Section 2.2
Build and Test a Common Emitter Amplifier (AC)
In this section of the lab we added the AC circuit which includes a 1kHz AC input signal. The difference between the DC circuit and AC circuit is there is a Vin, Vout and three capacitors connected to the base, collector and emitter. After building the circuit we set up the function generator to output a 1kHz sine wave with 20 mVpp.
Section 2.1
Build and Test a Common Emitter Amplifier (DC)
In this section of the lab we had to breadboard the DC circuit portion of the CE amp. After using the DMM I found the voltages of my transistor. Since it was operating in forward-active mode Vb= 1.84V, Vc= 3.50 V, Ve= 1.12 V, Vbe= 0.68 V and Vce= 2.38 V.
Section 2.3-2.4
Determine the amplifier voltage gain
In these sections we had to determine the ratio of output voltage amplitude to input voltage amplitude and record the data in Table 2.1. To understand how the gain is influenced by the choice in load resistance we plotted load resistances, that ranged from 100k ohms to 10 ohms vs gain.
Pictures Section 2.1-2.4
Common-Emitter Amplifier
Table 2.1
Gain Compared with load resistance
This table represents the voltage gain depending on the value of RL(ohms) in Figure 2.11 (CE amp with AC circuit added). Figure 2.11 is shown at the top of the page to give the audience an idea of what the table is trying to show.
Figure 2.14
Blank Gain vs resistance for plotting Table 2.1 data
This graph represents the relationship between gain and resistance. From the table 2.1 10k and 100k both have a voltage gain of 12.9 mV which supports figure 2.14 leveling out.
Section 2.6
Plot Gain(dB) against frequency
In this section of the lab I plotted gain(dB) versus the frequency data I collected to produce a Bode plot.
Section 2.5
Bode Plot
In this section we replaced the load resistance with its default value of 1kHz. For frequencies ranging from 10Hz-10MHz I obtained 11 different voltage gains which I than changed into Gain(dB). The formula to change voltage gain into Gain(dB) is 20*log(Vo/Vin). When going through this section of the lab I needed to change the time base on my oscilloscope to have a clear output.
Section 2.7
3 dB bandwidth
In this section of the lab we had to find the 3 dB bandwidth which is often referred to has the half power bandwidth. I estimated that the bandwidth of my plot was in-between 800 Hz and 3MHz.
Pictures Section 2.5-2.7
Common-Emitter Amplifier
Table 2.2
Bode Plot Data for CE amp
This table shows the values of voltage gains (5-150 typical) for a variety of different frequencies.
Figure 2.15
Blank Gain (dB) vs frequency for plotting Table 2.2 data
The graph shows that the voltage gain increased as the frequency increased until it hit 3kHz-100kHz and than the voltage gain decreased as the frequency continued to increase.
Bode Plot 1
Frequency @ 100kHz
In this bode plot the blue sine wave is the input signal and the yellow sine wave is the output.
Bode Plot 2
Frequency @ 10kHz
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In this bode plot the blue sine wave is the input signal and the yellow sine wave is the output.
Reflective Writing
LAB 2
Before this lab started I was not use to the pre-lab being mixed in with the lab manual. Therefore I missed the majority of the points but have learned since. It has definitely been a change and somewhat of a struggle using LTspice instead of Multi-sim. While preforming this lab there was an issue using the DMM to probe voltage at my transistor's base, collector and emitter but the issue was resolved. The only other issue I had with this lab was getting the correct Gain(dB) value for Table 2.2 because I was not using log base 10.