Electronics Problem

[Scarfacé]

Evening all,

I have a little issue with an electronics problem I'm having trouble with.

I have to design a simple circuit to give a gain of 10 with a minimum bandwidth of 180 kHz using the 741 Op Amp.

Using either inverted or non-inverted circuits, the bandwidth will only be 100 kHz (according to the bode diagram for the 741 op amp).

Would it be possible to simply connect for example, two inverting op amps together in a row, say, one with a gain of 5 and then a gain of 2? How would this affect the bandwidth?


Thank you for any help, as I'm puzzled on this.

 

[Bear]

The bandwidth of the LM741 is about 1MHz look up the data sheet for it. You sure you are reading the bode plot correctly as the axis should be a log scale.

 

[Scarfacé]

Bear,

In open loop conditions it is 1Mhz, yes... but with an AV gain of 10, the bandwidth is only 100mHz, and I require a minimum of 180mHz.


Cheers.

 

[Jotun]

Would it be possible to simply connect for example, two inverting op amps together in a row, say, one with a gain of 5 and then a gain of 2? How would this affect the bandwidth?

What you have said is correct you can indeed put two in series and multiply the individual gains

With a 1MHz op amp the bandwidth would be 200kHz I believe as that will be the bandwidth for the one set up with the gain of 5, which would be the limiting factor.

 

[Scarfacé]

What you have said is correct you can indeed put two in series and multiply the individual gains

Jotun,

How do I then calculate the bandwidth (with two op amps in a row)? Does it not just lower back down to 100mHz after this, as if there were one?

Hopefully it will be that simple.

Cheers.

 

[Jotun]

Jotun,

How do I then calculate the bandwidth (with two op amps in a row)? Does it not just lower back down to 100mHz after this, as if there were one?

Hopefully it will be that simple.

Cheers.

Edited my original post to make it a bit clearer I hope.

If you think about it, setting up an op amp with a gain of 5, it can amplify a signal up to 200kHz before attenuation, and so 1V 180kHz signal will be amplified by a factor of 5 so it will be 5V, and as its within the limits won't be attenuated.

Then if you put the 5V 180kHz signal into an op amp with a gain of 2, and a max frequency of 500kHz before attenuation, the output will be multiplied by 2 to become 10V, as as that is less than 500kHz won't be attenuated either. So the maximum frequency is determined by the amplifier with the highest gain.

Hope that helps

 

[Scarfacé]

Edited my original post to make it a bit clearer I hope.

If you think about it, setting up an op amp with a gain of 5, it can amplify a signal up to 200kHz before attenuation, and so 1V 180kHz signal will be amplified by a factor of 5 so it will be 5V, and as its within the limits won't be attenuated.

Then if you put the 5V 180kHz signal into an op amp with a gain of 2, and a max frequency of 500kHz before attenuation, the output will be multiplied by 2 to become 10V, as as that is less than 500kHz won't be attenuated either. So the maximum frequency is determined by the amplifier with the highest gain.

Hope that helps

Cheers for your help, it most definitely helps.

Thank you.

 

[Bear]

Aye Jotun is correct, lower the gain so you get a wider bandwidth and add more stages to get the gain you want. been a long time since I was messing around with 741s as a student.