| Sigma-delta modulators (SDM) can achieve high resolution thanks to the oversampling and nosie-shaping technique. The major disadvantage is the limited bandwidth due to the need o f oversampling. Extending these converters to broadband applications requires lowering the oversampling ratio (OSR) in order for sigma-delta modulator to be realizable within the technology limitations with moderate power dissipation. In addition, due to the limited voltage headroom, conventional modulator architectures result in reduced full-scale input range and limited op-amp structure because high output swing are required for op-amps.The aim of this thesis is the investigation on the new topology and structure of sigma-delta modulators suitable for wideband applications, e.g. wireline or wireless communication system applications having a digital baseband above 1 MHz.It has recently become very popular to feedforward the input signal in wideband sigma delta modulators, so that the integrators only process quantization errors. The advantage being that the actual signal is not distorted by opamp and integrator nonlinearities. An improved feedforward 2-2 cascaded structure is presented based on unity-gain signal transfer function (STF). The improved signal-to-noise-ratio (SNR) is obtained by optimizing zero placement of the noise transfer function (NTF) and adopting multi-bit quantizer. The proposed structure has low distortion across the entire input range.To achieve high precision, low power dissipation and low cost, a wideband, low voltage and low powerΣ-Δmodulator structure is proposed which is based on single op-amp architecture by moving the internal feedback path to outer loop, and the forward loop filter only contain cascaded integrator, thus can be implemented in a passive way with only one op-amp for the summing operation. By moving the feedforward path after the quantizer, the signal will be processed in digital way, thus reduce the analog complexity and make a low voltage, low power implementation possible. The simulation results show the improved performance.In high order single loop continuous-time (CT) sigma delta modulator, excess loop delay may cause instability. Previous techniques in compensation of internal quantizer and feedback DAC delay are studied especially for the feedforward structure. Two alternative low power feedforward continuous-time sigma delta modulators with excess loop delay compensation are proposed. Simulation based CT modulator synthesis from discrete time topologies is adopted to obtain the loop filter coefficients. Design examples are given to illustrate the proposed structure and synthesis methodology.Continuous time quadrature bandpass sigma delta modulators (QBSDM) efficiently realize asymmetric noise-shaping due to its complex filtering embedded in the loops to. The effect of different feedback waveforms inside the modulator on the NTF of quadrature sigma delta modulators is presented. An observation is made that a complex NTF can be realized by implementing the loop as a cascade of complex integrators with a SCR feedback DAC, which is desirable for its lower sensitivity to loop mismatch. The QBSDM design for different bandpass centre frequencies relative to the sampling frequency is illustrated.The last part of the thesis is devoted to the design of a wideband reconfigurable sigma delta pipelined ADC, which consists of a 2-1-1 MASH modulator and a pipelined ADC as a multi-bit quantizer in the last stage. It achieves a high SNR over a wideband and be scalable for different bandwidth/resolution application. The detail design is presented from system to circuit level. The prototype chip is fabricated in TSMC 0.25um process and tested. The measuring results show that a SNR over 60dB is obtained with a sampling frequency of 70 MHz and an OSR of ten.
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