A 265μW Continuous-Time 1-2 MASH ADC Achieving 100.6 dB SNDR in a 24 kHz Bandwidth

We present a high-performance audio CTΔΣM that uses an FIR-filtered 1-2 MASH architecture. The modulator uses a singe-bit first-order input stage that achieves a maximum stable amplitude close to full-scale in spite of using a 1-bit quantizer. We show that FIR feedback can be used to advantage in a MASH converter by effectively filtering the first-stage error that is coupled to the second stage. Our design achieves 100.6 dB peak SNDR in a 24 kHz bandwidth, resulting in a Schreier FoM in excess of 180 dB.