Abstract: The acquisition of phase lock to a reference frequency by a signal acquisition system is accomplished using a voltage controlled oscillator, a wideband frequency discriminator, a prepositioning circuit, and a phase lock loop. The voltage controlled oscillator is prepositioned within a loop bandwidth of the reference frequency by the prepositioning circuit and the wide band frequency discriminator which provide coarse tuning. The voltage controlled oscillator achieves phase lock with the reference frequency when it receives the fine tune signal from the phase lock loop. Using both the discriminator and the phase lock loop allows fast acquisition without the need to calibrate the voltage controlled oscillator. Since the discriminator pull-in range is much larger than the phase-lock loop bandwidth, the number of bits can be much smaller than in an acquisition circuit using a digital prepositioning circuit alone.

Abstract: A digitally controlled microwave phase lock loop for switching rapidly from one lock frequency to another is disclosed. A digital word corresponding to a desired input voltage for a selected frequency is converted to an analog voltage for application to the coarse tuning port of the loop's voltage controlled oscillator. Prior to switching to another frequency, the error voltage for the fine tuning port is compared with a zero error reference voltage. The least significant bit of the digital word for such frequency is increased or decreased by one depending on the direction difference between the compared voltages. This incrementally changed word controls the coarse tuning voltage during the next selection of the particular frequency. The system is initialized by repetitively selecting each of the possible frequencies until the digital word for each selected frequency is within one increment of the zero error reference voltage for the fine tuning port.