Photocurrent measurement through frequency domain analysis

This paper presents the technique of using the frequency response function statistics of a photosensor to perform indirect light intensity measurement. Both random phase multisine and Gaussian noise source were designed as the excitation signals to the photodetector circuit. A miniature solar cell was used to provide the photo-generated current in tandem with different light irradiance from a LED light bulb with brightness control. The results show that the standard deviation of the frequency response function is a monotonic function of the photo-generated currents. Larger current (or light intensity) produces larger standard deviation. This promising result provides an indirect method to measure the photo response of optical sensors especially those sensors that produce minute photocurrent, thus avoiding environmental interference faced in wide-band direct current measurement technique.