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Page 1 of 32
University of North Carolina at Charlotte
Department of Electrical and Computer Engineering
Laboratory Experimentation Report
Name: Ethan Miller Date: July 10, 2014
Course Number: ECGR 3155 Section: L01
Experiment Titles: [5] BJT Basics, [6] BJT Amplifier Configurations, [C] BJT Amplifier
Input/Output Impedances
Lab Partner: None Experiment Numbers: 5, 6, 7
Objectives:
Experiment 5:
The purpose of this experiment was to examine the three operation regions of a
Bipolar Junction Transistor: cutoff, active, and saturation.
Experiment 6:
The intention of this experiment was to examine the response to three different
Bipolar Junction Transistor (BJT) amplifier configurations.
Experiment 7:
The purpose of this experiment was to observe measurements of the input and
output impedances of a Bipolar Junction Transistor single-stage amplifier.
Equipment List:
Items Asset #
MB-106 Breadboard 00000001
Agilent 33509B Function Generator 00000002
Agilent InfinniiVision 2000-X Series Oscilloscope 00000003
E3612A Power Supply 00000004
Agilent 34461A 61/2
Digital Multimeter 00000005
Cadence Design System (P-spice) 00000006
Q2N3904 (BJT) 00000007
1KΩ, 100KΩ, 10Ω, 43KΩ, 13KΩ, 33KΩ, 2356Ω 00000008
Rpot 10KΩ 00000009
2333Ω 00000010
100µF, .1µF 00000011
10KΩ 00000012
Page 2 of 32
Relevant Theory/Background Information:
Experiment 5:
A Bipolar Junction Transistor (BJT) has three terminals called base, emitter, and
collector. A BJT consists a pair of PN junction connected in series back to back, either a
PN-NP to form a PNP or NP-NP to form NPN transistor shown in Figure 1. Both BJT’s
have electrons and holes that conduct current which is why the transistor is called bipolar.
Figure 1: BJT Diagram NPN (left) and PNP (right)
There are three different regions of operations in a BJT cutoff, active and saturation. The
cutoff region is when both PN junctions are in reverse biased. From this region the entire
terminal currents are small and the transistor is said to be off. These switching circuits are driven
into cutoff when a preferred state of the switch is open. No current or little current is though the
diode.
The Active region of the BJT has the base-emitter junction in forward bias and the
collector-base junction in reverse bias. In the active operation the collector-base current is
relativity close to the base-emitter current and consequently, the collector-base voltage for a
certain current is much greater than the emitter base voltage for the same current. In Figure 2, the
NPN transistor is bias to operate in the active region. When the collector voltage falls below the
base voltage by an amount that surpassed the threshed voltage of this junction, the collector
voltage will become forward bias and the transistor will enter saturation. Thus the desired region
of a BJT is the active region.
The saturation region of the BJT transistor will take place when the collector-base
junction becomes forward bias. As the base-emitter current is increased there is a point where
this becomes forward bias and beyond this point, a small increase in the collector current
corresponds to small decreases in the collector voltage. As a result the base emitter current will
increase further from the collector-base current. When the transistor is this region it is said the
transistor is on in order to minimize the voltage drop across the collector-emitter junction. Deep
saturation is said to have a collector-emitter voltage of 200mv and edge saturation is said to have
a collector-emitter voltage of 300mv.
Collector
Emitter
Base
Collector
Base
Emitter
Page 3 of 32
Figure 2: BJT Transistor Biasing
Experiment 6:
There are three basic configurations and are generally defined as common-
emitter, common-base, and common-collector. Each one of this configurations exhibit
different characteristics for a more desirable design. Shown in Table 1 is the comparison
between the different BJT amplifiers. Normally, the common-collector and the common-
emitter have a lower frequency bandwidth than the common-base. This was found by the
effects caused by the internal capacitance and how the external capacitance is configured
in the amplifier. Another caused for the loss of bandwidth is the miller effect.
