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Verilog-A model and temperature in AC-Sim

HoWei

I have a verilog-a model that is dependent on the simulation temperature, using the "$temperature" variable.

The temperature value changes vs. corner simulations. The simple model gives a voltage in dependence on the temperature.

The following code works:

analog begin

   V(out,vss) <+ $temperature-273.15*V(in,vss); //Input voltage is always 1V

end

This code does always give me 27 degC:

real temp_degC = 27;

analog begin

   temp_degC = $temperature-273.15;

   V(out,vss) <+ temp_degC*V(in,vss); //Input voltage is always 1V

end

Why is that and how can I make the model evaluating the "temp_degC" correctly ?

Parents

  • I figured, when I do not initialize the variable, it is evaluatting the variable value at runtime as expected and ist working:

    real temp_degC; //not initialized

    analog begin

       temp_degC = $temperature-273.15;

       V(out,vss) <+ temp_degC*V(in,vss); //Input voltage is always 1V

    end

    Why is that ?

    Is an initialized variable treated like a constant ?

  • in reply to HoWei

    This appears to be a bug. I've tried in various versions, and if the variable is initialized and then assigned to an expression including $temperature, it doesn't work. If instead the assignment within the analog block is:

    temp_degC=55.0;

    then it works (so it's not a constant). Also, if you do:

    @(initial_step) temp_degC=$temperature-273.15;

    then it also works. I filed CCR 1887528 for this - it would be a good idea if you report this to customer support yourself and request a duplicate CCR is filed (that way it is clear it's coming from a real customer) - however, I'm hopeful that we'll get this inconsistency fixed anyway.

    Regards,

    Andrew.

Reply
  • in reply to HoWei

    This appears to be a bug. I've tried in various versions, and if the variable is initialized and then assigned to an expression including $temperature, it doesn't work. If instead the assignment within the analog block is:

    temp_degC=55.0;

    then it works (so it's not a constant). Also, if you do:

    @(initial_step) temp_degC=$temperature-273.15;

    then it also works. I filed CCR 1887528 for this - it would be a good idea if you report this to customer support yourself and request a duplicate CCR is filed (that way it is clear it's coming from a real customer) - however, I'm hopeful that we'll get this inconsistency fixed anyway.

    Regards,

    Andrew.

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