I. Characteristics of Semiconductor Devices
The purpose of this lab is to become familiar with the laboratory equipment and to measure the I-V
characteristics of a semiconductor diode and Zener diode.
I.A. Pre-Lab Procedure
Read this lab.
I.B. Oscilloscope Familiarity
Wire the circuit of Figure I-1. We will use this circuit to become familiar with the oscilloscope functions.
Use the "high" output of the signal generator and set the waveform to a 1 kHz sine wave. We now wish to measure
Vs with the oscilloscope.
Waveform Display
•
Hook the channel A scope probe to Vs .
Remember that all grounds must be tied to one point.
DIGITAL
button until DIGITAL
•
Press the MEMORY
MEMORY is no longer displayed on the LCD panel. This sets
the scope to act as a conventional analog oscilloscope.
•
Press the A/B button until only channel A is
displayed on the LCD panel.
•
Press the AC/DC button for channel A to
select DC coupling.
•
Press the
TRIG or X
SOURCE
button until A is displayed as
Figure I-1: Circuit to measure the I-V
characteristic of a resistor.
the trigger source. This means that the scope will trigger using
the signal on channel A.
•
Set the TB switch to select 0.2 ms/Div. The TB button sets the time scale seconds per division.
TRIG
to select AUTO.
•
Press the TBMODE
•
You should now be able to see the 1 kHz sine wave on your scope screen.
•
Press the channel A GND button to zero the input.
•
Use the channel A Y Pos knob to set the zero level of channel A to the center of the screen.
•
Once the zero level is set press the GND button to display the sine wave.
•
Set the channel A volts per division to 2 V/Div and vary the signal generator amplitude to obtain a 4
V-amplitude sine wave.
Display Cursors
To assist you in waveform measurement this oscilloscope has cursors and numerical displays.
DIGITAL
•
Press the MEMORY
button until DIGITAL MEMORY is displayed on the LCD display. The scope is
now in digital mode.
•
Under the scope display screen press the RETURN or right most button until you reach a screen
with no cursors or letters.
•
Press the right most button under the screen.
•
Press CURSORS.
•
Press the V-CONTROL button. This allows you to control the vertical position of the cursors.
•
Press the REF, UP, or DOWN button to line up the bottom line with the trough of the sine wave.
•
Press the ∆ , UP, or DOWN button to line up the top line with the peaks of the sine wave.
LAB I
I-1
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•
Read the ∆ value in the upper left corner of the screen for channel A. The value should be
approximately 8 V.
•
We now wish to measure the frequency. Press the RETURN button.
•
Press the T-CTRL button to control the horizontal position of the cursors.
•
Press the REF right or left buttons to move the cursor line to line up with the first peak of the sine
wave.
•
Use the ∆ left or right buttons to line up the second cursor line with the second peak.
•
In the upper right corner of the screen we see the frequency of the sine wave and in the center we
see the period of the sine wave.
I.C. Resistor I-V Characteristic
I-V characteristics tell you how the current through a device varies with the voltage applied across the
device. We will first observe the I-V characteristic of a resistor since we are all familiar with a resistor's operation.
From Ohm's law we know that the current
through a resistor is proportional to its resistance
Current
1
I =  V
R
Slope=1/R
Volts
This is an equation of a straight line with a slope
of 1 and a Y-intercept of zero. A graph of this equation
R
is shown in Figure I-2. Notice that current is non-zero for
both positive and negative values of voltage.
Figure I-2: The I-V characteristic of a resistor
We will now display the I-V characteristic of a
1 kΩ resistor on the oscilloscope.
•
Set the channel A volts per division to 5 V/Div.
•
Set the amplitude of the signal generator to 15 V or as large as possible.
•
Press the A/B button to display both A and B channels.
•
Press the channel B GND button and set the zero level of channel B.
•
Measure Vs with channel A and V x with channel B.
V
R sens is called a current sensing resistor. Since R sens << R, I ≅ s , and the voltage across R is
R
approximately Vs . Thus R sens does not have much of an effect on the circuit but the voltage across R sens is a
measure of I :
V
V
I = x = x amps
Rsens 10
•
Set the frequency of the signal generator to 150 Hz and display Vs and V x on the scope. Switch the
DIGITAL
scope between digital and analog operation by pressing the MEMORY
switch. Notice the difference between the two
modes. It is much easier to view low frequency signals using digital mode.
•
Set channel B to 0.1 V/Div.
Since V x is a measure of current we would like an amps per division (A/Div) equivalent so that we can
easily interpret the scope display.
I=
Vx
0.1 V / Div 0.1 (V / 10Ω )
=
=
= 0. 01 A / Div = 10 mA / Div
Rsens
10Ω
Div
Obtain a printout of this display. Record all scope settings. Make sure you identify each trace and where it
was measured in your circuit. Make sure you record the V/Div setting for the Vs and V x traces and the equivalent
A/Div setting for the current trace.
