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电子专业中英文翻译

电子专业中英文翻译
电子专业中英文翻译

基于单片机控制的光收发器设计

1 引言

在“三网合一”的推动下,光纤到户等光纤接入方案的应用日益广泛。在光进铜退的呼声下,光网络迅速发展。光收发器在光通信中起到光电、电光转换的作用,是光通信必不可少的器件。由于涉及到高速电路设计、精密机械加工和光学设计,光收发器的成本占据了光纤通信系统和的重要部分,而较高的光收发器价格成了制约光纤接入推广的瓶颈。进一步降低光收发器的成本将有利于光接入的应用推广,加快光进铜退的步伐。

光收发器主要由电路部分、光发送组件和光接收组件组成。其中电路部分又包括激光驱动、光接收信号放大和控制部分。目前市场上的光收发器的电路部分使用的是三个专用芯片。一直有公司在研究把激光驱动和接收信号放大电路集成在一个器件上,控制器使用普通的嵌入式处理器的方案。由于只使用一个专用芯片和一个通用芯片,这样就可以大幅降低电路部分的成本。PHYWORKS 公司研制的PHY1076芯片就是一款这样的芯片。它主要针对1.25Gbps到2.5Gbps的光收发器,具有外围电路简单,控制电路只需要普通的8位单片机就可以实现的特点。本文主要研究了PHY1076 的性能,选择了ATMEL 公司的ATMEGA88 单片机进行控制,设计出光收发器样品,并进行了性能测试,最终成功设计了1.25G 光收发器。

2光收发器设计方案及工作原理讨论

光收发器在发展的过程中,有许多种不同的外形封装。SFP(小型化可热插拔光收发一体模块)是目前在5Gbps以下速率中最先进的一种封装形式,具有小型化、可热插拔、功耗小、系统可集成度高以及能够进行数字诊断功能等特点。

本设计中使用激光驱动电路和光接收放大电路集成的PHY1076 作为专用芯片,使用ATMEL 的AVR 单片机ATMEGA88 进行控制和实现DDM功能,加上相应的TOSA(光发射组件),ROSA(光接收组件)和结构件,设计了一款工作在1.25Gbps传输距离为10km 的SFP 光收发器。系统方框图如图1所示:

图 1

光纤收发器的内部结构图

1) 发射部分工作原理:

系统的串行数据信号从TX+/-端以差分信号形式输入到PHY1706 的激光器驱动部分。驱动电路进行放大处理后,转换成差分调制电流信号加载到TOSA(光发射组件)上,控制TOSA中的激光器发出光脉冲,耦合入光纤发送到远端。

2)接收部分工作原理:

光脉冲信号输入到ROSA(光接收组件),ROSA将光脉冲信号转换成差分电压信号输出到PHY1076的限幅放大部分。该信号经过限幅放大处理后,从PHY1076的RX+/-端输出差分电压串行数字信号。

3) 控制及DDM 部分:

PHY1076 是一款模拟数字混合芯片,其内部包括多个模数(A/D)、数模转换(D/A)器。发射和接收通路上的参数都是通过ADC 转换成数字量存入状态寄存器进行监视,通过DAC把设置寄存器的值转换成模拟量来进行控制的。这些寄存器都可以由外部控制器进行读取和设置。

DDM(Digital Diagnostic Monitor),数字诊断和监控是指的光纤收发器能够对发射功率(Tx_power),接收功率(Rx_power),激光器偏置电流(Ibias),工作电压(Vcc),模块内部温度(Temperature)这些参数进行实时监视,并能够在各项参数超过设定值时设置报警标志位的功能。PHY1076内部集成的ADC 能够对发射功率、接收功率和偏置电流进行监测。工作电压和温度传感则需要另外ADC进行转换。而所有这些报警的实现则需要外部控制器来实现。

ATMEL 公司的AVR单片机ATMEGA88 是一款8 位单片机,内部集成FLASH、RAM、EEPROM、内部时钟和ADC。无需任何外围电路即可构成系统,支持在线编程下载和单步调试。系统设计和软件调试都很方便。集成硬件I2C模块,可直接对外提供符合SFP-MSA 规范要求的外部I2C 接口。而且此单片机是一款在家电和工业控制领域使用广泛的芯片,用量大,性能稳定可靠,价格低。本设计选用此芯片控制PHY1076的工作参数和实现DDM功能。

