Patent ID: 6828864
Filing Date: 2004-12-07
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 wherein the proportional path circuit provides an independent proportional path output; and an integral path circuit that is separate and independent from 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 integral path circuit provides an independent integral path output; and a summer that receives and sums the independent proportional path output and the independent integral path output to provide a low-jitter loon filter output.