Common-Emitter Common-Base Common-Collector
Input Impedance Medium Low High
Output Impedance High Very High Low
Current Gain High( ) Low ( ) High
Voltage Gain Medium High Low
Power Gain Very High Low Medium
Phase Angle 180 0 0
Table 1: Qualitative BJT Amplifier Comparison
Experiment 7:
In the prior experiments the DC biasing and AC amplification of BJT’s have been
examine. This BJT experiment trial will build upon the previous experiments as well be
introduced to input and output impedances of a BJT amplifier. The amplifier selected for
this experimented is the common emitter shown in Figure 8. Procedure for suitably
biasing the BJT amplifier and setting up AC amplification will be investigated as well as,
techniques for measuring the input and output impedances.
The input impedance of an amplifier is a difficult measure, in the midband gain
the impedances is predominantly resistive. The input resistance/impedance is defined as
the ratio of input voltage divided by the input current. Input impedances are calculated
from the small signal circuit/AC Equivalent circuit by looking into the input with all
current source replaced as open circuit and voltages source as short circuits. The
VCC
VEE
VEE
VCC
RC
RE
RC
RE
Page 4 of 32
importance of input impedances shows how low input impedances reflect on the overall
circuit as well as high input impedances. Low input impedances generally have a poor
low-frequency response and large power requirement. For example the LM741 op-amp
has high input impedance which results in a good low-frequency response and low input
power consumption.
As well as output impedance play a role in the circuit. Output impedance are
restive in the midband gain and generally a complex measure. To calculate the output
impedance the load is removed and the impedance is found by looking back into the
small signal circuit/AC Equivalent circuit. Once again it is essential all current sources
with a open circuit and voltage sources with a short circuit. The importance of the output
impedance offer power to an amplifier. The idyllic output impedance is zero; an amplifier
with low output impedance preserve a larger output current without a major reduction of
the output voltage.
Experimental Data/Analysis:
Experiment 5:
Two circuits were constructed to establish if the BJT was in the following three
regions saturation, active and cutoff, shown in Figures 3 and 4. By adjusting the power
supply to 10 volts and measuring RC to be 1.0059 kilohms and RB to be 99.182 kilohms
;VOUT was found to be approximant 5 volts when the potentiometer was adjusted to a
certain resister value. Found in Equation 1 was the calculated measured value of VCE.
Since this VCE was found to be 5.1 volts the BJT was found to be in the active region
(0<VCE<VCC). Shown in the laboratory computation section VIN was constricted to the
saturation voltage of the BJT. The calculated value was found to be 5.6 volts. With the
VCE voltage held at 5.1 volts the voltage at the base was measured to be 100mvolts and
beta was then calculated, beta is shown in Equation 2. From observing VOUT the transistor
had gotten warmer by pinching the BJT between the thumb and forefinger. VOUT was
changed by this little difference in temperature increase. Beta was related to the
temperature by the amount of increasing temperature hence, increased the amount of
beta.
