Guangtongxin yanjiu (Oct 2024)
Board Level Signal Integrity Study of Ultra-High-Speed Optical Module for Data Centers
Abstract
【Objective】The rapid development of artificial intelligence has put forward higher requirements for data center computing. As the core device of the data center optical interconnection, the design of optical module will also encounter big challenges. With the increasing speed of optical modules, the signal integrity problem has become a bottleneck that restricts the performance of optical modules. In order to design a high-speed optical module that can meet the speed requirements of optical interconnects in data centers, especially high performance computing application, it is necessary to implement optimal design on the ultra-high-speed link inside the optical module.【Methods】In this paper, the factors affecting the integrity of the signal in the optical module are simulated and optimized with a Quad Small Form-factor Pluggable Double Density (QSFP-DD) optical module as an example. The specific work is to theoretically analyze the parts of the channel that may deteriorate the signal integrity, such as vias and Ball Grid Array (BGA) solder balls, and discuss the optimization and improvement methods of these parts. In particular, this paper analyzes the optimization method for signal transmission in the frequency band above 50 GHz, so that the high-speed channel can realize the low-loss transmission for ultra-high-speed 4-Level Pulse Amplitude Modulation (PAM4) signal. In addition, the transmission performance of the whole high-speed channel is also studied and tested by the four-port vector network analyzer.【Results】The results show that the design scheme can achieve the required transmission bandwidth without resonance. The simulation results of full channel show that the return loss of all channels is less than -15 dB and the insertion loss is less than 3 dB, and 224 Gbit/s PAM4 signal low-loss transmission can be achieved. The test results are basically consistent with the simulation results, which proves that the design scheme can meet the requirement of high speed optical interconnects in Datacenters.【Conclusion】The method of signal integrity design of optical modules proposed in this paper has important guiding significance for the design of ultra-high-speed optical modules in the future, and will also provide a reference for the design of other kinds of high-speed circuits.
