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settling timeof opamp

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manissri

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hi all ..
for u high speed opams in which the fast settling time is needed. i want to know for that opamps why the high UGB ( bandwidth) is needed.
plz reply
manish
 

i think I AM CORRECT BU SAYING risetime*BW =3.5
I WANT KNOW HOE U ARE SAYING RISETIME=SETTLING TIME


Setting time (Rising time ) * 3dB
 

HI electronics_kumar

What I say is that only for intuition
Your saying is right.
Setting time is not rising time.
But I mean zero to destinated Voltage rising time.

Could you tell me why risetime*BW=3.5 ?

Thanks
 

I remeber the rule of thumb is Tr=0.35/BW
and it's related to the first order low pass filter and the time constant.
You may get some ideas from the principle of communication wrote by
Zemer.
 

is the Bw mean the UBG?
 

Hi,for a 1-pole system,rise time Tr=0.35/BW ,here the BW is the -3dB bandwidth.

For a 2-ploe system, if the phase marging is less than 60 degree, there will be overshoot and settling.What I remember is UBG=2*D*Wn ,here D is the damping factor and Wn is the natural frequency and the settling time is protial to exp(-D*Wn).

Thus,it is clearly that if the fast settling time is needed the high UGB is also needed.

Regards!
 

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