Crystal oscillator noise compensation method for a multi-loop PLL

摘要

A multi-loop phase locked loop (PLL) system with noise attenuation has a first PLL including a local oscillator, a second PLL coupled to an output of the first PLL, and a third PLL in a feedback path between the second PLL and first PLL. A first phase comparator compares an input signal with the first feedback signal to generate a first phase error signal for the first PLL. The first phase error signal is multiplied by a scaling factor k determining the amount of noise attenuation. The third PLL has a bandwidth preferably at least ten times higher than the second PLL so that the overall transfer function of the second and third PLLs is approximately the transfer function of the second PLL. The transfer function of the third PLL is multiplied by a scaling factor 1/k. This arrangement allows the use of an uncompensated local oscillator in the first PLL. The noise generated in the uncompensated local oscillator is reduced by the attenuation factor k.

主权项

1. A multi-loop phase locked loop (PLL) system with noise attenuation, comprising:
a first PLL including a local oscillator; a second PLL coupled to an output of the first PLL; a third PLL in a feedback path between said second PLL and said first PLL, said third PLL providing a first feedback signal; a first phase comparator for comparing an input signal with said first feedback signal to generate a first phase error signal for said first PLL; and a first multiplier for multiplying said first phase error signal by a scaling factor k determining the amount of noise attenuation; and wherein the third PLL has a bandwidth significantly higher than the second PLL, and the transfer function of the third PLL is multiplied by a scaling factor 1/k.