Bipolar analog signal transmission circuit

Abstract

The utility model discloses a bipolar analog signal transmission circuit, belongs to an analog signal transmission circuit in the technical field of analog signal transmission, and aims to solve the technical problem of poor quality of transmitted weak signals in the prior art. The circuit comprises an operational amplifier N1-A, an operational amplifier N1-B, an operational amplifier N3-A and a photoelectric coupler N2. A pin 1 of the operational amplifier N1-B is electrically connected with a pin 1 of a photoelectric coupler N2 through a resistor R5, a pin 2 of the photoelectric coupler N2 is electrically connected with a power VCC interface, a pin 3 of the photoelectric coupler N2 is electrically connected with a node C, a pin 4 of the photoelectric coupler N2 is electrically connected with a node G between the pin 3 of the operational amplifier N1-B and a node D, and a pin 7 of the photoelectric coupler N2 is electrically connected with a pin 2 of an operational amplifier N3-A; a pin 8 of the photoelectric coupler N2 is electrically connected with a pin 3 of the operational amplifier N3-A. A node H between the pin 8 of the photoelectric coupler N2 and the pin 3 of the operational amplifier N3-A is grounded GNDB. The transmission circuit can ensure the accuracy of signal transmission and solve the problem of poor signal transmission quality under the conditions of extremely small and weak signals and small signal variation.

Description

Technical Field

[0001] This utility model belongs to the field of analog signal transmission technology, and relates to an analog signal transmission circuit, and more particularly to a bipolar analog signal transmission circuit. Background Technology

[0002] Nowadays, analog signals are needed in many fields and situations. For example, in parameter measurement in aerospace, aviation, and nuclear testing, extremely weak sensor measurement signals are required. The collected analog signals need to be input to the controller, which then outputs corresponding control signals. However, these analog signals are often not grounded with the controller, and their voltages may even differ by hundreds or thousands of volts, so isolation methods are necessary for transmission.

[0003] In existing technologies, the main methods for isolating and transmitting analog signals include: transformer isolation, optocoupler isolation valve, and capacitor isolation.

[0004] Patent application number 202010769990.0 relates to transformer isolation, disclosing a broadband analog signal isolation transmission circuit based on magnetic field coupling. This circuit includes an isolation transformer, an isolation-side high-impedance amplifier, and a non-isolation-side high-impedance amplifier. The primary side of the isolation transformer has a primary winding and a tertiary winding, while the secondary side has a secondary winding. Both the primary and tertiary windings are connected to the isolation-side high-impedance amplifier, and the secondary winding is connected to the non-isolation-side high-impedance amplifier. The output signal of the entire isolation circuit is equal to the input signal, thus achieving isolation of the original signal. Furthermore, when using a transformer capable of covering higher frequency bands, simply adding capacitors or resistors to lower the corner frequency of the two first-order RC high-pass filter circuits improves high-frequency signal isolation while maintaining the amplitude-frequency response of low-frequency analog signal isolation transmission.

[0005] Utility model patent application No. 202222291578.X relates to an optocoupler isolation valve, which discloses a circuit for achieving isolated transmission of analog signals. The circuit includes: the output of a first integrator connected to the input of a first PWM modulator; the output of the first PWM modulator connected to the input of a first isolation module; the output of the signal after passing through the first isolation module and a first filter module connected to the non-inverting input of a second integrator; the output of the second integrator connected to the input of the second PWM modulator; the output of the second PWM modulator connected to the input of a second filter module; the output of the second filter module connected to the inverting input of the second integrator; the output of the second PWM modulator also connected to the input of the second isolation module; the output of the second isolation module also connected to the input of a third filter module; and the output of the third filter module connected to the inverting input of the first integrator. The initial analog signal is input from the non-inverting input of the first integrator, and the isolated analog signal is output from the non-inverting input of the second integrator.

