A Fully Analog High Performances Automatic System for Phase Measurement of Electrical and Optical Signals

In this paper, we present a high performance, automatic fully analog phase-to-voltage converter (PVC) circuit for phase shift measurements of periodic waveforms and repeated pulsed signals with zero and nonzero mean values. The PVC operation is fully automatic because an internal closed feedback loop guarantees the self-phase alignment (self-locking) between the reference and input signals. The system has been tested by measuring the phase shifts between the electrical signals generated by digital waveform generators and by photodiodes. The PVC output voltage dynamic range is ±10 V, independently from the phase-shift full-scales equal to ±10°, ±1°, and ±0.1°. The increase of the PVC sensitivity, expressed in volts/degree, which can be easily set to about 1, 10, and 100 V/°, is achieved without any amplification of the signal so avoiding the increasing and/or introduction of additional electronic noise to the measurements. As a consequence, for the smallest phase-shift full-scale equal to ±0.1°, the proposed PVC circuit is capable to achieve phase resolutions in the order of 0.0001°, a value one order of magnitude better than that one of commercial lock-in amplifiers. In the case of optical applications, the PVC is able to detect laser power variations with sensitivity values settable to about 6, 60, and 600 V/μW so achieving the best resolution of 16 pW.