Frequency synthesizer with improved automatic control of loop bandwidth selection

摘要

A method of and apparatus for automatically selecting one of first and second loop bandwidth states of a phase lock loop circuit of a frequency synthesizer. The phase lock loop circuit is governed by a reference frequency signal and a feedback frequency signal to adjust the frequency of the synthesized frequency signal to a frequency channel setting. Each of the reference and feedback frequency signals include one phase indication per frequency period. The feedback frequency signal is phase and frequency representative of the synthesized frequency signal. The loop bandwidth of the phase lock loop circuit is automatically switched from the first to the second state based on an initial occurrence of three successive phase indications of a selected one of the reference and feedback frequency signals between successive phase indications of the other, and automatically switched back from the second to the first state based on an initial occurrence of two successive phase indications of the other frequency signal between successive phase indications of the selected frequency signal.