A low-power low-noise and high swing biopotential amplifier in 0.18 µm CMOS

In this paper, a low-power, low-noise and high swing capacitively coupled instrumentation amplifier for biomedical applications is proposed. It uses the folded cascode operational transconductance amplifier (FC-OTA) with current scaling at the output branch to reduce the noise. To overcome the reduction in the effective transconductance of the OTA due to current scaling, series–series and shunt–shunt feedback techniques are proposed at the folded node of the FC-OTA and the composite transistor is proposed at the bottom current source of the FC-OTA. An optimization procedure is also proposed for sizing the input transistors of the FC-OTA to obtain better noise-power tradeoff. To assess the efficacy of these techniques, a biopotential amplifier is designed in 0.18 µm CMOS process and it is studied through simulation. From this study, it is found that the proposed amplifier has a 1.5–22 times and 1.4 times higher input swing and output swing respectively compared to those reported in literature. It has a gain of 39.75 dB, a bandwidth of 0.3 Hz–4.4 kHz and a total input-referred noise of 3.19 µVrms integrated over 1 Hz–10 kHz. The power consumption of the amplifier is 4.07 µW at a VDD of 1.8 V. It achieves a noise efficiency factor of 2.78, and provides input and output signal swings of 14.86 mVpp, and 1.38 Vpp respectively at THD of 1%.