Which errpreset takes precedence, APS accuracy+speed or tran analysis?

Dear fireonthesee,

The errpreset you selected in the transient analysis GUI panel will be chosen for the transient analysis. I just checked by selecting an errpreset of “liberal” in the APS GUI panel and an errpreset of “conservative” in the transient analysis GUI panel for the version of Cadence I am using and the latter is selected for the transient analysis. Two comments if I may...

1. An easy way to check the value of errpreset used is to examine the relevant analysis statement in the netlist file (input.scs file in the netlist directory), I am displaying the transient analysis command for the test case I performed below:

tran tran stop=210n errpreset=conservative noisefmax=10e9 noisefmin=1 \
noiseseed=1 noisescale=1 noiseoff=[ R12 E2 V25 C3 C2 E12 E11 E9 E10 \
C6] maxstep=1e-12 write="spectre.ic" writefinal="spectre.fc" \
annotate=status maxiters=5

2. Within the APS GUI panel, you should see a “Do not override” radio button under the Accuracy Setting”. Selecting this option will guarantee your APS errpreset option has a lower priority than the value you select in an analysis.

Does this help fireonthesee?

Shawn

Hi Shawn,

Actually, the setting on the High Performance Simulation form does override the transient analysis setting (the clue is in the presence of the "Do not override" choice; if it didn't override, there would be no need to have that button).

The point is that when setting APS you may well want to override the settings that an individual has put on the analysis. It's not unusual for users to overdo the accuracy settings unnecessarily.

If you specify it on the High Performance Simulation form for APS then errpreset gets passed on the command line and the netlist retains the analysis options as on the form. The way you can tell what it's doing is to look at the Important parameter values section of the output log. In this case below I had moderate on the tran form and liberal on the High Performance Simulation form:

***********************************************
Transient Analysis `tran': time = (0 s -> 1 us)
***********************************************
DC simulation time: CPU = 2.999 ms, elapsed = 3.21388 ms.

Opening the PSFXL file ../psf/tran.tran.tran ...
Important parameter values:
start = 0 s
outputstart = 0 s
stop = 1 us
step = 1 ns
maxstep = 20 ns
ic = all
useprevic = no
skipdc = no
reltol = 10e-03
abstol(V) = 1 uV
abstol(I) = 1 pA
temp = 27 C
tnom = 27 C
tempeffects = all
errpreset = liberal
method = trapgear2
lteratio = 3.5
relref = sigglobal
cmin = 0 F
gmin = 1 pS
rabsshort = 1 mOhm

As you can see, the result was liberal (the other red settings are because of liberal having been picked).

Regards,

Andrew.

Hi Andrew,

Hmmm...very interesting. Is there any chance the behavior has changed with IC version?

Unlike the case you are showing, the behavior I am experiencing is not consistent with your result. I've attached a png of my High Performance Simulation and Transient analysis GUI panels noting the difference in errpreset settings. In the second png I've included, I'm showing two sections of the resulting spectre.out file. As you correctly indicated the "liberal" setting is passed on the spectre command line. However, in the transient analysis summary (which I am quite familiar with), note that an errpreset of "conservative" is selected - consistent with the transient analysis command line in the input.scs file for the transient analysis and transient analysis GUI panel. I've also displayed the IC and MMSIM versions I am using in case there has been a change in the behavior....

My apologies, to both fireonthesee and you, if I am overlooking something!  However, I did check the behavior prior to responding to fireonthesee as I was trying to be sure my response was accurate...(sigh)...

Shawn

Hi Andrew,

Hmmm...very interesting. Is there any chance the behavior has changed with IC version?

Unlike the case you are showing, the behavior I am experiencing is not consistent with your result. I've attached a png of my High Performance Simulation and Transient analysis GUI panels noting the difference in errpreset settings. In the second png I've included, I'm showing two sections of the resulting spectre.out file. As you correctly indicated the "liberal" setting is passed on the spectre command line. However, in the transient analysis summary (which I am quite familiar with), note that an errpreset of "conservative" is selected - consistent with the transient analysis command line in the input.scs file for the transient analysis and transient analysis GUI panel. I've also displayed the IC and MMSIM versions I am using in case there has been a change in the behavior....

My apologies, to both fireonthesee and you, if I am overlooking something!  However, I did check the behavior prior to responding to fireonthesee as I was trying to be sure my response was accurate...(sigh)...

Shawn