Application Note 1080 Contents Introduction Interconnec

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Application Note 1080 Contents Introduction Interconnec

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Versatile Link with Plastic Optical Fiber Hard Clad Silica Fiber (HCS Factory Automation Industrial Control Applications
Application Note 1080
Contents
Introduction
Interconnects without Crosstalk International Regulations Fiber Optic Connectors Electrical Connectors Galvanic Insulation
Manufacturing Consideration
Handling Assembly Guidelines Connectoring Guidelines Plastic Fiber Crimp Cleave Termination 2.3. Optical Port Protection
Introduction
This application note discusses functions features HFBR-0508 Fiber Optic Versatile Link, which designed variety industrial applications. These include serial data interfaces robots, machine tools, assembly printing machines, gatedrive circuits frequency inverters. Circuit design hints other subjects found product data sheet will also presented. reader this information design reliable fiber-optic links based plastic optical fibers (POF) distances below hard clad silica (HCS®) fibers distances Further information about fiberoptic link design found Application Briefs Application Notes 1035 1066, which listed appendix VII. HewlettPackard applications engineers your local certified distribution application engineers available further design assistance.
Product Description
Housing Optical Port Transmitter Technology Receiver Technology Types Fiber-Optic Cables Polymer Optical Fiber (POF) Hard Clad Silica Fiber (HCS®)
Application Examples
Introduction Industrial Communication Networks Interface Controller Area Network (CAN) Gate Driving using Fiber Optic Interfaces
III. Fiber Optic Link Design
Link Length Considerations Optical Power Budgeting Computation Dynamic Range Temperature Drift Considerations Reliability Considerations Connector Loss Coupling Loss Transmitter Drive Circuits Pros Cons Parallel Series Transmitter Drive Circuits Series Driver Circuit using Standard Buffer simplest Transmitter Shunt Drive Circuit Receiver Interface Circuit Design Sensitivity Off-State-Limit Overdrive Limit 3-184
Introduction Optical Power Loss Measurements
Recommended Equipment Accessories Transmitter Output Power Measurement Receiver Sensitivity Measurement Cable Attenuation Measurement
VII. Appendix
Literature Reference Supplier Reference
HCS® registered trademark SpecTran Corporation
5963-6756E
Interconnects without Crosstalk Fiber-optic technology completely changing data communications, particularly industrial environments, where data must transferred between machines more quickly than ever before. believes that fiber optics replacing copper cabling many these applications because wide range advantages inherent fiber cable. Glass plastic fibers, being dielectric materials, completely immune stray electromagnetic fields, which common industrial applications that motors power switches. These fibers placed duct alongside high-voltage metal cables without being susceptible crosstalk. This feature simplifies system installation. Twisted-pair copper cables require minimum distance from power lines guarantee error-free data transfer. International Regulations increasingly stricter international control over elec-
tromagnetic compatibility electronic equipment, manufacturers often cannot legally sell their products many countries unless specific immunity emission limits met. These limits based standards such FCC, VCCI, CISPR, IEC, VDE, forth. example, beginning January 1996, equipment systems that will sold into European Union have meet European standards, otherwise they excluded from market. generic standards industrial field 50081-2 (emission) 50082-2 (immunity). many applications design engineers have cost-effective alternative fiber optics their systems must meet national international regulations electromagnetic compatibility. Fiber Optic Connectors Electrical Connectors past, many design engineers were reluctant design with fiber optics. Terminating fiber cable more time consuming than connecting twisted-pair wire because fibers
required epoxy their ends needed polished. Largecore polymer optical fiber [POF] crimp cleave technology Versatile Link Snap-in connector (V-System) allow fiber optic cables terminated more easily than shielded twisted-pair cables, while offering electromagnetic-compatible communication link. This very strong reason using fiber optic cables, reason that installation service divisions company should also accept. Galvanic Insulation Ground-loop currents different ground potentials common problem industrial communication networks. Ground loops their associated noise problems totally eliminated insulation characteristics fiber, allowing straightforward fast system integration. addition, insulating property glass plastic fibers ideal many monitor control functions needed high-voltage applications. intrinsically safe applications, which
SHIELDED TWISTED PAIR
FIBER OPTIC SNAP-IN CONNECTOR
Figure Comparison Shielded Twisted Pair Fiber Optic Snap-in Connector.
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common chemical industry, fiber optics easy qualify also best medium connecting electrical device another through isolation barrier.
