2.5Gb/s突发模式光接收机设计
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摘要
无源光网络(PON)是当前最热门的高速接入网技术,采用点对多点拓扑结构。上行传输运用时分多址接入技术(TDMA),多个用户共享一个光线路终端(OLT),OLT接收的是幅度和相位变化很大的突发信号。在光纤骨干网中,光突发交换(OBS)作为实现光分组交换(OPS)的前身,极具实用价值和发展前景。在PON和OBS中,都需要高速处理突发信号,突发模式光接收机(BMR)作为其关键技术,一直是研究的热点。
本文针对传输速率为2.5Gb/s的突发信号进行突发模式光接收机的研究。对比各种突发模式光接收机技术的优劣,采用目前流行的前馈直流耦合方案。完成BMR的各部分关键电路设计和仿真,包括PIN光电二极管电路模型,前置跨阻抗放大器(TIA),自动增益控制电路(AGC),自动判决电平产生电路(ATC),延时电路,限幅放大器和复位信号产生电路。最后得到完整的突发模式光接收机电路。
论文特点:在跨阻抗放大器中加入AGC,扩展动态范围。采用迟滞比较器设计AGC,避开一般自动增益电路中使用的RC结构,在2.5Gb/s速率下能在一个比特时间内实现增益的调节,复位也只需要一个比特时间,实现及时响应,提高信道利用率。TIA通过自动增益电路的调节,其跨阻增益根据输入突发信号的幅值大小实现7dB的调节。采用自适应检波获得判决电平,检波电路包括峰值探测电路和底部探测电路,分别探测突发信号的顶部和底部电平,通过电阻分压器得到突发信号的中间电平,有效取消了直流偏移电压,提高限幅放大器输出信号质量。复位信号产生电路探测突发信号的包络,利用逻辑电路自动产生复位信号,不需要外围辅助放电电路,使BMR更具适应性和升级性。延时电路使得复位信号在BMR接收完每一个突发包信号后及时对AGC和ATC复位至稳态,有效缩短保护带时间。另外,利用复位信号电路得到的包络信号,通过与门对限幅放大器的输出信号进行关断,消除保护带内噪声。
在传输速率为2.5Gb/s,对突发模式光接收机进行仿真验证。其性能指标为:灵敏度-24.7dBm,动态范围25.1dB,前导码时间15ns,保护带时间30ns。
Nowadays passive optical network(PON) is the most popular high-speed access network technology, it adopts point-to-multipoint topology structure. The upstream transmission of PON uses Time-Division-Multiple-Access(TDMA) protocol, multiple subscribers share the same optical line termination(OLT). The OLT receives burst-signals whose power and phase vary significantly. In fiber-optic backbone network, optical burst switching(OBS) as the former of optical packet switching(OPS) has highly practical value and development prospects. Both PON and OBS systems should quickly process burst-signal. Burst mode receiver(BMR) as the key technology of PON and OBS was being researching hotly.
Focuse on researching BMR for burst-signal at rate of 2.5Gb/s. The advantages and shortcomings of existing schemes of BMR are summed up and the popular feed-forward DC-coupled topology is selected. All circuits of BMR are designed and simulated that they are: circuit model of PIN photodiode, pre-trans-impedance amplifier(TIA), automatic gain control circuit (AGC), automatic threshold control circuit (ATC), time-delay circuit, limiting amplifier and reset signal circuit. Then get the whole circuit of BMR.
Creative points of this paper: Add AGC into TIA to extend dynamic range. AGC is designed by using of a hysteresis comparator so avoiding using RC circuit which is always in regular AGC. AGC responds instantaneously because setting and resetting it just take one bit time at rate of 2.5Gb/s so that this technology improves the channel utilization. TIA has 7dB adjustment for different burst-signal according to their amplitude with the help of AGC. Automatic threshold voltage is obtained by adaptive detector circuit including peak detector and bottom detector which detect the peak and bottom level of burst-signal, then by the use of a resistive divider getting the middle level of the burst-signal so that ATC cancels the DC offset voltage effectively and improves signal quality of limiting amplifier. Reset signal circuit detecting burst-signal envelope and get reset signal by the use of logic circuit. Internal reset signal circuit make a free of external reset circuit, enhancing receiver’s flexibility and scalability. Time-delay circuit makes the best respond of BMR that after each burst-signal ending the reset signal just begins to reset AGC and ATC to steady state, reducing guard time. In addition, use envelope signal getting from reset circuit separate two burst packets through a AND gate to reduce noise during guard time.
