Browse Prior Art Database

Phase-Locked Loop Center Frequency Adjustment System

IP.com Disclosure Number: IPCOM000041270D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Call, MG: AUTHOR [+3]

Abstract

A processor is used to adjust the center frequency of the VCO (voltage-controlled oscillator) portion of a phase-locked loop. The automatic adjustment of the center frequency of the VCO portion of the phase-locked loop (PLL) 10 uses a digital-to-analog converter (DAC) 11 to set the current IRFR. Processor 12 sets latch A to 0. A nominal INPUT signal is applied to the phase detector input of PLL 10. Since the IRFR current is 0, the SET output of comparator B is high. Processor 12, in response to the high SET signal, increases the count stored in latch A any number of times until the output of the low pass filter D is equal to the reference voltage VRFR at E, at which time the SET output of comparator goes low.

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Phase-Locked Loop Center Frequency Adjustment System

A processor is used to adjust the center frequency of the VCO (voltage- controlled oscillator) portion of a phase-locked loop. The automatic adjustment of the center frequency of the VCO portion of the phase-locked loop (PLL) 10 uses a digital-to-analog converter (DAC) 11 to set the current IRFR. Processor 12 sets latch A to 0. A nominal INPUT signal is applied to the phase detector input of PLL 10. Since the IRFR current is 0, the SET output of comparator B is high. Processor 12, in response to the high SET signal, increases the count stored in latch A any number of times until the output of the low pass filter D is equal to the reference voltage VRFR at E, at which time the SET output of comparator goes low. In response to this change in the SET output, processor 12 discontinues changing the count in latch A and records the last count value in permanent storage 13. The process is continued for other nominal INPUT signals until a table of values is identified and stored in permanent storage 13. In subsequent application the center frequency is adjusted directly by setting the count stored in the table. The arrangement has application in disk recording, where the frequency of the data stream may vary depending on disk speed during reading operations, as well as other devices where longer term changes in frequency of operation must be tolerated.

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