For The Sigma Delta Modulator For Rf Baseband Processor Design And Research

Sigma-Delta Analog to Digital Converter (ADC) adopts oversampling, noise shaping and digital filtering techniques to reduce the requirement of component matching. It overcomes limitations on resolution that can not be achieved by conventional Nyquist ADC. Now Sigma-Delta ADC has been mostly used for high resolution A/D conversion. It has extensive applications in such fields as measurement of the instrument, digital audio, ISDN, ADSL and radio frequency (RF) receiver, etc.This dissertation has studied various architectures of Sigma-Delta modulator systematically. According to power dissipation, stability and circuit implementation, a 2-2 cascade architecture is introduced. Oversampling ratio is 32. The attenuation factors of each integrator and interstage coefficients are obtained from behavioral simulation. The impacts of circuit nonidealities and noises on the performance of Sigma-Delta modulator are analyzed. The performance requirements of each circuit block are derived from the transfer function of Sigma-Delta modulator that the nonidealities of integrator are considered. The 14-bit Sigma-Delta modulator for bluetooth receiver baseband channel application is implemented with fully differential switch-capacitor circuits consisting of bootstrapped sampling switch and two-stage OTA. Different input and output common mode voltages are used to improve the modulator's performance. The prototype Sigma-Delta modulator is fabricated in SMIC 0.18um single-poly six metal MIM CMOS technology and occupies 0.7×0.9mm~2. The modulator consumes about 20mW from a 1.8V supply. The chip works well and achieves 78dB of dynamic range with input direct current signal.The distribution of zero-pole and settling performance of two-stage OTA are analyzed. The MATLAB optimization program can find the optimal damping factor and natural frequency that makes the settling time of OTA minimum quickly. The simulation results show that the OTA satisfies all the requirements of the Sigma-Delta modulator.Finally, the work is summarized and the direction of future work is proposed.