[BJT] Changing bandwidth without changing gain

Hi everybody!

If I have a 2 stage Bjt circuit amplifier with a common emitter and then a emitter follower how can i make the bandwidth to grow without changing the gain of the circuit?

Maybe a common base between the 2 stages (like a cascode configuration)?

Thanks in advance.

Two words: Negative feedback. Think about it and tell us your thoughts on how you might do it.

As you probably understand gain and bandwidth have an inverse relationship. Read my full comments here.

mlog said:

Two words: Negative feedback. Think about it and tell us your thoughts on how you might do it.

Click to expand...

Negative feedback generally reduces gain.

Guitarras said:

Hi everybody!

If I have a 2 stage Bjt circuit amplifier with a common emitter and then a emitter follower how can i make the bandwidth to grow without changing the gain of the circuit?

Maybe a common base between the 2 stages (like a cascode configuration)?

Thanks in advance.

Click to expand...

Cascode helps if you have a source impedance, which in conjunction with Miller capacitance lowers the bandwidth. A cascode stage can be used to reduce Miller capacitance. If you have a zero impedance source, Miller capacitance will not be much of an issue.
You can reduce the Ccb of the emitter follower by bootstrapping it with another emitter follower. This will increase the bandwidth.

Ron H said:

Negative feedback generally reduces gain.

Click to expand...

Agreed. In my haste, I misinterpreted the question. I know that if the gain bandwidth product is fixed, then you trade off bandwidth vs. gain. I thought the question was about maintaing a fixed transistor gain (hfe or beta).