Figure 3: BJT Transistor Circuit
RB
100K
RC
1K
0
VCC
10Vdc
Rpot
10K
2
1
VCC
10Vdc
++VIN
CB
E
--VIN
++VOUT
--VOUT
Page 5 of 32
Figure 4: BJT Curve Tracer Circuit
Vin
(Volts)
Vout
(Volts)
VBE
(Volts)
VCE
(Volts)
Vin
(Volts)
Vout
(Volts)
VBE
(Volts)
VCE
(Volts)
0 0.000007 0.000027 10.013 4.5 7.44 0.713 2.568
0.25 0.000001 0.188 10.013 5 8.375 0.719 1.651
0.5 0.000998 0.485 10.012 5.5 9.044 0.724 0.949
0.75 0.248 0.63 9.766 6 9.572 0.732 0.443
1 0.785 0.66 9 6.5 9.707 0.734 0.3038
1.25 1.229 0.668 8.783 7 9.768 0.735 0.244
1.5 1.738 0.675 8.2783 7.5 9.768 0.736045 0.2268
2 2.726 0.686 7.306 8 9.803 0.7363 0.2093
2.5 3.683 0.698 6.332 8.5 9.812 0.7368 0.20005
3 4.743 0.699 5.261 9 9.819 0.7369 0.19245
3.5 5.788 0.704 4.219 9.5 10.012 0.737 0.18276
4 6.616 0.709 3.403 10 10.012 0.738 0.18194
Table 2: Transfer Characteristics
RE
10
0
RB
100K
VIN
FREQ = 100VAMPL = 10VOFF = 2.5
AC = 0
CHANNEL 1
CHANNEL 2VBB
10Vdc
AMPS
Page 6 of 32
Figure 5: Transfer Characteristics
Shown in Table 2 and Figure 5 are the transfer Characteristics for the BJT in
Figure 3. The region of the BJT is also shown in Figure 5. The saturation region was
found to be in the bottom left hand of the graph where VCE=0.The saturation region was
meet when VCE was in the range of 300 millivolts (edge saturation) or 200 millivolts
(deep saturation). The cutoff region was found to be in the bottom right hand of the graph
where VCE=VCC. The active region was found to be in the middle of the graph where
0<VCE<VCC. The calculated value of the average beta (DC Current Gain) was found to be
166 shown in Equation 3.
VBB (V) IB (A) IC (A) Beta (DC Current Gain)
1.69 0.00001 0.001 100
2.72 0.00002 0.002 100
3.74 0.00003 0.003 100
4.76 0.00004 0.0039 97.5
5.791 0.00005 0.0049 98
6.124 0.00006 0.0059 98.33333333
Table 3: DC Current Gain
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
6.5
7.5
8.5
9.5
10.5
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5
Ou
tpu
t V
olt
ag
e
Input Voltage
Transfer Characterics
Vout
VBE
VCE
Transfer Characterics
ECGR 3155- Systems and Electroincs Lab
Experiment # 5 BJT Baics
Ethan Miller
Cutoff Region BJT fully off Vce =Vcc Saturation Region BJT fully on
VCE=0
Active Region (Q-point) 0<VCE<VCC
Page 7 of 32
Figure 6: IC VS VCE at IC = 40 microamps
Figure 7: IC VS VCE
Page 8 of 32
Shown in Figure 6 and Figure 7 are the IC VS VCE curve. Table 3 shows the calculated beta values
found from the circuit shown in Figure 4. The DC current gain was found to be approximately 100. A DC
current gain of 100 or greater was found to be exceptionally great. When a DC current gain was found to
be 100 or greater the bias currents IC and IE equaled each other and the current of IB was approximately 0
amps. The region that was best suited for a linear BJT was found to be in the active region for a class A
amplifier. The uses for the other two regions were found to be in the following saturation region- high
current conduction from the emitter to the collector current and the cutoff region- to form a digital switch
(1010) for computers.
Laboratory Computation
VIN that caused the BJT to enter saturation
(Eqn.1)
(Eqn. 2)
Page 9 of 32
(Eqn.3)
Experiment 6:
Common emitter, common base and common collector circuits were constructed
to determine the lower and upper 3db frequencies, bandwidth midband voltage gain and
the phase of the sinusoidal output voltage compared to the input sinusoidal voltage. Table
4 shows the differences between the lower and upper 3db frequencies, phase, midband
voltage gain and bandwidth.
Each circuit was biased to have the following parameters threshold voltage was
set to 25 millivolts, beta was 100, IEQ was set to 1.5 milliamps, early voltage was
100volts, VCEQ was set to 5 volts, RE was set to 1kiliohms, and VBE was set to .7 volts.
Shown in Equations 4,5 and 6 were solved to find the certain resister for RC,R1, and R2.
Also the midband voltage gain was calculated to ensure the laboratory results were
relatively close to the theoretical results. A small-signal circuit was constructed to
calculate the midband voltage gain. Each circuit from laboratory and P-spice results were
then plotted to show the difference in the results.
