A preamplifier circuit for an engine cylinder pressure signal

Abstract

The utility model belongs to weak signal amplification technical field discloses a kind of front-stage amplification circuit for engine cylinder pressure signal, including charge amplifier circuit, active feedback network, T-type resistance feedback network and noise gain compensation network;Charge amplifier circuit is used to amplify the charge signal of engine cylinder pressure sensor output as voltage signal;Active feedback network is used to replace the direct current passage of conventional front-stage amplification circuit feedback resistance;T-type resistance feedback network is used to reduce feedback resistance resistance value;Noise gain compensation network is used to increase the phase margin of front-stage amplification circuit.The front-stage amplification circuit provided by the utility model compared to conventional front-stage amplification circuit will greatly improve phase margin, while greatly reduce the resistance value of feedback resistance, so that it can be better applied to large sensitivity cylinder pressure sensor and engine heavy load condition, and has better stability and applicability.

Description

Technical Field

[0001] This invention belongs to the field of weak signal amplification technology, specifically relating to a pre-amplifier circuit for engine cylinder pressure signals. 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 the signal. A traditional preamplifier circuit consists of an operational amplifier and a negative feedback network composed of a feedback capacitor and a feedback resistor.

[0003] When the engine cylinder pressure sensor has high sensitivity and measures a large cylinder pressure, the amount of charge output by the sensor will also increase. Therefore, it is necessary to increase the capacitance of the feedback resistor in the preamplifier circuit to increase the range of the preamplifier circuit. As the capacitance of the feedback capacitor increases, the resistance of the corresponding feedback resistor will also increase. Since the preamplifier circuit is in a deep negative feedback state, increasing the resistance of the feedback resistor will increase the instability of the entire amplification system, reduce the phase margin of the circuit, and make the output voltage signal more prone to overshoot or even oscillation. At the same time, increasing the resistance of the feedback resistor will also affect the noise characteristics of the circuit.

[0004] To ensure the system stability of the amplifier circuit, the phase margin should be compensated by a compensation network. However, the compensation network often brings new problems to the amplifier circuit.

[0005] Therefore, it is necessary to design a preamplifier circuit for engine cylinder pressure signals. Summary of the Invention

[0006] The purpose of this invention is to provide a preamplifier circuit for engine cylinder pressure signals, in order to solve the problem mentioned in the background art that when the engine cylinder pressure sensor has high sensitivity and the measured cylinder pressure is also high, the traditional preamplifier circuit setting will increase the instability of the entire amplification system, reduce the phase margin of the circuit, and make the output voltage signal more prone to overshoot or even oscillation, while also affecting the noise characteristics of the circuit.

[0007] To achieve the above objectives, this utility model provides a preamplifier circuit for engine cylinder pressure signals, including a charge amplifier circuit, an active feedback network, a T-type resistor feedback network, and a noise gain compensation network.

[0008] The charge amplification circuit includes operational amplifiers U1 and U2, and a feedback capacitor C. f The active feedback network includes operational amplifier U3, resistor R1, and resistor R2; the noise gain compensation network includes resistor R aResistance R b Capacitor C a ;

[0009] The specific connection method is as follows: In the charge amplifier circuit, the inverting input terminal of operational amplifier U1 serves as the input terminal for receiving the charge signal; the non-inverting input terminal of operational amplifier U1 is grounded; the output terminal of operational amplifier U1 is connected to the non-inverting input terminal of operational amplifier U2; the output terminal of operational amplifier U2 serves as the voltage output terminal of the preamplifier circuit; and the feedback capacitor C... f The first terminal is connected to the inverting input terminal of operational amplifier U1, and the feedback capacitor C f The second terminal is connected to the output terminal of operational amplifier U2;

[0010] In the active feedback network, the first end of resistor R2 is connected to the inverting input of operational amplifier U1, the second end of resistor R2 is connected to the output of operational amplifier U3, the first end of resistor R1 is connected to the output of operational amplifier U2, and the second end of resistor R1 is connected to the non-inverting input of operational amplifier U3.

[0011] One end of the T-type resistor feedback network is connected to the inverting input terminal of operational amplifier U1, and the other end of the T-type resistor feedback network is connected to the output terminal of operational amplifier U2.

