Frequently asked questions (FAQ)¶

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Characterization of analog circuits¶

For measurements of analog circuits see [Bruederle2009PhD]. Note that version 3 of the Spikey chip was used in this thesis.

NEST model of hardware STDP synapses¶

In the scope of [Pfeil2012STDP] we implemented an STDP synapse in NEST considering the following features of STDP synapses on the Spikey chip:

Local measurement and accumulation of correlations between pre- and postsynaptic spikes.
Global mechanism that sequentially evaluates these accumulated correlations and updates the synaptic weight.
Discretization of synaptic weights with a 4-bit resolution (16 values).
Reduced symmetric nearest-neighbor spike pairing scheme (see [Morrison2008]).

Please not that parameter variations (fixed-pattern noise) are not considered, but can be implemented by distributing the thresholds for the evaluation of the charge on the capacitors.

NEST model of hardware STDP synapses — Figure 56: Regular pairs of pre- before postsynaptic spikes are presented (with a frequency of 10 hertz). The charge on the capacitor for causal correlations (green) accumulates and after crossing the threshold (dashed line) the discretized synaptic weight (blue) is increased (source code of NEST model of hardware STDP synapse).¶

List of publications¶

Bruederle2009PhD: Brüderle, D. (2009). Neuroscientific Modeling with a Mixed-Signal VLSI Hardware System. PhD thesis, Heidelberg University. HD-KIP 09-30.