3 关键参数控制和实现

在光纤通信系统中,发射光脉冲的平均光功率和消光比是两个非常重要的参数。根据传输距离不同,需要设定不同的值。对具体某一个光收发器则希望其发光功率和消光比能够长期维持在一定范围内。要维持稳定的光功率则需要使用APC(自动功率控制)电路。又由于激光器的温度特性和老化特性,其发光效率会变化,所以又需要进行温度补偿。消光比的自动控制则需要根据温度变化而实时的调整调制电流的大小。

早期的光收发器中,大都使用专用模拟器件,所以要实现功率APC、温度补偿和消光比自动控制都非常困难,或者很难得到满意的效果。PHY1076是一个模数混合器件,其高速通道部分使用模拟设计,而其功率控制、调制电流则是使用寄存器进行的。从而只要外部控制器能够监测温度,就能根据温度调整寄存器的值,达到自动更改输出功率和调制电流,使功率和消光比维持在一定得范围内的目的。

1) 平均光功率的控制实现:

PHY1076 内部APC电路如图2所示。TOSA 内部集成了一个激光发射二极管和一个光电感应二极管。激光器的发光功率与电流成正比,激光器的阴极接到PHY1076的Laser_bias引脚。PHY1076内部功率设置寄存器的数据直接输入到DAC,DAC 产生一个模拟电压输出控制压控电流源的输出电流,此电流源输出电流经过电感耦合后给激光器的提供直流偏置电流。因此修改功率设置寄存器的值就可以直接修改激光器的输出光功率。光电感应二极管的反向漏电流与激光器的发射功率成正比。该电流从MPD引脚接入PHY1076内部,经过放大和转换成电压信号后,作为负反馈信号引入到压控电流源的控制端,起到自动功率控制的作用。但是APC 能够控制的功率变化范围是有限的。当温度变大时,由于激光器的发光效率降低,APC将不能提供足够大的电流来保持功率稳定。此时就需要调节功率设置寄存器的值来获得更大的偏置电流以保持功率稳定。本设计中是通过外接单片机来根据温度进行寄存器设置,达到温度补偿的目的。

图2 APC 工作原理图

2) 消光比控制的实现:

PHY1076内部调制电流控制电路如图3 所示。消光比在光纤通信系统中定义为发送数据为1 时与发送0 时的光功率的比值。其值的大小会影响通信系统的误码率,因此需要控制在一定范围内。在使用交流耦合的调制激光器的电路中,平均发射功率受直流偏置电流影响,消光比的大小受调制电流的影响。在PHY1076 的内部,激光器的调制电流由专门的寄存器进行设置后,经过模数转换器(DAC)输出控制电压,进而控制输出调制电流的大小。因此适当设置该寄存器的值就可以得到理想的消光比。由于没有办法检测工作中消光比的大小,因此无法引入反馈电路实现消光比自动控制。比较可行的办法是寻找消光比与温度变化的统计规律,然后通过外部控制器依规律进行温度补偿。

图3调制电流控制原理图

3)ATMEGA88 的控制算法分析和DDM 实现:

从上面的分析可以看出,光收发器的关键参数平均发射功率和消光比都是通过对PHY1076的内部寄存器的设置来控制的,而PHY1076提供I2C 接口进行访问。本设计中,使用ATMEGA88 单片机进行控制。ATMEGA88 单片机内部有一个标准的硬件I2C接口,可以用来为系统设备提供SFP-MSA(SFP多源协议)要求的对外I2C。为了与PHY1076进行通信,本设计中用软件模拟了一个I2C 接口。单片机的主要工作内容包括:为功率控制提供温度补偿功能;为消光比提供自动控制

功能;设置PHY1076 的接收放大部分的一些工作参数;对PHY1076进行初始化;提供DDM 功能和记录产品信息。ATMEGE88 与PHY1076的连接如图4所示。

