EE 221 - ANALOG ELECTRONICS
LABORATORY EXPERIMENTS
Anh Dinh, Rory Gowen, Chandler Janzen
Department of Electrical and Computer Engineering
University of Saskatchewan, Canada
0. Self-taught tutorial - Circuit measurements using Analog Discovery Design kit:
Students construct a circuit on a breadboard then use the Analog Discovery Module® and
Waveforms® software to measure and plot various current and voltage nodes on the
circuit.
1. Non-ideal operational amplifier and op-amp circuits: In this lab, the students evaluate
characteristics of the non-ideal operational amplifiers. Students use a simulation tool
(SPICE) to simulate the two most popular configurations op-amp circuits (inverting and
non-inverting amplifiers). Students also build, predict the results, and observe the gain
and frequency response of the amplifiers.
2. Diode characteristics and diode circuits: At the end of this lab, the students should be
able to compare the experimental data to the theoretical curve of the diodes. The students
use the Analog Discovery Module® and Waveforms® software to plot the I-V
characteristics of the diodes. The students also construct rectifier and filter circuits using
diodes and capacitors.
3. BJT I-V characteristics: Students identify the current-control terminal of a threeterminal active device. The students will use the scanned-load-line methods to obtain the
I-V characteristic of the BJTs. The measurement results are to be compared with the I-V
curve obtained from the specification posted by the manufacturers.
4. BJT amplifier: In this lab, students design and implement single-stage BJT amplifiers
and learn the frequency response of an amplifier.
5. MOSFET I-V characteristics: students discover the voltage-control terminal of the
four-terminal MOSFET. The students will construct the circuit and use scanned-load-line
method to obtain the MOSFET I-V characteristics. The Analog Discovery Kit is to be
used as the main equipment in this experiment. The measurement results are to be
compared with the I-V curve obtained from the specifications posted by the
manufacturers.
6. FET amplifier: In this lab, students design and implement single-stage FET amplifiers
and explore the frequency response of the real amplifiers. The students will compare the
gain and frequency response of the MOSFET amplifier and the BJT amplifier in Lab 4.
HEALTH AND SAFETY
Any laboratory environment may contain conditions that are potentially hazardous to a
person’s health if not handled appropriately. The electrical engineering laboratories
obviously have electrical potentials that may be lethal and must be treated with respect. In
addition, there are also mechanical hazards, particularly when dealing with rotating
machines, and chemical hazards because of the materials used in various components. Our
LEARNING OUTCOME is to educate all laboratory users to be able to handle laboratory
materials and situations safely and thereby ensure a safe and healthy experience for all.
Watch for posted information in and around the laboratories, and on the class web site.
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LAB REPORT
Students work in a group of 2, the laboratory is on alternative week. Each student must
have a notebook for the labs. The notebook is used for lab preparation, notes, record, and lab
reports. The reports must be handed before 5:00pm on the due date into the box labeled to your
section. The reports are due on the same date of the following week. The lab book is marked and
returned before the next lab.
Marking Scheme
Your grade in the laboratory section is based on two criteria:
 Day-to-day lab performance
 Lab books/notebook keeping
The day-to-day lab performance is based on the lab instructor’s observation of you and
your conduct. This includes your competency at setting experiments up and working the test
equipment. It also includes your preparation for the labs, attendance, tardiness, attitude,
accuracy, and is also based on your answers, should he/she ask you any questions during the
course of the lab. Keep in mind that your behavior influences your grade; act professionally at
all times.
Your lab write-ups may be marked with one of the following grades:
 Unsatisfactory (repeat)
 Beginning
 Developing
 Satisfactory
 Advanced
Combinations of any two may also be used. These word grades are translated into number
grades by your instructor when compiling your grade for the class. All labs must be performed
and a write-up submitted in order to pass the class. If one or more labs have not been performed,
then a grade of “INC” (incomplete) will be submitted.
Lab notebooks can be considered to be fulfilling the same functions as logbooks in
industry. Logbooks are used to record the results of all tests performed on systems, subsystems
and equipment during the various phases of a project including R&D, design, systems
integration, etc. Logbooks are official, permanent documents, and can be used in court to prove
ownership of a design!
The following points must be followed when writing up lab reports:
 The first page must contain a table of contents.
 All pages in the notebook must be numbered.
 Formal structure is not critical; logical order is important.
 Try to use pen, avoid pencil.
 Legibility and neatness are important, as is orderly notes.
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The lab book is standalone. There should be no references to any outside
documents. Remember that you may be allowed to bring in your lab books for
the final exam. They are your cheat sheets—make sure they’re complete!
Theory and background information must be completed prior to the lab.
Cross out unwanted or erroneous material with a single large X. Do not remove
any pages from your lab book.
The left-hand page can be used for rough calculations, notes, measurements, etc.
This page is not considered part of the “official” write-up, unless you ask that it
be considered.
Do not cut and paste any material from the lab manual into your lab book; only
graphs, plots, experimental waveforms, and schematics can. Use glue wherever
possible; tape is acceptable, but staples are not!
One lab partner must have the original of any experimental waveform; his/her
partner may have a photocopy of that waveform.
Label all diagrams and schematics; include an equipment list.
Schematic diagrams and waveforms without explanation are not acceptable.
Discussion of results and/or conclusions resulting from each portion of the lab
should be found with that portion. The end of the lab should have a short
summary of all conclusions.
The instructors may request you to hand-in your lab books at the end of the term
for accreditation purposes.
If in doubt about what to include (and how), remember that it should be clear, concise
and complete.
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TUTORIAL
This is a self-taught tutorial, go through the tutorial in your own time. If you have any
question or need help, contact the support engineers or your instructor.
Analog Discovery Module
Each group should have a hardware module called Analog Discovery from Analog Devices and
the software called Waveforms from Digilent installed in a PC or laptop. More information can
be found in the following Digilent website
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOGDISCOVERY . You can read more information about the device and watch the “Getting started
with the Analog Discovery” video:
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOGDISCOVERY&CFID=196410&CFTOKEN=96896438
Figure below shows the Analog Discovery and its pinout diagram
- Connect the Analog Discovery into the computer using the USB cable provided and start the
Waveforms software. The main window of the Waveforms should appear.
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- Click on “in”, “out”, and “Voltage” on the “Analog” side of the above window. The following
windows will appear (may not be exactly as shown). Size the windows to your best view. These
are the 3 main functions of the Analog Discovery and Waveforms.
- The Power Supply (Voltage window) provides +5V (red wire) and -5V (white wire) with
respect to ground (black wires).
- The Scope (Oscilloscope 1 window) has 2 channels with differential input. Channel1has 2
wires: positive is orange and negative is orange-white. Channel2 has 2 wires: positive is blue and
negative is blue-white. The differential channels allow you to connect the positive or negative
side of the channel to anywhere on the circuit (i.e., the scope channels are not grounded unlike
those found in a typical oscilloscope). The channel will measure the difference in voltage (in
time) between its positive and negative wires.
