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Measurements >> Other Measurements >> opamp stablity analysis
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Message started by analog_cha on Aug 28^th, 2007, 4:38am

Title: opamp stablity analysis
Post by analog_cha on Aug 28^th, 2007, 4:38am

Hi
I am doing the stb analysis( cadence spectre) for the single ended two stage op amp. To do the stb analysis i used iprobe in the feed back.
But i found some parameters while instantiating iprobe. What r these properties??
And in the stb summary it is saying " NO PHASE MARGIN, PHASE STARTS BELOW 0DGREEE"
" NO GAIN MARGIN GAIN STARTS BELOW 0DB" ?
can any body explain this??
thanks..

Title: Re: opamp stablity analysis
Post by sheldon on Aug 28^th, 2007, 9:57pm

Cha,

In general this message means that there is no gain or phase crossover in the
the selected frequency range so the gain margin and phase margin can not be
calculated. If you plot the open loop characteristics, what do you see?
1) Is the amplifier setup properly, that is, is there positive open loop gain?
2) Does the gain/phase crossover occur in the specified frequency range?

Best Regards,

Sheldon

Title: Re: opamp stablity analysis
Post by analog_cha on Aug 30^th, 2007, 11:42pm

i found the mistake in the set up.

thank u Sheldon..