Transition detection circuit for psk signals using the saw chirp-z

Abstract

This disclosure relates to a circuit for detecting the phase transitions in a PSK signal in the presence of a stronger CW signal. A SAW transform circuit carries out 'piecewise' Chirp-Z transformations of the PSK and CW signals so as to achieve a separation of the same in the time domain. A gate and a pulse width discriminator are both coupled to the output of the Chirp-Z transform circuit. The discriminator rejects all signals except the transformed phase transitions of the PSK signal. The output of the discriminator is utilized to periodically enable the gate for short durations (e.g., 2nsec.) to selectively pass the transformed PSK signal including transformed phase transitions thereof. The gated output is delivered to a dual channel SAW differential delay line whose two channels are of different lengths to provide a predetermined amount of delay (t) therebetween (t.ltoreq.PSK bit duration). A comparator serves to compare the output signals of said two channels and when they differ it produces an output pulse. A counter serves to count the output pulses from the comparator.