OP-Amp Labs

Part 1: Inverting Amplifer

Theory
       The first lab with Op-Amps was to first get a very simple negative gain circuit working on a breadboard. In order to get a inverting gain we have to tie the positive terminal of the op-amp to the ground and drive power through the negative terminal. It is also required to tie feedback from the output to the negative input. Due to the large input resistance of the circuit there is practically no current running through those terminals, thus both positive and negative terminals are the same. When we have the positive to zero then we also have a zero voltage and the negative terminal.When you perform a nodal analysis of the negative input node then you can equate the current heading to the terminal as the current going through the feedback resistor.

Experiment

       We set up this circuit and applied the voltages to the terminals while we measured the v-out with a multi-meter. 



Measurements

Conclusion

       You can see the way in which the op amp reaches the saturation point at -3.5 volts.

Part 2: summation circuits

Theory
       We simplified this circuit by requiring the resistors along the input voltages legs were the same. This op amp works by using the fact that the current though the two voltage legs has to also the same current through the current along the feedback leg.

Experiment
      While the two values of R1 and R2 are not equal an assumption was made to neglect the 2k ohm difference between the resistors.

Measurements

Conclusion


       You can see from this chart how the op amp works. Before reaching the saturation point of the voltages you can see the error is within a narrow range.