We done some practices in class.
By doing this lab, we can know and prove how a Summing Amplifiers combines two input signals. For any amplifier shown in the circuit, the Vout = - R3/R1 * (Va+Vb).
We fix R1 and R2 equal to 1K and need to find out the value for R3. We don't want the resulting voltage be greater than 4V so that the OP will saturate. We need R3/R1 smaller than 4/6, so we choose R3 to be 220.
The results are pretty close to what we expected. The percentage difference is quit small.
Real circuit
The purpose of this lab is to find and prove output voltage to be the difference between two input voltages. the pre-lab section, we figure out that if we use four identical resistors, the out put voltage is simply Vout = Va - Vb. we use four 10K resistors We get our four resistor to have true value around 9.7 k ohm.
Ciucuit
Lab results for Va=1V
The Graph of Vin and Vout, we can see the relationship between vin and Vout is almost linear. The non-linear part may due to the saturation in high voltage input.
Now we changes the Va to -1V and adjust different Vb again. The results are pretty good since the percentage difference is quite small.
as we see the graph reaches negative saturation at high voltage, the rest part of graph is linear which fits our expectations.
Summery
Today, we learn more about two different types of operational amplifiers. summing Op add up the input signals while the difference OP subtract one signal from another. In the lab we did good job because the experimental results are very close to the predicted values. The difference may due to the non-ideal OP and the inaccurate resistance value.
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