Re: Luma signal delay

Hi!,


On 2020. 01. 14. 16:48, Istvan Hegedus wrote:
> Hi All,
> 
> Does anyone have a good suggestion how could I delay the analog luma
> signal with approximately 90-100ns? I am trying to connect an AD725 to
> the RF modulator and that bloody RF modulator delays the chroma signal
> too much. I would like to get them to sync.

Such trick is at least used in analog color TV sets. With the
introduction of a modulated composite color signal, luma and chroma
inherently slip from each other by some-100 ns after the U/V
demodulation step (and further group delays can be introduced by the
different bandwidth of Y and U/V). To compensate for that, luma needs to
be slightly delayed. In older TV sets, they usually use circuits built
around "series L / parallel C" type luma delay lines. (One can still
find such analog delay lines (of some-10 to some-100 ns nominal delay
values) in component catalogs, the question would be, IMHO, the circuit
that incorporates them). Later (but still analog) TV sets probably have
that function integrated into some video signal processor chip.

BTW, do I understand correctly that the delay is explicitly introduced
by the RF modulator, that is - there's "no delay" at the output of the
AD725, and "there is" already delay at the point the luma and chroma
signal (baseband signals just as they are), leave the RF modulator?


Best regards,


Levente