Last N, First N - Lab 4 Report

ID: 1234567
                                                                    Han Q. Le (c)

Part 0 -  Background: AC voltage

0.1 AC voltage

Appliances in our house run on AC voltage.* When we use things like phones, computers, flash lights, we use batteries, which give DC voltage. What exactly is the difference between AC voltage and DC voltage? (description in words is good enough). 
__________________________________________________________
*Actually, most appliances except for AC motors run on DC voltage. The household AC voltage is only to supply power, which is converted to DC to be used by the appliances.

Hint: this is from Lab 2:

0.2  an AC voltage mathematical description

How is AC voltage described mathematically (i. e. with a mathematical formula), Can we plot it?

Hint (see the formula and run the code below)

v[t]=amplitude Sin[2 π * frequency*time]

Manipulate[
Plot[a (Sqrt[2])Sin[2 π f t],{t,0.,0.1}
,PlotRange->{-300,300}
,PlotStyle->{Thickness[0.008],Hue[0.15,1,1]}
,FrameLabel->{"time (sec)","voltage (V)"}
,Frame->True, GridLines->Automatic
,FrameStyle->White, GridLinesStyle->LightGray
,Background->Black]

,{{a,120,"RMS voltage"},100,200},{{f,60,"frequency (Hz)"},60,120}]

0.3 Simulation of a function generator (lab instrument)

We can generalize the concept of AC voltage. It is not just what comes out of a wall plug, but any voltage that changes as a function of time can be considered as AC voltage. The change vs time doesn’t even have to be of any specific function. As long as it is a change, it is enough. In fact, in the lab, one useful instrument is known as waveform or signal or function generator. Here, we use an app to simulate the output of a waveform generator. Follow instruction in the Lab Guide.

0.4  Generalized AC voltage concept

Can we human generate AC voltage? Follow the Lab Guide (Part 0 -Step 4), then answer and discuss each question in the Lab Guide (i-, ii-, and iii-) here.

0.5 Sound measurement

There is another way we can generate AC voltage, follow the Lab guide and answer here. Your answer will include the recording of your whistle (that you can hear), and a subselect segment of the signal, showing its sinusoidal property. If you do not use Mathematica, export your sound files and embed them in your report.

0.6 Generating sound

Generate an AC “signal” voltage that we can sense, follow the Lab guide and answer here.

0.7 Phasor concept review

As long as you have the phasor concept, just review and there is no need to do anything in the report. But you are welcome to write if you wish to explain the reader of your report (not TA or instructor) about phasor.

Part 1 - Lab instrumentation

1.1 Power supply

To power an op amp, we need ± (Subscript[v, S]) voltage, where (Subscript[v, S]) can be from a few Volts to ≥ 15 V, depending on the op amp. In the lab, the BK Precision power supply has two isolated DC outputs. If both can give +15 V, how can we get one to give -15 V? More important: report how you will power your op amp, e. g. batteries, or AC adapters, of ± 5 V from Digilent AD2 if you have low voltage op amps.

1.2 Transmission concept - 1

Consider the case below and answer. This is an information research question; you should do an Internet search to find the answer. Follow the Lab Guide for hint.

1.3 Transmission concept - 2:  For reading fun. Answer or discuss the things in Lab Guide

What is the common theme of all the things presented in the Lab Guide?

1.4 Coaxial cable and BNC

Bob in Q. 1.2 above should not do a “penny-wise and pound foolish” thing by using appliance electric cord for his Internet and video service, which uses high-frequency AC signals. In this Lab (also Labs 5 and 6), we need to transmit the AC signal in a special conductor known as the coaxial cable, which is similar to but not identical to the video cable we have at home. Go to the Lab Guide to see more information and answer the question there here.

1.5 Function generator and the oscilloscope

In the Lab, two instruments, the function/waveform generator and the oscilloscope are learned together. The output of the former needs the latter for measurements. Below shows how we use them in this Lab. To see what our circuit does to a signal, we use the signal genetor to generate a test signal, which is split into two. One is the reference, to be measured with one channel of the oscilloscope and the other is the input into the circuit. The circuit output is fed into another channel. The objective is to compare the output vs. the reference input.

ByteUse a BNC splitter to split the function generator output into two.
One goes to the oscilloscope to be used as a reference. The other goes to the input of the op amp circuit. The circuit output should to another channel of the oscilloscope. If the test signal is sinusoidal, measure the relative amplitude and phase of the output versus the reference input. If the function generator output is set for 50 Ohm load, either use a 50-Ohm terminator on the output before the splitter, or select 50-Ohm input impedance on the oscilloscope reference channel.ByteTextByte

A typical oscilloscope can perform many measurements. For this lab, the three basic measurements are: amplitude, phase, and frequency. Without real instruments, discussion of these measurements are meaningless. If you have the Digilent AD 2, please follow the entire instructions in Lab 4, Part 1, Step 5 Guide (which is both embedded in the Lab 4, Part 1 Guide, and is also available as a stand alone app).

Part A -  Op amp and voltage amplifier

Please review the theory of op amp if necessary. Here are some links:

Part 1                          Part 2

This lab is about using the op amp for signal amplification:
                              (Subscript[v, out])= g (Subscript[v, in])

where (Subscript[v, in]) is the input voltage ((Subscript[v, in2]) in the above figure) , (Subscript[v, out]) is the output voltage ((Subscript[v, out2]) in the above figure), and the gain factor g for the circuit above is:
                    g=- ((Subscript[R, feedback])/(Subscript[R, in]))=((Subscript[R, feedback])/(Subscript[R, in])) (e^(i π))  ( (Subscript[R, input]) is (Subscript[R, 1]) in the figure above)

For the sake of completeness (since this is lab course is to support a course in circuit theory), the above circuit is represented as a dependent source shown below:

Notice that (Subscript[v, input]) in the figures above is represented by (Subscript[v, X])[t], which suggests that it is an AC voltage, varies as a function of time. Why? the reason is that for a vast majority of applications, the op amp is used to process time-dependent signals. A constant voltage is not interesting. Hence, in the follow, we are interested only in AC voltage signals.

A.1 Build the circuit

Build the circuit. With a jumper wire, one FB resistor can be selected at a time.

Experiments: Step A.2 - A.7 : see summary table below, and follow Lab Guide, Part A.

ByteOutputByte

Part B -  Transimpedance amplifier for a photodiode (skip)

Part C -  Photoreceiver (skip)

Discussion, summary, and conclusion