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Product Unit

Infrared Data Communication

About IrDA

Compatible Data Transmission:Physical Layer

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Table of Contents

Introduction: Paving the Way to a Wireless Information Environment............................. 3IrDA-Compatible Data Transmission ............................................................................... 5

What is IrDA?............................................................................................................... 5How IrDA Transmission Works .................................................................................... 6What Do I Need to Enable IrDA Transmission?........................................................... 7

IrDA Standard – Physical Layer....................................................................................... 9Specification................................................................................................................. 9

Media Interface Specifications......................................................................................... 9Overall Links ................................................................................................................ 9

Active Output Interface ........................................................................................... 13Tolerance Field of Angular Emission ......................................................................... 14

Active Input Interface.............................................................................................. 15Active Input Specifications ......................................................................................... 15

Test Conditions (ref: IrDa Physical Layer ver 1.2) ......................................................... 17Appendix A of the physical layer spec. .......................................................................... 17

A.1. Background Light and Electromagnetic Field .................................................... 17Transmission Distance............................................................................................... 18

New Standards .............................................................................................................. 19IrBus........................................................................................................................... 19Future Developments ................................................................................................. 19

The Future of the IrDA Standard ................................................................................... 21The Future of the Technology .................................................................................... 21Technologies.............................................................................................................. 21Integrated circuits....................................................................................................... 21Emitters ...................................................................................................................... 21Detectors.................................................................................................................... 22

Eye Safety of Diode Emitters ......................................................................................... 24

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Introduction: Paving the Way to a Wireless InformationEnvironmentThe world of information processing isconstantly striving to create ever morepowerful tools to produce, retrieve,present and transmit information. Thehardware and software needed –regardless of how highly sophisticated itmay be – has to provide a user-friendlyinterface. The interface to the user shouldappear simple, self explanatory, efficientand – of course – wireless. Wirelesscommunication and wireless control of anyequipment is the cornerstone of appeal tothe user. Infrared (IR) communication isthe most cost-efficient approach to providea cordless user interface. Moreover, it isreliable, short-ranged, already available,and as natural as sun light. It is nowaccepted that IR communicationtechnology will have a big future inPersonal Area Networks (PANs). Themarket growth since 1996 has beentremendeous. The first applicationsstarted in small Personal Digital Assistants(PDAs), desk top and notebook PCs. Inonly 2 years, these pioneer applicationsreached a deep market penetration, innotebook PCs approaching already100 %. In 1999 probably the majority ofprinters will be equipped with wireless IR.Dongles are widely available to interfacewith Local Area Networks (LANs) or toretrofit PCs, printers, etc. New ideas andapplications relate to digital cameras,toys, wrist watches. The building blocks toform your individual PAN are nowubiquitous. And the IrDA standards havehelped to make this happen.

IR communication started in Europe,actually in Germany, as far back as 1974.The remote control of TV sets via infrared

transmission conquered the world within10 years. Today, beside TV sets, VCRsand audio equipment, nearly everyproduct of consumer electronics iscontrolled via IR communication. In addi-tion to this, IR technology has spread tothe development of car keys andautomobile immobilizing systems.

Vishay Telefunken has been a major su-pplier of infrared communication devicesfrom the beginning. Vishay Telefunken isthe world's leading supplier of infraredreceivers, which integrate a photo-pindiode and an elaborate amplifier IC, and isa leading supplier of optimized IR emittersor transmitters. The technological basis ofinfrared transmission links is wide-spread.

Highly efficient emitters are based on III-Vcompound semiconductors. An optimizedlayer structure is needed, made fromseveral compositions, mostly of the mixedcompound GaAlAs. The active layer ispart of a pn junction and either doped bythe amphoteric impurity Si, or, withoutintentional doping, embedded into adouble-hetero structure. By varying theGaAlAs composition, the energy band gapcan be adjusted within a wide range tomeet specific design requirements. Therequired structure is produced by liquidphase epitaxy. Vishay Telefunken is anexperienced specialist of this technology,not only capable of achieving leading-edge results, but also providing largeproduction capacity.

Detectors are photo pin diodes made fromSi with low capacitance and high dynamicsensitivity at long IR wave lengths. Thebipolar production process of these

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devices has to be capable of achievingunwanted impurity levels below 1011 cm-3.

The integrated first signal processingstage is a dedicated circuit. VishayTelefunken's development effort for IrDA-compatible receiver circuits is based on itslong-standing experience with remotecontrols. These circuits are produced byVishay Telefunken in very large quantitiesexceeding now 100 million units per year.They use sophisticated gain control whichcompensates for adverse ambient lightenvironments. This circuit principle is alsoincorporated into the new IrDA amplifiers.

Last but not least, custom packaging andlens design are used to create optimizedIrDA-suitable devices. Vishay Telefunkenhas the knowledge and the experienceneeded to develop and produce dedicatedopto-electronic packages.

The standardization effort of IrDA and thetechnological leadership of VishayTelefunken, as well as its commitment tocordless IR communication are cornerstones of our business strategy. They canbe fruitfully combined to contribute to thebig future of IR data communication.

