高速光通信发射机芯片设计

       随着5G时代的降临、大数据技术的广泛应用以及AI算法的日益普及，数据中心的数据交互量呈现井喷式增长，这无疑对通信系统提出了更为严苛的要求。然而，传统的电缆通信受限于信道和背板等传输媒介带来的高损耗，难以实现高数据率的传输。此外，电缆通信还面临着高发热和高电磁干扰等问题，难以满足数据中心内部通信的复杂需求。近年来，光通信系统因其超低损耗、高数据传输速率、强大的抗干扰能力以及低噪声特性而备受瞩目。在众多激光器中，垂直腔面发射激光器（VCSEL）凭借其高集成度、低功耗、封装便捷以及低成本等诸多优势脱颖而出。因此，基于VCSEL的光发射机成为数据中心内部短距通信的理想选择。电子与电气工程师协会（IEEE）最新发布了100Gb/s短距离光通信协议标准（IEEE802.3db-2022），这一标准的推出显著促进了基于VCSEL的光发射机向100 Gb/s高速率的演进。
  本论文对高速光通信的链路进行了分析，并重点探讨了基于VCSEL的高速光发射机芯片技术。本论文以高速率和低功耗为核心目标，设计了一款满足IEEE最新短距光通信标准的基于VCSEL的高速光发射机，适用于数据中心内部短距通信。该高速光发射机由连续时间线性均衡器（CTLE）、可变增益放大器（VGA）、前馈均衡器（FFE）、输出驱动器（DRV）和自动增益控制电路（AGC）组成。CTLE创新性地将均衡电路与吉尔伯特单元相结合，同时能实现均衡功能和输入信号极性反转的功能。输出驱动器创新性地采用大阻值负载电阻与PMOS并联的输出方案，将输出驱动器的功耗降低了45%，同时可以通过调整PMOS尺寸来改变充电电容，从而改变输出充电路径的时间常数，实现对输出眼图上升下降沿的非对称补偿。
       本论文基于130nm SiGe BiCMOS工艺，对高速光发射机进行了电路设计、版图绘制、后仿真验证与流片。光发射机系统整体带宽为40.4 GHz，最高数据率为112 Gb/s。输出偏置电流为2-15 mA，输出调制电流为2-12 mApp。 由于没有使用电感，单通道版图核心电路面积仅为0.18 mm²。创新型的低功耗设计使得单通道光发射机功耗为256 mW，能量效率为2.28 pJ/bit，达到国际领先水平。

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