26-Mar-2015: Inverting Voltage Amplifier

PURPOSE

The purpose of this experiment was to use the relationship of Vout and Vin we learned about inverting amplifiers and implement this newfound knowledge in an experiment.

PRE-LAB

Figure 1: Mathematical process of the pre-lab

Before starting the experiment, we were given the task of designing an inverting amplifier that resulted in a gain of approximately 2. In order to do this, we used the equation shown in Figure 1 and plugged in two arbitrary resistance values. We chose 1.8 kΩ and 3.6 kΩ as resistors R1 and R2, respectively, because they divided nicely into 2.

PROCEDURES

Figure 2: Schematic of our design

Figure 3: Measured resistance values of the resistors used in our design

After figuring out which resistors to use, we drew out the schematic of our design. We also measured the actual resistance values of the resistors before proceeding with our experiment.

Figure 4: Set-up of our designed circuit

The actual set-up of our circuit is shown above in Figure 4. After setting up our circuit, we applied a voltage to the amplifier and measured its output voltage. We repeated this process for a range of voltages, from -3 V to +4V, in increments of 0.5 V.

Figure 5: Data table of Vin and Vout

All the input voltages and their corresponding output voltages in this experiment are shown in the data table above (Figure 5).

Figure 6: Graph of Vout vs Vin

We then plotted the data with Vout on the y-axis and Vin on the x-axis. From this graph, it can be seen that our design was successful. This is because the slope of the linear portion of the graph is -1.97 (this is how Vout was changing with respect to Vin). This is very close to the -2 we solved for in the pre-lab. In fact, the percent error was only 1.5 percent.

Another thing that can be observed from this graph is the voltages at which the amplifier reached saturation. This can be seen from the areas where the graph level out and do not change. The saturation voltages were approximately 3.0 V on the positive end and -2.5 V on the negative end.

CONCLUSION

As mentioned before, our percent error between the expected and measured values was only 1.5 percent. Therefore, it can be concluded that our experiment was successful. This is pretty much the closest to the expected value that we can get because no experiment is perfect. There are always random errors that we cannot account for. The results are especially impressive considering that our experiments are relatively low-budget when compared to the experiments conducted by researchers that work for big corporations.