Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
2004-05-10
2009-10-20
Do, Chat C (Department: 2193)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
Reexamination Certificate
active
07606849
ABSTRACT:
The present invention is directed to the use of a DDS to generate a high purity reference signal with high frequency resolution by switching a frequency tuning word (FTW) between particular values for particular time durations to produce two or more closely spaced frequencies that appear at the DDS output as a single frequency. Given a DDS switching between F1and F2such that F1is present for time T1and F2is present for time T2, with the total period of the repeating pattern being T=T1+T2, in order for the output of the DDS to produce a single high-purity frequency that is the time-weighted average of the alternating frequencies, the condition |F1−F2|<<π/T must be satisfied. The time-weighted average frequency Favg=(T1·F1+T2·F2)/(T+T2). By an appropriate choice of T1and T2, Favg can be set to any frequency between these two frequencies.
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Analog Devices data sheet; AD9954; 400 MSPS 14Bit, 1.8 V CMOS—Direct Digital Synthesizer; 2003 (cover sheet plus pp. 1-36).
Advantest Corporation
Do Chat C
Morrison & Foerster / LLP
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