Diode Curve Tracer Using Digilent Analog Discovery … · Diode Curve Tracer ... Diode Curve Tracer...
Transcript of Diode Curve Tracer Using Digilent Analog Discovery … · Diode Curve Tracer ... Diode Curve Tracer...
© August 10, 2015 Dr. Lynn Fuller
Diode Curve Tracer
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Rochester Institute of Technology
Microelectronic Engineering
ROCHESTER INSTITUTE OF TECHNOLOGY ELECTRICAL & MICROELECTRONIC ENGINEERING
Diode Curve Tracer Using Digilent Analog Discovery Module
Dr. Lynn Fuller, Adam Wardas Webpage: http://people.rit.edu/lffeee
Electrical and Microelectronic Engineering Rochester Institute of Technology
82 Lomb Memorial Drive Rochester, NY 14623-5604
Tel (585) 475-2035 Email: [email protected]
8-10-2015 DiodeCurveTracer.ppt
© August 10, 2015 Dr. Lynn Fuller
Diode Curve Tracer
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Rochester Institute of Technology
Microelectronic Engineering
INTRODUCTION
The Analog Discovery module is used with your computer and the “free” WaveForms software to turn your computer into a two channel oscilloscope, curve tracer, 16 channel logic analyzer, arbitrary waveform generator, 16 channel digital pattern generator, power supplies and voltmeters, network analyzer, spectrum analyzer and more. The module connects to your USB port. Find more information on line at www.digilentinc.com
Academic price ~$159
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Rochester Institute of Technology
Microelectronic Engineering
ANALOG DISCOVERY PIN-OUT
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THEORY
The equations on the next two pages should be familiar to you from your basic course in semiconductor devices. The ideal diode equation used to model the current-voltage characteristics of a diode in forward and reverse bias. The second page gives the equations for the space charge layer within a uniformly doped pn junction. Including build in voltage, width of space charge layer, maximum electric field, and junction capacitance. These equations are use in the Excel spread sheet that follows. You can download this Excel file from Dr. Fuller’s web page.
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Microelectronic Engineering
THEORY - CURRENTS IN PN JUNCTIONS
Vbi = turn on voltage
~ 0.7 volts for Si
VD
Id VRB = reverse
breakdown voltage
p n
Id
+ VD -
Forward Bias
Reverse Bias
Id = Is [EXP (q VD/KT) -1]
Is
Ideal diode equation
Is = qA (Dp/(LpNd) +Dn/(LnNa))ni2
Is = CT2 exp (-qEg/KT)
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Microelectronic Engineering
THEORY - UNIFORMLY DOPED PN JUNCTION
WW1W2= [ (2q+VR) (1/NA 1/ND)]1/2
W1= W [ND/(NA ND)] W2= W [NA/(NA ND)]
= - [(2q/+VR) (NA ND/(NA ND))]1/2
Cj’rW= r[(2q+VR) (1/NA 1/ND)]1/2
= KT/q ln (NA ND /ni2)
ni = 1.45E10 cm-3
Built in Voltage:
Width of Space Charge Layer, W: with reverse bias of VR volts
Junction Capacitance per unit area:
Maximum Electric Field:
o r = 8.85E-12 (11.7) F/m
= 8.85E-14 (11.7) F/cm
W1 width on p-side W2 width on n-side
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Microelectronic Engineering
THEORY – pn JUNCTION CALCULATOR
To use this spread sheet change the values in the white boxes. Results are given in the purple boxes and the I-V plot is updated. You can investigate effects of doping, temperature and photocurrent, determine reverse breakdown and junction capacitance. Enjoy!
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Rochester Institute of Technology
Microelectronic Engineering
COMPONENTS USED FOR THIS LAB
100 ohm resistor 1N4448 Diode Vishay BPW46 Photodiode LED any color 9 Volt Battery and connector 47 ohm ¼ watt resistor (used as heater) Protoboard
Diode
1N4448
Resistors Photodiode LEDs
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Microelectronic Engineering
SCREEN CAPTURE OF DIGILENT SETUP AND DATA
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CIRCUIT SCHEMATIC FOR DIODE I-V CURVE
Vd +
-
+ -
p
n
I R
VR
+
-
Scope ch1+
Scope ch2-
Scope ch2+
Scope ch1-
4 volt peak
triangle wave
100 hZ
+4
-4
I = VR/R
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Microelectronic Engineering
PHOTO OF SET UP FOR DIODE I-V CHARACTERISTICS
100 ohm resistor in
series with 1N4448
diode.
I = VR/R
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WAVEFORM GENERATOR SETUP
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OSCILLOSCOPE SET UP
R=100 ohm
I = VR/R
or 10mA/volt
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SCREEN CAPTURE OF DIGILENT SETUP AND DATA
R=100 ohm
I = VR/R
or 10mA/volt
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DATA IS ALSO AVAILABLE
10,000 data points are measured. Some are shown here.
~ -2 V ~ 0 V ~ +0.2 V ~ +0.6 V ~ +0.67 V ~ +0.75 V
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Rochester Institute of Technology
Microelectronic Engineering
CIRCUIT SCHEMATIC FOR DIODE I-V CURVE
Vd
+
-
+ -
I R VR
+
-
Scope ch1+
Scope ch2-
Scope ch2+
Scope ch1-
4 volt peak
triangle wave
100 hZ
+4
-4
I = VR/R
V+ = 9V
On/Off 47 ohm heater
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PROTOBOARD FOR TEMPERATURE EFFECT
A 47 ohm resistor under the diode is used as a heater and is connected to 9V battery. I will get hot and the diode curve will shift to the left. Theory predicts a ~ -2.2 mV/°C Caution: don’t let the 9V wires touch wires going to Analog Discovery module…
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Rochester Institute of Technology
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DIODE I-V AT ROOM TEMPERATURE
I = ~ -200 uAat Room T ~25°C
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DIODE I-V HEATED
Shift ~.05 volts
Temperature ~100°C above ambient
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CIRCUIT SCHEMATIC FOR DIODE I-V CURVE
Vd
+
-
+ -
I R VR
+
-
Scope ch1+
Scope ch2-
Scope ch2+
Scope ch1-
4 volt peak
triangle wave
100 hZ
+4
-4
I = VR/R
120 ohm V+ = 5V
On/Off LED
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PROTOBOARD FOR PHOTODIODE I-V
Triangle wave from the
waveform generator and 100
ohm resistor in series with
1N4448 diode. Plus 5 volt
power supply and 120 ohm
resistor in series with LED.
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Microelectronic Engineering
LED IS OFF – V+ OFF
I = ~ 0
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LED IS ON – V+ IS ON
I = ~ -200 uA
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SUMMARY
We were able to investigate diode I-V characteristics. We observed the effect of
light on the I-V characteristics. We observed the effect of heat on the I-V
characteristics. The diode I-V characteristics were compared to theoretical
calculations.
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Rochester Institute of Technology
Microelectronic Engineering
HOMEWORK – DIODE CURVE TRACER
1. Use the excel spread sheet to investigate diode I-V characteristics.
2. What happens to the I-V characteristic when a diode is heated?
3. What happens to the I-V characteristic when a diode is exposed to light?
Bonus: Modify the excel spreadsheet to include ideality factor (n) and internal
series resistance (RS).