CN211656211U

CN211656211U - On-vehicle CVBS composite video signal keeps apart filter circuit

Info

Publication number: CN211656211U
Application number: CN202020786382.6U
Authority: CN
Inventors: 盛家进; 印树华; 周伟; 胡智慧
Original assignee: Yangzhou Hangsheng Technology Co ltd
Current assignee: Yangzhou Hangsheng Technology Co ltd
Priority date: 2020-05-13
Filing date: 2020-05-13
Publication date: 2020-10-09
Anticipated expiration: 2030-05-13

Abstract

The utility model discloses a vehicle-mounted CVBS composite video signal isolation filter circuit, which comprises an interface isolation and protection circuit, a low-pass filter circuit and an impedance matching circuit which are connected in series in sequence; the utility model effectively solves the problems of direct current isolation and alternating current coupling of the CVBS signal input structure, and plays a role in blocking and protecting the interface part; the secondary filter circuit ensures the effective bandwidth of 0-10 MHz, ensures the pass band of the CVBS, and simultaneously achieves the bandwidth cut at 28MHz, thereby effectively filtering the interference problem of the non-CVBS; the level of the matching interface circuit can be adjusted, and the requirement of a CVBS decoding chip on the input amplitude of a CVBS can be effectively met; the circuit is simple in structure, high in reliability, excellent in performance, independent of a traditional video isolation IC chip and low in price and cost.

Description

On-vehicle CVBS composite video signal keeps apart filter circuit

Technical Field

The utility model relates to a vehicle-mounted information entertainment system technical field, in particular to filter circuit is kept apart to on-vehicle CVBS composite video signal.

Background

At present, a dedicated video isolation chip is mostly adopted for CVBS signal isolation processing, the CVBS signal isolation processing is influenced by performance parameters of chips, video decoding and displaying effects are different, instability conditions under high and low temperatures and EMC interference exist, a dedicated isolation chip circuit is high in cost, and high-performance chips such as vehicle specifications are quite expensive.

SUMMERY OF THE UTILITY MODEL

The utility model aims at overcoming the prior art defect, providing a filtering circuit is kept apart to on-vehicle CVBS composite video signal, form by traditional electric capacity, inductance, the combination of resistance passive component, parameter adjustment can be done according to the practical application scene to the performance parameter, and the passband width is adjustable, and circuit structure is stable, and the cost advantage is obvious.

The purpose of the utility model is realized like this: a vehicle-mounted CVBS composite video signal isolation filter circuit comprises an interface isolation and protection circuit, a low-pass filter circuit and an impedance matching circuit which are sequentially connected in series;

the interface isolation and protection circuit comprises a first input end CVBS +, a second input end CVBS-, a protection circuit output end, a resistor R1, an electrostatic tube D1 and a capacitor C1, wherein the first input end CVBS + is connected with the protection circuit output end through the capacitor C1, the first input end CVBS + is grounded through the electrostatic tube D1, and the second input end CVBS-is grounded through the resistor R1;

the low-pass filter circuit comprises a low-pass filter circuit input end, a low-pass filter circuit output end, two inductors L1 and L2 connected between the low-pass filter circuit input end and the low-pass filter circuit output end in series, a capacitor C2 connected with an inductor L1 in parallel, a capacitor C3 connected with an inductor L2 in parallel, a capacitor C4, a capacitor C5, a capacitor C6 and a capacitor C7, wherein the low-pass filter circuit input end is grounded through a capacitor C4, one ends of the capacitor C5 and the capacitor C6 are connected between an inductor L1 and an inductor L2, the other ends are grounded, and the space between the inductor L2 and the low-pass filter circuit output end is grounded through a capacitor C7; the input end of the low-pass filter circuit is electrically connected with the output end of the protection circuit;

the impedance matching circuit comprises an impedance matching circuit input end, a resistor R2, a resistor R3, a capacitor C8 and an impedance matching circuit output end, wherein the resistor R2 is connected with the capacitor C8 in series, the impedance matching circuit input end is connected with the impedance matching circuit output end through a resistor R2 and a capacitor C8, and the resistor R2 and the capacitor C8 are grounded through a resistor R3; and the input end of the impedance matching circuit is electrically connected with the output end of the low-pass filter circuit.

