Designer’s Guide Community

raja.cedt Senior Fellow Offline Posts: 1516 Germany	pole/zero analysis Jun 08^th, 2009, 10:45pm hi, In hspice i am getting list of all poles and zero's, i just want to know in hspice is there any way to find which pole is corresponding to which node. I used to see every node phase shift whichever have more shift that is dominant and remaining also like that only, but what abut complex poles? thanks for your time rajasekhar.
Back to top	IP Logged

buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: pole/zero analysis Reply #1 - Jun 9^th, 2009, 12:31am Hi Rajasekhar, Question: Why do you expect that each pole does correspond to a certain node within the circuit ? Think of an active filter of 2nd degree. The complete circuit may exhibit 2...4 nodes (sometimes even more) - and which node belongs to the pole ? It can�t be answered.
Back to top	LvW (buddypoor: In memory of the great late Buddy Rich) IP Logged

raja.cedt

Senior Fellow

Offline

Posts: 1516
Germany

Re: pole/zero analysis
Reply #2 - Jun 9^th, 2009, 1:04am

hi buddypoor,
thanks for your answer and what my intension is lets say hspice gave some 6 poles now i want to move 2nd and 3rd dominate pole to higher value, so i need which node is giving those poles so that i can compensate them. Interestingly in one my opamp 2nd dominate pole is complex i just want from where it is originated?

Thanks
Rajasekhar.

Back to top

IP Logged

buddypoor

Community Fellow

Offline

Posts: 529
Bremen, Germany

Re: pole/zero analysis
Reply #3 - Jun 9^th, 2009, 4:40am

Yes, I understand the problem. However, for my understanding a real pole belongs ton RC combination (not necessarily to be identified as a single R or a single C) and , theoretically, it can be allocated to one specific node. But a complex pole pair belongs either to an LC resonance circuit (not in your case) or to a part which includes some sort of feedback - and that�s a circuitry which certainly has more than one node. However, it should be possible to identify this part of the circuit - at least by inspecting/modifying the capacitances belonging to it. Would this approach work ?
LvW

Back to top

LvW (buddypoor: In memory of the great late Buddy Rich)

IP Logged

raja.cedt

Senior Fellow

Offline

Posts: 1516
Germany

Re: pole/zero analysis
Reply #4 - Jun 9^th, 2009, 5:17am

hi,
i will try but i am getting complex pole for an telescopic op amp in open loop, up to my knowledge there shouldn't be any complex for open loop. For finding pole if you see particular node wave form that will have more phase advance (means node associated with dominate will give phase shift earlier than 2nd dominate and complex pole means phase shift from 0 180 suddenly.)

thanks,
rajasekhar.

Back to top

IP Logged

buddypoor

Community Fellow

Offline

Posts: 529
Bremen, Germany

Re: pole/zero analysis
Reply #5 - Jun 9^th, 2009, 5:39am

raja.cedt wrote on Jun 9^th, 2009, 5:17am:

hi,
� �i will try but i am getting complex pole for an telescopic op amp in open loop, up to my knowledge there shouldn't be any complex for open loop................
.............................

In this case, there should be a hidden feedback path within your circuitry (for example CB-capacitances).

Back to top

LvW (buddypoor: In memory of the great late Buddy Rich)

IP Logged

raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: pole/zero analysis Reply #6 - Jun 9^th, 2009, 9:04am hi buddypoor, � � � � � � � � � �your guess is correct, but it less gain loop i think you can visualize whats the loop (It is a nmos based telescopic opamp and pmos load is diode with wide swing) ,so may be that's the culprit.. thanks, Rajasekhar.
Back to top	IP Logged