A single DAC CT sigma-delta modulator with Butterworth STF characteristic

In this paper a continuous time Sigma-Delta modulator filter structure is proposed, which combines the known feed forward structure and an excess loop delay (ELD) compensation technique in order to realize an ELD compensated modulator with Butterworth signal transfer characteristic, which employs only one digital to analog converter (DAC) in the feedback path. A mapping strategy for the coefficient values is given and an exemplary modulator is evaluated through simulation. It is compared to a modulator with feed forward filter structure and an additional feedback path for ELD compensation. Furthermore an investigation on the sensitivity to coefficient variation is presented.