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IrDA-Compatible Data Transmission

What is IrDA?IrDA is the abbreviation for the InfraredData Association, a non-profitorganization for setting standards in IRserial computer connections. Thefollowing is an original excerpt from theIrDA Web site (http://www.irda.org).

EXECUTIVE SUMMARY

IrDA was established in 1993 to set andsupport hardware and software standardswhich create infrared communicationslinks. The Association's charter is tocreate an interoperable, low-cost, low-power, half-duplex, serial datainterconnection standard that supports awalk-up, point-to-point user model that isadaptable to a wide range of applicationsand devices. IrDA standards support abroad range of computing,communications, and con-sumer devices.

International in scope, IrDA is a non-profitcorporation headquartered in WalnutCreek, California, and led by a Board ofDirectors which represents a votingmembership of more than 160 corporatemembers worldwide. As a leading hightechnology standards association, IrDA iscommitted to developing and promotinginfrared standards for the hardware,software, systems, components, periph-erals, communications, and consumermarkets.

INDUSTRY OVERVIEW

Infrared (IR) communications is based ontechnology which is similar to the remote

control devices such as TV and enter-tainment remote controls used in mosthomes today. IR offers a convenient,inexpensive and reliable way to connectcomputer and peripheral devices withoutthe use of cables. IrDA connectivity isbeing incorporated into most notebookPCs to bring the most cost-effective andeasy to use support available for wirelesstechnologies.

There are few US, European or otherinternational regulatory constraints.

Manufacturers can ship IrDA-enabledproducts globally without any constraints,and IrDA functional devices can be usedby international travellers wherever theyare, and interference problems areminimal.

Standards for IR communications havebeen developed by IrDA. In September1993, IrDA determined the basis for theIrDA SIR Data Link Standards. In June1994, IrDA published the IrDA standardswhich includes Serial Infrared (SIR) Linkspecification, Link Access Protocol (IrLAP)specification, and Link ManagementProtocol (IrLMP) specification. IrDAreleased extensions to SIR standardincluding 4 Mbit/s in October 1995. TheIrDA Standard Specification has beenexpanded to include high speedextensions of 1.152 Mbit/s and 4.0 Mbit/s.This extension will require an add-in cardto retrofit existing PCs with high speed IR,and a synchronous communicationscontroller or equivalent.

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In 1995, several market leadersannounced or released products with IRfeatures based on IrDA standards. Theseproducts include components, adapters,printers, PCs, PDAs, notebook com-puters, LAN access, and software appli-cations. In November 1995, the MicrosoftCorporation announced it had addedsupport for IrDA connectivity to theMicrosoft Windows 95 operating system,enabling low-cost wireless connectivitybetween Windows '95 based PCs andperipheral devices.

IrDA's interoperable infrared serial datalink features low power consumption withdata speeds up to 4 Mbit/s, allowing acordless 'walk-up-to' data transfer in asimple, yet compelling way. Applicationsare in both consumer and commercialmarkets with a universal data connectionrelevant in the use of docking and inputunits, printers, telephones, desktop/ laptopPCs, network nodes, ATMs, and hand-held mobile peers (PDA meets PDA).Yesterday’s systems with IR capabilitiessuch as Newton, Omnibook, Wizard andZoomer are not easily compatible witheach other or other complementarydevices. IrDA is the response in whichmany segments of the industry havecommitted themselves to realizing theopportunity of a general standardproviding data links which are non-interfering and interoperable.

How IrDA TransmissionWorks

The transmission in an IrDA-compatiblemode (sometimes called SIR for serial IR)uses, in the simplest case, the RS232port, a built-in standard of all compatible

PCs. With a simple interface, shorteningthe bit length to a maximum of 3/16 of itsoriginal length for power-saving require-ments, an infrared emitting diode is drivento transmit an optical signal to thereceiver.

This type of transmission covers the datarange up to 115.2 kbit/s which is themaximum data rate supported by standardUARTs (see figure 1). The minimumdemand for transmission speed for IrDA isonly 9600 bit/s. All transmissions must bestarted at this frequency to enablecompatibility. Higher speeds are a matterof negotiation of the ports after estab-lishing the links.

Higher speeds require special interfaceswhich operate at 1.152 Mbit/s and use asimilar pulse-shortening process as in theRS232-related mode, but with a pulsereduction to ¼ of the original pulse length.The fastest data rate supported by IrDA is4.0 Mbit/s (often called FIR), operatingwith 125-ns pulses in a 4-PPM (PPM =Pulse-Position Modulation) mode. Thetypical interfaces for the various modesare shown in figure 2. In the followingchapter "IrDA Standard - Physical Layer",the definitions of the IrDA standard aregiven.

Optical output power and receiversensitivity are set to a level where a point-and-shoot activity (± 15°) is sufficient forpoint-to-point communication, but preventsthe pollution of the ambient by strayingneedless power. Transmission over adistance of at least 1 m is ensured. Thedetector front end receives the transmittedsignal, reshapes the signal and feeds it tothe port. The system works in a half-duplex mode that allows only onetransmission direction to be active at anygiven time.

