transistor configuration

[Gaston]

as i understand it, common emmiter is for voltage gain, and common collector is for current gain. is that correct? and what would you use a common base for?

 

[eng1]

The CE configuration has both voltage and current gain. The CC has a voltage gain around unity and quite good curret gain. The CB configuration has both voltage and current gain less than unity and it is sometimes used as a current buffer.
Other parameters you should evaluate when choosing an amplifier are the input and the output resistance (Ri, Ro). For example, the CC stage has high Ri and low Ro; the CB has low Ri and quite high Ro.

 

[AllVol]

Just an addition:

The CC (also known as emitter follower) has a voltage gain always slightly less than unity due to voltage drop across the B-E junction.

 

[ljcox]

as i understand it, common emmiter is for voltage gain, and common collector is for current gain. is that correct? and what would you use a common base for?

It depends upon how the transistor is configured. It can be configured to provide:-
Voltage gain, Current gain, Transconductance or Transresistance.

 

[kchriste]

and what would you use a common base for

The only time I've seen a common base configuration used, was as an RF amplifier stage in a radio reciever. It's low input impedance is easy to match to the 50hm: commonly used in RF.

 

[Dean Huster]

Back in 1970 in the U.S. Navy's Basic Electricity and Electronics school in San Diego, we were told the story of Azaza Vopini. It's a really slick way of outlining the basic characteristics of CE, CB and CC amplifiers with regard to input impedance, output impedance, voltage gain, current gain and power gain. Anyone ever hear that one?

Dean

 

[dinesh.s]

From my experience what i would tell is the bandwidth of CB amplifier is greater than CE amplifier, that is the point where it gains advantage and comparing to CC amplifier CB amplifier's voltage gain is large.....
This is why we use CB amplifier...

 

[Roff]

A common-base amplifier cannot provide current gain. It can provide voltage gain, but the input impedance is low, so it is generally most useful with low-impedance sources.

 

[dinesh.s]

The main reason is its bandwidth....
We face less effect of this miller capacitor.