The Study Of Structure And Circuits Of High Resolution Sigma-delta Modulator

Oversampled sigma-delta ADC based on sigma-delta (Σ?) modulation technology are well-suited to the implementation of analog interfaces in digital communication and signal processing systems. These converters exploiting the enhanced speed and circuit density of modern VLSI technologies , have been widely used for high resolution A/D conversion. Sigma-delta modulator, combined with oversampling, effectively attenuate the in-band quantization noise in the output signal and enhance the signal-to-noise ratio(SNR) through the shaping of the quantization error. So far, sigma-delta modulator becomes the most attractive technology in VLSI when using it to deal with high resolution A/D converter. In China, the research fall a large distance behind the international. There are few converters having the resolution above 16 bits produced. So, it is very important to research on high resolution modulators.The structure and circuits of high resolution ADC's modulator which applied in audio signal range with 20KHz base band and 16 bits resolution have been researched. The principles of sigma-delta modulator have been discussed firstly and the influences of structure and parameters on resolution have been analyzed. Then on the base of theories, the Simulink toolbox of Matlab has been used to make behavior simulation and FFT analyse of two main structures:2-1-1 and 2-2.The related parameters of modulator such as: PSD,SNDR and ENOB have been gotten by Simulink toolbox on the conditions of different oversampling rates. From the analyses above, topology of modulator has been chosen. In order to make full behavior simulation of sigma-delta modulator, the noise models have been set, taking into account most of the sigma-delta modulator's non-idealities and the final result supports the noise models. Last, the main circuits of modulator have been designed, such as operational amplifier,comparator and clock generator , the design principle of noise- killed logic circuit has been presented. These circuits have been simulated...