Hi guys! in these days I was evaluating the possibility of creating a variable band active bandpass filter with a working frequency from 5 to 10Mhz. It's possible to do it? I have seen that there are specific ICs for this but they have much higher working frequencies which are not for me. Thanks for your help!

 

Hi guys! in these days I was evaluating the possibility of creating a variable band active bandpass filter with a working frequency from 5 to 10Mhz. It's possible to do it? I have seen that there are specific ICs for this but they have much higher working frequencies which are not for me. Thanks for your help!

Of course, this is possible. However, there are still some questions:
* What about the filter-Q resp. bandwidth? No requirement ?
* In most cases (for most filter configurations) two parts must be tuned simultaneously. Is this allowed?
* How many opams ?

 

Hi @LvW , I try to answer within the limits of my knowledge. You need a Q that allows for a rather narrow band. Based on the graph that I am attaching, the ideal is to obtain a Q20 setting as a limit the use of a maximum of 5/6 opamps. Simultaneous tuning of several parts is allowed and this is an obstacle that I ran into but let me explain better. If it is a question of using potentiometers simultaneously, there are no particular problems. the problem arises when the variable components are capacitors and inductance and this is the reason why I discarded a passive filter preferring the active one.

So to answer your questions :
Q = 20
Max 5/6 opamps if needed
Ok for simultaneous tuning

 

Do you require a constant filter Q=20 over the whole tuning range ?
This could be a problem.

 

It's preferable but non mandatory. It could be calculated in the center band (10Mhz). Then as you move it would tend to decrease I think. Quite right?