Noise analysis for position-sensitive detectors

A study of the different noise sources in a position sensitive detector (PSD)-transimpedance amplifier (TIA) sensing system is presented and the dominant noise sources are identified. The effect of these noise sources on the position detection capability of the sensing system is analyzed. An expression derived for the position resolution of the phase method of position detection reveals the position resolution depends inversely on the modulation frequency of the light source and the square of the amplitude of the currents flowing through the metal electrodes, and is dependent on the position of the incident light beam. Simulation results show that the best achievable position resolution is at the center of the PSD and becomes worse as one moves away from the center toward the edges. Compared to the 4 nm//spl radic/Hz position resolution that is achievable using the amplitude method of position detection, the phase method of position detection provides a resolution of 9 nm//spl radic/Hz and 6 nm//spl radic/Hz corresponding to a modulation frequency of 50 kHz and 70 kHz respectively.