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For frequencies up to 115.2 kbit/s, theminimum output intensity is defined with40 mW/sr. For higher speeds, a higheroutput intensity of 100 W/sr minimum isused. The sensitivity thresholds are40 mW/m2 and 100 mW/m2 for SIR andFIR respectively.

The wavelength chosen for the standard isbetween 850 nm and 900 nm.

An additional IrDA standard wasgenerated in 1997 (voted Feb. 1998) forControl applications, the so-called IrBUS(or CIR) standard. This standard is usingthe IEC1603-1 subcarrier frequencyallocation with a carrier at 1500 kHz. Thetransmission capacity is 72 kbit/s. Thissystem has still some compatibilityproblems with the SIR/FIR IrDA Standard.One of the disadvantages is that thedetector circuitry is different from theother, base-band system. Therefore,integrating both into one application isexpensive. Using IrBUS and SIR/FIR inone application would imply that two IRhardware channels must be built-in.Future other more compatible standardsare under development, the so-calledAdvanced IR (AIR, 256 kbit/s, 7mcoverage) and the Very Fast IR (VFIR,min. 16 MBit/s transfer rate over morethan 1 m).

What Do I Need to EnableIrDA Transmission?

The simplest way of optical interfacing inthe SIR mode is shown in figure 1. Forpulse shaping and recovery, the VishayTelefunken devices TOIM3000 orTOIM3232 are recommended. The frontend including transmitter and receivershould be realized for example by theintegrated transceiver module TFDS4500or other devices of the 4000 series. TheTFDS4500 can also be directly connectedto Super I/Os™ . A transimpedanceamplifier is used in the receiver for inputamplification. Its output signal is fed to thecomparator input, whose reference level isadjusted to efficiently suppress noise andinterferences from the ambient.

Additionally, the digital pulse-shapingcircuit must be inserted for shortening thepulse to be emitted to 1.6 µs (i.e., 3/16 ofthe bit length at 115 kbit/s) and pulserecovery of the detected signal to complywith the IrDA standard. Only the active lowbits (0) are transmitted.

For the high-speed mode, the TFDS6000or other devices from the 6000 series arerecommended to be operated with NSC'sor SMC's IrDA-compatible Super I/O™circuits. Circuit proposals for the variousmodes can be found in our applicationsection.

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front end

IR output

IR input

UART16550/ RS232

Receiver

TOIM3000or TOIM3232

4000 seriestransceiver

TransmitterPulse shaping

Pulse recovery

Figure 1. Block diagram of one end of the overall SIR link

front end

IR output

IR input

Detectorand receiver

IR transceivermodule

Output driverand IRED

I/O

Up to 115.2 kbit/s

1.152 Mbit/s0.576 Mbit/s

4.0 Mbit/s

Activeoutput

interface

Activeinput

interface

Figure 2. Block diagram of one end of the link for signaling rates up to 4.0 Mbit/s

The IrDA standard documentation can befound on the IrDA web sitehttp://www.irda.org. The documents areavailable for downloading by anonymousftp. The following documents are availableas of June, 23, 1998 atftp://irda.org/standards/by_coducment_type/doc/:

The physical layer is responsible for thedefinition of hardware transceivers for thedata transmission. The physical layer istherefore discussed in the followingchapters which define the properties of thefront end devices manufactured by VishayTelefunken.

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IrLAN.doc 421 kByte November 12 1997IrPHY_1_2.doc 445 kByte December 12 1997Lite_Ver1.doc 219 kByte November 12 1997Obex_Errata_Word95.. 43 kByte January 20 1998guide.doc 82 kByte November 12 1997ircomm10.doc 1018 kByte November 12 1997irlap11.doc 850 kByte November 12 1997irlmp11.doc 1004 kByte November 12 1997irphy11.doc 388 kByte November 12 1997irpnp1_0.doc 290 kByte November 12 1997obex10.doc 249 kByte November 12 1997physical.doc 500 kByte November 12 1997physical04.doc 561 kByte November 12 1997protocol.doc 57 kByte November 12 1997tinytp11.doc 335 kByte November 12 1997tnytp10.doc 299 kByte November 12 1997

IrDA Standard – Physical Layer

SpecificationIn SIR mode, the data is represented byoptical pulses between 1.6 µs and 3/16 ofthe bit length of the RS232 data pulse inSIR mode. Pulse-length reduction is alsoapplied in the higher frequency modes.The limits of the standards are shown intables 1 and 2. The optical radiantintensity and detector sensitivity are

adjusted to guarantee a point-to-pointtransmission in a cone of ± 15° over adistance of at least 1 m. The radiantintensity and the sensitivity of the frontend can be increased to ensure atransmission over 3 m (see figure 4). Datafrom the optical interface standard aredocumented in tables 1 to 3.