The “Time” can be changed in “Position” (time) and “Base” (time/division in the horizontal
display of the scope).
Note that Channel1 and Channel2 (“C1” and “C2”) have “Offset” (DC level) and “Range”
(volt/division on the vertical display of the scopes).
If you need more channels on the scope display, simply click Add Chan. The added channels are
derived from C1 and C2. For example, if you want to display the current through a 100 Ω
resistor, put C1 across that resistor and Control  Add mathematic channel  Custom
C1/100. This “M1” is the math channel represents the current with the unit of
Volt/Ohm=Ampere. By default, the units of the math channel will be Volts. To change the units
) and select units  select the unit from the dropclick the math channel settings button (
down menu.
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- The Waveform Generator (Arbitrary Waveform Generator 1 and 2 windows) allow you to
simultaneously generate 2 arbitrary waveforms with respect to ground. Signal from the AWG1 is
connected to the yellow wire and the signal AWG2 is connected to the yellow-white wire. The
waveforms can be generated using standard shapes (sinewave, square wave, triangular wave, …)
or custom made shape using an external file (to be instructed later in the subsequence labs). Note
that you can change various parameters of these 2 waveforms such as DC offset, amplitude,
frequency, symmetry, and phase.
Explore these windows and familiar with the controls of the windows since they are directly
connected to the wires of the Analog Discovery and in turn, to be connected to your circuit.
More information on the Waveforms software can be found in the Digilent website.
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Experiments:
1. Voltage divider circuit.
Construct the circuit below on a breadboard. Connect a sine wave signal (generated by AWG1)
with the following parameters (sinewave, 60 Hz frequency, 2.5V amplitude, 2.5V offset, 50%
symmetry, 0 degree phase). Perform the followings:
- Display C1, C2, M1 (current through R1) at least 4-5 cycles on the oscilloscope
window. Note that the alternating current signals (ac) run on top of the DC signal (offset).
- Calculate rms values of VR1, VR2, IR1. Note that the ac rms is: VRMS 
V peak
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- Observe what happen to the waveforms when you change the signal offset to 3.5V,
1.5V, 0V, and -2.5V.
- Stop AWG1.
AWG1
Connected horizontally
R1=100Ω
Connected vertically
R2=470Ω
Connected horizontally
The breadboard
+
CH1
-
+
CH2
-
Ground
Voltage divider circuit
Note: You may have to adjust the “trigger level” on the scope to stabilize the waveform on the
display. The trigger level causes a periodic waveform that crosses the trigger voltage level to
snap to the crossing point making the waveform appear stationary in time. To adjust the trigger
level select the trigger source (
) from the drop-down list. After selecting
the trigger source a triangle will appear on the right side of the scope window ( ), left click and
drag the triangle to set the trigger voltage level. Observe what happens as you adjust the trigger
level to cross a waveform.
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Example of the scope display. Note: Math Channel M1 displays the current (I=V/R)
2. LED circuit:
Using the above circuit, insert a light emitting diode (LED) between R2 and Ground (make sure
the flat side of the LED connected to Ground). Change AWG1 into a standard flat line (DC
only). Adjust the DC level from 0-5V and observe at which voltage of AWG1 you can see the
LED emitting light. Now change AWG1 to sinewave at an amplitude such that you have an
excess at most 1V above the offset you obtain above. Adjust the frequency of the waveform to
have a comfortable flashing rate of the LED to be observed (for example 2 flashes per second).
Display the voltage waveform across the LED and its current. Change the waveshape to
triangular and squarewave (in the AWG1 generator) to observe the LED operation. Stop AWG1.
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3. RC circuit:
Now replace the LED by a 10uF capacitor. Make sure the negative leg of the capacitor is
connected to ground if this is a polarized capacitor. Change AWG1 into squarewave of 0 to 5V
with a frequency of 10Hz. Display 1 cycle of the waveforms of AWG1 and the voltage across the
capacitor. Find the time when the voltage of the capacitor reaching around 63% of its maximum
voltage from its minimum voltage. What is the difference of this time to the product of total
resistance and capacitance? What is this time called?
Note: A polarized capacitor will either have a “+”, “-” or band indicating the positive or
negative sides of the capacitor. If you are unsure about whether or not your capacitor is
polarized, please ask your instructor, support engineers or teaching assistants for help.
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LAB 1: NON-IDEAL OPERATIONAL AMPLIFIER AND OP-AMP
CIRCUITS
LEARNING OUTCOMES
In this lab, the students evaluate characteristics of the non-ideal operational amplifiers.
Students use a simulation tool (SPICE) to simulate the two most popular configurations opamp circuits (inverting and non-inverting amplifiers). Students also build, predict the results,
and observe the gain and frequency response of the amplifiers.
MATERIAL AND EQUIPMENT
Material
TL081 op-amp
Resistors
Photo diode, PNZ334 (or PD204-6C)
Equipment
Analog Discovery module
Waveforms software
PRELAB
The TL081 is used for this lab. The pin-out diagram for the TL081 op-amp IC is shown in
Figure 1. Check its datasheet and make notes of its maximum ratings such as power supply,
power dissipation, input voltage, and output current.
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dot
4
1
Figure 1: The TL081 op-amp
PROCEDURE
1. Inverting Amplifier
One of the most common applications of the op-amp is the simple inverting amplifier. The
output is inverted and the amplification gain is determined by the ratio of the feedback
resistor (R2) to the input resistor (R1). Use R1 = 1kΩ and R2 = 10kΩ.
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C2 0.5nF
R2 10KΩ
R1
1KΩ
+5V
1
2
+
C1
_
vin
~ (AWG1, sinewave,
_
7
TL081
3
+
4
1KHz, 100mV, 0V,
50%, 0)
-5V
6
vo
+
R3
C2
1KΩ
_
Figure 2: Inverting Amplifier (node numbers in circle correspond to the pin of the TL081 opamp)
- Simulate the inverting amplifier using ideal op-amp: follow the demonstration by the
instructor of how to simulate the circuit using the Simulation Program with Integrated
Circuit Emphasis (SPICE). A sample of a circuit file (inverting.cir) for Figure 2 to be
used in the simulation is as follow:
Inverting Amplifier Configuration
** Circuit description
**
* opamp circuit
.subckt ideal_opamp 1 2 3
Eopamp 1 0 2 3 1e6
.ends ideal_opamp
** Inverting amplifier
Vi 1 0 DC 0 AC 0.5V
R1 1 2 1k
R2 2 6 10k
C2 2 6 0.5nF
R3 6 0 1k
X_A1 6 0 2 ideal_opamp
** Capacitor C2 is put in parallel with resistor R2 to observe frequency response of the
amplifier**
*Analysis
.AC LIN 100 1Hz 100KHz
.PLOT AC VdB(6) Vp(6)
.probe
.end
Simulate the circuit and save the plot of the response (output voltage at different
frequencies) of the circuit as the sample below.
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- Neatly construct the inverting amplifier circuit shown in Figure 2 on a breadboard. See a
neatly construct of a circuit breadboard shown in Figure 3 below. Power the op-amp by
connecting the power supply of the Analog Discovery (+-5V, red and white wires) to the
circuit. Properly ground the circuits using the Analog Discovery ground (the black wire).
