S-Video output

Hello everybody

We need to connect the BB to a monitor with a BNC connector and the S-
Video to composite adapters do not work with BB. These adapters have
got a 400 pF capacitor used to mix the chroma signal with the Y one
into a composite signal. Unfortunally it seams S-Video output has not
a 75 Ohm impedance so the simple adapter does not work. Any suggestion
to fix such an issue from an HW point of view (I did already post
asking for a SW help, then I thought there could be a post for the HW
engineer there out...).

Thanks in advance for any help

Ciao,
Ska

Hello everybody

We need to connect the BB to a monitor with a BNC connector and the S-
Video to composite adapters do not work with BB. These adapters have
got a 400 pF capacitor used to mix the chroma signal with the Y one
into a composite signal. Unfortunally it seams S-Video output has not
a 75 Ohm impedance so the simple adapter does not work. Any suggestion
to fix such an issue from an HW point of view (I did already post
asking for a SW help, then I thought there could be a post for the HW
engineer there out...).

Thanks in advance for any help

Why did you conclude the S-Video output is not 75ohm? Is there a manual or
docs that suggests that? Or were you able to do some real measurements with a
VNA? Or did you do the math for parts used per the schematic? Or werre you
able to setup a measurement and see reflections?

What rev of the board are you using?

The quality of the S-Vdeo does seem iffy and would be nice to chase it down.
Just thought maybe you had some datapoints. I know the S-Video output signal
quality is different between a stock C2 and a RevB base on observations. The
C3 change list does mention some changes in this area.

Hi all

We fixed the issue by compiling a new kernel and setting the Omap
output to composite video.

There is not a 75 Ohm output impedance on the Y/C singlas (RevC2).
Three consideration lead to this conclusion
1. A fast glance to the documentation
2. When you connect the output to a oscilloscope, the signal does not
change its amplitude by connecting a 75 Ohm termination
3. When you connect a S-Video to composite adapter it does not work.
This adapter couples the chroma with the luma by using a 390 pF
capacitor. If you have a 75 Ohm out impedance and a 75 Ohm load the
chroma amplitude should be simply devided (from about 200 mv to 100
mv), whereas the chroma amplitute is very low.

Are we missing something?

Ciao,
A.

Hi all

Another issue.

According to OMAP documentation the signal output should be 100 IRE on
PAL that is 1.0Vpp (0.7 V for the signal and 0.3V for the
synchronization) by setting the VENC_GAIN_Y register to 0x140. Instead
the signal is about 66 IRE (0.45 V) and 0.2V the synchronization.
Any explanation for such a behaviour?

Ciao,
Ska