# Cutoff Freq of Inverting Op Amp

#### KevC

Joined Jan 15, 2012
2
Hi guys,

The question I need help with is
"Determine the maximum gain possible that meets the high-frequency roll-off specification of fH = 20 kHz."

http://i44.tinypic.com/ezlo2x.png

As you can see from my schematic & bode plot, I designed the roll-on to be at 100Hz and it rolls off at 815kHz.

How do I mathematically find the bandwidth or the cutoff frequency? I understand that to find the roll-on you simply do 1/(2piR2C1). I assume that once I find out how to find cutoff freq, I can design the roll-off at 20kHz and find the gain.

Thank you,

KC

#### crutschow

Joined Mar 14, 2008
34,833
Do you understand the "gain-bandwidth product" specification of op amp amplifiers? It's determined by the internal frequency response of the op amp, not the external components. If you understand that (Google if needed) then you can answer your own question.

#### 2010ee179

Joined Jul 1, 2011
12
For a single OP-AMP you just need to know gain bandwidth product...
May be you should read this:

Gain bandwidth product (Google it) is also specified as fT (transition frequency)...It is given in data sheets.

#### KevC

Joined Jan 15, 2012
2
Thank you guys. I didn't understand GBP before and now I do!