Product Description
Housing optical port Versatile Link family been used successfully many different industrial applications based plastic fibers. Users have benefit reliable system that easy install field. compact package made flame retardant V-0) material standard, sixpin DIP. Transmitters receivers stacked together, creating duplex optical ports that save printed circuit board space avoid fault connections. conductive housing HFBR2528 receiver provides excellent shield. color-coded packages eliminate confusion between transmitters receivers. plug protects optical port during auto-insertion soldering. Versatile Link package uses active alignment system ensure proper coupling between fiber optoelectronic converter. Figure illustrates alignment system operates. precision-molded lens insert located bottom depression shape truncated cone. connector inserted into package; jaws housing force bevelled connector into cone-shaped depression. This accurately centers fiber directly above molded lens insert ensures efficient, reliable repeatable connections.
Figure Package Construction.
INSERT
CONNECTOR
LEAD FRAME LENS
FIBER
Figure Connector Alignment Transmitter Receiver
Transmitter Technology HFBR-1528 transmitter uses high quantum efficiency based AlInGaP technology. drive current, coupled power into typically dBm, improvement over previously used transmitters. With center wavelength room temperature, transmitter minimum attenuation window POF. Typical link distances with low-cost plastic fibers reality. When using
Pt-OUTPUT POWER (dBm)
200/230 If-TRANSMITTER DRIVE CURRENT (mA)
Figure Typical Transmitter Output Power Drive Current.
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fiber link, distances possible. addition higher coupled power, optical rise fall times have become much faster, allowing much simpler drive circuits without need peaking pre-biasing data rates MBd. Receiver Technology HFBR-2528 receiver with TTL/CMOS-compatible output specified data rates from (nonreturn zero). sensitivity peak with POF, sensitivity peak with HCS® fiber. Propagation delay times tPLH (output high) tPHL (output high low) equally distributed achieve pulse-width distortion (PWD) less than over large input power range. result, drive current adjustments different link lengths fiber types unnecessary. patented first-bit correction circuit makes HFBR2528 ideal product arbitrary duty-cycle links frequency inverters such gate-drive applications.
Other products market with similar optical electrical specifications require transmission overhead bits prior data because heavily distorted first bits. Therefore, user additional circuitry transmit preamble prior data bits, making transmit receive circuit more complex costly. better electromagnetic compatability, conductive housing material been chosen shielding receiver electromagnetically polluted industrial environments. Types Fiber Optic Cables Historically, glass fibers have been used long-haul telecommunication links local-area networks because attenuation large bandwidth. Ethernet FDDI (Fiber Distributed Data Inter-face) standards, example, have specified multimode 62.5/125 glass fibers. These small-core fibers need high-precision connectors minimize coupling loss. industrial application, fibers with lowercost connectors, which easier install less sensitive dirty environments,
quired. these applications, (Polymer Optical Fibers) (Hard Clad Silica) fibers best media. While there many types fiber-optic cables cable composed fiber jacket), only types, HCS, specified with Versatile Link Snap-In Connectors. These step-index fibers made from silica (HCS) polymer (POF) which core higher refractive index than cladding. jacket around fiber protects against mechanical thermal damage increases strength cable. 4.1. Polymer Optical Fiber (POF) large-core diameter (980/ 1000 numerical aperture (Polymer Optical Fiber) well matched large effective diameter numerical aperture optical ports, allowing power launched into core high with HFBR1528 transmitter. also offers comparably low-cost termination, which done
COMPARATOR AMPLIFIER FIRST BURST CORRECTION
DATA OUTPUT
THRESHOLD GENERATOR REFERENCE VOLTAGE GROUND
Figure Receiver Block Diagram.
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CLADDING
ATTENUATION (dB/km)
ATTENUATION (dB/km)
CORE
PARAMETER TENSION min) TENSION YEAR) BEND RADIUS (1H) FLEX ATTENUATION (660 INSTALLATION TEMPERATURE FLAMMABILITY
1,000 dB/km 0.47
200/230 100N 50,000 dB/km 0.37 RISER PLENUM
WAVELENGTH (nm)
WAVELENGTH (nm)
Figure Attenuation Wavelength POF.
