another op-amp question

[orhanli1]

i have a question i don't understand anything from this question

thanks for your helps friends

 

[LvW]

It's not complicated:

Go=K/(s*tau+1) is the formula for a first order lowpass with gain K.
This expression is used here to approximate the frequency-dependent opamp gain Go(s) by a first order function.
Thus: Vout=Go*Vdiff with Vdiff=Vp - Vn (differential input).

The bandwidth of the opamp with 100% feedback (unity follower) can be determined using the classical feedback formula
G=Go/(1+Go*Fr)
The feedback factor Fr in this case is "1".

 

[orhanli1]

i understand the question now but i have a new question.we have k and tau values but if i want to get Go value, ı should use s in formula.What value does s take.i know it is a domain not a value and should i transform it aything else?What is the purpose

 

[LvW]

Hi orhanli1,

here, the symbol s is nothing else than an abbreviation for jw. Thus s=jw=2*Pi*f.
Introduce Go into the expression for G and rearrange so that you get the same form as in the formula for G (that means: the constant in the denumerator is "1").
Then you can determine the new tau-value which is identical to 1/w.

 

[orhanli1]

yes i know that s=jw=2*pi*f but for it it is necessary to know f value right?

and do you use G for BW(Bandwidth) ?

---------- Post added at 07:36 ---------- Previous post was at 07:34 ----------

and w=2*pi*f or sw=2*pi*f

i think w=2*pi*f

 

[LvW]

The symbol G (overall gain) was defined by me yesterday.
I don`t know the meaning of "sw".

 

[orhanli1]

i want to ask if s=jw=2*pi*f in this quesiton what do i use for f value in this problem

 

[LvW]

Your task is to find the transfer function, right?
A function is an equation with one parameter that can assume different values. The frequency f is such a parameter.
Was this really your question?

 

[orhanli1]

the really question is above on the picture thats all

 

[LvW]

the really question is above on the picture thats all

OK, and I think, the question is answered now. Combine both formulas, rearrange as mentioned (denumerator has "1") and read the new time constant tau. Then the bandwidth is BW=1/(2*pi*tau).