JNTU
JNTU B.Tech II ELECTRONIC CIRCUIT ANALYSIS Previous Question Paper (August/September - 2022 - R15)
Answer any five questions. All questions carry equal marks.
Main
Draw the block diagram of n-stage cascaded amplifier and analyze its various parameters.
Answer
An n-stage cascaded amplifier consists of multiple individual amplifier stages connected in series, where the output of one stage serves as the input to the next. This configuration is used to achieve higher overall gain than a single stage can provide.
The block diagram consists of n blocks connected in series, labeled Stage 1, Stage 2, ..., Stage n. Each stage has an input voltage Vi and output voltage Vo, with the output of stage k connected to the input of stage k+1.
The parameters are analyzed as follows:
- Overall Voltage Gain (Av): The total gain is the product of individual stage gains: Av = Av1 × Av2 × ... × Avn.
- Overall Current Gain (Ai): Similarly, the total current gain is the product of individual current gains: Ai = Ai1 × Ai2 × ... × Ain.
- Input Resistance (Ri): The input resistance of the first stage is the input resistance of the entire cascade, as it determines the loading effect on the source.
- Output Resistance (Ro): The output resistance of the last stage is the output resistance of the entire cascade, as it determines the loading effect on the load.
Determine Voltage Gain, Current Gain, Input resistance and Output resistance for a CE amplifier using NPN transistor with hie = 1200Ω, hre = 0, hfe = 36 and hoe = 2 × 10-6 mhos, RL = 2.5kΩ and RS = 500Ω (neglect the effect of biasing circuit).
Answer
Given parameters: hie = 1200 Ω, hre = 0, hfe = 36, hoe = 2 × 10-6 mhos, RL = 2.5 kΩ, Rs = 500 Ω.
1. Voltage Gain (Av): The formula is Av = -hfeRL / (hie + ΔhRL), where Δh = hiehoe - hfehre. Since hre = 0, Δh = hiehoe = 1200 × 2 × 10-6 = 0.0024. Av = -(36 × 2500) / (1200 + 0.0024 × 2500) = -90000 / 1206 ≈ -74.63.
2. Current Gain (Ai): The formula is Ai = hfe / (1 + hoeRL) = 36 / (1 + 2 × 10-6 × 2500) = 36 / 1.005 ≈ 35.82.
3. Input Resistance (Ri): The formula is Ri = hie - (hfehreRL / (1 + hoeRL)). Since hre = 0, Ri = hie = 1200 Ω.
4. Output Resistance (Ro): The formula is Ro = 1 / (hoe - (hfehre / (hie + Rs))). Since hre = 0, Ro = 1 / hoe = 1 / (2 × 10-6) = 500,000 Ω or 500 kΩ.
State and derive equivalent input, output impedance of amplifier using Miller’s theorem.
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Draw the circuit diagram of Darlington pair circuit derive input impedance (Ri) and current gain (AI).
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Deduce the expression for Current gain with resistive load and discuss the variation of frequency response with RL.
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Derive the expression for Hybrid-π capacitance of CE transistor at high frequency.
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Derive the expression for the hybrid-π parameters gm, gb’e, gb’c, rbb’ and gce.
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Explain Common source amplifier with Resistive load using MOS transistor?
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Derive the expressions of input and output resistances for Voltage Shunt feedback amplifier?
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A voltage series negative feedback amplifier has a voltage gain without feedback of A = 500, input resistance Ri = 3kΩ, output resistance R0 = 20kΩ and feedback ratio β = 0.01. Calculate the voltage gain Af, input resistance Rif, and output resistance Rof of the amplifier with feedback.
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Determine the condition for sustained oscillations for an RC phase shift Oscillator with necessary circuit diagrams.
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A Colpitts oscillator is designed with C1 = 100 pF and C2 = 7500 pF. The inductance is variable. Determine the range of inductance values, if the frequency of oscillation is to vary between 950 KHz to 2050 KHz.
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Describe Complementary Symmetry Class B Power Amplifier with diagram and write about crossover distortion in class B power amplifiers.
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Discuss the need of Heat sink for power transistors. Mention about thermal stability of power transistors.
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With circuit diagram, explain the stagger tuning operation. Give necessary graph.
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Explain the stability considerations of a tuned amplifier.
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