Figure Typical Attenuation Wavelength Fibers.
attenuation visible wavelength range fiber. attenuation typically dB/km. core fiber silica cladding proprietary hard polymer that also acts strength enhancer makes impervious moisture impurities. High temperature specifications extended industrial temperature ranges, ratings plenum riser applications also available. snap-in V-System connectors crimped directly onto fiber because proprietary hard cladding bonds silica core material, thus eliminating need messy epoxies. patented cleaving tool cuts excess fiber protruding from connector end. simplicity termination process, Versatile Link Snap-In connector mounted less than seconds. III. Fiber Optic Link Design HFBR-0508 family designed characterized data rates from MBd; Hewlett-Packard specifies link
Figure Polymer Hard Clad Silica Cables.
field" less than minute using simple inexpensive crimping cutting procedure. attenuation minimum typically about dB/m. should noted that spectrum transmitter center wavelength minimum attenuation POF. 4.2. Hard Clad Silica Fiber (HCS) Step-index silica fibers, such (Plastic Clad Silica) HCS® (Hard Clad Silica) fibers with large-core (200 diameter compared glass fibers with 62.5 core diameter) permit low-cost transmitter/receiver lensing systems. Because high attenuation visible wavelength range, fibers commonly used lower attenuation window with higher-cost infrared LEDs. fiber with lowest
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length fibers fibers Power supply variations, connector coupling loss temperature drift effects part guaranteed data sheet specifications. addition, margin takes aging into account. specifies link performance using transmitter receiver interface circuits described product data sheet, which gives customers maximum available design security. following considerations will help design engineer become more familiar with low-cost, fiber-optic link design gives guidelines optimize link performance particular applications. Link Length Considerations fiber-optic system basically consists LED, length fiber, optical detector. transmitter, modulated electrical input signal, couples light into fiber. light travels along fiber optical detector, which converts light into electrical signal again. important specifications fiber-optic links much light coupled into fiber, much light
TRANSMITTER (HFBR-1528)
SHOULD CONNECTED GROUND 75451
RECEIVER (HFBR-2528)
SHOULD CONNECTED GROUND
OUTPUT
INPUT
Figure Versatile Link Set-Up.
receiver needs function properly, much light lost fiber between transmitter receiver. Depending upon fiber length wavelength signal source, data rates very high (125 greater), optical signal distorted. This effect, called dispersion[3], limits bandwidth fiber-optic system. Fortunately, most industrial communication systems data rate less than dispersion effect contributes only link length exceeds with 1000 with Fibers. Below these values links limited attenuation, straightforward optical power budget calculation only consideration. Optical Power Budgeting Computation optical power budget difference between output power transmitter sensitivity receiver. maximum length optical fiber determined attenuation fiber, additional losses feed-through connections "safety factor" called optical power margin (see
DATA RATE
LINK SPAN
HFBR-1528 COUPLED POWER SPECIFICATION
TRANSMITTER OUTPUT POWER
INPUT COUPLING LOSS
HFBR-2528 COUPLED POWER SPECIFICATION
FIBER ATTENUATION (dB/m)
POWER BUDGET
OUTPUT COUPLING LOSS POWER INTO RECEIVER LINK DISTANCE
Figure Fiber Optic Link Main Parameters.
chapter III/1.4). Formula III/1 gives maximum link length worst-case conditions:
Equation III/1:
l(max)
(min) PRL, (max)
PT(min) PRL, (max):
Minimum coupled power transmitter (dBm) Sensitivity receiver (dBm) insertion loss feed-throughs (dB) Optical power margin, which accounts degradation, supply voltage variation, etc. (dB) Maximum attenuation fiber (dB/m)
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NORMALIZED SPECTRAL OUTPUT POWER
RECEIVED
Versatile Link transmitter receiver specifications account coupling losses from fiber. 1.2. Dynamic Range important link design consideration receiver's optical dynamic range, difference between sensitivity PRL, overdrive conditions PRL, other words, dynamic range specifies minimum-to-maximum link length. Exceeding dynamic range receiver lead increase PWD. maximum allowed power level receiver specifies minimum link length needed avoid overdrive condition. maximum optical power that HFBR-1528 launch, however, well matched HFBR-2528 receiver's overdrive characteristics. drive circuit recommended HFBR-1528 data sheet used, transmitter cannot over-drive HFBR-2528 receiver even when length fiber-optic cable virtually zero meters. Equation III/2:
l(min)
(max) PRL, (min)
-40°
RECEIVER OPTICAL INPUT POWER
WAVELENGTH (nm)
Figure Typical Receiver PulseWidth Distortion Optical Input Power MBd.
