Sigma-Delta Modulators Operating at a Limit Cycle

S.F. Ouzounov, J.A. Hegt, A.H.M. Roermund, van

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A new type of sigma–delta modulator that operates in a special mode named limit-cycle mode (LCM) is proposed. In this mode, most of the SDM building blocks operate at a frequency that is an integer fraction of the applied sampling frequency. That brings several very attractive advantages: a reduction of the required power consumption per converted bandwidth, an immunity to excessive loop delays and to digital–analog converter waveform asymmetry and a higher tolerance to clock imperfections The LCMs are studied via a graphical application of the describing function theory. A second-order continuous time SDM with 5 MHz conversion bandwidth, 1 GHz sampling frequency and 125 MHz limit-cycle frequency is used as a test case for the evaluation of the performance of the proposed type of modulators. High level and transistor simulations are presented and compared with the traditional SDM designs.
Original languageEnglish
Pages (from-to)399-403
Number of pages5
JournalIEEE Transactions on Circuits and Systems II: Express Briefs
Issue number5
Publication statusPublished - 2006


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