[0012] The resistor R in the noise gain compensation network a The first terminal and resistor R b The first terminal of each is connected to the inverting input terminal of operational amplifier U1, and the resistor R a The second terminal is connected to capacitor C a The first end is connected, and the capacitor C is... a The second terminal is grounded, and the resistor R b The second terminal is connected to capacitor C a The second end is connected.

[0013] In one specific embodiment, the T-type resistor feedback network includes a feedback resistor R. f Resistors R3 and R4; resistor R in the T-type resistor feedback network f The first terminal of resistor R4 is connected to the inverting input terminal of operational amplifier U1, the second terminal of resistor R4 is connected to the output terminal of operational amplifier U2, and the first terminal of resistor R3 is connected to resistor R... f The second end of the resistor is connected to the first end of the resistor R4, and the second end of the resistor R3 is grounded; the T-type resistor feedback network is used to reduce the overall resistance of the feedback loop.

[0014] In one specific embodiment, the charge amplification circuit is used to amplify the charge signal output by the engine cylinder pressure sensor into a voltage signal; the inverting input terminal of the operational amplifier U2 is connected to its own output terminal.

[0015] In one specific implementation, the active feedback network is used to replace the DC path of the feedback resistor in a traditional preamplifier circuit; the inverting input of the operational amplifier U3 is connected to its own output.

[0016] In one specific implementation, the noise gain compensation network is used to increase the phase margin of the preamplifier circuit.

[0017] In one specific implementation, the operational amplifiers U1, U2, and U3 have the same specifications.

[0018] In one specific implementation, the operational amplifiers U1, U2, and U3 are all of model RS8491.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] Compared with traditional preamplifier circuits, the preamplifier circuit provided by this invention significantly improves the phase margin and greatly reduces the overall resistance of the feedback loop, making it more suitable for high-sensitivity cylinder pressure sensors and high-load engine conditions, and also has better stability and applicability.

[0021] This invention increases the system phase margin through a noise gain compensation network, effectively avoiding overshoot or oscillation when amplifying engine cylinder pressure signals. It adopts a T-type resistor feedback network to reduce the capacitance value of the feedback resistor, while taking into account system stability and noise characteristics. By replacing the DC path of the feedback resistor with an active feedback network, the measurement accuracy of the preamplifier circuit under quasi-static conditions is improved, enabling it to have higher accuracy during the amplification of cylinder pressure signals in the intake and exhaust phases of the engine.

[0022] This invention adds a zero-pole pair to the feedback network, resulting in a large feedback quantity at low frequencies but a small feedback quantity at high frequencies, thereby increasing the gain in the high-frequency band. Due to the increased high-frequency gain, the high-frequency noise also increases. At the same time, the increased coupling feedback resistance leads to resistive thermal noise. Therefore, the T-type resistor feedback network reduces the overall resistance of the feedback loop, suppresses the increase in noise, and prevents the effective signal from being submerged in noise. This allows the engine to accurately and stably amplify the charge signal when using a high-sensitivity cylinder pressure sensor to measure the cylinder pressure.

[0023] This invention increases the accuracy of measurements during the engine's intake and exhaust phases through an active feedback network.

[0024] In addition to the objectives, features, and advantages described above, this utility model has other objectives, features, and advantages. The present utility model will now be described in further detail with reference to the figures. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0026] Figure 1 This is a circuit schematic diagram of one embodiment of the present invention;

[0027] Figure 2 This is the schematic diagram of a traditional preamplifier circuit.

[0028] Figure 3 The Bode plot of a traditional preamplifier circuit;

[0029] Figure 4 This is a circuit Bode diagram of one embodiment of the present invention;

[0030] Among them, 1. charge amplifier circuit; 2. active feedback network; 3. T-type resistor feedback network; 4. noise gain compensation network. Detailed Implementation

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0032] Example 1

[0033] This utility model provides a preamplifier circuit for engine cylinder pressure signal, including a charge amplifier circuit 1, an active feedback network 2, a T-type resistor feedback network 3, and a noise gain compensation network 4.

