Method of providing and circuit for providing phase lock...

Details Method of providing and circuit for providing phase lock... Method of providing and circuit for providing phase lock...

2000-06-30

2001-11-20

Tran, Toan (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By phase

C327S157000, C327S049000

Reexamination Certificate

active

06320424

ABSTRACT:

FIELD
This invention relates to phase-lock loop circuits and more particularly relates to a phase frequency detector of a phase-lock loop circuit.
BACKGROUND
Phase-lock loops (PLL) include a phase-frequency detector (PFD) that provides control signals indicative of a phase difference between a reference clock signal and a feedback clock signal such as a VCO clock of a voltage controlled oscillator (VCO). A charge pump converts a digital output of the PFD to an analog current (or signal) which is then integrated by a loop filter to generate a control voltage. The VCO provides an oscillation signal responsive to the voltage signal. However, prior to the reference clock signal becoming stabilized with the feedback clock signal, a phase-lock loop transient overshoot may exceed a clock tree bandwidth. In such a circumstance, the phase-frequency detector may not receive any feedback clock signal and thus synchronization may not occur. The phase-lock loop may not be able to recover from this condition. Another problem with transient overshoot is the power management while the phase-lock loop is acquiring the lock between the reference clock signal and the feedback clock signal. If the phase-lock loop produces a very high frequency upon starting up, then a large current may cause the power to collapse in such a way that the circuit may not be able to recover. Accordingly, it is desirable to prevent the phase-lock loop from generating a transient overshoot of its frequency while acquiring synchronization between the reference clock signal and the feedback clock signal.


REFERENCES:
patent: 5592113 (1997-01-01), Quiet et al.
patent: 5815041 (1998-09-01), Lee et al.
patent: 5825210 (1998-10-01), Oh
patent: 5909130 (1999-06-01), Martin et al.

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