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Draw a labelled circuit diagram of n - p - n germanium transistor in common emitter configuration. Explainbriegfly , how this transistor is used as a voltage amplifier. |
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Answer» Solution :Transistor as an amplifier is based on the principle that a weak input signal given to a base region produces an amplified out signal in the collector region. The input voltage signal`V_("i")` is connected between base and emitter through a capacitor `C_(1)` which filters d .cvoltage `V_(BB)` from going towards a . c input source . The output is taken from the collector resistance `R_(c)`. The capacitor `c_(2)` filters the dc voltage `V_( c c)` from the output signal `V_(0)`. Applying kirchhoff 's second law on input loop `V_(BB)=V_(BE)+I_(B)R_(B)`. . . (i) Applying Kirchhoff 's second law on output loop `V_(C C)=V_(CE)+I_(C)R_(C)` . . . (ii) From equation (i) ,`V_(BB)+V_("i")=V_(BE)+(I_(B)+DeltaI_(B))R_(B)` . . . (iii) Subtracting (i) from (iii) ,`V_("i")=DeltaI_(B)R_(B)rArrDeltaI_(B)=(V_("i"))/(R_(B))`  CHANGE in collector current`DeltaI_(c)=beta_(AC)=DeltaI_(B)=(beta_(ac)*V_("i"))/(R_(B))` . . . (iv) Where ,`beta_(ac)=(DeltaI_(c))/(DeltaI_(B))=(I_(c))/(I_(B))` From (ii) and (iv) ,Voltage gain`AV=(V_(0))/(V_("i"))=-beta_(ac)(R_(c))/(R_(B))`  Negative sign SHOWS that input and output signals differin phase by `pi` radian (out of phase). |
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