Analog Electronics

21. Negative feedback in an amplifier

  1. Reduces gain
  2. Increase frequency & phase distortion
  3. Reduces bandwidth
  4. Increases noise

Correct answer: (A)
Reduces gain

22. A dc power supply has no-load voltage of 30v,and a full-load voltage of 25v at full-load current of 1A. Its output resistance & load regulation ,respectively are

  1. 5 Ω & 20 %
  2. 25 Ω & 20 %
  3. 5 Ω & 16.7 %
  4. 25 Ω & 16.7 %

Correct answer: (B)
25 Ω & 20 %

23. The current gain of a bipolar transistor drops at high frequencies because of

  1. Transistor capacitances
  2. High current effects in the base
  3. Parasitic inductive elements
  4. The early effect

Correct answer: (A)
Transistor capacitances

24. The ideal OP-AMP has the following characteristics.

  1. Ri=∞ ,A=∞ ,R0=0
  2. Ri=0 ,A=∞ ,R0=0
  3. Ri=∞ ,A=∞ ,R0=∞
  4. Ri=0 ,A=∞ ,R0=∞

Correct answer: (A)
Ri=∞ ,A=∞ ,R0=0

25. An npn BJT has gm=38mA/v, cμ =10¯14 F, cπ =10¯13F and DC current gain β0=90.For this transistor fT & fβ are

  1. fT =1.64 x 108 Hz & fβ = 1.47 x 1010 Hz.
  2. fT =1.47 x 1010 Hz & fβ = 1.64 x 108 Hz
  3. fT =1.33 x 1012 Hz & fβ = 1.47 x 1010 Hz
  4. fT =1.47 x 1010 Hz & fβ = 1.33 x 1012 Hz

Correct answer: (B)
fT =1.47 x 1010 Hz & fβ = 1.64 x 108 Hz

26. A 741-type OP-AMP has a gain-bandwidth product of 1MHz.A non-inverting amplifier using this opamp & having a voltage gain of 20db will exhibit -3db bandwidth of

  1. 50 KHz
  2. 100KHz
  3. 1000/17 KHz
  4. 1000/7.07 KHz

Correct answer: (B)
100KHz

27. An amplifier using an opamp with slew rate SR=1v/μsec has a gain of 40dB. if this amplifier has to faithfully amplify sinusoidal signals from dc to 20 KHz without introducing any slew-rate induced distortion, then the input signal level must not exceed

  1. 795mV
  2. 395mV
  3. 795 mV
  4. 39.5mV

Correct answer: (C)
795 mV

28. In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db & 2db respectively, then its common mode rejection ratio is

  1. 23dB
  2. 5dB
  3. 46dB
  4. 50dB

Correct answer: (C)
46dB

29. Generally, the gain of a transistor amplifier falls at high frequencies due to the

  1. Internal Capacitance of the device
  2. Coupling capacitor at the input
  3. Skin effect
  4. Coupling capacitor at the output

Correct answer: (A)
Internal Capacitance of the device

30. An amplifier without feedback has a voltage gain of 50,input resistance os 1 KΩ & Output resistance of 2.5KΩ.The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedbacik factor of 0.2 is

  1. 1/11KΩ
  2. 1/5KΩ
  3. 5KΩ
  4. 11KΩ

Correct answer: (A)
1/11KΩ

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