Hi all, i have designed a butterworth bandpass filter that passes frequencies between 100Hz to 10kHz and with gain of 2 using LM741. But the bode plot of the simulation result seems incorrect. Can anyone help? Thank you.

 

Here you have a "body plot" that I got from LTspice.

 

Here you have a "body plot" that I got from LTspice.

Thanks for the reply. I am using NI multisim in designing my filter. Yet i unable to get the bode plot as shown in your figure. Do u know anything wrong with my circuit? I am combining a highpass and a low pass filter in designing my bandpass filter.

 

The crappy and obsolete 741 opamp maxes out at about 9 kHz. It has no capability to do much of anything. Abandon it in favor of a part that was designed in the last decade instead of the last century.

 

The crappy and obsolete 741 opamp maxes out at about 9 kHz. It has no capability to do much of anything. Abandon it in favor of a part that was designed in the last decade instead of the last century.

But the problem is the questions request me to design the filter using LM741. So can't abandon it.

 

I think you need to swap R3 and R4.

 

But the problem is the questions request me to design the filter using LM741. So can't abandon it.

Then you need to change instructors because he is an idiot for giving such an assignment. Using an LM741 you have no idea weather the response is limited by the opamp or the frequency determining components. Can you say for sure how the rolloff is affected by those things? It is extremely poor design practice to use a device so close to its limits. If you worked for me and proposed such a thing I'd have to think seriously about firing you. No joke Sherlock, I don't have time to waste on boneheaded ideas from instructors who are decades behing the times.

 

Do u know anything wrong with my circuit?

Your main problem is the Bode plotter block is set for a linear horizontal axis. Set it for a logarithmic horizontal (frequency) axis.

 

Your main problem is the Bode plotter block is set for a linear horizontal axis. Set it for a logarithmic horizontal (frequency) axis.

Ya, i did changed the axis for logarithmic horizontal but the results still not so good..

 

I think you need to swap R3 and R4.

ya.I swap the resistor values already. But my bode plot still incorrect.

 

Show the uA741 datasheet on page 9 to your instructor, the frequency response about 12 Khz when you supply a ±12V for it, and ask the instructor what should you do for the next step.

 

ya.I swap the resistor values already. But my bode plot still incorrect.

R3 and R4 still look the same as post #1. Make R3 = 10k and R4 = 20K.

 

Show the uA741 datasheet on page 9 to your instructor, the frequency response about 12 Khz when you supply a ±12V for it, and ask the instructor what should you do for the next step.

Could you please suggest another opamp that could replace LM741 in my circuit? Thanks.

 

Hello,

In post # 7 of the following thread there are several opamps mentioned:
Components Selection Guide

Bertus

 

Could you please suggest another opamp that could replace LM741 in my circuit? Thanks.

If you wish to output the higher voltage(p-p) and over 100Khz, then you can use LF357, maybe LF356 also can reach it.

Please see the Figure 31 on page 11 from here.

 

I see that your bode plot sweeps 100 Hz to 100 kHz. The plot by jony plots from 1 Hz to 1 MHz.