Day 14 (4/6/17)
Lecture:
In lecture today, we focused on ideal op amps (thankfully).
To begin, we predicted the output from an OP27 op amp package when a -100mv to 100mv square wave was input to it.
Now we predicted what the output is when we apply a 0-200mv input to it.
For this problem we had to calculate V0 if the source Vs = 0. This was done using nodal analysis, and after much simplification, a more simple equation was obtained.
And from there a value was found for one of the voltages.
As practice with difference amplifiers, we got a chance to conceptually design one focused on the criteria that it had a gain of 2 and a common mode input resistance of 10K ohms at each input. From there we were set to find what the input resistances would have to be using nodal analysis.
Lab:
Summing Amplifier
In this lab, my team and I designed, implemented, and analyzed what is known as a Summing amplifier. A configuration that will make use of an OP27 package that essentially sums up multiple inputs and outputs the result of the mathematical operation:
Where R3 is the feedback resistor and R1 is the input. Which basically means that if the resistor values on the feedback portion and the inputs are equal, your gain is 1 and the output is just the sum of the voltages from the sources.
Prelab:
First, we got down the connections and named our resistors, inputs, outputs, and voltage supplies.
We then chose a value for the 3 resistors to be (in this case 2.2K Ohms was chosen).
The resistors were measured for their live values.
During the prototype stage, the only thing that posed a challenge was working with a new pin diagram for the OP27. Even then our lab manual made it easy to follow along.
Since the lab manual proved trustworthy thus far, we decided to also use its recommended values for the inputs during the implementation phase!
(Use channel 2 waveform for Vb at 1V, and channel 1 for the "soon to be variable" input Va)
Setting the Va input to the voltages in the 1st column below, we read the following outputs displayed on the 3rd column.
The magnificence of this amplifier isn't found in the terribly boring "constant trend" in the Vb column! No! It is in the fact that if you read each row as a summing problem, the output is the result! (-4 + 1 = 3 more or less!) Amazing!
Lab:
The Difference Amplifier
To add to the theme of operational amplifiers, we explored the behavior of a similar element that was intended to actually subtract two separate voltage inputs!
Before any fabrication or prototyping could begin, we had to predict the behavior of such a fascinating configuration! Primarily we had to understand the relationship between Va, Vb, and the output!
After a lot of Algebra, we found that the output was dictated somewhat similarly to the summing amplifier!
Once we knew what to look for, we set into fabricating the prototype! After triple checking our pin diagrams and making sure everything was kosher, this was our product.
For good measure, we recorded the live values for each of the resistors.
The relation between the output and the resistor values was then determined for our specific circuit.
A procedure similar to the previous lab was called for in which we fed two separate voltages, one fixed on -1V and the other variable from -4V to 5V.
Summary:
A quick glance at the table here shows a similar pattern to the one from the inverting op amp where we hit a saturation region from 1V Va and higher. The beginnings can be seen at -4V Va input as well. The rest of the data points fall into the formula for difference amplifiers with an output of approximately 2(Vb-Va).
No comments:
Post a Comment