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Phase Locked Loop Phase Adjustment

IP.com Disclosure Number: IPCOM000078238D
Original Publication Date: 1972-Dec-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Turner, DP: AUTHOR

Abstract

A closed loop variable-frequency oscillator includes a voltage controlled oscillator 10 that provides a nominal frequency signal to a counter 12. The counter provides a pulse to a phase discriminator 14, which also receives an input data pulse. The output of the phase discriminator is a pulse having a duration equal to the time difference between the input pulse and the pulse provided by the counter. If the input pulse occurs before the oscillator pulse, then switch 18 is closed for the duration of the output pulse from the phase discriminator. A charge equal to the charge current generated by current source 20 multiplied by the duration of the pulse is transferred to a filter 22, thereby increasing the control voltage which is applied to the VCO 10.

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Phase Locked Loop Phase Adjustment

A closed loop variable-frequency oscillator includes a voltage controlled oscillator 10 that provides a nominal frequency signal to a counter 12. The counter provides a pulse to a phase discriminator 14, which also receives an input data pulse. The output of the phase discriminator is a pulse having a duration equal to the time difference between the input pulse and the pulse provided by the counter. If the input pulse occurs before the oscillator pulse, then switch 18 is closed for the duration of the output pulse from the phase discriminator. A charge equal to the charge current generated by current source 20 multiplied by the duration of the pulse is transferred to a filter 22, thereby increasing the control voltage which is applied to the VCO 10. As a result, the frequency of VCO is increased, so that the next counter pulse will occur closer in time to the next input pulse. On the other hand, if the counter pulse occurs before the input pulse to the phase discriminator, a switch 26 will close, causing the control voltage to decrease and the frequency of the VCO to decrease accordingly, by action of decrease current network 28. In essence, the closed- loop servo serves to adjust the oscillator frequency and phase, so that the counter pulses coincide with the input pulses.

The addition of leakage current by current source generator 24 causes a charge equal to the leakage current times the time interval between input pulses to...