Characterisation of a phase-sensitive detector

The phase-sensitive detector (PSD) operating particularly as a synchronous rectifier has an important role in many benchtop instruments, typical of which is the modern LCR component meter. The performance of the PSD determines the accuracy and frequency range of the overall instrument. Its characterisation by direct methods is particularly difficult to achieve by virtue of the necessity for an accurate knowledge of the relative phase between sine and switching waveforms at the PSD. The authors offer an alternative approach to characterisation of the PSD that circumvents the need for direct phase measurements. It calls for the use of a purpose designed sine-square generator which is relatively easy to achieve with today´s technology. PSDs in the form of a buffered voltage-switching circuit and a track/hold circuit are examined in some detail. A statistical analysis is provided for the error bounds expected in the phase estimates. The work described can be readily adapted to improvements in phase measurement in existing LCR component meters. A technique called adaptive reference phase is introduced for this purpose.