A 1.8V MOSFET-only sigma-delta modulator using compensated MOS-capacitors in depletion with substrate biasing

A low-voltage high-linearity MOSFET-Only ΣΔ 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 2^nd-order fully-differential single-loop architecture has been realized in a conventional 0.25µm digital n-well CMOS process without extra layers for capacitors. An SNDR of 72dB is obtained with 8kHz signal bandwidth. The circuit consumes about 1mW from a single 1.8V power supply and occupies an area of 0.08mm².