ECA BITS

ECA

JNTUH OBJECTIVE EXAM

UNIT-5: Feedback amplifiers

SECTION-I: Multiple choice questions

Note: 1.Don’t think that these bits only will be repeated in second mid.go through the concepts of last four units thoroughly then solve bits .these bits to cross check your knowledge

1. Negative feedback in amplifier [ b ]

(a) Improves SNR at the input (b) improves SNR at the output (c) Increases distortion (d) None of the above

2. The gain of an amplifier with feedback is ______. [ a ]

(a) A/1+Aβ (b) β/1+βa (c) β/1-βa (d) A/1-Aβ

3. In voltage shunt feedback, the input impedance [ b ]

a. increases b. decreases

c. depends on dc voltage applied d. depends on frequency of operation

4. Which of the following combination can be used as a buffer_____ [ c ]

a. CE b. CB c. CC d. All

Section-II: Fill in the blanks

1. The Trans conductance amplifier is also called as Series – Series amplifier (or) Current – Series amplifier

2. In an ideal voltage amplifier, the values of Ri & R0 are ∞, 0

3. The ratio of input impedance with feedback to without feedback is 1+Aβ

UNIT-6: Oscillators

SECTION-I : Choose the correct answers

1.An oscillator of LC type having a split capacitor in the tank circuit is [b ]

a. Hartley b. Colpitts c. Tuned d. Wein Bridge

2. In a Crystal oscillator the frequency is very stable due to ___________ of the crystal [c ]

a. rigidity b. high Q c. vibration d. none

3. For generating a sinusoidal wave of 1KHz frequency, the most suitable oscillator is ____ [ c]

(a) Hartley (b) Colpitts (c) Wien bridge (d) None of the above

4. The frequency stability of LC oscillator is _______ than RC oscillators. [ a]

(a) less (b) more (c) either a or b (d) None of the above

5. An important limitation of a crystal oscillator is ________. [ a]

(a) its low output (b) its high Q (c) less availability of quartz crystal (d) its high output

SECTION-II: Fill in the blanks

1. Non sinusoidal oscillators are also called Multivibrators.

2. The oscillator which uses inductive feedback is Hartley

3.The oscillator that uses tapped capacitors in the tuned circuit Armstrong Oscillator.

4. Electronic oscillations in which amplitude doesn’t change with time are called _

Sustained or Undamped oscillations

5 An oscillator using LC tuned circuit has L= 58.6μH & C=300pF, then the frequency of oscillations will be 1200 kHz

6. In a RC phase shift oscillator, each RC section provides a phase shift of 60˚

UNIT-7: Large signal amplifiers

SECTION-I : Choose the correct answers

1. With transformer connection to load the maximum efficiency of the class A amplifier will go up to a maximum of [c ]

a. 78.5% b.25% c.50% d.66%

2. The units of derating factor in power amplifier is [b ]

a. Volts/oC b. Watts/ oC c. Watts/ Cm2 d. None

3. In ____ power amplifier, the output signal varies for a full 3600 of the cycle. [a ]

(a)Class A (b) Class B (c) Class AB (d) None of the above

4. Maximum theoretical efficiency of Class B push pull amplifier is ___. [d ]

(a)25.5% (b) 50% (c) 75% (d) 78.5%

SECTION-II: Fill in the blanks

1. Thermal resistance of the heat sink will be typically 30C/W

2. If output power=20W and the input dc power=60W,then the efficiency of power amplifier is 33.3%

3. In Class B power amplifier, Q-point is set near cutoff

4. The input transformer in push-pull power amplifier is Step-up

5. The output transformer in push pull power amplifier isStep down

UNIT-8: Tuned amplifiers

SECTION-I : Choose the correct answers

1. The purpose of resonant circuits in tuned circuits is [d ]

a. TO provide properly matching load impedence b. To reset unwanted harmonics

c. To couple power to load d. All of the above

2. To reduce further harmonic distortion in large signal tuned amplifiers_______- is used [c ]

a. feedback configuration b. transformer coupling

c. Push Pull configuration d. all of the can be used

3. In tuned amplifiers, harmonic distortion is ____________. [c ]

(a) Infinite (b) more (c) less (d) None

4. Double tuned amplifier provides ____ bandwidth than single tuned amplifiers. [ a]

(a)larger (b) smaller (c) negligible (d)constant

5. Tuned amplifiers can be used in _____. [c ]

(a)Radar (b) IF amplifiers (c) both a and b (d) None

SECTION-II: Fill in the blanks

1. Small signal tuned amplifiers are operated in Class A mode.

2. Parallel tuned circuit is also known as Anti resonant circuit