Hi

Can someone explain to me why the bandwidth of overall system is 20kHZ for the following question on the attachment:
View attachment tut_5_qns3.pdf

Hope someone can answer my question

P.S

 

Hi

Can someone explain to me why the bandwidth of overall system is 20kHZ for the following question on the attachment:
View attachment 43280

Hope someone can answer my question

P.S

The bandwidth is found as follows,

\(f_{3dB} = \frac{f_{unity}}{A_{f}}\)

Where, \(A_{f} = \frac{A}{1 + A\beta}\)

Typically the loop gain \((A\beta)\) is large (i.e. much larger than 1) and thus \(A_{f} \rightarrow \frac{1}{\beta}\)

Clearly the if the bandwidth of the 2nd stage is 20kHz, the overall bandwidth is limited to 20kHz.

Who cares if you can pass frequencies of 20kHz+ in the first stage if they are cut off in the second stage, correct?

 

Look at the frequency response curve of an old 741 opamp that has a unity-gain bandwidth of about 1MHz. With a voltage gain of 50 its cutoff frequency is about 20kHz.
Its very poor slew rate cuts maximum output above only 9kHz.

 

thanks for the answer

 

help on how to design a notch filter with band reject frequency of 20khz