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4ATMEGA88 与PHY1076连接图

激光器的发光效率和阈值电流与环境温度成反比,即当环境温度升高时,激光器的发光效率会降低,阈值电流会升高。为了达到输出光功率和消光比的稳定性,就要根据温度变化来响应调节激光器的偏置电流和调制电流。本设计中采用查表法来设置偏置和调制电流。具体就是建立两个数据表,功率设置表和调制电流设置表,每个值对应一段温度下的功率设置寄存器的值。如图4 所示,调制电流设置表为80 个字节,每两摄氏度占一个字节;功率设置表占用40 个字节,每4 摄氏度占用一个字节;温度范围都是-40~120℃,满足工业温度的要求。给单片机外接一个温度传感器,单片机通过模数转换器把温度传感器送来的电压转换成温度值,然后根据温度查表,找到对应的数据,把数据分别送往PHY1076 的功率设置寄存器和调制电流设置寄存器,调整激光器的偏置电流和调制电流,由此调整输出光功率和消光比。

数据表的数值确定则使用测试的方法得出。在收发器的调试过程中,对样品在每个温度下的输出眼图进行测试,并修改对应温度下的数据,使得光收发器的输出光眼图、光功率和消光比满足要求。最后把这些数据保存到温度查找表中,并同时保存到ATMEGA88 内部的EEPROM 中。收发器在实际的应用环境下,重新加电后,就先从EEPROM 中把数据加载到RAM区,然后就可以在全温度范围内稳定平均输出光功率和消光比。

4设计结果及测试分析

本设计根据以上讨论的方案,选择PHY1076专用芯片和ATMEGA88 单片机,外加适当的外围电路设计电路板,把TOSA、ROSA焊接到一起装入定制外壳,实现了一款1.25Gbps 的SFP光收发器。调试PHY1076 内部寄存器使光收发器各项参数符合802.3z协议中对10km 千兆以太网光接口的要求。同时设计的上位机调试软件对ATMEGA88 的温度查找表进行调试,确定了具体每个温度下的值。由此完成了整个光收发器的设计工作。然后对光收发器在低温,常温,高温三种环境下的所有参数进行测试。结果如表1 所示。

表1光收发器的参数测试结果

从表中可以看出。激光器的输出光功率和消光比都在参数要求范围内,且变化小。测试了各个温度下的眼图,发现光收发器在低温,常温,低温下的性能都比较好。由于温度变高时需要提供较大的调制电流,因此信号的下冲比较明显,表现在眼图中就是在眼图中的“0”信号出现轻微双眼线。但总体上模板测试余量都大于40%。由此验证了此设计方案的可行性和正确性。

5 总结

经过方案讨论、硬件设计、软件设计和样品调试、测试。最终成功设计了1.25GSFP 单芯片SFP 光收发器。此方案的特点是把激光驱动和接收放大部分集成在一起,使用了普通单片机进行控制,理论上能够降低了产品的成本和提高生产效率。由于此方案是一个新的方案,技术成熟度有待提高,系统兼容性和市场应用的潜在问题有待验证。加上用量的关系,其成本的优势也体现不出很大的优势。但是可以相信,随着网络速率的加快和光接入对成本的压力,新技术会越来越完善,市场占有率也会越来越高,届时成本优势就会体现出来。

Microcontroller-Based OpticalTransceiver

Design

1 Introduction

Under the impetus of the“ThreeNet Combined”,Fiber access programme such as FTTH(fiberto the home) is widely used. Underthe voice ofthe lightfor copper,the opticalnetworkis developing rapidly. Optical transceiver plays a role ofelectro- optical, electro - opticalconversion in optical communications, and is an essential device for optical co mmunication.As it relates tohigh-speedcircuit design,precision machining and optical design,the cost of optical transceivers occupiesan important part in fiberoptical communication systems andwhile thehigh prices of optical transceivers become thebottleneck of restricting fi ber access promotion.Further reduce the cost of opticaltransceivers will be nefit topromotethe application ofoptical access and speed up thepaceof light forcopper.

Opticaltransceiver mainly consists ofcircuits, opticaltransmitter components and opticalreceivercomponents.And the Part of thecircuit whichalsoincludes laser driver,optical receiver signal amplifierandc ontrolsection. In current,The circuitpart ofoptical transceivers on the market isusing three specific chip.The company has always beeninthe study oflaserdriver and receivingsignal amplifier circuit integration in a device,with thecontrollerusing the common embeddedpro cessor solutions. Due to onlyuse a specific chip and acommon chip, we can significantly lowthecost of the circuit part.The PHY1076chip developed by PHYWORKS companyis such a chip.Itis intended mainly for1.25Gbpsto 2.5Gbpsoptical transceiver withasimpleexternal circuit,andit requires only anordinary 8-bit microcontroller to realize the control circuit.Thispaperstudies the performanceof the PHY1076whichcontr oled bythe selected ATMEL company'sATMEGA88microcontroller, designed the optical transceiversamples, andconducted theperformance test, with the ultimate success of the design ofthe1.25G optical transc eiver.