Figure 8: Common-Emitter Circuit
VOUT
Q2N3904
RC
2356
RE
1k
R2
13K
R1
43K
RL
10K
CC
.1uF
CE
100uF
CB
.1uF
VCC
10Vdc
VIN
1Vac
0
Page 10 of 32
Figure 9: Common-Emitter Small Signal Circuit
Figure 10: P-spice Midband Voltage Gain Common-Emitter
ro RCR-PI RLRB
0 0 0 0 0
0
VIN BI_B
VOUT
Page 11 of 32
Figure 11: Common-Base Circuit
Figure 12: Small-Signal Common-Base Circuit
VOUT
Q6
Q2N3904
RC
2356
RE
1k
R2
13K
R1
43K
RL
10K
CC
.1uF
CE
.1uF
CB
100uF
VCC
10Vdc
0
VIN
1Vac
VOUT
R-PI
RE
RCro
00
0 00
BI_B
VIN
RL
0
Page 12 of 32
Figure 13: P-spice Midband Voltage Gain Common-Base
Figure 14: Common-Collector Circuit
VOUT
Q2N3904
RC
2356
RE
1K
R2
13K
R1
43K
RL
10K
CC
100uF
CE
.1uF
CB
.1uF
VCC
10Vdc
VIN
1Vac
0
Page 13 of 32
Figure 15: Small-Signal Common-Collector Circuit
Shown in Table 4 are the Amplifier results comparing the P-spice results to the laboratory results.
As shown there were some little differences in the resulted values. P-spice showed a higher midband
voltage gain, low and high cutoff frequencies. As a result P-spice was found to have a greater bandwidth
and voltage gain than the lab resulted in. The higher cutoff frequency was not reached in the lab due to
the capacitance of the breadboard. This capacitance of the breadboard interfered with the internal
capacitance of the BJT (the depletion region of the electrons in the BJT) which contributes to the overall
high frequency. The lower cutoff frequency of the lab resulted relativity close to P-spice results. The
lower frequency was affected by the external capacitances in the circuit. The phase of the two sinusoidal
waveform were exactly 90 degrees from each other, this was due to the amplifier configuration and
current direction through the BJT.
RE
RB R-PIVIN
BI_B
0 0
0
0
VOUT
r0
Midband
Voltage Gain
(V/V)
Lower Cutoff
Frequency (Hz)
High cutoff
Frequency
(Hz)
Bandwidth
(Hz)
Circuit
Type
Phase
(degree
s)
P-
Spice
Laborat
ory
P-
spice
Laborat
ory
P-
spice
Labora
tory
P-
spice
Labo
rator
y
Common-
Emitter
90 105.89
4
88.878 804.95
5
800 26.465
8M
1.1M 26.46
499M
1.099
M
Common-
Base
90 105.93
6
88.888 90.481
K
70K 26.543
0M
1M 26.45
251M
930K
Common-
Collector
90 883.23
2m
1.0461 257.26
53
100 7.3001
G
1M 7.300
0G
999K
Table 4: Amplifier Results
Page 14 of 32
Figure 16: P-spice Midband Voltage Gain Common-Collector
Page 15 of 32
Figure 17: Amplifier Gain of Common-Emitter and Common-Base Lab Results
0
10
20
30
40
50
60
70
80
90
100
100 1000 10000 100000 1000000 10000000
Gain
Volt
age (
v/v
)
Frequency (Hz)
Amplifier Gain (v/v) Configurations
CE CB
Common-Emitter Amplifier
Gain
ECGR 3155-Systems and
Electronics Lab
Experiment #6 BJT Amplifier
Configurations
Ethan Miller
Page 16 of 32
Figure 18: Common-Collector Amplifier Gain Lab Results
0
0.2
0.4
0.6
0.8
1
1.2
1 10 100 1000 10000 100000 1000000 10000000
Gain
Volt
age (
v/v
)
Frequency (Hz)
Common Collector Amplifer Gain (v/v)
Common-Collector Amplifier
Gain
ECGR 3155-Systems and
Electronics Lab
Experiment #6 BJT
Amplifier Configurations
Ethan Miller
Page 17 of 32
Frequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
Frequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
10 0.0084 0.4 47.619047
62
10000 0.035 3.06 87.428571
43
20 0.008 0.4 50 20000 0.0342 3.06 89.473684
21
40 0.007 0.4 57.142857
14
40000 0.034 3.06 90
70 0.011 0.6 54.545454
55
60000 0.034 3.06 90
80 0.015 0.8 53.333333
33
80000 0.034 3.06 90
100 0.013 0.8 61.538461
54
100000 0.033 3.02 91.515151
52
200 0.018 0.82 45.555555
56
200000 0.033 3.05 92.424242
42
400 0.0129 0.82 63.565891
47
400000 0.027 2.45 90.740740
74
600 0.0141 0.9 63.829787
23
600000 0.022 2.05 93.181818
18
800 0.019 1.29 67.894736
84
800000 0.019 1.69 88.947368
42
1000 0.034 2.57 75.588235
29
1000000 0.017 1.45 85.294117
65
2000 0.031 2.6 83.870967
74
1200000 0.03 1.25 41.666666
67
4000 0.0338 3.02 89.349112
43
2000000 0.03 0.84 28
6000 0.034 3.06 90 2500000 0.03 0.68 22.666666
67
8000 0.034 3.06 90 3000000 0.03 0.56 18.666666
67
Table 5: Common-Emitter Amplifier Gain V/V
Page 18 of 32
Frequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
Fequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
10 0.0133 0.024 1.8045112
78
10000 0.039 0.326 8.3589743
59
20 0.0096 0.02 2.0833333
33
20000 0.036 0.547 15.194444
44
40 0.0088 0.02 2.2727272
73
40000 0.019 0.691 36.368421
05
70 0.0109 0.024 2.2018348
62
60000 0.018 0.752 41.777777
78
80 0.0064 0.02 3.125 80000 0.011 0.764 69.454545
45
100 0.0113 0.028 2.4778761
06
100000 0.01 0.772 77.2
200 0.0153 0.032 2.0915032
68
200000 0.009 0.8 88.888888
89
400 0.017 0.026 1.5294117
65
400000 0.008 0.68 85
600 0.021 0.033 1.5714285
71
600000 0.0065 0.56 86.153846
15
800 0.023 0.038 1.6521739
13
800000 0.018 0.5 27.777777
78
1000 0.028 0.038 1.3571428
57
1000000 0.017 0.42 24.705882
35
2000 0.025 0.048 1.92 1200000 0.016 0.36 22.5
4000 0.03 0.088 2.9333333
33
2000000 0.014 0.24 17.142857
14
6000 0.032 0.161 5.03125 2500000 0.015 0.2 13.333333
33
8000 0.036 0.271 7.5277777
78
3000000 0.019 0.2 10.526315
79
Table 6: Common-Base Amplifier Gain V/V
Page 19 of 32
Frequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
Fequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
10 0.03 0.0072 0.24 10000 0.006 0.0064 1.0666666
67
40 0.018 0.0064 0.3555555
56
40000 0.0065 0.0068 1.0461538
46
80 0.016 0.0068 0.425 80000 0.0065 0.0068 1.0461538
46
100 0.011 0.0072 0.6545454
55
100000 0.0078 0.0084 1.0769230
77
200 0.008 0.0064 0.8 200000 0.0076 0.008 1.0526315
79
600 0.0074 0.0072 0.9729729
73
600000 0.027 0.0253 0.9370370
37
1000 0.0064 0.0068 1.0625 1000000 0.033 0.0221 0.6696969
7
6000 0.0076 0.0084 1.1052631
58
2500000 0.0354 0.0189 0.5338983
05
3000000 0.07 0.0209 0.2985714
29
Table 7: Common-Collector Amplifier V/V
Laboratory Computation
Biasing BJT
Page 20 of 32
(Eqn.4)
(Eqn.5)
(Eqn.6)
Common-Emitter Amplifier Gain
Common-Base Amplifier Gain
Common-Collector Amplifier Gain
Page 21 of 32
Experiment 7:
A common-emitter circuit was constructed in order to find the input/output
impedance and the gain of the circuit, shown in Figure 19 is the common-emitter circuit.
