In Reply to: Re: log-antilog multiplier posted by xwindy on 01/06/03 at 6:09 PM:
There's some discussion on lock-in amplifiers in 'Art of Electronics', Horowitz and Hill.
If I recall correctly, one of the waveforms used in the multiplier is just a squarewave, so the other waveform is alternately multiplied by +1 and -1. This can be done by a Gilbert cell, or by using an analog switch (e.g. 4066 or similar). With the analog switch, the signal waveform is alternately passed through non-inverted (effectively multiplied by +1) and inverted (effectively multiplied by -1); the switch is controlled by the reference signal.
Hopefully, this will give you some clues.