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ECE Objective Questions { BJT Amplifiers and Transistor }



78. The fundamental requirement for oscillations in an amplifier is
A. positive feedback from output to intput
B. negative feedback from output to input
C. ample powir gain of the amplifier
D. all the above

79. Which of the undergiven oscillator has best frequency stability?
A. Clapp
B. phase-shift circuit
C. crystal
D. multivibrator

80. An oscillator that consists of two interdependent circuits such that output of each controls the input of the other is called a ? oscillator. in cascading, each stage's Vc gets larger which leads to ct.,-off after a few stages when Vc becomes equal to Vcc they provide low amplification per stage
A. sinewave
B. feedback
C. relaxation
D. negative resistance

81. The Wien-bridge oscillator is
A. free-running oscillator
B. a square-wave generator
C. a stable sine-wave audio generator
D. also called sine-cosine oscillator

82. Crystal oscillators are often used for providing
A. square wave output
B. triangular wave output
C. stable carrier wave in radio transmitters
D. frequency multiplication

83. If the frequency of incoming rectangular waves in a staircase generator is 100 Hz, the number of steps in the output staircase pattern is
A.100
B.200
C.500
D.50

84. A CB amplifier has very low input resistance because
A. low emitter ac resistance re' shunts all other resistances
B. it handles small input signals
C. emitter bulk resistance is small
D. its base is at ac ground

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