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The Function Generator and the
Oscilloscope
ECE 2100
Dr. Len Trombetta and Dr. Dave Shattuck
1
Sinusoid Basics
General form of the sinusoid:
•
•
•
•
v(t) = Vm sin(2pf t + f) [V]
Vm is the amplitude
f is the frequency
f is the phase
2Vm = Vpp (peak-to-peak)
We usually write w = 2pf, and w is the angular frequency. But note that what
you set on the function generator is f, not w.
v(t)
Vm
Vpp
t
2
Sinusoid Basics
A sinusoid may also have a dc offset.
v(t) = Vm sin(2pf t) [V] + Vdc
v(t)
0
Vdc
t
3
Function Generator
Let’s explore basic function generator properties...
Power
4
Displays and Output
The default setting is
1 [kHz], displayed here…
…and 100 [mV] peak-peak
amplitude, displayed by
pressing this button.
You won’t get an output until
you press “Output”.
scope
BNC to BNC
Next, connect Output to
the oscilloscope using a
BNC-to-BNC cable.
5
Oscilloscope
Voltage
The oscilloscope displays input signal as voltage vs. time.
time
Power
From Function Generator
(You don’t have these inputs.)
6
Scale Factors
Horizontal scale
factor (in sec/Div)
Vertical scale factor
(in Volts/Div)
20 mV/
f = 1/T
T
scale factor adjustments
500 uS/
Vpp
Change the scale factors to see how the display is changed on the ‘scope.
Convince yourself that the signal frequency and amplitude are what
is stated on the function generator display.
7
Waveform (Function)
Step through the functions to
observe each one.
A ramp with a 50%
asymmetry is a
triangle wave…
8
Amplitude
v(t) = Vm sin(2pf t) [V]
To adjust the amplitude:
v(t)
Vm
Use the keypad and the
Vpp*
t
button…
…or…
…the wheel and the
“ten’s place” buttons.
*
For this course, we recommend that you set your signal generator to be
driving a high impedance (resistance in this case) load.
9
Frequency
v(t) = Vm sin(2pf t) [V]
v(t)
To adjust the frequency:
t
Use the keypad and the Hz,
kHz, or MHz button…
T
T = 1/f
…or…
…the wheel and the
“ten’s place” buttons.
10
dc Offset
v(t) = Vm sin(2pf t) [V] + Vdc
To adjust the offset:
Use the keypad and the Vpp* button…
v(t)
0
Vdc
t
…or…
…the wheel and the
“ten’s place” buttons.
*
This procedure will give you twice the offset you key in,
unless the load is 50 W, or you set it to “High Z Load”.
11
The “T” Connector
output connected
to BNC “T”
The three BNC connectors are in parallel,
effectively providing two FGEN outputs.
Typically one will go to the scope and the
other will be your circuit input.
scope
circuit input
12
Coupling
Whether or not you observe the dc component
on the scope depends on the coupling.
1. Generate a signal with a dc offset, and connect it to
the oscilloscope.
2. Select whichever channel your signal is connected to.
3. Toggle through the coupling options:
dc: dc AND ac components are displayed.
ac: only the ac component is displayed.
The dc coupling option is named
badly. It should be called
something like, “everything”. 13
RMS Measurements
Another way to characterize the
amplitude of a periodic waveform is
the rms (root-mean-square)
amplitude:
When set to measure ac voltage or
current, the Agilent automatically
displays rms.
Vrms
1 t0 T
2

v
(
t
)
dt .



T t0
If v(t) is a sine or cosine (sinusoid), then
Vrms
Vm

.
2
14
Triggering
Trigger Menu
Trigger Level
When the oscilloscope is properly triggered, the image is “stable” because
it is displayed the same way each time it sweeps across the screen. By “the
same way”, we mean that it starts at the same point every time. If the
triggering is not correct, the image looks garbled , like it is “running”
across the screen. Try adjusting the trigger level, and see what happens.
15
External Triggering
The external trigger input of
the oscilloscope is on the
back, at the top.
An external trigger signal is provided by the SYNC output of the
function generator. This provides a square wave of about 3[Vpp]
amplitude at the frequency of the Output waveform, and synchronized
with it. So as long as your signal is coming from the Output of the
signal generator, the scope knows exactly when to trigger!
16
Fun With Speakers!
Play with the speakers by connecting
one output to the speaker and one to
the ‘scope. Observe the effects of
amplitude and frequency.
speaker
What happens to the sound if you change
the wave-form (sine/triangle/square)?
oscilloscope
17