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Design >> Analog Design >> stability analysis for differential feedback loops
https://designers-guide.org/forum/YaBB.pl?num=1185502656

Message started by tosei on Jul 26^th, 2007, 7:17pm

Title: stability analysis for differential feedback loops
Post by tosei on Jul 26^th, 2007, 7:17pm

Hi all,

In trying not break the loop for analyzing stability for a diff-diff opamp I tried to use the stb analysis, but found it does not allow to use more than one port or voltage source for reference (in a single-ended feedback loop one reference is enough). Consequently I found I could not use it.
Is there something I´m missing? If in fact stb cannot be used for differential circuits, is the only option (apart from breaking the loop to measure the RR) to directly measure the loop gain (a×f)?

Your comments are welcome.
Thanks

tosei

Title: Re: stability analysis for differential feedback l
Post by ACWWong on Jul 27^th, 2007, 1:57am

differential stability analysis is available in spectre.

do spectre -h stb for details or read this previous relevant post.

http://www.designers-guide.org/Forum/YaBB.pl?num=1170321868/1#1

Title: Re: stability analysis for differential feedback l
Post by Frank Wiedmann on Jul 27^th, 2007, 2:11am

Alternatively, you can use two ideal baluns (as decribed in http://www.designers-guide.org/Analysis/diff.pdf) connected back to back and put probes in the connections between them. Page 198 of http://eeclass.stanford.edu/cgi-bin/handouts.cgi?s=&t=1185524820&cc=ee214&action=handout_download&handout_id=ID11581983201703&viewfile=reader.pdf shows how to perform an analysis of the differential mode loop gain in this way. For the common mode loop gain, put an additional probe into the Vcm branch and specify this probe in the stb analysis.

Title: Re: stability analysis for differential feedback l
Post by tosei on Jul 27^th, 2007, 4:54am

Hi Frank/ACWWong,

Many thanks for your response.

tosei