Media Interface SpecificationsOverall LinksThere are two different sets oftransmitter/receiver specifications. Thefirst, referred to as Standard, is for a linkwhich operates from 0 to at least 1 meter.The second, referred to as the Low PowerOption, has a shorter operating range, andis only defined up to 115.2 kbit/s. There

are three possible links (See Table 1below): Low Power Option to Low PowerOption, Standard to Low Power Option;Standard to Standard. The distance ismeasured between the optical referencesurfaces.

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Table 1. Link Distance Specifications

Low Power -Low Power

Standard -Low Power

Standard -Standard

Link Distance Lower Limit,meters

0 0 0

Minimum Link Distance UpperLimit, meters

0.2 0.3 1.0

The Bit Error Ratio (BER) shall be nogreater than 10-8. The link shall operateand meet the BER specification over itsrange.

Signaling Rate and Pulse Duration: AnIrDA serial infrared interface must operateat 9.6 kbit/s. Additional allowable rateslisted below are optional. Signaling rateand pulse duration specifications areshown in table 2.

For all signaling rates up to and including115.2 kbit/s the minimum pulse duration isthe same (the specification allows both a3/16 of bit duration pulse and a minimumpulse duration for the 115.2 kbit/s signal(1.63 microseconds minus the 0.22microsecond tolerance)). The maximumpulse duration is 3/16 of the bit duration,plus the greater of the tolerance of 2.5 %of the bit duration, or 0.60 microseconds.

For 0.576 Mbit/s and 1.152 Mbit/s, themaximum and minimum pulse durationsare the nominal 25 % of the bit durationplus 5 % (tolerance) and minus 8 %(tolerance) of the bit duration.

For 4.0 Mbit/s, the maximum and minimumsingle pulse durations are the nominal25 % of the symbol duration plus andminus a tolerance of 2 % of the symbolduration. For 4.0 Mbit/s, the maximum andminimum double pulse durations are 50 %of the symbol plus and minus a toleranceof 2 % of the symbol duration. Doublepulses may occur whenever two adjacentchips require a pulse.

The link must meet the BER specificationover the link length range and meet theoptical pulse constraints.

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UART Frame

IR Frame

Data Bits

Data Bits

StartBit

StartBit

StopBit

StopBit

UART Frame

0 0 0 0 01 1 1 1

0 0 0 0 01 1 1 1

11

BitTime

Pulse Width =3/16 Bit Time

IR Frame

1

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Table 2. Signaling rate and pulse-duration specification

SignalingRate

Modulation RateTolerance% of Rate

PulseDurationMinimum

PulseDurationNominal

PulseDurationMaximum

2.4 kbit/s RZI* ±0.87 1.41 µs 78.13 µs 88.55 µs

9.6 kbit/s RZI* ±0.87 1.41 µs 19.53 µs 22.13 µs

19.2 kbit/s RZI* ±0.87 1.41 µs 9.77 µs 11.07 µs

38.4 kbit/s RZI* ±0.87 1.41 µs 4.88 µs 5.96 µs

57.6 kbit/s RZI* ±0.87 1.41 µs 3.26 µs 4.34 µs

115.2 kbit/s RZI* ±0.87 1.41 µs 1.63 µs 2.23 µs

0.576 Mbit/s RZI* ±0.1 295.2 ns 434.0 ns 520.8 ns

1.152 Mbit/s RZI* ±0.1 147.6 ns 217.0 ns 260.4 ns

4.0 Mbit/sSingle pulseDouble pulse

4 PPM4 PPM

±0.01±0.01

115.0 ns240.0 ns

125.0 ns250.0 ns

135.0 ns260.0 ns

• RZI = Return to Zero Inverted

NRZ

≤ 115.2 kbit/s

1.6 µsor

3/16

0.576 Mbit/s1.152 Mbit/s

1/4 Bit cellRZI- IR

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Data Bit Pair (DBP) 4PPM Data Symbol(DD)

00 100001 010010 001011 0001

ONE COMPLETESYMBOL

chip 1 chip 2 chip 3 chip 4

Ct

Dt

Ct = 125 nsDt = 500 ns

Active Output Interface

At the active output interface, an infraredsignal is emitted. The specified active out-

put interface parameters in table 2 aredefined in the physical layer specificationof the IrDA standard. The completestandard is available from IrDA.

Table 3. Active output specification

Specification Data Rates Type Minimum Maximum

Peak wavelength, λp, µm All Both 0.85 0.90

Maximum intensity in angularrange, mW/sr

All Std – 500*)

Maximum intensity in angularrange, mW/sr

All LowPower

– 28.8

Minimum intensity in angularrange, mW/sr

115.2 kbit/s andbelow

Std 40 –

Minimum intensity in angularrange, mW/sr

115.2 kbit/s andbelow

LowPower

3.6 –

Minimum intensity in angularrange, mW/sr

Above 115.2kbit/s

Std 100 –

Half angle, degrees All Both ± 15 ± 30

Signaling rate (known as clockaccuracy)

All Both See table2

See table2

Rise time tr 10 - 90%, fall timetf 90 - 10%, ns

115.2 kbit/s andbelow

Both – 600

Rise time tr 10 - 90%, fall timetf 90 - 10%, ns

Above 115.2kbit/s

Std – 40

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Pulse duration All Both See table2

See table2

Optical overshoot, % All Both – 25

Edge jitter, % of nominal bitduration

115.2 kbit/s andbelow

Both – ± 6.5

Edge jitter, relative toreference clock,% of nominal duration

0.576 and 1.152Mbit/s

Std – ± 2.9

Edge jitter % of nominal chipduration

4.0 Mbit/s Std – ± 4.0

*) For a given transmitter implementation, the IEC 60825-1 AEL Class 1 limit may beless than this.

