Day Nine is Exam Day, Day Ten - Inverting Voltage Amplifier - 4/4/2017

Today, we talked about the operational amplifier, which has the basic ability of mathematical operations, such as addition, multiplication, differentiation, and integration.
Because of its comprehensive functionalities, it is a useful tool on any circuit.
There are two types of operational amplifier we talked about, inverting(-) and non-inverting(+) operational amplifier.
The inverting amplifier is called "inverting" because the output is the input multiplied by a negative constant, and the non-inverting amplifier is called "non-inverting" because the output is the input multiplied by a positive constant. Those negative and positive constant are called the open-loop voltage gain (A). However, when there is a feedback feeding from the output back to the input, we called the ratio of output voltage to input voltage is closed-loop voltage gain. Feedback is negative when it is fed to the inverting terminal of the "op-amp", and it is positive when it is fed to the non-inverting terminal.

Here is the schematic of the non-ideal operational amplifier.

Non-Ideal Operational Amplifier is called "non-ideal" because an ideal op amp must have 1. an infinite open-loop gain, 2. infinite input resistance, and 3. zero output resistance.

There are three modes of the op amp.

1. Positive saturation, where the voltage is limited by the supply voltage.

2. A linear region, where we find that useful.

3. Negation saturation, where the voltage is limited by the supply voltage.

Note: There are two voltage supplies (+) and (-) to make the operational amplifier in use, and if one of the voltage supply is connected to ground, that output will also be zero.

(eg. The negative voltage supply is connected to zero, then all the output voltage below zero will be zero, but not negative.)

We had some circuit drawings which transforms the op-amp into a real circuit element.

After that, we had our inverting voltage amplifier lab.
Designing:

Because we have to consider the guarantee voltage gain of 2 and R1 is approximately 2kohms in our inverting voltage amplifier circuit, we have to pick the closest value available in the class, which is 2.2k ohms for R1 and 4.7k ohms for R2. We also transformed the op-amp into the schematic above.

Result:
After the actual implementation of the circuit, we had the measured result for the output voltage in varying input voltage.

NOTE: The left column is the varying input voltages, and the right column is the varying output voltages.
ERROR: We probably measured the output voltage using the opposite polarity so that our voltage is not inverted.

Here is the graph of output voltages vs. input voltages. As we can see, the output voltages at the top and the bottom have reached the saturation point where no more voltage can be attained.

Comparing the gain R2/R1 = 2.136 to the actual voltages gain in the lab, which has an average of 2.133472 at the linear region without the zero point, this experiment is done successfully, and the percent error is really low.

Summary:

In day ten, we successfully verified the inverting op-amp by measuring the voltage output with varying voltage input. We used the ratio to compare with the ratio R2/R1, and we found almost zero percent error. One important point on this lab is to see that once the output voltage has passed the saturation point (usually the VCC), the output voltage is useless and inaccurate; therefore, we always use the linear region in our experiment for accuracy.