Design of Low-Voltage MOSFET-Only Switched-Capacitor Filters

A 1.8-V switched-capacitor (SC) and a 1-V switched-opamp (SO) filter in standard digital CMOS technology is presented. The filters use substrate-biased MOSFETs in depletion region as capacitors linearized by parallel compensation technique. The simulation results confirm the capability of compensated depletion-mode MOS capacitors to fulfill analog circuit requirements at low supply voltages. A novel SO biquadratic structure is also presented to realize high-Q filter specifications. At a 1.8-V supply, the SC filter achieves - 40 dB THD, and at a 1-V the SO filter has -46.3 dB THD in 0.18-μm CMOS process.