Transceiver Circuits for Optical Backplanes

长期以来，光纤链路一直被认为是铜缆的更轻、更清洁、更快的替代品，用于长途数据通信，在这种情况下，通信节点之间的距离以公里为单位。然而，在过去的十年中，随着铜缆的重量和体积大幅增加，光纤链路已经取代了铜缆在更短距离上的通信，例如数据中心计算机之间的几米距离。如今，光链路正在与铜线竞争，距离只有几厘米，比如微处理器和打印机电路板上的存储器之间的距离超过25 GB/S。在这种速度下，铜线会极大地衰减电信号，以至于无论链路两端包含多少电子设备，都极难在接收端恢复正确的数据。另一方面，众所周知，即使在更高的数据速率下，光信道的衰减在这些距离上也是可以忽略的。到目前为止，阻止光学背板更广泛使用的主要是电到光和光到电接口以及周围电子设备的成本，以补偿这些接口的各种缺陷。这还不包括机载芯片的组装成本，因为需要更精确的对准。 该提案涉及光/电接口以及围绕这些接口的电子设备的设计(器件和电路)的创新。特别是，我们建议设计光学器件，如环形调制器、光电探测器和滤光器，以及电子电路，如跨阻抗放大器(TIA)、限幅放大器、均衡器以及时钟和数据恢复电路。这项研究的长期目标是展示一种用于光学背板的全集成收发器。短期目标是设计、制造和测试完整收发器的各个构建块。 作为这项研究的一部分，我们还开发了一个系统级模型(在MatLab或Simulink中)，它包括所有的构建块，以及它们非理想的主要来源。该模型将用于确定链路性能作为关键设计参数的函数。因此，我们确定链路性能对每个设计参数的敏感度，以确定体系结构的性能极限。一旦我们确定了最终的体系结构，我们将在电路级别上一次实现一个模块。我们将分别测试每个模块，然后再进行更高级别的集成。

Optical links have long been known as lighter, cleaner, and faster alternatives to copper cables for long-haul data communication where the distance between communicating nodes is in kilometers. In the last decade, however, as the sheer weight and volume of the copper cables have increased substantially, optical links have replaced copper cables in communication over shorter distances, such as a few meters between computers in data centers. Today, optical links are competing against copper at distances as short as a few centimeters, such as those between a microprocessor and a memory on a printer circuit board (PCB), for speeds in excess of 25Gb/s. At these speeds, the copper traces attenuate the electrical signal so much that it is extremely hard to recover the correct data at the receiver end no matter how much electronics one includes at the two ends of the link. On the other hand, the attenuation of an optical channel is known to be negligible at these distances even at far higher data rates. What has prohibited so far the wider use of optical backplanes is mainly the cost of electrical to optical and optical to electrical interfaces and the surrounding electronics to compensate for various imperfections of these interfaces. This is in addition to the assembly cost of the chips on board as much more precise alignments are necessary. This proposal relates to the innovation of designs (devices and circuits) for optical/electrical interfaces, and the electronics surrounding these interfaces. In particular, we propose designs for optical devices such as the ring modulators, photo-detectors, and optical filters, and electronic circuits such as trans-impedance amplifiers (TIA), limiting amplifiers, equalizers, and clock and data recovery circuits. The long-term objective of this research is to demonstrate a fully integrated transceiver for optical backplanes. The short-term objectives are to design, fabricate, and test individual building blocks of the complete transceiver. As part of this research, we also develop a system-level model (in Matlab or Simulink) that includes all the building blocks, along with their main sources of non-idealities. This model will be used to identify the link performance as a function of key design parameters. Accordingly, we determine the sensitivity of the link performance to each design parameter in order to identify the performance limits of the architectures. Once we determine the final architecture, we will move towards implementing one block at a time in circuit level. We will test each block individually before moving on to higher levels of integration.