which kind of amp should I use ?

Status
Not open for further replies.
u are probably wrong.
1. consider the simpe single pole model of OP, a high impedance Vin, a gm , Ro, and the loading Cap , CL
2. the transfer function:
A(s)=Vo(s)/Vi(s)=gm*(Ro||CL)=gm*Ro/(s/ω0+1)=A0/(s/ω0+1)
where ω0=1/(Ro*CL) is the cut-off frequency (i.e. -3dB frequency, or bandwidth of the open loop OP) and A0=gm*R0
3. unit gain frequency calcualtion:
let |A(s)|=1 ,
===> 1=A0/(ωu/ω0+1)
===> because ωu >> ω0
===> 1~=A0*ω0/ωu
===> ωu=A0*ω0=gm*Ro/(Ro*CL)=gm/CL
4. u can also check these derivation from some text book, such as John Martin's book.
 

Btrend,


i agree with your calculations. i mistook 1/gm as the output resistance in my previous post.

but i think what i said could be another way to find the characteristics. as i said, from the settling error and closed loop gain, we can estimate the open loop gain that the opamp should deliver. the calculation is depicted in my previous post.

then we plug the open loop gain into the unit gain frequency that you calculated, ωu=A0*ω0. thus we can find a much smaller ω0, which equals 1/(Ro*CL).

later, the current can be calculated in terms of Ro.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…