Tolerance Fieldof Angular EmissionThe optical radiant intensity is limited to amaximum of 500 mW/sr and an angle of± 30° to enable the independent operation

of more than one system in a room. Infigure 4, the tolerance field of an infraredtransmitter's emission is shown. A typicalfarfield characteristic of a transmitter isalso shown in this figure.

0

50

100

150

200

250

300

350

400

450

500

-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90

IrDA tolerance field

Typical emission

characteristic

SIRFIR

Figure 4. Tolerance field of angular emission

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Active Input InterfaceIf a suitable infrared optical signalimpinges on the active input interface, thesignal is detected, conditioned by the

receiver circuitry, and transmitted to the IRreceive decoder.

Table 4. Active input specifications

Specification Data Rates Type Minimum Maximum

Maximum irradiance in angularrange, W/m 2

All Both – 5000

Minimum irradiance in angularrange, mW/m2

115.2 kbit/s andbelow

LowPower

90 –

Minimum irradiance in angularrange, mW/m2

115.2 kbit/s andbelow

Std 40 –

Minimum irradiance in angularrange, mW/m2

Above 115.2 kbit/s Std 100 –

Half angle, degrees All Both ±15 –

Receiver latency allowance, ms All Std – 10

Receiver latency allowance, ms All LowPower

– 0.5

Active Input Specifications

The following five specifications form a setwhich can be measured concurrently: - Maximum irradiance in angular range,mW/m2

- Minimum irradiance in angular range,uW/m2

- Half-angle, degrees - Bit Error Ratio, (BER) - Receiver Latency Allowance, ms

These measurements require an opticalpower source and means to measureangles and BERs. Since the optical powersource must provide the specifiedcharacteristics of the Active Output,calibration and control of this source canuse the same equipment as that required

to measure the intensity and timingcharacteristics. BER measurements re-quire some method to determine errors inthe received and decoded signal. Thelatency test requires exercise of thenode's transmitter to condition thereceiver.

Definitions of the reference point etc., arethe same as for the Active OutputInterface optical power measurementsexcept that the test head is now an opticalpower source with the in-bandcharacteristics (peak wavelength, rise andfall times, pulse duration, signaling rateand jitter) of the Active Output Interface.The optical power source also must beable to provide the maximum power levelslisted in the Active Output Specifications.It is expected that the minimum levels can

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be attained by appropriately spacing theoptical source from the reference point.

Figure 5 illustrates the region over whichthe Optical High State is defined. Thereceiver is operated throughout this regionand BER measurements are made toverify the maximum and minimumrequirements. The ambient conditions ofA.1 apply during BER tests; BERmeasurements can be done with worstcase signal patterns. Unless otherwiseknown, the test signal pattern shouldinclude maximum length sequences of"1"s (no light) to test noise and ambient,and maximum length sequences of "0"s(light) to test for latency and otheroverload conditions.

Latency is tested at the MinimumIrradiance in angular Range conditions.The receiver is conditioned by the

exercise of its associated transmitter. Forrates up to and including 1.152 Mbit/s, theconditioning signal should includemaximum length sequences of "0"s (light)permitted for this equipment. For4.0 Mbit/s 4PPM operation, various datastrings should be used; the latency maybe pattern dependent. The receiver isoperated with the minimum irradiancelevels and BER measurements are madeafter the specified latency period for thisequipment to verify irradiance, half-angle,BER and latency requirements.

The minimum allowable intensity value isindicated by “minimum” in figure 5, sincethe actual specified value is dependentupon the data rate, SIR or FIR

-30 -15 0 15 30Angle (Degrees)

Figure 5. Optical High State Acceptable Range

5 kW/m2

minimum

OpticalUndefined Region

HighState

Undefined Region

(Vertical axis is not drawn to scale.)

Irradiance (or Incidance) (W/m2)

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Test Conditions (ref: IrDa Physical Layer ver 1.2)

Appendix A of the physical layer spec.

Note- A.1 is Normative. The rest of Appendix A and all of Appendix B are Informative,not Normative {i.e., it does not contain requirements, but is for information only}.Examples of measurement test circuits and calibration are provided in IrDA SerialInfrared Physical Layer Measurement Guidelines.