[0006] Patent application number 202210095051.1 relates to a capacitive isolation method, disclosing a voltage-to-digital conversion circuit based on capacitive isolation. This circuit includes a signal conditioning circuit for receiving a bipolar voltage signal and outputting a unipolar voltage signal to a voltage-to-digital conversion circuit; a voltage-to-digital conversion circuit for receiving the unipolar voltage signal and an isolated clock signal, and outputting a digital signal to a capacitive digital isolator; and a capacitive digital isolator for receiving the clock signal from the FPGA system, outputting an isolated clock signal to the voltage-to-digital conversion circuit, and finally outputting an isolated digital signal to the FPGA system. By modulating the bipolar analog signal into a digital signal through the voltage-to-digital conversion circuit, and then processing it in the FPGA system after passing through the capacitive digital isolator, distortion-free analog signal transmission can be achieved. This fundamentally eliminates the problems of isolated analog signal transmission in traditional solutions, enhances noise immunity, and improves the measurement accuracy of the system.

[0007] The advantages of transformer isolation are high isolation voltage, high reliability, and long lifespan; its disadvantage is that the transformer itself is a radiation source, posing an EMI interference problem. The advantages of optocoupler isolation are unidirectional signal transmission, complete electrical isolation between the input and output ends, minimal impact of the output signal on the input signal, strong anti-interference capability, stable operation, contactless operation, long lifespan, and high transmission efficiency; its disadvantages mainly lie in speed limitations, high power consumption, and LED light aging. The advantages of capacitive isolation are high communication speed, short signal transmission delay, long lifespan, good EMI immunity, and good signal tracking; its disadvantages are the need for modulation and relatively low isolation voltage.

[0008] Therefore, based on the current actual usage background and needs, the existing isolation scheme cannot achieve extremely small signal strength, minimal signal change, undistorted signal transmission, extremely high accuracy requirements, and extremely strong anti-interference requirements when the transmitted signal is converted from DC to F0, resulting in poor transmission signal quality. Utility Model Content

[0009] The purpose of this invention is to provide a bipolar analog signal transmission circuit to solve the technical problem of poor signal quality in the prior art.

[0010] To achieve the above objectives, this utility model specifically adopts the following technical solution:

[0011] A bipolar analog signal transmission circuit includes operational amplifier N1-A, operational amplifier N1-B, operational amplifier N3-A, and optocoupler N2;

[0012] Pin 3 of op-amp N1-A is electrically connected to the optocoupler isolation input terminal V_IN. Pin 2 of op-amp N1-A is electrically connected to the reference voltage output terminal REF through resistor R1. Pin 1 of op-amp N1-A is electrically connected to pin 2 of op-amp N1-B through resistors R3 and R4 in sequence. Node A between pin 1 of op-amp N1-A and resistor R3 is electrically connected to node B between pin 2 of op-amp N1-A and resistor R1 through resistor RF. Node C between resistors R3 and R4 is grounded to GNDA through capacitor C1.

[0013] Pin 3 of operational amplifier N1-B is electrically connected to node D between capacitor C1 and ground GNDA. Pin 1 of operational amplifier N1-B is electrically connected to pin 1 of optocoupler N2 through resistor R5. Node E between resistor R4 and pin 2 of operational amplifier N1-B is electrically connected to node F between pin 1 of operational amplifier N1-B and resistor R5 through capacitor C2.

[0014] Pin 2 of optocoupler N2 is electrically connected to the power supply VCC interface; pin 3 of optocoupler N2 is electrically connected to node C; pin 4 of optocoupler N2 is electrically connected to node G between pin 3 of operational amplifier N1-B and node D; pin 7 of optocoupler N2 is electrically connected to pin 2 of operational amplifier N3-A; pin 8 of optocoupler N2 is electrically connected to pin 3 of operational amplifier N3-A; and node H between pin 8 of optocoupler N2 and pin 3 of operational amplifier N3-A is grounded to GNDB.

[0015] Pin 1 of op-amp N3-A is electrically connected to the optocoupler isolation output terminal V_OUT. Resistor R6 and capacitor C3 are connected in parallel between node I between pin 7 of optocoupler N2 and pin 2 of op-amp N3-A and node J between pin 1 of op-amp N3-A and the optocoupler isolation output terminal V_OUT.

[0016] Furthermore, capacitors C2 and C3 are compensation capacitors.

[0017] Furthermore, resistor R6 is a high-precision, low-temperature drift resistor.

