IRLED.DEC–pm
Portable communication to exploit infrared technology
Infrared devices have long enjoyed varied but mature markets. Now a
standard for infrared data exchange may pave the way for exciting new
applications
BY PATRICK MANNION Associate Editor
As we plunge into the information-age abyss, a veritable flood of
small, low-cost, portable computers and personal digital assistants (PDAs)
is waiting to engulf the consumer market. With these devices comes a
demand for low-cost and efficient remote communication between them. These
potential products present an exciting window of opportunity for those in
the near-infrared arena who for many years have had to make do with
relatively mature markets. Also, a standard is on the horizon to rein in
the tendency for diverse formats. These mature markets range from alarms
and remote controls in industrial/consumer applications, to pulse-rate
detection and glaucoma measurement instruments in the medical field. The
demands of these markets have been met by ever-improving LED (transmitter)
and photodiode (receiver) technology. On the LED front, GaAlAs devices
have doubled the output power, efficiency, and switching speed of their
GaAs predecessors. Typical of the latest batch of infrared LEDs is the
SIR-481 STS from Rohm Corp. The device has a peak wavelength of 940 nm, a
half-power angle of 50 degrees, and an output intensity of 15 mW/steradian
(sr), The SIR-481 STS costs $0.20 each in lots of 10,000, with a delivery
time of 8 weeks ARO. Available in industry-standard T 1-3/4 packaging, the
SIR-481 is designed for touchscreen, remote control, beam break, and other
consumer/industrial applications.
While the SIR-481 achieves a high-intensity output for its angle of
radiance, high-speed communication requires an even higher output power.
The DN305 from II Stanley Co. (see Fig. 1), achieves this output power by
reducing the angle-to-half-power to 8 degrees. This results in an output
intensity of 80 mW/sr (25 mW/sr min.) The DN305 has a peak wavelength of
850 nm and a cutoff frequency of 30 MHz–$0.67 each in lots of 50,000. On
the detector side, the majority of near-infrared applications can be
accommodated by relatively inexpensive silicon photodiodes. The OSD35-LR
from Centronic, Inc. (see Fig. 2), is a silicon photodiode for low-light
conditions with a large sensitive area of 35 mm2 and a large
shunt resistance of 2 Gϐ. The unit has a sensitivity range of 350 to
1,100 nm with a peak sensitivity at 800 nm and a zero-bias capacitance of
1,000 pF. The high shunt resistance ensures low noise for high-gain
amplification. The device measures 10.1 (L) x 8.9 (W) x 2.2 (H) mm, gives
a responsivity at 900 nm of 0.47 A/W min, and has a response time of 0.5
microsecond. Depending on the dark current specified (5 or 100 pA), the
device costs up to $10 ea/500. Increasing the response time for
high-speed applications requires a smaller active area and capacitance.
The lower capacitance can increase dark current, giving potentially higher
noise levels. The 1A354 GaAs photodiode from ABB Hafo (see Fig. 3), has a
response time of 0.4 ns at 850 nm. Suited to fiber-optic communication,
the 1A34 comes in a TO46 package that can optionally be mounted in an ST,
FC, or SC device housing. The responsivity, capacitance, and dark current
are 0.35 A/W min, 2 pF max, and 1.0 nA, respectively. As infrared
technology itself continues to evolve, the packaging methods used for the
devices are also changing to suit user requirements. Surface-mount
technology continues to make inroads as designers demand smaller and
smaller devices. The TOP-LED series of surface-mount infrared LEDs
introduced by Siemens Corp. last year has recently been augmented by a
true right-angle version. The SIDE LEDs are actually mounted on their
right side, with the beam directed sideways (see Fig. 4). To date,
right-angle LEDs have depended on additional optics, reflectors, and bent
leads to give the appearance of a right-angle lamp. The SIDE LED is
available with peak wavelengths of 880 or 950 nm and is aimed at
touchscreen applications, among others. Hamamatsu Corp. has released its
S5106 and S5107 surface-mount detectors (see Fig. 5). The
chip-carrier-type silicon PIN photodiodes measure 1.26 mm thick and have a
responsivity of 0.72 A/W at 960 nm. The dark current ranges from 0.3 nA
(S5106) to 1 nA (S5107).
Low power is the key An essential quality of infrared devices is their
low power consumption in the near-infrared region of 0.8 to 3 microns. The
other two sections of the infrared spectrum are middle infrared (3 to 30
microns) and far infrared (30 to 100 microns). This low-power feature has
made infrared LEDs the short-range communications medium of choice for the
new wave of personal computers and PDAs. Other advantages include low
cost, security (beam cannot penetrate walls), and immunity to
electromagnetic interference. They also obviate the need for an FCC
license–a major headache for proponents of RF data communication. There
are two basic infrared communication paradigms–diffuse and
point-to-point. Diffuse infrared communicators flood a room with infrared
radiation containing the pertinent information. Rohm's SIR 481 STS could
typically be used for this application. The Collaborative infrared
communication device from Photonics Corp. allows for diffuse communication
at a rate of up to 1 Mbits/s within a room measuring 25 x 25 ft. The
device comprises an ISA or PCMCIA interface card and a small external
tethered transceiver. Information is transmitted through two apertures in
the transceiver. Software drivers configure the hardware to interface with
standard network operating systems like Ethernet and token ring systems.