[0034] The charge amplifier circuit 1 is used to amplify the charge signal output by the engine cylinder pressure sensor into a voltage signal; the active feedback network 2 is used to replace the DC path of the feedback resistor in the traditional preamplifier circuit, reduce the output offset voltage of the amplifier circuit, thereby reducing zero drift and increasing the accuracy of engine intake and exhaust phase measurements; the T-type resistor feedback network 3 is used to reduce the overall resistance of the feedback loop, thereby reducing resistor thermal noise, to balance the noise gain network and the noise characteristics reduced by the increase in the overall resistance of the feedback loop; the noise gain compensation network 4 is used to increase the phase margin of the preamplifier circuit, thereby avoiding signal overshoot or oscillation caused by the capacitive load of the subsequent stage during the amplification process of the preamplifier circuit.

[0035] The charge amplifier circuit 1 includes operational amplifiers U1 and U2, and a feedback capacitor C. f The active feedback network 2 includes an operational amplifier U3, resistors R1 and R2; the noise gain compensation network 4 includes resistor R aResistance R b Capacitor C a ;

[0036] The specific connection method is as follows: the inverting input terminal of operational amplifier U1 in charge amplifier circuit 1 serves as the input terminal for receiving charge signals; the non-inverting input terminal of operational amplifier U1 is grounded; the output terminal of operational amplifier U1 is connected to the non-inverting input terminal of operational amplifier U2; the output terminal of operational amplifier U2 serves as the voltage output terminal of the preamplifier circuit; and the feedback capacitor C... f The first terminal is connected to the inverting input terminal of operational amplifier U1, and the feedback capacitor C f The second terminal is connected to the output terminal of operational amplifier U2; the inverting input terminal of operational amplifier U2 is connected to its own output terminal.

[0037] In the active feedback network 2, the first end of resistor R2 is connected to the inverting input of operational amplifier U1, the second end of resistor R2 is connected to the output of operational amplifier U3, the first end of resistor R1 is connected to the output of operational amplifier U2, and the second end of resistor R1 is connected to the non-inverting input of operational amplifier U3; the inverting input of operational amplifier U3 is connected to its own output.

[0038] The resistor R in noise gain compensation network 4 a The first terminal and resistor R b The first terminal of each is connected to the inverting input terminal of operational amplifier U1, and the resistor R a The second terminal is connected to capacitor C a The first end is connected, and the capacitor C is... a The second terminal is grounded, and the resistor R b The second terminal is connected to capacitor C a The second end is connected.

[0039] The T-type resistor feedback network 3 includes a feedback resistor R. f Resistors R3 and R4; resistor R in the T-type resistor feedback network 3 f The first terminal of resistor R4 is connected to the inverting input terminal of operational amplifier U1, the second terminal of resistor R4 is connected to the output terminal of operational amplifier U2, and the first terminal of resistor R3 is connected to resistor R... f The second terminal of resistor R3 is connected to the first terminal of resistor R4, and the second terminal of resistor R3 is grounded.

[0040] Figure 3 This is a Bode plot of a traditional preamplifier circuit, used to represent the loop gain of the circuit. The loop gain, also known as the open-loop gain of the system, represents the factor by which the signal is amplified after passing through the operational amplifier and the compensation network from the operational amplifier input. It includes two components: the open-loop gain of the operational amplifier and the gain of the feedback loop.

[0041] 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.

[0042] Traditional preamplifier circuits have a 2000pF feedback capacitor and a 2G feedback resistor, resulting in a phase margin of -10.85°, which makes them highly prone to oscillation.

[0043] In this embodiment, the operational amplifiers U1, U2, and U3 have the same specifications, and the model of the operational amplifiers U1, U2, and U3 is RS8491.

[0044] In this embodiment, C f R1 is 2.6MΩ, R2 is 2.6MΩ, C is 2000pF. a For 1nf, R a 1kΩ, R b It is 1kΩ;

[0045] When R in a T-type resistor network f When the R3 is 20MΩ, the R4 is 100Ω, and the R5 is 10kΩ, the effect is comparable to that of a traditional preamplifier circuit with a feedback resistor of 2GΩ.

