I am testing a 34 Mhz amplifier in an inverting configuration with a gain of 20.
The cutt-off freqeuncy of amplification stops almost at 15 Mhz , which is very low. I want it to continue up to 27 Mhz to 30 Mhz. (It doesn't stop , but the amplification ratio becomes very low).
I searched a lot for op-amps with a high cutt off freqeuncy an d I found many , but when I look at the data sheet for Freqeuncy VS Outut Voltage the freqeuncy stops before 10Mhz. The gain VS freqeuncy graph looks fine and shows that it can amplify untill 30 Mhz and more.
Here is a picture of the nearest one I found ,at 26db (20 volts) the freqeuncy I think approches 30 or 40 Mhz , is that correct?
Links : The first the voltage isn't amplified properly at 30 Mhz and stops amplifying before 10 Mhz almost , second link similar problem , but gain seems to be OK.
Best Answer
Your first op-amp is the AD8041 and most of the story is revealed in the open-loop gain response: -
If you want 26 dB of gain (20 v/v) you can't have a bandwidth greater than about 8 MHz - that's the limits that this device is capable of. This is what GBW means: -
Gain x Bandwidth is usually constant (or thereabouts) for a normal op-amp - you can see that the bandwidth is 0dB (unity gain) at 160MHz. Take a look at the gain at 16MHz to the left of the red arrow - the gain is 20dB (i.e. a gain of 10) AND 10 x 16MHz = 160MHz.
At 1.6 MHz the gain is 40dB etc etc..
The picture in the question is of some importance for amplifier designers but it's the open loop gain graph that tells you what the GBWP is.
Choose an op-amp that has the gain AND bandwidth. The AD9631 I reckon is slightly worse than the AD8041.
Once you have got that op-amp spec sorted out check that the slew rate capability of the device will give you the desired p-p output level that you need. Data sheets sometimes have graphs or pictures that show the sort of amplitude you can expect so, read the data sheet. It's your best friend when picking the "right" op-amp.