MOSFET - Effect of signal shift between input and drain to source voltage

Q.  What would happen if 180° phase shifted signal between input voltage (Vi) and drain-to-source voltage (VGS) will be passed through the output coupling capacitor during the operation of MOSFET as an amplifier?
- Published on 23 Sep 15

a. DC value will be reduced to unity
b. DC value will be reduced to zero
c. DC value will be reduced to infinity
d. None of the above

ANSWER: DC value will be reduced to zero
 

    Discussion

  • Satyawati Patil   -Posted on 07 Oct 15
    When the MOSFET operates as an amplifier, the drain-to-source voltage is an amplified version of an input voltage inclusive of 1800 phase-shift between them. Therefore, the output is regarded as an inverted inversion of an input.

    According to the function of capacitor, it blocks DC and passes AC signals. The main functioning role of output coupling capacitor is to perform coupling on AC part of the signal at the output and to block the DC part of the signal.

    Hence, the signal obtained from the coupling capacitor comprises only AC signal without any DC part. Therefore, the value of DC signal is absolutely zero due to its absence in the output signal obtained from the coupling capacitor.

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