As a further improvement of the utility model, the first input end CVBS +, the second input end CVBS-of the interface isolation and protection circuit is connected with the CVBS signal output end.

As a further improvement of the present invention, the impedance matching circuit output is electrically connected to the decoding chip terminal.

As a further improvement of the present invention, the capacitor C1 is an electrolytic capacitor.

As a further improvement of the present invention, the sum of the impedances of the resistor R2 and the resistor R3 is 75 ohms.

When the utility model works, the camera or the video generator outputs the standard CVBS signal and then passes through the interface isolation and protection circuit, and the interface isolation and protection circuit performs interface isolation and ESD protection processing on the CVBS signal; meanwhile, the interface isolation and protection circuit is connected with the low-pass filter circuit to form a low-pass filter circuit, interference of other frequency ranges is filtered on the premise that the pass band of the CVBS is effectively guaranteed, the CVBS is output to the impedance matching circuit through the low-pass filter circuit, the impedance matching circuit adjusts the signal level in an amplitude mode, meanwhile, the impedance matching requirement of a 75-ohm terminal of the CVBS is met, the signal parameter requirement is adjusted according to the CVBS decoding chip, and the CVBS meeting the terminal requirement of the decoding chip is output to be decoded.

Compared with the prior art, the beneficial effects of the utility model reside in that: the utility model effectively solves the problems of direct current isolation and alternating current coupling of the CVBS signal input structure, and plays a role in blocking and protecting the interface part; the interface isolation and protection circuit and the low-pass filter circuit are combined to form a 0-10 MHz low-pass filter network, the secondary filter circuit ensures the effective bandwidth of 0-10 MHz, the pass band of the CVBS signal is ensured, the bandwidth is cut at 28MHz, the interference problem of the non-CVBS band can be effectively filtered, and various interference resistance problems in EMC test are effectively solved;

the voltage resistance of the electrolytic capacitor C1, the protection level of the electrostatic tube D1 and the power of the resistor R1 can be adjusted according to the level protection requirement of the adapter interface, the parameters of R2 and R3 can be adjusted to meet the attenuation of the CVBS signal amplitude, the capacitance capacity and the voltage resistance parameter of the capacitor C8 can be adjusted according to the design requirement of the CVBS decoding chip, and the requirement of the CVBS decoding chip on the CVBS signal input amplitude can be effectively guaranteed;

the circuit is formed by combining traditional capacitors, inductors and resistor passive elements, has a simple structure, high reliability and excellent performance, does not depend on a traditional video isolation IC chip, and has the advantage of lower price cost.

Drawings

Fig. 1 is a control schematic block diagram of the present invention.

Fig. 2 is a schematic circuit diagram of the interface isolation and protection circuit of the present invention.

Fig. 3 is a schematic circuit diagram of the low-pass filter circuit of the present invention.

Fig. 4 is a schematic circuit diagram of the impedance matching circuit of the present invention.

Fig. 5 is an exemplary diagram of an impedance matching circuit when the ADV7180 chip is connected.

Detailed Description

As shown in fig. 1, in the CVBS composite video signal isolation filter circuit for a vehicle, a CVBS signal output by a vehicle-mounted camera includes (CVBS +/CVBS-), and the CVBS signal output by the vehicle-mounted camera sequentially passes through an interface isolation and protection circuit, a low-pass filter circuit, and an impedance matching circuit and then is connected to a CVBS decoding chip.

As shown in fig. 2, the interface isolation and protection circuit includes a first input terminal CVBS +, a second input terminal CVBS-, a protection circuit output terminal, a resistor R1, a static tube D1, and a capacitor C1, the first input terminal CVBS + is connected to the protection circuit output terminal through the capacitor C1, the first input terminal CVBS + is grounded through the static tube D1, and the second input terminal CVBS-is grounded through the resistor R1; the withstand voltage of the electrolytic capacitor C1, the protection level of the electrostatic tube D1 and the power of the resistor R1 can be adjusted according to the level protection requirement of the adaptive interface.

