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PSS does not converg

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Saraadib

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Hi All,
I design a kind of switch capacitor filter which include a clock generator that create 4 non overlap clock to drive the switch for switch capacitor filter.

So,I have done simulation for 1GHZ and 1.25GHz (clock frequency).
The problem is for fclck=1GHz,schematic and RLC extraction works but For fclck=1.25GHz , schematic work but RLC extraction simulation ,PSS does not converge.

I should mention that I use PSS+PAC to simulate the filter response.

I have attached the log file for more information
Any body have idea how to solve converge problem for PSS?

Here is my log file:

Code dot - [expand]
1

 
 

It would be nice to have netlist part with analysis definition and simulator options.
However, in Spectre documentation - you can find it in spectre installation directory/doc/spectreref/ (or by CIW→Help→type spectre in search bar and look for user guide in help window) is whole section describing troubleshooting for PSS convergence issue. I would start from this point and following these tips.

Also, enabling a save transient option in PSS and look on waveforms to check whether everything works properly is a good idea.
 

I have upload netlist.
 

Attachments

  • netlist.txt
    5.9 MB · Views: 71

First try to reduce accuracy, e.g. errpreset=liberal or moderate.

Increase tstab.
Or adjust tstab, e.g. 5.1n, 5.2n, etc.
 
Hi Pancho,
Thanks for your reply
Actullay,I increase tstab,but it did not help.The problem is schematic work for this frequency,but RLC extraction did not work
did you see my netlist that I have attached?
 

Thanks Pancho, I adjust tstab for 5.1 and it does not still converge.
how should I adjust tstab?I should just play around with this number?
Since I am doing RLC extraction simulation ,it takes too long to run the simulation.
 

Hi Pancho,
I did try to change accuracy: liberal and then play with tstab and adjust it to 5.1n,5.2n and 7n,but it is not converge yet.
I have attached netlist for tstab=7n and Accuracy :liberal
can you please help me how should I adjust tstab ?
 

Attachments

  • netlist2.txt
    17.4 MB · Views: 51

@pancho
I am wondering ,if you can help me how to adjust tstab ,I have try it for 5.1,5.2 ,7.5 and 10.Non of them does not converge,Also as you said I have changed the accuracy to liberal
 

what do you mean by adjusting step?do you mean adjusting tstab?
based on your advice,tstabe should be less that (1/1.25G/10=80ps)80Ps?
so,I have try tstab =5n or schematic,it converge but it did not converge for RLC extraction
 

Use correct terminologies.

You do post layout simulation with RLC extraction ?
It can converge for fclk=1GHz.
However it can not converge for fclk=1.25GHz.
Truely does it include L ?
Your circuit could be unstable, since Converge Norm is too large in Shooting-PSS.

BTW, “Schematic simulation”, such terminology does not exist.
It is pre layout simulation.

Use correct terminologies.
 
Last edited:

Yes,My schematic include L and C .I design N -path filter which include inductor ,capacitor and switch.
 
Last edited:

my circute inclulude L and C .
If it is unstable for 1.25GHz , the shooting-newton method can solve it ?
 

Saraadib said:
Yes,My schematic include L and C .I design N -path filter which include inductor ,capacitor and switch.
Click to expand...
Why don’t you extract R ?
Can it truely converge for fclk=1GHz ?

Saraadib said:
my circute inclulude L and C .
If it is unstable for 1.25GHz , the shooting-newton method can solve it ?
Click to expand...
It can not.

My schematic ? my circute ?

Use correct terminologies.

L are included in netlist of pre layout simulation ?

Or L are included only in netlist of post layout simulation ?
 
Last edited:

Yes,I use RLC extraction.
Yes,it can converg for fclck=1Ghz
my N-path filter include clcokgenrator which create 4 non overlapp clcok
 

pancho,
Thank you very much for your reply,
To be clear,I have attached the schematic of N-path filter.
I create layout for that and I did RLC extraction.
So,you ask why you do not do R extraction ?
Answer is:I did RLC exraction which consider parasitic of R,L and C that means I did R extraction too.
your qustion:L are included in netlist of pre layout simulation ?
Yes,I have L in netlist of pre layout simulation since I have inductor in my schematic.

your qustion:Or L are included only in netlist of post layout simulation ?
L are included in netlist of post layout simulation too.
My question is :If I assume that circuit is unstable ,why In pre layout simulation for 1.25Ghz it converge ,but in post layout si,ulation for f=1.25ghz does not converg?
 

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    12.png
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