To achieve faster communication rates at or approaching that of 10-Mbits/s
Ethernet, 16-Mbit/s token ring, or even 125-Mbit/s FDDI networks, the
angle of emission must be narrowed. If it is kept the same, the power
required to transmit at this speed will increase at a rate unsuited to
portable and handheld communicators. This narrow angle of emission is the
realm of point-to-point communication and is the paradigm of choice for
power-conscious devices. Many computer manufacturers are hard at work
devising proprietary ways of implementing a point-to-point infrared scheme
that will allow them to mine this motherlode of possible applications.
Infrared communication standard To head off the inevitable confusion
resulting from individual efforts, Hewlett-Packard in June urged the
industry to work on a standard hardware and software implementation. This
call resulted in the formation of the InfraRed Data Association (IRDA), a
nonprofit standards development organization for infrared communication.
So far, the list of more than 50 member companies reads like a who's who
of the electronics industry. The companies include Intel, IBM, Sun
Microsystems, Apple, Motorola, Sony, Siemens, Hewlett-Packard, Sharp,
Toshiba, National Semiconductor, and NEC Electronics. IRDA is charged
with deciding on a standard that would allow for interoperability of
infrared links between equipment of various component manufacturers and
system providers. The primary objectives are low cost and high data rates.
Initially, three possible means of achieving these objectives were up for
consideration: * Sharp Electronics Corp. proposed an amplitude shift
keying approach with a 500-kHz subcarrier. This is the approach it uses in
the RY5 series of devices which comprises a discrete receiver ($13),
transmitter ($10.30), and bidirectional data transceiver unit ($15), all
capable of data rates of up to 19.2 kits/s. The 500-kHz subcarrier ensures
that the bit error rate remained less than 10 e-07 . The RY5 is used
in in Sharp's Wizard OZ-9600 computer as well as other PCs, subnotebook,
and palmtop computers from major manufacturers, including Apple. * A
second proposal, put forward by Motorola, Sony, and General Magic, was
based on a frequency shift keying modulation. * A third proposal, and the
one that was eventually decided upon, was a modified version of
Hewlett-Packard's own baseband modulation approach. According to Homer
Gee, program manager at Intel Corp. and marketing chair for IRDA, the
scheme provides for communication rates of up to 115 kbits/s at distances
of 0 to 3 m. The transmitter in the proposed standard will comprise a
GaAlAs LED with a peak wavelength of 880 nm and a half-angle value of 15
degrees. The QED523 IRLED from Quality Technologies Corp. conforms almost
exactly to these specifications and achieves an output power of 0.20 mW/10
degrees (multiply by 41.8 to get the value in milliwatts per steradians at
a current of 20 mA. GaAlAs LEDs were chosen as the transmitter as their
peak wavelength of 880 nm more closely matches the peak response of
silicon photodiodes (around 850 nm) that are to be used as the receiver.
This matching will have the ever-desirable effect of lessening the
communication power requirement. The transmit and receive power
consumptions are specified at 100 and 15 mW, respectively. The system
uses a 15660 UART and can be implemented in an application-specific IC.
Although initial data rates may seem relatively slow, the scheme does
allow for an upgrade path to 1- or 2-Mbit/s rates once the standard is
implemented. At a cost of about $1 per device, Hewlett-Packard has
already incorporated the technology into its 95LX and 100LX palmtop PCs as
well as a line of desktop PCs announced in June. While most of the
hardware issues are resolved, the software is now a major bone of
contention among members. However, these issues are expected to be settled
early in the new year.
The following companies supplied information used in this article.
Call or circle the reader service numbers for more information.
* Denotes member of the InfraRed Data Association .
Quality Technologies Corp. Carrollton, TX Albert Bomchill 214-418-2953
Centronic, Inc. Newbury Park, CA Yuval Tamari 805-499-5902
*Siemens Corp. Cupertino, CA Susan Shaw 408-777-4959
Hamamatsu Corp. Bridgewater, NJ David Leinwand 908-231-0960
ABB Hafo Inc. San Diego, CA Sune Andersson 619-485-8200
Rohm Corp. Antioch, TN Mike Halvorson 615-641-2020, ext.121
*Photonics Corp. San Jose, CA Dawn Nielsen 408-955-7930, ext. 203
*Sharp Corp. Camas, WA Robert Stuart 206-8d34-8948
II Stanley Co. Irvine, CA Bill Roth 800-LED-LCD1
*Intel Corp. Folsom, CA Homer Gee 916-356-5240
*Temic/Siliconix Santa Clara, CA Mike Watson 408-970-5675
IRDA Administration Brookdale, CA John LaRoche 510-943-6546
*Hewlett-Packard Co. Santa Clara, CA John Romano 408-553-7606
Oki Semiconductor Sunnyvale, CA Cliff Vaughan 408-737-6366
CAPTIONS:
Fig. 1. The DN305 IRLED from II Stanley Co. has an angle-to-half-power of
8 degrees. This results in an output intensity of 80 mW/sr.
Fig. 2. The OSD35-LR from Centronic, Inc. is a silicon photodiode for
low-light conditions. It has a large sensitive area of 35 mm
2> and a high shunt resistance of 2 GΩ.
Fig. 3. The 1A354 GaAs photodiode from ABB Hafo, has a bandwidth of up to
1 GHz and is suited to fiber-optic communication.
Fig. 4. Ideally suited to touchscreen applications, the SIDE LED from
Siemens Corp. is a true, right-angle, surface-mount LED.
Fig. 5. The chip-carrier-type silicon PIN photodiodes from Hamamatsu
measure 1.26 mm thick and have a responsivity of 0.72 A/W at 960 nm.
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