A Design And Analyse For The High-powered Modulator Of The Fourth Order Sigma-Delta

The sigma-delta analog to digital converter (ADC), as a kind of ADC with high precision, is achieved by using the technology of sigma-delta modulation and digital filter. Conventional Nyquist Analog-to-digital converters require precise analog circuits .In contrast,oversampling converters use oversampling technique ,make the quantization noise power small in baseband , increase the SNR in baseband and achieve the more ENOB . Sigma-delta ADC uses sampling technique, the application of plastic technology and digital filtering noise technology to achieve high performance. In sigma-delta ADC, modulator can through relatively simple, not high demand on accuracy of analog conversion analog signals, such as switch electric volume controller, a comparator, etc, in dealing with analog signals, the same resolution precision of ADC is higher than analog circuit processing ability . In today's integrated circuit design and technology level of sigma-delta ADC , it has become a major development direction.In this paper, firstly, the theory about signal sampling, SNR, quantized error, quantized noise and noise modulating is analyzed, On the base of which, first order and second order mathematic model of modulator are founded differently. Non-linear factors in system is considered as the same time such as the limited gain of the OPAMP, the limited band, heat noise and non-matched capacitor. Simulation for mathematic model is completed in MATLAB, so the result is that the adjusted gain in system is obtained and SNR is much more than 110dB.Secondly, circuits, including OPAMP, comparator, switch, non-overlap clock, are designed by referring to mathematic model. All simulation for circuits is done in HSPICE, and the result from circuits'simulation is compared with that from model's simulation. At last, layout is finished in Cadence. The whole of design is completed in environment of CZ6H.