This paper proposes a full differential and low-noise chopper-stabilized amplifier for input signal amplification of sigma-delta analog to digital converter (ADC). Based on chopper stabilizing and dynamic matching techniques, folded-cascode structure with class AB output stage is adopted and chopper switches are used at low-resistance nodes in the current paths to improve the signal bandwidth and output voltage swing. The simulation results based on chartered 0.35um CMOS process show that with the power supply of 3.3V, the chopper-stabilized amplifier has open-loop gain of 84 dB and gain bandwidth (GBW) of 483 kHz. Between 1 Hz and 1 kHz, the input equivalent noise is 1.6uV/ z H without chopper signals and is reduced to 40nV/ z H after chopper signals of 38.4 kHz are added.