The question;
I have been trying design a second-order Butterworth band reject filter
The voltage gain is |Av|=2
and
low cut off freq=10kHz
high cut off freq=20kHz

I used the f3dB equtions also decibel voltage gain table and transfer function equations; after that by using pspice I simulated the circuit and ac sweep analysis however I could not obtain the gain and I have a problem for output. How can I fix the error and obtain the gain? Should I add sth...

 

Why do you expect a gain of two? All your amps have a gain of one. If you change the feedback resistor in the summing amp circuit from 50kΩ to 100kΩ, that will give you a gain of two.

Is there another problem besides that?

 

We did it thanks however; it is the same output and than we started to calculate again;
we will share the results but have you any different idea?

 

Is there any differeneces for the output graph of filter which I uploaded. I thought that graph is unexpected because of the right side is lower.

 

Yes, the right side of the graph should have a flat gain. It may not be due to the limited frequency response of the old 741 op amp. Try a more modern op amp with a higher gain-bandwidth.

Note: ±20V is too high a supply voltage for a 741 (and most op amps). It should be no more than ±15V. Check the data sheets.

 

Thank you.
I changed the values from 10V to 20V. However I can not use any otjer opamp because this is the pspice student version So I uploaded the graphs on the same figure; The High pass low pass and the output graphs you can see the differences can you make any comment. By the way thank you for help me you are the one who helped me in this topic! Thanks a lot

 

Thank you.
I changed the values from 10V to 20V. However I can not use any otjer opamp because this is the pspice student version So I uploaded the graphs on the same figure; The High pass low pass and the output graphs you can see the differences can you make any comment. By the way thank you for help me you are the one who helped me in this topic! Thanks a lot

Why did you change from 10V to 20V? The maximum should be 15V.

The curves look about right, with a second-order rolloff of 12dB/octave for each filter, but I measured a -3dB point of about 11kHz for the LP section and 26kHz for the HP section so your filter values are a little off. (Note that filter curves are normally plotted on a logarithmic or dB scale to make them easier to read).

If you want a higher rejection value you will need to go to higher order filters or perhaps a notch type filter.

 

thank you again...