Design of low-voltage MOSFET-only ΣΔ modulators in standard digital CMOS technology

A design strategy of low-voltage high-linearity MOSFET-only ΣΔ modulators in standard digital CMOS technology is presented. The modulators use substrate-biased MOSFETs in the depletion region as capacitors, linearized by different compensation techniques. This work shows the design, simulation and measured results of a number of MOSFET-only ΣΔ modulators using different implementations of so called compensated depletion-mode MOS capacitors. The modulators are designed for the demands of speech band applications. The performance of the modulators proves the capability of compensated depletion-mode MOS capacitors to fulfill analog circuit requirements at low supply voltages with reduced processing efforts.