CN110601724B - Weak photoelectric signal anti-interference long-distance transmission system - Google Patents
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Abstract
The invention relates to the field of weak signal detection, in particular to an anti-interference long-distance transmission technology applicable to weak photoelectric signals, wherein a system comprises a U1 photoelectric detector, the photoelectric signals collected by the U1 photoelectric detector are input into a signal preprocessing unit containing a transimpedance amplifying circuit, and the signal output end of the signal preprocessing unit is connected with the input end of a single-ended to differential signal circuit; the main control unit comprises a differential-to-single-ended signal circuit; the single-ended to differential signal circuit is connected with the differential to single-ended signal circuit through twisted pair wires. The technical scheme of the invention converts the weak signals into analog differential signals, and solves the key problem of anti-interference long-distance transmission measurement system weak signals in severe industrial environments. The method has the advantages that the signals are transmitted in a long distance in a balanced transmission mode, the common mode interference can be restrained very strongly, and especially when the system ground wire is complex and serious interference exists, the twisted pair is used for transmitting the analog differential signals, so that the interference can be eliminated effectively.
Description
Technical Field
The invention relates to the field of weak signal detection, in particular to an anti-interference long-distance transmission technology suitable for weak photoelectric signals.
Background
In an industrial field, in an optical signal-based acquisition and measurement system, namely a detection system, parameters of physical quantity change of an optical signal are rapidly and accurately captured, and are the basis and conditions for implementing automatic detection of the optical detection system. In most optical detection systems, the photoelectric detector is always at a certain distance from the main control unit, and if the weak photoelectric current signal collected by the photoelectric detector is directly connected to the main control unit, the signal is very easy to introduce interference on a transmission path, so that the measurement accuracy of the system is seriously deteriorated. Because the current signal output by the detector is weak, the signal must be amplified and transmitted, and the amplification result will cause signal distortion and noise interference signal filtering difficulty.
Disclosure of Invention
The invention aims to provide a circuit which can preprocess weak current signals generated by a photoelectric detector so as to filter most of noise and convert the signals into analog differential signals suitable for anti-interference long-distance transmission.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a weak photoelectric signal anti-interference long-distance transmission system is characterized in that: the system comprises a U1 photoelectric detector, wherein photoelectric signals acquired by the U1 photoelectric detector are input into a signal preprocessing unit, and the signal output end of the signal preprocessing unit is connected with the input end of a single-ended to differential signal circuit; the main control unit comprises a differential-to-single-ended signal circuit; the single-ended to differential signal circuit and the differential to single-ended signal circuit are connected and transmitted by twisted pair;
the signal preprocessing unit comprises a bias voltage generating circuit, a transimpedance amplifying circuit and a gain adjusting circuit, wherein bias voltage Vb generated by the bias voltage generating circuit is connected with an anode of a U1 photoelectric detector, a shell of the U1 photoelectric detector is connected with a ground wire, a cathode of the U1 photoelectric detector is connected with a cathode of an operational amplifier U2A, a capacitor C1 and a resistor R3 which are mutually connected in parallel, an anode of the operational amplifier U2A is connected with the ground wire, a VCCP5VA voltage source is sequentially connected with the capacitor C3 and the ground wire, an input end of the capacitor C3 is connected with the operational amplifier U2A, a VCCN5VA voltage source is sequentially connected with the capacitor C7 and the ground wire, an input end of the capacitor C7 is connected with the operational amplifier U2A, an output end of the capacitor C1 and the resistor R3 which are mutually connected in parallel is connected with an output end 1 pin of the operational amplifier U2A, and an output voltage Vo of the transimpedance amplifying circuit is connected with the gain adjusting circuit;
the bias voltage circuit comprises a resistor R11 connected with a negative power supply voltage VCCN5VA, the output end of the resistor R11 is respectively connected with a capacitor C8, a diode D1 and a resistor R12 which are connected in parallel, wherein the anode end of the diode D1 is connected with the resistor R11, the cathode end of the diode D1 is connected with a ground wire, so that-1.2V voltage can be generated at the anode end of the diode D1, the-1.2V voltage is connected with the resistor R12, the output end of the resistor R12 is connected with the cathode of an operational amplifier U3, a VCCP5VA voltage source is sequentially connected with a capacitor C4 and the ground wire, the input end of the capacitor C4 is connected with the operational amplifier U3, the VCCN5VA voltage source is sequentially connected with a capacitor C9 and the ground wire, the input end of the capacitor C9 is connected with the operational amplifier U3, the anode of the operational amplifier U3 is connected with the output end of the operational amplifier to form a voltage follower circuit, the output end of the operational amplifier U3 is connected with the resistor R8, and the output end of the resistor R8 outputs a voltage Vb as bias voltage.