2 Discussion About The Design AndWorking Principle Of OpticalTransceiver

In the development processof optical transceiver, there are many dif ferentoutline package. SFP (Miniaturization hot-soptical transceiver module)iscurrently oneofthe mostadvanced package in5Gbps rate, with a small, hot-s,low power consumption, high systemintegration and the ability todigitallyDiagnostics and so on.

Thisdesign uses laserdrivercircuit and opticalreceiveramplifiercircuitntegratedPHY1076as aspecial chip ,using ATMEL's AVR ATMEGA88microcontrollertocontrol andimplementDDM functionality,coupled withthe corresponding TOSA(transmitteroptical components), ROSA (r eceiver optical components)and structural parts to designe a SFPoptical tra nsceiverwhich canwork in 1.25Gbps10kmtransmission distance.

System block diagramshown in Figure 1:

Figu re 1the internal structure offiber optictransceiversmap

1)Transmitter works:

Serialdatasignal from the TX + /-side ofthe system input to the PHY1706 laser drive sectionin theform of differential signalterm inal. After amplificationd, drivecircuit convertedtodifferent ial modulation currentsignal loading to the TOSA(transmitter opti

calcomponents) to control the laserTOSA to emit light pulses, and

couple into the fiberto sentto theremote.

2)Receive partworkprinciple :

Opticalpulse signal inputs to the ROSA (receiver optical componen ts), and ROSA converts optical pulse signalinto thedifferential voltage signaloutput tothePHY1076 the limiting amplifier section. After limiting amplified thesignals,it outputs differentialvoltage serial digital signalsfrom the RX + / - sideofPHY1076.

3) Control and DDM parts:

PHY1076 isa mixedanalog-digital chip, its internal includesmultiple analog-digital(A / D) anddigital-analog converter (D /A) devices. Parameters onthe transmitandreceive pathsare converted into digita lstored in theState register for monitoring throughADC, and converts registervalue into analogfor control byaDAC.Theseregisters can be read and setby an externalcontrolle.

DDM (Digital Diagnostic Monitor) meansthat the fiber-optical transceiv ers iscapableof monitoringparameters such as ransmittingpower (Tx_power), receivedpower (Rx_power), laserbias current(Ibias),operating voltage (Vcc)and the module internal temperature (Temperature )in real-time and set alarmflag when the parametersexceed the setted-value. The ADC integrated within PHY1076canmonitorthe transmit power,receivepowerandbiascurrent. However the operating voltage andtemperatu re sensingis requiredfor another ADCconversion.The realization ofall these alarmsrelays onexternal controller.

ATMEGA88AVR microcontroller fromATMEL Corporationis an 8-bit microcontroller,withFLASH,RAM,EEPROM, internal clockand the ADCintegrated inside. Without any external circuit to constitute asy stem,and supporting on-line programming downloads andsingle-stepdebugging.System design andsoftware debugging is veryconvenient. Integrated hardwareI2Cmodule can directly provide theexternal I2Cinterface inlinewith SFP-MSA specifications.And this isasingle chip widely used inthefield of homeappliances and industrial control withlarge use,stableandreliable performance, low prices.The design usesthechip PHY1076to controltheoperatingparameters and implement DDM functions.

3Control And ImplementationOfKeyParameters

Inopticalfiber communicationsystem,the average opticalpower ofemitted light pulse and extinctionratioare two veryimportant parameters.According tothedifferenttransmission distance,we need to set a different value. Onone specific optical transceiver is hoped thatthe lightemission powerandtheextinction ratio can be maintained within a certainrange. To maintain a stable light poweryouneed touse APC (automatic power control) circuit. Atthesame time, because of temp eraturecharacteristics andaging characteristics of thelaser, the luminous efficiency will change, itis also the need for temperature compensation. Theautomatic control of extinction rat requires adjustmentthe size ofmodulation currentaccording to temperaturechangesin real time.

