Patent ID: 6690240
Filing Date: 2004-02-10
Classification: H03L

Abstract:
A loop filter for a phase locked loop (â€œPLLâ€ ) circuit which locks a frequency of a signal to a reference frequency, comprising:a proportional path circuit which receives a charge pump output and determines and holds a charge to be directed to or taken from a PLL circuit throughout an update period based on a detected phase difference for the update period for locking a frequency of a signal for the PLL circuit to a reference frequency; and an integral path circuit coupled to the proportional path circuit wherein the integral path circuit receives another charge pump output and tracks a total charge level for the PLL circuit based on phase differences for present and prior update periods; and wherein the charge pump output is a predetermined scaled charge output and the another charge pump output is another predetermined scaled charge output wherein the predetermined scaled charge output and the another predetermined scaled charge output are both from a single charge pump.