The technical scheme of the invention converts the weak signals into analog differential signals, and solves the key problem of anti-interference long-distance transmission measurement system weak signals in severe industrial environments. The method has the advantages that the signals are transmitted in a long distance in a balanced transmission mode, the common mode interference can be restrained very strongly, and especially when the system ground wire is complex and serious interference exists, the twisted pair is used for transmitting the analog differential signals, so that the interference can be eliminated effectively.
Drawings
FIG. 1 is a system schematic block diagram of the present invention;
FIG. 2 is a circuit diagram of a signal preprocessing unit;
FIG. 3 is a circuit diagram of a single-to-differential signal;
FIG. 4 is a circuit diagram of a differential to single ended signal;
fig. 5a, 5b are field test comparison diagrams.
In the figure: 10. the photoelectric detector, 20, signal preprocessing unit, 21, transimpedance amplifying circuit, 22, bias voltage generating circuit, 23, gain adjusting circuit, 30, single-end to differential signal circuit, 40, differential to single-end signal circuit,
Detailed Description
Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a technique for gas detection using the principle that laser intensity is absorbed by a gas to be measured to form an absorption spectrum. The method has the advantages of high sensitivity, good selectivity, real-time, dynamic and rapid measurement, multi-component measurement and the like. The gas detection is affected by many factors in the system, one factor is the performance of each functional module of the system, wherein the photoelectric detector is an indispensable component part of the TDLAS system, and is required to be accurately measured in the field of weak signal measurement such as photocurrent.
If the photoelectric conversion is needed TO be carried out on the laser with the center wavelength of 1512nm, the photoelectric detector with the InGaAs material is selected after comprehensive consideration, TO-46 encapsulation is adopted, the detector has strong response TO the light with the wavelength near 1512nm by referring TO the technical parameters, the responsivity is more than 0.9A/W, the high-sensitivity detection can be carried out on the laser carrying ammonia gas, and the output current range of the detector is generally 10 < -3 > TO 10 < -6 > A when different optical powers are irradiated TO the detector according TO the parameters. In the measurement of the weak signal, a small defect of a certain link can seriously deteriorate the measurement precision, and the subsequent preprocessing and transmission conversion circuit of the weak current signal is very critical.
As shown in fig. 1 and 2, the anti-interference long-distance transmission system for weak photoelectric signals provided by the invention is characterized in that: the system comprises a U1 photoelectric detector 10, wherein photoelectric signals acquired by the U1 photoelectric detector 10 are input into a signal preprocessing unit 20, and the signal output end of the signal preprocessing unit 20 is connected with the input end of a single-ended differential signal circuit 30; the main control unit comprises a differential-to-single-ended signal circuit 40; the single-ended to differential signal circuit 30 and the differential to single-ended signal circuit 40 are connected and transmitted by twisted pair wires;
the signal preprocessing unit 20 comprises a bias voltage generating circuit 22, a transimpedance amplifying circuit 21 and a gain adjusting circuit 23, wherein bias voltage Vb generated by the bias voltage generating circuit 22 is connected to the anode of the U1 photoelectric detector 10, the shell of the U1 photoelectric detector 10 is connected to the ground wire, the cathode of the U1 photoelectric detector 10 is connected to the cathode of the operational amplifier U2A, the capacitor C1 and the resistor R3 which are mutually connected in parallel, the positive electrode of the operational amplifier U2A is connected to the ground wire, a VCCP5VA voltage source is sequentially connected with the capacitor C3 and the ground wire, the input end of the capacitor C3 is connected to the operational amplifier U2A, the VCCN5VA voltage source is sequentially connected with the capacitor C7 and the ground wire, the input end of the capacitor C7 is connected with the operational amplifier U2A, the output end of the capacitor C1 and the resistor R3 which are mutually connected in parallel is connected with the pin1 of the output end of the operational amplifier U2A, and the output voltage Vo of the transimpedance amplifying circuit 21 is connected to the gain adjusting circuit 23;
the bias voltage circuit comprises a resistor R11 connected with a negative power supply voltage VCCN5VA, the output end of the resistor R11 is respectively connected with a capacitor C8, a diode D1 and a resistor R12 which are connected in parallel, wherein the anode end of the diode D1 is connected with the resistor R11, the cathode end of the diode D1 is connected with a ground wire, so that-1.2V voltage can be generated at the anode end of the diode D1, the-1.2V voltage is connected with the resistor R12, the output end of the resistor R12 is connected with the cathode of an operational amplifier U3, a VCCP5VA voltage source is sequentially connected with a capacitor C4 and the ground wire, the input end of the capacitor C4 is connected with the operational amplifier U3, the VCCN5VA voltage source is sequentially connected with a capacitor C9 and the ground wire, the input end of the capacitor C9 is connected with the operational amplifier U3, the anode of the operational amplifier U3 is connected with the output end of the operational amplifier to form a voltage follower circuit, the output end of the operational amplifier U3 is connected with the resistor R8, and the output end of the resistor R8 outputs a voltage Vb as bias voltage.
