Electronics > Projects, Designs, and Technical Stuff
Level shifting
syntax333:
Correct me if I am wrong , Clamper circuits are for limiting voltage right? how does it help me to DC shift the signal? I didn't get that part. The waveform that I am trying to achieve is in attachment.
Edit: Okay I get the point. You mean "keyedclamping.png" circuit.
Benta:
Exactly. This is how it's done in all the video circuits I've seen, except it's usually deeply embedded in the video processors. The LM1881 is an exception as stand-alone IC.
The simplest is clamping on the sync tips, where the switch is controlled by the CSOUT signal, a bit more complicated is using the BPOUT for clamping on black/blank.
syntax333:
What is the main difference between clamping using CSOUT and BPOUT? Is there any specific reason to use BPOUT to clamp since it is more complicated?
Benta:
Sync tips are not always correct in amplitude. Black/blank is the reference level in a CVBS signal and preferable. It's a question of signal integrity and precision.
That being said, you probably won't notice any visual difference when looking at the video.
As vk6zgo said, you need to be careful not to mess with the colour burst when choosing black/blank clamping.
syntax333:
I think safest option for me to go is sync tips since I am not experienced about CVBS. So I have two final questions?
1. Is it enough to simply connect the lm1881 CSOUT pin to key to achieve DC biasing? or do I need any additional circuitry?
2. Can you recommend Analog Switch alternatives to DG419B?
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