Pro: Ultra-broadband, excellent phase and amplitude balance
Con: requires 2xLO frequency, lag resulting in phase difference as the result of the NOR gate on one flip-flop
For a perfect quadrature phase shift, it is difficult to beat a digital phase splitter. The circuit is very simple – it just takes a double rate clock and switches one output on the rising edge, and one of the falling edge. The result is two outputs that are in quadrature with each other. It is implemented with two D flip-flops with the inverted signal connected to the input.
This is then fed into a representation of MUX logic that would allow a signal to be sampled at 4 times per cycle of the incoming signal. This is typically done with capacitors, which hold the charge voltage long enough to be sent to an op-amp.
