Exploring Millimeter-Wave Interconnect for Chip-to-Chip Communication By M. Meraj Ahmed With aggressive scaling of device geometries, yield of complex Multi-Processor Systems-on-Chips (MP-SoCs) will decrease due to higher probability of manufacturing defects. Disintegration of large SoCs into smaller chips called chiplets will improve yield and cost of complex platform-based systems. AMD’s EPYC which was released in 2017, is an example of such multichip system having 4 chiplets. However, performance of multichip systems is limited by the off-chip I/Os as they provide high power and latency overheads. On the other hand, millimeter-wave (mm-wave) wireless interconnects can establish single hop communication between multiple chips to provide high speed and energy-efficient communication. Fig. 1 conceptualize such multichip communication. Here, we briefly discuss the architecture and how to leverage mm-wave interconnect for multichip communication.
Fig. 1. Multichip communication using mm-wave interconnect.
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Fig. 2. Block diagram of the OOK (a) Transmitter, (b) Receiver.
System and Wireless Interface (WI) Architecture: We consider a tile-based multicore-multichip (MCMC) architecture typically used in high performance computing nodes such as server blades. Each tile in the MCMC system is composed of a processing core, a switch, L1 private cache and a distributed shared last level cache (LLC). Tiles in each chip are connected with each other through a regular wired mesh-based Network-on Chip (NoC). For inter-chip communication, in each chip, we equip some or all the NoC switches with WIs as shown in Fig. 1. A WI can have both Transmitter (Tx) and Receiver (Rx) circuitry or can have only Rx circuitry. We call such WI as TR-WI and R-WI respectively and shown in Fig. 1. The Tx used in a WI typically consists of Voltage Controlled Oscillator (VCO), modulator, Drive Amplifier (DA) while the Rx circuitry includes Low Noise Amplifier (LNA), Envelop Detector (ED) and Baseband Amplifier as shown in Fig. 2. As modulation technique On-Off Keying (OOK) along with a zig-zag antenna have been chosen due to their low implementation overhead. 18 | The ROCHESTER ENGINEER OCTOBER 2020
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