[0018] The beneficial effects of this utility model are:

[0019] In this invention, a signal is superimposed with a stable voltage signal to shift the signal to a suitable region to meet the requirements of optical isolation transmission. The optocoupler output adopts a dual-output signal mode. One signal is subtracted from the stable voltage before input to obtain the original signal. The other output signal serves as a feedback signal at the signal input to ensure the accuracy of the signal in optical isolation. This ensures the accuracy of signal transmission even when the signal is extremely small and weak or the signal change is very small, effectively solving the problem of poor signal quality. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of this utility model. Detailed Implementation

[0021] This embodiment provides a bipolar analog signal transmission circuit suitable for distortion-free transmission of minute signals in the 0.1-1uV range. A typical application is the output of a micro-strain gauge bridge, which can map a signal representing a 0.1g pressure change to a 0.1uV output, thus obtaining accurate and reliable results in scientific research. Its core lies in the two photosensitive terminals having identical electrical characteristics, both measuring the intensity of emitted light. The first is used for negative feedback control at this stage to obtain a precise output, while the second is used for signal output. In actual product transmission measurements, the distortion is less than 0.01%.

[0022] The bipolar analog signal transmission circuit includes operational amplifiers N1-A, N1-B, and N3-A, and optocoupler N2.

[0023] Pin 3 of op-amp N1-A is electrically connected to the optocoupler isolation input V_IN. Pin 2 of op-amp N1-A is electrically connected to the reference voltage output REF through resistor R1. Pin 1 of op-amp N1-A is electrically connected to pin 2 of op-amp N1-B through resistors R3 and R4. Node A between pin 1 of op-amp N1-A and resistor R3 is electrically connected to node B between pin 2 of op-amp N1-A and resistor R1 through resistor RF. Node C between resistors R3 and R4 is grounded to GNDA through capacitor C1. Resistor R3 and capacitor C1 form a low-pass filter circuit, where resistor R3 is a high-precision, low-temperature-drift resistor used to filter the signal received at the optocoupler isolation input V_IN to remove residual high-frequency noise and prevent the device from operating in the distortion region.

[0024] Pin 3 of operational amplifier N1-B is electrically connected to node D between capacitor C1 and ground GNDA. Pin 1 of operational amplifier N1-B is electrically connected to pin 1 of optocoupler N2 through resistor R5. Node E between resistor R4 and pin 2 of operational amplifier N1-B is electrically connected to node F between pin 1 of operational amplifier N1-B and resistor R5 through capacitor C2. Capacitor C2 is a phase compensation capacitor used to improve circuit stability and prevent self-oscillation.

[0025] Pin 2 of optocoupler N2 is electrically connected to the power supply VCC interface; pin 3 of optocoupler N2 is electrically connected to node C; pin 4 of optocoupler N2 is electrically connected to node G between pin 3 of operational amplifier N1-B and node D; pin 7 of optocoupler N2 is electrically connected to pin 2 of operational amplifier N3-A; pin 8 of optocoupler N2 is electrically connected to pin 3 of operational amplifier N3-A; and node H between pin 8 of optocoupler N2 and pin 3 of operational amplifier N3-A is grounded to GNDB. Optocoupler N2 is an HCNR201 analog optocoupler, which features good stability and high linearity.

[0026] Pin 1 of operational amplifier N3-A is electrically connected to the optocoupler isolation output terminal V_OUT. Node I between pin 7 of optocoupler N2 and pin 2 of operational amplifier N3-A, and node J between pin 1 of operational amplifier N3-A and the optocoupler isolation output terminal V_OUT, are connected in parallel with resistor R6 and capacitor C3. Capacitor C3 is also a compensation capacitor, used to improve circuit stability and prevent self-oscillation; resistor R6 is a high-precision, low-temperature-drift resistor.

[0027] The optocoupler N2 includes a light-emitting diode (LED) D1 and two highly similar photodiodes pd1 and pd2. The negative terminal (cathode) of LED D1 is electrically connected to resistor R5 via pin 1 of optocoupler N2, and the positive terminal (anode) of LED D1 is electrically connected to the power supply VCC interface via pin 2 of optocoupler N2. The negative terminal (cathode) of photodiode pd1 is electrically connected to node C via pin 3 of optocoupler N2, and the positive terminal (anode) of photodiode pd1 is electrically connected to node G via pin 4 of optocoupler N2. The negative terminal (cathode) of photodiode pd2 is electrically connected to node I via pin 7 of optocoupler N2, and the positive terminal (anode) of photodiode pd2 is electrically connected to node H via pin 8 of optocoupler N2.

