Design of a 1-V operational passive sigma-delta modulator

The 1-V operation of a passive sigma-delta modulator has been realized. The dc voltage in the signal paths in the second-order switched capacitor filter section was set at 0.2 V so that metal-oxide-semiconductor (MOS) switches in the signal paths would have enough gate-to-source voltage to turn on without using a voltage boosting scheme. The input switch was replaced by a passive resistor to avoid floating. By modifying gain coefficients in the feedback and the input paths, the bias voltage of digital-to-analog converter (DAC) can be set to 1 V and 0 V and MOS switches become easily activated. Moreover, the correlated double sampling (CDS) scheme was adopted to suppress the 1/f noise and offset voltage produced at the input of a comparator. Successful operation from 1-V supply voltage was confirmed by circuit simulation using the 0.18-mum complementary MOS (CMOS) process.