So here is the deal: I am driving a polarization rotator to attenuate light. The polarization rotator takes a 3-5kHz AC signal, they suggest a square wave. I have a frequency generator chip that can generate a 2Vpp signal, but I want something a signal of 0Vpp-10Vpp (though most of the extinction happens around 5V). At my disposal, I have DAC that I can run with labview, and it will generate any DC voltage from 0-10V. If this were a DC problem then I would simply configure the a differential amplifier to use a 0-2V DAC voltage to subtract the other signal (so the total signal can be anywhere from 0-2V), and then amplify with a gain of 5. However, I am not quite sure what to do with the mixed DC/AC signals. So in summary, I am given a 2V square wave, and I want to control its amplitude with a DAC. Could I AC couple the DC signal, such that I could still use the idea of the differential amplifier to amplify the square wave to the desired value? If so, I don't really know anything about AC coupling, do you just put a capacitor to ground such that the impedence matches the impedance of the resistor next to it (what it looks like from Horrowitz and Hill)?