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Testing Triple Differential Driver AD 8147

Question asked by MavenM on Oct 12, 2015
Latest reply on Oct 16, 2015 by MavenM

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).

AD8147 Board.PNG

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:

 

1. Pin 1 of J1 with pin 2 of J1.

2. Pin 1 of J2 with pin 2 of J2.

3. 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 :

 

1. 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.

2. I'll be connecting the grounds of my probes to each other and nothing else.

3. 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:

 

1. Do I need to connect a load to P2 to be able to observe my output?

2. 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.

3. Is my testing procedure correct?

4. Do I need to connect ground on Vs-ve?

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