Figure 3: Sample of wiring circuits on the breadboard.
- Use the waveform generator of the Analog Discovery (AWG1) to generate the sinewave
input signal and connected the signal into the amplifier. Use the scope channels (C1orange wire and C2 – blue wire) of the Analog Discovery to measure input and output of
the amplifier (Vin and Vo). Note: C1 and C2 are the scope channels, not the capacitors.
- Turn on the power supply, run AWG1 and the oscilloscope. The samples of the AWG1
and the scope display are shown in Figure 4.
Derive the gain formula Av= -R2/R1 and experimentally verify the gain for a 1 kHz sine
wave. For your lab report, show the input and output waveforms. Give your derivation and
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compare the two calculated and measured gains. Why this amplifier is called an inverting
amp?
Change the frequency of the input signal in AWG1 in step of 5KHz, plot the response of the
non-ideal op-amp and compare with the ideal op-amp simulation result above. Show this in
your lab report. Find the frequency at which the gain equal to 0.707 of the maximum gain in
both cases. Record this frequency in your lab book. Is there a specific name for this
frequency?
Figure 4: Sample display of the inverting amplifier
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2. Non-inverting Amplifier
Repeat step 1 for the non-inverting amplifier shown in Figure 5 with R1 = 1kΩ and R2 =
10kΩ. Don’t forget to provide the supply voltage to the op-amp. For your report, show the
input and output waveforms. Derive and experimentally verify the gain relationship Av=
(R1+R2)/R1.
R2=10KΩ
R1
1KΩ
+5V
2
3
vin
(sinewave, 1KHz,
~
100mV,0V, 50%,0)
_
7
TL081
+
4
6
vo
RL
1KΩ
-5V
Figure 5: Schematic diagram of a non-inverting amplifier
3. Current-to-Voltage Converter (optional)
An op amp can be used to produce a voltage proportional to a given current, this is called a
current-to-voltage converter. Construct a circuit as shown in Figure 6. Don’t forget to provide the
supply power to the op-amp.
Step 1: Verify that V out = −Iin R2 for this circuit. That is, do the following for several input
voltages (1V, 2V, 3V, 4V, and 5V, show the lab instructors how you generate these voltages
using the Analog Discovery module). Measure the input voltage and from this calculate Iin. Use
the formula to calculate a theoretical Vout and compare this to the measured Vout. Include these
measured values and calculations in your report along with a brief discussion of the agreement
between theory and measurement.
1-5V
Figure 6:
h di
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Step 2: Now replace the current source with a photodiode as shown in Figure 7. Notice that the
photodiode is reverse-bias connected. The current of the diode is proportional to the illuminance
of the light. Look at Vout with the oscilloscope. Find the currents Iin with the light in the room and
another light source provided in the lab for your report. The experiment can be done by replacing
the photodiode with a Flexiforce sensor connected in series with a 2KΩ resistor. The resistance
of the sensor is inversely proportional to the force applied to the sensor (by squeezing on the
sensing portion of the sensor). The current is proportional to the force hence the output voltage
relates to the force.
5V
Figure 7: Photodiode with current-to-voltage converter
5V
Flexiforce to replace the photodiode
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LAB 3: DIODE CHARACTERISTICS AND DIODE CIRCUITS
LEARNING OUTCOME
At the end of this lab, the students should be able to compare the experimental data to the
theoretical curve of the diodes. The students use the Analog Discovery module to plot the
I-V characteristics of the diodes. The students also construct rectifier and filter circuits
using diodes and capacitors.
MATERIAL AND EQUIPMENT
Material
Equipment
1N4005 (rectifier diode)
Analog Discovery module
1N4733 (zener diode)
Waveforms software
1N4148 (signal diode)
Assorted resistors (100ohms,
10Kohms), capacitors
PRE LAB
Look up the characteristics of the 1N4005 diode by making a web search. The
specifications for different kinds of diode vary. Copy the maximum/minimum rates and the
electrical characteristics of the specifications for the diode to your lab report as part of your
lab report. Understand the terms used in the specifications.
THEORY
The simplest and most fundamental nonlinear circuit element is the diode. The diode is a
device formed from a junction of n-type and p-type semiconductor material, shown in
Figure 1(a). The lead connected to the p-type material is called the anode and the lead
connected to the n-type material is the cathode, shown in Figure 1(b). In general, the
cathode of a diode is marked by a solid line on the diode package, shown in Figure 1(c).
Figure 1: (a) PN-junction model, (b) schematic symbol, and (c) physical part for a diode.
One of the primary functions of the diode is the rectification. When it is forward biased (the
higher potential is connected to the anode lead), it will pass current. When it is reverse
biased (the higher potential is connected to the cathode lead), the current is blocked. The
characteristic curves of an ideal diode and a real diode are seen in Figure 2.
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I
V
Figure 2: I-V curve for a real diode
The current i in the forward direction can be expressed in the following exponential
relationship
i  I S e vD / nVT
(1)
where IS is usually called saturation current, it is a constant for a given diode at a given
temperature. It can be as low as 10-15 A. VT is also a constant called thermal voltage, and it is
given by equation 2 in which k= Boltzmann constant (1.3806488 × 10-23 (m2 kg)/(s2K)), T is
temperature (K), and q is the electron charge (1.60217657 × 10-19 coulombs).
VT 
kT
q
(2)
When analyzing circuits, the real diode is usually replaced with a simpler model. The simplest
form, the diode is modeled by a switch. The switch is closed when the diode is forward biased
and open when the diode is reverse biased.
PROCEDURE
1. Diode I-V Characteristics
A) Study the 1N4005 rectifier diode
The I-V characteristics for the diode can be displayed using the Analog Discovery module along
with the Waveforms software. Construct the circuit below on a breadboard. Through the proper
setup, the Y-axis can be used to display the current through the diode, and the X-axis can be used
to display the voltage across the diode. This can be done by using the “Add XY” button
) in the Waveforms Oscilloscope in which the X value is C1 (voltage across the diode,
(
VD) and the Y value is the diode current (M1) in amperes. This current is simply the voltage
across resistor R divided by resistance R (M1=C2/R). The input signal of AWG1 should be a
sinewave or triangular wave (why not a squarewave?) with a frequency about 10Hz, 2.5V
amplitude, and 2.5V offset. Note: you may have to adjust the offset and scale of the channels to
see the IV characteristic on the screen.
Study the I-V curve carefully and fill in the following table with appropriate values. Document
the knee voltage of this diode in your report.
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AWG1
R=560Ω
+
CH2
+
CH1
-
Ground
Points
Diode Voltage (V)
Diode Current (A)
Characteristic
1
Off
2
Off
3
Just turning on
4
0.6
5
0.65
6
Figure 3: Diode IV characteristic circuit
B) Repeat the same procedure for 1N4148.
