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spectre bsource for current stimuli

saumyaj

Hi,

I am a new spectre user. 

I need to implement a current stimuli which starts at a time tstart >0, has a linear rise till a certain time trise until the current reaches a peak Ipeak and then has an exponential fall with time constant taufall.

I understand that I can implement an exponential function : Ixy (x y) bsource I=Ipeak*exp(-($time - trise)/taufall)

But how can join the linear rise part to this? 

This is not a periodic source.

I would also like to add, when I try the similar function with an inhouse SPICE simulator, I have the possibility of using an if else statement in behavioral source, which functions like below :

if time <= trise + tstart, then 

     if time < tstart

       Ixy = 0

    else

     Ixy … defining a pwl function

else

I=Ipeak*exp(-($time - trise)/taufall)

Is something similar possible in spectre?

  • Andrew Beckett

    Yes, this is possible with the "ternary" operator condition?thenExpr:elseExpr which allows you to do this kind of thing in-line. I don't have time right now to put together your example, but it might help if I showed one I created a few years ago. Before spectre supported the edgetype=halfsine option on a vsource (which I requested for a customer), I implemented this using a bsource:

    //

inline subckt sinsq (a b)
parameters rise=1n fall=1n period=20n width=10n delay=1n v1=1 v2=5 pi=3.1415926535
sinsq (a b) bsource v=\
($time-floor($time/period)*period)<delay?v1:\
($time-floor($time/period)*period)<delay+rise?\
cos((($time-floor($time/period)*period)-delay-rise)*pi/rise)*(v2-v1)/2+(v1+v2)/2:\
($time-floor($time/period)*period)<delay+rise+width?v2:\
($time-floor($time/period)*period)<delay+rise+width+fall?\
cos((($time-floor($time/period)*period)-delay-rise-width)*pi/fall)*(v2-v1)/2+(v1+v2)/2:\
v1
ends sinsq

v1 (1 0) sinsq rise=2n fall=2n

tran tran stop=40n maxstep=0.01n

    The idea is that it's a pulse source with the rise and fall parts replaced with half a sine wave, and so this uses the ternary operators to piece-wise join up the segments of the waveform as needed. I could have just used M_PI instead of defining pi (not sure why I didn't do that). Anyway, hopefully this gives you some idea as to how you could go about it?

    Regards,

    Andrew.

  • saumyaj
    in reply to Andrew Beckett

    Dear Andrew,

    Thank you so much for your reply. I am impressed by your response time. Your solution certainly worked!!

    I used the ternary operators in SPICE, however forgot the keyword "ternary". Thanks a lot once more.

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