一個２.５Gb/s可控制雷射光亮暗功率比之雷射二極體光驅動電路

Abstract

摘要

由於在光通訊系統對資料頻寬的需求量與日俱增，所以發展出了乙太被動光纖網路這種全新的技術去解決未來對於資料傳輸能力的需求。乙太被動光纖網路單元除了可以提供Gbps的資料速度去符合多媒體的傳輸外，它也改良了以往光纖通訊點對點的資料傳送方式，而改採點對多點的傳送方式來避免光纖使用上的浪費。而此篇論文的脈衝式雷射二極體驅動電路則是應用在乙太被動光纖網路的傳送端部份。 在這一篇論文中,我們提出一可以控制雷射光亮暗功率比的脈衝式雷射二極體驅動電路，它改善了以往單迴路功率控制的缺點，而改採一雙迴路功率控制的機制來實現脈衝式雷射二極體驅動電路，藉由此一功率控制的方法，雷射二極體輸出代表資訊一和代表資訊零的發光功率比在溫度變化後可以被精確控制，除了此為一新架構外，在電路的實現中，為了可以使功率控制可以能夠有快速鎖定的效果，我們引入了雙頻帶的切換動作，目的是可以使功率控制在寬頻帶可以有快速鎖定的效果，而在窄頻帶可以有高準確度的效應，最後，至於在光量測上由於電流驅動雷射二極體的開啟和關閉的驅動能力不同，因此在光量測上可能造成輸出的眼圖不對稱的效應，為了解決此一問題，我們在前置放大器中引入了前置失真的技巧來消除光量測上眼圖不對稱的問題。 在論文中我們所實現的雷射二極體驅動電路以著tsmc018的製程來完成設計，預計資料速度為2.5Gb/s，可驅動的調變電流和偏壓電流約為70亳安培。至於電路的細節部份我一一描述如下。

Abstract

With the increasing demands at data bandwidth in optical system, a novel Ethernet optical network (EPON) was developed to overcome the demands for data transmission ability. The Ethernet optical network (EPON) can offer Gbps data rate to correspond to multi-media communication. Besides, it was adopted point to multipoint optical network structure to avoid a large of optical fiber’s use in point to point optical network structure as presented before. In Thesis a burst-mode laser driver is applied in the Ethernet optical network (EPON) as transmitter. In thesis, we presented a burst-mode laser driver with automatic extinction ratio control. It improved single-loop-automatic power control method’s drawbacks, and used a novel dual-loop-automatic-power control method to realize the burst-mode laser driver. With the novel control method, laser diode’s optical power ratio for representing data 1 and data 0 can be controlled exactly in different temperature. Besides a novel structure, in circuit design, in order to have a fast power locking speed we included a dual-band switch. The aim is to utilize that wide band case has fast power locking speed, and narrow band case has high exact ER control ability. Finally, as for optical testing aspect, laser’s current driving ability is different for turning on and turning off case, and then it might cause optical eye diagram to be dissymmetrical. So, for canceling this problem, we also included a pre-distortion skill to get a symmetrical eye diagram in pre-driver stage. This work was fabricated in 0.18um CMOS process, and delivers a 1mA to 70mA modulation current as well as 1mA to 70mA bias current. As for circuit design detail, I describe it as below.