Points
Diode Voltage (V)
Diode Current (A)
Characteristic
1
Off
2
Off
3
Just turning on
4
0.6
5
0.65
6
C) Explain the differences of the data between 1N4148 and 1N4005 if applicable and
document it in your final report. Hints: silicon diodes can be classified as signal diodes and
rectifier diodes.
2. Half-Wave Rectifier Properties
The half-wave rectifying properties of the diode can be displayed using the circuit shown in
Figure 4. Build the circuit on a breadboard. Use R = 1k ohms and a 1N4005 diode. Set the signal
generator AWG1 so that it can provide an output of:
• Sinusoidal signal
• Amplitude: 5V p-p with an offset of 0V
• Frequency: 60Hz
A. Display the waveforms for the input and output voltages (Vin and Vout) using the
oscilloscope. Copy the waveforms in your lab report, and label the peak voltages of the
waveforms. Explain the amplitude and time differences between Vin and Vout.
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B. Add a 10 μF capacitor in parallel with resistor R, the other parts remain the same. Please
notice the + and - signs on the capacitor if you use a polarized capacitor, make sure the
polarization is correct, otherwise it may blow up. Display the input and output voltage
waveforms and copy into your report. Label the ripple voltage (peak-peak) in the
waveform.
In your report, hand in the labeled waveforms obtained in (A) and (B). In addition, calculate the
ripple voltage using information from the text book and compare it to the experimental result.
Figure 4: Schematic of the half-wave rectifier diode circuit.
Optional: Build a full-wave rectifier using 2 diodes and the Analog Discovery module.
3. Zener Diode Characteristics
The zener diode has the unique property of maintaining a desired reverse biased voltage. This
makes it useful in voltage regulation. In this exercise, you are to tabulate the regulating
properties of the Zener diode. Connect the circuit as shown in Figure 5, use 220 ohms resistor
and 1N4733 zener diode.
Vin
220 Ohms
1N4733
Id
Figure 5: Zener diode voltage regulation
Measure the zener diode properties by varying the input voltage and measuring the voltage
across the diode and the current through the diode. Fill in the following table when you measure
the voltage and current. Show the lab instructor how you connect the circuit to have the input
voltage up to 7V from the Analog Discovery module.
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LAB 3: BJT I-V CHARACTERISTICS
LEARNING OUTCOME
Students identify the current-control terminal of a three-terminal active device. The students
will use the scanned-load-line and modified scanned-load-line methods to obtain the I-V
characteristic of the BJTs.
BACKGROUND
The BJT is best described as a current-controlled active element while the MOSFET and
JFET are voltage-controlled. The base current iB is usually considered the controlling
quantity. Although iB in turn depends upon vBE, the change in vBE for a given change in iB is
so small because of the exponential relationship that is often neglected. This approximation
(vBE =0.7 V) is often a source of confusion for the students who do not realize that a truly
constant vBE implies no change in iB. This point should be emphasized in this experiment.
MEASUREMENTS
There are many methods to measure the I-V characteristic of the BJT using equipment
available in the laboratory.
Scanned-load-line method:
Set up the circuit in Figure 1 and the arbitrary waveform generators to the circuit as
shown. Follow the screen shot of the AWG window to set the signals. For AWG2, see
Appendix at the end of the lab to generate 10 voltage steps input into the base resistor R1.
Figure 1: Experiment set-up for NPN transistor
Note: When calculating F from the measured collector currents and base currents, the
students should be sure to use values that correspond to the forward active region. It should
be pointed out that iC is practically independent of iB in the saturation region. The data
obtained by different students will probably differ significantly because F is not wellcontrolled quantity. The data sheet of 2N2222, for example, specifies a range of 30 to 150.
The reason is that small changes in iC/iE, or  , cause large change in F because  is close
to unity and is related to F by:
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F 

1
(1)
where F varies from 30 to 150,  changes only from 0.967 to 0.993.
The saturation voltage VCEsat is subject to the same kind of misinterpretation by the students
is Vf. Its value is often quoted as 0.2 or 0.3 V, but it is actually a monotonically increasing
function of iB.
Generate 2 waveforms similar to those shown in the above example (refer to the appendix for
further setup instructions). Click on the XY cursor in the oscilloscope window to turn on the XY
plot to show the I-V characteristics of the 2N2222 transistor similar to the sample below. The X
axis should be the voltage across collector and emitter (VCE in volts) and the Y axis should be the
collector current (IC in mili-ampere). The current is to be calculated by using the math channel
M1 after clicking on the “Add channel” cursor.
Change the waveform into sinewave and squarewave to observe (and explain) if there any
change in the I-V characteristic display.
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Setting up the signals and the scopes as described below:
AWG:
• AWG1: generates Vcc. A triangular wave with the range from 0V…5V (i.e.,
amplitude = 2.5V, offset=2.5V), frequency 100Hz. There are 10 ramps (rising or falling),
each synchronized with one of the steps of AWG2. Each ramp will generate a branch in
the Ic-Vce characteristic for a specific value of the Ib parameter.
• AWG2: generates Vbb. There are 10 steps uniformly distributed in the range
(0.5V…2.5V). See the appendix below for setting up the step voltages in AWG2.
Scope channels:
• C2: Vcc->Vc, the voltage drop across R2
• C1: Vc->GND, the collector to emitter voltage drop
• M1: Math channel calculating C2/R1 = Ic current. Since C2 is expressed in Volts and
R2 value is given as Ohm, M1 is expressed in Amps.
• Turn on the XY cursor in the oscilloscope window, “Add XY”. Designate X=C1,
Y=M1 to plot the I-V characteristics of the 2N2222 transistor.
Repeat the steps for the 2N2907 (pnp) transistor. The setup for the pnp transistor is shown in
Figure 2. (Note: the set-up of AWG1 and AWG2 for pnp transistor is different from
npn transistor)
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Figure 2: Experiment set-up for PNP transistor
Samples of the oscilloscope display are in the figure below.
Once you have your results for each of the NPN and PNP transistors, calculate Fdc and Fac
for the two transistors at the point where the magnitude of the voltage across the collector
and emitter is 2.5V. Compare these values with those given in the datasheets for the 2N2222
and the 2N2907. Is there any difference between Fdc and Fac? Why might there be a
difference?
Note: Fac can be calculated by taking the change in collector current and dividing by the
change in base current between two or more steps of base current and averaging them.
Example of calculating Fac (this is an average of 2 Fac):
 Fac
I c 2  I c1 I c 3  I c1

I b 2  I b1 I b 3  I b1

2
24
Appendix: SOME DETAILED INFORMATION IN THE EXPERIMENT:
Some hints for experiment building:
1- To generate the “stairs” signal of AWG2, start from an Excel file with 1,2,3,4,5,… 10
in 10 rows. Save that in .csv or .txt format (source file) and then import in the AWG (set
Channel 2 to “Custom”, click “File” and select the source file).
a- When imported, the data in the source file is scaled both in time and range
domain:
- Each value in the source file is replicated as needed, such a way to fulfill the
AWG buffer.
