Abstract: Disclosed is an improved phase detector apparatus which includes a charge pump. The charge pump includes a first integrating node and a second integrating node. The first and second integrating nodes generate node voltages which ramp downward and upward during a given period of a reference signal. When a signal is received to which a reference signal is to be locked on, the integrating sequence of the first and second nodes is altered so that the differential voltage across the nodes indicates a difference in phase between the reference signal and the second signal. A filter is connected between the output signal and the first integrating node, while the second integrating node is referenced to a DC bias level and returns to that level at the beginning and end of each cycle. The charge pump apparatus is driven by variable current sources which give the apparatus a variable frequency response.