SFH4450_ データシートの表示（PDF） - OSRAM GmbH

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SFH4450_

Emitters and Detectors for Infrared (IR) Touchscreens

OSRAM GmbH 

mandatory. To minimize irritations caused by

unintentional radiation (scattering) out of the

glass at the coupling interface a baffle might

be useful. Furthermore it is recommended to

minimize the air-gap between the IRED and

the acrylic glass.

The MIDLED® product family (SFH 46XX)

with its 15° half-angle and flat top is an

excellent candidate, whereas for wide-angle

components the DRAGON or TOP-

/SIDELED® products fulfil the above criteria.

For simple applications the spacing might be

one to two IREDs per inch.

3.6 In-Cell Optical Sensing

Typically, this design does not feature active

IR illumination. However, to overcome the

main drawback of this principle the

SMARTLED® family (SFH4050) of IREDs

with its slim package might be a potential

solution for integration without compromising

the slim overall design.

4. General Design Guidelines

4.1 Emitter Wavelength

Infrared LEDs for camera-based applications

are usually available in two wavelengths:

Around 850 nm and 940 nm. The following

general guidelines will help you to choose

the proper wavelength for your application:

Using an 850 nm IRED results in a higher

sensitivity for CMOS cameras. But due to

factors described below, 940 nm IRED

emitters might be preferable. Additionally,

detectors with ‘day-light blocking filter’ (black

resin) often have their maximum at around

900 nm as well. Thus, 940 nm IREDs may

be used with discrete phototransistors/-

diodes. The detector’s data sheet should be

consulted to find the best match.

Although human eyes are nominally

insensitive to wavelengths above 800 nm

according to the CIE V(λ) curves, it has been

shown that a red glow is perceived in 850

nm IREDs at high power levels. This effect is

around 50 – 100 times lower at 940 nm,

therefore this wavelength should be chosen

if a faint red glow is visible to the user and

definitely undesired in the application.

Eye safety standards should be observed at

all times. An application note specifically on

this topic is available from OSRAM (“Eye

Safety of Infrared Light Emitting Diodes”).

4.2 Suppression of Ambient Light

The influence of ambient light on the

detector signal may be suppressed and

reduced in several ways.

The most important technique is to block

visible light in a way that the detector is only

sensitive to a narrow wavelength range in

the IR region. OSRAM offers to the designer

a range of products with so called ‘daylight

blocking filter’. OSRAM silicon-detectors with

daylight blocking filter are sensitive within

the narrow 800 nm - 1100 nm wavelength

range. These components are characterized

by their black (visible-absorbing, IR-

transmitting) packages.

This measure generally provides sufficient

ambient visible light suppression for most

applications. Please refer to the product

selection guide for further details and

availability.

Note that usage of devices with daylight

blocking filter is recommended in every case

to avoid detector saturation.

However, there are additional sources of IR

light which might interfere with the signal of

interest. The following gives a brief overview

of possible distortions and sketches a more

demanding solution, if the conventional

‘daylight blocking filter’ is not sufficient.

4.3 Suppression of Infrared Noise

Minimizing and counterfighting unintended

infrared light, which acts as noise in the

detector, is the main design challenge.

August 13, 2010

page 7 of 14

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