| A/D converter is an essential circuitry module to most circuitry system, it can convert analog signals into digital signals. There is increasingly demanding for high accurate systems, which put up higher standard for A/D converter. Performance of traditional Nyquist A/D converter is so vulnerable to the impact of device mismatch, that it is difficult to get high precision. Based on oversampling and noise shaping, ?-? ADC is able to achieve very high resolution. ?-? ADC is mainly composed of two modules, ?-? modulator and a digital filter, and the standard CMOS technology is compatible with mixed analog-digital circuit. ?-? ADC has aroused general interest in the research of high precise A/D converter.Firstly, the basic principles and fundamental structures of ?-? ADC is analyzed. According to requirements of the analog front end in sensor nodes system for the accuracy, bandwidth of A/D converter, the first-order single-bit ?-?ADC structure is chosen. As to the nonideality in analog circuit, qualitative analyses are made, and by means of modeling with matlab, behavioral verifications and simulations of modulator are completed. And then transistor-level circuits of modulator are designed and verified with cadence. Folded-cascade structure is used in integrator amplifier; preamplifier and dynamic latch comparator used in quantizer and a DAC is fulfilled with CMOS switches. Secondly, with the help of fdatool toolbox, digital filter is designed and validated. And, the Verilog code is implemented and verified with ISE platform.?-?ADC with accuracy of 12 bit is realized in SMIC0.18 um 3.3V mix signal 1P5 M process, and the sampling clock is 2MHz. Modulator and digital filter are verified respectively, the effective resolution is 12.46 bit, SNDR reaches 77.8d B. |
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