A 1.8-V MOSFET-only Sigma Delta modulator using substrate biased depletion-mode MOS capacitors in series compensation

A low-voltage high-linearity MOSFET-only Sigma Delta modulator for speech b and applications is presented. The modulator uses substrate biased MOSFETs in the depletion region as capacitors, linearized by a series compensation technique. A second-order fully differential single-loop architecture has b een realized in a conventional 0.25-mum digital n-well CMOS process without extra layers for capacitors. An SNDR of 72 dB and an SNR of 77 dB is obtai ned with 8-kHz signal bandwidth at an oversampling ratio of 64, The circuit consumes about 1 mW from a single 1.8-V power supply and occupies a core a rea of 0.08 mm(2).