Designer’s Guide Community

pancho_hideboo

Senior Fellow

Offline

Posts: 1424
Real Homeless

Re: Signal exceeds blowup quantity
Reply #30 - Sep 17^th, 2010, 8:55am

Ken Kundert wrote on Sep 17^th, 2010, 8:48am:

I am convinced that the circuit contains a negative inductor and so is unstable.

No.
This is "Internal Unstability" problem.
http://www.designers-guide.org/Forum/YaBB.pl?num=1190272820/18#18

You always never admit defect and weak points of Cadence Spectre.

Anyway Cadence Spectre very tends to diverge esepecially in Shooting-Newton.
http://www.designers-guide.org/Forum/YaBB.pl?num=1284058751/4#4

Ken Kundert wrote on Sep 17^th, 2010, 8:48am:

In general, using a coupling factor of 1 is almost always wrong.

We can never realize K=1.0.
I always set K < 0.99 even for pure frequency domain analysis such as AC and SP Analyses.

Back to top

Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

IP Logged

pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: Signal exceeds blowup quantity Reply #31 - Sep 17^th, 2010, 9:10am When Rp=0.1ohm, no RHP poles are reported. But this is not canceling of RHP pole by zero. This is simply short of negative inductor.
Back to top	test_Negative_L_sch.png Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!! http://www7.plala.or.jp/ungeromeppa/flash/kita.html http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related IP Logged

pancho_hideboo

Senior Fellow

Offline

Posts: 1424
Real Homeless

Re: Signal exceeds blowup quantity
Reply #32 - Sep 17^th, 2010, 9:11am

Attached is a result of Transient Analysis of Cadence Spectre.

Here it results in "blowup" after 30nsec for Rp=1.0ohm.
"Rp=0.1ohm" never results in "blowup".

Synopsys HSPICE gives completely same result regarding Transient Analysis.

But results of Pole-Zero analysis are completely different between Cadence Spectre and Synopsys HSPICE.

Pole-Zero analysis of HSPICE have very long history.
On the other hand, Cadence Spectre don't have much history regarding Pole-Zero Analysis.

I also don't think Agilent GoldenGate is reliable since originally it has been developed by Xpedion.

Back to top

test_Negative_L_out.png

Kita━━━━━━(ﾟ∀ﾟ)━━━━━━ !!!!!
http://www7.plala.or.jp/ungeromeppa/flash/kita.html
http://www.youtube.com/watch?v=mjIxGh55bMM&feature=related

IP Logged

sheldon

Community Fellow

Offline

Posts: 751

Re: Signal exceeds blowup quantity
Reply #33 - Sep 17^th, 2010, 10:16am

Matteo,

� It probably was discussed earlier and I just missed it. Could you
explain why L7, K2/L5/R10, and L8, K3/L7/R7, have eddy current loss
but L6 and L9 do not have eddy current loss? Also are all the mutual
inductances included, there is no L0/L8 or L1/L9 inductance?

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Best Regards,

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Art Schaldenbrand

Back to top

IP Logged

Ken Kundert

Global Moderator

Offline

Posts: 2384
Silicon Valley

Re: Signal exceeds blowup quantity
Reply #34 - Sep 17^th, 2010, 11:40am

Quote:

You always never admit defect and weak points of Cadence Spectre.

Pancho Hideboo,
� �In this case I am defending Spectre's transient analysis because I believe it is giving the right answer. The circuit contains a negative inductance, of course the circuit is unstable. Spectre correctly reports that instability, and HSpice does not. Your argument that you can somehow make the circuit stable by using either a very large or very small resistor is incorrect. Even the circuit you give to prove your point is unstable, as you will see if you simulate it for 1us (when you reduce the value of the resistor you increase the time constant of the LR circuit, so you have to simulate for longer to see the waveform explode).

-Ken

Back to top

IP Logged