Roper Photometric manual Introduction Theory of Operation, Potential Wells

Page 35

Chapter 3.

Introduction

Theory of Operation

Potential Wells

Advanced CCD Theory

The charge-coupled device (CCD) is the imager of choice for use in quantitative image acquisition systems. This chapter familiarizes you with CCDs and the terminology used in describing them. It also discusses CCD performance characteristics. If these are already familiar topics, you may still find this chapter useful as a refresher or a reference.

Most CCD imagers are made from silicon, because of its properties when exposed to electromagnetic radiation in the visible spectrum.

In crystalline silicon, each atom is covalently bonded to its neighbors. Incident photons that penetrate the lattice can break these bonds and generate electron- hole pairs. Silicon becomes transparent at 1000–1100 nm and is opaque to light at wavelengths shorter than 400 nm. The photon-produced electronic charge is proportional to the incident light between these wavelength limits.

However, charge can be created by other energy sources. High-energy particles, x-rays, and cosmic rays can break many thousands of bonds. Excessive exposure can damage the crystal lattice.

Bonds can also be broken by thermal agitation. The rate of electron-hole pair generation due to thermal energy is dependent on temperature and can be reduced arbitrarily through cooling. The unwanted charge produced by thermal agitation is called dark current, because it is produced in the absence of light.

To measure the electronic charge produced by incident photons, there must be a means of collecting the charge. The figure A Potential Well illustrates the concept.

A Potential Well

Electrical connection

Polysilicon gate Silicon dioxide

Silicon

Potential well

Incoming light

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e- e-

e-

e-

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Contents Page Rev C1 Limited Warranty Roper Scientific Analytical Instrumentation Your Responsibility Table of Contents Index Description IntroductionBenelux Software Roper Scientific Customer ServiceICL Multiple Parameter Functions Following parameters are illegalICL Function Syntax Readout / Display Clearparallelclearcount Function DefinitionsExposeuntiltrig Exposewhiletrigclearfirst ClearuntiltrigPixelreadoutsoffset, ssize, sbin, psize, pbin LoopendPixeldisplayx,y Shiftimagetostorage ScriptbeginScriptendcontinclear Shiftmodeismalt ShiftmodeisShiftmodeisalt ShiftmodeismShutteropen Single Image Example ScriptsOpen the Shutter TDI Time Delay Integration Panorama Ratio Imaging 2-Frame Ratio CCD E Ratio Imaging Multi-Frame RatioColor Sequence Signal to Begin the ExperimentGood Exposure Time Intermittent ExposureDone EXPOSING, NOW Readout High-Speed SpectroscopyError Codes Class 101 ICL Plexpdisplayscript101 Man PagesBoolean plexpinitscriptvoid Class 101 ICL Plexpinitscript101Class 101 ICL Plexplisterrscript101 Class 101 ICL Plexpsetupscript101 Boolean Plexpstartscriptint16 hcam, voidptr pixelstream Class 101 ICL Plexpstartscript101Boolean plexpuninitscript void Class 101 ICL Plexpuninitscript101ICL This page intentionally left blank Potential Wells Introduction Theory of OperationCharge Transfer Typical CCD Imager CCD Readout Subarray Readout Binned Readout CCD Architectures CCD ArchitecturesFrame Transfer Variations CCD Camera Implementations Resolution SensitivityThick and Thinned CCDs Fiberoptics Sources of NoiseSNR Additional Reading This page intentionally left blank Index Page Index Benelux France Germany Japan
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