A circuit for constant phase shift using a narrow pulse duty cycle all-pass filter

A technique for providing constant phase shift irrespective of frequency for sinusoidal signals is presented. The system contains a loop with a narrow pulse duty cycle all-pass switching filter whose phase shift is regulated by the switching frequency. By using narrower switching pulses and a higher switching frequency, the quality of the sine wave output and the phase accuracy is improved. Experimental results verify the theoretical analysis of the closed-loop system behavior