Simulate the whole BMR at rate of 2.5Gb/s, the performance of designed BMR is greatly improved. Sensitivity is -24.7dBm , Dynamic range is 25.1dB, preamble time is 15ns, guard time is 30ns.
本文针对传输速率为2.5Gb/s的突发信号进行突发模式光接收机的研究。对比各种突发模式光接收机技术的优劣,采用目前流行的前馈直流耦合方案。完成BMR的各部分关键电路设计和仿真,包括PIN光电二极管电路模型,前置跨阻抗放大器(TIA),自动增益控制电路(AGC),自动判决电平产生电路(ATC),延时电路,限幅放大器和复位信号产生电路。最后得到完整的突发模式光接收机电路。
论文特点:在跨阻抗放大器中加入AGC,扩展动态范围。采用迟滞比较器设计AGC,避开一般自动增益电路中使用的RC结构,在2.5Gb/s速率下能在一个比特时间内实现增益的调节,复位也只需要一个比特时间,实现及时响应,提高信道利用率。TIA通过自动增益电路的调节,其跨阻增益根据输入突发信号的幅值大小实现7dB的调节。采用自适应检波获得判决电平,检波电路包括峰值探测电路和底部探测电路,分别探测突发信号的顶部和底部电平,通过电阻分压器得到突发信号的中间电平,有效取消了直流偏移电压,提高限幅放大器输出信号质量。复位信号产生电路探测突发信号的包络,利用逻辑电路自动产生复位信号,不需要外围辅助放电电路,使BMR更具适应性和升级性。延时电路使得复位信号在BMR接收完每一个突发包信号后及时对AGC和ATC复位至稳态,有效缩短保护带时间。另外,利用复位信号电路得到的包络信号,通过与门对限幅放大器的输出信号进行关断,消除保护带内噪声。
在传输速率为2.5Gb/s,对突发模式光接收机进行仿真验证。其性能指标为:灵敏度-24.7dBm,动态范围25.1dB,前导码时间15ns,保护带时间30ns。
Nowadays passive optical network(PON) is the most popular high-speed access network technology, it adopts point-to-multipoint topology structure. The upstream transmission of PON uses Time-Division-Multiple-Access(TDMA) protocol, multiple subscribers share the same optical line termination(OLT). The OLT receives burst-signals whose power and phase vary significantly. In fiber-optic backbone network, optical burst switching(OBS) as the former of optical packet switching(OPS) has highly practical value and development prospects. Both PON and OBS systems should quickly process burst-signal. Burst mode receiver(BMR) as the key technology of PON and OBS was being researching hotly.
Focuse on researching BMR for burst-signal at rate of 2.5Gb/s. The advantages and shortcomings of existing schemes of BMR are summed up and the popular feed-forward DC-coupled topology is selected. All circuits of BMR are designed and simulated that they are: circuit model of PIN photodiode, pre-trans-impedance amplifier(TIA), automatic gain control circuit (AGC), automatic threshold control circuit (ATC), time-delay circuit, limiting amplifier and reset signal circuit. Then get the whole circuit of BMR.
Creative points of this paper: Add AGC into TIA to extend dynamic range. AGC is designed by using of a hysteresis comparator so avoiding using RC circuit which is always in regular AGC. AGC responds instantaneously because setting and resetting it just take one bit time at rate of 2.5Gb/s so that this technology improves the channel utilization. TIA has 7dB adjustment for different burst-signal according to their amplitude with the help of AGC. Automatic threshold voltage is obtained by adaptive detector circuit including peak detector and bottom detector which detect the peak and bottom level of burst-signal, then by the use of a resistive divider getting the middle level of the burst-signal so that ATC cancels the DC offset voltage effectively and improves signal quality of limiting amplifier. Reset signal circuit detecting burst-signal envelope and get reset signal by the use of logic circuit. Internal reset signal circuit make a free of external reset circuit, enhancing receiver’s flexibility and scalability. Time-delay circuit makes the best respond of BMR that after each burst-signal ending the reset signal just begins to reset AGC and ATC to steady state, reducing guard time. In addition, use envelope signal getting from reset circuit separate two burst packets through a AND gate to reduce noise during guard time.
