loop gain and bode plot

Do you mean open or closed loop Bode Plot? Do you mean open or closed loop gain?

Ray

Hi Ray, I mean Closed loop Bode plot. And I want to detrmine loop gain (ie, forward path gain multiplied by feed back path gain). I have a bode plot , from which I can determine phase margin and gain margin of the system. But I dont know how to determine loop gain (GH) from Bode plot. can you pls help me? Best Rgds Suresh

"from which I can determine the phase...gain margin" ?? You will have to explain how that is done. In any case... If you do know the gain and phase margin then you just write down the formula for the gain and phase margin in terms of open loop gain and closed loop gain and then invert (solve) the equation.

Ray

Hi Ray, Thank you very much for your help. I was following

but i could not find any formula which relates PM, GM, open loop gain and closed loop gain. I am Using PSpice (Analog/ Mixed AD simulator) and I managed to get a Bode plot for a circuit . Now, i want to know whether it is possible to determine loop gain from Bode plot.(ie, forward path gain multiplied by

Can you help me?

Best Rgds Suresh.

You could try a Nicols Chart their a little tricky from what I remember but they do go from ol to cl graphically. Their a bit like the equivalent to a Smiths chart in the RF world but a bit simpler IMO

HUgh