One aspect relates to a method for operating a charge pump including comparing a drain voltage of a current sink transistor of the charge pump with a drain voltage of a current reference transistor, adjusting a gate bias voltage of the current sink transistor and the current reference transistor using a first error amplifier in a direction that reduces a difference between the drain voltage of the current sink transistor and the drain voltage of the current reference transistor, comparing a common-mode voltage of a loop filter with a reference voltage, and adjusting a gate bias voltage of a current source transistor of the charge pump using a second error amplifier in a direction that reduces a difference between the common-mode voltage of the loop filter and the reference voltage, wherein the first error amplifier includes a larger number of amplifying stages than the second error amplifier.