Second order Active filters!

[crash@home]

Hey all..

im trying to create a second order active LPF with a -3dB frequency of 150Hz for a project, i've created a circuit using the guide from Texas Instruments -Active Filter Design Techniques but i cant get the desired stop-band characteristic. (pics attached).

It is envisaged that this second order LP will be cascaded with a HPF that i have already to my ideal spec to form a 4th order bandpass, i've been working on this for almost 3 weeks now any help would be much appreciated!!

 

[JimB]

Looking at the screen dump of your computer game, err sorry, I mean simulator...

What om earth do the F and I boxes mean?

Using units of Giga Hertz on an audio filter is crazy.
Similarly -200dB is one hell of an attenuation! About like pulling the plug out!

Reconsider what the PC is telling you, remember: garbage in, garbage out.
Then try building it and see how it works in the real world.

JimB

 

[Winterstone]

Hey all..

im trying to create a second order active LPF with a -3dB frequency of 150Hz for a project, i've created a circuit using the guide from Texas Instruments -Active Filter Design Techniques but i cant get the desired stop-band characteristic. (pics attached).

It is envisaged that this second order LP will be cascaded with a HPF that i have already to my ideal spec to form a 4th order bandpass, i've been working on this for almost 3 weeks now any help would be much appreciated!!

I really don´t know what your problem is. Have you problems to design the circuit (parts values) according to the attached formulas?
Or have you problems in applying the software?
As you have mentioned the "desired stop band characteristic" - what are your requirements? Perhaps you`ll need a higher order?

 

[crutschow]

Download the free FilterPro software from Texas Instruments. It will generate a design for whatever you need.

 

[MrAl]

Hey all..

im trying to create a second order active LPF with a -3dB frequency of 150Hz for a project, i've created a circuit using the guide from Texas Instruments -Active Filter Design Techniques but i cant get the desired stop-band characteristic. (pics attached).

It is envisaged that this second order LP will be cascaded with a HPF that i have already to my ideal spec to form a 4th order bandpass, i've been working on this for almost 3 weeks now any help would be much appreciated!!

Hi,

How about showing your circuit so we can take a look here?
Show all component values too if you chose them already.

 

[ronv]

I like this one:

https://www.cepd.com/calculators/lowpass_ana.htm

 

[audioguru]

If you use a lousy old opamp like a 741, LM324 or LM358 then it runs out of gain at high audio frequencies then the output impedance rises and the signal passes through the feedback capacitor connected to its output causing the signal to rise at high frequencies.