-3dB frequency estimation for basic OpAmp configurations

[dawwwid]

Hi all,

I would like to ask you a basic question, how to estimate -3dB cut-off frequency of basic OpAmp circuits like inverting amplifier, non-inverting amplifier and unity gain amplifier(buffer).

Thank you,
David

 

[BradtheRad]

This has to do with the gain-bandwidth product. It is different for different op amps.

The faster the frequency, the less gain you can get.

The slew rate may also have some influence.

Some devices are known for being faster than others.

You may find the datasheet gives a graph of gain-vs-frequency.

Or, it might be possible to derive a 3dB cutoff frequency by calculating with the gain-bandwidth product. You get max gain at lower frequencies, then there is a frequency where gain starts to drop.

 

[FvM]

The closed loop bandwidth can be estimated based on the OP GBW (gain-bandwidth product) and the circuit feedback factor respectively closed loop gain G. For the standard non-inverting and inverting configurations you get

Non-Inverting: BWcl = GBW/G

Inverting: BWcl = GBW/|G+1|