CN109802748B - High-immunity differential camera signal processing circuit - Google Patents
High-immunity differential camera signal processing circuit Download PDFInfo
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- CN109802748B CN109802748B CN201910201047.7A CN201910201047A CN109802748B CN 109802748 B CN109802748 B CN 109802748B CN 201910201047 A CN201910201047 A CN 201910201047A CN 109802748 B CN109802748 B CN 109802748B
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Abstract
The high-noise immunity differential camera signal processing circuit comprises a resistor R1, a capacitor C2 and a resistor R3, wherein one end of the resistor R1 is connected with the positive electrode of an output signal of a camera, the other end of the resistor R1 is connected with one end of the resistor R2 and one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the other end of the resistor R2 is connected with the negative electrode of the output signal of the camera, the other end of the capacitor C2 and one end of the resistor R5, the other end of the resistor R5 is connected with one end of the resistor R6 and one end of the capacitor C4, the other end of the resistor R3 is connected with one end of the resistor R4 and one end of the capacitor C3, the other end of the resistor R4 is connected with the other end of the resistor R6 and grounded, and the other ends of the capacitor C3 and the capacitor C4 are respectively connected with the positive electrode and the negative electrode of the signal sampling end of the video decoding chip. The invention can effectively inhibit common mode interference and electromagnetic interference of the vehicle body of the differential or pseudo-differential camera, has low cost, simple and convenient parameter adjustment and high reliability, and is suitable for automobile electronic products.
Description
Technical Field
The invention relates to the technical field of electricity, in particular to an electrical appliance for an automobile, and particularly relates to a high-immunity differential camera signal processing circuit.
Background
In the prior art, cameras are increasingly used on automobiles, wiring harness networks on automobiles are complex, electromagnetic environments are severe, camera signals are very easily affected by wiring harness arrangement and electromagnetic interference, and water ripple or jitter phenomenon is often caused on pictures. Therefore, an input signal processing circuit with strong interference resistance is required to ensure that the image display is normal.
At present, the following camera input network circuits are commonly used:
the single-ended camera inputs to the network circuit. The scheme has simple circuit but poor anti-interference performance, and particularly when common mode interference exists on a local line, water ripple can appear on a display picture.
The pseudo-differential camera inputs to the network circuit. The scheme is scheme->The ground wire common mode interference problem is solved, but when electromagnetic interference exists on the vehicle, particularly when BCI (Bulk Current Injection, vehicle-mounted visual reversing system) exists, water ripple or screen shaking phenomenon can occur on the picture.
The differential camera inputs to the network circuit. The scheme and scheme->Compared with the prior art, the display picture has clear quality, but when the BCI exists, the picture has water ripple or screen shaking phenomenon, and is only suitable for the output type of the differential camera.
An application specific integrated processing chip. Scheme->Scheme->And protocol->In contrast, dedicatedThe filtering and anti-interference performance of the integrated processing chip is improved, but the cost is higher.
Disclosure of Invention
The invention aims to solve the technical problem of providing a signal processing circuit which can avoid common mode interference and electromagnetic interference of a vehicle body existing on a camera ground wire, and has the advantages of low cost, high reliability and strong stability.
In order to solve the technical problems, the technical scheme of the invention is to provide a high-immunity differential camera signal processing circuit, which is characterized in that: the camera comprises a resistor R1, wherein one end of the resistor R1 is connected with an output signal positive pole CVBS+ of a camera, one end of a capacitor C2 and one end of a resistor R3, the other end of the resistor R1 is connected with one end of the resistor R2 and one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the output signal cathode CVBS-, the capacitor C2 other end and the resistor R5 one end of camera are connected to the resistor R2 other end, resistor R6 one end and capacitor C4 one end are connected to the resistor R5 other end, resistor R4 one end and capacitor C3 one end are connected to the resistor R3 other end, the resistor R4 other end with the resistor R6 other end is connected and ground, video decoding chip signal sampling end positive electrode AN1 is connected to the capacitor C3 other end, video decoding chip signal sampling end negative electrode AN2 is connected to the capacitor C4 other end.
Preferably, the resistors R1 and R2 are end matching resistors, and the sum of series resistance values of the resistors R1 and R2 is equal to the output impedance of the external camera.
Preferably, the resistors R1 and R2 are used for eliminating signal reflection in the cable of the camera, so as to ensure that the output signals of the camera can be transmitted to the subsequent stage circuit.
Preferably, the resistor R1 is used for eliminating signal reflection in the cable of the camera, so as to ensure that the output signal of the camera can be transmitted to the subsequent stage circuit.