A.1. Background Light and Electromagnetic Field

There are four ambient interference conditions in which the receiver is to operatecorrectly. The conditions are to be applied separately:• Electromagnetic field: 3 V/m maximum (refer to IEC 801-3. severity level 3 for

details)

• Sunlight: 10 kilolux maximum at the optical port

This is simulated with an IR source having a peak wavelength within the range 850nm to 900 nm and a spectral width less than 50 nm biased to provide 490 µW/cm²(with no modulation) at the optical port. The light source faces the optical port.

This simulates sunlight within the IrDA spectral range. The effect of longerwavelength radiation is covered by the incandescent condition.

• Incandescent Lighting: 1000 lux maximumThis is produced with general service, tungsten-filament, gas-filled, inside-frostedlamps in the 60 Watt to 150 Watt range to generate 1000 lux over the horizontalsurface on which the equipment under test rests. The light sources are above thetest area. The source is expected to have a filament temperature in the 2700 to3050 degrees Kelvin range and a spectral peak in the 850 nm to 1050 nm range.

• Fluorescent Lighting : 1000 lux maximumThis is simulated with an IR source having a peak wavelength within the range 850nm to 900 nm and a spectral width of less than 50 nm biased and modulated toprovide an optical square wave signal (0 µW/cm² minimum and 0.3 µW/cm² peakamplitude with 10% to 90% rise and fall times less than or equal to 100 ns) overthe horizontal surface on which the equipment under test rests. The light sourcesare above the test area. The frequency of the optical signal is swept over thefrequency range from 20 kHz to 200 kHz.Due to the variety of fluorescent lamps and the range of IR emissions, thiscondition is not expected to cover all circumstances. It will provide a commonbasis for IrDA operation.

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Transmission DistanceFrom figure 6, the transmission distanceas a function of the sensitivity (necessaryirradiance on the detector) can be read.For example: Sensitivity given as aminimum irradiance on the detector of 40mW/m2, combined with an intensity of 40mW/sr, results in a transmission distance

of 1 m. A combination of a detector with aminimum irradiance of 10 mW/m2 and anemitter with 250 mW/sr can transmit overalmost five meters.

The physical layer properties of thedevices are defined under ambientconditions listed in an appendix which hasbeen reprinted in the following chapters:

1,00E-02

1,00E-01

1,00E+00

1,00E+01

1,00E+02

1,00E+03

1,00E+04

1,00E+05

1,00E+06

1,00E+07

0,01 0,1 1 10 100

Distance [m]

Irrad

ianc

e E

e in

det

ecto

r pla

ne [m

W/m

2 ]

Ie = 500 mW/srIe = 240 mW/srIe = 100 mW/srIe = 40 mW/srIrDA FIR StandardIrDA SIR StandardRemote Control, guaranteedRemote control, typical

Figure 6. IrDA transmission distance

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New StandardsIRBus

A block diagram of the hardware implementation for the IrBus system is given in figure 7

Figure 7: Hardware implementation exsample of IRBUS

The signals at [1] are normally a serial bitstream. Those in [2] are the modulatedelectrical signals of the above bit streamand those in [3] are the correspondingoptical signals. Various schemes can beused to implement these parts of the IrBussystem. This specification defines thetransmission speeds, modulationschemes, infrared wavelengths etc. of theoptical signals emitted by the infraredtransmitter and of those coming into theinfrared receiver in [3]. It does notmandate the signals in [1] and [2], or thesignals in the infrared transmitter/receiveror the modulator/demodulator. Moreover,this specification does not define thevoltage waveform of the driver circuit thatdrives the LED of the infrared transmitteror the current waveform after thephotoelectric conversion done by the Pin-PD of the infrared receiver.

The IRBus system operates at atransmission speed of 75.0 kbit/s. Thedata to be transmitted is coded by the 16-Pulse Sequence Modulation (16PSM)scheme, modulated on a 1.5 MHz sub-carrier and then output by the infraredtransmitter. This frequency conforms tothe frequency allocation specified inIEC1603-1. However, spurious signal inthe lower frequency range are notsuppressed completely. The 16PSMscheme is able to reduce the interferencebetween an IrBus system and a RemoteControl System that uses frequencies inthe 33kHz - 40kHz band.

Future DevelopmentsAIR: (From: Advanced Infrared (AIr) IrPHYDraft Physical Layer Specification, Version0.4, January 1998)

IRTransmitter

IRReceiver

IR Transceiver

Encoder Modem Decoder

Controller

1)

2)

3)Infrared Interface

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AIr-IrPHY uses only one commonmodulation format for all supported datarates in the range from 250 Kbit/s up to4 Mbit/s. This is defined as four-slot PulsePosition Modulation with Variable Repe-tition encoding (4-PPM/VR). The redun-dancy introduced with repetition encodingis exploited to gain an improvement of thelink signal-to-noise ratio, which in turn canbe used to provide an additionaltransmission range for lower data rates, orto maintain a reliable link under hostile Irchannel conditions such as brightbackground light or interruption of the line-of-sight path. In addition, the emissionspectrum of 4-PPM/VR produces lessinterference to existing Ir remote controldevices than IrDA (9.6 Kb/s to 115 Kb/s).In order to increase receiver detectionsensitivity the initialization fields of thetransmission frames have been designedto allow a pulse pattern-oriented detectionmethod, rather than the method ofdetecting individual pulses requiring ahigh comparator threshold to blockunwanted noise pulses. In contrast to IrDA1.x IrPHY, AIr-IrPHY places no emphasison achieving a fixed transmission range

under specified environmental conditions.Instead the concept of Ir system parity andrepetition encoded robust frame headersis introduced to support reliable collisionavoidance with the IrMAC protocol. Thisallows the coexistence of devices withdifferent angular and range characteristicswhile maintaining the collision avoidanceproperties.

