Lock indicator for phase locked loop circuit

Details Lock indicator for phase locked loop circuit Lock indicator for phase locked loop circuit

Filed on

1994-08-31

Date issued

1996-06-11

Examiner

Grimm, Siegfried H.

Patent Class

Oscillators

SubClass

Automatic frequency stabilization using a phase or frequency...

SubSubClass

Afc with logic elements

Other Related Categories

331 11, 331 17, 331 25, 331DIG2, H03L 7095

Type

Patent

Status

active

Patent number

055259324

Description

ABSTRACT:
A phase locked loop circuit which includes a phase/frequency detector which uses a divider circuit and feedback from a clock distribution tree to generate INC and DEC pulses which have no "dead zone" is provided. A pair of charge pumps receives the INC and DEC pulses. One charge pump is a differential pump and has a voltage controlled common mode feedback circuit to maintain a common mode controlled voltage. A differential current is outputted to a loop filter capacitor by this charge pump. The other charge pump is a single-ended output pump which supplies current to a current controlled oscillator which also receives input from a voltage to current converter. The current controlled oscillator includes a variable resistance load which varies inversely with the magnitude of the input current. A jitter control circuit is provided which reduces jitter in the current controlled oscillator output in the locked phase. Also, a lock indicator is provided which is time independent, and provides a lock indication when the loop enters the locked condition.

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