Simulate the whole BMR at rate of 2.5Gb/s, the performance of designed BMR is greatly improved. Sensitivity is -24.7dBm , Dynamic range is 25.1dB, preamble time is 15ns, guard time is 30ns.
引文
[1] S. Devadhar and K. Ryan. Dynamic bandwidth allocation over passive optical networks. Lightwave, Vol. 17. 2000, 138-142
[2] P. E. Green. Fiber to the home: the next big broadband thing. IEEE Commun. Mag., Vol. 42. 2004, 100-106
[3]邱昆邱琪.光纤通信系统.电子科技大学出版社,2005. 112-114
[4] M. Ross. Space Optical Communications with the ND: YAG Laser. Proceedings of the IEEE, March 1978, Vol. 66, 327-338
[5] J. C. Livas et al. Gbps-Class Optical Communications Systems for Free-Space Applications. In Free-Space Laser Communication Technologies. 1993
[6] J. Cao, et al. OC-192 Receiver in Standard 0.18um CMOS. ISSCC Dig of Tech Paper. 2002, 187-188
[7] A. X. Widmer and P. A. Franaszek. A DC-Blanced, Partitioned-Block, 8B/10B Transmission Code. J. Res. And Develop. 1983, 440-451
[8] F. Herzl and B. Razavi. A study of oscillator jitter due to supply and substrate noise. IEEE Trans Circuits and system, Vol. 46. 1999, 56-62
[9] B. Lung. PON architecture future proofs FTTH. Lightwave, vol.16, no.10. 1999, 104-107
[10] G.. Pesavento and M. Kelsey. PONs for the broadband local loop. Light-waue, Vol. 16 1999, 68-74
[11] S. Hardy. Verizon staffers find fiber-to-the-home cheaper than copper. Lightwave, Vol. 17, no. 134, 2000
[12] M. Listanti and R. Sabella. Optical Networking Solutions for Next-Generation Internet Networks. IEEE Commun. Mag, Vol. 9, 79-122
[13] M. Hossain A. C. Carusone. 5-10Gb/s 70 mW Burst Mode AC Coupled Receiver in 90-nm CMOS. IEEE. JSSC. 2009,524-537
[14] B. C. Thomsen. 10Gb/s AC-Coupled Digital Burst-Mode Optical Receiver. OFC/NFOEC. 2007, 1-3
[15] S. Han. M. S. Lee. Burst-Mode penalty of AC-copled optical receivers optimized for 8B/10B Line Code. IEEE, Photonics Tech Letter, Vol. 16, no.7. 2004, 1724-1726
[16] R. G. Swartz and Y. Ota. A DC-500Mb/s burst mode preamplifier for optical data links. IEEE 1990 Bipolar Circuit and Technology Meeting. 240-243
[17]朱灿.高速光突发模式传输关键技术研究:[硕士学位论文].成都:电子科技大学,2006
[18] G. T. kanellos and D. Petrantonkis. All-Optical 3R burst-mode reception at 40Gb/s using for integrated MZI switches. Lightwave Tech, Vol. 25, no.1, 2007, 184-192
[19] K. Nishimura and H. Kimura. A 1.25-Gb/s CMOS burst-mode optical transceiver for Ethernet PON system. IEEE, JSSC, Vol. 40, no. 4, 2005, 1027-1034
[20] P. Ossieur and D. Verhulst. A 1.25-Gb/s burst-mode receiver for GON applications. IEEE, JSSC. Vol. 40, no. 5, 2005, 1180-1189
[21] Z. Belfqih and G. Girault. 10Gb/s TDM passive optical network in burst mode configuration using a continuous block receiver. OFC/NFOEC, 2008, 1-3
[22] P. Ossieru and T. D. Ridder. A 10Gb/s burst-mode receiver with automatic reset generation and burst detection for extended reach PONs. OSA/OFC/NFOED. 2009, 1-3
[23] Q. Le and S. G. Lee. A burst-mode receiver for 1.25-Gb/s Ethernet PON with AGC and internally created reset signal. IEEE, JSSC. Vol.39, no. 12, 2004, 2379-2388
[24] J. M. Delgado Mendinueta and P. Bayvel. Impact of burst header length in the performance of a 10Gb/s digital burst-mode receiver. OSA/OFC/NFOEC. 2009, 1-3
