Hello,
we are facing a problem with TVP5151: the decoded image contains "flashes" (bursts with corrupted luminance) that cannot be observed when AGC is disabled or frozen.
I must say, the signal fed into the TVP is a bit "malformed", that is, it contains a relevant DC component (which should not be a problem, due to the input capacitor) and the relative zero (i.e., the bottom of sync pulse) is unstable, slightly floating. Unfortunately, this is what we have to deal with - we have no control over the video source.
We found a temporary solution by scaling down the signal level using a resistor divider of 150/37.5 instead of 37.5/37.5, forcing the AGC to use higher gains - but this increases the noise and might be not compatible with other video sources.
The problem can be seen also using the evaluation board, so we tend to exclude hardware issues like layout or component values. It seems that the AGC tries to cope with the variations of the input signal, generating visible luminance bursts in the converted signal.
I'm wondering if there is a way to fine tune the behaviour of the AGC in the TVP5151, to slow down its response or to adjust the filtering scheme. FYI, I've tried with other low-end devices (from other manufacturers) and the problem doesn't exist.
We are approaching the release of the product, but we still have a chance to use a different device with a more performing/resilient AGC. Any suggestion is really appreciated.
Regards,
Stefano Voulaz