An insight a digital sensor for delta-sigma modulator investigation

Even an ideal delta-sigma modulator exhibits certain nonlinear behaviour. So its comprehensive analytical description has been both an absorbing and confusing task. Hence simulation and measurement are the key factor for a successful evaluation of the delta-sigma structure. This work is about high-quality decimation filters (digital sensors) for delta-sigma modulator investigations. They are based on a two-phase (two-branch) parallel structure using recursive allpasses which are particularly suitable for decimation by a factor of two. Moreover the repeated use of a basic decimation stage (BDS) makes this structure highly modular and well fittted for silicon implementation. An important BDS with only three coefficients (1/8, 9/16 and -1/16) has been presented in detail. Applied in the five stage decimaior and compatible with CMOS technology, it achieves a 20-bit processing accuracy for the passband of 20 kHz -without the design complexity and cost penalties incurred in alternative approaches. The paper includes some design results with performance evaluation under fixed point arithmetic. The in-situ developed software tools are also described.