THS7347 setting issue

Hi Chang,

For layout guidance, I would size the signal line trace widths to be close to 75ohms for video signals depending upon the top layer material dielectric constant (either FR-4 which is cheap or Rogers RO4350). The pcb layer stack up could be standard 5-layer with top layer - gnd - power supply - gnd - bottom layer.

One important comment would be is if the Monitor or Buffer output pcb trace is > 25mm, it is recommended to place at least a 10ohm resistor in series with each signal (close to THS7347 outputs) to reduce PCB parasitic or coupling issues. Also, I would recommend to separate the signal traces satisfactorily (when routing long distances) to minimize coupling in-between them.

The choice of 0.1uF, 2.2uF and 1uF for RGB signal is purely dependent upon attenuating the lowest frequency content of the video signal (with higher the value of capacitor for a given resistor value , lower the lowest frequency content it passes). I would recommend on using a 1uF ac coupling capacitor as it usually is sufficient to pass RGB signals without sync and 1uF capacitors are usually available now-a-days in the same form factor as 0.1 or 2.2uF. 

In normal ac coupled mode at THS7347 input, the sync signal could be attenuated with either of the mentioned capacitors. But, if you program the THS7347 input channel into AC sync tip clamp mode, the sync signal should be restored at the output. (For example, AC sync tip clamp enabled on the channel that has - Sync on green applied).

Best Regards,

Rohit