I'm working on project that requires me to convert my single ended RGB signal(VGA from PC) to differential ended RGB. I made this circuit given below the only change that I made was using a 4.7K resistance in place of R2 (4.02K).
I connected my VGA output from PC to connector P1 and left connector P2 open. I observed the signals at the end of my cable (The end that I shall connect to my board) and I wasn't getting proper pulses of Hsync and Vsync till I connected it to my board. I'm using a single 5V supply. So I didn't connect Vs-ve and left it open. I used three jumpers to short:
- Pin 1 of J1 with pin 2 of J1.
- Pin 1 of J2 with pin 2 of J2.
- Pin 1 of J3 with pin 2 of J3.
Then came the problem of observing my output signal which is differential. Now I tried looking for the procedure to observe a differential signal on an oscilloscope. I found out that :
- I'll be needing two channels. One will be connected to the positive output end and the other will be connected to the negative output end.
- I'll be connecting the grounds of my probes to each other and nothing else.
- I'll have to keep both channels on "AC coupling"
But when I did these three things and observed my output at R+ and R- I wasn't getting a proper output.
My questions are:
- Do I need to connect a load to P2 to be able to observe my output?
- What kind of output I should be expecting? I tried googling images of a random RGB signal but I didn't get anything that would give me an idea of what I should be seeing on the oscilloscope.
- Is my testing procedure correct?
- Do I need to connect ground on Vs-ve?