Colortrac SmartLF Ci 40, Service Manual

Page: 11 / 101

Page 11
Ci Scanner Service Manual
8. CIS TECHNOLOGY
A Contact Image Sensor (CIS) is an integrated module that comprises an illumination system, an
optical system and a light-sensing system - all within a single compact component.
Cross-section of a CIS scanner sensor.
The light-sensing system is the silicon surface which is
divided up into (e.g. 5000) discrete square cells, the size
of each being a fraction of an inch depending upon the
required scanning resolution (a 600 dpi scanner will use
a CIS whose cells are 1/600" across). The optical
system is a rod lens array that directs light from the
document surface onto the silicon surface. Such an
optical system is 1:1; i.e. there is no reduction or
enlargement; and this results in a scanner offering the
best performance in terms of resolving power and
geometric accuracy.
The illumination is provided by Light Emitting Diodes
(LED’s) shining down a light guide, which in turn directs
the light onto the document. There are three LED’s
(Red, Green, and Blue) which strobe rapidly, thereby
providing the colour content in the scan. Note that there
are no colour filters in the optical or light-sensing
system.
Ci scanner CIS Array
The colour gamut of a CIS scanner is therefore determined by the spectrum of each of the LED’s,
rather than by colour filters as is the case with CCDs. Because colour filter technology is more
developed than LED spectrum technology, a CIS scanner will not provide as wide a colour gamut
as a CCD scanner.
However, rapidly strobed LED’s require no warm-up period. Therefore, a CIS scanner can be
switched on and used immediately. Furthermore, LED’s are very stable which means that a CIS
scanner does not require frequent re-calibration.