The value of RC was picked for the following parameters VCE was set to 5 volts, beta was
set to 100, VBE was .7 volts, early voltage was 100 volts and the threshold voltage was
25milivolts. The calculation of RC was found to be 2333 shown in the laboratory
computation section.
Figure 19: Common-Emitter Circuit
Figure 20: Small Signal Circuit Common-Emitter
Q2N3904
RC
2333
RE
1k
R2
10K
R1
33K
CE
100uF
C19
100uF
VCC
10Vdc
0
VIN1Vac
VOUT
RCr0R-PIRBBI_BVIN
0 0
0
0 0
VOUT
RINPUT IMPEDANCE ROUTPUT IMPEDANCE
Page 22 of 32
Figure 21: P-spice Common-Emitter Amplifier Gain V/V
VC VE VB
6.491 1.575 2.252
IC IE IB
0.00295 0.001575 0.000293
RC RE RB
2200 1000 7674
Table 8: Measured Bias Values of the Common-Emitter
Page 23 of 32
Figure 22: P-spice Input Impedance Common-Emitter
Figure 23: Input Impedance Common-Emitter Circuit
Q2N3904
RC
2333
RE
1k
R2
10K
R1
33K
CE
100uF
C19
100uF
VCC
10Vdc
0
VS1Vac
RX
1K VINPUT ++
VINPUT--
Page 24 of 32
Figure 24: P-spice Output Impedance Common-Emitter
Figure 25: Output Impedance Common-Emitter Circuit
Q2N3904
RC
2333
RE
1k
R2
10K
R1
33K
CE
100uF
CB
100uF
VCC
10Vdc
0
VS1Vac
CC
.1uF
RX
1KVIN ++
VIN --
Page 25 of 32
Figure 26: Common-Emitter Amplifier Gain V/V Lab Results
During the lab experiment of the common-emitter circuit shown in Figure 25 the input
impedance was found to be approximately 2.5 kilohms which was found to be relatively close to
the P-spice results 2.0692 kilohms. The input resistance was found by varying the input
frequency of the input voltage (VS) and by having another probe at VIN. The current was first
found by the difference of the two voltages, and then the input resistance was found by dividing
the VIN by the input current. The output resistance was found in a similar way except the input
voltage was shorted and put on the output of the BJT shown in Figure 25. The resulted value of
the output impedance was found to be 2.5 kilohms. The measured values of the lab results did
not match with the calculated values for the BJT circuit. These different results could have been
achieve by a slight difference in the DC currents and DC voltages, DC current gain of the BJT
and the slight difference in the resister values found in the lab.