- Each value in the source file is scaled to (-100%...+100%) range. The smallest
value results in -100%, the biggest one results in +100% and all other data is
linearly interpolated.
b- After importing the file, the amplitude, frequency and offset can be set to fit the
needed signal specs. Frequency is here understood as the “buffer iteration
frequency”; 10Hz means that the whole stair sequence takes 100mS (10ms/step).
2- To generate the “triangle” signal of AWG1, set the phase offset to 90 degrees (we are
trying to line up the start/stop of a rising or falling ramp with the start and stop of an AWG2
voltage step). This way the project uses the rising and falling ramp for a value of Vbb. If the
frequency is set to 50Hz this results in 10ms for each rising and falling ramp (i.e. one entire
rising or falling ramp per voltage step of AWG2).
3- Scope and other things:
- To hide the “connections” between branches of the XY view of the characteristic
family, the XY view of the Oscilloscope is set (by default) to show only points. You can
change to the curve mode by clicking in the Oscilloscope window: Settings  Options
Display-XY dots = False.
- To keep absolute synchronism between AWG1 and AWG2, set “Auto sync” mode
), With AWG2 as Master. Also set “Run: Infinite” (should be set
(
), for AWG2 channel. Then click the “Run All”
by default
button (
) to start both waveform outputs. “Auto sync” mode re-synchronizes
channels at the largest period of the two channels (100ms from AWG2, in this case)
25
LAB 4: BJT AMPLIFIER
LEARNING OUTCOMES:
In this lab, students design and implement single-stage BJT amplifiers and observe
amplitude and frequency responses. Breadboard and the Analog Discovery module are to be
used. The students will use various tools and functions from the Waveform software to
perform measurement and plotting the amplifier response.
MATERIAL AND EQUIPMENT:
Material
2N2222 npn BJT transistor
Capacitors
Resistors
2N2907 pnp BJT transistor
Equipment
Breadboard
Multimeter
Analog Discovery
Digilent Waveform software
PRE-LAB
Look at this handout and be familiar with the CE amplifier described in the text book. You
need to know how to calculate the DC voltage, current and small-signal gain. Design an
amplifier with a voltage gain of -4, a collector current of 5 mA, bias the collector voltage to
provide a maximum output voltage swing (i.e., collector voltage Vc equals to ½ of Vcc).
The bias resistance R1 and R2 should be in the range of 1K to 20K (why?). Use a Vcc of +5
V from the power supply of the Analog Discovery module.
PROCEDURES
1. NPN transistor characteristics
Obtain 2N2222 Si npn from the lab instructor or from the teaching assistant. Measure its
βDC at VCE =2.5V if you don’t have the current gain of this transistor from the previous lab.
You need to include the transistor characteristics in your lab report. Label βDC on the curves.
The normal βDC of 2N2222 is between 100-200. Also use the information in Lab 3 BJT I-V
characteristics.
2. Common Emitter (CE) amplifier
Design and construct the circuit shown in Figure 1. You can use 1 uF for capacitor CB and
4.7 uF for the capacitor CC.
A. Measure the DC currents and voltages: IB, IC, IE, VC, VB, VE. Remember to measure one
at a time with NO input AC signal. In your report, make a table and list the results from
26
your experiment and hand calculations. In your hand calculation, use β determined from
your I-V curve. Assume VBE = 0.7V.
B. At this time, DO NOT connect the load resistor RL . Generate an input signal from
AWG1 (100 mVpp, 1 KHz) and send the signal to the input of the amplifier. Observe the
input and output voltage waveforms using two probes of the oscilloscope (Channel 1 and
Channel 2). First observe the waveforms of the input signals that are before and after CB.
Note that how DC voltage at the base is preserved by using the coupling capacitor CB.
Then observe the waveforms of signals Vc and Vo that are before and after coupling
capacitor CC. The waveform at Vc has both ac and DC components and waveform at Vo
is a pure ac signal because of the coupling capacitor CC blocking all the DC component in
the signal. Capture the waveforms at Vi, VB, Vc and Vo and copy them to your lab
report. Find the voltage gain from the waveforms (Vo/Vi).
+5V
RC
R1
To Channel 1 of the
oscilloscope
VC
CB
~
R2
CC
VO
VB
2N2222
Vi
AWG1
To Channel 2 of
the oscilloscope
RE
RL
CE
Figure 1: CE amplifier
C. Perform hand calculations for the output voltage and voltage gain. List the results from
your experiment and hand calculation in a table in your lab report.
D. Connect the load resistor RL = 1K to the amplifier. Read the output voltage from the
oscilloscope and find the voltage gain.
E. Connect a polarized capacitor CE =22 uF to the circuit as shown in Figure 1 so that it is in
parallel with RE . At this time, the emitter is ac shorted to ground. Observe the output
waveform at Vc and Vo and copy it to your lab report. Explain why the waveforms are
distorted. Once you have finished this step, recover the circuit connection according
to Figure 1 by removing CE and RL.
F. At the last step, you need to adjust the frequency of the input signal from the signal
generator. First you need to reduce the frequency (below 1kHz) and observe the voltage
gain. The gain will reduce after a certain frequency. Find the low frequency, fL, when the
voltage gain is decreased to 70% (half-power). Then you need to increase the frequency
(about 1kHz) and find the high frequency, fH, when voltage gain is reduced to 70%. The
amplifier bandwidth is defined as fH-fL. Document the frequencies and bandwidth in your
report. Read Appendix 1 and Appendix 2 in Lab5 FET Amplifier (page 37).
27
G. Optional: Use “Sweep” function in the Arbitrary Waveform Generator to sweep the
frequency of the input signal and observe the response of the amplifier. Describe the
response of the amplifier.
H. Optional: Repeat the steps using 2N2907 (pnp) transistor. Comment on the differences
between npn and pnp amplifiers.
I. Scope sample for npn BJT (2N2222) amplifier:
R1=10K, R2=3.9K, Rc=560, Re=150, 1KHz, 100mV, Vb=1.35V. Ve=0.709V, Vc=2.463V
28
Scope sample for pnp BJT (2N2907) amplifier:
(R1=10K, R2=27K, RE=100, RC=560)
(VB=3.85V, VC=2.6V, VE=4.54V)
+5V
CB
VB
2N2907
Vi
AWG1
~
CE
RE
R1
To Channel 1 of the
oscilloscope
VC
R2
RC
CC
VO
To Channel 2 of
the oscilloscope
RL
29
LAB 5: MOSFET I-V CHARACTERISTICS
LEARNING OUTCOME:
In this lab, the students discover two voltage-control terminals of a four-terminal MOSFET.
The students will construct a circuit to observe the change in threshold voltage of a
MOSFET transistor due to the change in substrate-to-source voltage. The students will
collect and analyze data to find the transconductance parameters of a particular MOSFET.
The students will acquire the MOSFET I-V by setting up a simple circuit connecting to the
Analog Discovery module.
