The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> is this bandpass filter design possible
https://designers-guide.org/forum/YaBB.pl?num=1352117749

Message started by lhlbluesky_lhl on Nov 5^th, 2012, 4:15am

Title: is this bandpass filter design possible
Post by lhlbluesky_lhl on Nov 5^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.

Title: Re: is this bandpass filter design possible
Post by buddypoor on 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.

Title: Re: is this bandpass filter design possible
Post by Flynn Rider on 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!

Title: Re: is this bandpass filter design possible
Post by buddypoor on 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).

Title: Re: is this bandpass filter design possible
Post by loose-electron on 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?