Özet:
The widespread use of mixed-signal based systems in conjunction with the various bene ts provided by digital techniques have signi cantly increased the need for high resolution analog-to-digital (A/D) and digital-to-analog (D/A) converters. The (A/D) converter based on the sigma-delta modulation sigma-delta is capable of providing a very high resolution for low-to-medium signal bandwidth applications. It utilizes oversampling and noise-shaping to trade-o operation speed for amplitude resolution. In this study the theory and advantages of sigma-delta converters are introduced. Low-pass and narrow-band band-pass sigma-delta modulators are designed, examined and analyzed. A variety of sigma-delta converter topologies are modeled in Simulink and MATLAB routines are written. Various Butterworth and inverse Chebyshev based (sigma-delta) modulators are designed and implemented at the behavioral-level to enhance SNRs. The system performance analysis and tradeo s are analyzed via various single-loop and multi-stage low-pass and resonator-based band-pass sigma-delta modulator simulations. A user-friendly software tool is developed to speed up the design, analysis, evaluation and measurement of single-loop and multistage sigma-delta modulators at the system-level. Using second-order low-pass sigma-delta modulator built in the design tool is used in the medical ultrasound beamforming implementation. For this aim, a comparison of ultrasound images constructed by beamformer architectures that use 10-bit ADC's and single-bit sigma-delta modulators are performed. The bene ts and trade-o s of using 1-bit sigma-delta modulators are examined.|Keywords: Sigma-delta modulator, A/D converter, low-pass and band-pass sigma-delta modulators design tool.
