Hardware Neuromorphic System for STDP Synapse and LIF Neuron Simulation

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Solution Overview

Problem

Software models of neuromorphic systems with spike time dependent plasticity (STDP) synapse and leaky integrate and fire (LIF) neuron models are computationally slow, even for simple simulations like handwritten number recognition, due to the complexity of modeling neuron and synapse activities.

Innovation Solution

A hardware-implemented neuromorphic system that models neuron membrane potential based on the LIF model and spike time-dependent plasticity rule, using timers to measure spike times and updating synapse weights, with a serial to parallel converter for efficient data processing, allowing for faster operation and real-time learning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If software models are used to simulate neuromorphic systems with STDP synapse and LIF neuron models, then the system can model neuron and synapse activities, but the computing operation takes a long time

Engineering Contradiction:
Improvemodeling capabilityVSAvoidcomputing speed
Core Design Contradiction:
Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent replaces software-based mathematical modeling with hardware-based electronic circuit implementation. The LIF neuron model is implemented using electronic circuits that naturally perform integration and threshold detection, while STDP synapse modeling is implemented using hardware logic circuits that compute weight updates based on spike timing differences. This substitution of software computation with hardware circuitry achieves real-time neuromorphic simulation with significantly improved computing speed.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If hardware implementation is used to model neuron membrane potential and synapse weights, then the operation speed increases significantly, but the device complexity increases

Engineering Contradiction:
Improveoperation speedVSAvoidsystem complexity
Core Design Contradiction:
ProductivityVSDevice complexity

Solution Approach 1:

The patent divides the neuromorphic system into distinct functional modules: LIF neuron model circuits for membrane potential simulation, STDP synapse model circuits for weight update computation, timer units for spike timing measurement, and a serial-to-parallel converter for data processing. Each module is implemented as a separate hardware component with dedicated functionality, making the complex system manageable through modular design while maintaining high operation speed.

Inventive Principle:
Principle #1Segmentation

3Measurement precision

If timers are added to measure elapsed time between axon spikes and dendrite spikes, then the spike time-dependent plasticity rule can be accurately implemented, but the device complexity increases

Engineering Contradiction:
Improvespike timing measurementVSAvoidtimer unit complexity
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent incorporates timer units that continuously track and measure the elapsed time between axon spikes and dendrite spikes in real-time. These timers perform the time measurement action preliminarily and continuously, so when a spike event occurs, the precise time difference is already available for immediate use in the STDP weight update computation, eliminating the need for complex post-processing time calculations.

Inventive Principle:
Principle #10Preliminary action

4Productivity

If a serial to parallel converter is used to convert serial neuron fire data streams to parallel data streams, then the processing efficiency improves, but the device complexity increases

Engineering Contradiction:
Improvedata processing efficiencyVSAvoidconverter complexity
Core Design Contradiction:
ProductivityVSDevice complexity

Solution Approach 1:

The patent employs a serial-to-parallel converter that processes neuron fire data streams in periodic cycles, converting serial incoming data into parallel output formats at regular intervals. This periodic conversion approach enables efficient batch processing of spike events, allowing multiple neurons' fire data to be processed simultaneously in parallel, thereby improving overall data processing efficiency while using a relatively simple converter architecture.

Inventive Principle:
Principle #19Periodic action

Data Source

PatentUS10762419B2Digitial STDP synapse and LIF neuron-based neuromorphic system
Publication Date: 2020.09.01 INTERNATIONAL BUSINESS MACHINE CORPORATION
  • US10762419B2 patent drawing
  • US10762419B2 patent drawing
  • US10762419B2 patent drawing

AI summary

Described is a neuromorphic system implemented in hardware that implements neuron membrane potential update based on the leaky integrate and fire (LIF) model. The system further models synapse weights update based on the spike time-dependent plasticity (STDP) model. The system includes an artificial neural network in which the update scheme of neuron membrane potential and synapse weight are effectively defined and implemented.