Sampling and switching–sampling-type phase-sensitive detectors

Two circuits which accept two sinusoidal waveforms of same frequency with phase difference Ø and provides two dc output voltages in which one dc output voltage is proportional to the quadrature component sin Ø and the another is proportional to the in-phase component cos Ø, by using (1) sampling and (2) switching–sampling techniques, are described in this article. In sampling-type phase-sensitive detector (PSD), a phase-shifted signal VI of peak value VS is sampled by a sampling pulse generated during positive zero crossings of the reference signal VR. Then the sampled output will be VQ = VS sin θ, where θ is the phase difference between VI and VR. This is illustrated graphically in this article. In the switching-type PSD, the need of a 90° phase shifter is eliminated to obtain quadrature component. Verification of the feasibility of circuit configuration is established by way of test results on a proto type.