Research On Low Voltage Low Power Design Of Sigma-Delta ADC

As the feature size of modern integrated circuit (IC) keeps reducing, its operation frequency, density and complexity as well as its power dissipation is continuously increasing. Meanwhile, battery-charged portable electronic devices such as mobile phone, digital camera, PDA and so on are also developing very fast. The demand of long stand-by time of the consumer products keeps increasing. So, low voltage low power design of integrated circuits becomes one of the hot and difficult research areas in both academia and industry. On the other hand, more and more Sigma-Delta ADCs are applied to the portable electronic devices recently, which could offer quite a high resolution at a low cost due to utilizing the oversampling and noise shaping technology. For these reasons, as a good example, the thesis focused the research of low voltage low power mixed-signal IC on Sigma-Delta ADC.Because of differences between design methods for analog and digital circuits, the recent approaches to low power design of digital and analog circuits were discussed, summarized and organized respectively. The fundamental principles, current technologies and developments on Sigma-Delta ADC were introduced. And the low voltage low power design for analog and digital circuits in it was conducted.As to the analog part, Sigma-Delta modulator, all kinds of essential and non-ideal factors that are related to the power consumption of modulators were analyzed in the system level. Based on the analysis, it was discussed that how to fix the order for modulators to fulfill the system requirements as well as to achieve the minimum power. In the structure level, a new structure of switched-capacitor integrators was proposed to realize a small coefficient and solve the problem in zero optimization. Compared to the traditional one, this new structure largely reduced the area and power consumed by capacitors. In circuit level, the power consumption in operational amplifiers was analyzed. After analyzing and comparing several classical structures of operational amplifiers, a new structure of class AB/AB was proposed to reduce the power consumption in general operations. A kind of cross-couple load was used to eliminate the CMFB circuit in the first stage to further reduce the power. This thesis also analyzed all kinds of important non-idea factors in Sigma-Delta modulators, and introduced methods to calculate the minimum spec for all modules according to these factors, which means the required minimum power in order to fulfill the system requirements. The validity of research results was verified by system simulation.As to the digital part, decimation filter, different characteristics under different down-sampling rates were analyzed. Two structure optimization schemes for decimation filters working in different down-sampling rates were presented respectively. As to the low down-sampling rate, three different structures to implement the sinc filter were analyzed and compared, a modified polyphase structure was proposed. Simulation results showed that in comparison with traditional CIC structure, the new structure could save about 36% area and 50% power. The results were also better than the latest reported polyphase structure: about 14% area and 3% power could be saved. As to the high down-sampling rate, the advantage of CIC structure was testified. And the optimization for the decimation structure was brought forward based on the distribution of power dissipation. All work in this part was completed in TSMC 0.18μm technology.