LAB I
I-2
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We would now like to see the I-V characteristic of this resistor on the scope screen.
DIGITAL
•
Set the scope to analog mode. (Press the MEMORY
until DIGITAL MEMORY is not displayed on the
LCD panel.)
•
Press the
X −DEFL
LEVEL VIEW
button. The signal on channel A controls the X-axis and the signal on channel B
controls the Y-axis.
•
Set channel A and channel B to GND and center the two dots using both Y-POS knobs and the XPOS knob. Once centered, display the I-V characteristic by pressing the GND buttons again.
•
Your scope screen will display two traces, Channel A versus Channel A ( a straight line), and
Channel B Versus Channel A (the I-V characteristic). Press the A/B button until only “B” is displayed on the scope
LCD panel.
•
Adjust the Volts per division settings to fill screen with the I-V characteristic.
The Y-axis Amps per division setting is the channel B Volts per division setting divided by 10. The X-axis
Volts per division setting is the channel A Volts per division setting. Draw a picture of the scope display and record
all important scope and signal generator settings. We cannot printout a copy of this screen because an x-y plot will
not work in digital mode.
I.D. Semiconductor Diode I-V Characteristic
Wire the circuit of Figure I-3. Obtain scope plots showing Vs and V x versus time, and Vs and Vd versus
time. Measure the diode voltage (Vd )with channel A and measure V x with channel B. We would now like to see the
I-V characteristic of this diode on the scope screen.
DIGITAL
until DIGITAL MEMORY is not displayed on the
•
Set the scope to analog mode. (Press the MEMORY
LCD panel.
•
Using the Y-POS knob move channel A off the screen.
X −DEFL
•
Press the LEVEL
button. The signal on channel A controls the X-axis and the signal on channel B
VIEW
controls the Y-axis.
•
Set channel A and channel B to GND and center the dot using the channel B Y-POS knob and the
X-POS knob. Once centered, display the I-V characteristic by pressing the GND buttons again.
•
Your scope screen will display two traces, Channel A versus Channel A ( a straight line), and
Channel B Versus Channel A (the I-V characteristic). Press the A/B button until only “B” is displayed on the scope
LCD panel.
•
Change the channel A setting to 0.5 V/Div and show me this plot.
Draw the diode I-V characteristic recording all important scope and signal generator settings. From your plot
identify values for the diode turn-on voltage Vγ and the diode saturation current IS . Notice that for a diode current
only flows when the diode voltage is positive. When the diode voltage is negative the current is zero.
I.E. Semiconductor Diode I-V
Characteristic
Wire the circuit of Figure I-4. Obtain plots of Vs and V x
versus time, and Vs and V z versus time. Measure the Zener voltage
(VZ ) with channel A and measure V x with channel B. We would now
like to see the I-V characteristic of this Zener diode on the scope
screen.
DIGITAL
•
Set the scope to analog mode. (Press the MEMORY
until
DIGITAL MEMORY is not displayed on the LCD panel.
•
Using the Y-POS knob move channel A off the
LAB I
I-3
Figure I-3: Circuit to measure the I-V
characteristic of a diode.
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screen.
•
Press the
X −DEFL
LEVEL VIEW
button. The signal on channel A controls the X-axis and the signal on channel B
controls the Y-axis.
•
Set channel A and channel B to GND and center the dot using the channel B Y-POS knob and the
X-POS knob. Once centered, display the I-V characteristic by pressing the GND buttons again.
•
Your scope screen will display two traces, Channel A versus Channel A ( a straight line), and
Channel B Versus Channel A (the I-V characteristic). Press the A/B button until only “B” is displayed on the scope
LCD panel.
•
Change the channel A setting to 1 V/Div and show me
this plot.
Notice that when the Zener voltage is positive the Zener looks
like the diode of the previous section. However when the Zener voltage
becomes large and negative the Zener breaks down and current flows.
The voltage where the Zener breaks down is called the knee voltage,
V ZK .
Figure I-4: Circuit to measure the IDraw the diode I-V characteristic recording all important scope V characteristic of a Zener diode.
and signal generator settings. From your plot identify values for the diode
turn-on voltage Vγ , the diode saturation current IS , and the Zener break-down voltage, V ZK .
I.F. Lab 1 Check Sheet
You must have me initial all items on this list to verify that you have made all of the measurements.
1.
2.
3.
4.
LAB I
Oscilloscope Familiarity
•
Scope display of VS with cursors.
•
Printout of scope display of VS with cursors.
Resistor I-V Characteristic
•
Scope display of VS and V x .
•
Printout of scope display of VS and V x .
•
Scope display of I-V characteristic.
Semiconductor Diode I-V Characteristic
•
Scope display of I-V characteristic.
•
Plots of Vs , Vd , and V x
Zener Diode I-V Characteristic
•
Scope display of I-V characteristic.
•
Plots of Vs , VZ , and V x .
I-4
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