We herein formulate the concept of a generalized lock-in amplifier for the
precision measurement of high frequency signals based on digital cavities.
Accurate measurement of signals higher than 200 MHz using the generalized
lock-in is demonstrated. The technique is compared with a traditional lock-in
and its advantages and limitations are discussed. We also briefly point out how
the generalized lock-in can be used for precision measurement of giga-hertz
signals by using parallel processing of the digitized signals