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SFH4059 Datasheet(PDF) 7 Page - OSRAM GmbH |
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SFH4059 Datasheet(HTML) 7 Page - OSRAM GmbH |
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7 / 14 page  August 13, 2010 page 7 of 14 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. |
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