Figure Typical Normalized Optical Spectra Peak 25°C.
room temperature, maximum adjustment-free distances possible over temperature range specified HFBR-0508 series data sheet. Temperature Drift Considerations data sheet includes transmitter output power range ambient temperatures 25°C, +70°C, -20°C +85°C, addition guaranteed link length specifications. knowing understanding different temperature drift effects that link depends design engineer will able optimize link performance, particularly, maximum fiber length. output power transmitter inversely proportional junction temperature, resulting lower output power high temperatures (PT/T). Equation III/3:
(25)
Output power room temperature specified data sheet (dBm) PT/T: Output power temperature coefficient (dB/°C) forward voltage (VF/T) will drop with increase temperature, causing increase drive current, which partially compensates decreasing output power. Equation III/4:
PT(25):
Maximum coupled power transmitter (dBm) PRL, (max): Maximum optical power level receiver (dBm) (min): Minimum attenuation fiber (dB/m) extremely large dynamic range HFBR-2528 receiver typically allows room-temperature distances from meters when using plastic fibers. Typically, current adjustments needed length plastic fiber vary from meters
PT(max):
VF(T):
Forward Voltage desired temperature VF(25): Forward Voltage room temperature, specified data sheet PT/T: Forward Voltage temperature coefficient (V/°C)
PT(T):
center wavelength transmitter, typically room temperature, changes Output power wavelength temperature desired temperature changes. data sheet, (dBm) attenuation specified
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because compatibility with older type, lower output power GaAsP transmitters. room temperature center wavelength AlInGaP transmitter exactly minimum attenuation window POF. Therefore, optical power budget allows longer link distance 25°C than specified data sheet. Attenuation about 0.05 dB/m less than which permits link (Please note HFBR0508 Series data sheet. [5])
NORMALIZED
lifetimes. POFs estimated 20-year lifetimes. Shortterm long-term bend radius, tensile load, flexing, well mechanical properties connectors specified cable data sheet [8]. detailed discussion about fiber [11,12] connector reliability beyond scope this application note. More concern useful lifetime short-wavelength transmitters, which must taken into account power budget calculations. assumed that receiver sensitivity will change over time. transmitter light output reduction function junction temperature, drive current, endurance time. useful lifetime transmitter typically defined when initial light output reduced Reliability tests HFBR-1528 transmitter project median useful life years -3dB, 85°C, duty cycle, forward current equal Therefore, optical power budget must decreased expected reduction light output end-of-life specification. More detailed information found reliability data sheet [6].
RELATIVE ATTENUATION (dB/m) (TIMES 1E-1)
1.5. Connector Loss Connector coupling losses transmitter receiver already included data sheet specifications. Connector coupling losses connections through bulkhead adapters need determined. following table shows minimum maximum insertion loss specifications HP's bulkhead connections. number bulkhead connections increases, range losses increases, does magnitude losses. Coupling loss characterization special bulkhead connectors fiber completed when this application note printed.
Table III/2. Feed Through Loss Specifications. Part 45X5 Fiber Min. Typ. Max. Size Loss Loss Loss
HFBR-
-0.2 -0.4 WAVELENGTH (nm)
Figure Typical Normalized Spectral Attenuation POF.
Because complexity receiver circuit detailed discussion about sensitivity temperature drift beyond scope this application note. Drift effects specified product data sheet should concerned about them. 1.4. Reliability Considerations service lifetime fiberoptic link however, quite often concern. separate link reliability into transmitter, receiver, connector fiber reliability. fibers known very stable under harsh ambient conditions have been qualified 30-year
1.6. Coupling Loss light from larger-core fiber coupled into smaller-core fiber, significant loss optical power measured. loss function difference area numerical aperture (NA), expressed following formula: Equation III/5:
Table III/1: Projected useful life various temperatures, where life defined drop (-3dB) light output. [mA] [°C] Median Useful Survival Life Life
IL(dB)
Emitting fiber diameter Receiving fiber diameter NA1: Numerical Aperture emitting fiber NA2: Numerical Aperture receiving fiber Light from smaller core fiber will coupled into larger core fiber without area losses.
