Electronic – How Significant is VGA Impedance Matching


I've seen a multitude of different resistor DAC solutions for a VGA signal, however they almost always have an impedance of >200 ohms per color, e.g.

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when I've been lead to believe that we want to match the 75 ohm input impedance of the VGA destination. How significant is this large difference in impedance? Will the signal reflection effects be more visible on a CRT vs. LCD monitor, or even at all?

For an implementation where number of resistors and obscurity of their values isn't an issue, this can be solved with an R2R ladder DAC:

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where each color output has an effective impedance of 75 ohms.

However for a project where the expectation is that people should be easily able to acquire and construct the circuit, this isn't ideal whatsoever.

Thank you!

Best Answer

Since the monitor end tends to be correctly terminated, you can usually get away with the other end mismatched without getting [too much] ghosting or ringing on the screen.

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