An ultra-low-voltage OTA in 28 nm UTBB FDSOI CMOS using forward body bias

Abstract

This paper presents an ultra-low-voltage, sub-µW fully differential operational transconductance amplifier (OTA) designed in 28 nm ultra-thin buried oxide (BOX) and body (UTBB) fully-depleted silicon-on-insulator (FDSOI) CMOS process. In this CMOS process, the BOX isolates the substrate from the drain and source and hence enables a wide range of body bias voltages. Extensive use of forward body biasing has been utilized in this work to reduce the threshold voltage of the devices, boost the device transconductance (gm) and improve the linearity. Under nominal process and temperature conditions at a supply voltage of 0.4 V, the OTA achieves −64 dB of total harmonic distortion (THD) with 75% of the full scale output swing while consuming 785 nW. The two-stage OTA incorporates continuous-time common-mode feedback circuits (CMFB) and achieves DC gain = 72 dB, unity-gain frequency of 2.6 MHz and phase margin of 68°. Sufficient performance is maintained over process, supply voltage and temperature variations.