In the above scheme, the U2A amplifier and its peripheral circuit form a transimpedance amplifying circuit connected with the U1 photodetector, when light with a corresponding wavelength is irradiated to the U1 photodetector, the photodetector will output a weak current signal Io, and the circuit can switch in the weak photocurrent Io and flow through the resistor R3 to convert it into a weak voltage output signal Vo: v (V) o ＝I o ·R 3 . In order to meet the detection requirement of high-speed change of optical power, the anode of the U1 photoelectric detector is connected with negative bias voltage Vb, and the negative bias voltage Vb is set to be in a reverse bias state, so that higher switching speed is realized, and the frequency characteristic of the detector is improved. After the D1 voltage stabilizing tube is connected into a voltage source VCCN5VA, the anode of the voltage stabilizing tube outputs-1.2V voltage, and the voltage is output to the positive end of U1 through an isolation follower U3 and used as negative bias voltage Vb, wherein: vb= -1.2V.
The output voltage Vo of the transimpedance amplifying circuit 21 is connected to the positive electrode of the operational amplifier U2B of the gain adjusting circuit 23, the negative electrode of the operational amplifier U2B is connected to the resistor R2, the resistor R5 and the capacitor C2 which are connected in parallel, the output end of the resistor R2 is connected with the ground wire, the output end of the resistor R5 and the output end of the capacitor C2 which are connected in parallel are connected with the pin 7 of the output end of the operational amplifier U2B, and the voltage signal Vsig is output. The circuit function of the scheme is to meet the wider application range of the circuit, the gain adjusting circuit takes the weak voltage signal Vo in the 2 as input, and the peripheral resistors R2 and R5 of the amplifier U2B can be adjusted to obtain the proper output voltage Vsig, and the adjusting formula is as follows:
referring to fig. 3, the single-ended to differential signal circuit 30 includes a resistor R15 connected to a voltage Vsig, an output terminal of the resistor R15 is connected to an anode of the operational amplifier U4 and a resistor R14 and a capacitor C12 connected in parallel with each other, a 2 pin of the operational amplifier U4 is connected to the capacitor C15, an output terminal of the capacitor C15 is connected to a ground line, a1 pin of the operational amplifier U4 is connected to a resistor R18 and a resistor R19 and a capacitor C17 connected in parallel with each other, an output terminal of the resistor R18 is connected to the ground line, an output terminal of the resistor R14 and an output terminal of the capacitor C12 connected to a negative output terminal 5 pin of the operational amplifier U4 and a resistor R16 are connected to an anode of a TVS diode D2, a cathode of the diode D2 is connected to the ground line, an output terminal of the resistor R16 outputs a negative signal Vsig-of a differential signal pair, an output terminal of the capacitor C17 is connected to a positive signal Vsig-of the operational amplifier U4, an output terminal of the capacitor C17 is connected to a positive signal vcs diode D3 anode of the capacitor C4, and an output terminal of the capacitor C16 is connected to a positive signal VCCP of the capacitor C13, and a ground line is connected to the positive signal vcc 13 of the capacitor C4, and a ground line is connected in sequence.
In the scheme, the signal conversion circuit converts the Vsig single-ended voltage signal into a differential pair Vsig-/vsig+ signal, and the differential pair Vsig-/vsig+ signal is transmitted to the circuit main control unit through the twisted pair. The conversion process is performed by the operational amplifier U4 and its peripheral resistance-capacitance to convert a single-ended (unbalanced) signal into a differential (balanced) signal.
