Download Experiment 8 - Signal Waveforms and Measurements

İzmir University of Economics
EEE 205 Fundamentals of Electrical Circuits Lab
EXPERIMENT 8
Signal Waveforms and Measurements
A. Background
A.1. Basic Signal Waveforms
Although the term DC stands for "direct current", DC often is used to refer
"constant" signals. It is possible to refer a constant voltage as DC voltage, or
similarly a constant current as DC current. The waveform of a 10 volt DC
voltage is plotted in Fig.8.1.
10
VCC, volts
t, sec
Fig. 8.1. DC Voltage waveform
In electrical circuits, besides DC signals, most commonly used signal types are
sinusoidal, triangular and square waveforms as shown in Fig. 8.2.
xS(t)
Sinusoidal
t, sec
xS(t)
Triangular
t, sec
xS(t)
Square Wave
t, sec
Fig. 8.2. (a) Sinusoidal Waveform, (b) Triangular Waveform, (c) Square Waveform
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Above waveforms are periodic. Usually the time reference t=0 sec is not
reachable. For periodic signals, the period must be defined. The period T is
measured as shown below in Fig. 8.3.
xS(t)
T
Vp
Vp-p
t, sec
Fig. 8.3
It is usually more convenient to measure peak-to-peak voltage instead of peak
voltage. The peak-to-peak voltage Vp-p is defined in Fig. 8.3. If the periodic
voltage has zero average value, then the peak voltage is just the half of peakto-peak voltage, i.e., Vp = Vp-p/2.
A.2. Oscilloscope
Oscilloscope is a device that is used to display periodic waveforms. (If a signal
is not periodic, then sample values are taken and then displayed.) The
oscilloscope that is used in the laboratory is given in Fig. 8.4.
Fig. 8.4. Tektronix TDS100 Oscilloscope
An oscilloscope has always a display section (monitor) on the front panel to
display the time waveform. Only voltage waveforms are measured and
displayed using an oscilloscope. If current waveforms are needed to be
measured, a voltage that is proportional to the current must be generated.
The display details of the screen of the oscilloscope used in the laboratory is
given on Fig. 8.5.
The display section has 10 horizontal (time) divisions and 8 vertical (voltage)
divisions. It is possible to measure two signals (Channel 1 – CH1 and Channel
2- CH2) simultaneously using TDS1000.
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Fig. 8.5. Display Section of Tektronix TDS100 Oscilloscope
The voltage value (500mV) on the right to CH1 indicates the voltage scale of
each vertical division for CH1 (yellow waveform). According to this scaling,
CH1 has a peak-to-peak voltage of approximately 3.6x500mV=1.8 V. For
Channel 2 (light blue waveform) has peak-to-peak voltage of approximately
2.6 V since the voltage scale for CH2 is 1.00V as given on the display.
For time measurements, the scale of the each division is given on the right of
M parameter. For the above signals, each time division is 25.0nsec. Then the
period of CH1 is 2x25.0nsec=50 nsec. Similarly the period of CH2 is just 25.0
nsec.
The frequency of a signal is determined using T as f=1/T. The unit of the
frequency is hertz (Hz).
For CH1 voltage waveform, f = 1/50 nsec = 20x106 Hz = 20 MHz as displayed
on the screen as 20.0002MHz. For CH2 f = 1/25 nsec = 40x106Hz = 40 MHz.
The signs 1 and 2 indicate the zero voltage axis of the voltages at CH1 and
CH2 respectively.
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B. Preliminary Work
1. Consider the voltage waveforms given below in Fig. 8.6. Determine the
peak-to-peak voltage, period and the frequency of each waveform.
100 mV/div
10 nsec/div
Vp-p = ……….
T = ………..
f = …………
1 V/div
10 sec/div
Vp-p = ……….
T = ………..
f = …………
10 V/div
100 nsec/div
Vp-p = ……….
T = ………..
f = …………
Fig.8.6
2. Consider the inverting amplifier circuit given in Fig. 8.7.
Circuit Parameters
R2
VCC
Vi
R1
-
Vo
R1 = 10 k
R2 = 100 k
VCC = 12 V
-VCC = -12 V
+
-VCC
Fig.8.7
8-4
i. Determine the voltage gain
.
ii. Determine and plot VO corresponding to the following sinusoidal input Vi.
Vi, volts
2
100 sec/div
-2
VO, volts
20
10
100 sec/div
-10
-20
Fig.8.8
8-5
C. Experimental Work
1. Using the signal generator of your laboratory set-up, generate a
sinusoidal voltage with 4 volt peak-to-peak and frequency of 4 kHz. Plot
the oscilloscope display on Fig. 8.9. Indicate the zero voltage level on the
plot.
Channel 1 scale:
…………
……./div
Time division:
…………
……./div
Vp-p = ……………
T = ……………….
f = ………………..
Fig.8.9
2. Using the signal generator of your laboratory set-up, generate a
triangular voltage with 2 volt peak-to-peak and frequency of 1 kHz. Plot
the oscilloscope display on Fig. 8.10. Indicate the zero voltage level on the
plot.
Channel 1 scale:
…………
……./div
Time division:
…………
……./div
Vp-p = ……………
T = ……………….
f = ………………..
Fig.8.10
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3. Using the signal generator of your laboratory set-up, generate a square
wave voltage with 5 volt peak-to-peak and frequency of 10 kHz. Plot the
oscilloscope display on Fig. 8.11.
(Important: Indicate the zero voltage level on the plot.)
Channel 1 scale:
…………
……./div
Time division:
…………
……./div
Vp-p = ……………
T = ……………….
f = ………………..
Fig.8.11
4. Construct the circuit given in Fig. 8.12.
Circuit Parameters
R2
Vi
VCC
R1
-
Vo
R1 = 10 k
R2 = 100 k
VCC = 12 V
-VCC = -12 V
+
-VCC
Fig.8.12
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i. Apply a sinusoidal with amplitude 4 volt peak-to-peak and with
frequency 1 kHz to the input Vi.
ii. Measure Vi (CH1) and VO (CH2) using the oscilloscope. Plot both signals
on Fig. 8.13. (Important: Indicate the zero voltage levels on the plot.)
Channel 1 scale:
…………
……./div
Channel 2 scale:
…………
……./div
Time division:
…………
……./div
Vp-p = ……………
T = ……………….
f = ………………..
Fig.8.11
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