How to invert a sine wave so that the output is 180 degrees out of phase with the input?
The inverting amplifier is one of the first op-amp circuits you should learn:



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If Rf = Ri, the gain will be -1.

This circuit is probably good up to 100's of MHz, if you choose the right op-amp. You'll want to watch out for both the gain-bandwidth product and the slew rate specs to find the right op-amp.