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This paper presents the analysis and design of high speed, high gain fully differential operational amplifier(op-amp). The op-amp is designed for sample and hold circuit of 14 bit 100 MS/s pipelined analog-to-digital converter (ADC). Both the main op-amp and the boosting op-amp are fully differential folded-cascode. The main op-amp has a switched capacitance common mode feedback circuit. The boosting op-amp is connected as a follower. The op-amp is designed in 0.18 mum CMOS process with 3.0 V power supply. Spectre simulation shows that the op-amp has the DC gain of 112 dB and the unity gain bandwidth of 1.15 GHz.