CIR: The activities of the IrDA to alsogenerate a (uni-directional) Control IRstandard for low speed controlapplications have been stopped. Thereare many low speed applications whichonly use very limited bandwidths ashuman entry links as keyboards and mice.IrDA likes to support these application viathe IrBUS standard. Many of theseapplications, however, are very cost-sensitive and will also use the standardremote control frontend solutions in thefuture which are very cost efficient andalso supported by standard computer I/Os.Vishay Telefunken is one of the biggestsuppliers of remote control receiversworldwide.

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The Future of the IrDA StandardIt is Vishay Telefunken‘s policy to supportthe further development of the standardand not to support hardwaredevelopments in order to short cut anystandardization efforts. It is firmly believedthat this is in the best interest of the futureof the IR communication market and allindustrial participants in it.

Vishay Telefunken is actively involved inthe further development of the standardand will use its influence to reach mostbeneficial rules for practical operation.

The Future of the Technology

The future of the IrDA standard is notlimited by the technology. The technologyof IRED series implemented in thetransceiver is capable of a bit rate of up to20 Mbit/s. Even higher bit rates can beachieved in the future with littletechnological measures. Lasertechnologies are available for bit rates inthe 100 Mbit/s range. Similarly, the band-width of the detecting pin diode can beincreased beyond the requirements of theexisting IrDA standards.

TechnologiesIntegrated circuitsDepending on the requirements of thespecific device Vishay Telefunken is usingbipolar BICMOS or CMOS technologies.The ASICs built into the hybrid integratedfrontend transceiver modules for the 4000series use bipolar technology, whereasthe 5000 and 6000 series rely on CMOSand BICMOS technologies, respectively.

Emitters

Any reliable supplier of advanced IRtransceivers must have control over thenext generation IR technology. VishayTelefunken is an acknowledged leader inIR technology for IR emitters as well asdetectors.IR technology for emitters is based on theternary III-V material system (GaAl)As.The emitter diodes are double heterostructures optimized for high efficiencyand low forward voltage. In addition thebandwidth needed for the IR transmissionmust be designed into the emitter diodes.All three features are important for IR datacommunication: high efficiency savesbattery power through a low forwardcurrent to reach the emission intensityrequested e.g., by the IrDA standards.The importance of a low forward voltage isnot so easy to understand. The firstreason why a low forward voltage isimportant is the temperature coefficient ofthe efficiency: the efficiency decreaseswith temperature, therefore the thermalheating of the emitter diode must beminimized. Thermal heating cannot beneglected because the current needed toreach 100 mW/sr in the ± 15° core forexample is typically 350 mA. The trend todecrease package size and therefore lenssize tends to increase the requiredcurrent. The second reason why a lowforward voltage is important is theincreasing popularity of 3 V applications. Itis not trivial to achieve low enough forwardvoltages. What is requested? The pnjunction voltage of a diode emitting in theIrDA defined wavelength range is byphysical law fixed at about 1.3 V, the

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switching transistor of an IR transceiverneeds typically 0.6 V, therefore in anapplication with a weakened Li ion batteryrunning at 2.7 V only 0.8 V are availablefor the ohmic voltage drop of the emitterdiode and the current limiting resistor. At0.35 A this means an ohmic resistance ofthe diode plus the current limiting externalresistor of only about 2.3 Ohm!

Bandwidth is no problem at the present4 Mbit/s requirement, but might becomemore difficult to achieve in future systemswhen considering data rates up to30 Mbit/s.

Figure 7 shows a typical double hetero-structure diode for IrDA applications. It isa 4 layer structure grown by liquid phaseepitaxy. The layers are all made of ternarymaterial (GaAl)As grown on a binary GaAssubstrate. The band gap of GaAs issmaller than that of the ternary material.Therefore, the radiation emitted in thispart of the structure is absorbed in theGaAs substrate. To avoid this detrimentaleffect the substrate is chemically removed.The active layer is sandwiched betweenhigher band gap cladding layers in orderto prevent injected carriers from diffusingaway from the pn junction region. Thedoping level in the active layer controlsthe bandwidth which will be achieved. Theinternal optoelectronic efficiency of theheterostructure is close to 100 %.However, because of the high refractiveindex of the material, the reflection at thesurface of the material is high and theescape efficiency of the radiation is low.To improve escape efficiency the surfaceis roughened and the metallic contacts areoptimized not only for low resistivity, butalso for high optical reflectivity. The

cladding layers have to be transparentand must be optimized for the highestpossible conductivity.

