Order Sigma-delta Modulator Structure And Data Simulation

With the development of electronic technology, A/D converter requires higher precision, Sigma-delta modulator structure has so far been the most attractive way to meet the requirement. Sigma-delta conversion technology is based on over sampling, noise shaping, and decimation filtering. Sigma-delta A/D converter can achieve high resolution based on over sampling and noise shaping. Comparing with conventional Nyquist converter, sigma-delta converters greatly release the requirements for high performance of analog circuit and precisely matched components. And, these converters can take advantage of the enhanced speed,circuit density and low cost of modern VLSI technologies. Also,because of the major advantages that it is based predominantly on digital signal processing due to its digital nature sigma-delta converters can be integrated into other digital devices. Manufacture technology is not special, hence the cost of implementation is low and will continue to decrease. It is the greatest advantage of all in the cost.The structure and circuits of sigma-delta modulator which applied in low frequency signal with 5kHz base band and 12bits resolution have been researched .The principles of sigma-delta modulator have been discussed firstly and the influences of structures and parameters on resolution have been analyzed. Then on the base of theories,the Simulink toolbox of MATLAB has been used to make behavior modeling simulation. spectrum and SNR can be gotten by FFT analysis .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 circuit modulator have been designed,such as operational amplifier, integrator, comparator and clock generator. These circuits have been simulated and verified with HSPICE. The results were analyzed in MATLAB to check the performance.It is shown that, the designed structure of second-order sigma-delta modulator can achieve 74dB SNR, 12 bits ENOB on the condition of 2.56MHz over sampling clock, 256 over sampling rate. The structure can be used with low frequency signal input to achieve a moderate resolution, such as ADC in temperature compensated oscillator.