[SI-LIST] : Flatpanel VGA questions

Lenny Baledge ([email protected])
Wed, 13 Jan 1999 14:14:30 -0600


My company is currently designing two new VGA products. The first is a
standard isa-based flatpanel driver card. We have a prototype board that we
made and have it working, but we have experienced some random noise in the
picture. The card drives the panel through a 6" flex cable.

Project Notes:
Clock signal is 25mhz for 640x480 and 40mhz for 800x600.
8 data lines
hsync line - once/line
vsync line - once/frame
Clock signal looks ok without panel connected, yet looks much worse when
panel is connected.
Noise can get better/worse by touching/squeezing/moving flex cable.
Noise was greatly reduced when we added a 47ohm series resistor in clock
line, however, it is not completely gone on all units.
4 layer board, internal power/ground plane.

Questions raised are:
Best termination on clock,data,hsync/vsync?
Routing of clock for crosstalk issues?
How best to combat noise inside the PC case and power supply?
Will adding ferites on incoming VCC help any/greatly/little?

The second project takes the analog VGA signal -> digital -> drives flatpanel.
Again, we have a prototype board with noise. Again, we have the same
questions. Although this board has some analog issues which aren't realy SI

Has anyone in the group messed with flat-panel signals? Any suggestions or
observations would be appreciated.

Thanks in advance,

Lenny Baledge

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