Design of CMOS Sigma-Delta modulators for audio applications

Sigma-delta ADC, not only has adopted the technology of oversampling, but also utilized noise shaping which modulate the quantization noise in the baseband to the high frequency area. It increases the SNR in baseband and the effective quantization number of the converter. Because of the modulation technology, it makes sigma-delta ADC allowed to use one bit comparator, in addition Conventional Nyquist converters require analog components that are precise and highly immune to noise and interference while Sigma-delta converters can be implemented using simple and high-tolerance analog components. Currently, sigma-delta ADCs have been widely used for audio A/D conversion. In this thesis, the principles of sigma-delta ADCs are discussed firstly. Then the 16 bits audio sigma-delta ADC has been designed using the top-down design method. The architecture and design methods of sigma-delta modulators are studied. Based on it, the bits of quantizer, oversampling ratio and the orders and topology of modulator have been analyzed and designed. Then a stable 3 order single loop modulator has been implemented. This novel architecture is more insensitive to the performance of analog circuit and the matching of component. At the same time the influence of various non-ideal factors also has be considered.