In this embodiment, a ±5v dual power supply is used to supply power, and the capacitor C15 is connected to the signal ground through the chip Pin2, so as to set the output common mode voltage vcm=0v. The positive input Pin8 is connected to the single-ended signal Vsig through resistor R15 and to the negative output Pin5 through parallel R14/C12. While negative input Pin1 is connected to ground through R18 and to positive output Pin4 through parallel R19/C17. To ensure balance of the signals, r15=r18, r14=r18 must be made to set gain=r14/R15. In this embodiment, since the Gain adjustment circuit has been added separately in the preceding stage, r14=r15=r18=r19, and gain=1 is set.
When an output signal is transmitted on a twisted pair, a matching resistor R16/R17 (R16 = R17) with a small resistance value is designed at a differential signal output end so that a parasitic capacitance of a circuit is isolated from the amplifier and an impedance matching effect with a high-impedance circuit of a subsequent differential signal receiving end is achieved. Meanwhile, a surge protection circuit is designed at the signal output end, namely, the D2/D3 TVS tubes are respectively connected to the Vsig-/Vsig + output end to realize the surge protection, and meanwhile, the D2/D3 is used together with the front-stage resistor R16/R17, so that the surge protection effect is further improved.
The differential-to-single-ended signal circuit module utilizes a differential signal receiving amplifier to complete the conversion from a differential (balanced) signal to a single-ended (unbalanced) signal so as to meet the signal requirement of a subsequent signal processing circuit, and is described in detail with reference to fig. 4, the differential-to-single-ended signal circuit 40 comprises a differential pair negative signal Vsig-respectively connected to an anode of a diode D8 and a resistor R30, a cathode of the diode D8 is connected with a ground wire, an output end of the resistor R30 is respectively connected to a capacitor C33 and a cathode input end of an operational amplifier U5, an output end of the capacitor C33 is connected with the ground wire, a positive signal vsig+ in the differential pair is respectively connected to an anode of a diode D9 and the resistor R33, a cathode of the diode D9 is connected with the ground wire, an output end of the resistor R33 is respectively connected to a capacitor C37 and an anode input end of the operational amplifier U5, an output end of the capacitor C37 is connected with the ground wire, a voltage source of a voltage of a voltage_ _ 5V is sequentially connected with a capacitor C34 and a ground wire, an input end of the capacitor C34 is connected with the operational amplifier U5, an input end of the voltage source of the capacitor C35 is sequentially connected with the ground wire, an input end of the voltage source of the capacitor C35 is connected with the voltage pin of the voltage pin1 and the voltage pin, and the ground wire is connected with the ground wire, and an output pin1 is connected with the voltage pin 32 is connected with the ground pin 32.
In the above technical scheme, the conversion process from the differential signal to the single-ended signal is completed by the U5 differential signal receiving amplifier and the peripheral resistor-capacitor thereof, and the conversion function from the differential pair Vsig-/vsig+ signal to the Vout single-ended voltage signal is completed.
Similarly, in order to ensure the high-speed signal to be received with high precision and high signal to noise ratio, the differential signal receiving amplifier is very critical in selecting an INA134 differential line receiver produced by TI company, and consists of a high-performance operational amplifier and an on-chip precise resistor. Is well suited for high performance audio applications and has excellent ac performance, including low distortion (0.0005% at 1 kHz) and high slew rate (14V/μs), ensuring good dynamic response. It also has a large voltage swing and high output drive capability allowing for a variety of demanding applications. The chip has completely independent circuits for signal processing at two input ends, and has the lowest crosstalk.
In the circuit shown in fig. 4, the Gain gain=1, vout=vsig+ -Vsig-, and the present embodiment is optimized in the chip peripheral circuit to ensure signal integrity and signal to noise ratio:
1. adding a terminal matching resistor; when the differential signal reaches the receiving terminal along the differential pair, the terminal differential impedance is larger, so that the differential signal is reflected, noise is generated, and the signal quality is affected; the twisted pair cable for differential transmission has a standard characteristic impedance of 100 ohms, and therefore a 100 ohm termination matching resistor R31 is added to the receiving circuit.
2. Surge protection circuit design: the D8/D9 TVS tubes are respectively connected to the Vsig-/Vsig + input ends, and meanwhile, the D8/D9 is used together with the rear-stage resistor R30/R33, so that the surge protection effect is further improved.
