Problem
Research questions and friction points this paper is trying to address.
subharmonic injection locking
oscillator-based Ising machines
on-chip variations
scaling
PVT variations
ROA-Based Subharmonic Injection Locking for Oscillator-Based Ising Machines
🤖 AI Summary
This work addresses the susceptibility of on-chip subharmonic injection locking (SHIL) to process, voltage, and temperature (PVT) variations, which induces phase instability in oscillator-based Ising machines (OIMs) and limits their scalability. To overcome this challenge, the authors propose a rotating oscillator array (ROA) module based on rotating traveling-wave oscillators (RTWOs) as a highly robust external perturbation source that generates stable high-frequency SHIL signals. The designed ROA “brick” topology substantially enhances SHIL stability under PVT variations while preserving near-ideal solution accuracy and improving system scalability. Evaluated on a 324-node Max-Cut problem, the ROA-SHIL approach achieves solution accuracies of 93%–97% under PVT perturbations with an energy consumption of only 2.49 nJ, significantly outperforming conventional ring oscillator-based implementations.
📝 Abstract
This paper introduces on-chip integrated rotary traveling wave oscillators (RTWOs) organized into rotary oscillator array (ROA) bricks as an external perturbation to induce subharmonic injection locking (SHIL) in oscillator-based Ising machines (OIMs). The implementation of SHILs on chip is challenging, as the frequency of SHILs must be multiples of the operating frequency of the OIM nodes, with on-chip variations affecting the phase, degrading the SHIL process. This impedes the scaling of OIM implementations, regardless of the topology of Ising nodes, coupling or graph mapping mechanisms. The ROA brick topology implementation of RTWOs generates high frequency signals that are shown to provide a stable 2.31 GHz SHIL signal under process, voltage, and temperature (PVT) variations. Under PVT variations, distributed ring oscillator-based SHILs (ROSC-SHIL) fail to perform injection locking while the proposed ROA brick-based SHIL (ROA-SHIL) preserve 93% to 97% accuracy (the same accuracy of an ideal SHIL signal) in the OIM solutions of a sample 324-node max-cut problem. The driving strength and floorplan of the ROA brick are also shown to be amenable for scaling with an energy-to-solution impact of 2.49 nJ for the proposed ROA-SHIL.
Innovation
Methods, ideas, or system contributions that make the work stand out.
subharmonic injection locking
rotary oscillator array
oscillator-based Ising machine
PVT variation resilience
on-chip integration
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