[25] D. Lian and S. Liter. A 1.8V, 2.5Gbps burst mode optical receiver with feedforward created reset for EPON system. ISIC, 2007, 69-72
[26] T. Nakanishi and Y.Fukada. Wide dynamic range and high sensitivity APD burst receiver configuration based on M-Switching technique for 10 GEPON system. LEOS, 2007, 876-877
[27] W. Z. Chen and R.M Gan. A single-chip 2.5-Gb/s CMOS burst-mode optical receiver. IEEE Transactions on circuits and systems. Vol.56, no.10, 2009, 2325-2331
[28] M. Nakamura and N. Ishihara. A 156-Mb/s CMOS Optical Receiver for Burst-mode Transmission. IEEE, JSSC. Vol.33, no.8, 1998, 1179-1187
[29] M. Nakamura and Yuki Imai. 1.25GHz Burst-Mode Receiver ICs With Quick Response for PON Systems. IEEE, JSSC. Vol. 40, no.12, 2005, 2680-2688
[30] M. Nakamara and N. Ishihara. An Instantaneous Response CMOS Optical Receiver IC with Wide Dynamic Range and Extremely High Sensitivity Using Feed-Forward Auto-Bias Adjustment. IEEE, JSSC. Vol. 30, no.9, 1995, 991-997
[31] T. Ajmal and R. Razavi. Design of a 10Gbps Optical Burst Mode DPSK Receiver for Data and Clock Recovery. ECOC, 2008, 1-2
[32] S. Kang and S. Hwang. Low-power CMOS Limiting Amplifier for Burst mode Receiver in ATM-PON system. Microwave and Millmeter Wave Tech Proceedings. 2002, 997-1000
[33] E. Sacknger and W. Guggenbuhl. A High-Swing, High-Impedance NMOS Cascode Circuit. IEEE, JSSC. Vol. 25, no.1, 1990, 289-298
[34] S. M. Park and J. Lee. 1-Gb/s 80-dBΩfully differential CMOS transimpedance amplifier in multichip on oxide technology for optical interconnects. IEEE, JSSC. Vol. 39, no.6, 2004, 971-974
[35] S. M. Park and H. J. Yoo. 1.25-Gb/s regulated cascade CMOS transimpedance amplifier for Gigabit Ethernet application. IEEE, JSSC. Vol. 39, no.1, 2004, 112-121
[36] S. Yamashita. Novel packet-AGC technique for burst-mode CMOS preamplifer with wide dynamic range and high sensitivity for ATM-PON system. IEEE, JSSC. Vol.37, 2002, 182-185
[37] K. Tanaka and N. edagawa. Experimental study on 10Gb/s E-PON system using XENPAK-based burst-mode transceivers. Proc.ECOC, 2005, 139-140
[38] K. Schneider and H. Zimmermann. Three-stage burst-mode transimpedance amplifier in deep-sub-um CMOS technology. IEEE Trans.Circuits Syst. Vol. 53, no.7, 2006, 1458-1467
[39] L. Lunardi and S. Chandrasekhar. A high speed burst mode optoelectronic integrated circuit photoreceiver using Inp/InGaAs HBT’s. IEEE, Photonics Technology Letter. Vol. 6, no.7, 1994, 817-818
[40] T. Bakker and Kun-Yii Tu. Decision Threshold Based on Dynamic Offset Compensation for Burst Mode Receiver. Proc.27th Eur. Conf. 222-223
[41] S. Takahashi and K. Shiba. Over 25-dB Dynamic Range 10-/1-Gbps Optical Burst-mode Receiver using High-power-tolerant APD. OSA/OFC/NFOEC, 2009, 1-3
[42] J. Nakagawa. Key technologies of GE-PON burst-mode receivers and future PON systems. OFC/NFOEC, 2007, 1-3
[43] H. Tagami and S. Kozaki. A burst-mode bit-synchronization IC with large tolerance for pulse-width distortion for gigabit Ethernet PON. IEEE, JSSC. Vol. 41 2006, 2555-2565
[44] W. Z. Chen A 1.8-V 10-Gb/s fully Integrated CMOS Optical Receiver Analog Front-END. IEEE, JSSC. Vol .40, no. 6, 2005, 1388-1396
