# Opamp, Amplify square wave or video

Suppose I have a digital signal, or at least a signal that is gnd referenced. Like a NTSC video signal for instance like this:

Then I have a single supply opamp, and I want to amplify this by 2x say. I think that if I just input this to a simple opamp circuit with 2x gain that my signal will clip because it will be amplified around my virtual GND.

So then instead I have to add a DC offset probably equal to my virtual gnd voltage so I can amplify without clipping? I think I understand that to be true but maybe my understanding is wrong.

Then my last question is after I've done this and amplified the signal the output is going to be centered around my virtual gnd voltage. So how do I get my signal back to DC (assuming my receiver is not AC coupled and he expects levels referenced to 0V DC). I can't just subtract the DC offset, since my signal amplitude will vary I don't know the right amount to subtract.

I've read a little bit about DC restoration circuits, but I'm not sure if I'm on the right path or not.

• If you use an op-amp with rail-to-rail input, you should be able to just use ground as the reference level. The sync level might not be precisely preserved but I expect that isn't critical to reproducing the image. Mar 12, 2015 at 16:52
• If I am not understanding this incorrectly, one idea might be use a feedback with a Clamper circuit. Mar 12, 2015 at 16:56
• @ThePhoton Ah so I didn't understand this about rail to rail opamps, but I'm learning. I just did a sim with a TI OPA344 and a sin wave and that did work. Mar 12, 2015 at 17:51