A new approach to the calculation of current noise in single quantum well infrared photodetectors is proposed. The modulation noise due to the fluctuation of the emitter barrier potential is taken into account by considering the correlation between the elementary pulses constituting the excess current injected from the emitter when the quantum well is depleted by electrons. A simple relationship between the noise gain and the photoconductive gain of the device is obtained. A comparison with experiments is also reported. ©1997 American Institute of Physics.