A
gain compensator compensates for the
gain variation of a varactor-tuned
voltage tuned oscillator (VCO) in a phase lock loop (PLL). The VCO includes a parallel
LC circuit having multiple fixed capacitors that can be switched-in or switched-out of the
LC circuit according to a
capacitor control signal to perform band-select tuning of the VCO. The
gain compensator compensates for the variable VCO gain by generating a
charge pump reference current that is based on the same
capacitor control signal that controls the fixed capacitors in the
LC circuit. The gain compensator generates the
charge pump reference current by replicating a reference scale current using unit current sources. The number of times the reference scale current is replicated is based on the fixed
capacitance that is switched-in to the LC circuit and therefore the
frequency band of the PLL. The reference scale current is generated based on a PLL control that specifics certain PLL characteristics such as reference frequency,
loop bandwidth, and loop damping. Therefore, the reference pump current can be efficiently optimized for changing PLL operating conditions, in addition to compensating for variable VCO gain.