Robert S Wechsler, Age 7470 Donald Dr, New Rochelle, NY 10804

4845685, Jul 4, 1989

Jul 17, 1987

7/074658

Robert E. Wechsler - Great Neck NY
Joseph A. Horch - Melville NY

Unisys Corporation - Blue Bell PA

G01S 968

367 97

A digital phase-locked loop provides substantially real-time measurements of frequency differences between an applied input signal and a reference signal. The system is especially adapted for the measurement of Doppler frequency shift in a Doppler sonar detection system. A two phase clock receives a reference signal and generates complementary clock signals. A phase-frequency detector receives an applied input signal containing a frequency shift and a further reference signal derived and applied in closed loop fashion. Frequency and phase discrepancies between the applied input signal and a second reference signal are gated to a counter to increment the frequency count or blank the frequency count for a predetermined period, thereby to synchronize the second reference signal with the applied input signal in frequency and phase. The frequency difference is detected by counting pulses gated into a divide by N counter thereby to advance or retard the phase of the second reference signal to match the incoming signal under observation. Since no filtering or integration is required, the circuit obtains loop lock within one cycle of the input frequency.