MATERIAL AND EQUIPMENT
Material
MIC94050 p-channel MOSFET
BS107 n-channel MOSFET
IRFD110 n-channel MOSFET
Resistors
Equipment
Analog Discovery
Digilent Waveforms software
Breadboard
BACKGROUND:
The MOSFET is actually a four-terminal device, whose substrate, or body, terminal must be
always held at one of the extreme voltage in the circuit, either the most positive for the
PMOS or the most negative for the NMOS. One unique property of the MOSFET is that the
gate draws no measurable current. Another is that either polarity of voltage maybe applied
to the gate without causing damage to the transistor. Although enhancement-mode
MOSFETs respond to only one polarity, the students need not fear the consequences of
using the opposite polarity.
A MOSFET with its gate and drain connected together always operates in the constantcurrent region, its iD-VGS relationship is
iD  K vGS  K VTR
(1)
where the threshold voltage depends on the source-body potential vSB as
VTR  VTR 0   [ VSB  2F  2F
(2)
Using the typical values γ=0.4 V0.5 and F=0.3 V gives the following values for the change
in threshold voltage of an nMOS.
vSB (V)
1
2
3
VTR-VTR0
0.20
0.34
0.45
30
OBSERVE THE CHANGE IN THRESHOLD VOLTAGE DUE TO SUBSTRATE-TOSOURCE VOLTAGE (VSB):
Set up the circuit as shown in Figure 1 below. Use the MIC94050 p-channel MOSFET, this
transistor has 4 terminals in which the substrate is marked on the mounting PCB. Connect
the circuit to the Analog Discovery module, pay attention to the polarities of the scope
Channels 1 and 2. Start Digilent Waveforms software and WaveGen (out). Set-up the 2
output waveforms AWG1 and AWG2 using the parameters provided in Table 1. Consult the
detailed information at the end of this document of how to set-up the desired waveforms in
the Analog Discovery module. Start the Scope (in) and set-up the channels (C1, C2, and
Math Channel M1) as shown in the example waveforms in Figure 3. Add XY in the
Oscilloscope 1 window and select X=C1 and Y=M1. Run two waveforms generated in the
WaveGen (Run all). Run the oscilloscope and observe the waveform of the window XY#1.
The waveform should be similar to the samples in Figure 3.
Table 1: Initial Waveforms parameters set-up
Waveform Gen.
Frequency (Hz)
Amplitude
Offset
AWG1 (sawtooth)
10
2.5V
-2.5V
AWG2 (5 steps)
1
1.5V
1.5V
Channel
Math
S
Offset
Range
C1
-1.1V
100mV/div
C2
-2V
500mV/div
1mA/div
M1
C2/RD
-5mA
Time
Start 0
Base 200ms/div
MIC94050
Substrate
G
+
To AWG2 Channel 1
_
D
RD,560
+
Channel 2
_
To AWG1
Figure 1: Circuit set-up to observe the substrate voltage
The plots of iD vs vGS will look like these in Figure 2. Each curve corresponds to a
different value of vSB. The slope of each curve is K . Extrapolating each curve to iD=0
gives threshold voltage, VTR, for each value of vSB. The curves are not equally spaced
because the change in VTR is proportional to VSB . Measure the voltage vGS, current iD with
the Digilent scope for different values of vSB. Plot as shown in Figure 2.
Obtain a printout of the XY waveform, label the values of VSB on each curve. (The
waveform can be exported as data and can be saved into your computer). Use your favorite
software to plot the linear region of the curves. The slope of each curve is K . Find K in
mA/V2. Using your measurements find VTR0 (i.e., threshold voltage when VSB=0V).
31
Setup of step voltage on AWG:
-
Digilent waveforms 1  Analog  Out Wave Gen  Open new.
-
DWF1 – Arbitrary Waveform Generator 1 will appear.
-
Generator 1  Select Channels  Channel 1 (AWG1)  Chanel 2 (AWG2)
-
Selecting Ch. 2 AWG2 Generator opens the second Generator. Run All, Stop All will
control both Generators.
-
Generator AWG2  Custom  File  Five Setps.csv  open  open. This file was
created in Excel (1 column with 5 rows of values: 1, 2, 3, 4, 5), the file can be saved as
csv file or text file.
-
Adjust Gen. Frequency, Amplitude and Offset.
Use Figure 1: Determine VTR0
-
Connect substrate to source (ground the substrate to make VSB=0V).
-
Disconnect AWG2.
-
From XY Plot determine VTR0.
Increasing vSB
iD
VGS
Figure 2: Effect of bulk (substrate) voltage on the drain current
32
Note: This figure is only an example of the waveforms, your settings may be slightly different!
33
Figure 3: Sample waveform generators and source current vs. substrate-source voltage
MIC94050 TRANSISTOR I-VCHARACTERISTICS EXPERIMENT USING
ANALOG DISCOVERY MODULE
The experiment shows Id as function of Vds, with Vgs parameter varying using the Analog
Discovery Module and Waveforms software.
- Build the circuit as shown in the schematic diagram of Figure 4 and connect the Analog
Discovery instrument as indicated. Connect Scope probes and power supply of the
Analog Discovery as shown.
- Start the Digilent WaveForm software
The initial settings of the generated waveforms are:
 AWG1: generates Vss. A triangle browses the range from (0V…-5V), (i.e.,
Amplitude = 2.5V, Offset=-2.5V, frequency=100Hz).
 AWG2: generates VG. There are 11 steps uniformly distributed in the range (you must
create an exel or text file to generate 11 steps). Adjust Amplitude=-800mV, Offset=1.7V, frequency=10Hz.
 Ground the substrate.
34
AWG1(100Hz, 2.5V,-2.5V),
(Scope 1+)
MIC94050
VG
(AWG2,step,
10Hz, -800mV,
1.7V)
R1
560
Analog GND
Vd
(Scope1-, Scope2+)
GND (Scope2-)
Figure 4: Schematic diagram to obtain I-V characteristics of the p-channel MOSFET
Scope channels:
 C2: the voltage drop across R1
 C1: the source to drain voltage drop
 M1: Math channel calculating C2/R1 = Id current. Since C2 is expressed in Volts and R1
value is given as Ohm, M1 is expressed in Amps.
 M2: Math channel calculating (C2/R1)*C1 = Is*Vds = P, the power dissipated by the
transistor. Expressed in Watts.
 M3: Math channel calculating (C1+C2) = Vss, as generated by AWG1.
 Main time plot: shows the time diagrams. Only C1, M1 are activated, to keep the image
clean.
 XY#1: show a representation of the IV characteristics of the transistor in XY plot: vertical =
M1 is the source current Is (or Id, as function of C2) and horizontal = C1 is the source-drain
voltage Vds. There are multiple branches of the IV characteristics corresponding to different
values of VGS. Get a printout of the waveform, label the values of VGS for each curve.
 Measurements: What is the average value of P (transistor dissipated power)? Expressed in
Watts. (Hint: P = M2)
Additional Measurements and Questions:


Change Vsb (in steps of 500mV) by applying an external voltage to the substrate instead of
connected to GND. Observe, record, describe, and explain the change in IV characteristic of
the transistor due to the change of Vsb.
