System Design of Σ-Δ Modulator for VoIP Chip

Dependency of SNR with the structure,order,quantizer bits and over-sampling rate of Σ-Δ modulator was analyzed in detail. Effects of nonidealities,such as 1/f noise,switching thermal noise,clock jitter and finite DC gain of op-amp on Σ-Δ modulator,were discussed. Parameters of the modulator were defined through Matlab behavioral simulation. And based on the analysis,system structure of a third-order 2-1 cascaded Σ-Δ modulator was designed. Simulink simulation indicated that,with the above mentioned nonidealities taken into consideration,the modulator still had an SNR of 96 dB,which met the specification of a 16-bit A/D converter in a certain VoIP chip.