JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year ELECTRONIC CIRCUIT ANALYSIS Previous Question Paper (December - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
How the amplifiers are classified?
Answer
Amplifiers are classified based on several criteria:
- Based on the output signal: Voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers.
- Based on the frequency range: Audio frequency (AF) amplifiers, radio frequency (RF) amplifiers, and direct coupled (DC) amplifiers.
- Based on the mode of operation: Class A, Class B, Class AB, and Class C amplifiers, which are categorized by the portion of the input cycle for which the active device conducts.
- Based on the coupling method: RC coupled, transformer coupled, and direct coupled amplifiers.
State and prove Miller’s theorem.
Answer
Miller's Theorem states that a floating impedance Z connected between two nodes with voltages V1 and V2 can be replaced by two grounded impedances Z1 and Z2 at the respective nodes, where the gain is defined as A = V2/V1.
The equivalent impedances are given by:
Proof: Consider current I1 entering node 1 through Z: I1 = (V1 - V2) / Z. Substituting V2 = AV1, we get I1 = V1(1 - A) / Z. Thus, the effective impedance at node 1 is Z1 = V1 / I1 = Z / (1 - A). Similarly, for current I2 entering node 2: I2 = (V2 - V1) / Z = V2(1 - 1/A) / Z, resulting in Z2 = V2 / I2 = Z / (1 - 1/A).
What is gain bandwidth product?
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Why emitter bypass capacitor is needed?
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How the stability of amplifier will affect by negative feedback amplifier?
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State the necessary conditions for oscillator.
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Define conversion efficiency of power amplifiers.
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How is crossover distortion eliminated in class AB amplifier?
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What are the applications of tuned amplifier?
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What is the coefficient coupling in a double tuned amplifier?
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Part B
Draw the equivalent circuit for the CE and CC configurations subject to the restriction that RL = 0. Show that the input impedance of the two circuits are identical.
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The transistor amplifier shown in figure 1 uses a transistor with typical h parameter values. Calculate Ai, AV, AVs, Ro and Ri.
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Draw the circuit diagram of Darlington emitter follower and derive the expression for input impedance.
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Explain the working of cascade amplifier with neat circuit diagram.
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Draw the hybrid π equivalent circuit of a transistor in CE configuration and explain the various parameters in it.
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A transistor biased at 5mA, 10V, hie = 600Ω, hfe=100, CC=3pF and current gain of 10 at a frequency of 20MHz. Find β cut off frequency, gain band width product, Ce, rb'e and rbb'.
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Calculate the voltage gain of the FET amplifier shown in the figure 2. Assuming blocking capacitor to be large. gm=4mA/V and rd =5K.
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Sketch the small signal model of a CD FET amplifier and derive equation for the voltage gain.
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Draw the negative feedback topologies and explain them.
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An open loop amplifier has a midband gain of 500 and a pass band from 50Hz to 50KHz. Find voltage gain and cut off frequencies if 10% of output voltage is fed back.
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Derive an expression for frequency of oscillations of a wien bridge oscillator using transistor.
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Explain how the efficiency of the class A power amplifier is improved by the transformer coupled amplifier configuration?
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A transformer coupled class A power amplifier supplies the power to an 80Ω load connected across the secondary of a transformer having turns ration of 5:1. If Ic = 120mA, find maximum output power?
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Derive an equation of output power of a class B power amplifer.
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Draw the circuit diagram of complementary symmetry class B pushpull amplifier and explain its working.
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Why is double tuning employed in tuned amplifier? What are the advantages of it?
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What are applications of stagger tuned amplifier?
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What are the high frequency limitations of a tuned amplifier? How are they eliminated?
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How is the bandwidth of tuned amplifier improved? Draw such a circuit and explain its working.
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