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SFH4258 데이터시트(PDF) 2 Page - OSRAM GmbH

부품명 SFH4258
상세설명  Emitters and Detectors for Infrared (IR) Touchscreens
PDF  14 Pages
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제조업체  OSRAM [OSRAM GmbH]
홈페이지  http://www.osram.com
Logo OSRAM - OSRAM GmbH

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August 13, 2010
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complexity.
The third constraint, the ambient light
sensitivity, remains a very relevant design
challenge. There are several methods to
deal with this, both optically and electrically.
This will be discussed, among other issues,
in
‘General
Design
Considerations’
in
section four.
At the end a brief product selection guide
provides information for a rapid and
successful design-in.
2. Overview of IR Touchscreen
Principles
Generally speaking, IR touchscreens have
several desirable attributes that are not all
present in competing technologies. The
object used to generate the ‘touch’ can have
almost any shape and size and be made of
almost any material. This is in contrast to
most other touchscreen technologies where
some sort of stylus is required.
As IR touchscreens are a solid state
technology they have no moving mechanical
parts or anything placed on top of the
display to reduce the brightness. The latter
fact ensures crystal clear image quality and
robustness over time. This is especially
important as many device or display vendors
sell their products on the customers
perceived display quality. During the past
years several different technologies for IR
touchscreens have come up on the market.
The major ones will be explained in the
following sections.
2.1 IR Matrix-based Touchscreens
The
traditional
IR
matrix
touchscreen
technology is based on the interruption of a
light path in an invisible light grid in front of
the screen. A simplified schematic is
presented in Fig. 1.
In this concept an array of emitters (IREDs)
is employed and covered behind two
adjacent bezels of the screen frame and
creates the invisible optical grid. The
opposite bezels contain the respective
detector arrays (typically phototransistors or
-diodes). This arrangement shields the
active parts from environmental influences
and maintains the quality and brightness of
the image. Additionally it enables screen
retrofits,
and
is
in
fact
completely
independent of the screen for all practical
purposes.
If an obstacle (e.g. a stylus or finger tip)
appears inside the grid matrix it interrupts
the light beams and causes a reduction of
the
measured
photocurrent
in
the
corresponding detectors. Based on this
information the x- and y-coordinates can be
easily obtained.
The IR-matrix based principle is suitable to
recognize static operations as well as
motions. It is not really suitable for high
resolution motion detection, e.g. handwriting
recognition.
Fig. 1: Concept of an IR matrix-based
touchscreen. The influence of a stylus on
the
photocurrent
of
individual
detector
elements is sketched below.



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