一個 4-PAM 20-Gbps 具有可調主動式阻抗匹配電路之雷射二極體驅動電路

Abstract

傳統的雷射驅動電路是採用被動性負載做為阻抗匹配，但是會消耗額外功率在被動性負載上，在這篇論文中，提出利用主動性元件作為負載，來取代被動性負載的雷射驅動電路，除了有作為阻抗匹配的功能之外，相較於傳統採用被動性負載的雷射驅動電路，它能減少傳統的雷射驅動電路功率消耗。另外為了提高輸出波形抖動量的效能因此在主動式阻抗匹配電路裡加入輸出阻抗可調的機制。同時為了補償雷射二極體開與關的不平衡因此加入預先失真電路。最後為了能於有限頻寬內傳送更多的資料，於此利用四個位階的脈衝振幅調變的方式如此可達到總資料傳送量為頻寬的兩倍。編碼上在此使用葛雷碼，每一等份的振幅變化只改變一個位元，如此一來可降低位元錯誤率。 在論文中我們所實現的雷射二極體驅動電路以台積電90奈米標準金氧半技術的製程來完成設計，在1.2伏特與1.8伏特的操作電壓下，量測到的資料傳輸速率為每秒160億位元；功率消耗約為100毫瓦；晶片大小為0.53平方毫米。

Conventional laser diode drivers adopt passive back-termination as impedance matching; however it consumes additional power on passive load. In this thesis we propose a new active back-termination for laser driver. It consumes less power dissipation compared to conventional driver with passive back-termination. Moreover, for pervasive adaptation, the active back-termination is tunable with reference resistor to match the characteristic impedance of transmission line. At the meantime, we use a pre-distortion circuit to compensate the on/off asymmetry of the laser diode. In order to achieve a higher data rate under the bandwidth limitation, the quadri-pulse amplitude modulation is used. In this way the total data rate is doubled under the same bandwidth. The Gray code is adopted to reduce the bit error rate (BER), since there is only one-bit changed between different levels.

The laser diode driver is fabricated in TSMC 90nm CMOS process. Under 1.2Vand1.8V supply, the delivered data rate can reach 16Gbps, power consumption is about 100mW, and the die area is 0.53mm2.