Abstract
This chapter presents the concepts behind the BrainScales (BSS) accelerated analog neuromorphic computing architecture. It describes the second-generation BrainScales-2 (BSS-2) version and its most recent in silico realization, the HICANN-X Application Specific Integrated Circuit (ASIC), as it has been developed as part of the neuromorphic computing activities within the European Human Brain Project (HBP). While the first generation is implemented in a 180 nm process, the second generation uses 65 nm technology. This allows the integration of a digital plasticity processing unit, a highly parallel microprocessor specially built for the computational needs of learning in an accelerated analog neuromorphic systems.
The presented architecture is based upon a continuous-time, analog, physical model implementation of neurons and synapses, resembling an analog neuromorphic accelerator attached to build-in digital compute cores. While the analog part emulates the spike-based dynamics of the neural network in continuous time, the latter simulates biological processes happening on a slower timescale, like structural and parameter changes. Compared to biological timescales, the emulation is highly accelerated, i.e., all time constants are several orders of magnitude smaller than in biology. Programmable ion channel emulation and inter-compartmental conductances allow the modeling of nonlinear dendrites, back-propagating action potentials, and NMDA and Calcium plateau potentials. To extend the usability of the analog accelerator, it also supports vector-matrix multiplication. Thereby, BSS-2 supports inference of deep convolutional networks as well as local learning with complex ensembles of spiking neurons within the same substrate. A prerequisite to successful training is the calibratability of the underlying analog circuits across the full range of process variations. For this purpose, a custom software toolbox has been developed, which facilitates complex calibrated Monte Carlo simulations.
Keywords
- BrainScaleS (BSS)
- Neuromorphic architecture
- Neuromorphic computing
- Analog
- Vector-matrix multiplication
- PyNN
- Spike-timing dependent plasticity (STDP)
- Single Instruction Multiple Data (SIMD)
- Plasticity Processing Units (PPU)
- Integrate-and-Fire
- Tsodys-Markram model
- Digital to Analog Converter (DAC)
- Analog to Digital Converters (ADC)
- Analog inference
- Event-routing
- Python
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- 1.
The Layer1 data format codes a neural event as a parallel bit field containing the neuron address and a valid bit. It is real-time data with a temporal resolution of the system clock, which is 250 MHz in HICANN-X.
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Acknowledgements
The authors wish to express their gratitude to Andreas Grübl, Yannik Stradmann, Vitali Karasenko, Korbinian Schreiber, Christian Pehle, Ralf Achenbach, Markus Dorn, and Aron Leibfried for their invaluable help and active contributions in the development of the BrainScaleS 2 ASICs and systems.
They are not forgetting the important role their former colleagues Andreas Hartel, Syed Aamir, Gerd Kiene, Matthias Hock, Simon Friedmann, Paul Müller, Laura Kriener, and Timo Wunderlich had in these endeavors.
They also want to thank their collaborators Sebastian Höppner from TU Dresden and Tugba Demirci from EPFL Lausanne for their contributions to the BrainScaleS 2 prototype ASIC.
Very special thanks go to Eric Müller, Arne Emmel, Philipp Spilger, and the whole software development team, as well as Mihai Petrovici, Sebastian Schmitt, and the late Karlheinz Meier for their invaluable advice.
This work has received funding from the European Union Seventh Framework Programme ([FP7/2007-2013]) under grant agreement no 604102 (HBP rampup), 269921 (BrainScaleS), 243914 (Brain-i-Nets), the Horizon 2020 Framework Programme ([H2020/2014-2020]) under grant agreement 720270 and 785907 (HBP SGA1 and SGA2) as well as from the Manfred Stärk Foundation.
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J.S. created the concept, has been the lead architect of the BSS systems, and wrote the manuscript except for Sect. 4, which was written by S.B. S.B. also created the teststand software and conceived the simulations jointly with P.D, who performed the simulations and prepared the results. J.W. performed the measurements for the HAGEN mode and created Fig. 6.10. All authors edited the manuscript together.
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Schemmel, J., Billaudelle, S., Dauer, P., Weis, J. (2022). Accelerated Analog Neuromorphic Computing. In: Harpe, P., Makinwa, K.A., Baschirotto, A. (eds) Analog Circuits for Machine Learning, Current/Voltage/Temperature Sensors, and High-speed Communication. Springer, Cham. https://doi.org/10.1007/978-3-030-91741-8_6
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