Lab Report on CE BJT Amplifier

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Northwestern State University of Louisiana *

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EET-2320

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Electrical Engineering

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Jan 9, 2024

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docx

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5

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Lab Report on CE BJT Amplifier By: Kalyah Rushing Due: 10/30/23
Objective: Construct the following circuit. Measure base voltage, emitter voltage, emitter current at the Q point. Apply an AC signal to the circuit. Observe the output. Measure the voltage gain. Then, compare your measurement with theoretical calculation. Materials: One 68k ohms resistor, one 27k ohms resistor, two 3.9k ohm resistors, one 2.2k ohms resistor One 100uF capacitor, one 10uF capacitor, one 1.0uF capacitor One 2N3904 transistor
Introduction: In the common-emitter (CE) amplifier, the input signal is applied to the base and the inverted output is taken from the collector. The emitter is common to ac signals. Theory: When a signal is applied across the emitter-base junction, the forward bias across this junction increases during the upper half cycle. This leads to an increase in the flow of electrons from the emitter to a collector through the base, hence increases the collector current. The increasing collector current makes more voltage drops across the collector load resistor RC. The negative half cycle decreases the forward bias voltage across the emitter-base junction. The decreasing collector-base voltage decreases the collector current in the whole collector resistor Rc. Thus, the amplified load resistor appears across the collector resistor. Procedure: 1. Connect the circuit to a Vcc of +15V and connect the probes accordingly to DMM and measure the base voltage. 2. Connect the probes accordingly to measure the emitter voltage. 3. Connect the probes accordingly to measure emitter current at Q-point. 4. Apply AC voltage and observe the output. 5. Connect the probes accordingly to measure voltage gain.
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6. Compare measurements with theoretical calculations. Data/Observations: VB= 4.24 V VE= 3.54 V IE= 1.59 mA Output when AC voltage is applied:
Voltage Gain= 125 The measurements are very close to the theoretical measurements. Conclusion: In conclusion, the resistances R1, R2, and RE used to form the voltage biasing and stabilization circuit . The alternating current is applied to the base of the transistor of the common emitter amplifier circuit then there is a flow of small base current. The amount of current flow through the collector helps the RC resistance. Hence there is a huge amount of current present in the circuit which amplified from the weak signal, therefore common emitter transistors work as an amplifier circuit. References: Hands-on Lab on CE BJT Amplifier PDF on MOODLE.