[45] J. Nakagawa and M. Nogami. 10.3-Gb/s Burst-Mode 3R Receiver Incorporating Full AGC Optical Receiver and 82.5-GS/s Over-Sampling CDR for 10G-EPON System. IEEE, Photonics Technology Letter. Vol. 22, no.7, 2010, 471-473
[2] P. E. Green. Fiber to the home: the next big broadband thing. IEEE Commun. Mag., Vol. 42. 2004, 100-106
[3]邱昆邱琪.光纤通信系统.电子科技大学出版社,2005. 112-114
[4] M. Ross. Space Optical Communications with the ND: YAG Laser. Proceedings of the IEEE, March 1978, Vol. 66, 327-338
[5] J. C. Livas et al. Gbps-Class Optical Communications Systems for Free-Space Applications. In Free-Space Laser Communication Technologies. 1993
[6] J. Cao, et al. OC-192 Receiver in Standard 0.18um CMOS. ISSCC Dig of Tech Paper. 2002, 187-188
[7] A. X. Widmer and P. A. Franaszek. A DC-Blanced, Partitioned-Block, 8B/10B Transmission Code. J. Res. And Develop. 1983, 440-451
[8] F. Herzl and B. Razavi. A study of oscillator jitter due to supply and substrate noise. IEEE Trans Circuits and system, Vol. 46. 1999, 56-62
[9] B. Lung. PON architecture future proofs FTTH. Lightwave, vol.16, no.10. 1999, 104-107
[10] G.. Pesavento and M. Kelsey. PONs for the broadband local loop. Light-waue, Vol. 16 1999, 68-74
[11] S. Hardy. Verizon staffers find fiber-to-the-home cheaper than copper. Lightwave, Vol. 17, no. 134, 2000
[12] M. Listanti and R. Sabella. Optical Networking Solutions for Next-Generation Internet Networks. IEEE Commun. Mag, Vol. 9, 79-122
[13] M. Hossain A. C. Carusone. 5-10Gb/s 70 mW Burst Mode AC Coupled Receiver in 90-nm CMOS. IEEE. JSSC. 2009,524-537
[14] B. C. Thomsen. 10Gb/s AC-Coupled Digital Burst-Mode Optical Receiver. OFC/NFOEC. 2007, 1-3
[15] S. Han. M. S. Lee. Burst-Mode penalty of AC-copled optical receivers optimized for 8B/10B Line Code. IEEE, Photonics Tech Letter, Vol. 16, no.7. 2004, 1724-1726
[16] R. G. Swartz and Y. Ota. A DC-500Mb/s burst mode preamplifier for optical data links. IEEE 1990 Bipolar Circuit and Technology Meeting. 240-243
[17]朱灿.高速光突发模式传输关键技术研究:[硕士学位论文].成都:电子科技大学,2006
[18] G. T. kanellos and D. Petrantonkis. All-Optical 3R burst-mode reception at 40Gb/s using for integrated MZI switches. Lightwave Tech, Vol. 25, no.1, 2007, 184-192
[19] K. Nishimura and H. Kimura. A 1.25-Gb/s CMOS burst-mode optical transceiver for Ethernet PON system. IEEE, JSSC, Vol. 40, no. 4, 2005, 1027-1034
[20] P. Ossieur and D. Verhulst. A 1.25-Gb/s burst-mode receiver for GON applications. IEEE, JSSC. Vol. 40, no. 5, 2005, 1180-1189
[21] Z. Belfqih and G. Girault. 10Gb/s TDM passive optical network in burst mode configuration using a continuous block receiver. OFC/NFOEC, 2008, 1-3
[22] P. Ossieru and T. D. Ridder. A 10Gb/s burst-mode receiver with automatic reset generation and burst detection for extended reach PONs. OSA/OFC/NFOED. 2009, 1-3
[23] Q. Le and S. G. Lee. A burst-mode receiver for 1.25-Gb/s Ethernet PON with AGC and internally created reset signal. IEEE, JSSC. Vol.39, no. 12, 2004, 2379-2388
[24] J. M. Delgado Mendinueta and P. Bayvel. Impact of burst header length in the performance of a 10Gb/s digital burst-mode receiver. OSA/OFC/NFOEC. 2009, 1-3
[25] D. Lian and S. Liter. A 1.8V, 2.5Gbps burst mode optical receiver with feedforward created reset for EPON system. ISIC, 2007, 69-72