Can the resistor be connected to +5V instead of GND? If so, re-draw the schematic diagram
of the circuit (no need to set-up the circuit).
35
Sample of the scope windows of MIC94050 characteristic:
36
Optional observation: In the AWG window, observe the preview for the two generated signals:
Vg and Vss.
 in the oscilloscope Main Time plot, activate M2 to see Vss. Notice the voltage drop at high
currents, as AWG limitation. The triangle signal distortion does not affect the XY
representation, except the high current branches are a bit shorten (upper right end).
Uncheck M2 to return to the clean image.
 in the oscilloscope Main Time plot, C1 shows the source voltage, Vs, while M1 shows the
source current, Is.
 the XY#1 window shows the Is(Vds) characteristic. Each branch is generated during a single
step in the Vgg signal. The direction of browsing Vss (rising or falling) does not matter in the
XY representation.
o Quiz: what happens if you change the wave shape of AWG2 from triangle to
sinusoid?
 the Measurement window shows the transistor dissipated power. This value is computed as
average for the displayed time frame.
 You can start a scope ZOOM window to see the time domain and XY view corresponding to
the Zoom1 rectangle in the main time window. Click and drag the Zoom1 rectangle to see
what portion of the time diagram corresponds to each branch in the XY view.
 Explore further in amplitude, frequency, offset of AWG1 and AWG2. Change time scale,
offset, range, … on C1,C2,M1,M2,M3,M4 as necessary. Report what you have explored and
observed with clear explanation the characteristic of a p-MOSFET.
OPTIONAL:
BS107 N-CHANNEL TRANSISTOR CHARACTERISTICS EXPERIMENT
ON ANALOG DISCOVERY
Revise the above method to obtain an IV characteristic of the n-channel MOSFET
BS107. Describe your work, draw the schematic diagram, build the circuit, take measurements,
and obtain the IV characteristic.
To AWG1
RD,560
To
AWG2
G
D
BS107A
+
Channel 2
_
+
Channel 1
_
S
Figure 5: Setup for BS107A IV characteristic experiment
37
Sample scope window of BS107 IV characteristic:
SOME DETAILED INFORMATION IN THE EXPERIMENT:
Some hints for experiment building:
-
To generate the “stairs” signal of AWG2, start from an Excel file with 1,2,3,4,5 in 5
rows. Save that in .csv or .txt format (source file) and then import in the AWG (set
Channel 2 to “Custom”, click “File” and select the source file). When imported, the data
in the source file is scaled both in time and range domain:
o Each value in the source file is replicated as needed, such a way to fulfill the
AWG buffer (in our case, each of the 100 records generated 20 (or 21) samples, to
fill the 2048 samples in the AWG buffer.
o Each value in the source file is scaled to (-100%...+100%) range. The smallest
value results in -100%, the biggest one results in +100% and all other data is
linearly interpolated.
38
-
-
After importing the file, the amplitude, frequency and offset can be set to fit the needed
signal specs. Frequency is here understood as the “buffer iteration frequency”; 10Hz
means that the whole stair sequence takes 100mS (10ms/step).
To generate the “triangle” signal of AWG1, set the initial Phase to 270 degrees. This way
the project uses each rising and falling ramp for a value of Vbb. Frequency is set to 50Hz,
to result in 10ms for each rising or falling ramp.
-
To hide the “connections” between branches of the XY view of the characteristic family,
the XY view of the Oscilloscope is set (by default) to show only points. You can change
to the curve mode by clicking in the Oscilloscope window: Settings  Options
Display-XY dots = False.
-
- To keep absolute synchronism between AWG1 and AWG2, set “Auto sync” mode
(
), With AWG2 as Master. Also set “Run: Infinite” (should be set
), for AWG2 channel. Then click the “Run All”
by default
button (
) to start both waveform outputs. “Auto sync” mode re-synchronizes
channels at the largest period of the two channels (100ms from AWG2, in this case)
39
Appendix 1 – MIC94050 Specifications: http://www.micrel.com/_PDF/mic94050.pdf
40
LAB 6: FET AMPLIFIERS
LEARNING OUTCOME:
In this lab, students design and implement single-stage FET amplifiers and explore the
frequency response of the real amplifiers. A breadboard and an Analog Discovery Module
are used in this experiment. The students will use various tools and functions from the
Waveforms software to perform measurements and to plot the amplifier response.
MATERIAL AND EQUIPMENT
Material
IRFD110 n-channel MOSFET
Capacitors
Resistors
Equipment
Breadboard
Analog Discovery
Digilent Waveform software
Multimeter
IRFD110 Transistor Characteristics:
-
Build the circuit as shown in the schematic diagram in Figure 1 and connect the Analog
Discovery instrument as indicated. Connect Scope2 probes across R1 and Scope1 across
the drain and the source.
Start the Digilent WaveForm software
The initial settings to generate the waveforms required are:
 AWG1: generates Vss. A triangle browses the range from (0V…5V) (i.e., Amplitude
= 2.5V, Offset=2.5V, frequency=140Hz, symmetry=50%, phase=90 degrees).
 AWG2: generates VG. There are 13 steps uniformly distributed in the range
(Amplitude=250mV, Offset=3V, frequency=10Hz, you may have to adjust the
amplitude and offset values slightly to get a good result. Try to have a curve fall
along Id = 1.5mA).
(AWG1, Scope 2+)
R1, 510
IRFD110
Vs (Scope 2-, Scope 1+)
VG
(AWG2)
GND (Scope 1-, Analog GND)
Figure 1: Schematic diagram to obtain I-V characteristics of the n-channel MOSFET
41
Sample of scope windows:
Figure 2: Scope sample of the n-channel MOSFET I-V characteristic
42
DESIGN A MOSFET AMPLIFIER:
Design a FET amplifier (Figure 3) with a voltage gain AV = -2. The design is based on the IV characteristics of the IRFD110 obtained in the previous step. Design for VDD = 10 V (i.e.,
5 V supply from the Analog Discovery module, ID = 1.5 mA, VDS = 2 V, and Rin > 100 kΩ.
Assume a gm of 0.5mS in the design if necessary. Draw the operation point of your amplifier
on the I-V characteristic curve of the IRFD110 n-channel MOSFET and attach it to the lab
report.
The following analysis is appropriate for good quality transistors where the output
current, ID, is largely independent of the output voltage VDS (the output characteristic curves
are approximately “flat”). We calculate amplifier ac gain using the small signal FET
transconductance gm and we assume ro can be neglected because it is very large in
comparison to other circuit resistances, therefore A=-gmRD. The small signal FET equivalent
circuit is also shown in Figure 3. The input resistance is essentially R1 // R2 and the output
impedance is equal to RD if ro is very large. Small signal ac gain is calculated assuming that
capacitors have negligible impedance. See Appendix 1 on selecting appropriate capacitors.
.
Figure 3: FET amplifier and FET small signal model (Ch1 – and Ch2 – to Digilent GND to
reduce noise)
where gm is valid in exponential region.
