Method and apparatus for maintaining an ideal frequency...

Communications: electrical – Continuously variable indicating – With meter reading

Reexamination Certificate

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C340S003200, C340S536000, C341S061000, C375S356000, C348S497000

Reexamination Certificate

active

11088446

ABSTRACT:
A method and apparatus for maintaining an ideal frequency ratio between numerically-controlled frequency sources provides a mechanism for maintaining coherence between multiple synchronization references where a known ideal rational relationship between the sources is known. Multiple numerically controlled oscillators (NCOs) generate the multiple synchronization references, which may be clock signals or numeric phase representations and the outputs of the NCOs are compared with a ratiometric frequency comparator that determines whether there is an error in the ratio between the NCO outputs. The frequency of one of the NCOs is then adjusted with a frequency correction factor provided by the ratiometric frequency comparator. The NCO inputs can represent ratios of the synchronization reference frequencies to a fixed reference clock and the NCOs clocked by the fixed reference clock.

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Vankka, et al., “A GSM/EDGE/WCDMA Modulator With On-Chip D/A Converter for Base Stations”, IEEE Transactions on Circuits and Systems, vol. 49, No. 10, Oct. 2002.

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