Presetting circuit for the voltage-controlled oscillator of a phase lock loop

摘要

An improved presettable integrator circuit is disposed in a fast frequency changing phase lock loop for presetting the voltage-controlled oscillator thereof as governed by a preset signal and a pulsed signal generated by a frequency controller. One input of the integrator circuit is coupled to the preset signal, another input is coupled to an integrator control signal, and the output is coupled to the voltage-controlled oscillator for use as a tuning signal thereof. A switch is included in the integrator circuit and is governed in a first state by the pulsed signal to cause the integrator circuit to respond rapidly to an applied preset signal to preset the output signal thereof. In a second state, the switch renders the integrator circuit responsive to an integrator control signal which is selected by a phase lock condition of the loop from either a reference signal or a filtered phase error signal, being coupled to the other input of the integrator circuit. Also disclosed are methods for calibrating the voltage-controlled oscillator of the phase lock loop using the improved presettable integrator circuit when the phase lock loop is selectively governed by one of either a first or second frequency reference source.