As shown in fig. 3, the low-pass filter circuit includes a low-pass filter circuit input terminal, a low-pass filter circuit output terminal, two inductors L1 and L2 connected in series between the low-pass filter circuit input terminal and the low-pass filter circuit output terminal, a capacitor C2 connected in parallel with the inductor L1, a capacitor C3 connected in parallel with the inductor L2, a capacitor C4, a capacitor C5, a capacitor C6 and a capacitor C7, the low-pass filter circuit input terminal is grounded through a capacitor C4, the capacitor C5 and the capacitor C6 are connected between the inductor L1 and the inductor L2 at one end, and are grounded at the other end, and the inductor L2 and the low-pass filter circuit output terminal are grounded through a capacitor C7; and the input end of the low-pass filter circuit is electrically connected with the output end of the protection circuit.

As shown in fig. 4, the impedance matching circuit includes an impedance matching circuit input terminal, a resistor R2, a resistor R3, a capacitor C8 and an impedance matching circuit output terminal, the resistor R2 is connected in series with the capacitor C8, the impedance matching circuit input terminal is connected with the impedance matching circuit output terminal through a resistor R2 and a capacitor C8, and the resistor R2 and the capacitor C8 are grounded through a resistor R3; the input end of the impedance matching circuit is electrically connected with the output end of the low-pass filter circuit; the parameters of R2 and R3 can be adjusted to meet the attenuation of the amplitude of the CVBS, the capacitance and the voltage resistance of the capacitor C8 can be adjusted according to the design requirements of the CVBS decoding chip, and the requirements of the CVBS decoding chip on the input amplitude of the CVBS can be effectively guaranteed.

When the utility model works, the camera or the video generator outputs the standard CVBS signal and then passes through the interface isolation and protection circuit, and the interface isolation and protection circuit performs interface isolation and ESD protection processing on the CVBS signal; meanwhile, the interface isolation and protection circuit is connected with the low-pass filter circuit to form a 0-10 MHz low-pass filter circuit, interference of other frequency bands is filtered on the premise of effectively guaranteeing a pass-band of the CVBS, the CVBS is output to the impedance matching circuit through the low-pass filter circuit, the impedance matching circuit adjusts the signal level in an amplitude mode, meanwhile, the impedance matching requirement of a 75-ohm terminal of the CVBS is met, the signal parameter requirement is adjusted according to the CVBS decoding chip, and the CVBS meeting the terminal requirement of the decoding chip is output to be decoded. As shown in fig. 5, when the circuit is adapted to a decoding chip to ADV7180, R2=36 ohm, R3=39 ohm, and C8=100 nanofarads, if the decoding chip is selected from other chips, the parameters of R2, R3, and C8 need to be adjusted according to the chip specification requirements, but the impedance requirement of R2+ R3=75 ohm cannot be changed.

The present invention is not limited to the above embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some replacements and transformations for some technical features without creative labor according to the disclosed technical contents, and these replacements and transformations are all within the protection scope of the present invention.

Claims

1. A vehicle-mounted CVBS composite video signal isolation filter circuit is characterized by comprising an interface isolation and protection circuit, a low-pass filter circuit and an impedance matching circuit which are sequentially connected in series;

2. An on-board CVBS composite video signal isolation filter circuit as claimed in claim 1, wherein the first input CVBS +, the second input CVBS-of the interface isolation and protection circuit are connected to the CVBS signal output.

3. The on-board CVBS composite video signal isolation filter circuit of claim 1, wherein the impedance matching circuit output is electrically connected to a decoder chip terminal.

4. The on-board CVBS composite video signal isolation filter circuit as claimed in any one of claims 1-3, wherein the capacitor C1 is an electrolytic capacitor.

5. The on-board CVBS composite video signal isolation filter circuit as claimed in any one of claims 1-3, wherein the sum of the impedances of the resistor R2 and the resistor R3 is 75 ohms.