Browse Prior Art Database

CURRENT DUMP VCO TOPOLOGY

IP.com Disclosure Number: IPCOM000009855D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-24
Document File: 4 page(s) / 111K

Publishing Venue

Motorola

Related People

Prakash Chacko: AUTHOR

Abstract

Whenever the frequency of the railio is changed, the synthesizer is programmed into adapt mode. During this mode, the loop filter of the synthesizer is configured to wide band mode for fast locking.

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MOTOROLA

Technical Developments

CURRENT DUMP VCO TOPOLOGY

by Prakash Chacko

INTRODUCTION

Whenever the frequency of the railio is changed, the synthesizer is programmed into adapt mode.

During this mode, the loop filter of the synthesizer is configured to wide band mode for fast locking.

Mter the adapt mode (usually about 2.Oms), the Joop fiJter of the synthesizer is reconfigured to a narrow mode for optimum noise and spurious performance. During the adapt mode, the control voltage to the VCQ is indeterminate. The voltage can range from zero to the maximum of 12V.

In an improper designed VCQ, the VCO may not oscillate at control voltage of zero volts. Hence the designer has to ensure the start-up of the VCO at this voltage even though the occurrence is about two ms.

Optimization for start up do degrade the performance of the VCO in the area of phase noise and bandwidth. Trailitionally, optimization for start-up is a lengthy process with sacrifice in the bandwidth and phase noise performance of the VCO.

Motorola. Inc. 2000

DESCRIPTION OF THE INVENTION

The standard VCO topology as shown in Figure I is modified with an adilitional switching transistor (Q3) on the emitter of the active device. During adapt mode of the synthesizer, Q3 is turned on which bypassed the emitter resistor R4 and RF for high current operation. The current drain of the VCO is approximateJy 35ma during thjs mode. The loop gain of the VCO is sufficiently high to ensure no start-up problem at the control voltage of O Vat this current dra...