Dynamic biasing current source for highly linear OTA with constant transconductance and wide input common—mode range

This paper discusses the design of a new dynamic bias current source circuit for a low-power (1 muW) sub-threshold transconductance operational amplifier (OTA) with a wide input common mode voltage range. This was done by cancelling the g_m sensitivity to voltage changes by using a replica differential pair and a current subtractor circuit to sense and generate the main bias current and injecting the opposite polarity of the current offset into the auxiliary current source. The simulation results confirm the efficiency of the dynamic biasing circuit by significantly reducing the g_m variation up to 96% in comparison with identical differential pair with a fixed biased current source in a standard 0.25 mum CMOS process with 1 V power supply. The power consumption is 469 nW.The proposed linear amplifier is intended for use in state of the art biomedical wireless sensor, where it is desirable to have highly linear amplifier gain.