Dendrites, Difusors, and WTA

Overview:

• One key objective in this lab is looking at the behavior and modeling of dendritic components and how they come together for computation.
• One objective is to explore the behavior of an elegant current-mode implementation of a resistive network called a diffusor network and understand some of the things that these circuits are used for. Resistive networks are often used in biological systems for a variety of tasks. In particular, they can be used to perform local spatial averaging . Such averaging is used to improve the signal-to-noise ratio or to obtain a local reference to which signals can be compared. In this lab we will examine a one-dimensional resistive network made up of diffusors. The diffusor relies on the exact linear relationship between channel current and the carrier concentration in subthreshold conduction.

Reading:

• Key lab material available ( pdf ).
• First dendritic transistor channel modeling paper, including reconfigurable capability as part of the resulting architecture ( pdf ).
• Dendrite Channel Model with direct comparisons / extensions to Rall's formulation ( pdf ). All of the data was compiled on an FPAA device. Note the use of amplifiers (FG OTA of gain between 20-30) for the data.
• Discussion of Dendritic Wordspotting related to HMM classifiers typical for speech recognition ( pdf ). All of the data was compiled on an FPAA device. Note the use of amplifiers (FG OTA of gain between 20-30) for the data.
• Board Pictures

Project Questions:

The focus of this project is to get a working dendritic line, built from a diffusor circuit approach with biasing approximating a dendrite cable diameter changes, and then pulling multiple lines together to visualize characterization behavior.

Adding Synapses and Dendrite Diameter

This section discusses adding of synapses and dendritic diameter to the initial model.

We started in a previous case that we utilize additional pFET switch devices, which are potentially already compiled and used as current sources in the previous case, where you put in a waveform in the pFET source to emulate the synaptic concepts.

Second, you will shift the effective diameter down the line, from distal to proximal direction. Remember, this effectively shifts the horizontal conductance to increase at each pFET horizontal tap, effectively giving a linear decrease in the floating-gate voltage at each tap.

Bulding a Dendritic-Modelled Neuron Classifiers