Organizations: Intrinsic Lab, Centre for Sensors, Instrumentation and Cyber-Physical System Engineering (SeNSE), Indian Institute of Technology Delhi, New Delhi 110016, India
Stochastic spiking neurons trade exact arithmetic for controlled randomness, lowering area and tolerating input noise, which suits event-driven edge hardware. We present a compact, configurable stochastic leaky integrate-and-fire neuron in standard-cell CMOS on the SkyWater 130 nm process, released openly. A 16-bit configurable-polynomial linear-feedback shift register drives an eight-entry programmable activation table that sets a Bernoulli firing probability, and a saturating 16-bit leaky integrator with a programmable threshold and a refractory period of zero to seven cycles produces the spike train. All parameters are set through a sixteen-register serial interface, and the neuron runs from parallel inputs or entirely from the register file. From a model checked bit-exact against the register-transfer code, the period is 65535 states for a maximal-length polynomial and 63 for the shipped default, the eight-bit comparison value is uniform over the full period, and the per-entry firing probability equals the table value divided by 256. We also characterise a property a system-level model would not expose: the comparator output is serially correlated at short lags, with a negative lobe near lag eight, because the compared byte shifts by one bit each cycle; subsampling every sixteen cycles restores whiteness. Rate-coding sweeps show monotonic control of the output rate by the input weight and the threshold, and the refractory period caps the rate at one spike per refractory-plus-one cycles. The neuron occupies about 10,600 square micrometres at 70 per cent utilisation on a single Tiny Tapeout tile, meets 50 MHz timing with positive margin, and passes eighteen directed cocotb tests at register-transfer and gate level. All results are pre-silicon, from simulation and the open flow. The neuron is an openly released companion to a four-block neuromorphic suite reported separately.
Edge neuromorphic systems need compact, configurable hardware that combines probabilistic inference, local learning, and an interface to emerging analogue memory. We present four interface-compatible digital IP blocks implemented as standard-cell CMOS on the SkyWater 130 nm process: a process, voltage and temperature (PVT) sensor built from five selectable ring oscillators that also provides a jitter-based true-random-number generator and a frequency-bounds health monitor; a stochastic leaky integrate-and-fire (LIF) neuron with a configurable LFSR, a programmable activation table, and a refractory period; an on-chip spike-timing-dependent plasticity (STDP) controller with a programmable curve and reward-modulated, eligibility-trace, and anti-Hebbian modes; and a memristive-crossbar controller supporting forming, set, reset, read, and automated current-voltage sweep with current-compliance limiting and half-select biasing. All four blocks share a common serial peripheral interface (SPI) register file; the sensor also exposes a parallel readout. Each occupies a single tile at a 50 MHz target. The suite was verified with 99 cocotb tests at register-transfer and gate level (all passing) and taken through an open standard-cell flow, then submitted for tapeout via the Tiny Tapeout shared-silicon programme. Mapped to the open cell library, each block occupies a post-synthesis cell area of 9.3 to 10.6 thousand square micrometres, places at 61 to 70 per cent tile utilisation, meets the 50 MHz constraint with positive setup and hold margin after clock-tree synthesis, and draws an estimated 0.64 to 0.70 mW under a default switching-activity assumption. The contribution is a coherent, openly released set of building blocks unified by one register interface and one verification flow. All results are from simulation and the implementation flow; no fabricated silicon is reported.
Short-term plasticity (STP) is fundamental to temporal information processing in biological neural systems but remains difficult to realize efficiently in neuromorphic hardware. Memristive electrochemical random-access memory (ECRAM) devices naturally exhibit non-equilibrium ionic dynamics that produce transient conductance modulation; however, these behaviors are typically treated as undesirable variability or tolerated as side effects in memory-centric computing paradigms. In this work, we instead transform these volatile dynamics from a tolerated device artifact into a computational resource through a cross-layer device-circuit-system co-design framework. We introduce a delay-feedback leaky integrate-and-fire (LIF) neuron architecture co-designed with ECRAM synapses that exploits activity-dependent conductance modulation with negligible additional circuit overhead. The architecture integrates ECRAM-based synapses with a tunable delay-feedback spike-generation path, enabling transient device dynamics to directly modulate neuron excitability and synaptic efficacy. We used experimentally characterized ECRAM devices exhibiting transient conductance modulation (1.5 KOhms per spike) to develop a compact behavioral model suitable for circuit-level simulation. Circuit simulations demonstrate two key STP behaviors -- synaptic facilitation and intrinsic excitability modulation -- while consuming 2 pJ per spike, and the same device-driven mechanisms extend across multiple neuron topologies. Network-level analysis further demonstrates frequency-selective spike processing, allowing individual synapses to act as tunable temporal filters within spiking neural networks. This work demonstrates that non-equilibrium ECRAM dynamics can serve as a native hardware substrate for STP and temporal computation in neuromorphic circuits.
Alex Currie, Sean Borkholder, Nithil Harris Manimaran +4
Spiking Neural Networks (SNNs) provide an attractive framework for energy-efficient inference due to their event-driven computation and biologically inspired dynamics. However, efficient hardware realization of SNNs remains challenging because neuronal computations incur significant power and area costs, and uncontrolled approximate arithmetic can destabilize recurrent state updates when precision is not properly managed. To address these challenges, this paper presents ReSCom, a reconfigurable SNN accelerator that leverages stochastic computing to reduce hardware complexity while maintaining stable inference. The proposed architecture employs stochastic arithmetic for multiplication operations in neuron dynamics, while preserving exact fixed-point addition/subtraction operations. This stochastic strategy enables runtime trade-offs between accuracy, latency, and energy consumption. A unified reconfigurable neuron design supports Integrate-and-Fire (IF), Leaky Integrate-and-Fire (LIF), and Synaptic neuron models within a single hardware framework. Experimental results for MNIST inference on a Xilinx Artix-7 FPGA show that ReSCom achieves 92.80% classification accuracy while consuming just 0.05mJ of operational energy per image at 100MHz, outperforming the energy efficiency of recent state-of-the-art implementations. Furthermore, managing the stochastic bit-stream length allows explicit, dynamic control over accuracy-latency-energy trade-offs to meet target application constraints.
Ali Alipour Fereidani, Mohammad Rasoul Roshanshah, Saeed Safari