JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year ANALOG ELECTRONICS Previous Question Paper (May/June - 2019 - R16)
Part A is compulsory (25 Marks). Answer all questions. Part B consists of 5 Units. Answer any one full question from each unit (50 Marks).
Part A
What are the types of distortion in amplifiers?
Answer
Distortion in an amplifier refers to any change in the signal waveform between the input and output terminals, resulting in an output that is not a perfect replica of the input signal. The primary types of distortion are:
- Linear Distortion: This occurs when the amplifier does not provide equal amplification to all frequency components of the input signal. It is further categorized into Frequency Distortion, where different frequencies are amplified by different amounts, and Phase Distortion, where different frequency components experience different phase shifts.
- Non-linear Distortion: This occurs due to the non-linear characteristics of the active devices (transistors or FETs) used in the amplifier circuit. It results in the generation of new frequencies at the output that were not present in the input, specifically harmonics and intermodulation products. This is often referred to as Harmonic Distortion.
Write the difference between cascade and cascode amplifiers?
Answer
The primary differences between cascade and cascode amplifier configurations lie in their structural arrangement and their intended performance characteristics in analog circuit design:
- Cascade Amplifier: This configuration involves connecting multiple amplifier stages in a series (daisy-chain) arrangement, where the output of one stage is fed into the input of the next. The main objective of a cascade amplifier is to achieve a high overall voltage gain by multiplying the gains of individual stages (Atotal = A1 × A2 × ... × An).
- Cascode Amplifier: This configuration consists of two stages connected in a specific vertical stack: a common-emitter (or common-source) stage followed by a common-base (or common-gate) stage. The common-emitter stage provides transconductance, while the common-base stage acts as a current buffer. This arrangement is specifically designed to minimize the Miller effect, thereby significantly improving the high-frequency response and bandwidth of the amplifier.
| Feature | Cascade Amplifier | Cascode Amplifier |
|---|---|---|
| Primary Goal | Increase total voltage gain | Improve bandwidth and output resistance |
| Configuration | Series connection of stages | Stacked common-emitter/common-base |
| Miller Effect | Significant impact on bandwidth | Effectively eliminated |
Define Gain Bandwidth Product.
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What are the elements in the hybrid π model?
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Distinguish between enhance mode and depletion mode of MOSFET.
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What is folded Cascode amplifier?
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What is meant by positive and negative feedback?
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What are the conditions for oscillation?
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Compare class A and class B amplifier.
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Define Q-Factor in tuned amplifiers.
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Part B
Draw the h-parameter equivalent circuit for a typical common emitter amplifier and derive expression for Ai, AV, Ri and RO.
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For any transistor amplifier, Prove that Ri = hi / (1 - hrAv)
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Draw the circuit diagram of RC coupled amplifier. Explain the operation and its frequency response.
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Derive the expression for the CE short circuit gain Ai as a function of frequency using hybrid – π model.
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In hybrid ‘Pi’ model of a transistor at high frequencies, show that the gm is proportional to collector current.
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Mention important characteristics of CE amplifier.
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With the help of a neat diagram explain the operation of an n-channel enhancement type MOSFET.
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Explain how you set a Q point in a self-biased JFET.
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Derive the relation between μ and gm of JFET amplifier.
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A JFET has a drain current of 6mA. If IDSS = 12mA and VP = 4V find: i) VGS ii) For an n-channel amplifier FET IDSS=5.8 mA. VP=-3V and VGS=-2V find ID and gm.
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An amplifier has a midband gain of 125 and a bandwidth of 250KHz. If 4% negative feedback is introduced, find the new bandwidth and gain.
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Derive an expression for frequency of oscillations of a RC phase shift oscillator.
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What are the advantages and disadvantages of the introduction of negative feedback in amplifiers? Explain.
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Draw and explain the operation of Colpitt’s oscillator.
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Draw the circuit diagram of class B push pull amplifier and explain its operation. Also prove that its conversion efficiency is 78.5%.
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Explain the principle of operation of class-AB power amplifier with a neat sketch.
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Discuss in detail about frequency response of tuned amplifiers.
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