A novel low-voltage two-stage operational amplifier employing class-AB architecture is presented. The structure utilizes level-shifters and current mirrors to create the class-AB behavior in the first and second stages. With this structure, the transconductances of the two stages are double compared with the normal configuration without class-AB behaviors with the same current consumption. Thus power can be saved and the operation frequency can be increased. The nested cascode miller compensation and symmetric common-mode feedback circuits are used for large unit-gain bandwidth, good phase margin and stability. Simulation results show that the sample-and-hold of the 12-bit 40-Ms/s pipelined ADC using the proposed amplifier consumes only 5.8 mW from 1.2 V power supply with signal-to-noise-and-distortion ratio 89.5 dB, spurious-free dynamic range 95.7 dB and total harmonic distortion -94.3 dB with Nyquist input signal frequency. A novel low-voltage two-stage operational amplifier employing class-AB architecture is presented. The structure utilizes level-shifters and current mirrors to create the class-AB behavior in the first and second stages. With this structure, the transconducts of the two stages are double compared with the normal configuration without class-AB behaviors with the same current consumption. The nested cascode miller compensation and symmetric common-mode feedback circuits are used for large unit- Simulation results show that the sample-and-hold of the 12-bit 40-Ms / s pipelined ADC using the proposed amplifier consumes only 5.8 mW from 1.2 V power supply with signal-to-noise -and-distortion ratio 89.5 dB, spurious-free dynamic range 95.7 dB and total harmonic distortion -94.3 dB with Nyquist input signal frequency.