JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III ELECTRONIC CIRCUIT ANALYSIS Previous Question Paper (July - 2021 - R18)

The three basic BJT amplifier configurations are Common Emitter (CE), Common Collector (CC), and Common Base (CB).

• Common Emitter (CE): The emitter is common to both input and output. It provides high voltage gain, high current gain, and high power gain. It is widely used in general-purpose amplification and audio frequency applications.
• Common Collector (CC): The collector is common to both input and output. It provides high input impedance and low output impedance with a voltage gain of approximately unity. It is primarily used as a buffer or impedance matching stage.
• Common Base (CB): The base is common to both input and output. It provides low input impedance and high output impedance with a current gain less than unity. It is typically used in high-frequency applications due to its excellent stability.

Given parameters: R_S = 1KΩ, R₁ = 50KΩ, R₂ = 2KΩ, R_C = 1KΩ, R_L = 1.2KΩ, h_fe = 50, h_ie = 1.1KΩ, h_re = 0, h_oe = 0.

1. Input Resistance (R_i): The base bias resistors R₁ and R₂ are in parallel. R_B = (R₁ || R₂) = (50K || 2K) ≈ 1.923KΩ. The input resistance looking into the base is h_ie = 1.1KΩ. Thus, R_i = R_B || h_ie = (1.923K || 1.1K) ≈ 0.7KΩ.
2. Current Gain (A_I): The load resistance R_L' = R_C || R_L = (1K || 1.2K) ≈ 0.545KΩ. A_I = -h_fe * (R_C / (R_C + R_L)) = -50 * (1 / 2.2) ≈ -22.73.
3. Voltage Gain (A_V): A_V = (A_I * R_L') / R_i = (-22.73 * 0.545K) / 0.7K ≈ -17.69.
4. Output Resistance (R_o): Since h_oe = 0, the output resistance looking into the collector is R_o = R_C = 1KΩ.
5. Power Gain (A_P): A_P = |A_V * A_I| = |-17.69 * -22.73| ≈ 402.08.