Converting continuous signal to digital signal

Questions
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1

Hi,
I am trying to create a neuron model that fires action potentials (spikes) when a certain threshold is reached. The spikes are slowly reduced and eventually reaches noise level in the refractory period and again fires after the refractory period. The initial input is a continuous signal.
Thanks

2

Hi Lakshmi,

You can use events (if, when statements) to convert your continuous signal to discrete signals. A simple model that mimics the first part of your case is as follows:

model Model
  Real contSignal;
  Real outputSignal(start = 1);
  parameter Real slope = 2;
  parameter Real threshold = 5;
equation
  der(contSignal) = slope;
  if contSignal < threshold then
    der(outputSignal) = 0;
  else
    der(outputSignal) = -outputSignal;
  end if ;
3

Hi Ankit,
What does the slope do? I tried to use this code in system modeler. I used an exponential sine wave (from the modelica blocks library) as my source with an amplitude of 10. I used a slope of 2 and threshold of 5, but I get an output signal of 0 amplitude (a flat signal). Please let me know.
Thanks
Lakshmi

4

I think you want to do this. ‘Slope’ was just a parameter I used to define the continuous signal.

    model EventGen
      Modelica.Blocks.Sources.ExpSine source(amplitude = 10, freqHz = 1, damping = 1) ;
      parameter Real threshold = 1;
      Real outputSignal(start = 0);
    equation
     der(outputSignal) = -outputSignal;
      when source.y < threshold then
      reinit(outputSignal,1);
    end when;
    end EventGen;