Adjustable lock detector for a phase-locked loop circuit

Details Adjustable lock detector for a phase-locked loop circuit Adjustable lock detector for a phase-locked loop circuit

1996-03-25

1998-03-03

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Afc with logic elements

331 25, 331DIG2, H03L 7095

Patent

active

057240078

ABSTRACT:
A lock detector suitable for detecting when an output signal of a phase-locked loop circuit is phase-locked to an input reference signal. The lock detector includes a pair of delay lines, that are adjustable, which are used to create a window signal around the reference clock signal. UP and DOWN signals from the PLL circuit are fed to an OR gate to generate an actual out-of-lock signal. When the PLL circuit is phase-locked within an acceptable phase error range, the UP, and DOWN signals, if any, will appear within the generated window signal. When the PLL circuit is not phase-locked within the acceptable phase error range, the UP, and DOWN signals occur outside of the window. The window signal, and the output of the OR gate are connected to an AND gate to generate a gated out-of-lock signal. The gated out-of-lock signal is connected to a switched-capacitor charge pump. So long as the switched-capacitor charge pump does not receive an active gated out-of-lock signal, the charge pump will, after a predetermined number of input clock signals, generate a logical lock signal, indicating that the PLL circuit has reached steady-state phase-lock. However, when the switched-capacitor charge pump receives an activated gated out-of-lock signal, the charge pump will deassert the logical lock signal.

REFERENCES:
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patent: 5126690 (1992-06-01), Bui et al.
patent: 5256989 (1993-10-01), Parker et al.
patent: 5525932 (1996-06-01), Kelkar et al.
Shariatdoust et al. (AT&T Bell Laboratories), IEEE 1992 Custom Integrated Circuits Conference, pp. 24.2.1-24.2.5. no month.
Alvarez et al., 1994 Symposium on VLSI Circuits Digest of Technical Papers, pp. 37-38. IEEE Apr. 1994.

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