phase sensetive detector

phase sensitive detector described here has two principal applications: a- to produce a d.c out put proportional to- the amplitude of an incoming a,c signal and indicate, by the outut polarity, the phase of the signal with respect to an internal reference. b- to detect the presence of a signal of known phase and frequency which would otherwise be lost in «background noise» and to measure its amplitude. this phase sensitive detector has high linearity over an inpu- range of 10 : 1:up to 100 khz. and besides having a quick response consistent with good rejcetion of quadrature component and interfering frequencies, has excellent long term stability. this circuit could also be used as a modulator