Active band pass filter.

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shomikc

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Hi everyone. I want to make an active band pass filter that will receive a signal which is broadcast at 800 kHz center frequency and a certain bandwidth.. At the same time I want the filter to reject a signal that is broadcast at 600 kHz and a bandwidth of 100 kHz and reject another signal broadcast at 1 MHz with bandwidth of 100 kHz.

So my question is should the bandwidth of the signal of the broadcast at 800 kHz will be 650 kHz to 950 kHz.
 
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Consider that the two filters do not necessarily have to be placed in series. They might be in parallel.
Try experimenting with simple LC arrangements. An inductor & capacitor create a resonant frequency. You can put the LC in series or in parallel. You can: (a) divert signal to ground through an LC arrangement, or (b) pass signal along through an LC arrangement.
 

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    shomikc

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Hi,

usually it´s the other way round:
* You determine the bandwidth you need. (@800kHz)
* and how much you want to attenuate the other frequencies.

Klaus
 

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    shomikc

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Simple 2 stage, 2 second order sections, cascade of LPF anf HPF ?

How much rejection you want for the out of band principal components ?


Regards, Dana.
--- Updated ---

Fooling around with a designer uitilty this is close, and you might be able to adjust the
notches to suppress the two frweqs you want to suppress.







Regards, Dana.
--- Updated ---

You would play with the order of the filter and / or BW of the primary 800 Khz.

You would have to do a T and component tolerance analysis / sim to insure it
meets your specs. Or if a one off tune it by changing its component values


Regards, Dana..
 
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It is a cascade of HPF and LPF and the center frequency of 800 kHz.
 

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What do you mean with "reject"? A bandpass can only attenuate unwanted frequecies.
However - theoretically - it is possible to completely suppress one single out-of-band frequency.
 

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Post #5 is suggesting first order high and low pass filters. Did you calculate achievable filter transfer functions with this filter type or is it just a shoot in the dark?
 

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shomikc, you still need to answer the most basic of questions regarding filters :

1) Spec for out of band rejection ?
2) Linear phase solution needed ?
3) Input output impedance requirements ?
4) G thru filter ?
5) Allowed passband ripple ?
6) Noise considerations ?
7) What is the application, why is filter needed ? Answer may reveal other possible
solutions.

Regards, Dana.
 

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