The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> LDO Line transients simulation in Spectre
https://designers-guide.org/forum/YaBB.pl?num=1259380759

Message started by Dipankar on Nov 27^th, 2009, 7:59pm

Title: LDO Line transients simulation in Spectre
Post by Dipankar on Nov 27^th, 2009, 7:59pm

Dear Experts,
Yesterday I hit an interesting thing. I was running transient analysis in Spectre to check my LDO line regulation by ramping up and down the VDD using a square wave pulse. For both Errpreset = Conservative and Moderate. The output was stable - no ringing observed.

Now by default Spectre choose Gear2Only alogorithm when you take Errpreset = Conservative. I was affraid whether Gear2Only is subduing any ringing actually may present in the circuit. So I changed the algorithm to Trap, Traponly , TrapGear2. And to my horror all of these algorithms was showing ringing at the output. Then I force the step and maxstep to be really small ( smaller than the VDD rise time) Gear2Only also started showing ringing. It prompted me to increase the PM of one loop causing potential instability.

But I am affraid from now on whether "Conservative" with Gear2Only is safe. Because normally we dont change any simulator setting and just choose the errpreset from ADE setting.

Hope you already have faced this kinds of experience. Looking to hear from you all.

Title: Re: LDO Line transients simulation in Spectre
Post by pancho_hideboo on Nov 28^th, 2009, 12:00pm

See http://www.designers-guide.org/Forum/YaBB.pl?num=1243078889,
although it might be of no use.

Also see http://www.designers-guide.org/Forum/YaBB.pl?num=1237627988/5#5