A 0.4-V 410-nW opamp-less continuous-time ΣΔ modulator for biomedical applications

A 0.4-V opamp-less Σ∆ modulator for biomedical applications is presented. The continuous-time (CT) 2nd order Σ∆ modulator is realized using a passive filter topology. In order to obtain a small area, all capacitors are realized using parallel compensated depletion-mode MOSCAPs. To maximize the performance, genetic algorithms (GAs) are used to optimize the circuit for smaller area and higher signal-to-noise-plusdistortion ratio (SNDR). In the dynamic comparator, which is the only active block in the circuit, bulk-driven technique is used to obtain lower supply voltage operation. The circuit was designed in a 130 nm CMOS technology and, using a clock frequency of 2 MHz, has a bandwidth of 10 kHz to cover the most common biopotential signals. The electrical transient noise simulation results show that the circuit achieves a peak SNDR of 58 dB and a dynamic range of 64 dB while dissipating only 410 nW, which corresponds to an energy efficiency of 32 fJ/conv.-step.