Browse Prior Art Database

Automatic Voltage-Controlled Oscillator Center Frequency Adjustment

IP.com Disclosure Number: IPCOM000047121D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Lee, HR: AUTHOR

Abstract

Equipment designed to store digital information on magnetic media historically has used phase-locked loops to generate a phase and frequency coherent clock from the incoming data stream. These phase-locked loops include a voltage-controlled oscillator that requires a manually adjustable potentiometer to set the center frequency. The center frequency must be set at the time of manufacture and occasionally thereafter to compensate for offsets in the VCO and associated buffer, and to compensate for external timing capacitor tolerances. A simple circuit is illustrated in the figure that will eliminate the requirement for a potentiometer, thereby increasing reliability and lowering manufacturing costs by replacing it with a circuit which will automatically set the VCO center frequency each time the equipment is powered up.

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Automatic Voltage-Controlled Oscillator Center Frequency Adjustment

Equipment designed to store digital information on magnetic media historically has used phase-locked loops to generate a phase and frequency coherent clock from the incoming data stream. These phase-locked loops include a voltage- controlled oscillator that requires a manually adjustable potentiometer to set the center frequency. The center frequency must be set at the time of manufacture and occasionally thereafter to compensate for offsets in the VCO and associated buffer, and to compensate for external timing capacitor tolerances. A simple circuit is illustrated in the figure that will eliminate the requirement for a potentiometer, thereby increasing reliability and lowering manufacturing costs by replacing it with a circuit which will automatically set the VCO center frequency each time the equipment is powered up. This scheme could also be extended to enable, measure, and set the VCO center frequency between each record during the inter-record gap (IBG). This would provide the additional benefit of providing the VCO with a nominal frequency reference during periods where it would not have data to lock on. Instead of allowing the VCO to "coast" and drift to an equilibrium dictated by its offsets, which could increase acquisition time when the data stream returned, the VCO would lock on the external reference which would "pull" the VCO back to the center frequency. The circuit does not require any s...