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Transient Analysis in PSS (Read 10182 times)

The_One

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Transient Analysis in PSS
Dec 18^th, 2003, 11:02pm

Hi....

I have a problem with my ckt.
My ckt is some sort of mixed signal ckt. it is a fully differential opamp with Switched cap CMFB.

I want to test its slewing rate and its settling time.
Therefore i connected my ckt in the same configuration as suggested in the http://www.designers-guide.com/Analysis/diff.pdf

but the problem is the conventional trans analysis could not be used since there are also two clocks incorporated.

I have also read that PSS can do it. is it true? would you suggest the simulation setup i can use? e.g. the tstab, tstart, etc.

Thanks a lot.

ps: fyi, my opamp specification is 100dB gain Shocked

, 150MHz GBW.

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Ken Kundert

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Silicon Valley

Re: Transient Analysis in PSS
Reply #1 - Dec 18^th, 2003, 11:42pm

Hmmm. Fully differential amplifier with switched-capacitor common-mode feedback. There seems to be a lot of those out and about these days.

So why is it that you feel you cannot simulate slew rate and settling time using transient analysis? You indicate it is because of the clocks, but I don't understand how the clock interfere.

PSS anc PAC/PNoise can be used to compute the small-signal characteristics of the circuit (transfer characteristics, noise, etc. with the clock present), it is not really for transient behavior such as slew rate and settling time. You can find out more about using SpectreRF to simulate switched-capacitor circuits by reading "Simulating switched-capacitor filters with SpectreRF" at http://www.designers-guide.com/Analysis/.

-Ken

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The_One Junior Member Offline Posts: 14	Re: Transient Analysis in PSS Reply #2 - Dec 19^th, 2003, 12:10am Hi, so you mean that the conventional tran analysis should be able to do that? Thx.
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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: Transient Analysis in PSS Reply #3 - Dec 19^th, 2003, 12:57am Sure, why not? -Ken
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The_One Junior Member Offline Posts: 14	Re: Transient Analysis in PSS Reply #4 - Dec 19^th, 2003, 1:26am Hi, Ken...i have tried to do it just now, but it cant work...weird....do you have any other suggestion how to perform the Tran analysis? can PSS do the tran analysis? Thx
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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: Transient Analysis in PSS Reply #5 - Dec 19^th, 2003, 8:27am I must be missing something. Can you explain exactly what you are trying to do and why it does not work? -Ken
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The_One Junior Member Offline Posts: 14	Re: Transient Analysis in PSS Reply #6 - Dec 19^th, 2003, 7:10pm Hi Ken, I have sent u a pm... thanks for your help.
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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: Transient Analysis in PSS Reply #7 - Dec 20^th, 2003, 2:33pm I recommend you also read http://www.designers-guide.com/Forum/?board=analog_design;action=display;num=107... -Ken
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The_One

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Re: Transient Analysis in PSS
Reply #8 - Dec 25^th, 2003, 6:41pm

[quote author=Ken Kundert link=1071817367/0#7 date=1071959620]I recommend you also read http://www.designers-guide.com/Forum/?board=analog_design;action=display;num=107...

-Ken [/quote]

Hi Ken,

are there any guidelines to design the SC CMFB? in most of the books, there is only explanation how it works, but no design guidelines mentioned, eg. how large is the cap 1 and cap 2, how fast should i clock it.

Thanks for your help.

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Paul Community Fellow Offline Posts: 351 Switzerland	Re: Transient Analysis in PSS Reply #9 - Dec 28^th, 2003, 12:01pm Hi, You must define the minimum equivalent resistance your amplifier can drive, this gives the upper limit to the capacitance value - clock frequency product. The lower limit of this product is given by loss of accuracy due to leakage currents and other practical issues. Paul
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