure 1 This utility model discloses a high-stability active feedback charge amplifier circuit, comprising: a charge amplifier circuit 1, a dual-pole compensation circuit 3, and a dual operational amplifier active feedback circuit 2;

[0023] The charge amplifier circuit 1 is used to amplify the charge signal output by the piezoelectric sensor into a voltage signal. The dual-pole compensation circuit 3 shifts the overall phase forward through dual-pole compensation, increases the system phase margin, and improves system stability. The dual operational amplifier active feedback circuit 2 replaces the DC path of the large feedback resistor with a small resistor, thereby significantly reducing the output offset voltage of the active feedback charge amplifier circuit.

[0024] The charge amplifier circuit 1 includes a first operational amplifier U1 and a feedback resistor R. f Feedback capacitor C f The dual-pole compensation circuit 3, used to amplify the charge signal output by the piezoelectric sensor into a voltage signal, includes a capacitor C. a Input resistance R of the compensation circuit in The first resistor R in the compensation circuit a The second resistor R in the compensation circuit b The dual operational amplifier active feedback circuit 2, used to increase the system phase margin, includes a second operational amplifier U2, a third operational amplifier U3, a first feedback circuit resistor R1, and a second feedback circuit resistor R2, which are used to replace the DC path of the feedback resistor.

[0025] The specific connection method is as follows: In the double-pole compensation circuit 3, the input resistor R of the compensation circuit... in As the input terminal for receiving charge signals, the first resistor R of the compensation circuit a One end is connected to the feedback resistor R in charge amplifier circuit 1 f One end is connected as the voltage output terminal, and capacitor C a The inverting input and output terminals of the first operational amplifier U1 in charge amplifier circuit 1 are connected in parallel, and the dual operational amplifier active feedback circuit 2 is connected in parallel with the feedback resistor R in charge amplifier circuit 1. f In parallel, the first resistor R1 of the feedback circuit is connected to the voltage output terminal.

[0026] Feedback resistor R f and feedback capacitor C f It is connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier U1, and the non-inverting input terminal of the first operational amplifier U1 is grounded.

[0027] Input resistance R of the compensation circuit in Capacitor C a The first resistor R in the compensation circuit a The second resistor R in the compensation circuit is connected in series. b One end is connected to the first resistor R of the compensation circuit. a One end is connected as the voltage output terminal, and the other end is grounded.

[0028] In the feedback circuit, one end of the first resistor R1 is connected to the non-inverting input of the second operational amplifier U2, and the other end serves as the voltage output. In the feedback circuit, one end of the second resistor R2 is connected to the inverting input of the first operational amplifier U1, and the other end is connected to the output of the third operational amplifier U3. The inverting input of the second operational amplifier U2 is connected to its output, and the inverting input of the third operational amplifier U3 is connected to its output.

[0029] Figure 2This is a schematic diagram of a traditional charge amplifier circuit. In this embodiment, the operational amplifier is model LMC6081.

[0030] Figure 3 This is a Bode plot for a traditional charge amplifier circuit, used to represent the loop gain of the circuit.

[0031] Loop gain, also known as the open-loop gain of a system, represents the factor by which a signal is amplified after passing through the operational amplifier and compensation network from the operational amplifier input.

[0032] This includes two components: the open-loop gain of the operational amplifier and the gain of the feedback loop. Therefore, the formula for calculating the loop gain is:

[0033] LoopG = Aol * Beta

[0034] The loop gain curve on the Bode plot can clearly determine the stability of the system. If the gain on the Bode plot is 0 and the phase is negative, the feedback signal returns to the operational amplifier input and its gain is still positive. In this way, the loop can be completed by itself without any input signal, and the system will oscillate.

[0035] Traditional charge amplifier circuits have a feedback capacitor of 1000pF and a feedback resistor of 500MΩ, corresponding to a phase margin of -22.7°, making them highly prone to oscillation.

[0036] Figure 4 The circuit Bode plot of this utility model is shown. In the embodiments of this application, the operational amplifiers U1, U2, and U3 are all LMC6081.

