JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    Two triodes having amplification factors \[30\] \[\text{and}\] \[21\] and plate resistances \[5k\Omega \] and \[4k\Omega \] respectively are connected in parallel. The composite amplification factor of the system is

    A) \[\text{25}\]                                     

    B) \[\text{50}\]

    C)  \[75\]                                  

    D)  \[100\]

    Correct Answer: A

    Solution :

    Since,\[\mu ={{r}_{p}}\cdot {{g}_{m}}\] \[\therefore \]  \[{{g}_{{{m}_{1}}}}=\frac{{{\mu }_{1}}}{{{r}_{{{p}_{1}}}}}=\frac{30}{5}=6\] and        \[{{g}_{{{m}_{2}}}}=\frac{{{\mu }_{2}}}{{{r}_{{{p}_{2}}}}}=\frac{21}{4}\] Since, triodes are connected in parallel, hence effective plate resistance,                 \[{{r}_{p}}=\frac{{{r}_{{{p}_{1}}}}{{r}_{{{p}_{2}}}}}{{{r}_{{{p}_{1}}}}+{{r}_{{{p}_{2}}}}}\]                     \[=\frac{5\times 4}{5+4}=\frac{20}{9}k\Omega \] and trans conductance,                 \[{{g}_{m}}={{g}_{{{m}_{1}}}}+{{g}_{{{m}_{2}}}}=\left( 6+\frac{21}{4} \right){{(k\Omega )}^{-1}}\] \[\therefore \]Amplification factor                 \[\mu ={{r}_{p}}\cdot {{g}_{m}}=\frac{20}{9}\left( 6+\frac{21}{4} \right)=25\]


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