New Mexico Tech
EE 321L
EE321L - Analog Electronics
Fall 2013
A nalog Elect r onics L abor at or y
Laboratory Exercise 7
BJT IV Characteristics and theLCommon-Emitter
Amplifier
ab 7
B JT I V Char act er ist ics and com m on-em it t er am plifi er
Pre-Lab
Fall 2012
P rBJT
e-Ltransistor.
ab
Find the data sheets for the 2N3904
Determine the maximum power
dissipation for this component? Derive an approximate expression for the power
in the BJT.
that hFE on
the2N3906
data sheet
is β.transistors. What is t hemaximum
Find dissipation
t hedat a sheets
for Note
t he 2N3904
and
BJT
1.
1.
power dissipat ion that this component can t olerat e? Derive an approximat e expression
Hint: Pages. 408 and 450 of the Sedra and Smith text will be very helpful.
for t he power dissipat ion in the BJT. Not e t hat hF E on t he dat a sheet is what we call
β2.in Compute
class. RB and RC in step 1.
2. Compute
RBreand
RC 3.in st ep 1.
3. Compute
for step
Note: rDo
not use
3. Compute
st epRB3.and RC from part 2.
e for
4. Prepare
calculationof
fortthe
step
5. 5.
4. Prepare
t hethe
calculation
he “Early
Earlyvoltage”
volt ageinin
st ep
Point
slope
5. Pick Hint:
RB for
st ep
6. formula and figure out what you need.
5. Calculate
for stepical
6, ingain
termsinofstep
β. 9.
6. Compute
theRtBheoret
6. Compute
theoretical
gain in step 9.
7. Think
about the
st ep
11.
7.
Think about step 11.
wewill
will look
look at
IVIV
characteristics
ofics
BJTs
buildand
andbuild
characterize
simple voltage
In t In
histhis
lablabwe
atthe
t he
charact erist
ofand
BJTs
and charact
erize a simple
amplifier.
volt age amplifier.
BJT Common-Emitter Characteristics
B JT com m on-em it t er char act er ist ics
In
this
section
you
will
examine
thetIV
of BJT.
In t his section you will examine
hecharacteristic
IV charact erist
ic of a BJT.
1.
Build the common-emitter circuit:
1. Build t he common-emit ter circuit,
choosing
a current
base current
of when
0.01 mA
VB B do
= you
10 expect
V. What
expect
IC
Choose RBRfor
base
of 0.01mA
VBB =when
10V. What
IC to do
be? you
Pick R
C
B afor
to
get
V
=
5V
when
V
=
10V.
CE
CC
to be? Pick RC to get VCE = 5 V when VCC = 10 V.
1
New Mexico Tech
EE321L - Analog Electronics
Fall 2013
2.
What are the actual values of IB and IC? What is β? Compare with the datasheet. What is
the power dissipation in the BJT? Are you operating with in the components power
dissipation limits?
3.
Choose a value for RE, re << RE << RC, and again make VCE = 5v and get IB, IC, and effective
β again.
4.
Map iC as a function of vCE: attach VCC to the function generator outputting a largeamplitude of 10V 100 Hz sine wave. Measure vCE: with one scope probe and iC with the
other by measuring across R E. Plot in XY mode. If the signal is noisy try to amplify it with
an op-amp (null the circuit,) averaging on the scope, or filtering with a capacitor.
Hint: pg. 400 and use a capacitor.
5.
Estimate the Early Voltage from the slope of iC versus vCE.
The Common-Emitter Amplifier
In this section you will measure the gain and linearity of the common-emitter amplifier.
6.
Using the same circuit as before, without RE, connect VCC = VBB = 10V. Pick RB such that
you get IC = 5 mA (use your previously found β.) Pick RC to get VCE = 5V.
7.
Measure VCE, then adjust VBB to get VCE = 5V. What is the value of β and how does it
compare to what you measured in step 2?
8.
Connect a function generator to the base through a large capacitor. How large should the
capacitor be? It depends on the frequency of the function generator signal.
Hint: Use a .1μF.
9.
Connect AC coupled probes to input, vB, and the output, vC. Plot the AC input, vb, and
output, vC, together for the smallest input amplitude you can get and compare with a
theoretical prediction.
10. Measure the gain for a few increasingly larger amplitude inputs up to the point of
clipping and conclude something about the linearity of the gain with input amplitude.
You can also plot output versus input in XY mode.
11. Explain what causes the clipping at the top and bottom of the curve by increasing the
amplitude to have clipping about 50% of the time and plotting vBE and vCE with vC.
Not So Mysterious Challenge # 7:
Define and describe the origin of the following terms with respect to the physics/electrical
engineering discipline: Resistance, Voltage, Current, Capacitance and Inductance.
Hint: Tell me who discovered/defined each of these terms and describe how they are
scientifically/officially defined. NIST may be helpful.