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Design of a High Resolution Sigma-Delta Modulator

Mesgarani, Ali | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39074 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Haj Sadeghi, Khosro
  7. Abstract:
  8. Sigma-delta modulators have largely been implemented as discrete-time (DT) circuits because of their low sensitivity to circuit nonidealities, and their frequency scaling specification, however a continuous-time (CT) design offers significant advantage in the design of high accuracy, high speed analog to digital converters (ADC). A CT design allows for relaxed amplifier(s) bandwidth and power requirements, which enables the realization of high accuracy modulators with bandwidths of several megahertz at low power consumption. Furthermore CT modulators provide inherent anti-aliasing filtering which becomes especially important at low oversampling ratios. This thesis reports the design of a CT-DT cascaded sigma-delta modulator which combines the advantages of CT and DT design to realize of a high resolution, wideband ADC at moderate power dissipation. The first stage of proposed cascaded architecture is implemented in CT while the second stage is a DT circuit. It is shown in this research that a DT second stage is preferred over a CT one in terms of design simplicity, modulator performance and power dissipation. Power consumption of CT first stage is reduced by accurate selection of CT integrators gain coefficients in a feedforward topology. In this research the benefits of CT modulators and the challenges of CT design are investigated accurately. Moreover common CT to DT transformation methods are compared in terms of accuracy. The proposed architecture is implemented in 0.18um CMOS technology. Simulations show that the modulator provides 83.8dB dynamic range and 83.2dB peak SNDR over 10MHz signal bandwidth while consuming 42mw of power from a 1.8V supply voltage. These specifications compare favorably to the most designs reported in the literature. The proposed modulator can be utilized in Wimax systems
  9. Keywords:
  10. Analog to Digital Converter ; Cascade Sigma-Delta Modulator ; Continuous-Time Sigma-Delta Modulator

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