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lhlbluesky_lhl Senior Member Offline Posts: 115	is this bandpass filter design possible Nov 05^th, 2012, 4:15am i have to design a bandpass filter with adjustable center frequency f0=20khz, 26khz, 38khz. and for all the three f0, requiring that: Q>10, gain attenuation at 120hz is larger than 80db, gain attenuation at 50khz is larger than 70db. how to realize the bpf circuit? and is it possible? thanks.
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buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: is this bandpass filter design possible Reply #1 - Nov 6^th, 2012, 12:29am Seems to be not possible (attenuation requirements require unrealistic Q values) according to filter design software. Question: Is a multi-stage realization allowed? For example: 3 or 4 stages (each of 2nd order). In this case, you must rewrite the specification and specify the pass band width.
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Sx_cut

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Posts: 16
Dresden, Germany

Re: is this bandpass filter design possible
Reply #2 - Nov 6^th, 2012, 10:38am

Well, I believe there a number of things you need to keep in mind. Firstly which application you are targeting? This will define your specifications. Look back at your specifications!! Then you must decide which methodology you will be following for your filter design. Do you want to make a simple passive filter? Or is it active (op amp and resistors/capacitors), Gm-C type or a switched capacitor (resistors replaced with switches and capacitors in active filters). If you have to make op amp based filters, which transistor technology are you using? BJT, CMOS etc. An excellent reference is chapter 16 of the book "Op amps for everyone" by Texas instruments!!!!! Plz go thru this chapter!

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buddypoor

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Posts: 529
Bremen, Germany

Re: is this bandpass filter design possible
Reply #3 - Nov 6^th, 2012, 1:16pm

Sx_cut wrote on Nov 6^th, 2012, 10:38am:

...Firstly which application you are targeting? This will define your specifications. Look back at your specifications!! Then you must decide which methodology you will be following for your filter design. ...

For my opinion, the first step is a clear specification. Then, technology and realization aspects are only one of the next steps.
Up to now, the required bandwidth of the passband is unknown (Q>10 says absolutely nothing since a filter order above n=2 will be required).

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LvW (buddypoor: In memory of the great late Buddy Rich)

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: is this bandpass filter design possible Reply #4 - Nov 7^th, 2012, 1:13pm ADC followed by a BPF done with a FIR filter in DSP? One ADC and a pile og DSP logic is smaller and lower power than three analog filters running. Sigma Delta on the ADC?
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