Patent ID: 7649421

Claim:
A phase locked loop circuit, comprising: an oscillator operative for providing an output frequency; a detector operative for detecting the output frequency of the oscillator, comparing the output frequency with a first reference signal and outputting a first signal and a second signal as a function of the output frequency and first reference signal comparison; a charge pump operatively connected to the detector, the charge pump comprising: a differential amplifier operative for receiving the first and second signals, receiving a predetermined threshold from a second reference signal at an input of the differential amplifier, monitoring a deviation of the first and second signals from the predetermined threshold, and generating a third signal as a function of the deviation, and a comparator operative for receiving the third signal, comparing the third signal to a window threshold, and generating a fourth signal as a function of the third signal and window threshold comparison, wherein the window threshold is set based on a predetermined loop variable; and an alarm circuit which receives the fourth signal and is adaptable to provide an alarm.