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

A low-voltage high-linearity MOSFET-only /spl Sigma//spl Delta/ modulator for speech band 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 been realized in a conventional 0.25-/spl mu/m digital n-well CMOS process without extra layers for capacitors. An SNDR of 72 dB and an SNR of 77 dB is obtained 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 area of 0.08 mm/sup 2/.