1、科技論文題 目 microcontroller-based optical transceiver design 系 別 尚德光伏學(xué)院 專 業(yè) 微電子技術(shù) 班 級 微電0901 學(xué)生姓名 學(xué) 號 1指導(dǎo)教師 2012年 4 月microcontroller-based optical transceiver design1 introductionunder the impetus of the “three net combined”, fiber access programme such as ftth (fiber to the home) is widely used. under

2、the voice of the light for copper, the optical network is developing rapidly. optical transceiver plays a role of electro - optical, electro - optical conversion in optical communications, and is an essential device for optical communication. as it relates to high-speed circuit design, precision mac

3、hining and optical design, the cost of optical transceivers occupies an important part in fiber optical communication systems and while the high prices of optical transceivers become the bottleneck of restricting fiber access promotion. further reduce the cost of optical transceivers will benefit to

4、 promote the application of optical access and speed up the pace of light for copper. optical transceiver mainly consists of circuits, optical transmitter components and optical receiver components. and the part of the circuit which also includes laser driver, optical receiver signal amplifier and c

5、ontrol section. in current ,the circuit part of optical transceivers on the market is using three specific chip. the company has always been in the study of laser driver and receiving signal amplifier circuit integration in a device, with the controller using the common embedded processor solutions.

6、 due to only use a specific chip and a common chip, we can significantly low the cost of the circuit part. the phy1076 chip developed by phyworks company is such a chip. it is intended mainly for 1.25gbps to 2.5gbps optical transceiver with a simple external circuit, and it requires only an ordinary

7、 8-bit microcontroller to realize the control circuit. this paper studies the performance of the phy1076 which controled by the selected atmel company's atmega88 microcontroller, designed the optical transceiver samples, and conducted the performance test, with the ultimate success of the design

8、 of the 1.25g optical transceiver.2 discussion about the design and working principle of optical transceiverin the development process of optical transceiver, there are many different outline package. sfp (miniaturization hot-swappable optical transceiver module) is currently one of the most advance

9、d package in 5gbps rate, with a small, hot-swappable, low power consumption, high system integration and the ability to digitally diagnostics and so on.this design uses laser driver circuit and optical receiver amplifier circuit ntegrated phy1076 as a special chip , using atmel's avr atmega88 mi

10、crocontroller to control and implement ddm functionality, coupled with the corresponding tosa (transmitter optical components), rosa (receiver optical components) and structural parts to designe a sfp optical transceiver which can work in 1.25gbps 10km transmission distance. system block diagram sho

11、wn in figure 1:figure 1 the internal structure of fiber optic transceivers map1) transmitter works: serial data signal from the tx + / - side of the system input to the phy1706 laser drive section in the form of differential signal terminal. after amplificationd, drive circuit converted to different

12、ial modulation current signal loading to the tosa (transmitter optical components) to control the laser tosa to emit light pulses, and couple into the fiber to sent to the remote.2) receive part work principle : optical pulse signal inputs to the rosa (receiver optical components), and rosa converts

13、 optical pulse signal into the differential voltage signal output to the phy1076 the limiting amplifier section. after limiting amplified the signals ,it outputs differential voltage serial digital signals from the rx + / - side of phy1076.3) control and ddm parts: phy1076 is a mixed analog-digital

14、chip, its internal includes multiple analog-digital (a / d) and digital-analog converter (d / a) devices. parameters on the transmit and receive paths are converted into digital stored in the state register for monitoring through adc, and converts register value into analog for control by a dac. the

15、se registers can be read and set by an external controlle. ddm (digital diagnostic monitor) means that the fiber-optical transceivers is capable of monitoring parameters such as ransmitting power (tx_power), received power (rx_power), laser bias current (ibias), operating voltage (vcc) and the modul

16、e internal temperature (temperature ) in real-time and set alarm flag when the parameters exceed the setted-value. the adc integrated within phy1076 can monitor the transmit power, receive power and bias current. however the operating voltage and temperature sensing is required for another adc conve

