Summing Amplifier

Before beginning the lab, we conducted two exercises.

First, the output of an inverting amplifier supplied by +5V and -0V with input of two square waves, with and without DC offset. In both cases we see the input amplified and reflected about zero, and in both cases the resulting negative component is clipped.

Second, we use nodal analysis to evaluate an ideal op amp circuit.

We then proceed to the lab, wherein we build a summing amplifier and supply it with two DC signals, one a constant 1V and the other ranging from -4V to +5V.

Circuit diagram with measured resistance values

Constructed circuit

Data (columns va, vb, vout) and comment

Summary

 We get results largely as expected for this circuit. All resistances equal, the two inputs are weighted equally in the sum and the op amp gives unity gain. Of note are the results of va=3V,5V, where the output is lower than expected, and the same value. This is presumably due to saturation of the op amp, and is consistent with there being two internal ~0.7V transistor voltage drops inherent to it.