[0037] Among them, C f For 1000pf, R f 500MΩ, R in 10kΩ, C a 20pf, R a 1kΩ, R b R1 is 47Ω, R2 is 2.6MΩ, and R3 is 2.6MΩ.

[0038] The phase margin of the high-stability active feedback charge amplifier circuit in this application embodiment is 79.57°, which is 102.27° higher than that of the conventional charge amplifier circuit.

[0039] As can be seen from the above, the charge amplifier circuit provided in this embodiment significantly improves the phase margin compared to the traditional charge amplifier circuit, giving the charge amplifier circuit better stability and versatility.

[0040] The parts of this utility model not described in detail are existing technologies.

[0041] This utility model is not limited to the specific embodiments described above. Those skilled in the art can implement this utility model using other specific embodiments based on the disclosed content of the embodiments and drawings. Therefore, any design that adopts the design structure and concept of this utility model and makes some simple changes or modifications falls within the protection scope of this utility model.

Claims

1. A highly stable active feedback charge amplifier circuit, characterized in that, The high-stability active feedback charge amplifier circuit includes: a charge amplifier circuit (1), a dual-pole compensation circuit (3), and a dual operational amplifier active feedback circuit (2); The double-pole compensation circuit (3) includes capacitor C a Input resistance R of the compensation circuit in The first resistor R in the compensation circuit a The second resistor R in the compensation circuit b ; Input resistance R of the compensation circuit in Capacitor C a and the first resistor R of the compensation circuit a The input resistance R of the compensation circuit is connected in series. in As the input terminal for receiving charge signals, the first resistor R of the compensation circuit a One end serves as the voltage output terminal; the second resistor R in the compensation circuit b One end is connected to the voltage output terminal, and the other end is grounded; The charge amplifier circuit (1) is used to amplify the charge signal output by the piezoelectric sensor into a voltage signal, including a first operational amplifier U1 and a feedback resistor R. f Feedback capacitor C f ; The inverting input of the first operational amplifier U1 is connected to the first resistor R of the compensation circuit. a The output of the first operational amplifier U1 is connected to a capacitor C. a and the first resistor R of the compensation circuit a The positive input terminal is grounded; the feedback resistor R f and feedback capacitor C f All are related to capacitor C a and the first resistor R of the compensation circuit a in parallel; The dual operational amplifier active feedback circuit (2) and feedback capacitor C f Parallel connection is used to shift the overall phase forward through double-pole compensation, thereby increasing the system's phase margin and improving system stability.

2. The high-stability active feedback charge amplifier circuit according to claim 1, characterized in that, The dual operational amplifier active feedback circuit (2) includes a second operational amplifier U2, a third operational amplifier U3, a first feedback circuit resistor R1, and a second feedback circuit resistor R2. One end of the first resistor R1 in the feedback circuit is connected to the voltage output terminal, and the other end is connected to the positive input terminal of the second operational amplifier U2. The inverting input terminal of the second operational amplifier U2 is connected to its output terminal. The output terminal of the second operational amplifier U2 is connected to the positive input terminal of the third operational amplifier U3. The inverting input terminal of the third operational amplifier U3 is connected to its output terminal. The output terminal of the third operational amplifier U3 is connected to the second resistor R2 in the feedback circuit. The other end of the second resistor R2 is connected to the feedback capacitor C. f .

3. The high-stability active feedback charge amplifier circuit according to claim 1, characterized in that, The first operational amplifier U1, the second operational amplifier U2, and the third operational amplifier U3 have the same specifications.

4. The high-stability active feedback charge amplifier circuit according to claim 2, characterized in that, Feedback capacitor C f 1000pF, feedback resistor R f The input resistance R of the compensation circuit is 500MΩ. in 10kΩ, capacitor C a The first resistor R of the compensation circuit is 20pF. a The second resistor R in the compensation circuit is 1kΩ. b The resistance is 47Ω, the first resistor R1 in the feedback circuit is 2.6MΩ, and the second resistor R2 in the feedback circuit is 2.6MΩ.

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