Microcontroller based precision variable-phase phase-shifter

An analog and digital feedback compensation technique employing an active RC all pass filter is described for obtaining a frequency and amplitude independent, drift free phase shift for sinusoidal signals. While the analog feedback for realising the active R is of conventional type, the digital feedback for controlling C is implemented with a modified successive approximation (SA) technique. The implementation of the SA scheme employing discrete digital ICs as well as a microcomputer is described. A prototype built works well over a frequency range of 20 Hz to 50 kHz and has a phase stability of /spl plusmn/0.2.<
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