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# ac_generator – Produce an alternating current (AC) input¶

## Description¶

This device produces an AC input sent by CurrentEvents. The current is given by

$I(t) = \mathrm{offset} + \mathrm{amplitude} \cdot \sin ( \omega t + \phi )$

where

$\begin{split}\omega = 2 \pi \cdot \mathrm{frequency} \\ \phi = \frac{\mathrm{phase}}{180} \cdot \pi\end{split}$

All stimulation devices share the parameters start and stop, which control the stimulation period. The property origin is a global offset that shifts the stimulation period. All three values are set as times in ms.

• For spike-emitting devices, only spikes with times t that fulfill start < t <= stop are emitted. Spikes that have timestamp of t = start are not emitted.

• For current-emitting devices, the current is activated and deactivated such that the current first affects the target dynamics during the update step (start, start+h], i.e., an effect can be recorded at the earliest at time start+h. The last interval during which the current affects the target’s dynamics is (stop-h, stop].

The property stimulus_source defaults to an empty string. It can be set to the name of a stimulation backend, in which case it will take its parameters from the configured backend instead of from the internally stored values. More details on available backends and their properties can be found in the guide to stimulating the network.

## Parameters¶

label

A string (default: “”) specifying an arbitrary textual label for the device. Stimulation backends might use the label to generate device specific identifiers like filenames and such.

origin

A positive floating point number (default : 0.0) used as the reference time in ms for start and stop.

start

A positive floating point number (default: 0.0) specifying the activation time in ms, relative to origin.

stimulus_source

A string (default: “”) specifying the name of the stimulation backend from which to get the data for updating the stimulus parameters of the device. By default the device uses its internally stored parameters for updating the stimulus.

stop

A floating point number (default: infinity) specifying the deactivation time in ms, relative to origin. The value of stop must be greater than or equal to start.

amplitude

Amplitude of sine current (pA)

offset

Constant amplitude offset (pA)

frequency

Frequency (Hz)

phase

Phase of sine current (0-360 deg)

Setting start and stop only windows the current as defined above. It does not shift the time axis.

### Set parameters from a stimulation backend¶

The parameters in this stimulation device can be updated with input coming from a stimulation backend. The data structure used for the update holds one value for each of the parameters mentioned above. The indexing is as follows:

1. amplitude

2. offset

3. frequency

4. phase

## References¶

1

Rotter S and Diesmann M (1999). Exact digital simulation of time- invariant linear systems with applications to neuronal modeling, Biol. Cybern. 81, 381-402. DOI: https://doi.org/10.1007/s004220050570

CurrentEvent