PURPOSE
The purpose of this experiment was to utilize the theoretical knowledge we gained on summing amplifiers and put it into practice.
PRE-LAB
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| Figure 1 |
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| Figure 2 |
To begin, we were instructed to design a circuit that performed an addition of two signals. We drew out the schematics of this circuit in Figure 1. As it can be seen from the image, we chose two 3.6 kΩ resistors for the input resistance and a 1.8 kΩ resistor for the output resistance. We did this because we wanted the output voltage to be about half of the sum of the two input voltages (refer to Figure 2).
PROCEDURES
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| Figure 3 |
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| Figure 4 |
Before implementing our design, we measured the actual resistances of the three resistors. We redrew the schematics of the circuit with these measured values (Figure 3). Then, we set up our circuit as shown in Figure 4 (click to enlarge). The input resistors are encircled in red, while the output resistor is marked with green. The voltage sources are labeled with the black circles, and the positive and negative op amp supplies are within the orange circles. The output voltage that resulted from this set-up was measured with the multimeter as shown with the purple circles.
After constructing the circuit, we applied voltages across the two terminals. We varied Va from -4 V to +5 V, as shown in Figure 6, and kept Vb constant at 1 V. As it can be seen in Figure 5, when we set Va at -4.0 V, the output voltage was 1.49 V. This value was very close to the theoretical voltage that we found by using the equation displayed in Figure 2 (they were equal to the hundredth decimal place; the rest of the digits are not shown in the data table above).
