Phase -locked loop with a programmable frequency detector

摘要

A frequency detector (204) for use with a PLL utilizes a counter (232) and a preset value to produce frequency information related to a VCO signal. The frequency information is used to control the frequency of the VCO signal and to determine whether the VCO signal should be controlled by the frequency detector (204) or a phase detector (102). Using the counter and preset value involves establishing a preset value that is used to obtain the desired frequency information. The preset value is set such that the counter is at one-half full-scale at the end of a known time period when the VCO signal is oscillating at a target frequency. When the preset value is set to such a value, the most significant bit of the counter after the known time period indicates whether the frequency of the VCO signal is above or below the target frequency. <IMAGE> <IMAGE>