Emitters and Detectors for Infrared (IR) Touchscreens
Application note
1. Introduction
Touchscreens as a popular user interface
are more and more common. Applications
span from public information systems to
customer self-service terminals. Thus, as a
logical step, more and more devices today
feature this kind of user interface, e.g. bank
automatic teller machines (ATMs), personal
digital assistants (PDAs), mobile phones and
PC displays. The widespread popularity is
actively supported by standard computer
based operating systems, like e.g.
Windows
®
7.
The rapid development of CMOS imaging
sensors and the development of high power
infrared (IR) emitters in slim packages have
led to a series of new optical touchscreen
technologies. Many of them contain
proprietary technology and solutions. Tab. 1
presents a general overview of different
technologies and their features.
This paper will give an overview on IR-based
touchscreen technologies with a special
focus on infrared emitting diodes (IREDs)
and photodetectors to be used in such
applications. It shall help touchscreen
designers to select suitable IR components
for their system and provide some general
optoelectronic guidelines.
Traditionally, IR touchscreens have faced
three criticisms: Size, cost, and ambient light
sensitivity. The first two concerns stem from
traditional matrix-based systems. However,
new technology and slim packages enable a
significant decrease in bezel height
combined with a decrease in cost. Camera-
based systems go even further by reducing
significantly the number of parts at the cost
of
added
computing
and
software
Surface
acoustic
wave
+
o
-
+
+
o
-
o
+
o
+
-
m
IR
matrix-
based
++
-
-
+
++
+
++
++
o
+
-
+
m/l
IR
camera-
based
++
++
++
+
++
+
++
++
++
+
o
++
m/l
IR
projector-
based
++
++
++
++
++
+
-
++
++
+
-
+
l
In-cell
optical
++
++
+
o
++
+
-
-
+
+
-
o
s
Feature
Clarity of image
quality
Resolution
Cost effective for
larger screens
Resistance to
vandalism
Stable calibration
Easy to manufacture
Retrofit possibility
Any object can
create a touch
Touch accuracy
Multitouch capability
Ambient light
insensitivity
Sealable, resistance
to dust
Main market
Resistive
-
+
-
-
-
+
++
o
o
-
+
+
s
Capacitive
o
+
-
-
+
o
o
-
+
+
+
+
m
Table 1: Summary of touchscreen technologies and their features.
(++: excellent, +: good, o: ok, -: does not perform well/does not have this function,
screen size: s: small (2” – 10”), m: medium (12” – 30”), l: large (>32”))
August 13, 2010
page 1 of 14
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