[0028] The working principle of this transmission circuit is as follows: when there is a current I in the light-emitting diode D1... d1 When light is emitted, the internal packaging structure of the optocoupler N2 enables photodiodes pd1 and pd2 to generate a current I of approximately the same magnitude. pd1 I pd2At the moment the circuit is powered on, the operational amplifier N1-B outputs a low level, turning on the light-emitting diode D1. The photodiode pd1 then receives the light and generates a photocurrent I. pd1 The photodiode pd1 reduces the net input of operational amplifier N1-B, thus creating negative feedback; at the output of optocoupler N2, operational amplifier N3-A converts the current I generated by photodiode pd2... pd2 It is converted into a high linearity signal and output through the optocoupler-isolated output terminal V_OUT.

[0029] Compared to existing optocoupler isolation methods, this embodiment provides a certain offset to the signal, thus enabling forward and reverse signal transmission. Furthermore, it employs one of the dual outputs for signal feedback, ensuring signal integrity and significantly improving accuracy in extremely weak signals.

[0030] Compared to existing transformer isolation methods, this embodiment solves the problem that transformers cannot transmit DC signals, as well as the electromagnetic compatibility and anti-interference problems of transformer isolation methods.

[0031] Compared to existing capacitive coupling isolation methods, this embodiment solves the problem that capacitive coupling isolation methods cannot transmit DC signals, and also solves the problem of poor low-frequency signal transmission.

[0032] Furthermore, the performance parameters of the transmission circuit adopted in this embodiment are as follows:

[0033] 1) Supports the transmission of signals with a change of less than 1uV.

[0034] 2) Transmission signal range: 0-12000Hz

[0035] 3) Transmission signal accuracy: 0.01%

[0036] 4) Isolation voltage: 5000Vdc.

Claims

1. A bipolar analog signal transmission circuit, characterized in that: Including operational amplifier N1-A, operational amplifier N1-B, operational amplifier N3-A and photocoupler N2; Pin 3 of the op amp N1-A is electrically connected to the optocoupler isolation input terminal V_IN, pin 2 of the op amp N1-A is electrically connected to the reference voltage output terminal REF through the resistor R1, pin 1 of the op amp N1-A is electrically connected to pin 2 of the op amp N1-B through the resistor R3 and the resistor R4 in sequence, node A between pin 1 of the op amp N1-A and the resistor R3 is electrically connected to node B between pin 2 of the op amp N1-A and the resistor R1 through the resistor RF, and node C between the resistor R3 and the resistor R4 is grounded to GNDA through the capacitor C1; Pin 3 of the operational amplifier N1-B is electrically connected to a node D between the capacitor C1 and the ground GNDA, pin 1 of the operational amplifier N1-B is electrically connected to pin 1 of the photocoupler N2 via the resistor R5, and node E between the resistor R4 and pin 2 of the operational amplifier N1-B is electrically connected to a node F between pin 1 of the operational amplifier N1-B and the resistor R5 via the capacitor C2; Pin 2 of the photocoupler N2 is electrically connected to the power supply VCC interface, pin 3 of the photocoupler N2 is electrically connected to node C, pin 4 of the photocoupler N2 is electrically connected to node G between pin 3 of the operational amplifier N1-B and node D, pin 7 of the photocoupler N2 is electrically connected to pin 2 of the operational amplifier N3-A, pin 8 of the photocoupler N2 is electrically connected to pin 3 of the operational amplifier N3-A, and node H between pin 8 of the photocoupler N2 and pin 3 of the operational amplifier N3-A is connected to ground GNDB; Pin 1 of the operational amplifier N3-A is electrically connected to the optocoupler isolation output terminal V_OUT, and a resistor R6 and a capacitor C3 are also connected in parallel to a node I between pin 7 of the optocoupler N2 and pin 2 of the operational amplifier N3-A and a node J between pin 1 of the operational amplifier N3-A and the optocoupler isolation output terminal V_OUT.

2. A bipolar analog signal transmission circuit as claimed in claim 1, characterized in that: Capacitor C2 and capacitor C3 are compensation capacitors.

3. A bipolar analog signal transmission circuit as claimed in claim 1, characterized in that: Resistor R6 is a high-precision, low-temperature drift resistor.

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