Our diodes optimized for IrDA 1.2applications achieve about 45 mW at aforward current of 100 mA or 155 mW at350 mA. At a forward current of 550 mA,which is the thermally limited maximumcurrent at a duty cycle of 25 %, theforward voltage is below 2.1 V. The pulserise and fall times are about 30 ns. This isa combination of excellent values unsur-passed in the industry.

Future higher bandwidth systems needfaster emitters. In the Vishay Telefunkendevelopment lab rise times of around 5 nshave already been achieved. Thechallenge here is to minimize theunavoidable drop of the efficiency whengoing to higher bandwidth.

Detectors

The Si detector diodes used in IRtransceivers interface with a mixed signalASIC built into the transceiver. The ASICamplifies the signal of the diode andtransforms it into a digital output signal.The user of an IR transceiver thereforehas no direct interface with the diode. Hecan only evaluate the combinedperformance of the diode and the ASIC.Nevertheless a few remarks with respectto the trade-offs involved in thedevelopment of these detectors could behelpful.

The diodes used are photo pin diodes.Photons of higher energy than the bandgap of Si are absorbed in the material and

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create a pair of charge carriers: electronsand holes. Charge carriers created in theelectric field of the space charge region ofthe pn junction are quickly separated anddriven to the n or p-side depending on thesign of the charge. In contrast, carrierscreated in the neutral material can moveonly by diffusion and produce a relativelyslow signal in the range up tomicroseconds.

The designer of a suitable pin diode willtake care to see that most, if not allradiation is absorbed in the space chargeregion. In this case clean signals without aslow tail are provided to the amplifierfacilitating signal processing. However,especially in a 3 V application, it is noteasy to meet this goal because the space

charge region decreases like the squareroot of the voltage across the pn junction.

The design of our pin diodes is optimizedin the sense of avoiding slow tails of thesignal, caused by diffusing carriers, asmuch as possible. This means that theabsorption length at the IrDA definedwavelengths between 850 nm and 900 nmis roughly the same as the width of thespace charge region. The resistivity of thequasi intrinsic material has been pushedup beyond 1000 Ohmcm, resulting in aspace charge region of about 30 µm at5 V.

p-side contact

n-side contact

N -(GaAl)As

P -(GaAl)As

active layer

[Al]

x

IR Emitting Diode (IRED) Chip Al content

Figure 7. Typical double heterostructure diode for IrDA applications

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Eye Safety of Diode EmittersIEC and CENELEC, the InternationalElectrotechnical Committee and theEuropean Committee for ElectrotechnicalStandardization have included DiodeEmitters such as IREDs and LEDs into thelaser safety standard. This is due to thetechnological similarity of the devices tosemiconductor lasers, however, notforgetting very different radiance of thesedevices in comparison to lasers. In the1997 - edition of the standard EN 60825-1(and the IEC equivalent IEC 825-1) thebasic errors were cancelled out. However,the risk is still overestimated and thestandard in respect to LEDs and IREDswill change in the future.

On a worldwide level no eye damagecaused by these devices has beenreported as of yet. Recent studiesperformed on monkeys in the US showedthat eye damage could not occur evenwhen using the brightest LEDs available.Nevertheless, the efficiency of DiodeEmitters is increasing. At shorterwavelengths especially, a certain risk ofeye damage due to the blue light effectsmay arise if systems are not designedcarefully enough.

The eye safety standard describes theMaximum Possible Exposure (MPE) andthe Accessible Emission Levels (AEL) forthe human eye depending on exposuretime, wavelength, and other parameters.For extended sources like Emitter Diodesthe so-called "apparent" or "virtual" sourcesize is the key figure to assess the riskfactors.In standard applications, it is important fordiode emitters to be classified in CLASS 1which means safe under all reasonable

conditions, also in case of a single failureevent. In this case, no labelling ofCLASS I products is necessary. In themanual of a CLASS I product, it must beidentified as being such a product. Thesingle failure philosophy must be used inall classifications!

CLASS IIIa also indicates that the productis also safe for the unprotected eye.However, no optical instruments (e.g.,magnifying glasses) are allowed toobserve such a source at close range.Light collecting optics may increase therisk of eye damage. Labeling is necessaryin this case with a CLASS IIIa label asdescribed in the standard document whichis available from the distributionorganizations of the national standard-ization committees.It must be expressed here that only thefinal product can and must be classified.Classifying an IRED or LED as a device isimpossible by definition. The operation ofthe IRED or LED in combination with thecomplete application, including optics,windows, power supplies and failureprotection electronics has to be classified.The Diode Emitter manufacturer cannot beresponsible for the application into whichthe diodes are implemented.

As a supplier of LEDs and IREDs, VishayTelefunken is designing products tominimize the eye safety risk and providingall data necessary for classifying the"laser product".

The data are the minimum and maximumintensity or output power, the peakwavelength range, and the virtual source

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size. All data are set down in the VishayTelefunken data sheets.