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AUTOMATED FACTORY TUNING OF OSCILLATORS USING ELECTRICALLY ADJUSTABLE CAPACITORS AND PHASE LOCK

IP.com Disclosure Number: IPCOM000005849D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-12
Document File: 1 page(s) / 59K

Publishing Venue

Motorola

Related People

D. Schick: AUTHOR [+3]

Abstract

Increased demands on crystal oscillator accuracy in production radios has required that oscillators be tuned in the factory to remove initial offset error. Generally, tuning is accomplished by adjustment of a mechanical variable capacitor. This method adds labor and decreases overall reliability of the product. Thus, a solid state tuning method is more desirable.

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MOlOROLA Technical Developments Volume 10 March 1990

AUTOMATED FACTORY TUNING OF OSCILLATORS USING ELECTRICALLY ADJUSTABLE CAPACITORS AND PHASE LOCK

by D. Schick, J. Parkes and D. Winfree

   Increased demands on crystal oscillator accuracy in production radios has required that oscillators be tuned in the factory to remove initial offset error. Generally, tuning is accomplished by adjustment of a mechanical variable capacitor. This method adds labor and decreases overall reliability of the product. Thus, a solid state tuning method is more desirable.

   A solid state precision electrically adjustable capacitor (PEAC) has been used in several products to warp, or tune, low frequency crystal oscillators (2 MHz and below). The PEAC is a MOS device whose capacitance is raised or lowered through the application of positive or negative voltage pulses applied over time to a programming terminal. Following programming, the PEAC retains is programmed capacitance indefinitely.

   Typically the PEAC capacitance is adjusted by an operator using a manual programming fixture. The programming fixture has several buttons which apply positive or negative pulses to the oscillator, and the operator selects the ap- propriate buttons as many times as necessary to bring the oscillator on frequency.

   Phase lock tuning of PEA& in oscillators reduces labor and improves tuning accuracy and reliability. As shown in figure 1, a phase locked loop (PLL) feedback circuit is used to compare the produ...