Preferably, the capacitor C1 is a filter capacitor, and is configured to filter out a ground interference signal on the output signal negative CVBS-terminal of the camera.
Preferably, the resistor R2 is used to equalize the differential monitor voltage, so as to eliminate common mode voltage interference on the output signal negative CVBS-terminal of the camera.
Preferably, the capacitor C2 is configured to absorb differential mode signal interference between the positive cvbs+ output signal of the camera and the negative CVBS output signal of the camera.
Preferably, the resistor R3 and the resistor R4 form a voltage division network, and the resistor R5 and the resistor R6 form a voltage division network, so that the signal of the positive electrode cvbs+ of the output signal of the camera is divided into a range which can be born by a later stage video decoding chip, and transient pulse voltage is restrained, current is reduced, and the later stage video decoding chip is protected.
Preferably, the resistors R3, R4, R5, R6 are resistors of the same error.
Preferably, the capacitors C3 and C4 are AC decoupling capacitors for eliminating dc bias voltage of the input video signal.
Preferably, when the output signal positive electrode cvbs+ of the camera or the output signal negative electrode CVBS-of the camera is shorted to the battery voltage, "resistor R3, resistor R4 and capacitor C3" or "resistor R5, resistor R6 and resistor C4" can reduce the voltage and current input to the next stage video decoding chip, effectively protecting the video decoding chip.
Compared with the prior art, the high-immunity differential camera signal processing circuit provided by the invention has the following beneficial effects:
1. common mode interference existing at the negative end of the camera can be effectively restrained;
2. electromagnetic interference of the BCI differential mode vehicle body can be effectively inhibited;
3. the method is suitable for both differential cameras and pseudo-differential cameras;
4. the design of discrete components is adopted, the cost is low, the design is flexible, and the parameter adjustment is simple and convenient;
5. the automobile component is selected, so that the reliability is high, the stability is strong, and the automobile electronic product is suitable.
Drawings
Fig. 1 is a schematic diagram of a signal processing circuit of a differential camera with high noise immunity according to the present embodiment;
fig. 2 is a diagram illustrating an application example of the high noise immunity differential camera signal processing circuit according to the present embodiment.
Detailed Description
Fig. 1 is a schematic diagram of a signal processing circuit of a high-immunity differential camera provided in this embodiment, where the signal processing circuit of the high-immunity differential camera includes resistors R1 to R6 and capacitors C1 to C4, one end of the resistor R1 is connected to an output signal positive electrode cvbs+ of the camera, one end of the capacitor C2 is connected to one end of the resistor R3, the other end of the resistor R1 is connected to one end of the resistor R2 and one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the other end of the resistor R2 is connected with AN output signal cathode CVBS-, the other end of the capacitor C2 and one end of the resistor R5, the other end of the resistor R5 is connected with one end of the resistor R6 and one end of the capacitor C4, the other end of the resistor R3 is connected with one end of the resistor R4 and one end of the capacitor C3, the other end of the resistor R4 is connected with the other end of the resistor R6 and grounded, the other end of the capacitor C3 is connected with AN anode AN1 of a signal sampling end of a video decoding chip, and the other end of the capacitor C4 is connected with a signal sampling end cathode AN2 of the video decoding chip.
The resistors R1 and R2 are terminal matching resistors, and the sum of series resistance values of the resistors R1 and R2 is equal to the output impedance of the external camera. Since the output impedance of the differential camera is usually 75Ω, in this embodiment, the resistance of the resistor R1 and the resistance of the resistor R2 are both 37.5 Ω. The resistor R1 and the resistor R2 are used for eliminating signal reflection in the cable of the camera, ensuring that output signals of the camera can be transmitted to a next-stage circuit, reducing signal reflection loss and improving transmission efficiency.
The capacitor C1 is a filter capacitor and mainly filters out ground wire interference signals on the negative CVBS-terminal line of the output signal of the camera.
Meanwhile, the resistor R1 and the resistor R2 enable differential monitoring voltages to be equal, and common-mode voltage interference of an output signal cathode CVBS-end of the camera is effectively eliminated.
The capacitor C2 can effectively absorb differential mode signal interference of the positive electrode CVBS+ of the output signal of the camera and the negative electrode CVBS-of the output signal of the camera, is particularly obvious in eliminating interference signals with the frequency being more than 1MHz, and can effectively improve EMC BCI interference.
The resistor R3 and the resistor R4 form a voltage division network, and the signal of the positive pole CVBS+ end of the output signal of the camera can be divided into a range which can be born by a later stage video decoding chip. Meanwhile, transient pulse voltage can be restrained, current can be reduced, and a later-stage video decoding chip can be protected.
