Automatically tuning a voltage controlled oscillator for minimum side band noise

摘要

A VCO (Voltage Controlled Oscillator) (10) operates in a phase-locked loop at a desired frequency. One input to the VCO is a variable control signal (24) that holds the VCO at the desired frequency. Another input is a bias input (40) that changes the operating point of a transistor (34) in the VCO and also tends to change the VCO's frequency. The value of the variable control signal (24) is sensed while the bias input (40) is changed until a desired, minimum value of the control signal is sensed. The value of the bias input at that point is held constant while operating the VCO at the desired frequency and with minimal side band noise.