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Jeremy C. Zodinliana posted an Question
November 22, 2021 • 16:15 pm 30 points
  • IIT JAM
  • Physics (PH)

13. explain why the voltage gain of an rc coupled ampifier declines beyond 20 khz ac. signal frequency. 14. what is positive feedback of an amplifier? obtain th

13. Explain why the voltage gain of an RC coupled ampifier declines beyond 20 KHz ac. signal frequency. 14. What is positive feedback of an amplifier? obtain the relation between open loop and closed loop gain under positive feedback. 15 unant ovauataismael aill,

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    Anshum Sharma Best Answer

    13.) At High frequencies (i.e. above 20 KHz) Again considering the same point, we know that the capacitive reactance is low at high frequencies. So, a capacitor behaves as a short circuit, at high frequencies. As a result of this, the loading effect of the next stage increases, which reduces the voltage gain. Along with this, as the capacitance of emitter diode decreases, it increases the base current of the transistor due to which the current gain (β) reduces. Hence the voltage gain rolls off at high frequencies. 14.) The feedback in which the feedback energy i.e., either voltage or current is in phase with the input signal and thus aids it is called as Positive feedback. Both the input signal and feedback signal introduces a phase shift of 180o thus making a 360° resultant phase shift around the loop, to be finally in phase with the input signal. Though the positive feedback increases the gain of the amplifier, it has the disadvantages such as •Increasing distortion •Instability The equation of gain of the feedback amplifier, with positive feedback is given by Af=A/1−Aβ Af = closed gain A = open gain

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