Patent ID: 7834707
Filing Date: 2010-11-16
Classification: H03L

Abstract:
1. A charge pump for providing a charge based on a phase difference between a first and second signal, the charge pump comprising: an operational amplifier having an output terminal, a positive input terminal, and a negative input terminal; a first switch coupled between a first current source and the positive input terminal; a second switch coupled between the first current source and the output terminal; a third switch coupled between the output terminal and a second current source; and an offset current circuit coupled to the positive input terminal, wherein the offset current circuit is configured to move a bias point of the charge pump, using an offset current, away from a zero point such that the charge pump provides a non-zero charge if the phase difference is zero, wherein the offset current circuit includes a current mirror that is configured to receive a bias current from a digital-to-analog converter, and wherein the bias current is coupled to a diode-connected transistor of the current mirror that is configured to establish the offset current, proportional to the bias current, in a separate transistor.