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Transmitter Drive Circuits LED-based transmitters easy simple drive because current through proportional optical output power. current amplitude modulated using only switching transistor single resistor series with LED. Because simplicity drive circuit, design engineer many options realize this function. mentioned previously, HFBR0508 link performance guaranteed when using drive circuit data sheet (see also 2.2), meets most application requirements. pros cons other approaches that will help design engineers optimize their link performance specific applications discussed following section. 2.1. Pros Cons Parallel Series Transmitter Drive Circuits Basically, methods exist driving LEDs. uses series driver (Figure other based parallel driving scheme (Figure 14). Series driving circuits consume only half power generate higher transient noise power supply line when current switching. parallel driver uses constant current from power supply rail, thus minimizing power supply noise, which could couple into receiver degrade sensitivity. parallel drive circuit also presents very impedance junction during turn off. This impedance rapidly discharges junction quickly extinguishes optical output LED. should keep mind that transmitter drive circuit
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HFBR-1528
CMOS INPUT SHOULD CONNECTED GROUND
Figure Shunt Drive Circuit.
RISE/FALL TIME (ns)
FALL TIME
47.5 47.0 46.5 46.0 45.5
2.2. Series Driver Circuit using Standard Buffer Data sheet Drive Circuit driver circuit, Figure designed such that series with opencollector output driving gate. Resistor sets drive current through LED, resistor provides discharge path when forward current turned off. Equation III/2:
Vcc-Vce-VF
45.0 PARALLEL RESISTOR (OHM) THOUSANDS
Figure Typical Optical Switching Speed Parallel Resistor
Figure shows forward current deviates from intended nominal room temperature design value when using series drive circuit, following factors: part-to-part variations forward voltage,
PULSE WIDTH DISTORTION
topology contributes overall pulse-width distortion (PWD) fiber optic link. Therefore, important that optical rise fall times fast compared symbol time. transmitter propagation delay times, tPLH tPHL, should also equally balanced entire link low. Fortunately, HFBR1528 transmitter rise fall times that fast enough switched without peaking prebias[3] data rates high MBd. This keeps drive circuit simple possible. Drive circuits rise fall times order discussed AN1066[3].
low-impedance path quickly discharges LED, decreasing optical fall time. kOhm resistor empirically found optimum value best PWD. important note that capacitors near anode filter noise power supply line during switching periods.
25°C, RISE TIME
48.5 48.0
current-limiting resistor tolerance, power supply tolerance, variations saturation potential 75451 peripheral driver. Figure also shows that increases, total variation forward current, other circuit tolerances, minimized. recommended driver shown Figure takes advantage negative temperature coefficient HFBR-1528 forward voltage. When temperature rises, forward voltage decreases greater percentage supply potential must dropped across resistor temperature increases forward voltage declines, potential difference across increases Ohm's dictates that current through HFBR-1528 will increase. This increase drive current partially equalizes reduced light output negative output-power temperature coefficient.
coupled power into specified minimum maximum values versus temperature range Intermediate power levels calculated based Figure HFBR-1528 data sheet. drive currents less than specified data sheet, part-topart variation output power increases. 2.3. Simplest Transmitter Shunt Drive Circuit circuit shown Figure simple-shunt drive transmitter circuit that uses transistor. primary feature simplicity: only components required circuit interfaced CMOS gates without additional components. circuit also fast several reasons: transistor never saturates, presents very impedance during turn LED, emitter base junction voltage "prebiases" junction resulting faster optical rise time
addition, drive circuit generates power-supply ripple because constant load during switching. drawback increased power consumption constant current flow through bias resistor. Receiver Interface Circuit Design HFBR-2528 receiver push/pull digital output. capable sourcing sinking current high (receivers HFBR-25X1,2,3,4 need pull-up resistors) drive CMOS logic families without external resistors. recommends that firstorder, low-pass filter (see Figure used minimize power-supply noise between ground power supply terminals receiver. This arrangement will meet powersupply rejection specification. bypass capacitor should connected close possible power supply terminals HFBR-2528 receiver. ground plane underneath conductive receiver housing connected pins provides excellent shield against electric fields high kV/m, which could otherwise interfere with receiver 3.1. Sensitivity DC-coupled receivers, such HFBR-2528, specified sensitivity different conditions than ac-coupled receivers[3] which bit-error ratio (BER) important criterion. HFBR-2528, sensitivity minimum optical power level less than |30| measured with percent duty cycle, square-wave signal.
TOLERANCES ±15%; Vce: ±75%,
49.7%, t(r) (ns)
IF/IF NOMINAL
RISE FALL TIME (ns)
MAXIMUM MINIMUM
t(f) (ns)
(VOLTS)
IF-FORWARD CURRENT THROUGH (mA)
Figure Output Power Variation Supply Voltage Components Tolerances.
Figure Switching Speed Drive Current.