Optical transceiver in the early,mainly uses a dedicated analog devices, soia is difficultachievethepower of APC, temperature compensationand automaticextinction ratio control,or itisdifficult to obtain satisfactory results. PHY1076 is a modularmixing device,using the analog partof its high-speed channel design, while itspower control andmodulation current iscarried outby the register. So longas the externalcontroller can monitor thetemperature,you can adjusttheregist ervaluesbasedon the temperature in orderto automaticallychange the output power and modulation current,with thepower and extinction ratio maintained ata certain range of purposes.

1) Control And AchieveOf The AverageOpticalPower:

PHY1076internal APC circuitis shown in Figure 2.TOSA is integ rated with alaserdiode anda photoelectric sensor diode. Laser lightpower is proportionalto andthe current, andthe laser's cathode connect ed withthe PHY1076’sLaser_biaspin. PHY1076’sdata in internalpowerset registeris input directly to theDAC, thenDAC produces an analog voltage output tocontrol output current in voltage-controlled current source.And the output current of current source supply the laser withDC bias currentthrough the inductive coupling. Therefore,to modifythevalue of thepowersetting register is to modifythe laser’s output optical power. The reverse leakagecurrent of photoelectricsensordiode isproportional to th elaser’s emissionpower.The current accesses PHY1076 fromthe

MPDpin, after amplified and converted into a voltage signal,itis introduced in to thecontrol side ofvoltage-controlledcurrent source as a negativefeedbacksignal inorder to play the role ofautomatic power control.But the power range controled by APC islimited. When the temperature beco mes larger, APC willnot provide enough currentto maintain power to bestable due to the reduceoflaser’slight-emittingefficient. At this moment weneed toadjustthevalueof thepowersettingregisterto gain greater biascurrent tomaintain powerstable.This design is settingthevalue ofregisterbasedon temperature by an externalmicrocontroller toachievetemperature compensation purposes.

Figure 2 WorkingPrincipleof APC

2) The Realize of ExtinctionRatio Control:

PHY1076internal modulation current control circuit is shown inFigure 3. Extinction ratio is defined astheratio of opticalpower whensending data to 1andoptical power when sending data0 in optical fibercomm unication system. Its value will affect the bit errorrateofcommunication systems,hence weneedto controlwithina certain range. InAC coup led circuits of modulatedlasers,the average transmitpower is affecte dby theDC bias current with the extinction ratio affectedby modulation cu rrent. Withinthe PHY1076, when laser’s modulation current is set by a specia lregister,thenoutput control voltage afterdigital-to-analog conversio nso asto control the size of theoutputmodulationcurrent. Therefore,s et the valueof the register properly canobtain theideal extinction ratio. Sincethere is no way to detect the sizeof theextinction ratio during working,wecann’t introduce the feedbackcircuit to achieve theautomat icextinctionratiocontrol.Itis more feasibleto look fort

he statisticallaw inextinction ratioand temperaturechange, and conduct temperature compensation byan externalcontroller accordancewith law.

Figure 3 Schematic modulation current control

3) ATMEGA88 Control AlgorithmAnalysisAnd DDM Implementation:

Fromthe above analysiswe can see that the key parameters of optical transceivers like theaverage power and extinction ratiorelay onsettings PHY1076’s internal register to control. While the PHY1076provides I2C interface for accessing.We useATMEGA88 microcontrollerto control in this design.ATMEG A88 microcontroller hardware insidehas astandardI2C interface to provide sys tem equipmentwith external I2C required as SFP-MSA(SFPMultiSource Agreement). In order to communicatewith the PHY1076, the design using softwareto simulateaI2Cinterface.MCU’smaintasks include providing temperature compensation functionforthepowercontrol,providing extinctionratio automaticcontrol function,setting parameters of enlargeand receiver part in PHY1076,initializing the PHY1076, providingDDMfunctionality andrecord product information. ATMEGE88 connected with the PHY1076 asshownin Figure 4.

