A 0.8-V 816-nW delta–sigma modulator for low-power biomedical applications

This letter discusses the implementation of a low-voltage, low-power delta–sigma modulator as a sensing stage for biomedical applications. A distributed feed-forward structure and bulk-driven operational transconductance amplifier are used in order to achieve efficient operation at a supply voltage of 0.8 V. Instead of conventional low-voltage amplifier architectures, our design uses folded-cascode amplifiers, although they are not used in most low-voltage circuits. A wide input swing is achieved by using the bulk-driven approach, and the drawback of the limited voltage swing of the cascoded output stage is overcome by the distributed feed-forward modulator. The designed modulator has a dynamic range of 49 dB at a 0.8-V supply voltage and consumes only 816 nW of power for the 250-Hz bandwidth. The core chip size of the modulator is 1000 μm × 500 μm by using the 0.18-μm standard CMOS process.