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2-stage opamp - question about settling time and gain...

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otac123

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2-stage opamp

hi all,
what is the relation between settling time,and unity gain bandwidth of an opamp.reply asap.
 

Re: 2-stage opamp

V(t)=Vo(1-exp(t*GBW)) for close loop.
 

Re: 2-stage opamp

otac123 said:
hi all,
what is the relation between settling time,and unity gain bandwidth of an opamp.reply asap.
Click to expand...

For a one pole system you have Tr = 0.35/F-3dB where F-3dB = GBW/A0. For a close system you have F-3dB = GBW/gain. Gain is the gain of your system.

Bastos
 

Re: 2-stage opamp

Thank you guys.................
 

Re: 2-stage opamp

dear bastos,
if i have unity gain opamp.what should be its settling time in respect of UGB(open loop).
moreover how do you get the factor of 0.35 in your equation.
thanks for reply in advance.
 

Re: 2-stage opamp

avinash said:
dear bastos,
if i have unity gain opamp.what should be its settling time in respect of UGB(open loop).
moreover how do you get the factor of 0.35 in your equation.
thanks for reply in advance.
Click to expand...

For the case of unity gain F-3dB = GBW. The 0.35 is taken from Paul Gray book which corresponds to the time it takes to go from 10% to 90% of output.

Bastos
 

Re: 2-stage opamp

is this book available on this forum.
 

Re: 2-stage opamp

avinash said:
is this book available on this forum.
Click to expand...

Yes, search in the forum for " Analysis and design of analog integrated circuits"

Bastos
 

2-stage opamp

I think the frequency compensation is difficult.
 

Re: 2-stage opamp

Hi.
tss = n*(1/ω-3dB) where n=ln(1/ess) and ess is small-signal steady-state error.
ω-3dB = βωu.
So by choosing a certain ess (it depends on accuracy or resolution you required) and tss (for a given clock rate) and β (for a given structure) you can find ωu and hence gm of your input devices. these are first steps in designing an opamp.

Regards,
EZT
 

Re: 2-stage opamp

The above statements are correct, but all based on the assumption that the slew rate of the opamp is big enough. If the slew rate is not so big, then you should also do calculation for large signal
 

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