17、rsion. the realization of all these alarms relays on external controller.atmega88 avr microcontroller from atmel corporation is an 8-bit microcontroller, with flash, ram, eeprom, internal clock and the adc integrated inside. without any external circuit to constitute a system ,and supporting on-line

18、 programming downloads and single-step debugging. system design and software debugging is very convenient. integrated hardware i2c module can directly provide the external i2c interface in line with sfp-msa specifications. and this is a single chip widely used in the field of home appliances and ind

19、ustrial control with large use, stable and reliable performance, low prices. the design uses the chip phy1076 to control the operating parameters and implement ddm functions.3 control and implementation of key parametersin optical fiber communication system, the average optical power of emitted ligh

20、t pulse and extinction ratio are two very important parameters. according to the different transmission distance, we need to set a different value. on one specific optical transceiver is hoped that the light emission power and the extinction ratio can be maintained within a certain range. to maintai

21、n a stable light power you need to use apc (automatic power control) circuit. at the same time, because of temperature characteristics and aging characteristics of the laser, the luminous efficiency will change, it is also the need for temperature compensation. the automatic control of extinction ra

22、t requires adjustment the size of modulation current according to temperature changes in real time. optical transceiver in the early, mainly uses a dedicated analog devices, so ia is difficultachieve the power of apc, temperature compensation and automatic extinction ratio control ,or it is difficul

23、t to obtain satisfactory results. phy1076 is a modular mixing device, using the analog part of its high-speed channel design, while its power control and modulation current is carried out by the register. so long as the external controller can monitor the temperature, you can adjust the register val

24、ues based on the temperature in order to automatically change the output power and modulation current, with the power and extinction ratio maintained at a certain range of purposes.1) control and achieve of the average optical power: phy1076 internal apc circuit is shown in figure 2. tosa is integra

25、ted with a laser diode and a photoelectric sensor diode. laser light power is proportional to and the current, and the laser's cathode connected with the phy1076s laser_bias pin. phy1076s data in internal power set register is input directly to the dac, then dac produces an analog voltage output

26、 to control output current in voltage-controlled current source.and the output current of current source supply the laser with dc bias current through the inductive coupling. therefore, to modify the value of the power setting register is to modify the lasers output optical power. the reverse leakag

27、e current of photoelectric sensor diode is proportional to the lasers emission power. the current accesses phy1076 from the mpd pin, after amplified and converted into a voltage signal,it is introduced into the control side of voltage-controlled current source as a negative feedback signal in order

28、to play the role of automatic power control. but the power range controled by apc is limited. when the temperature becomes larger, apc will not provide enough current to maintain power to be stable due to the reduce of lasers light-emitting efficient. at this moment we need to adjust the value of th

29、e power setting register to gain greater bias current to maintain power stable. this design is setting the value of register based on temperature by an external microcontroller to achieve temperature compensation purposes.figure 2 working principle of apc2) the realize of extinction ratio control: p

30、hy1076 internal modulation current control circuit is shown in figure 3. extinction ratio is defined as the ratio of optical power when sending data to 1 and optical power when sending data 0 in optical fiber communication system. its value will affect the bit error rate of communication systems,hen

31、ce we need to control within a certain range. in ac coupled circuits of modulated lasers, the average transmit power is affected by the dc bias current with the extinction ratio affected by modulation current. within the phy1076, when lasers modulation current is set by a special register, then outp

32、ut control voltage after digital-to-analog conversion so as to control the size of the output modulation current. therefore, set the value of the register properly can obtain the ideal extinction ratio. since there is no way to detect the size of the extinction ratio during working,we cannt introduc

33、e the feedback circuit to achieve the automatic extinction ratio control. it is more feasible to look for the statistical law in extinction ratio and temperature change, and conduct temperature compensation by an external controller accordance with law. figure 3 schematic modulation current control3

34、) atmega88 control algorithm analysis and ddm implementation: from the above analysis we can see that the key parameters of optical transceivers like the average power and extinction ratio relay on settings phy1076s internal register to control. while the phy1076 provides i2c interface for accessing

