Patent ID: 8847642

Claim:
An apparatus comprising: a charge pump phase-locked loop circuit comprising: an active loop filter comprising an amplifier that has a negative input node, a positive input node, and an output node, in which a feedback path is provided between the output node and the negative input node, the feedback path including a capacitor; an adjustable reference voltage source that is electrically coupled to the positive input node of the amplifier to provide a reference voltage that is adjustable; and a charge pump electrically coupled to the negative input node of the amplifier to provide a current to or sink a current from the active loop filter in response to a signal from a phase detector, the charge pump comprising a first current source electrically coupled to a first voltage and a second current source electrically coupled to a second voltage, the second current source comprising a resistor, and the second current source is configured such that a current provided by the second current source depends on a resistance value of the resistor and a difference between the reference voltage and the second voltage, wherein the adjustable reference voltage source comprises a digital-to-analog converter to receive a digital input signal and output the reference voltage provided to the positive input node of the amplifier.