August 13, 2010

page 1 of 14

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.

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

Feature

Resistive

Capacitive

Surface

acoustic

wave

IR

matrix-

based

IR

camera-

based

IR

projector-

based

In-cell

optical

Clarity of image

quality

-

o

+

++

++

++

++

Resolution

+

+

o

-

++

++

++

Cost effective for

larger screens

-

-

-

-

++

++

+

Resistance to

vandalism

-

-

+

+

+

++

o

Stable calibration

-

+

+

++

++

++

++

Easy to manufacture

+

o

o

+

+

+

+

Retrofit possibility

++

o

-

++

++

-

-

Any object can

create a touch

o

-

o

++

++

++

-

Touch accuracy

o

+

+

o

++

++

+

Multitouch capability

-

+

o

+

+

+

+

Ambient light

insensitivity

+

+

+

-

o

-

-

Sealable, resistance

to dust

+

+

-

+

++

+

o

Main market

s

m

m

m/l

m/l

l

s

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”))