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[SpectreMDL] Rise time not founf in transient analysis

iamKarthikBK

Hello.

I am trying to perform a few simulations, and I am unable to use the risetime function in spectremdl whereas the same expression is successfully evaluated in the calculator.
Here is my output in ViVA:



Here is the expression that evaluates successfully in the calculator:
riseTime(v("/OUT" ?result "tran") 0 nil 300m nil 10 90 nil "time" )

Here is the expression I have written within a measurement alias in spectremdl:
export real my_rise=risetime(sig=V(OUT), initval=0.0, inittype='y, finalval=0.3, finaltype='y, theta1=10, theta2=90)

Here is how the analysis is defined in the spectre netlist input.scs:
tran tran stop=1u write="spectre.ic" writefinal="spectre.fc" \
annotate=status maxiters=5

Here is how the analysis is defined in the measurement alias:
run tran( stop=1u, autostop='yes )

Can someone please tell me if I am making a mistake in either of these places? The calculator I talk about is the one accessed through ViVA (Send to calculator)
The expression successfully evaluates to some value 1.026E-9 as expected from the circuit.

Thanks in advance!

Parents
  • Andrew Beckett

    Well, it works for me. Here's my simple netlist:

    // simple example

Vout (OUT 0) vsource type=pulse rise=10n edgetype=halfsine val0=0 val1=300m \
  delay=0.1u width=0.4u 
Rout (OUT 0) resistor r=1k

tran tran stop=1u write="spectre.ic" writefinal="spectre.fc" \
annotate=status maxiters=5

    Here's the MDL:

    alias measurement trans {
    run tran( stop=1u, autostop='yes )
    export real my_rise=risetime(sig=V(OUT), initval=0.0, inittype='y, finalval=0.3, finaltype='y, theta1=10, theta2=90)
}

run trans

    Running:

    spectremdl -design forum.scs -batch forum.mdl

    gives this in the forum.measure file:

    Exported variables from results directory:  ./forum.raw/

date               :  1:16:03 PM, Sun Dec 5, 2021
design             :  //
simulator          :  spectre
version            :  20.1.0.382.isr12


Measurement Name   :  trans
Analysis Type      :  tran
my_rise               =  5.90338e-09

    and this matches what I get from running (note, I removed the / from before OUT because I'm running from a typed-in netlist rather than having a schematic, so no need to do the schematic to netlist name mapping that VIVA would do otherwise):

    riseTime(v("OUT" ?result "tran") 0 nil 300m nil 10 90 nil "time" )

    gives: 5.9033806E-9

    Andrew

  • iamKarthikBK
    in reply to Andrew Beckett

    Update:
    Seems like that is my circuit. for some particular sizes, spectre is unable to calculate the risetime because the waveform is different.



    Is there a way I can tell spectre to ignore points that result in NaN?
    Thanks

  • Andrew Beckett
    in reply to iamKarthikBK

    I don't really understand what you mean by "ignore points that result in NaN". Surely it won't know that until its tried the problematic sizes? That said, it does seem a bit odd that some of those sizes are very close to one that works OK.

    Perhaps you should contact customer support - it's really hard to see this without understanding the real problem.

    Andrew

Reply
  • Andrew Beckett
    in reply to iamKarthikBK

    I don't really understand what you mean by "ignore points that result in NaN". Surely it won't know that until its tried the problematic sizes? That said, it does seem a bit odd that some of those sizes are very close to one that works OK.

    Perhaps you should contact customer support - it's really hard to see this without understanding the real problem.

    Andrew

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