How can transistors be used as inductors, specifically for bandwidth extension?

 

How can transistors be used as inductors, specifically for bandwidth extension?

As far as I know transistors cannot be used as inductors. I'm curious about the origin of this notion; can you enlighten us?

 

As far as I know transistors cannot be used as inductors. I'm curious about the origin of this notion; can you enlighten us?

Is the TS thinking about gyrator circuits? Even so, not sure how they extend bandwidth.

 

Some transistor connections allow to increase the bandwidth.
Specifically, the CE is most slow. The CB is faster but has lower gain, CC is fast but has no voltage gain.
The CB and CC are faster because they remove the carriers from junctions more effectively.

Here is the example of CC for high input impedance + CB for voltage gain. It has higher bandwidth comparing to CE that has naturally has an advantage of high input impedance and voltage+current gain also.

 

Some transistor connections allow to increase the bandwidth.
Specifically, the CE is most slow. The CB is faster but has lower gain, CC is fast but has no voltage gain.
The CB and CC are faster because they remove the carriers from junctions more effectively.

Here is the example of CC for high input impedance + CB for voltage gain. It has higher bandwidth comparing to CE that has naturally has an advantage of high input impedance and voltage+current gain also.
View attachment 353720

But is changing the amplifier for one that has less reduction in bandwidth the same as increasing the bandwidth?

 

When using the terms "bandwidth extension" or "bandwidth increase", we should always state the basic circuit to which such an extension refers.
This leads to the basic question of which circuit can be increased in its bandwidth by adding an inductance.

 

But is changing the amplifier for one that has less reduction in bandwidth the same as increasing the bandwidth?

Yes - I agree. When one specific circuit has a larger bandwidth than another circuit - this has nothing to do with an "increase of bandwidth".

 

Here is the inductive correction on the transistor:

 

How can transistors be used as inductors, specifically for bandwidth extension?

Hi,

What I have to wonder about is what made you ask this question. It seems very vague and yet specific at the same time.
That is, 'transistors' are not usually used as inductors by themselves. I suppose you can say that they will act like small inductors at the right frequencies, but that would be a very unusual use unless there was some advantage found in a transistor designed for use on an integrated circuit die where it could act as an inductor of some type.
On the other hand, if you are talking about a regular transistor like a 2N2222 then the use would be sort of esoteric, or else it would have to be part of a whole circuit that was meant to show some sort of inductance.

Also, I don't think the usual way to increase bandwidth is to add an inductor. It would be more where you replace an inductor with a different type or just perhaps different value.

My suggestion is that you explain what it is you want to do with a little more detail. If your question has to do with a completely different design, then you might word your question a little differently.

 

Here is the inductive correction on the transistor:

Please, can you explain why the shown modification is an "inductive correction"?
To me, it is a gain enhancement for very high frequencies due to a corresponding increase of the (dynamic) collector resistance for the transistor Q2.

 

Please, can you explain why the shown modification is an "inductive correction"?
To me, it is a gain enhancement for very high frequencies due to a corresponding increase of the (dynamic) collector resistance for the transistor Q2.
Any "inductive" effect is connected with a corresponding phase shift.