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3.2. Off-State-Limit recommends that light coupled receiver when should remain logic-high state. some instances, might possible turn transmitter totally off. power delivered receiver should always less than fibers ensure that output does randomly change state. 3.3. Overdrive Limit overdrive limit specified where exceeds |30| example, temperatures, power levels above ,max exceed when using driver circuit topology other than specified data sheet. transmitter application circuit, recommended product data sheet, decreases drive current temperatures because higher voltage drop across transmitter.
standard tubes dual in-line packaged components easily picked placed with autoinsertion machines. During soldering, optical port plug recommended prevent contamination port. Solderability specified under Mil. Std. Method 2003. Please follow maximum time temperature guidelines given product reliability data sheet. Water-soluble fluxes, rosin-based fluxes, recommended. Connectoring Guidelines 2.1. Plastic Fiber Plastic optical cables terminated less than seconds using Versatile Link Snap-in connectors standard tools[27]. After cutting cable desired length, fiber jacket should removed with 16-gauge wire stripper. crimp ring connector positioned then crimped over cable. excess fiber protruding from connector off. better light coupling fiber must polished using 600-grit abrasive paper. detailed connecting instruction appendix fiber-optic cable data sheet [8]. 2.2. Crimp Cleave Termination fiber easily terminated using Snap-in V-System connector HFBR-4584 termination [28], which contains fiber buffer strip tool, cable strip tool, pair scissors diamond cleaving tool. entire process does need either epoxy polishing completed less than minute. following abstract from detailed Crimp Cleave
Connectoring manual: Remove cable jacket Remove fiber buffer Apply first crimp ring fiber buffer Crimp connector jacket Cleave fiber 2.3. Optical Port Protection During equipment manufacture recommends using optical port plug inserted into transmitter receiver when delivered prevent contamination port. During operational life communication equipment port plug misplaced lost. Therefore, very simple "optical short circuit" between transmitter receiver constructed short length duplex connector (Figure 18). small ring chain through cable opening screwed front back panel system that port plug always located. Whenever connector inserted station will receive signal function optical serial interface tested. addition, warning message telling user that serial port connected might displayed system monitor.
DUPLEX CONNECTOR
Manufacturing Consideration
Handling Assembly Guidelines Non-stacked Versatile Link parts require special handling during assembly onto printed circuit boards. advises, however, that normal static precautions taken handling assembly these components prevent damage and/ degradation, which induced electrostatic discharge (ESD). HFBR-1528 HFBR-2528 Class Class
CRIMP RING
Human Body Model Mil. Std. Method 3015 transmitters receivers delivered customers
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SIMPLEX PLASTIC OPTICAL CABLE
Figure Optical Port Protection Connector.
Application Examples
Introduction Industrial Communication Networks Compared years ago, today's industrial control equipment changed dramatically. longer many single twisted-paired lines from sensors actuators bundled into huge heavy cable connected programmable logic controller. Today, intelligence distributed network; actuators sensors connected bus, star ring topology master unit. Standards committees user groups have defined serial data rates from several more than twisted pair fiberoptic media interfaces. these open-system standards always meet application requirements because speed, noise immunity, distance specifications. Proprietary networks critical, real-time applications, example, must have faster response times than today's standards specified for. These applications need
serial noiseless communication channels with data rates high achieve desired performance control system. these conditions, worth considering de-facto industry standard HFBR-0508, fiber-optic link isolated reliable optical interconnects. 1.1. Interface Many networks based RS-485/422 physical media interface, which based topology. Different ground potentials noise sources allow non-isolated structure. Therefore, active star couplers with fiber-optic ports preferred. Quite often, mixed topology consisting fiber cable twisted-pair wire desired. this case, Versatile Link family most costeffective line products fiber-optic inter-repeater links. Versatile Link's small package allows HP's parts assembled into adapter housing electrical-optical converter. side
housing holds electrical subminiture connector interface with twisted-pair bus, opposite side duplex, snap-in, fiber-optic connection. Standard "off-the-shelf line drivers receivers RS-485 [15,16,20] interface between twisted-pair receiver output transmitter input. While majority industrial communication applications specified data rates below (much lower than speed HFBR-0508 link), large dynamic range HFBR-2528 receiver allows fiber-optic link designed without transmitter optical output power adjustment. This factor makes installation instruction much simpler avoids trouble-shooting exercises receiver overdrive conditions. Whether link anywhere from zero meters maximum length specified data sheet whether fiber POF, link will work reliably moment that power turned
FIBER OPTIC LINKS
TWISTED PAIR FIBER OPTIC LINK
DATA TERMINAL EQUIPMENT
REPEATER
ACTIVE STAR
TERMINAL
Figure Network Overview with Fiber Optic Active Star
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HFBR-1528
SN75451 SN75176A
HFBR-2528
SN74122
Figure Basic Fiber Optic Interface Adapter Data Terminal.
