Phase lock loop enabling smooth loop bandwidth switching over a

Details Phase lock loop enabling smooth loop bandwidth switching over a Phase lock loop enabling smooth loop bandwidth switching over a

1996-06-05

1997-10-07

Mis, David

Oscillators

Automatic frequency stabilization using a phase or frequency...

Particular error voltage control

331 8, 331 14, 331 25, 327157, H03L 7089, H03L 7107

Patent

active

056752920

ABSTRACT:
A PLL that enables smooth switching of loop bandwidth over a wide range. By switchably inserting a resistance between the output of a current-mode charge pump and a loop filter of the PLL, current sources of the charge pump are made to appear as voltage sources, and a suitably small trickle current may be obtained for wideband acquisition. During tracking, the resistance is bypassed, such that the current sources again function as current sources for narrowband tracking. More particularly, in accordance with one embodiment of the invention, a phase locked loop having a current-mode charge-pump loop filter including a current source is operated by, during narrowband operation, switching a resistive element into a current path of the current-mode charge-pump loop filter. The resistive element has a sufficient resistance to change an operating point of the current source on a V-I curve characterizing the current source. During wideband operation, switching the resistive element out of the current path causes the current source to resume a prior operating point on the V-I curve.

REFERENCES:
patent: 5047733 (1991-09-01), Nonaka et al.
patent: 5389899 (1995-02-01), Yahagi et al.
patent: 5534823 (1996-07-01), Kondou
patent: 5548829 (1996-08-01), Suzuki et al.
Byrd, David et al., "A Fast Locking Scheme for PLL Frequency Synthesizers", National Semiconductor Corporation, Application Note 1000, Jul. 1995, pp. 1-5.

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