The Joy of Electronics said:Hi... U guys really got me thnking!
As far as I know loop gain greater than one always causes instability. Because amplifiers are Minimum Phase Systems.
Plz tell me the truth if Im wrong.
Please explain where is the incorrectness of my explanations.jasmin_123 said:Hi, zorro, thanks for trying, but I cannot accept your explanations
because they are not correct. Attached is some nice example I have found
on the Net.
Regardsjasmin_123 said:Could somebody give an INTUITIVE(!) explanation why a loop-gain greater
than one does not necessarily causes instability?
zorro said:The gain G has to be >1 at the frequency at which phase is N*2*pi (with negative slope) in order to start oscillation.
zeeshanzia84 said:Thus, even though the +ve fb-system has a loop-gain greater than one (but only at frequencies where phase is 180 or more)....it is not unstable!!!
zorro said:I ask again: is the inner loop (the block formed by U1, the three Rs and the three Cs) stable?
jasmin_123 said:The block formed by U1, the three Rs and the three Cs is unstable.zorro said:I ask again: is the inner loop (the block formed by U1, the three Rs and the three Cs) stable?
zorro said:If G is real and G>1 for some frequency, the output is no more the same as the input, and that is not an equilibrium point. Not necessarily the ouput has to grow (although it does in many circuits) when the loop is closed.
jasmin_123 said:zorro said:If G is real and G>1 for some frequency, the output is no more the same as the input, and that is not an equilibrium point. Not necessarily the ouput has to grow (although it does in many circuits) when the loop is closed.
Do you know why?
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