Since a lock-in amplifier is effectively a high-precision AM demodulator, what are the most critical characteristics for amplifiers in the high-frequency signal chain? Take a 50kHz lock-in circuit for example where 40dB of gain is applied before performing synchronous detection by an AD630 or an ADC for digital mixing with and objective dynamic range >80dB. It is easy to find op-amps with <10nV/√Hz @ 50kHz so noise can be made negligible for a narrow output bandwidth (basically the rational for using lock-in detection). It seems to me that 1/f noise of the system may be dominated by amplifier power supply rejection, gain stability of feedback network, offset drift, etc.
Which amplifier parameters should be optimized in this case where we need to minimize introducing AM noise on a high-frequency narrow-band signal? Will some of these things (such as offset drift) be eliminated entirely by AC coupling?