[0046] The phase margin of the preamplifier circuit for engine cylinder pressure signal in this embodiment is 97.5°, which is 108.35° higher than that of the conventional preamplifier circuit.

[0047] Compared with traditional preamplifier circuits, the preamplifier circuit provided in this embodiment significantly improves the phase margin and greatly reduces the overall resistance of the feedback loop, making it more suitable for high-sensitivity cylinder pressure sensors and high-load engine conditions, and also has better stability and applicability.

[0048] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions and substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the protection scope of the present invention.

Claims

1. A preamplifier circuit for engine cylinder pressure signals, characterized in that, It includes a charge amplifier circuit (1), an active feedback network (2), a T-type resistor feedback network (3), and a noise gain compensation network (4). The charge amplifier circuit (1) includes operational amplifiers U1 and U2, and a feedback capacitor C. f The active feedback network (2) includes operational amplifier U3, resistor R1, and resistor R2; the noise gain compensation network (4) includes resistor R a Resistance R b Capacitor C a ; The specific connection method is as follows: In the charge amplifier circuit (1), the inverting input terminal of the operational amplifier U1 is used as the input terminal for receiving the charge signal, the non-inverting input terminal of the operational amplifier U1 is grounded, the output terminal of the operational amplifier U1 is connected to the non-inverting input terminal of the operational amplifier U2, and the output terminal of the operational amplifier U2 is used as the voltage output terminal of the preamplifier circuit. The feedback capacitor C f The first terminal is connected to the inverting input terminal of operational amplifier U1, and the feedback capacitor C f The second terminal is connected to the output terminal of operational amplifier U2; In the active feedback network (2), the first end of resistor R2 is connected to the inverting input of operational amplifier U1, the second end of resistor R2 is connected to the output of operational amplifier U3, the first end of resistor R1 is connected to the output of operational amplifier U2, and the second end of resistor R1 is connected to the non-inverting input of operational amplifier U3. One end of the T-type resistor feedback network (3) is connected to the inverting input terminal of the operational amplifier U1, and the other end of the T-type resistor feedback network (3) is connected to the output terminal of the operational amplifier U2. The resistor R in the noise gain compensation network (4) a The first terminal and resistor R b The first terminal of each is connected to the inverting input terminal of operational amplifier U1, and the resistor R a The second terminal is connected to capacitor C a The first end is connected, and the capacitor C is... a The second terminal is grounded, and the resistor R b The second terminal is connected to capacitor C a The second end is connected.

2. The preamplifier circuit for engine cylinder pressure signals according to claim 1, characterized in that, The T-type resistor feedback network (3) includes a feedback resistor R f Resistors R3 and R4; resistor R in the T-type resistor feedback network (3) f The first terminal of resistor R4 is connected to the inverting input terminal of operational amplifier U1, the second terminal of resistor R4 is connected to the output terminal of operational amplifier U2, and the first terminal of resistor R3 is connected to resistor R... f The second end of the resistor is connected to the first end of the resistor R4, and the second end of the resistor R3 is grounded; the T-type resistor feedback network (3) is used to reduce the overall resistance of the feedback loop.

3. The preamplifier circuit for engine cylinder pressure signals according to claim 1, characterized in that, The charge amplifier circuit (1) is used to amplify the charge signal output by the engine cylinder pressure sensor into a voltage signal; the inverting input terminal of the operational amplifier U2 is connected to its own output terminal.

4. The preamplifier circuit for engine cylinder pressure signals according to claim 1, characterized in that, The active feedback network (2) is used to replace the DC path of the feedback resistor in the traditional preamplifier circuit; the inverting input terminal of the operational amplifier U3 is connected to its own output terminal.

5. The preamplifier circuit for engine cylinder pressure signals according to claim 1, characterized in that, The noise gain compensation network (4) is used to increase the phase margin of the preamplifier circuit.

6. The preamplifier circuit for engine cylinder pressure signals according to claim 1, characterized in that, The operational amplifiers U1, U2, and U3 have the same specifications.

7. The preamplifier circuit for engine cylinder pressure signals according to claim 6, characterized in that, The operational amplifiers U1, U2, and U3 are all of model RS8491.

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