| Electronics > Projects, Designs, and Technical Stuff |
| Clamping DC Biased Composite Video Signal Back to ground |
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| syntax333:
circuit doesn't seem to work for biased CVBS signal. LM1881 does not trigger as it suppose to. Is this because bias? |
| xavier60:
The bias shouldn't matter because C1 would block the DC. Can you show us the input video waveform? What is the p-p and polarity? |
| syntax333:
Since my CVBS signal is biased 5V and it is 2Vpp overall voltage is approximately 5-7V. I just checked the datasheet of LM1881 which states that for Vcc=5V Input can 3Vpp. So I AC coupled the input and buffered then send to lm1881. Now lm1881 triggers correctly. However, as a buffer I use pnp follower configuration, output of my buffer seems noisy, this causes lm1881 to trigger wrong sometimes. I want to use dedicated buffer (opamp) for cvbs. I have only "MAX457CPA+"or "LMH6704MA" as a buffer. I have never used one before which one do you suggest to use? Unfortunately, I don't have LM6171 at the moment. |
| xavier60:
I don't know, I have only ever used discrete circuitry for amplifying, sync separating and clamping. |
| syntax333:
Your circuit seems interesting I have never tried to extract the sync information with discrete circuitry. |
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