Quantisation noise reduction in multibit oversampling Sigma - Delta A/D convertors

It is well known that when expanding the internal quantiser of a high-order single-path oversampling Sigma - Delta A/D convertor from 1 bit to n bits, the improvement of baseband quantisation noise is (n-1) bits. This result, however, ignores the enhanced stability characteristics of multibit systems. When full advantage is taken of multibit Sigma - Delta modulation, baseband quantisation noise reduction much greater than 1 bit per additional quantiser bit can be achieved. To realise this in a practical system, the feedback multibit D/A must exhibit sufficiently high linearity.