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Simulators >> Circuit Simulators >> stb and noise analysis fail at 125C
https://designers-guide.org/forum/YaBB.pl?num=1325593107

Message started by ywguo on Jan 3^rd, 2012, 4:18am

Title: stb and noise analysis fail at 125C
Post by ywguo on Jan 3^rd, 2012, 4:18am

Hi Guys,

I ran dc, ac, stb, and noise analysis for a voltage buffer that is implemented in 40nm LL technology. The stb and noise fail in almost all corners at 125 degree Celsius, but dc and ac analysis have good results.

For example, the stb and noise analysis fail at 125 degree Celsius if all devices are in ss corner. But I get expected stb and noise results at 124 degree Celsius. In other corner combinations, I cannot get correct stb and noise analysis results even at 124 degree Celsius.

Title: Re: stb and noise analysis fail at 125C
Post by ywguo on Jan 3^rd, 2012, 4:21am

This is the correct results at 124 degree Celsius.

I think this is probably a spectre model fault. But what can I do to verify it?

Best Regards,
Yawei

Title: Re: stb and noise analysis fail at 125C
Post by rfidea on Jan 3^rd, 2012, 12:32pm

Looks definitly like a model/simulator error, or a combination. You should send the test case to either the simulator vendor or the PDK vendor. Usually there is very difficult for the user to know in which the bug is.

Title: Re: stb and noise analysis fail at 125C
Post by raja.cedt on Jan 3^rd, 2012, 3:45pm

did you check the output file regarding some warnings like some kind of jakobian error, once i got this kind of error which some kind of convergence error, try tp initialize some node may be help full.

Thanks,
Raj.

Title: Re: stb and noise analysis fail at 125C
Post by ywguo on Jan 3^rd, 2012, 7:59pm

I find that Operating points had not been recomputed when stb and noise failed. It seemed that the simulator found DC solution for AC analysis and skipped this step for the succeeding stb and noise analysis.

Quote:

******************************************
AC Analysis `ac': freq = (1 Hz -> 100 GHz)
******************************************
Finding DC approximate solution failed. Try again with try_fast_op set to no.
Trying `homotopy = gmin'.
Trying `homotopy = source'.
Trying `homotopy = dptran'.

...
...

**************************************************
Stability Analysis `stb': freq = (1 Hz -> 100 GHz)
**************************************************

Notice from spectre during STB analysis `stb'.
Operating points will not be recomputed: the circuit and conditions were not changed since previous analysis.

...
...

************************************************
Noise Analysis `noise': freq = (1 Hz -> 100 GHz)
************************************************

Notice from spectre during Noise analysis `noise'.
Operating points will not be recomputed: the circuit and conditions were not changed since previous analysis.

I select DC analysis and stb only in ADE-L. Now the simulator finds DC solutions for stb analysis and gives correct loop response.

Yawei

Title: Re: stb and noise analysis fail at 125C
Post by ywguo on Jan 3^rd, 2012, 8:01pm

Tools are spectre sub-version 10.1.1.056.isr5, and IC6.1.4.500.9. I choose APS and Auto for Mutlithreading options.

Yawei

Title: Re: stb and noise analysis fail at 125C
Post by ywguo on Jan 9^th, 2012, 3:26am

This problem has been resolved when I replace spectre simulator with sub-version 11.1.0.249.isr2.

Yawei