3. Serial matching resistor design: in order to reduce the further reflection of differential signals and ensure the signal integrity on a transmission line, a matching resistor R30/R33 (R30=R33) with a small resistance is additionally designed, and a capacitor C33/C37 is additionally designed at the rear stage of the resistor R30/R33 in order to further improve the signal-to-noise ratio of the signals, so that RC low-pass filtering is formed, and high-frequency interference of the signals is filtered.
Signal transmission comparison test:
when the photoelectric detector is used in the actual industrial field, under the condition that other measurement conditions are not changed, the voltage signals output by the photoelectric detector through the transimpedance amplifying circuit are respectively tested and transmitted to the main control circuit unit through a 0.3m short-distance coaxial cable, and the differential signals after the photoelectric detection signals pass through the transimpedance amplifying circuit and the differential conversion circuit are transmitted to the main control circuit unit through a CAT-5 twisted pair with the length of 200 m.
| CH1 Signal Peak | 3.65V-2.65V＝1V | 3.59V-2.59V＝1V |
| Small signal peak-to-peak in CH1 signal | 3.425V-3.025V＝0.4V | 3.325-2.925V＝0.4V |
| Peak-to-peak value of CH2 signal | 1.815V-1.115V＝0.7V | 2.115V-1.415V＝0.7V |
| CH3 Signal Peak | 1.115V-0.315V＝0.8V | 1.105V-0.305V＝0.8V |
Table 1 comparison of test parameters
Fig. 5a is a test chart of 0.3m coaxial cable transmission signals, and fig. 5b is a test chart of 200m twisted pair transmission signals with shielding CAT-5 type. From the test results in fig. 5a, 5b and table 1, it can be seen that, although the 200m band-shielded CAT-5 twisted pair transmission is performed, the analog voltage signal received by the main control unit is less distorted, the amplitude is not obviously reduced, and the signal finally processed and output by the circuit system can be recovered and restored well.
The circuit has the advantages that:
1. the photoelectric detection circuit increases reverse bias voltage, so that the integrity of a weak signal is ensured when the medium-high frequency photocurrent changes;
2. the design of the gain adjusting circuit increases the application range of the circuit, and the circuit system can be applied in almost any expected voltage range;
3. the design of the differential transmission mode is a breakthrough especially for the transmission of medium-high frequency signals, fully considers and ensures the signal integrity and the improvement of the signal-to-noise ratio on the IC selection and the peripheral circuit design, and solves the problem of the transmission of weak photoelectric signals with strong interference resistance in long distance under severe industrial environment.
The differential transmission mode is adopted, twisted pair wires are used as transmission lines, the structure is simple, the cost is low, common mode interference can be well restrained, and the anti-interference performance is high. The photoelectric detection unit and the main control circuit unit can be separated from each other independently, and the power supply system supplies power separately, so that crosstalk between power supplies is greatly reduced, and reliability and integrity of signal transmission are improved.
Claims (4)
1. A weak photoelectric signal anti-interference long-distance transmission system is characterized in that: the system comprises a U1 photoelectric detector (10), wherein photoelectric signals acquired by the U1 photoelectric detector (10) are input into a signal preprocessing unit (20), and the signal output end of the signal preprocessing unit (20) is connected with the input end of a single-ended-to-differential signal circuit (30); the main control unit comprises a differential-to-single-ended signal circuit (40); the single-ended to differential signal circuit (30) and the differential to single-ended signal circuit (40) are connected and transmitted by twisted pair wires;
the signal preprocessing unit (20) comprises a bias voltage generating circuit (22), a transimpedance amplifying circuit (21) and a gain adjusting circuit (23), wherein bias voltage Vb generated by the bias voltage generating circuit (22) is connected with the anode of the U1 photoelectric detector (10), the shell of the U1 photoelectric detector (10) is connected with the ground wire, the cathode of the U1 photoelectric detector (10) is connected with the cathode of the operational amplifier U2A and a capacitor C1 and a resistor R3 which are mutually connected in parallel, the anode of the operational amplifier U2A is connected with the ground wire, a VCCP5VA voltage source is sequentially connected with the capacitor C3 and the ground wire, the input end of the capacitor C3 is connected with the operational amplifier U2A, the output end of the mutually parallel capacitor C1 and resistor R3 is connected with the output end 1 pin of the operational amplifier U2A, and the output voltage Vo of the transimpedance amplifying circuit (21) is connected with the gain adjusting circuit (23);
the bias voltage circuit comprises a resistor R11 connected with a negative power supply voltage VCCN5VA, the output end of the resistor R11 is respectively connected with a capacitor C8, a diode D1 and a resistor R12 which are connected in parallel, wherein the anode end of the diode D1 is connected with the resistor R11, the cathode end of the diode D1 is connected with a ground wire, so that-1.2V voltage can be generated at the anode end of the diode D1, the-1.2V voltage is connected with the resistor R12, the output end of the resistor R12 is connected with the cathode of an operational amplifier U3, a VCCP5VA voltage source is sequentially connected with a capacitor C4 and the ground wire, the input end of the capacitor C4 is connected with the operational amplifier U3, the VCCN5VA voltage source is sequentially connected with a capacitor C9 and the ground wire, the input end of the capacitor C9 is connected with the operational amplifier U3, the anode of the operational amplifier U3 is connected with the output end of the operational amplifier to form a voltage follower circuit, the output end of the operational amplifier U3 is connected with the resistor R8, and the output end of the resistor R8 outputs a voltage Vb as bias voltage.
