Resolution of a positioning system with signal conditioning, based on a PSD optical sensor. Influence of system noise

Abstract

This paper presents an analysis of the influence of electronic noise from sensors and electronic conditioning circuits on the resolution of measurement in a system based on a PSD (Position Sensitive Device) optical sensor. In a previous study, the authors proposed the design of signal conditioning circuits for optical sensors, which generally supply currents of tens of nA that must be suitably managed before the analogue-to-digital conversion process (total gain close to 20M). The present work comprises an analysis of resolution influenced by the noise of the proposed circuit, considering different choices for retrieving the desired information and taking into account the equivalent noise bandwidth (ENBW) used in each one. Shot noise, thermal noise and flicker noise have been considered for the different stages, as well as how next stages amplified noise of previous ones. Once the global expression of noise and its influence on resolution have been obtained, sensitivity from different parameters and the result of resolution were calculated and discussed. Some of the main results of this work indicate that the resolution on the sensor surface, depending on the method of information retrieval, is between 3 and $12\mu m$. This value translated to resolution in space, at a distance of 3.5 m and with a lens on the sensor of focal f=8 mm is from 1.3 to 5.2 mm.