Problem:bandpass filter design

[pullup]

220KH ±10%
Active
2 order
Filter implementation:As my try is Biauad bandpass filter, there are still some other types
unit gain
Q is about 30
the rest is not seriously restricted.
All above is my expect,not my teacher's demand,he just give me a work and say nothing,how can I say about it?

Of course I don't just want a pretty schematic,I need to know how and why,and the effect of components and so on,but what I can refer to is too limited.

 

[djalli]

"Biauad" term never heard it. What is it?

 

[pullup]

Sorry,It is "Biquad".

 

[djalli]

Got it, it took me while to recognize "Biauad" you were actually talking about "Biquads". Analysis and you build these filters from analysis from pole-zero plot rather than Bode plot done for other active filters. You can build an 8th order filter this way just using a single opamp.

Attached is an article of how to design single second order amplifier biquad bandpass active filter. It is pretty would be as much as a detailed tutorial for you.

To check your work, download NuHertz Filter Solution software. This software allows building them. **broken link removed**

good luck!
djalli

 

[pullup]

To djalli
You gave me so much help that I don't know how to express my appreciation to you.

Any way,thank you very much!

 

[Borber]

These two filters from djalli are dificult for realisation because of .4pF and 409Mohm in first circuit and a need for precise capacitors in second (can be solved using trimers) but 409Mohm seems impossible. I think Biquad is simpler and realizable.

 

[pullup]

Borber is right,It is hard to implement such two filters.

 

[Borber]

Simple solution could be a modification of Butherworth filter. Demands like Q=30 are hard to realize with Biquad. This topology is simple to tune appropriately change R1 or R2 for gain adjustement and R4 for center frequency. Elemenths can be 10%. I am not shure this will satisfy your needs if you want exact values.

 

[djalli]

Do not let that 40MOhm resistor scare you. There are 20, 30, 40Mohms resistors easily available.

2nd order positive sab. again NuHertz calculated values. It lowered Q to 23 only


and a second one more easily to implement. untitled2abc

 

[flatulent]

Another approach is to use a PLL. This will lock onto your signal. The lock detector output will indicate the presence of the signal. You may have to sweep the frequency to acquire lock.

Another approach is the superheterodyne method. Down convert the frequency range to the audio range where filtering is easier.

 

[Usamasardar]

Re: tl084 oscillating

I built the circuit according to <<Rapid Practical Designs of Active Filters>> written by DAVID E. JOHNSON,there are no balance resistors or capacitors.

since TL084 will arouse oscillating,what kind of op amps should I use?

Can you please share this ebook via rapidshare etc ? I need it urgently. Thanks.