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Simulators >> Circuit Simulators >> How to set piecewise function (pwl) in spectre
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Message started by Vivek Chandrasekhar on Feb 12^th, 2005, 7:08pm

Title: How to set piecewise function (pwl) in spectre
Post by Vivek Chandrasekhar on Feb 12^th, 2005, 7:08pm

Hi,

I had a problem setting a piecewise linear function as an input. The problem is that the input signal remains zero all the time after simulation . In the spectre simulator, i set the time 1, voltage 1, time 2, voltage 2 accordingly. I want one of my input B0 to be 0V for 200 ps , 1.2 V for the next 400ps, 0 for 800ps, 1.2V for next 400 p and 0 V for next 200 ps.The total time for this one cycle is 2000ps. This waveform should continue for 100 cycles. The total time then becomes 200ns.
I notice that in my spectre simulator when i run the simulation , input signal remains zero all the time eventhough i set the values correctly in piecewise linear format.
I would be grateful to anyone who could help me solve this problem.
Thanks

Vivek

Title: Re: How to set piecewise function (pwl) in spectre
Post by Ken Kundert on Feb 12^th, 2005, 9:18pm

You have to set the type parameter on the source, to pwl I think.

-Ken

Title: Re: How to set piecewise function (pwl) in spectre
Post by Vivek Chandrasekhar on Feb 13^th, 2005, 8:33am

Hi Ken,

Thanks for your suggestions. But, then i have already set the type parameter on the source to be pwl .

Thanks

Vivek

Title: Re: How to set piecewise function (pwl) in spectre
Post by Andrew Beckett on Feb 13^th, 2005, 10:00am

I suggest you post the source, and the analysis statement, from your netlist. That will allow us to give you some relevant advice.

I don't know if you're creating the netlist from the Analog Design Environment, or hand-writing the netlist? If using ADE, then pick the vsource component and set the type to "pwl" as Ken said, and enter the time-value pairs.

This should be quite straightforward - it's hard to know what you could have possibily got wrong!

Regards,

Andrew.

Title: Re: How to set piecewise function (pwl) in spectre
Post by Vivek Chandrasekhar on Feb 13^th, 2005, 3:11pm

Hi Andrew,

I am using the Affirma Analog Circuit Design environment. The netlist is created from it. The simulator is spectre
My analysis is
type= tran , arguments = 0 to 2n
My source is(Analog stimulus from source)
function pwl type voltage
source type=pwl
time1= 0p
voltage1= 0.0
time2 =0.000001p
voltage2=0.0
time3=200p
voltage3=0.0
time4=200.000001p
voltage4=1.2
time5=600p
voltage5=1.2
time6=600.000001p
voltage6=0.0
time7=1400p
voltage7=0.0
time8=1400.000001p
voltage8=1.2
time9=1800p
voltage9=1.2
time10=1800.000001p
voltage10=0.0
time11=2000p
voltage11=0.0

The input signal instead of being a piecewise linear signal remains zero all the time.

Thanks

Vivek
l

Title: Re: How to set piecewise function (pwl) in spectre
Post by Andrew Beckett on Feb 14^th, 2005, 3:10am

From the way you describe it, I assume you're setting up the stimulus with Setup->Stimuli in the Analog Design Environment window, rather than using a component (such as vsource, vpwl etc from analogLib) in your schematic.

If so, I think the most likely problem is that you've not set the "Number of pairs of points" parameter (which defaults to 2). Your first two points are at 0V, and so that would explain it.

If you had been adding the component to your schematic, this parameter controls the display of the time/voltage pair fields, and so you wouldn't have been able to set the values without increasing that. The Setup->Stimuli form is rather more primitive, and doesn't dynamically update the form based on the value of this parameter - but it _would_ be used to control how many points are netlisted, I think.

Try setting Number of pairs of points to 11, and see what happens.

Regards,

Andrew.

Title: Re: How to set piecewise function (pwl) in spectre
Post by Vivek Chandrasekhar on Feb 15^th, 2005, 8:36am

Hi Andrew,

I changed the number of time-voltage pairs to 11. I dont have any problem right now.
Thanks a lot for your guidance.

Vivek