So for a basic little inverting amplifier using a 741 op amp, measured at frequencies of 10 Hz, 1000 Hz, and 100 kHz...
we might expect the gain to behave like the theoretical at 10 Hz and 1000 Hz but begin to be measured less than the theoretical at 100 kHz?
Hello again,
Yes, that is just about right.
There are four things we have to consider when we want to evaluate the possibility of using the amp at a certain frequency:
1. The gain bandwidth product of the op amp (GBW)
2. The slew rate of the op amp (usually expressed in V/us)
3. The gain (G) we want for the circuit
4. The input voltage peak
We can then calculate VoutPeak from VinPeak*G and the band width BW from GBW/G and the max frequency from MaxFreq=SlewRate*1e6/(2*pi*VoutPeak)
and this information will tell us if it will work or not.
For the 741 the GBW can be as low as 500kHz and the slew rate around 0.5 V/us, so for an input peak of 1v and gain of 1 we would have:
BW=GBW/G=500000/1=500kHz
and
VoutPeak=VinPeak*G=1*1=1
and then
MaxFreq=SlewRate*1e6/(2*pi*VoutPeak)=0.5*1e6/(2*pi*1)=79.6kHz roughly
This means with a an input of 1v peak we can use this up to about 80kHz, but with an input of 2v peak it would divide in half to about 40khz.
Another interesting view is what if we want to use this amp with a gain of 100 with the same input of 1v peak?
Now we have G=100 so that changes things quite a bit...
BW=GBW/G=500kHz/100=5kHz
and MaxFreq will be the same as before at about 80kHz, so now what limits the usable range of the op amp is actually the GBW/G not the max frequency due to the slew rate and input peak. Here the slew rate is good enough to follow a 1v peak input sine but the GBW/G will not allow any frequency above 5kHz to work properly.
As others have pointed out, there are better op amps out there including the low cost LM358 which work much better than the 741. The slew rate and GBW are roughly the same, but the input voltage requirements are less demanding. The 741 has a nasty bias requirement that might not work with voltages closer than about 4v to either power supply rail. That's really bad for something that has to run off of 5v for example.