Electrical Engineering Department
Semester: Spring 2023
Subject: ELTE217 Electronic Circuits
Instructor: Ass. Prof. Dr. Ezz El Deen Farouk
Sheet 1: BJT as Amplifier (DC & AC Analysis)
1. The transistor in the circuit in Fig. 4-1 is biased at a dc collector current of 0.3mA.
What is the voltage gain? (Pb. 7_15)
2. When the amplifier circuit in Fig. 4-2 is biased with a certain VBE, the dc voltage at
the collector is found to be +2V. For VCC =+5 V and RC =1kΩ: (Pb. 7_18)
a. Find IC and the small-signal voltage gain.
b. For a change ΔvBE = +5mV, calculate the resulting ΔvO.
3. The transistor amplifier in Fig. 4-3 is biased with a current source I and has a very
high β. Find: (Pb. 7_48)
a. The dc voltage at the collector, VC.
b. The value of re.
c. Replace the transistor with the T-model and hence find the voltage gain vc/vi .
Fig. 4-1
Fig. 4-2
Fig. 4-3
4. For the circuit shown in Fig. 4-4, draw a complete small-signal equivalent circuit
utilizing an appropriate T-model for the BJT (use α =0.99). Your circuit should show
the values of all components, including the model parameters. What is the input
resistance Rin? Calculate the overall voltage gain vo/vsig . (Pb. 7_53)
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Fig. 4-4
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