Abstract: In this paper, a high gain and high speed fully differential gain boosted operational amplifier is proposed.The amplifier is designed for sample and hold circuit of pipelined analog-to-digital converter.Both the main amplifier and the boosted amplifier adopt fully differential folded-cascode structure.The main amplifier uses a switched capacitance common mode feedback circuit to stabilize the output.With 3.0 V power supply, this circuit is designed in 0.18μm CMOS process.Spectre simulation shows that the whole amplifier has the DC gain of 112 dB and the unity gain bandwidth of 1.17 GHz under 2 pF single ended load.