How to understand and calculate the -3dB bandwidth of the opamp?

for a closed-loop opamp, if the dominant pole is complex, such as -a+b*i, then how to understand and calculate the -3dB bandwidth of the opamp?

if an opamp has a complex pole or zero, then what is the meaning of it?

besides, as we know, GBW(open)=GBW(closed),then what is the relationship of p2(the second pole) for open and closed loop?

finally, what is the difference of UGF and GBW, and how to understand them? and what is the relationship of them?

pls help me, thanks all.

3 db bandwidth

anyone knows or can help me?

what is 3 db bandwidth

lhlbluesky said:

for a closed-loop opamp, if the dominant pole is complex, such as -a+b*i, then how to understand and calculate the -3dB bandwidth of the opamp?
if an opamp has a complex pole or zero, then what is the meaning of it?
besides, as we know, GBW(open)=GBW(closed),then what is the relationship of p2(the second pole) for open and closed loop?
finally, what is the difference of UGF and GBW, and how to understand them? and what is the relationship of them?
pls help me, thanks all.

Click to expand...

Your questions touch the basics and deserve rather long explanations. A good textbook is recommended.
Nevertheless, here are some answers in short:
(1) Pole frequency wp=magnitude of (-a+j*b) and pole Qp=wp/2a.
(2) For Qp=0.7071 wp=w(3dB) for a 2nd order system, for other Qp values: look into corresponding tables for different low pass approximations
(3) In case of a second complex pole pair, the situation is a bit more involved, but in most cases one can handle the system approximately as of 2nd order.
(4)UGF and GBW are identical for a single pole system. In case of a second pole GBW is larger than UGF.
(5) UGF is the frequency where the gain magnitude is 0 dB.
____________
Hope this could clarify a bit.

calculating 3db bandwidth

thanks LvW, but can you recommend a related book or some related papers,pls?

3-db bandwidth

lhlbluesky said:

thanks LvW, but can you recommend a related book or some related papers,pls?

Click to expand...

Perhaps the filter primer helps (see attachement)

-3db bandwidth calculation analog circuit

thanks LvW again.

calculate 3db bandwidth

lhlbluesky,
Regarding the first part of your question:
Let bi = jwb
The -3db point occurs where the real and imajinary parts are equal.
a =wb
w3db = a/b
Regards,
Kral