Operational Trans-conductance Amplifier (OTA) is a fundamental building block of analog circuits and systems. OTA has been used to implement many kinds of analog circuits such as; opamps, data converters, four-quadrant multipliers, mixers, modulators and continuous-time filters. In such application, as Asymmetrical Digital Subscriber Lines (ADSLs) and cable-modem, the linearity has to be 60dB while for example, video applications require at least 60dB of linearity at 5MHz. Gm-C topology is a good choice for realizing continuous time filter has better performance in frequency response and electronic tuning capability, but suffer from poor linearity.