43
PROCEDURE:
1. Construct the amplifier using an IRFD110 FET and other components indicated in Figure
1 of your design. Select C1 to have a cutoff frequency of 50Hz and C2 cutoff frequency
100Hz. Do not connect a signal generator and the capacitor C1 to the input yet. Measure
ID, VDS, VG, VS and VGS. Connect capacitor C1 and C2 and then apply a 50mV peak, 1
kHz signal to measure the ac voltage gain of the circuit without load. Compare your
measurements with your design values.
2. Devise a method to measure the input impedance of the amplifier at 1 kHz. Fully explain
and document your methods in your lab book. Hint: you can use a decade resistor box (or
potentiometer) and connect it in series to the input of the amplifier before the coupling
capacitor. Monitor the signal amplitude after the decade box when you adjust the decade
box values. Does this measurement agree with your calculation?
3. Place a bypass capacitor, CS = 1 μF, in parallel with RS. This bypass capacitance should
have impedance much smaller (< 10%) than 1/gm and the capacitor ac voltage should be
very, very small. Verify this in your record keeping. Calculate the gain of the amplifier at
1 kHz and verify it experimentally. You will need to use the approximate value of gm
which you calculated using the drain current.
4. Remove the bypass capacitor CS added in part 3. Connect a 10 kΩ load resistor as
shown in Figure 4. Measure and calculate VRL.
5. At the last step, you need to adjust the frequency of the input signal from the signal
generator. Recover the circuit to its original design (remove RL). First you need to reduce
the frequency and observe the voltage gain. The gain will reduce after certain frequency.
Find the frequency, fL, when the voltage gain decreases to 70%. Then you need to
increase the frequency and also find the input signal frequency, fH, when voltage gain
decreases to 70%. The amplifier bandwidth is defined as fH-fL. Document the frequencies
in your report.
+5 V
-5 V
Digilent
GND
Figure 4: FET amplifier with load
44
APPENDIX 1 – Selecting coupling capacitors:
Be careful when choosing your coupling capacitors (C1 and C2). For this experiment, our
largest non-polarized capacitors may be used. Polarized capacitors tend to have “higher”
capacitance values, usually ≥ 5 μF, and they are always marked with either a + or a – (or
both) next to one of their terminals. They may also be marked with a band to indicate the
negative end (same convention as a diode). Remember that the potential of the + terminal
should be always higher than the – terminal when connected in a circuit. Otherwise, it will
induce the leak current between the two terminals and eventually damage the capacitor. In
the signal path of a circuit such as C1 and C2, this condition may not be met in all cases since
the connected circuits are unknown. Therefore you should avoid polarized capacitors in the
signal path.
Coupling capacitors must be chosen so that they have a “small” impedance at the frequency
of interest compared with the input impedance of the circuit to which they’re connected.
This is to ensure that little voltage will be dropped or lost across the capacitor itself—after
all, an amplifier is supposed to amplify voltages, not attenuate them. A good rule of thumb
is that Zcoupling C should be no more than approximately 10% of the input impedance of the
amplifier (for the input coupling capacitor), or the input impedance of whatever circuit the
amplifier drives (for the output coupling capacitor). For the FET amplifier you just
constructed, the input impedance is supposed to be > 100 kΩ. Therefore the impedance of
C1 at the lowest frequency the amplifier is expected to see should be no more than
approximately 10 kΩ. If this lowest frequency is expected to be 100 Hz, then C1 > 0.16 μF.
For this experiment, select the appropriate coupling capacitors for C1 at lowest
frequency of 50 Hz.
Similarly, the amplifier drives a load of 1 kΩ (Figure 4). Following the same argument the
impedance of C2 at the lowest expected frequency should be no more than approximately
100 Ω. If this lowest frequency is 100 Hz, then C2 > 16 μF. If the largest non-polarized
capacitors available are 2 μF, then C2 would have to be made up of eight 2 μF capacitors in
parallel. Alternately, a polarized capacitor could be used with appropriate care given to the
polarity of the capacitor.
APPENDIX 2 – Frequency response of the FET amplifier:
The typical Frequency Response of an amplifier is presented in a form of a graph that shows
output amplitude (or, more often, voltage gain) plotted versus log frequency. Typical plot of
the voltage gain is shown in Figure 5. The gain is null at zero frequency, then rises as
frequency increases, level off for further increases in frequency, and then begins to drop
again at high frequencies. The frequency response of an amplifier can be divided into three
frequency regions.
45
Figure 5: Diagram of voltage gain versus frequency for an amplifier.
The frequency response begins with the lower frequency region designated between 0 Hz
and lower cutoff frequency. At lower cutoff frequency, fL ,the gain is equal to 0.707 Amid.
Amid is a constant midband gain obtained from the midband frequency region. The third, the
upper frequency region covers frequency between upper cutoff frequency and above.
Similarly, at upper cutoff frequency, fH, the gain is equal to 0.707 Amid. After the upper
cutoff frequency, the gain decreases with frequency increases and dies off eventually.
The Lower Frequency Response:
Since the impedance of coupling capacitors increases as frequency decreases, the voltage
gain of a FET amplifier decreases as frequency decreases. At very low frequencies, the
capacitive reactance of the coupling capacitors may become large enough to drop some of
the input voltage or output voltage. Also, the source-bypass capacitor, the capacitor in
parallel with the resistor from source to ground (source-resistor), may become large enough
so that it no longer shorts the source-resistor to ground. Approximately, the following
equations can be used to determine the lower cutoff frequency of the amplifier, where the
voltage gain drops 3 dB from its midband value (=0.707 times the midband Amid):
(1) f1 = 1/ ( 2πrinC1 ) where: f1 = lower cutoff frequency due to C1, C1 = input coupling
capacitance, rin = input resistance of the amplifier.
(2) f2 = 1/ ( 2πrout C2 ) where: f2 = lower cutoff frequency due to C2, C2 = output coupling
capacitance, rout = output resistance of the amplifier.
Provided that f1 and f2, are not close in value, the actual lower cutoff frequency is
approximately equal to the largest of the two.
The Upper Frequency Response:
Transistors have inherent shunt capacitances between each pair of terminals. At high
frequencies, these capacitances effectively short the ac signal voltage.
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The design using my available resistors, capacitors:
- R1=220K, R2=300K, C1=C2=100nF, Rd=3.9K, Rs=1.6K
- Vdd to Vss=9.96V, Vg=0.712V, Vs=-2.664V, Vd=-0.636V
- Input: 100mV-peak, 1KHz, note that polarities of Channel 2 are swapped to have the
same phase with input to calculate amplifier gain.
Scope:
- XY (C1:C2) shows the slope which is the gain of the amplifier)
- M1: 20* Lg ( ( Max ( C2 , 0.095) ) / ( Max ( C1 , 0.095) ) ) = gain in dB
- M2: ( Max ( C2 , 0.095) ) / ( Max ( C1 , 0.095) ) is the gain
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Appendix 3 – IRFD110 Specifications: http://www.vishay.com/docs/91127/sihfd110.pdf
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