EE 101
EE Dept., New Mexico Tech
Analog: Introduction to the Oscilloscope and Function Generator
Prelab Exercises
1. What is the a difference between peak-to-peak voltage and peak voltage? Explain your answer.
2. If a waveform has a period of 10ms, what is its frequency? If a waveform has a frequency of 25kHz,
what is its period?
3. Describe the relative position the cursors should be in if you wanted to measure the peak voltage of a
sinusoid. Describe their position if you wanted to measure the period of the waveform. Describe their
position if you wanted to measure the peak-to-peak voltage of the waveform.
4. Given Equation 1
v(t) = 5 cos(62832t + 0)
V
(1)
What is the frequency of the waveform in hertz? What is the period? What is peak voltage?
Lab Exercises
Part 1
1. Adjust the function generator to output the waveform in Equation 1. Start bringing up the frequency
from 1kHz to the value you calculated, while watching what happens to the waveform displayed on the
oscilloscope. Readjust the scope until one or two periods take up most of the screen. What happens
to the signal displayed on the scope as the frequency from the function generator rises?
2. With the cursors, measure Vp (peak) and Vpp (peak-to-peak) and record these values in your lab book.
3. With the cursors, measure the frequency of the waveform and record this value in your lab book.
4. Sketch the waveform in your lab book.
Note: When creating a sketch of the o-scope screen, it needs to be to scale and have the voltage and time
divisions labeled. It should closely resemble the screen, a box that is 10 divisions wide by 8 divisions
tall with a waveform inside. It also needs the 0V level marked on the left side, and the cursor positions
and values if used. It need not be a photocopy of the screen but a very good representation of it, such
that another person would easily recognize it for what it is and be able to describe the voltage and period
of the waveform.
Part 2
1. Build the circuit shown in Figure 1. The function generator will be used as Vs for the circuit. Set it
to output a 5V peak with a frequency of 330kHz.
Function
Generator
R1 = 150Ω
R2 = 10Ω
Vs
C1 = 1nF
Figure 1: RC Circuit
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EE 101
EE Dept., New Mexico Tech
2. Connect the function generator to your circuit. Next connect one oscilloscope probe to measure Vs
and another to measure Vc .
3. Adjust your o-scope in order to view both waveforms, Vs and Vc , simultaneously.
(a) Once the Vs and Vc waveforms are properly displayed, use the vertical cursors to measure the
frequency and period of each wave. Note that each waveform has the same frequency and period.
(b) Using your input waveform as the reference, measure the time difference between it and the
output waveform. Be sure to adjust your volts and seconds per division to maximize the size of
this difference on the screen for more accurate measurements. It is also easiest to get accurate
measurements if they are taken at the x-axis crossing and not the peaks. This time delay is ∆t.
Convert this value to degrees using Equation 2.
θ = 360
∆t
T
(2)
(c) Use the voltage cursors to measure the amplitude your output signal. The output signal Vp should
be smaller than the input Vp . Because this is in reference to the input voltage, figure out the
ratio of output voltage to input voltage (Vc /Vs ) and use it as a coefficient for Vs in your equation
in the next step. This ratio is what we call “gain”. Because the ratio is less than one (output is
smaller than input) we call this kind of gain “attenuation”.
(d) Write a sinusoidal equation for Vc based on the information you’ve gathered in this section.
Rather than using a constant value for Vp , specify it in terms of Vs using the ratio you found in
the previous step. For example, if your output Vp was 3/4 of your input Vp , then your equation
would look like Vc (t) = (3/4)Vs cos(ωt − θ), where Vs , ω and θ are the actual values. This is an
explicit way to refer to the output relative to the input, and allows us to easily see the signal
attenuation in the equation.
(e) Sketch the o-scope screen, including both waveforms. A second sketch is likely needed to show
show how you measured ∆t. Be sure to draw in and label the cursers.
Extra Credit
Before you dissemble your circuit, you can experiment with the input frequency to see how that impacts the
“output”.
1. With the plots displayed on your scope, double the frequency to 660kHz and measure the amplitude
of your output waveform (Vc ). Note that you’ll have to adjust the seconds/division to view the new
waveform.
2. Increment your frequency again by 330kHzand measure the output amplitude. Repeat this process
until you have five or six frequency/voltage data sets
3. Make a frequency response graph by plotting frequency on the horizontal axis and Vc on the vertical
axis. Plot your Vc value at each tested frequency (including the original values from part (c) and draw
the curve that connects the points.
4. Observe how the output voltage changes as frequency increases. What can you say about the response
of this circuit? If it were a filter what would you call it?
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201603
EE 101
EE Dept., New Mexico Tech
Notes on using the Tektronix o-scope
• Turn on the o-scope. Always start by reseting the o-scope setting to defaults by pressing the ”Default
Setup” button. Once it finishes, press the yellow ”CH 1 MENU” button and change the ”Probe
Voltage” from ”10X” to ”1X”. This needs done because normal leads are being used instead of 10x
probes.
• Use the yellow ”CH 1 VOLTS/DIV” knob to adjust the height of the waveform. The goal is to make
the waveform as tall as possible and still be completely visible on the screen.
• While adjusting the VOLTS/DIV, the associated POSITION knob can be used to move the waveform
up and down on the screen. The little color coded arrow on the left side of the screen represent 0v, or
the x-axis, for each waveform.
• Use the SEC/DIV knob to adjust the width of the waveform until you see one to two periods on the
screen. The associated POSITION knob allows you to move the waveform left or right on the screen.
• The end goal is adjust the waveform to appear like the one in Figure 2.
• Once the waveform is properly adjusted on the screen, there are many methods of measuring the
amplitude and the period of it. For this lab use the cursor feature. Press the CURSOR button and
select the Type. Adjust the cursor with the big knob at the top of the o-scope. Each cursor will need
to be selected in order to adjust it.
• If a second channel is needed, start by pressing the ”CH 2 MENU” button to enable it and then set
the ”Probe Voltage” to 1X. Both channels will share the same time scale but each has a separate
VOLTS/DIV adjustment and POSITION. Adjust the blue ”CH 2 VOLTS/DIV” knob as you would
channel 1. It is often useful to match channel 2 to channel 1 in both scale and position so that they
lay on top of each other.
• When sketching the screen of an o-scope in your lab book, be sure to do so in a box that contains a
grid of 8 divisions high by 10 divisions wide. The divisions on the screen have meaning and define the
waveforms displayed. Each vertical division is equal to the voltage noted for each channel and each
horizontal division is equal to the time ”M”. In Figure 2 the sine wave is 5 divisions of 200mV high,
representing 1V, and has a period of 4 divisions of 250µs, representing 1000µs. Always be sure to note
the the values for CH1 and M in order to give the divisions meaning.
Figure 2: Tektronix o-scope
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