Download 1 β iC 2N2222 2N3904 IS (at 20 Degrees Celsius

University of Pennsylvania
Moore School of Electrical Engineering
EE319
Laboratory Experiment 2 - BJT Linear Amplifier
1. Introduction. This lab is designed as a review of the characteristics of the single-stage bipolar
junction transistor amplifier. Temperature and device parameter variation effects will be examined
and biasing circuits which minimize these effects will be used in the experiment.
PRE-LABORATORY PREPARATION
2. Transistor models. For biasing and "low frequency" operation, we shall use the simple model:
iC = IS e
vBE
VT
and
iB =
1
i
β C
For the two transistors in the lab, the nominal parameter values for these equations are:
IS (at 20 Degrees Celsius)
β
2N2222
1.16E-14 A.
200
2N3904
7.62E-16 A.
204
The current, IS , is strongly temperature dependent, doubling for about a 5 degree Celsius increase in
temperature. For Celsius temperature measurements and a reference temperature of 20 Degrees
Celsius, this current versus temperature expression becomes
IS
IS(20)
=2
 (TC −20 )


5 

and, for VT , the expression is:
VT =
kT
;
q
with k = 1.38E − 23 and q = 1.6E −19 .
T is absolute temperature in degrees Rankine, k is Boltzmann’s constant and q is the charge of an
electron. VT is quite close to .025 volts at 20 degrees Celsius.
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3. Transistor temperature dependence. Complete the fill-in of following tables for the 2N2222 and
2N3904 transistors:
To show the dependence of IC on VBE at 20 degrees C:
2N2222
IC
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E-00
VBE
∆VBE
0.6295
0.6870
0.0575
2N3904
∆VBE
VBE
0.6975
To show the 2N2222 variation of IC with temperature for fixed VBE or variation in VBE for fixed
IC :
Fixed VBE = 0.6295 V.
Fixed IC = 0.001 A.
TC
TC
0
20
40
60
80
100
IC
0
20
40
60
80
100
0.001
0.0031
VBE
IS
0.6295
0.5602
1.16E-14
4. Voltage source biasing. Design a transistor amplifier using the circuit shown in the figure below.
Determine values of the resistors, RC , RE , R1, andR 2 to satisfy the following constraints:
VCE = 5 v; IC = 1ma;
RC
I
= 5; 1 = 10
RE
IB
Vcc =10 V.
I1
R1
RC
Cin
I
Vin
R2
B
Vout
RE
2
THE LABORATORY INSTRUCTOR MUST APPROVE THE ABOVE WORK BEFORE YOU CAN
PROCEED WITH THE LAB.
5. Construction. Construct the circuit as designed and measure and record VC ,
verify your design.
VB , and
VE to
6. Operation.
6.1 Common emitter amplifier with emitter degeneration. Capacitively couple a function generator to
the base input (node “B”) and set its output to deliver a 10KHz. sine wave with a peak amplitude less
than 0.5 volt. (Remember, this is an AMPLIFIER - DON’T OVERDRIVE IT) The input coupling
capacitor reactance should be negligible when compared to the input impedance of the amplifier. (Xc
< Rin /10). Using 10x probes, connect a scope simultaneously to the function generator output and to
the collector of the amplifier transistor. Measure the voltage gain ((Vout /Vin ) over the frequency
range where the gain is at least .707 times the value of the 10KHz. gain. The frequencies where the
output voltage falls to .707 of its mid-band value are called the “3dB” points of the amplifier and
are commonly used to specify amplifier bandwidth.
Set the function generator frequency to 10KHz. and set its amplitude at 0.5 volts peak. Configure the
oscilloscope to perform a “Fast Fourier Transform” on the collector output voltage. Note and record
the relative amplitudes of the fundamental frequency and the first five harmonic components of the
output signal Fourier spectrum. Repeat the process with the function generator amplitude set to 1.0 v.,
and 1.5 v. peak.
6.2 Amplifier with emitter resistor partially bypassed. replace RE with two series resistors each of
value RE /2. Then bypass the resistor on the ground side of the emitter to ground path with a capacitor
whose reactance is small relative to RE /2 (see above) and repeat the experiment. What happens to the
gain? The bandwidth? The distortion? For distortion measurements use one-half the input voltages
used in the previous part of the experiment.
7. Simulation. For both circuit designs above, simulate the same experiments on Electronics
Workbench. Do your design gain and your experimental frequency response results agree with those
from the simulation? If not, where do the results differ? Try to explain why they differ. What is
ignored in the pencil and paper design? What is missing form the Electronics Workbench circuit?
What is included in Electronics Workbench that is not present in the pencil and paper analysis?
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