適用於OC-192之10Gb/s矽鍺發射器電路

Abstract

光纖具備低耗損及寬頻之優點, 長久以來在高速和長程傳輸之網路骨幹扮演著重要角色. 今日，同步光纖網路（SONET）OC-192 之傳輸速率可達10Gbps，其下世代 （OC-768） 之傳輸速率更可高達 40 Gbps, 預計將可充分支援多媒體網際網路之頻寬需求. 然而, 如何實現低成本之光通信收發機積體電路與減低佈線成本, 向為高速光纖網路能否普及之主要關鍵. 本論文之主要目標在於開發適用於 10 Gbps 光通信發射機之串列式資料發射器和雷射二極體驅動電路, 所有電路將以 0.35 μm 矽鍺製程實現, 以期降低成本, 同時便於未來之數位系統整合。在光通信收發機之傳送端，原始資料經由編碼後, 將透過多工器將低速之並列信號轉成一高速串列信號，其藉由一時脈倍頻器電路產生多種頻率及相位輸出, 以對平行信號進行序列式傳送。而多工器之輸出電壓信號將藉由雷射二極體驅動電路轉換為大電流, 用以驅動雷射二極體, 進而完成發射端之電/光轉換. 串列式資料發射器主要包含一個9.9533GHz的時脈倍頻器電路及一個可將十六筆622.08Mb/s的平行式資料轉成一筆9.9533Gb/s串列式資料的多工器. 為考慮晶片測試的方便性，本電路內建一組十六路平行化之隨機碼產生器，以驗證發射機電路之效能。時脈倍頻器電路主要為一鎖相迴路式頻率合成器，其經由一622.08MHz參考信號合成一9.9533GHz之輸出信號, 藉此作為多工器資料取樣之參考信號源。多工器電路採用4級二對一多工器單元組成樹狀架構, 藉由時脈倍頻器提供的選擇信號, 可將十六筆622.08Mb/s的並列式信號轉成一筆9.9533Gb/s之串列式信號. 多工器之輸出結果將再經由一個取樣電路將信號重新取樣，以減低層級串接之雜訊累增效應。本電路操作電壓為3.3 V，總功率消耗為594.66毫瓦。 雷射二極體驅動電路將依據串列式資料發射器的輸出電壓轉換成電流信號，用以驅動雷射二極體, 雷射二極體的偏壓電流範圍為1~60mA，調變電流為40~100mA . 為提高輸出驅動能力及操作速度, 本電路包含兩級推挽式前置放大器及一大電流輸出級. 前置放大器的輸出振幅可依操作速度及輸出電流而作動態調整. 此外，輸出級並使用負電容米勒補償技巧來增加訊號頻寬. 為達電流穩定輸出之目的, 調變電流及偏壓電流均由一個能隙參考電流源產生. 經由量測顯示, 輸出信號之上昇/下降時間為47ps，雜訊抖動為22.2psp-p （2.86psrms），輸出眼圖符合SONET OC-192及10Gbps乙太網路之規範，操作電壓在3.3V/7V之下，總功率消耗為1.38瓦。

Fiber-optic has played an important role in long hall and high speed network backbone thanks to its superiorities in low loss and wide bandwidth performance. Nowadays, the data rate of synchronous optical network (SONET) OC-192 is about 10 Gbps, and that of its next generation (OC-768) is up to 40 Gbps. They provide sufficient bandwidth for multi-media data communication. So far, how to realize cost effective optical transceiver ICs and reduce the cost of fiber deployments remain the key issues of the popularity of optical communication. The objective goal of this thesis is to develop data serializer and laser diode driver for 10 Gbps optical transmitter. All the circuit blocks are implemented in 0.35μm SiGe BiCMOS technology for low cost and future system chip integration. In the transmitter side of the optical network, parallel source data are encoded and converted to a high speed serial bit stream through a multiplexer. The clock multiplier unit (CMU) provides multiple phase and frequency outputs for parallel to serial data conversion. The output voltage of data serializer is further converted to a modulation current though a laser diode driver, so as to drive a laser diode and accomplish electrical to optical conversion. The data serializer is composed of a 9.9533 GHz clock multiplying unit (CMU) and a 16 to 1 multiplexer, which converts 16 x 622.08 Mb/s parallel data into a 9.9533 Gb/s serial bit stream. To facilitate on-chip testing, a 16 x parallel pseudo random bit stream (PRBS) generator is also built in. The CMU is a phase-locked loop based frequency synthesizer. It generates 9.9533 GHz output frequency from a 622.08 MHz reference signal and serves as a clock source for multiplexer. The multiplexer is comprised of 4 stages 2 to 1 multiplexer and configured in a tree structure. 16 parallel data is converted to a serial 9.9533 Gbps bit stream according to the reference clocks provided by the CMU. The voltage output of data serializer will be resampled by a retimer so as to alleviate jitter accumulation introduced by the cascaded multiplexer. Operating under a 3.3 V supply, the total power dissipation of the data serializer is 594.66 mW. The laser diode driver converts the output voltage of data serializer to an AC current so as to modulate the laser diode. In addition, it provides biased current ranges from 1-60 mA and modulation current of 40-100 mA to accommodate various applications. To enhance its driving capability and accelerate its operating speed, the laser diode driver is composed of two push-pull pre-drivers followed by a large current switch. The output swing and rise-fall time of the pre-driver is adjustable according to its modulation current. Moreover, negative capacitor Miller compensation technique is utilized to enhance the data bandwidth of the laser driver. To stabilize its output currents, both the biased current and modulation current are derived from a bandgap reference. The measured rise/fall time of the driver output is about 47 ps, and jitter is about 22.2 ps p-p（2.86psrms）. The measured eye-diagrams meet the eye masks defined by SONET OC-192 and 10 Gbps Ethernet specifications. The total power consumption of the laser driver is about 1.38 W under a 3.3 V/7 V supply.