35、.we use atmega88 microcontroller to control in this design. atmega88 microcontroller hardware inside has a standard i2c interface to provide system equipment with external i2c required as sfp-msa (sfp multi source agreement). in order to communicate with the phy1076, the design using software to sim

36、ulate a i2c interface. mcus main tasks include providing temperature compensation function for the power control, providing extinction ratio automatic control function,setting parameters of enlarge and receiver part in phy1076,initializing the phy1076, providing ddm functionality and record product

37、information. atmege88 connected with the phy1076 as shown in figure 4.figure 4 atmega88 connection diagram with the phy1076 lasers luminous efficiency and threshold current is inversely proportional to the ambient temperature, that is, when the ambient temperature rises, the luminous efficiency will

38、 reduce with the threshold current will increase. in order to achieve the stability of the output optical power and extinction ratio, we must adjust the lasers bias current and modulation current according to temperature changes. the look-up table method is used to set the bias and modulation curren

39、t in the design. specifically, we establish two data tables-the modulation current power setting table and power setting table, each value corresponds to a temperature of the power setting register. as is shown in figure 4. ,modulation current set list is 80 bytes with one byte per two degrees, whil

40、e power setting table takes 40 bytes with one byte for every 4 degreess. both temperature range is -40 to 120 centigrade, which meets the requirements of industrial temperature . when an external temperature sensor added to the microcontroller, microcontroller converts voltage sent by the temperatur

41、e sensor into a temperature value through adc, then look up the temperature look-up table to find the corresponding data. sent the data to the power set register and modulation current setting register in phy1076 accordingly, adjust the lasers bias current and modulation current, which adjust the ou

42、tput optical power and extinction ratio. values of numerical data table are obtained from test. during the process of transceiver debugging, test the the samples each output of eye pattern under different temperature and modify the corresponding temperature data, so as to make the output optical eye

43、 pattern, optical power and extinction ratio of optical transceiver to meet the requirements. finally, save these data to a temperature lookup table and the internal eeprom in atmega88. in the real application environment, when repowers, the transceiver load the eeprom data into ram area, and then y

44、ou can stable the average output optical power and extinction ratio in the whole temperature range.4 analysis of results and test based on the above discussion of the design program, we select the phy1076 dedicated chip and atmega88 microcontroller, plus appropriate external circuit design circuit b

45、oards with the tosa, rosa welded together in custom enclosures to achieve a 1.25gbps sfp optical transceivers. debug internal registers in phy1076 in order to make parameters of optical transceivers meet requirements about 10km gigabit ethernet protocol optical interface in 802.3z agreement. meantim

46、e,using the designed debug software on the host computer to debug temperature lookup table of the atmega88 to determine the specific values for each temperature. which completed the design of optical transceivers. and then test all parameters of optical transceivers at low temperature, room temperat

47、ure and high temperature environment. the results is shown in table 1.table 1 the parameters of optical transceiver test resultsparametersunitsdesign requirementstest results-40ºc25ºc80ºcaverage transmitteddbm-9-3-6.54-6.10-6.01extinction ratiodb>912.7710.959.7emission eye socket80

48、2.3z-requirements-receiver sensitivitydbm<-23-28.2-29.6-29.4as it can be seen from the table. the lasers output optical power and extinction ratio are within the required parameter range with small changes. when tested eye pattern under each temperature,we found the performance at low temperature

49、s, room temperature, low temperature are all good. as the temperature goes high ,it need to provide greater modulation current. so the signals undershoot is obvious as a slight eye line appearing in the "0 " signals in the eye pattern. but the overall margin on the template test are greate

50、r than 40%. thus validated the feasibility and correctness of the design.5 summaryafter discussing the program, software design ,hardware design and samples debuging and testing. ultimately,we successfully realized the design of the single-chip design 1.25gsfp sfp optical transceivers. features of t

