Hello all,

In my last topic i understood how common emitter amplifier works and how to design it correctly given the requirements and then i look also to emitter follower circuit, which usually Is used in cascade with such circuit, in order to have a voltage gain and then having a current gain+ the advantage of having high current drive capability.

Now i started looking at another configuration, which Is called common base, from what i understood in this configuration basically there Is no current gain, but we can achieve a big voltage gain, then now i got a question,
How do i choose if its better to use an emitter amplifier and then a second stage and emitter follower ( buffer ) or maybe using a common base configuration then in cascade always and emitter follower? The result would be the same or not?
Whats the advantage or disadvantages? What i should prefer and why?

Thanks for sharing ur experience!

 

try it...

 

Whats the advantage or disadvantages?

In most types of one transistor amplifiers the internal C-B capacitance slows down the amplifier.
In a common Base amp the Base is at ground and the C-B capacitance does not feedback to the input of the amp. (faster amp)

 

Hello everyone... I'm not used to posting on forums, however, examining the naive tone of the topic title, I authenticated it and started writing, trying to clarify the issue. I apologize for the wording I used, as I haven't written in English for a long time, I've lost the habit...

Let's go. For the friend to understand, there are three basic configurations of transistor stages:

-common emitter (CE);
-common collector (CC), also known as emitter follower; and
-common base (CB).

Not to mention the countless other possibilities that electronics allows us. And, so that there are no doubts, the nomenclature adopted refers to the characteristics of the stage, in relation to the signal that travels through it, never to the quiescent bias.

Thus, each type of stage should be used according to its relevant characteristics, which we can summarize as follows:

-CE => high voltage and/or current gain; Suitable for intermediate amplifier stages, which are located in the core of the equipment, these are the most versatile.
-CC => high current gain, with high input impedance and low output impedance, but with voltage gain <1. and
-CB => high voltage gain, with low input impedance and medium output impedance, but with current gain <1.

My recommendation to the "sorcerer's apprentice" is to spend more of their time on theoretical articles, and move on to simulating 1-stage circuits, then 2-stage circuits, and then gain practice in designing excellent electronic circuits.

 

Hello everyone... I'm not used to posting on forums, however, examining the naive tone of the topic title, I authenticated it and started writing, trying to clarify the issue. I apologize for the wording I used, as I haven't written in English for a long time, I've lost the habit...

Let's go. For the friend to understand, there are three basic configurations of transistor stages:

-common emitter (CE);
-common collector (CC), also known as emitter follower; and
-common base (CB).

Not to mention the countless other possibilities that electronics allows us. And, so that there are no doubts, the nomenclature adopted refers to the characteristics of the stage, in relation to the signal that travels through it, never to the quiescent bias.

Thus, each type of stage should be used according to its relevant characteristics, which we can summarize as follows:

-CE => high voltage and/or current gain; Suitable for intermediate amplifier stages, which are located in the core of the equipment, these are the most versatile.
-CC => high current gain, with high input impedance and low output impedance, but with voltage gain <1. and
-CB => high voltage gain, with low input impedance and medium output impedance, but with current gain <1.

My recommendation to the "sorcerer's apprentice" is to spend more of their time on theoretical articles, and move on to simulating 1-stage circuits, then 2-stage circuits, and then gain practice in designing excellent electronic circuits.

Alright thanks for the informations!

 

For the common-base amp, the collector current is equal to the input (emitter) current minus the small base current.
The voltage gain is then basically the input current times the collector resistance.
Note that the emitter input impedance is very low, as it looks like a forward-biased diode to ground.

 

common-base amp
I built many video or RF amplifiers that have an input impedance of 75 or 50 ohms. I was looking for voltage gain.