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Simulators >> Circuit Simulators >> effective length less than or equal to zero?
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Message started by Bhupendra on May 3^rd, 2009, 12:55pm

Title: effective length less than or equal to zero?
Post by Bhupendra on May 3^rd, 2009, 12:55pm

Hi all,

I recently installed the AMI 0.6u NCSU design kit (C5N) and did a small simulation.

While spectre is able to generate the netlist it crashed and throws the following error:

Error found by spectre during initial setup.
ERROR (CMI-2213): I0.M0: Effective length is less than or equal to zero.

I checked the device length and it is set to 900n (min L = 600n)

Has anybody come across a similar problem while working the NCSU CDK?

I am in a fix right now as I cannot proceed from here on.
Any help/pointers in this regard would be really appreciated.

Regards,
Bhupendra

Ps.
The output log file is attached for reference.

Title: Re: effective length less than or equal to zero?
Post by Bhupendra on May 3^rd, 2009, 12:57pm

Just realized the forum would not allow me to attached txt files.
Attached is a snapshot of the log file.

-Bhupendra

Title: Re: effective length less than or equal to zero?
Post by Geoffrey_Coram on May 4^th, 2009, 7:49am

Check "input.scs" to make sure the 900n actually got there -- and that it didn't get scaled (eg, maybe the schematic entry tool expects values in microns, so you have (900n) um, which would be 900e-15m, and then a delta-L term could make it zero.

Try a longer drawn length, maybe delta-L is bad?

Try a different width.

Title: Re: effective length less than or equal to zero?
Post by Bhupendra on May 4^th, 2009, 8:01am

Hey Geoffrey,

Thanks a lot for the response.
You nailed the exact problem here!
That is precisely the reason. I figured it out yday itself.
Sorry for updating it so late in here for everyone else.

Turns out the schematic editor translates the W and L in micron so if I enter 1u it actually translates it as 1e-12 and hence the error.

Attached is the property window of one of the MOS. Here we enter the dimensions as W=3 and L=1 and the editor translates it to 3u and 1u respectively.

The interesting thing however was that irrespective of how we enter the W and L the input.scs (netlist) shows the dimensions correctly!

That brings me to couple of questions:

1) the W/L paramters (as in the picture) have # grids units associated with it. And in this current scheme it becomes humongous! Does that mean anything in terms of layout/pcells?

2) Is there a way I can set things the old fashioned way. Just enter the units along with the number?

-Bhupendra