Table V/1. Link Length Overview HFBR-0508 Fibers. Fiber Type Guaranteed Link Distance Temperature Range 25°C 0°C< TA<+70°C -20°C< TA<+85°C 25°C 0°C< TA<+70°C -20°C< TA<+85°C Conditions
more details please product data sheet!
1.2. Controller Area Network (CAN) special controller-area network (CAN), which meets stringent reliability requirements automobile manufacturers, been developed low-cost, realtime applications cars. found field buses because open-system interface high noise immunity. Semiconductor manufacturers [18,19,21] offer integrated circuits layer (Physical)
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(Data Link). When using fiber optics best network configuration passive star coupler. passive star coupler [23, ,29] divides optical signal from source into multiple optical signals nearly equal amplitude. Therefore, devices connected coupler receive transmitted data same time. past, high insertion loss passive star couplers
(see Table V/2) reduced optical power budget nearly making fiber optics impossible. transmitter technology, with dBhigher output power, allows expanded networks based passive star couplers. Because coding NRZ, dc-coupled receiver with output should used. Design engineers have choices receiver interface. data rates kBit/s
MASTER COMPUTER
PROCESS CONTROLLER
PROCESS CONTROLLER
PASSIVE STAR COUPLER
PROCESS CONTROLLER
PROCESS CONTROLLER
Figure with Passive Star Coupler.
(ISO/DIS 11519-1), they HFBR-25X2 receiver. serial rate MBit/s (ISO/ 11898), they should consider HFBR-2528 receiver because lower pulse-width distortion (PWD) specification large dynamic range. large dynamic range will compensate spread insertion loss coupler.
Table V/2: Typical Insertion Loss Star coupler. Ports Insertion Loss
maximum link length distance from transmitter bulkhead connector from bulkhead connector receiver. Equation V/2:
(min) IL(max) (max)
PT(min):
detailed specifications, please contact suppliers ,24, 25].
following equation (V/2) should used calculate maximum possible link length.
Minimum coupled power transmitter (dBm) (min): Sensitivity receiver [coupled power] (dBm) Insertion loss measured from input port output port (dB) passive star coupler OPM: Optical power margin (dB) (max): Maximum attenuation fiber (dB/m)
maximum data rate also function maximum distance between nodes, because propagation delay time must less than half time. propagation delay constant optical signals ns/m fiber-optic links because signal speed equal speed light divided refractive index. propagation delay transmitter receiver listed Table V/3. Transmitter receiver delays must added propagation delay fiber determine total delay fiber-optic link. Gate Driving Using FiberOptic Interfaces With improvements development power switches such GTOs IGBTs, frequency inverters operated higher speed higher power levels. hand, circuit needed drive gates IGBTs GTOs fast.
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other hand, gatedrives must reliably reject higher faster switching transient voltages caused large variations current power rails. Traditional techniques based transformers galvanic isolation shielded cables require very experienced engineers design "trouble free" interface. Even minimum distance requirements between signal lines power units good ground contacts make system larger more costly than would features inherent fiber optics taken advantage these applications, transformers will become redundant because dielectric property fiber fact that will easily meet regulatory requirements IEC, CSA, CENELEC, VDE, etc. addition, fiber immune kind electromagnetic fields placed alongside power lines without affecting transmission quality. result simplified design with higher reliability less sensitivity system failures during installation maintenance. following aspects should considered when taking advantage many features Versatile Link offers gate-drive applications. These include shielded housing, high-temperature fiber, PWD, fact that receiver accept arbitrary duty-cycle. recommends transmitter drive circuits from chapter because switching speed major design issue. Because link distance very short such applications, drive current value output power specified data sheet power budget calculation from
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chapter should followed. receiver conductive housing should grounded good power-supply filter should used because isolated power supply known very noisy. dead-time specification most important design parameters. worst-case propagation delay from controller gate power switch computed. fiber-optic link, overall propagation delay time transmitter, receiver fiber delay times. Typical fiber optic link delay times listed Table V/3. specified HFBR-2528 data sheet. Since speed light limited about 2.99E-8 vacuum, photons will travel lower speed dense media such glass plastic fibers. Equation V/2:
error, such mixing cables, cause only fail function will destroy power switches.
