Difference Between Pseudo Differential CVBS and Fully Differential CVBS

Document created by Rob.Analog Employee on Jul 14, 2014
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Pseudo differential CVBS and true differential CVBS can both be used to remove common-mode noise. Both systems should be as effective at removing common-mode noise.

 

The advantage of Pseudo differential CVBS is that you do not need to use external circuitry to generate the pseudo differential CVBS source. You just use a signal cable and a camera ground cable closely coupled together. This setup is more popular as it is cheaper to implement.

The camera ground cable will act as an antenna to absorb any EMI in the environment. It should be kept close (or wrapped around) the signal cable so that they both absorb the same amount of EMI. This EMI can then be removed in the head unit by an OPAMP circuit or by an ADI video decoder with a differential analog front end (e.g. ADV7182, ADV728x, ADV748x).

Note:

Do not connect the camera ground cable to the ground of the video decoder.

Do not connect the camera ground cable to the shield of the cables.

Do not connect the camera ground directly to the chassis ground of the car. Large coupling capacitors should be used to prevent noise in the chassis leaking into the camera ground.

 

The advantage of fully differential CVBS is that two signals that are inverse copies of each other are used. This allows common mode noise can be removed at the video decoder (just like pseudo differential) . It also means that the EMI generated by fully differential signals will be 180 degrees out of phase with each other and will cancel. Therefore fully differential systems will not act as a source of EMI to other electronics in the car.

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