Patent ID: 6476681
Filing Date: 2002-11-05
Classification: H03L,Y10S

Abstract:
Adjustable bandwidth phase-locked loop circuitry comprising:a phase-locked loop circuit including a first input node receiving an input signal having a first frequency, a second input node receiving a feedback signal, an error signal output node which has a signal indicative of an error signal characterizing a frequency error between the input signal and the feedback signal, and a bandwidth control signal output node configured to generate a bandwidth control signal when a lock is acquired between the input signal and the feedback signal; a voltage controlled oscillator, coupled to said second input node, receiving the error signal and generating the feedback signal wherein the feedback signal has a frequency that tracks the first frequency; a bandwidth control signal receiving element operating to receive the bandwidth control signal generated within the phase-locked loop circuit; a variable loop filter, coupled between the phase-locked loop circuit and the voltage controlled oscillator, the variable loop filter including a narrowband filter, a wideband filter, and a switch, the switch configurable to allow for the tracking of the input signal over both of a broad bandwidth and a narrow bandwidth operations, the switch operating to switch automatically to the narrowband filter when the bandwidth control signal receiving element receives the bandwidth control signal to switch to a narrow bandwidth operation, the wideband filter operating to provide filtering of said error signal during the broad bandwidth operation, the narrowband filter having a resistor and a capacitor, the narrowband filter configured to provide filtering of the error signal after the switch is toggled to the narrow bandwidth operation, where the wideband and narrowband filters have only passive elements; and a charging circuit coupled between the wideband filter and the narrowband filter, the charging circuit including an op-amp configured as a follower circuit, such that the charging circuit provides precharging of the capacitor in the narrowband filter to allow rapid phase lock and fast settling time of the filter, prior to the bandwidth control signal receiving element receiving the bandwidth control signal to switch automatically to the narrow bandwidth operation.