A 0.7-V MOSFET-only switched-opamp ΣΔ modulator in standard digital CMOS technology

A 0.7-V MOSFET-only ΣΔ modulator for voice band applications is presented. The second-order modulator is realized using a switched-opamp technique. All capacitors are realized using compensated MOS devices operated in the depletion region. A combination of parallel and series compensated depletion-mode MOSCAPs is used to obtain high area efficiency. The circuit is fabricated in a 0.18-μm CMOS process. The only components used are standard n-MOS and p-MOS transistors with threshold voltages of approximately 400 mV. All transistors are operated within the supply voltage window of 0.7 V; voltage boosting techniques are not used. The active area is 0.082 mm². The modulator achieves 67-dB signal-to-noise-and-distortion ratio, 70-dB signal-to-noise ratio, and 75-dB dynamic range at 8-kHz signal bandwidth and consumes 80 μW of power.