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Design >> Analog Design >> Transient Analysis in PSS
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Message started by The_One on Dec 18^th, 2003, 11:02pm

Title: Transient Analysis in PSS
Post by The_One on 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 :o, 150MHz GBW.

Title: Re: Transient Analysis in PSS
Post by Ken Kundert on 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

Title: Re: Transient Analysis in PSS
Post by The_One on Dec 19^th, 2003, 12:10am

Hi,

so you mean that the conventional tran analysis should be able to do that?

Thx.

Title: Re: Transient Analysis in PSS
Post by Ken Kundert on Dec 19^th, 2003, 12:57am

Sure, why not?

-Ken

Title: Re: Transient Analysis in PSS
Post by The_One on 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

Title: Re: Transient Analysis in PSS
Post by Ken Kundert on 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

Title: Re: Transient Analysis in PSS
Post by The_One on Dec 19^th, 2003, 7:10pm

Hi Ken,

I have sent u a pm...

thanks for your help.

Title: Re: Transient Analysis in PSS
Post by Ken Kundert on Dec 20^th, 2003, 2:33pm

I recommend you also read http://www.designers-guide.com/Forum/?board=analog_design;action=display;num=1071672270;start=0#6

-Ken

Title: Re: Transient Analysis in PSS
Post by The_One on Dec 25^th, 2003, 6:41pm

Ken Kundert wrote on Dec 20^th, 2003, 2:33pm:

I recommend you also read http://www.designers-guide.com/Forum/?board=analog_design;action=display;num=1071672270;start=0#6

-Ken

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.

Title: Re: Transient Analysis in PSS
Post by Paul on 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