EIA TEP105-16-A-2000

$21.45

Test Method for Phosphor Linearity

Published By	Publication Date	Number of Pages
ECIA	2000	9

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Category: ECIA

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Description

Introduction

An excited CRT raster is designed to give the impression of a
continuously excited display without any flicker or scan line
structure. High fiequeixj, field refresh rates and closely spaced
scan lines obscure from the human observer the way in which each
phosphor particle receives its excitation. These factors also
determine how fast the writing speed of the electron beam is across
a given point on the phosphor screen, and therefore how long a
dwell time and how large a charge impulse each particle receives. A
writing speed of one cm per microsecond would produce at each
particle a charge impulse 100 nanoseconds in width (for a one mm
beam spot diameter), a time much shorter than the rise or fall time
of most CRT phosphors. Consequently the product of the beam current
times the dwell time over a particle during each impulse may be
considered to be in effect an instantaneous charge. The phosphor in
this sense is an integrator.

On the opposite extreme are the refresh times between
consecutive pulses, or the time consumed in writing one complete
field. This is many orders of magnitude larger than the pulse width
dwell times and at least one order of magnitude larger than the
luminescent decay time of most phosphors used in CRT displays. Here
we make the reasonable assumption that the phosphor responds
independently to the separate impulses, with no accumulative effect
among them, so that the charge per single pulse determines the
phosphor linearity behavior. For these reasons we characterize the
excitation density in terms of charge dosage per unit area per
pulse rather than in terms of the per unit area beam current
density.