Abstract
As computing systems trend toward multi-die architectures to meet demands for greater bandwidth, density, and energy efficiency, optical interconnects are emerging as an appealing complement to traditional electrical links. This paper examines the role and benefits of bringing photonics into multi-die systems, enabling data transmission at the speed of light to maximize performance and minimize power.
Introduction
Multi-die computing, which combines dies of different process nodes and types, allows the optimization of system metrics like performance, power, and area (PPA). As these heterogeneous systems take hold across high-performance computing (HPC) and AI accelerators, their complex architectures open pathways to new interconnect solutions. Photonics, which harness the speed and efficiency of light to move data, offer transformative bandwidth, latency, and power advantages over electrical links alone. Technologies for 2.5D and 3D integration now make it possible to integrate photonic and electrical components together into advanced multi-die packages.
The Need for Light Speed Data Movement
Multi-die systems deliver higher bandwidth, lower latency, better power efficiency and density over large monolithic system-on-chips (SoCs). However, as data flows between dies increase into the terabytes, traditional silicon interposers struggle to provide the energy efficiency and performance needed. This is where photonics come in – transmitting data as light can increase bandwidth 100x while using 10-100x less energy per bit. As Figure 1 shows, optical fiber connections are already used for rack-to-rack links in data centers. As data demands rise, optical links are moving to shorter reach connections between hardware components. Optical I/O chiplets for CPUs, GPUs and memories will soon be commonplace.
Balancing Bandwidth and Power with Photonic ICs
There are two key applications utilizing photonics in multi-die systems today:
Optical I/O for CPU/GPUs: High-speed optical links from CPUs and accelerators to top-of-rack switches increase bandwidth while lowering power. On-chip optical transceivers and interfaces continue this advantage.
Optical memory I/O: The “memory wall” limits performance in machine learning training. Optical links to high-bandwidth memory provide abundant, power-efficient bandwidth to feed massive datasets.
Co-packaging electrical and photonic dies takes this further – combining the advantages of both technologies in a single, dense package. Synopsys predicts co-packaged optics moving inside advanced 3D packages soon. Alongside electrical links, optics will help balance soaring bandwidth demand with limited power budgets.
Integrated lasers ease the integration of photonics by removing the need for external light sources. Startups like OpenLight offer open silicon photonics platforms with integrated lasers to simplify the process.
New Design and Verification Challenges
Bringing multi-die systems with photonics to production involves adapting traditional flows for these unique co-dependencies. Latitude provides electronic and photonic design automation (EDA/PDA) tools to simulate, implement and verify these multi-domain systems. As optical-electrical integration continues, these comprehensive toolflows will be critical to overcome the complexity.
Integrating Photonics into Multi-Die Systems
As multi-die systems trend toward integrating photonic and electrical components for greater bandwidth, efficiency, and performance, the complexity of designing and verifying these heterogeneous systems increases substantially. PIC Studio is well-positioned to address these multi-die design challenges through its co-simulation capabilities spanning electronic, photonic, and RF domains.
PIC Studio enables early architecture exploration of system architectures containing photonic, electronic, and RF dies interfaced together. The tool allows rapid simulation of optical links and electronic chips concurrently using compact device models. This facilitates optimization of the system partitioning early on.
Once the architecture is defined, PIC Studio’s schematic driven layout can automatically generate layouts based on the photonic circuit diagrams. Through co-simulation of the electrical and photonic dies pre- and post-layout, the system can be verified and optimized as an integrated system – not as isolated dies. This is critical for balancing interface bandwidths, timing closure, and power constraints.
Finally, PIC Studio allows packaging traits like temperature profiles, bonding wiremodels, and signal integrity effects to be simulated in conjunction with the SoC dies. This holistic approach to multi-die verification, covering chip, package and board, provides an accurate final validation before tapeout.
With expertise in electronic-photonic co-simulation and an open, customizable environment, PIC Studio delivers a comprehensive solution for the unique verification needs of integrated multi-die computing systems. As optical interconnects become ubiquitous, tools like PIC Studio that span across domains will be vital to overcome the design complexity.
Conclusion
As bandwidth and efficiency demands increase, especially in HPC and AI, multi-die systems with integrated photonics offer a compelling path forward. Transmitting data via light waves alleviates the power and bandwidth constraints of electrical links alone. Continued innovation, like co-packaged optics and integrated light sources, will unlock the full potential. However, with these heterogenous systems comes increased design complexity, requiring EDA/PDA tools tailored for multi-die photonics co-simulation and implementation.
PIC Studio, with its unified environment for schematic capture, layout, and co-simulation across photonic, electronic, and RF domains, delivers the comprehensive solution needed. As optical interconnects become ubiquitous in next-generation computing, PIC Studio's capabilities will empower architects and designers to realize their most advanced multi-die visions without being limited by the design process itself. Just as EDA enabled the feats of the electronics industry, a new generation of EPDA tools like PIC Studio will drive the coming photonics revolution underpinning future systems.
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