Phase detector with frequency steering

摘要

A PLL (225) includes a phase detector (202) and a charge pump (210 or 212). The phase detector (202) includes a first D-type flip flop (302), a second D-type flip flop (304) and an AND gate forming a reset circuit (306). The charge pump (210 or 212) includes an up current source (308) and a down current source (310). The up current source (308) provides a constant current. The down current source (310) varies responsive to an output signal (207) generated by the second D-type flip flop (304). The constant current provided by the up current source (308) is made to be less than one half the current provided by the down current source (310) to bias the charge pump (210 or 212) in a negative direction to minimize false locks between the phase of a divided reference frequency signal (206) and the phase of a divided voltage controlled oscillator frequency signal (209). Alternatively, the up current source (308) may be controlled in an analogous manner with the down current source (310) being held constant to achieve a similar effect and advantage.