Introduction Optical Power Loss Measurements
theoretical methods used specify optical parameters were discussed chapter III. Theoretical values must verified, however, only empirical functional tests also optical power loss measurements. relevant standard loss measurements cables connectors 874-1. detailed discussion different methods described standard beyond scope this application note. Only most important methods will briefly described. recommendations this application note measurement equipment accessories will help newcomer fiber optics, even with financial constraints, quickly implement system.
Recommended Equipment Accessories Table V/3: Typical Propagation following items needed: Delay Times 25°C HFBRconnectors, several meters 0508 Link with cable, transmitters receivers, Parameters Tx(in) Units tools terminate plastic Rx(out) cable. lowest-cost with approach termination [27]. details, please fiber-optic cable data sheet [8]. Versatile Link transmitters used optical reference source. Power avoid fault connections, which meters with large-area cause shoot-through condetector, sources ditions half bridge, recPOF HCS, ommends that transmitters adapter accessories available single half bridge from several manufacturers latched pairs. Duplex conneclisted appendix [26]. tors have function will into latched pair only position. Therefore, human
Speed light vacuum 2.99E-8 Refractive index media =1.5 PMMA
1.1. Transmitter Output Measurement reference cable should terminated with carefully polished connector each end. cable connected transmitter optical power meter. coupled power into read display power (mW) reference power (dBm). Equation VI/1:
increasing Z-axis spacing fibers. When fiber disconnected from receiver inserted into optical power meter. optical power meter shows average received power. calculate receiver peak-power sensitivity, PRL,min, reading. 1.3. Cable Attenuation Measurement First reference cable connected transmitter power meter zero dB). Then attenuation fiber being tested measured. power meter displays incremental change attenuation. This value divided length fiber calculate optical loss meter dB/m. Typically, longer cables measured; attenuation reference cable (about neglected. recommends repeating measurement with connections reversed. different power reading will indicate coupling loss variation connectorport dimension tolerances and/or uneven polished fiber surfaces.
(dBm)
P(mW)
Data sheet; Plastic Optical Fiber Fiber Cable Connectors Versatile Link Fiber Optic Handbook, HewlettPackard, Christian Hentschel [10] 874-1 [11] Data book, Techno Research [12] High Strength, Reliable, Hard Clad Silica HCS® Fibers, EnsignBickford Industries [13] Elektronik Plus, Automatisierungstechnik [14] Fischer,Balzer,Lutz, Franzis Verlag
Supplier Reference
[15] Texas Instruments [16] Motorola [17] Thomson [18] Siemens [19] Philips [20] Maxim [21] Intel [22] Spectran [23] Kabelwerke Rheinshagen GmbH [24] MicroParts [25] Nichimen [26] RIFOCS "V-Kit Measurement Instruments" 557B Power Meter, 253B Source; Photodyne, Model 18XTA; Mitsubishi, Rayon, 100-205 [27] Plastic Fiber Termination Accessories, HFBR -4593 Polishing Kit, HFBR-4597 Plastic Fiber Crimping Tool [28] Termination Kit, HFBR-4584
P(mW): Power P(dBm): Power decibels referenced detector area larger than fiber's cross-sectional area, coupling loss between connector detector neglected. also recommends repeating measurement with connections reversed. different power-level reading will indicate coupling loss variation. also possible measure output power pulsed transmitter. duty-cycle pulse gives average power-level (Pavg) reading. actual peak amplitude (Ppk) twice high referenced power) average. Example: Pavg
VII.
Appendix
Literature Reference
Application Bulletin Cost Fiber Optic Transmitter Receiver Interface Circuits Application Bulletin Cost Fiber Optic Links Digital Applications Application Note 1066; Fiber Optic Solutions Communication Applications Copper Wire Prices Application Note 1035; Versatile Link Data sheet HFBR-0508 Series; Versatile Link Fiber Optic Transmitter Receiver Reliability Data sheet HFBR-1527/8 Reliability Data sheet HFBR-2528
1.2. Receiver Sensitivity Measurement transmitter receiver linked fiber-optic cable pulsed with desired data rate duty cycle. optical attenuator different fiber length used lower power receiver while monitoring pulse-width distortion (PWD). Using simple vise, also construct attenua-
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Application Note 1080 Contents Introduction Interconnec

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