| With the rapid growth of wireless communication systems, there is a great demand for developing low-power, wideband and high resolution analog-to-digital (A/D) converters to support new wireless standards. Oversampling A/D converters are well suitable to such applications. Compared with conventional Nyquist-rate A/D converters, oversampling A/D converters, based on DeltaSigma modulation, can achieve high resolution signal conversion with low precision analog component. Continuous-time DeltaSigma modulators are a viable approach for low-voltage, high-speed oversampling A/D converters.; This thesis describes the design and implementation of a low-voltage, wide bandwidth continuous-time DeltaSigma modulator with emphasis on transconductor-C realization. The design methodology of continuous-time DeltaSigma modulators is presented. The critical aspects in the design of continuous-time DeltaSigma modulators are investigated and solutions to them are proposed. The transconductor-C approach is the preferred one for implementing high frequency continuous-time filters and DeltaSigma modulators. The circuit techniques for improving the linearity of transconductors are discussed. A novel highly linear transconductor is developed for low-voltage applications. A fourth-order continuous-time DeltaSigma modulator is designed and implemented in a 0.25mum CMOS process. Experimental results from the two fabricated prototype DeltaSigma modulators are presented. Finally, some recommendations for improving the performance of the current modulator are provided. |
