Digital correction of non-ideal amplifier effects in the MASH modulator

An approach to remove the effects of amplifier finite gain and C-ratio mismatches in the MASH sigma-delta modulator is presented. By adding a digital correction term to the output of the digital noise cancellation filter, the parasitic quantization noise terms can be removed for all but the final stage, eliminating the intermediate quantization noise terms due to non-ideal integrators. Using this technique, the MASH can approach the performance of an ideal third-order modulator. We have confirmed an SNR+THD of 105.6 dB via a behavioral simulation of the MASH using an amplifier open-loop gain of only 500 and capacitor matching errors as large as of 1.0%.