How to fix the closed loop -3dB Bandwidth when the closed loop gain changes

[pz5921087]

Hi,
I am designing an amplifier in inverting configuration with variable gain.
But when switching the gain of by changing the value of the feedback resistor, the CL 3dB bandwidth also will change since the GBW is fixed. So how could I fixed the CL bandwidth?? acceptable variation will be +/- 20% over corners.
Thank you in advance!

 

[LvW]

One possible solution is to use a current-feedback amplifier (CFA) instead of a classical opamp.

 

[pz5921087]

Thanks for your answers!
Other than this, is there any simple way to do it? how about switching different size of caps in parallel with fb res to limit the bandwidth?

 

[FvM]

Other than this, is there any simple way to do it? how about switching different size of caps in parallel with fb res to limit the bandwidth?

Yes, if the amplifier has sufficient high GBW.

 

[D.A.(Tony)Stewart]

There are only a few active filters that lend themselves to variable gain and fixed bandwidth. Usually one must choose a feedforward , or wide band flat amp with variable gain independant of the filter as any negative feedback of the filter that controls gain will also control bandwidth.

**broken link removed**

Frequency response is within 0.25 dB of flat between 30 Hz and 15 kHz. The gain can be adjusted between unity and +15 dB.