[SOLVED] transistor biassing advantage

[p11]

please kindly answer me that why the input impedance of common collector mode is highest? why the output impedance of the commom base mode is lowest?i also want to know that why voltage divider method of biassing is popular in transistors?:-|

 

[milan.rajik]

Read how base, emitter and collectors are doped and what will be the size of each region. How much minimum voltage is needed to forward bias eb, cb junctions.

Make an experiment and find out what voltage you need to forward bias the eb junction of NPN transistor.

Make another experiment snd find out minimum voltage you need to forward bias the cb junction (c is N type and b is P type in NPN). So, connect collector to GND and base to +ve voltage.

Use a multimeter to check the forward resistance of eb and cb junctions.

 

[LvW]

The most important influence does not result from how the regions are doped, but simply from feedback.
In common collector configuration the gain determining resistor is in the emitter path.
Hence, we have maximum possible feedback (current controlled voltage feedback).
This kind of feedback drastically increases the input resistance of the circuit.

 

[FvM]

In addition, it's not right that common base has low output impedance. It has low input impedance (1/gm).

 

[p11]

yeah sorry..:sad:

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ok i got a question that arrange in asc order in terms of input impedances.....
the options are
1) DARLINGTON PAIR
2)CC MODE
3)CB MODE
4)CE MODE
please if possible answer me... thank you...=)


i would also like to know that which mode of biassing in transistors has highest input impedance and lowest output impedance in compare to the other modes...