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Figure 4ATMEGA88 connection diagram with thePHY1076Laser’s luminousefficiency and thresholdcurrent is inversely proportional tothe ambient temperature,that is, whenthe ambient temperaturerises, the luminous efficiency willreduce with the thresholdcurr ent will increase. Inorder to achieve thestability of the output optical power and extinctionratio, we must adjust the laser’s biascurrentandmodulation current according totemperature changes. The look-up

table methodis used to set thebias and modulation current in the design.Spe cifically, we establishtwodata tables-the modulation currentpowerse tting table and powersettingtable, each valuecorresponds to a temperature of the power setting register. As is shown in figure4.,mod ulationcurrent setlistis80 byteswithone byte per two degrees,w hile powersetting tabletakes40 bytes with one byte for every 4 degreess. Both temperature range is -40to120centigrade,which meets therequirementsof industrial temperature . When anexternal temperature s ensoraddedtothe microcontroller,microcontroller converts voltage sentby thetemperaturesensor into atemperature valuethrough ADC,thenlook upthetemperature look-up tableto findthecorresponding data.Sent the data to the power set register and modulation current settingregister in PHY1076accordingly,adjustthe laser’s bias current and mod ulation current, which adjust theoutput optical powerandextinction ratio.

Values of numerical datatableareobtainedfrom test. During the process oftransceiver debugging,testthe thesample’seachoutput of eye patternunder different temperature and modify the corresponding temp erature data, so as tomakethe output optical eye pattern, optical powerand extinction ratio ofoptical transceiver to meetthe requirements. Finally,save these data to atemperature lookuptable andtheinternalEEPROM inATMEGA88. In the real application environment,when repowe rs,thetransceiverloadthe EEPROMdata intoRAMarea,and then you can stablethe average output opticalpower andextinction ratiointhe whole temperature range.

4 AnalysisOfResults And Test

Basedon the above discussion of the design program,we select the

PHY1076 dedicatedchipandATMEGA88 microcontroller,plusappropriatee xternalcircuit design circuit boards with theTOSA,ROSA weldedtogether incustom enclosuresto achievea1.25Gbps SFP optical transceivers.Debug Internalregisters inPHY1076in orderto make parameter sofoptical transceiversmeet requirements about 10km Gigabit Ethernet protocoloptical interface in 802.3z agreement. Meantime,using the designed debug softwareon the hostcomputer to debugtemperature lookup tableof theATMEGA88todetermine thespecificvaluesfor eachtemperature.Which completed the design of optical transceivers. Andthen test all parameters ofopticaltransceivers at lowtemperature,roomtemperature and hightemperature environment. Theresults is shownin Table 1.

Table 1the parameters ofopticaltransceiver test results

As it can be seen from thetable.Thelaser’s output opticalpower and extinction ratio are within therequiredparameterrange with small chan ges. When tested eyepattern under each temperature,we found the perfo rmance at low temperatures,room temperature, low temperatureare allgood.As the temperaturegoes high,itneedto provide greater modu lation current.So the signal’s undershoot is obvious as a slight eye line a ppearingin the"0 "signals inthe eye pattern. Butthe overall margin onthe template testare greater than 40%. Thus validated the feasibility andcorrectness of the design.

5Summary

Afterdiscussing theprogram, softwaredesign ,hardware designandsample’sdebuging and testing. Ultimately,we successfullyrealizedt hedesign of thesingle-chip design1.25GSFPSFP optical transceivers.Featuresof this program isto integrated the laser -driven with r eceiving andamplifing section,to use a common single-chipmicrocontroller to control programs.Both are able to reduce product costsand increase productivitytheoretically.Since this program is a newprogram, technologymaturityisto beimproved,system compatibility and market

potential problems areyet to betested.In addition to the amount,the costadvantage isalso reflected no great advantage. Butyou can still believe that with the acceleration of networkspeed and the cost pressureswhenoptical access,newtechnologies willbecome moreperfect and ma rket sharewill grow.At the appointedtime ,cost advantage will be reflecte d.

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? . , . ? , a , a . , . ( ). a ( ). A . A . , , . : A " " . : a " " , a " " . "" . a 's . a " " 's . " " . ( ). . : a "" 's ; a "" a ; a "" . a , . a . 's , . a , a . , . A . , a . , , . Europe's a , a . a , ., . "'s a ," , , . " 's . 2002 . a ." , (), Toyota's 's 1, . 2010, a . . 2 , . , 's , . . , a Delphi , a a . " , , , ," . " ." Delphi '99. : , . . , . . " ," . , , Germany. "'s ." "

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