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.