The paper deals with fully-differential inverter-based Operational Transconductance Amplifier (OTA) designed using rectangular transistor arrays (RTA) and improved composite transistors (ICT). The two versions of the same OTA are designed and the respective performance has been shown under aggressive supply voltage scaling down to 0.3 V. Post-layout simulations referring to 180~nm CMOS process technology have shown how the ICT solution with its proper body bias offer a higher voltage gain, CMRR, PSRR and a lower power consumption compared to the respective RTA version.