# Band-pass filter problem

Discussion in 'Homework Help' started by davva, May 9, 2013.

1. ### davva Thread Starter New Member

May 9, 2013
2
0
Hey yall !
I've got quite the problem with an assignment related to designing a band-pass filter.

In the assignment i have to design a band-pass filter which filters out a specific frequency, 5 k Hz. I have uploaded a jpg of the circuit I'm using. The assignment spec gives the choice of using an inductor/coil with either 100 μH or 220μH. After choosing the coil with the inductance of 100 μH i used the equation, seen in the attachments, to calculate the capacitance.

The circuit works as intended but ....

As i re-read the assignment spec i discovered that the coil also has a "natural resistance" of 0.21 Ω resp. 0.43 Ω (for the coils with 100 μH and 220μH).
When i applied the resistance to the circuit the result was of course not at all as good as before.

So my question is ... What do i need to do in order to compensate for the resistance of the coil to get the "same" result as before introducing it ?

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2. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,255
311
Post the assignment spec.

3. ### davva Thread Starter New Member

May 9, 2013
2
0
The assignment spec is not in English, which is why i didn't post it. What kind of additional information were you looking for ?

I Should say that i have tried finding an equation which takes the coils resistance in to consideration but so far i have been unsuccessful. I'm not sure if i need to redesign the circuit entirely or if adding some component is enough, like a opamp perhaps ?

4. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,255
311
You obviously speak English, and presumably the other language as well.

Post the English translation of the spec.

The usual sorts of specs; allowable attenuation at the center frequency, required out of band attenuation, etc.

That shouldn't be too difficult.

No single passive component is going to fix the problem. You could add a fixed gain equal to the loss at the center frequency.

5. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
507
It's been decades for me since I was in school. All real coils have some resistance which degrade their performance compared to ideal coil. If you are using a simulator, you may want to experiment with adding a "peaking capacitor" at various places to see if you can peak up the response a little.