Ultra Low-Power OTA for Biomedical Applications

This paper presents a design of an ultra low-power operational transconductance amplifier (OTA) intended for biomedical applications and realized in a 0.18 gm CMOS technology. The proposed OTA take advantages of bulk-driven (OTA) scheme to reduce power consumption. The OTA uses a single 0.8 V supply and dissipates 5.5 pW of power and provides 70 dB gain which makes it suitable for use as a main block of many biomedical applications including implantable and wearable sensors. The simulation results are compared with conventional OTA structures and some recent works and indicate significant increase in gain while indicating a reduction in power consumption.

I. Introduction

Low voltage and low frequency operating ranges are the main characteristic of human physiological signals. The need for detecting these signals and enormous demand for portable biomedical devices, have resulted in the rapid development of low-voltage, low-power analogue circuit schemes. In the analogue biomedical circuits, OTAs are the most power-hungry analogue blocks. In this work the primary goal is to reduce power dissipation of an OTA. Typically reducing the operating current, or power supply voltage leads to a reduction in power consumption. In order to reduce the operating current and hence reduce the power consumption, the MOSFET is needed to be biased in subthreshold or weak inversion region [1]–[2]. In weak inversion region, the drain current of a MOSFET can be calculated by the following equation;

$$\begin{equation*}{{I}_{D}}={{I}_{o}}\frac{W}{L}\left[ \exp \left( \frac{-[{{V}_{GS}}+(\eta -1){{V}_{BS}}]}{\eta {{V}_{t}}} \right) \right]\left[ 1-exp\left( \frac{{{V}_{DS}}}{{{V}_{t}}} \right) \right] \tag{1}\end{equation*}$$