51、his program is to integrated the laser -driven with receiving and amplifing section, to use a common single-chip microcontroller to control programs. both are able to reduce product costs and increase productivity theoretically. since this program is a new program, technology maturity is to be impro

52、ved, system compatibility and market potential problems are yet to be tested. in addition to the amount, the cost advantage is also reflected no great advantage. but you can still believe that with the acceleration of network speed and the cost pressures when optical access, new technologies will be

53、come more perfect and market share will grow.at the appointed time ,cost advantage will be reflected.基于單片機(jī)控制的光收發(fā)器設(shè)計(jì)1 引 言在“三網(wǎng)合一”的推動(dòng)下，光纖到戶等光纖接入方案的應(yīng)用日益廣泛。在光進(jìn)銅退的呼聲下，光網(wǎng)絡(luò)迅速發(fā)展。光收發(fā)器在光通信中起到光電、電光轉(zhuǎn)換的作用，是光通信必不可少的器件。由于涉及到高速電路設(shè)計(jì)、精密機(jī)械加工和光學(xué)設(shè)計(jì)，光收發(fā)器的成本占據(jù)了光纖通信系統(tǒng)和的重要部分，而較高的光收發(fā)器價(jià)格成了制約光纖接入推廣的瓶頸。進(jìn)一步降低光收發(fā)器的成本將有利于光接入的應(yīng)用推廣，加

54、快光進(jìn)銅退的步伐。光收發(fā)器主要由電路部分、光發(fā)送組件和光接收組件組成。其中電路部分又包括激光驅(qū)動(dòng)、光接收信號放大和控制部分。目前市場上的光收發(fā)器的電路部分使用的是三個(gè)專用芯片。一直有公司在研究把激光驅(qū)動(dòng)和接收信號放大電路集成在一個(gè)器件上，控制器使用普通的嵌入式處理器的方案。由于只使用一個(gè)專用芯片和一個(gè)通用芯片，這樣就可以大幅降低電路部分的成本。phyworks公司研制的phy1076芯片就是一款這樣的芯片。它主要針對1.25gbps 到2.5gbps的光收發(fā)器，具有外圍電路簡單，控制電路只需要普通的8位單片機(jī)就可以實(shí)現(xiàn)的特點(diǎn)。本文主要研究了phy1076 的性能，選擇了atmel 公司的atm

55、ega88 單片機(jī)進(jìn)行控制，設(shè)計(jì)出光收發(fā)器樣品，并進(jìn)行了性能測試，最終成功設(shè)計(jì)了1.25g 光收發(fā)器。2 光收發(fā)器設(shè)計(jì)方案及工作原理討論光收發(fā)器在發(fā)展的過程中，有許多種不同的外形封裝。sfp（小型化可熱插拔光收發(fā)一體模塊）是目前在5gbps以下速率中最先進(jìn)的一種封裝形式，具有小型化、可熱插拔、功耗小、系統(tǒng)可集成度高以及能夠進(jìn)行數(shù)字診斷功能等特點(diǎn)。本設(shè)計(jì)中使用激光驅(qū)動(dòng)電路和光接收放大電路集成的phy1076 作為專用芯片，使用atmel 的avr 單片機(jī)atmega88 進(jìn)行控制和實(shí)現(xiàn)ddm 功能，加上相應(yīng)的tosa（光發(fā)射組件）,rosa（光接收組件）和結(jié)構(gòu)件，設(shè)計(jì)了一款工作在1.25gbps

