What are input and output impedances?

[magnetra]

What are input and output impedances? Please explain with reference to a CE amplifier.

Magnetra

 

[tyassin]

Re: I/O Imepdance

Hi

The input impedance for a CE amplifier, is looking into the base of the amplifier, when you have the transistor modelled as a small signal amplifier. These models can be found in most basic electronics textbooks. Common emitter (CE) in the most basic difenition, means that the input(base) and output(collector) has the emitter as the common reference point(ground). You can find the input impedence of the CE amplifier by applying a test voltage at the base and find the input current at the base, then you express the ratio of these two. This give you the input impedance.
If you use the most simple small-signal model of a BJT, then then you can find that the input impedance is given by: Zin=(β+1)*Re, where Re is the total resistance in the emitter.

The output impedance is the impedance seen looking into the collector, again using the most basic small-signal model gives you
Zout=Rc, where this is the collector resistance.

Hope this help.

Regards

 

[pankaj waghmare]

Re: I/O Imepdance

i/p impedence is impedence,we get by looking into base as it is bjt.
o/p impedence is impedence,we get by looking into collector