loop gain in multivibrators

Thread Starter

anchal

Joined May 6, 2012
1
How does loop gain in stable states of bistable multivibrators is less than unity whereas during unstable states , loop gain is more than unity?
 

count_volta

Joined Feb 4, 2009
435
I just took a course in control. Perhaps it has to do with the gain margin and phase margin? Each of those margins is a measure of stability. For an oscillator you want marginal stability. The poles should be located on the imaginary axis for sustained oscillation without growth or decay. The phase margin should be exactly zero degrees. The gain margin should be 1 or 0dB. Look up the Nyquist diagram on wikipedia for more information. I am guessing it has something to do with that. Not sure though.
 
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crutschow

Joined Mar 14, 2008
27,898
Typically for a non-linear bistable multivibrator you don't worry about loop gain and phase margin as such. That's generally used for linear feedback systems. You just design the circuit to have enough positive feedback to flip the state at the end of each half-cycle.
 
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