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Filter Network Phase / Gain Margin

Question asked by groger on Aug 12, 2014
Latest reply on Dec 26, 2014 by groger

Hi,

 

Part of the design files from the Filter Wizard included the "ACanalysis.cir" file which I'm able to run in SPICE.

 

Here is what appears to be a reasonable definition of phase margin (from simonbramble.co.uk)

"Phase margin is a measure of how close the loop gain is to having 180 degrees of phase shift when the loop gain is unity. If βA0 has 180 degrees of phase shift when it has a magnitude of unity, the circuit has zero degrees of phase margin and will oscillate. If the loop gain has a phase shift of 160 degrees, the circuit has a phase margin of 20 degrees."

 

The cursor is at 16Hz, the gain is at 0dB, and the phase is -180 degrees. Does this mean it is potentially unstable? Or is it a question of me misunderstanding the above definition?

 

Thanks for your suggestions and help.

 

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