JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II PULSE AND DIGITAL CIRCUITS Previous Question Paper (July/August - 2021 - R16)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Derive an expression for the output of a high-pass circuit excited by step input.
Answer
For a high-pass RC circuit, the input voltage Vi(t) is related to the output voltage Vo(t) by the differential equation:
For a step input of magnitude V, Vi(t) = V for t > 0. The Laplace transform of the equation is:
Since the capacitor is initially uncharged, Vo(0+) = V. Solving for Vo(s):
Taking the inverse Laplace transform, the output voltage is:
This shows that the output of a high-pass circuit for a step input is an exponential decay starting from the magnitude of the input step.
A symmetrical square wave whose peak-to-peak amplitude is 8V and whose average value is zero is applied to an RC integrating circuit. The time constant is equal to half-period of the square wave. Find the peak to peak value of the output amplitude.
Answer
Given a square wave with peak-to-peak amplitude Vpp = 8V, the signal swings between +4V and -4V. The time constant τ = RC is equal to half the period T/2. Let T/2 = τ.
During the first half-cycle (0 ≤ t ≤ τ), the input is +4V. The output of an integrator is:
At steady state, the output at the end of the first half-cycle (V2) must be the negative of the output at the start (V1), so V2 = -V1. Setting t = τ and Vin = 4V:
Using e-1 ≈ 0.368:
The output swings from V1 = 1.848V to V2 = -1.848V. The peak-to-peak output amplitude is:
Draw and explain the response of RLC circuit for a step input.
Answer
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Derive an expression for the percentage tilt of the output of a high pass circuit with large time constant excited by a symmetrical square wave with zero average value.
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Classify different types of clipper circuits. Give their circuits and explain their operation with the aid of transfer characteristics.
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Describe in detail about clipping at two independent levels.
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Design a negative clamper with positive and negative biases and then, explain the same.
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Give a brief note on piece-wise linear diode characteristics.
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Write short notes on diode switching times.
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Discuss in detail about breakdown voltages of a transistor.
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Write a short note on switching characteristics of transistor.
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Derive the relation between slope error, displacement error and transmission error.
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With the help of a neat circuit diagram, explain the working of a transistor constant current sweep circuit.
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Explain the working of four diode sampling gate with the help of neat circuit diagram.
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Why a OR gate is called mixing circuit? Draw a diode OR circuit for positive logic and explain how it works.
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