The signal processing for a position sensitive detector(PSD) using an amplitud emodulation/demodulation algorithm is addressed in this article.The external noises,such as daylight and fluorescent lights are eliminated by using the amplitude modulation/demodulation and a low pass filter.The proposed amplitude modulation method is proved to be more accurate and robust than the pulse ampitude modulation method(PAM) by using analysis and experiments.Multiple measurements technique using one PSD sensor by the am...