Voltage controlled oscillator operating with digital controlled loads in a phase lock loop

A method of controlling a maximum operating frequency of a phase lock loop, comprising the steps of:

• comparing a phase difference of first and second input signals and generating an output signal to charge and discharge a loop node and develop a loop node voltage;
• initializing said loop node voltage to a predetermined level;
• generating an oscillator signal operating at a frequency determined by said loop node voltage;
• dividing down said oscillator signal into first and second divided oscillator signals, said first divided oscillator signal operating as said second input signal;
• generating a first load control signal when said second divided oscillator signal changes logic state more than a predetermined number of times during a first logic state of said first input signal;
• and
• reducing said frequency of said oscillator signal in response to said first load control signal by increasing loading on said oscillator signal.

An integrated phase lock loop, comprising:

• first means for comparing a phase difference of first and second input signals and generating an output signal to charge and discharge a loop node;
• second means having an output coupled to said loop node and operating in response to the first input signal for initializing said loop node to a predetermined voltage;
• a VCO having an input coupled for receiving said output signal of said first means and having an output for providing an oscillator signal;
• third means for dividing down said oscillator signal into first and second divided oscillator signals, said first divided oscillator signal operating as said second input signal of said first means;
• fourth means coupled for receiving said second divided oscillator signal and said first input signal and generating a first load control signal when said second divided oscillator signal changes logic state more than a predetermined number of times during a first logic state of said first input signal;
• and
• a first load circuit coupled to said output of said VCO and operating in response to said first load control signal to increase loading at said output of said VCO.