[26] T. Nakanishi and Y.Fukada. Wide dynamic range and high sensitivity APD burst receiver configuration based on M-Switching technique for 10 GEPON system. LEOS, 2007, 876-877
[27] W. Z. Chen and R.M Gan. A single-chip 2.5-Gb/s CMOS burst-mode optical receiver. IEEE Transactions on circuits and systems. Vol.56, no.10, 2009, 2325-2331
[28] M. Nakamura and N. Ishihara. A 156-Mb/s CMOS Optical Receiver for Burst-mode Transmission. IEEE, JSSC. Vol.33, no.8, 1998, 1179-1187
[29] M. Nakamura and Yuki Imai. 1.25GHz Burst-Mode Receiver ICs With Quick Response for PON Systems. IEEE, JSSC. Vol. 40, no.12, 2005, 2680-2688
[30] M. Nakamara and N. Ishihara. An Instantaneous Response CMOS Optical Receiver IC with Wide Dynamic Range and Extremely High Sensitivity Using Feed-Forward Auto-Bias Adjustment. IEEE, JSSC. Vol. 30, no.9, 1995, 991-997
[31] T. Ajmal and R. Razavi. Design of a 10Gbps Optical Burst Mode DPSK Receiver for Data and Clock Recovery. ECOC, 2008, 1-2
[32] S. Kang and S. Hwang. Low-power CMOS Limiting Amplifier for Burst mode Receiver in ATM-PON system. Microwave and Millmeter Wave Tech Proceedings. 2002, 997-1000
[33] E. Sacknger and W. Guggenbuhl. A High-Swing, High-Impedance NMOS Cascode Circuit. IEEE, JSSC. Vol. 25, no.1, 1990, 289-298
[34] S. M. Park and J. Lee. 1-Gb/s 80-dBΩfully differential CMOS transimpedance amplifier in multichip on oxide technology for optical interconnects. IEEE, JSSC. Vol. 39, no.6, 2004, 971-974
[35] S. M. Park and H. J. Yoo. 1.25-Gb/s regulated cascade CMOS transimpedance amplifier for Gigabit Ethernet application. IEEE, JSSC. Vol. 39, no.1, 2004, 112-121
[36] S. Yamashita. Novel packet-AGC technique for burst-mode CMOS preamplifer with wide dynamic range and high sensitivity for ATM-PON system. IEEE, JSSC. Vol.37, 2002, 182-185
[37] K. Tanaka and N. edagawa. Experimental study on 10Gb/s E-PON system using XENPAK-based burst-mode transceivers. Proc.ECOC, 2005, 139-140
[38] K. Schneider and H. Zimmermann. Three-stage burst-mode transimpedance amplifier in deep-sub-um CMOS technology. IEEE Trans.Circuits Syst. Vol. 53, no.7, 2006, 1458-1467
[39] L. Lunardi and S. Chandrasekhar. A high speed burst mode optoelectronic integrated circuit photoreceiver using Inp/InGaAs HBT’s. IEEE, Photonics Technology Letter. Vol. 6, no.7, 1994, 817-818
[40] T. Bakker and Kun-Yii Tu. Decision Threshold Based on Dynamic Offset Compensation for Burst Mode Receiver. Proc.27th Eur. Conf. 222-223
[41] S. Takahashi and K. Shiba. Over 25-dB Dynamic Range 10-/1-Gbps Optical Burst-mode Receiver using High-power-tolerant APD. OSA/OFC/NFOEC, 2009, 1-3
[42] J. Nakagawa. Key technologies of GE-PON burst-mode receivers and future PON systems. OFC/NFOEC, 2007, 1-3
[43] H. Tagami and S. Kozaki. A burst-mode bit-synchronization IC with large tolerance for pulse-width distortion for gigabit Ethernet PON. IEEE, JSSC. Vol. 41 2006, 2555-2565
[44] W. Z. Chen A 1.8-V 10-Gb/s fully Integrated CMOS Optical Receiver Analog Front-END. IEEE, JSSC. Vol .40, no. 6, 2005, 1388-1396
[45] J. Nakagawa and M. Nogami. 10.3-Gb/s Burst-Mode 3R Receiver Incorporating Full AGC Optical Receiver and 82.5-GS/s Over-Sampling CDR for 10G-EPON System. IEEE, Photonics Technology Letter. Vol. 22, no.7, 2010, 471-473