Common-Emitter Amplifier

The purpose of this lab was to become familiar with gain/bandwidth, CE amplifier, LTspice and use it to analyzer the CE amplifier circuit, and breadboard and test a CE amplifier circuit.

In part 1, we were instructed to breadboard the DC circuit portion of the CE amplifier shown in Figure 1. Next, I used the DMM to probe voltage at the transistor's base, emitter and collector. Base voltage was found to be 1.82 V, collector voltage was found to be 5.61 V, and emitter voltage was found to be 1.09 V. Vbe was calculated to be 0.73 V and Vce was calculated to be 0.73 V. These results prove that the transistor is operating in the forward-active mode and the DC circuit is assembled properly.

Figure 1: CE amplifier DC circuit

Next, I added the AC circuit to the breadboard shown in Figure 2. The dual mode of the oscilloscope was used to view both the input and output signals. When I viewed the signals, there was a lot of noise. I decided to re-breadboard my circuit but this did not fix the signal. I changed stations to test the circuit but again, it did not work so I partnered up with Avion Foreman.

Figure 2: CE amplifier with AC circuit added

Next, we were to determine the amplifier voltage gain. The values are recorded in Table 2.1. We were to see how the gain is influenced by the choise in load resistance. The gain for a series of different values of load resistance was measured and recorded in Table 2.1. The data of Table 2.1 was used to plot gain vs. resistance in Figure 3.

Table 2.1: Gain compared with load resistance

Figure 3: Gain vs. Resistance

The load resistance was replaced the 1 Ohm resistor. I then measured the gain at different frequencies. This data is recorded in Table 2.2. The gain was calculated in dB using 20*log(v0/vin). The gain verses frequency is shown in figure 4.

Table 2.2: Bode Plot Data for CE Amp

Figure 4: Gain vs. Frequency

In conclusion, I became familiar with gain/bandwidth, a CE amplifier, LTspice, and testing a CE amplifier circuit. I did have issues that I am working to resolve. I plan to bring in two breadboards next lab to test.