/diy/ - Do It Yourself

>>1404266
Why not just use a discrete transistor based diff amp? Fast transistors with gain bandwidth products of several hundred MHz to over 1GHz are cheap. This amplifier isn't all that different to the differential amp in the front end of an op-amp the only real difference with the major difference being it lacks the power amplifier integrated in the output stage of most op-amps so it can't source much current. Don't try to drive low impedance loads with it. The reason it performs so much better than an op-amp is due to the lack of dominant pole compensation which makes an op-amp more stable but severely reduces the bandwidth. Another trade off is because it's all discrete components matching between components will be pretty poor.

Anyway this circuit seems to work okay in simulation though you might need to tweak it a bit for your specific application. I'd buffer the inputs and output too since I didn't take much care to make the inputs particularly high impedance nor the output particularly low impedance. It should work with DC as well as AC and seems to handle 500kHz sine and square waves alright.