Method and system for controlling a tuning voltage of a phase-locked loop circuit to an optimal value

Abstract

A method and system for controlling a tuning voltage of a phase-locked loop circuit to an optimal value are disclosed. Minimum and maximum bias current values are defined for a bias current from the linear control loop circuit. The linear control loop circuit is coupled to the phase-locked loop circuit. The linear control loop circuit infinitely varies a current value for a current-controlled oscillator of the phase-locked loop circuit. The current value is based on a tuning current of the phase-locked loop circuit and the bias current. The bias current infinitely varies in value between the minimum bias current value and the maximum bias current value to direct the tuning voltage to an optimal value. The phase-locked loop circuit includes a phase detector, a filter, a voltage-to-current converter, a current adder, and the current-controlled oscillator coupled together in series. The linear control loop circuit is an analog, voltage control loop that has a voltage summer, another filter, and another voltage-to-current converter coupled together in series. A reference voltage and the tuning voltage are inputted into the voltage summer, and a bias current is outputted and injected from the other voltage-to-current converter into the tuning current. The other voltage-to-current converter has a sufficient gain to provide the bias current between the minimum bias current value and the maximum bias current value. The linear control loop circuit is designed with a time constant characteristic that is slower than another time constant characteristic of the phase-locked loop circuit.