56、 傳輸距離為10km 的sfp 光收發(fā)器。系統(tǒng)方框圖如圖1 所示：圖 1 光纖收發(fā)器的內(nèi)部結(jié)構(gòu)圖1) 發(fā)射部分工作原理：系統(tǒng)的串行數(shù)據(jù)信號從tx+/-端以差分信號形式輸入到phy1706 的激光器驅(qū)動(dòng)部分。驅(qū)動(dòng)電路進(jìn)行放大處理后，轉(zhuǎn)換成差分調(diào)制電流信號加載到tosa（光發(fā)射組件）上，控制tosa 中的激光器發(fā)出光脈沖，耦合入光纖發(fā)送到遠(yuǎn)端。2) 接收部分工作原理：光脈沖信號輸入到rosa（光接收組件），rosa 將光脈沖信號轉(zhuǎn)換成差分電壓信號輸出到phy1076 的限幅放大部分。該信號經(jīng)過限幅放大處理后，從phy1076 的rx+/-端輸出差分電壓串行數(shù)字信號。3) 控制及ddm 部分：phy

57、1076 是一款模擬數(shù)字混合芯片，其內(nèi)部包括多個(gè)模數(shù)(a/d)、數(shù)模轉(zhuǎn)換(d/a)器。發(fā)射和接收通路上的參數(shù)都是通過adc 轉(zhuǎn)換成數(shù)字量存入狀態(tài)寄存器進(jìn)行監(jiān)視，通過dac 把設(shè)置寄存器的值轉(zhuǎn)換成模擬量來進(jìn)行控制的。這些寄存器都可以由外部控制器進(jìn)行讀取和設(shè)置。ddm(digital diagnostic monitor)，數(shù)字診斷和監(jiān)控是指的光纖收發(fā)器能夠?qū)Πl(fā)射功率（tx_power），接收功率（rx_power），激光器偏置電流（ibias），工作電壓（vcc），模塊內(nèi)部溫度（temperature）這些參數(shù)進(jìn)行實(shí)時(shí)監(jiān)視，并能夠在各項(xiàng)參數(shù)超過設(shè)定值時(shí)設(shè)置報(bào)警標(biāo)志位的功能。phy1076 內(nèi)部集

58、成的adc 能夠?qū)Πl(fā)射功率、接收功率和偏置電流進(jìn)行監(jiān)測。工作電壓和溫度傳感則需要另外adc 進(jìn)行轉(zhuǎn)換。而所有這些報(bào)警的實(shí)現(xiàn)則需要外部控制器來實(shí)現(xiàn)。atmel 公司的avr 單片機(jī)atmega88 是一款8 位單片機(jī)，內(nèi)部集成flash、ram、eeprom、內(nèi)部時(shí)鐘和adc。無需任何外圍電路即可構(gòu)成系統(tǒng)，支持在線編程下載和單步調(diào)試。系統(tǒng)設(shè)計(jì)和軟件調(diào)試都很方便。集成硬件i2c模塊，可直接對外提供符合sfp-msa 規(guī)范要求的外部i2c接口。而且此單片機(jī)是一款在家電和工業(yè)控制領(lǐng)域使用廣泛的芯片，用量大，性能穩(wěn)定可靠，價(jià)格低。本設(shè)計(jì)選用此芯片控制phy1076 的工作參數(shù)和實(shí)現(xiàn)ddm 功能。3 關(guān)鍵參數(shù)控制和實(shí)現(xiàn)在光纖通信系統(tǒng)中，發(fā)射光脈沖的平均光功率和消光比是兩個(gè)非常重要的參數(shù)。根據(jù)傳輸距離不同，需要設(shè)定不同的值。對具體某一個(gè)光收發(fā)器則希望其發(fā)光功率和消光比能夠長期維持在一定范圍內(nèi)。要維持穩(wěn)定的光功率則需要使用apc(自動(dòng)功率控制)電路。又由于激光器的溫度特性和老化特性，其發(fā)光效率會(huì)變化，所以又需要進(jìn)行溫度補(bǔ)償。消光比的自動(dòng)控制則需要根據(jù)溫度變化而實(shí)時(shí)的調(diào)整調(diào)制電流的大小。早期的光收發(fā)器中，大都使用專用模擬器件，所以要實(shí)現(xiàn)功率apc、溫度補(bǔ)償和消光比自動(dòng)控制都非常困難，或者很難得到滿意的效果。phy1076 是一個(gè)模數(shù)混合器件，其高速通道部分使用模擬設(shè)