Resistor R5 and resistor R6 also form a voltage divider network that functions similarly to resistor R3 and resistor R4. For better display performance, the resistors R3, R4, R5, R6 should be resistors with the same error, and the error rate should be as low as possible, so as to avoid image distortion.
The capacitors C3 and C4 are AC decoupling capacitors, and can cancel the dc bias voltage of the input video signal. When the positive electrode CVBS+ of the output signal of the camera or the negative electrode CVBS-of the output signal of the camera is short-circuited to the battery voltage, the resistor R3, the resistor R4 and the capacitor C3 or the resistor R5, the resistor R6 and the resistor C4 can reduce the voltage and the current input to the next-stage video decoding chip, and the video decoding chip is effectively protected.
Fig. 2 shows an application example diagram of the high-immunity differential Camera signal processing circuit provided in this embodiment, where positive cvbs+ and negative CVBS-output signals of the Camera are respectively connected to positive and negative output ends of the differential Camera. The positive and negative poles AN1 and AN2 of the signal sampling end of the Video decoding chip are respectively output to the positive and negative input ends of the Video decoder of the Video decoding chip. R7 and R8 are output impedance of the differential camera.
Experiments show that the high-immunity differential camera signal processing circuit provided by the embodiment can effectively inhibit common mode interference and BCI differential mode car body electromagnetic interference existing at the negative end of the camera, and has the advantages of simple and convenient parameter adjustment, high reliability and strong stability.
While the invention has been described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and additions may be made without departing from the scope of the invention. Equivalent embodiments of the present invention will be apparent to those skilled in the art having the benefit of the teachings disclosed herein, when considered in the light of the foregoing disclosure, and without departing from the spirit and scope of the invention; meanwhile, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present invention still fall within the scope of the technical solution of the present invention.
Claims (2)
1. The utility model provides a high immunity difference camera signal processing circuit which characterized in that: the camera comprises a resistor R1, wherein one end of the resistor R1 is connected with an output signal positive pole CVBS+ of a camera, one end of a capacitor C2 and one end of a resistor R3, the other end of the resistor R1 is connected with one end of the resistor R2 and one end of the capacitor C1, and the other end of the capacitor C1 is grounded; the other end of the resistor R2 is connected with AN output signal cathode CVBS-, the other end of the capacitor C2 and one end of the resistor R5, the other end of the resistor R5 is connected with one end of the resistor R6 and one end of the capacitor C4, the other end of the resistor R3 is connected with one end of the resistor R4 and one end of the capacitor C3, the other end of the resistor R4 is connected with the other end of the resistor R6 and grounded, the other end of the capacitor C3 is connected with a signal sampling end positive electrode AN1 of a video decoding chip, and the other end of the capacitor C4 is connected with a signal sampling end negative electrode AN2 of the video decoding chip;
the resistors R1 and R2 are terminal matching resistors, and the sum of series resistance values of the resistors R1 and R2 is equal to the output impedance of the external camera; the resistor R1 and the resistor R2 are used for eliminating signal reflection in a camera cable and ensuring that an output signal of the camera is transmitted to a subsequent circuit; meanwhile, the resistor R1 and the resistor R2 make the differential monitoring voltages equal, and common mode voltage interference of an output signal cathode CVBS-end of the camera is eliminated; the resistor R3 and the resistor R4 form a voltage division network, the resistor R5 and the resistor R6 also form a voltage division network, the signal of the positive pole CVBS+ end of the output signal of the camera is divided into the range born by the video decoding chip at the rear stage, and meanwhile, transient pulse voltage is restrained, current is reduced, and the video decoding chip at the rear stage is protected; resistors R3, R4, R5 and R6 are resistors with the same error; the capacitor C1 is a filter capacitor and is used for filtering ground wire interference signals on the negative CVBS-terminal line of the output signal of the camera; the capacitor C2 absorbs differential mode signal interference of an output signal anode CVBS+ of the camera and an output signal cathode CVBS-of the camera; the capacitors C3 and C4 are AC decoupling capacitors for canceling the dc bias voltage of the input video signal.
2. The high noise immunity differential camera signal processing circuit of claim 1, wherein: when the positive electrode CVBS+ of the output signal of the camera or the negative electrode CVBS-of the output signal of the camera is short-circuited to the battery voltage, the resistor R3, the resistor R4 and the capacitor C3 or the resistor R5, the resistor R6 and the resistor C4 can reduce the voltage and the current input to the next stage video decoding chip, and the video decoding chip is effectively protected.
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| CN201910201047.7A CN109802748B (en) | 2019-03-18 | 2019-03-18 | High-immunity differential camera signal processing circuit |
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