Design Of Second Order 16bit Resolution Delta-Sigma Modulator

Delta-Sigma ADC is the most robust ADC against circuit imperfections and fulfills an important role in today's mostly digital mixed-mode systems. Delta-Sigma ADC consists of an analog delta-sigma modulators part and the digital decimator part, and the analog delta-sigma modulators decide its performance. Because delta-sigma ADC is the system of adaptive delta modulation(ADM),with the technique of oversampling and noise shaping, its resolution can be 16bit to 24 bit.The principle of delta-sigma modulator (DSM) is introduced firstly. Then the design methods of second order 16bit delta-sigma modulators are discussed. The modulator consists of integrators, comparators and voltage reference, and we choose the full difference switched-capacitor circuit. At the beginning the topology of the modulator and its coefficients between adjacent stages are decided, then it is emphasized the effect of each block's performance to the system, and discussed the principle and design method of the key circuits. Though introducing the effect of the operational amplifiers'DC gain, operational amplifiers'GBW, operational amplifiers'DC output swing, operational amplifiers'slew rate, comparator, voltage reference and the switcher's resistance, we decide the parameters of each block and finish our design. It is implemented in the CSMC N-well0.5μm CMOS process with double-poly and three-metal. Simulation shows that, the modulator, operating from single 5 V power supply,±2.5V reference voltage, oversampling clock of 895 kHz, achieves SNR of 100dB at the condition of 50Hz input, satisfies our requirement.