This is a question stemming from this one where I search for the root cause of AD725 displaying wrong colors. Current step have shown that I must be out of the spec for the input of the chip: my RGB video signal is 1 Vpp (while AD725 accepts max 0.741 Vpp - and that's why CXA1645 shows perfect pic and AD725 may go crazy).
I can follow the reference circuit in the datasheet on page 12 lower part putting 470 pF caps in series on input and making opamps gain of 0.741 and putting decoupling caps on outputs which are to be connected to AD725. But:
- prefer +5V or +12V supply only circuit;
- can not find AD8073 or similar opamp available to use;
- circuit must not affect input wires as much as possible (they go further to other parts of the board), thus this solution does not look good.
Is there any more suitable circuit to do the task? Dot frequency is 25 MHz (PAL/NTSC). There're 2SC1815 transistors in the video signal conversion circuit in one of the other circuits attached to RGB lines, thus these transistors may do the task.
I am strong in digital stuff, but must improve in analog...