ljy4468
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ljy4468 said:
https://obrazki.elektroda.pl/24_1185873737.jpg
In above picture, I modeled b=1/2(green line),b=1/100(blue line)
open loop(red line) with matlab. (b=beta=feedback factor)
Then, If I made closed loop amp with b=1/100(blue line),
PhaseMargin is at point A with red line (~90 degree)
Now I've a question,
why we see redline (open loop phase function) instead of blue line(closed loop phase function)??
iamxo said:generally, we measure the loop gain phase function, not closed loop or open loop.
and the worst loop gain case is when the feedback factor equals one, so it seems
we measure the open loop phase function.
anyone correct!
li202 said:Phase margin is improved at frequency not the phase value.
analog_prodigy said:I have a question: How can the loop breaks when an inductor is placed in feedback?
Please give the explanation.
surianova said:analog_prodigy said:I have a question: How can the loop breaks when an inductor is placed in feedback?
Please give the explanation.
Bcoz inductor block AC signal.. in feedback, the AC singnal is the one that propogate and form the feedback. The inductor block AC but pass DC voltage.. that's why it work like open loop.
surianova said:what is the meaning of ac laod? is it the load to the output?
if yes, below is the explaination:
the output is connected to 2 node in parallel, one go to load and the other go nagative terminal of the opamp, the inductor is put between the output and negative terminal. so, it is nothing to do with the output load.
didibabawu said:surianova said:what is the meaning of ac laod? is it the load to the output?
if yes, below is the explaination:
the output is connected to 2 node in parallel, one go to load and the other go nagative terminal of the opamp, the inductor is put between the output and negative terminal. so, it is nothing to do with the output load.
Hi surianova,
For the left circuit in the left,can i use the circuit in the right to check the stability?
I input signal at a and see the phase margin at a'.
3x.
surianova said:can, no problem.. or u can replace the inductor with Iprobe in Cadence to do Stb analysis..
didibabawu said:surianova said:can, no problem.. or u can replace the inductor with Iprobe in Cadence to do Stb analysis..
Then when I see the phase margin at a',the inductor block some ofthe load of a', such as Zin, and the parasite capasite at the input of the amp, so I think some equivalent load need to be add at point a'.
And I have another question that how to add the input signal. Can I use an big capacitor like in the pic?
surianova said:yes,can. You connect voltage source with ac=1 to the capacitor and also put a big resistor to gnd after the inductor.
you can put inductor, cap and resistor as 10G.
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