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Browse Prior Art Database

Current Sources for a Phase Locked Loop

IP.com Disclosure Number: IPCOM000080313D
Original Publication Date: 1973-Nov-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Malone, DJ: AUTHOR

Abstract

A phase-locked loop that includes a voltage-controlled oscillator (VCO) 10, provides positive and negative current sources 12 with equal switching speed for turnoff and turnon. The circuit employs a PNP transistor circuit 14 as a current source, and a fast steering NPN transistor circuit 16 as a switching network. The transistor circuits function to steer the current, in response to an indication by a phase comparator 18 of the phase-locked loop whether an increase or decrease in frequency is needed.

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Current Sources for a Phase Locked Loop

A phase-locked loop that includes a voltage-controlled oscillator (VCO) 10, provides positive and negative current sources 12 with equal switching speed for turnoff and turnon. The circuit employs a PNP transistor circuit 14 as a current source, and a fast steering NPN transistor circuit 16 as a switching network. The transistor circuits function to steer the current, in response to an indication by a phase comparator 18 of the phase-locked loop whether an increase or decrease in frequency is needed.

The PNP circuit 14 provides positive current for increasing the frequency of the VC0 output signal, whereas the NPN circuit 16 provides for a decrease in frequency of the signal.

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