741 Op-Amp bandwidth

[canadianpoet2012]

Can anyone tell me how to increase the bandwidth of an Op-Amp (LM741CN).

I have two simple, non-inverting circuits with a gain of numerical 50 and numerical 10. They both only consist of only two resistors (to set the gain). I have measured the bandwidth of both, and I would like to increase it.

I'm not fussed how, in fact more than one suggestion would be good, because then I can compare them. It doesn't have to be super simple either; so long as it can be simulated it's ok. Although being able to fabricate in on strip board is preferable. Any suggestions are much appreciated.

 

[Roff]

Are the op amps in series, for a total gain of 500? If so, the optimum bandwidth will be attained when each has a gain of √500, or 22.4. You will get a bandwidth of about 28kHz. If you want more bandwidth, use a faster op amp.

 

[Russlk]

The bandwidth of the op amp (741) is given by the manufacturer as 1 mHz but that is actually the gain-bandwidth product when the gain is 1. When the gain is 2, the bandwidth is 0.5 mHz and for a gain of 10 the bandwidth is 100kHz, etc. You could cascade a number of op amps each having a gain of 10 but keep in mind that the gain at the upper frequency is 0.707 of the gain at low frequency, so the second stage will be down to a gain of 0.5 at 100 khz and the 10th stage will be down 30 dB at 100 kHz.

 

[canadianpoet2012]

Thank you for the help and advice so far.

I am to understand from the two posts that the only way to increase the BW is to either reduce the gain or cascade the op-amps. Is there no other way of doing it? With other components, like capacitors or something!

 

[Roff]

OK, you can get the -3dB bandwidth to increase by about 70% (with no peaking in the frequency response) by adding a series RC network in parallel with the input resistor. Make the series R about 10% of the value of the input resistor. I don't have the energy (brains?) to work out an equation for the cap value. If you can tolerate some peaking in the response, you can get a little more improvement.
I tested this by simulating it. It should work in hardware. Be aware that your input impedance is basically the network that connects to the inverting input of the op amp, so it will drop at high frequencies - generally not a good thing.

 

[Russlk]

When you cascade amplifiers the gain is multiplied, which reduces the bandwidth, but if the gains are added the bandwidth is not changed. This idea was invented in the 1940s (at MIT I think) and implemented in the Tektronix oscilloscopes.