Lab 02: Common-Emitter Amplifier

In this lab, I built and tested a common emitter amplifier circuit. Common emmiter amplifiers are built around a central transistor, using a biasing network of resistors to maximize its potential to amplify input signals. The circuit utilizes two voltages sources; a constant 9V source Vcc and an AC voltage source Vin. In order to stablilize the Q point of the circuit and therefore maximize gain of the amplifier, a 47 uF capacitor was placed in parallel with Re, at the emitter of the transistor.

After constructing the circuit, I tested its gain when connected to a load resistance of 1k Ohms. For this load, the measured gain was 45.83, meaning that the 19.2 mV input voltage was amplified to 880mV at the output. This process was repeated several times, each time with a different value for the load resistance Rl, from 10 to 100k Ohms. The results from these tests are included in the table below.

As you can see, as the load resistance increased, the gain of the CE amplifier increased.

For the next portion of the lab, I replaced the load resistance with the 1k resistor and varied the frequency of the input voltage Vin. The table included below shows the voltage gain and gain in decibels for an input frequency range from 100 Hz to 10 MHz.