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Register a new userIMPULSE: A 65nm Digital Compute-in-Memory Macro with Fused Weights and Membrane Potential for Spike-based Sequential Learning Tasks
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Added by
Amogh Agrawal
Publication date
2021
fields
Informatics Engineering
and research's language is
English
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The inherent dynamics of the neuron membrane potential in Spiking Neural Networks (SNNs) allows processing of sequential learning tasks, avoiding the complexity of recurrent neural networks. The highly-sparse spike-based computations in such spatio-temporal data can be leveraged for energy-efficiency. However, the membrane potential incurs additional memory access bottlenecks in current SNN hardware. To that effect, we propose a 10T-SRAM compute-in-memory (CIM) macro, specifically designed for state-of-the-art SNN inference. It consists of a fused weight (WMEM) and membrane potential (VMEM) memory and inherently exploits sparsity in input spikes leading to 97.4% reduction in energy-delay-product (EDP) at 85% sparsity (typical of SNNs considered in this work) compared to the case of no sparsity. We propose staggered data mapping and reconfigurable peripherals for handling different bit-precision requirements of WMEM and VMEM, while supporting multiple neuron functionalities. The proposed macro was fabricated in 65nm CMOS technology, achieving an energy-efficiency of 0.99TOPS/W at 0.85V supply and 200MHz frequency for signed 11-bit operations. We evaluate the SNN for sentiment classification from the IMDB dataset of movie reviews and achieve within 1% accuracy of an LSTM network with 8.5x lower parameters.
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Digital In-memory computing improves energy efficiency and throughput of a data-intensive process, which incur memory thrashing and, resulting multiple same memory accesses in a von Neumann architecture. Digital in-memory computing involves accessing multiple SRAM cells simultaneously, which may result in a bit flip when not timed critically. Therefore we discuss the transient voltage characteristics of the bitlines during an SRAM compute. To improve the packaging density and also avoid MOSFET down-scaling issues, we use a 7-nm predictive PDK which uses a finFET node. The finFET process has discrete fins and a lower Voltage supply, which makes the design of in-memory compute SRAM difficult. In this paper, we design a 6T SRAM cell in 7-nm finFET node and compare its SNMs with a UMC 28nm node implementation. Further, we design and simulate the rest of the SRAM peripherals, and in-memory computation for an advanced finFET node.
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