Loop filter for frequency multiplying phase locked loop

Details Loop filter for frequency multiplying phase locked loop Loop filter for frequency multiplying phase locked loop

1988-05-12

1989-05-09

LaRoche, Eugene R.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Particular error voltage control

307520, 328167, H03L 700

Patent

active

048292680

ABSTRACT:
A loop filter for a phase locked loop system having a voltage controlled oscillator (VCO), a divide-by-N circuit responsive to the output of the VCO, and an edge sensitive phase/frequency comparator responsive to the output of the divide-by-N circuit and a reference timing signal for providing a first control signal when the output of the divide-by-N circuit lags the reference timing signal or a second control signal when the output of the divide-by-N circuit leads the reference signal. The loop filter specifically includes first and second capacitors serially coupled between an output node and a ground reference node, wherein the second capacitor is connected to the ground reference node and the output node provides a control voltage to the VCO. A first current source is controllably connected by a first switch to the output node in response to the first control signal, whereby the first current source charges the first and second serially coupled capacitors. A second current source is controllably connected by a second switch to the output node in response to the second control signal, whereby the second current source discharges the first and second serially coupled capacitors. A third switch is coupled across the terminals of the second capacitor for controllably shorting the second capacitor.

REFERENCES:
patent: 4649353 (1987-03-01), Sonnenberg
Turner, Phase Locked Loop Phase Adjustment, IBM Technical Disclosure Bulletin, vol. 15, No. 7 Dec. 1972, pp. 2080-2081.
"The RCA COS/MOS Phase-Locked Loop, A Versatile Building Block for Micro-Power Digital and Analog Applications," Morgan, RCA Solid State '74 Databook Series pp. 360-367, RCA Corporation, 1973.
"A Single-Chip Code with Switched-Capacitor Filters," Iwata et al., IEEE Journal of Solid State Physics, vol. SC-16, No. 4, pp. 315-321, Aug. 1981.

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