Crystal oscillator noise compensation method for a multi-loop PLL

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 fir...

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Bibliographische Detailangaben
Hauptverfasser:	Rahbar Kamran, Jin Qu Gary
Format:	Patent
Sprache:	eng
Schlagworte:	AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATIONOF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES BASIC ELECTRONIC CIRCUITRY ELECTRICITY GENERATION OF NOISE BY SUCH CIRCUITS GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING,BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN ANON-SWITCHING MANNER
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Beschreibung
Zusammenfassung:	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.