2. The weak photoelectric signal anti-interference long-distance transmission system according to claim 1, wherein: the output voltage Vo of the transimpedance amplifying circuit (21) is connected to the positive electrode of the operational amplifier U2B of the gain adjusting circuit (23), the negative electrode of the operational amplifier U2B is connected to the resistor R2, the resistor R5 and the capacitor C2 which are connected in parallel, the output end of the resistor R2 is connected with the ground wire, the output end of the resistor R5 and the output end of the capacitor C2 which are connected in parallel are connected with the pin 7 of the output end of the operational amplifier U2B, and the voltage signal Vsig is output.
3. The weak photoelectric signal anti-interference long-distance transmission system according to claim 2, wherein: the single-ended to differential signal circuit (30) comprises a resistor R15 connected with a voltage Vsig, an output end of the resistor R15 is connected with a positive electrode of an operational amplifier U4 and a resistor R14 and a capacitor C12 which are connected in parallel, a pin2 of the operational amplifier U4 is connected with the capacitor C15, an output end of the capacitor C15 is connected with a ground wire, a pin1 of the operational amplifier U4 is connected with a resistor R18 and a resistor R19 and a capacitor C17 which are connected in parallel, an output end of the resistor R18 is connected with the ground wire, an output end of the resistor R14 and an output end of the capacitor C12 which are connected in parallel are connected with a negative output end 5 pin of the operational amplifier U4 and a resistor R16 respectively, an output end of the resistor R16 is connected with an anode of a diode D2, a cathode of the diode D2 is connected with the ground wire, an output end of the resistor R16 outputs a negative signal Vsig-of a differential signal pair, an output end of the capacitor C17 is connected with a positive output end 4 pin4 of the operational amplifier U4 and a resistor R17, an output end of the resistor R17 is connected with an anode of a capacitor D3, an output end of the diode D3 is connected with the ground wire, an output end of the differential signal pair of the resistor R16 is connected with the capacitor C13, and the output end of the capacitor VCCP signal VCCP is connected with the capacitor C13, and the output end of the voltage VCC 13 is connected with the ground wire in sequence.
4. The weak photoelectric signal anti-interference long-distance transmission system according to claim 1, wherein: the differential-to-single-ended signal circuit (40) comprises a differential pair negative signal Vsig-connected with an anode of a diode D8 and a resistor R30 respectively, wherein a cathode of the diode D8 is connected with a ground wire, an output end of the resistor R30 is connected with a capacitor C33 and a cathode input end of an operational amplifier U5 respectively, an output end of the capacitor C33 is connected with the ground wire, a positive signal vsig+ of the differential pair is connected with an anode of a diode D9 and a resistor R33 respectively, an output end of the diode D9 is connected with the ground wire, an output end of the resistor R33 is connected with a capacitor C37 and an anode input end of the operational amplifier U5 respectively, a VCC_ +5V voltage source is connected with a capacitor C34 and the ground wire in sequence, an input end of the capacitor C34 is connected with the operational amplifier U5, a VCC_ -5V voltage source is connected with the capacitor C35 and the ground wire in sequence, an input end of the capacitor C35 is connected with the operational amplifier U5, a pin1 of the operational amplifier U5 is connected with the ground wire, a pin5 of the operational amplifier U5 and a pin 6 is connected with a resistor R32 after being shorted, and an output end of the resistor R32 outputs a voltage signal.
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