Voltage-controlled oscillator and gain calibration technique for two-point modulation in a phase-locked loop

摘要

A VCO in a phase-locked loop (PLL) is arranged to receive low-pass data via a first input and high-pass data at a second input. The first input is coupled to a first set of varactors in the VCO. The second input is coupled to a second set of varactors in the VCO. The controller sets the input voltage at the first input and directs a charge pump to operate in a tri-state mode that opens the feedback loop of the PLL. The controller applies different voltages via the second input and measures the change in output frequency. A present gain of the VCO is determined from the ratio of the change in frequency and the change in voltage at the second input.