1 March 2020

Transistor Interview Short Question Answer - 2

1

Why common collector configuration is used for impedance matching?
OR
Why common collector configuration is not used for amplification?


Impedance matching
  • The input impedance of the common collector is very high whereas the output impedance is very low. 
  • Due to this reason the voltage gain of the common collector circuit is less than unity. 
  • The configuration in which input impedance is high and output impedance is low is useful for impedance matching.


2
Why the common emitter (CE) transistor is used an amplifier?


  • The common emitter transistor is used as an amplifier due to following reasons. 
  • The collector current is high as compared to base current in the common emitter configuration therefore the current amplification of the CE configuration is very high.

Current amplification factor β = IC / IB
  • The voltage gain and the power gain of the common emitter is highest of three transistor configuration. 
  • The ratio of the output impedance of the input impedance of the common emitter transistor is small therefore the common emitter configuration is used for coupling between the stages of the multistage amplifier.


3
What is operating point or quiescent point Q in the transistor?


Operating or quiescent point
  • The zero signal value of IC ( on x - axis ) and VCE ( on y - axis ) is known as operating point of quiescent point Q.


4
Describe the importance of the operating point.


Importance of operating point
  • If the operating point lies on the DC load line very close to collector current IC point, the transistor may be operated in the saturation region. 
  • If the operating point lies on the DC load line very close to operating point VCE, the transistor may be operated in the cut off region. 
  • Therefore the operating point on the DC load line should be such that the transistor operated in the active region. 
  • If the operating point is in the middle of the DC load line, the transistor is operated in the active region.


5
Which transistor configuration provides high voltage gain without current gain?


The common base (CB) configuration provides high voltage gain without current gain (The value of current gain almost unity).

6
Why common base (CB) configuration is useful for impedance matching in high frequency voltage source?
OR
What is buffer amplifier?


Buffer amplifier
  • The source impedance must is equal to the input impedance of the amplifier in order to maximum power transfer from source to load and load impedance must be same as that of the output impedance of the amplifier. 
  • The output impedance of high frequency voltmeter is low. When low impedance voltage source is connected to high impedance load, the circuit impedance should be match. 
  • The common base configuration consists of low input impedance and high output impedance therefore it is connected between source and load.  
  • Therefore the CB configuration is used for impedance matching applications.


7
In which operating region the transistor works as an amplifier?


Active region

8
Describe the advantages of transistor over vacuum tubes.


Advantages of transistor over vacuum tubes
  • Very high voltage gain
  • Smaller in size
  • Used in integrated circuit
  • Less heating
  • It requires low supply voltage





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