Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

help needed,Stability analysis and noise analysis

Status
Not open for further replies.

ASICK

Junior Member level 3
Joined
Apr 22, 2005
Messages
30
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Location
san jose,ca
Activity points
1,585
I need help with the Stability analysis and noise analysis, as how to run these using Spectre in cadence.
1. During stability analysis, what to choose for probe instance, and
how does this analysis work? if you could explain that will be great.
2. During noise analysis, there are 2 options, like input noise and output noise and for each there is option of choosing prove, voltage nd current. how does this analysis work? and what are these options about? I must have asked a lot at one time, but will really appreciate ur help and time,
thanks
 

sunking

Advanced Member level 3
Joined
May 25, 2004
Messages
873
Helped
70
Reputation
140
Reaction score
23
Trophy points
1,298
Activity points
6,283
1. open loop
The phase margin(Gain =0)
normal PM>45
2. read the candence open book
 

starcoming

Member level 1
Joined
Sep 8, 2005
Messages
40
Helped
2
Reputation
4
Reaction score
1
Trophy points
1,288
Activity points
1,630
1 it is better to be sure a pm>60 at the Unit GB point.
 

victoriya

Member level 2
Joined
Oct 26, 2010
Messages
50
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
1,594
stability for what kind of circuit?
meanwhile the pm have to be>70
 

threekingtiger

Member level 1
Joined
Jul 31, 2010
Messages
38
Helped
8
Reputation
16
Reaction score
8
Trophy points
1,288
Activity points
1,564
There are two ways to test the stability of the loop. One is that you can open your loop by inserting the testing elements, which are a very very large ideal cap, a very very large inductance and an AC small signal source, then perform AC analysis to see the AC maganitude and phase. You will get the BODE plot in which the PM, GM and GBW can be easily obtained. The other way more simple is using the STB analysis in spectre. Break the loop by inserting an iProbe from analoglib library. Perform the stb anlysis. Initiate the waveform window and PM GM and GBW can be read. Also this analysis can give you the bode plot. The latter method is what I used often in practice.
 

leo_o2

Advanced Member level 4
Joined
Sep 3, 2004
Messages
1,322
Helped
278
Reputation
558
Reaction score
241
Trophy points
1,343
Location
China
Activity points
5,761
Insert a voltage source into the loop. The voltage source is used to break the loop in stb analysis.
Output noise can be converted into an equivalence of input noise. And input noise can be converted into an equivalence of output noise too.
I need help with the Stability analysis and noise analysis, as how to run these using Spectre in cadence.
1. During stability analysis, what to choose for probe instance, and
how does this analysis work? if you could explain that will be great.
2. During noise analysis, there are 2 options, like input noise and output noise and for each there is option of choosing prove, voltage nd current. how does this analysis work? and what are these options about? I must have asked a lot at one time, but will really appreciate ur help and time,
thanks
 

jjx

Full Member level 3
Joined
Sep 12, 2008
Messages
168
Helped
40
Reputation
86
Reaction score
55
Trophy points
1,308
Location
Scania
Activity points
2,627
It could also be mentioned that rather than using the large L and C approach as per above, you have a couple of sptXswitch cells available in the analogLib. They are quite powerful (once one learns how to understand what the position buttons mean ...)

And indeed, the definition of phase margin is quite system dependent... There are quite a few rule-of-thumb's out there, but traditionally they consider only the two-pole idealized model. For example, certain comparators and regulators would follow other "laws".
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,861
Helped
1,749
Reputation
3,504
Reaction score
1,353
Trophy points
1,393
Location
Germany
Activity points
39,804
..................
And indeed, the definition of phase margin is quite system dependent... There are quite a few rule-of-thumb's out there, but traditionally they consider only the two-pole idealized model. For example, certain comparators and regulators would follow other "laws".

Hopefully, nobody in the forum believes this.
There is only one single and general definition for the phase margin, which is applicable for any system with feedback.
This definition - and several methods to determine the margin - was presented and discussed several times in this forum.
 
Last edited:

jjx

Full Member level 3
Joined
Sep 12, 2008
Messages
168
Helped
40
Reputation
86
Reaction score
55
Trophy points
1,308
Location
Scania
Activity points
2,627
Yes, you're right, I was referring to the target value of the phase margin (45, 60, 70, etc), not the definition as such.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,861
Helped
1,749
Reputation
3,504
Reaction score
1,353
Trophy points
1,393
Location
Germany
Activity points
39,804
Yes, you're right, I was referring to the target value of the phase margin (45, 60, 70, etc), not the definition as such.

OK, that's right. There are, of course, different requirements as far as the target specification for the PM is concerned.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top