An apparatus including: a current source configured to generate current; a switching current source circuit coupled to the current source and a first bias node to allow the current to flow through the switching current source circuit into the first bias node; a first bias circuit configured to receive a first control signal from a phase detector, the first bias circuit configured to mirror the current flowing through the switching current source circuit in response to the first control signal; a second bias circuit coupled to the first bias circuit at an output node and a second bias node, the second bias circuit configured to receive a second control signal from the phase detector; and a transconductance amplifier configured to receive a feedback signal from the output node and generate an output current to control the second biasing node.