A Design For The Modulator Of A 16-Bit Second Order Sigma-Delta Analog To Digital Converter

The sigma-delta analog to digital converter (ADC) is a IC product that is explored byBeijing MXH Device Co.,Ltd. Using top-down way, the design is finished with CSMC 0.5umtwo metal craft.This paper, "A Design for the Modulator of a 16-bit Second Order Sigma-delta ADC", isa part of sigma-delta analog to digital converter including setting up mathematic model ofmodulator, simulating model, designing and simulating schematic, drawing layout. Themodulator with good ability of noise's modulating is used in sigma-delta converter. Noise insignal band is moved to the scale of high frequency by over sampling. Noise in highfrequency is filtered by down sampling filter. So the SNR(Signal to Noise Ratio) can beimproved. The total circuit with differential input is supplied by 5 voltage. The input signalband is 22kHz. OSR(Over Sampling Ratio) is equal to 128.The SNR of output signal shouldbe 96dB. At the same time, the modulator is with the ability of selecting gain. The total circuitconsists of a thousand components.The main performance of circuit, including sampling, SNR, quantized error, quantizednoise and noise modulation, is analyzed in theory in detail after analyzing schematic. Throughconsidering non-linear factor in system such that the limited gain of OPAMP, the limitedband, noise and component parameter, both one order model and two order model are set upand simulated in MATLAB; According to the correct mathematic model, all circuits aredesigned and simulated in HSPICE, for example, OPAMP, comparator, sc, non-overlap clock;At last, layout is finished. After several modification, the result of simulation of mathematicmodel and schematic can be satisfied with. Both LVS and DRC for layout are passed.