HERMES-Core-A 1.59-TOPS/mm2PCM on 14-nm CMOS In-Memory Compute Core Using 300-ps/LSB Linearized CCO-Based ADCs
Riduan Khaddam-Aljameh (Zurich Lab, Axelera AI)
Milos Stanisavljevic (Axelera AI, Zurich Lab)
Jordi Fornt Mas (Zurich Lab, Barcelona Supercomputing Center)
Geethan Karunaratne (Zurich Lab)
Matthias Brandli (Zurich Lab)
Feng Liu (IBM Research)
Abhairaj Singh (TU Delft - Computer Engineering)
Silvia M. Muller (IBM Systems and Technology)
Urs Egger (Zurich Lab)
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Abstract
We present a 256 × 256 in-memory compute (IMC) core designed and fabricated in 14-nm CMOS technology with backend-integrated multi-level phase change memory (PCM). It comprises 256 linearized current-controlled oscillator (CCO)-based A/D converters (ADCs) at a compact 4-μm pitch and a local digital processing unit (LDPU) performing affine scaling and ReLU operations. A frequency-linearization technique for CCO is introduced, which increases the maximum CCO frequency beyond 3 GHz, while ensuring accurate on-chip matrix-vector multiplications (MVMs). Moreover, the design and functionality of the digital ADC calibration procedure is described in detail and the MVM accuracy is quantified. Finally, the measured classification accuracies of deep learning (DL) inference applications on the MNIST and CIFAR-10 datasets, when two IMC cores are employed, are presented. For a performance density of 1.59 TOPS/mm2, a measured energy efficiency of 10.5 TOPS/W, at a main clock frequency of 1 GHz, is achieved.
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