第4章常用传感器-6(3.22-3.25)汇编.ppt

* * Position sensitive device (PSD) is sensitive to incident light. Output signal relates to the location of light spot on photosensitive surface. The features comparing with quadrant detector (象限探测器). Its spot shape is not strictly required. Output signal independents on light focusing, only relates with the center location of light energy. Photosensitive surface need not part, eliminating the dead zone, can continuously measure the location of light spot with high resolution, 1D PSD up to 0.2μm. It can detect the location and intensity, the total photocurrent output of PSD is related with the intensity of incident light. 4.6.3 Photoelectric position sensor (光电位置传感器) 4.6 Photoelectric Effect and Sensors PSD applications: laser beam alignment (激光束对准), displacement and vibration measurements, flatness testing (平面度检测), two-dimensional coordinate (坐标) detection system. PSD consists of three layers, P, I and N, formed on the same si chip. Figure4-47 The schematic of an end face structure of PIN-based PSD 4.6 Photoelectric Effect and Sensors Working process: Light is launched onto the photosensitive layer of PSD A certain charge generate (proportional to incident light) Photocurrent through the resistive layer output by the electrodes. Assume the distance from the both electric poles to the center of photosensitive surface is L, and output photocurrent are I1 and I2, the total current I0 is 4.6 Photoelectric Effect and Sensors In terms of the center point of PSD is used as the origin (原点), distance from the light spot is x, so The energy center location of light spot (independents on I0). * * * * * * * * * * * * * * * * * * * * * * * * * Figure 4-36 (a): Back light injection method. (Front light injection method for transparent electrode透明电极). Conversion between optical and electrical signals (光电信号转换过程) Semiconductor absorbs light ? Electron-hole pairs produce ? minority carriers are collected into a deep potential well (reflecting the intensity of i