Automatic coefficients design for high-order sigma-delta modulators

An automatic-design methodology for designing high-tolerance modulator coefficients for high-order sigma-delta modulators (SDMs) from system specifications is presented. The methodology covers many design concerns including SDM coefficient tolerances for circuit component mismatch, stability, reduction of in-band tones, design tradeoffs among in-band noise suppression, oversampling ratio, and modulator order. Moreover, a high-order SDM synthesis tool (HOST) based on the methodology has been implemented in a C language program. Even for inexperienced designers, reliable and high-tolerance SDM coefficients for various applications can be automatically and efficiently generated using HOST. For synthesized SDM´s with orders from three to eight and oversampling ratios from 32 to 256, coefficient variations within 2% (1% for the eighth order) are allowed and the resulting peak signal-to-noise ratio degradation is less than 3 dB. Several design examples synthesized by HOST are included