科技论文-Microcontroller-Based Optical Transceiver Design.doc

科技论文题 目 microcontroller-based optical transceiver design 系 别 尚德光伏学院 专 业 微电子技术 班 级 微电0901 学生姓名 学 号 1指导教师 2012年 4 月17无锡科技职业学院科技论文titlemicrocontroller-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 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 machining 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 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 control 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. 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 8-bit microcontroller to realize the control circuit. this paper studies the performance of the phy1076 which controled by the selected atmel companys atmega88 microcontroller, designed the optical transceiver samples, and conducted the performance test, with the ultimate success of the design 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 advanced 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 atmels avr atmega88 microcontroller 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 shown 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 differential 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 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 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. these 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 module 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 conversion. 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 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 industrial 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 light 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 maintain 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 rat 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 difficult 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 values 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 integrated with a laser diode and a photoelectric sensor diode. laser light power is proportional to and the current, and the lasers 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 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 leakage 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 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 the 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: phy1076 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,hence 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 output 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 introduce 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) 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.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 simulate 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 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 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 current 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, while 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 temperature 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 output 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 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 you 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 boards 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. meantime,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 temperature and high temperature environment. the results is shown in table 1.table 1 the parameters of optical transceiver test resultsparametersunitsdesign requirementstest results-40c25c80caverage transmitteddbm-9-3-6.54-6.10-6.01extinction ratiodb912.7710.959.7emission eye socket802.3z-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 temperatures, 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 greater 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 this 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 improved, 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 become more perfect and market share will grow.at the appointed time ,cost advantage will be reflected.无锡科技职业学院科技论文标题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