JNTU
JNTU B.Tech II ELECTRONIC CIRCUITS Previous Question Paper (November/December - 2020 - R13)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
With neat diagram, explain the concept of feedback. Also explain each block used in feedback concept.
Answer
Feedback is a process where a portion of the output signal is sampled and returned to the input of an amplifier to modify its performance characteristics, such as gain, bandwidth, and input/output impedance. The system consists of four main blocks:
- Basic Amplifier: An amplifier with gain A that processes the input signal.
- Sampling Network: A circuit that extracts a portion of the output signal (voltage or current) to be fed back.
- Feedback Network: A passive network (usually resistive) with a feedback factor β that determines the fraction of the output signal returned to the input.
- Mixing Network: A circuit that combines the feedback signal with the external input signal to form the actual input to the amplifier.
In a negative feedback system, the feedback signal is 180 degrees out of phase with the input, resulting in a reduction of the overall gain but improving stability and linearity.
Derive an equation for the voltage gain of an amplifier that uses series voltage negative feedback. Draw any such type of circuit.
Answer
In a voltage-series negative feedback amplifier, a fraction of the output voltage is fed back in series with the input. Let the input signal be Vs, the feedback signal be Vf, and the amplifier input be Vi = Vs - Vf. The output voltage is Vo = A Vi, and the feedback voltage is Vf = β Vo.
Here, Af is the closed-loop gain. The term (1 + Aβ) is known as the desensitivity factor. A common circuit implementation is the emitter follower (common collector) amplifier, where the entire output is fed back to the input, making β = 1, resulting in a gain slightly less than unity but with high input impedance and low output impedance.
What are different types distortions in Amplifiers? Explain them.
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Compare CB, CE, CC amplifier in all aspects and in a system how these amplifiers preferable to use.
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Explain the concept of Miller’s Theorem along with example.
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Draw and explain the FET in high frequency mode.
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Explain the effects of coupling and bypass capacitors on the low frequency performance of CE amplifier.
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Define the terms fα and fβ and derive the relation between them.
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State and prove clamping theorem.
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Draw a circuit diagram of a clamper whose output shifts on negative axis and why clamper is called restorer.
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With the help of a neat circuit diagram, explain the working of an Astable multivibrator.
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Draw the circuit diagram of Transistor clipper and explain its operation.
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Draw the circuit diagram of Class-B Complementary Push-Pull Amplifier and explain its working.
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Prove that a low pass RC circuit with a large time constant acts as an integrator.
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Explain about Break down voltage consideration of transistor.
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When does a transistor act as a closed switch and open switch?
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How does a diode act as a switch?
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