Operational Transconductane Amplifier (OTA) is a fundamental building block of analog signal processing application. This paper demonstrates a wide-linear-range low voltage subthreshold-mode based fully differential OTA using bulk-driven technique. The proposed OTA is linearly tunable with the feature of low distortion and high output impedance. The open loop gain of OTA is enhanced through use of improved Wilson current mirror. The OTA provides an increase in its linearity to about +/- 1.9 volt. The open loop gain is enhanced to 65d8 at unity gain bandwidth (UGB) of 609.46 KHz. The proposed OTA operates at 0.9 volts and power consumption of the OTA remains in range of few hundreds of nanowatts. The OTA analysis has been performed in a standard TSMC 0.18 micrometer technology on BSIM 3v3 model using ELDO Spice Simulator.