[SI-LIST] Re: AC coupling at video circuits
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Roy M <roymesi@xxxxxxxxx>
- Date: Mon, 07 Feb 2011 03:01:19 -0800
Analog NTSC video is encoded into 59.94Hz frames. If you set the
high-pass cut-off frequency too high, you will see a shift in the
reference luminance level across the upper left to lower right diagonal
of each frame.
The coupling capacitor value is determined by the transmission line
impedance for long cables, or the receiver load impedance for localized
circuits. There are video line drivers that use feedback to correct for
a certain amount of DC drift, allowing smaller than normal capacitor
values to be used.
Steve.
Roy M wrote:
> Hi,
> How do I know which is the correct value for AC coupling in video interfaces
> (i mean the cap value)?
> I saw some circuits using 10uF while others use much less... both worked, by
> the way...
> is there some kind of rule of thumb for that issue?
> Regards,
> Roy
>
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Steve Weir
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