Operational Amplifier is the most common building blocks of most of the electronics system may not need introduction. They are integral part of many analog and mixed signal systems. Opamps with vastly different level of complexity are used to realize functions ranging from dc bias generation to high gain amplification, filtering or ADCs. The design of opamp continues to pose a challenge as the supply voltage and transistor channel lengths scale down with each generation of CMOS technology. Opamp consists of one or more differential stages and usually followed by additional gain stages depending upon the requirements.