Inverting Voltage Amplifier Lab

Today in lab we experimentally created a circuit that multiplied an input voltage by a negative constant, using a operational amplifier. The operational amplifier that we used was an OP27, and by connecting our power into the "-" input pin of the op-amp, we were able to invert the sign of the voltage. Also, by looping the output back to the input, we were able to manipulate the ratio of the magnitude of the output to the input. The circuit we built looked as follows:

^^^^ A downward arrow indicates ground ^^^^

The relationship between the Vin and Vout for the circuit is as follows, according to Ohm's law:

We wanted to create a gain of approximately negative 2, with an input resistance, R1, of 1.8K Ohms. In order to do that, we needed to use a loop resistance, R2,  of 3.6K Ohms, then test the circuit with a Vin range of (-3V, 4V). Below is the work that we did to design and analyze the theoretical circuit (using a value of 2K Ohms, for ease of calculation) :

We then began building the circuit:

^^^^ Measured resistances of the 1.8K Ohm resistor (Left), and 3.6K Ohm resistor (Right) ^^^^

^^^^ The constructed circuit, ready for testing ^^^^

With the circuit constructed, we began testing the circuit by varying the input voltage from -3V to +4V in 0.5V increments. The results are numerically and graphically represented below:

As the data suggests, the circuit behaved as expected, but with limitations; the Vout never went above a magnitude of 4.25V due to power loss within the system, as well as power supply limitations. Additionally, the op-amp only behaved as expected for a short period of data. From input voltages of ~ -2V to ~1.5V the output was very close to a -2 multiple. Beyond that range though, the op-amp couldn't provide the desired output due to saturation within the op-amp itself. That being said, it should be noted that whenever using an op-amp, you should aim to operate between its saturation values.