A Wide Linear Range Ultra-low Transconductance Amplifier for Biomedical Sensor Applications

In the field of biomedical sensors, active filters with very low cutoff frequencies are required because of the weak electrical signals from the human body. The Gm-C filters are more prominent among the filter designs, which consist of an operational transconductance amplifier (OTA) and a capacitor. The key design issues are transconductance and linearity. In this paper, a new ultra-low transconductance OTA structure is proposed. The basic idea is to extend the linear input range of the OTA using the source degeneration pseudo-resistor technique and the bulk-driven technique. The transconductance is reduced by using series-parallel current mirrors for the OTA. This ultra-low transconductance OTA has an extremely low bias current of 0.1nA and a shunt factor of 100, reducing the OTA transconductance to 0.4pS with 39.55μVrms noise. It also increases the linear input range from ±50mV to ±2.5V, extending it by a factor of 50.