0
20
40
60
80
100
120
5 50 500 5000 50000 500000 5000000
Gain
Volt
age V
/V
Frequency (Hz)
Common-Emitter Amplifier Gain V/V
Common-Emitter Amplifier Gain v/v
ECGR 3155 Systems and Electronics Lab
Experiment # 7 BJT Impedance
Ethan Miller
Page 26 of 32
Frequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
Fequen
cy (Hz)
Vin
(peak-
peak)
Vout
(peak-
peak)
Gain
(peak-
peak)
10 0.045 0.4 8.8888888
89
10000 0.06 6 100
20 0.055 0.6 10.909090
91
20000 0.06 5.8 96.666666
67
40 0.057 0.6 10.526315
79
40000 0.06 5.8 96.666666
67
70 0.059 1 16.949152
54
60000 0.06 5.8 96.666666
67
80 0.06 1.2 20 80000 0.057 5.8 101.75438
6
100 0.06 2.1 35 100000 0.056 5.6 100
200 0.06 3.2 53.333333
33
200000 0.054 5.4 100
400 0.06 4.2 70 400000 0.05 4.4 88
600 0.06 4.2 70 600000 0.05 3.8 76
800 0.06 4.8 80 800000 0.055 3 54.545454
55
1000 0.06 5 83.333333
33
1000000 0.05 2.6 52
2000 0.06 5.6 93.333333
33
1200000 0.048 2.3 47.916666
67
4000 0.06 6 100 2000000 0.05 1.6 32
6000 0.06 6 100 2500000 0.049 1.3 26.530612
24
8000 0.06 6 100 3000000 0.048 1.2 25
Table 9: Common-Emitter Amplifier Gain V/V
Page 27 of 32
Figure 27: Input Impedance Common-Emitter Lab Results
0
500
1000
1500
2000
2500
3000
3500
3000 30000 300000 3000000
Inp
ut
Res
ista
nce
K
ilio
hm
s
Frequency (Hz)
Input Impedance Common-Emitter
Input Impedance Common-Emitter
ECGR 3155 Systems and Electrioncs Lab
Experiment #7 BJT Impedance
Ethan Miller
Page 28 of 32
Frequency
(Hz)
Vin(2) pk-
pk
Vs(1) pk-
pk
Current
(A)
Resister (Ω) Output Resistance
(Ω)
4000 0.079 0.109 0.00003 1000 2633.333333
6000 0.076 0.105 0.000029 1000 2620.689655
8000 0.076 0.105 0.000029 1000 2620.689655
10000 0.08 0.109 0.000029 1000 2758.62069
20000 0.076 0.103 0.000027 1000 2814.814815
40000 0.076 0.103 0.000027 1000 2814.814815
60000 0.078 0.105 0.000027 1000 2888.888889
80000 0.071 0.103 0.000032 1000 2218.75
100000 0.07 0.105 0.000035 1000 2000
200000 0.05 0.1 0.00005 1000 1000
400000 0.04 0.1 0.00006 1000 666.6666667
600000 0.03 0.1 0.00007 1000 428.5714286
800000 0.0229 0.1 0.0000771 1000 297.0168612
1000000 0.0125 0.1 0.0000875 1000 142.8571429
1200000 0.011 0.1 0.000089 1000 123.5955056
2000000 0.01 0.1 0.00009 1000 111.1111111
2500000 0.0095 0.1 0.0000905 1000 104.9723757
3000000 0.008 0.1 0.000092 1000 86.95652174
Table 10: Common-Emitter Input Impedance
Page 29 of 32
Figure 28: Output Impedance Common-Emitter Lab Results
0
500
1000
1500
2000
2500
3000
3000 30000 300000 3000000
Ou
tpu
t Im
ped
an
ce K
ilio
hm
s
Frequency (Hz)
Output Impedance Common-Emitter
Output Impedace Common-Emitter
ECGR 3155 Systems and
Electronics Lab
Experiment #7 BJT Impedance
Ethan Miller
Page 30 of 32
Frequency
(Hz)
Vin(2) pk-
pk
Vs(1) pk-
pk
Current
(A)
Resister
(Ω)
Output Resistance
(Ω)
4000 0.074 0.103 0.000029 1000 2551.724138
6000 0.075 0.105 0.00003 1000 2500
8000 0.076 0.107 0.000031 1000 2451.612903
10000 0.077 0.107 0.00003 1000 2566.666667
20000 0.075 0.105 0.00003 1000 2500
40000 0.075 0.103 0.000028 1000 2678.571429
60000 0.072 0.101 0.000029 1000 2482.758621
80000 0.072 0.101 0.000029 1000 2482.758621
100000 0.07 0.101 0.000031 1000 2258.064516
200000 0.07 0.101 0.000031 1000 2258.064516
400000 0.062 0.101 0.000039 1000 1589.74359
600000 0.056 0.101 0.000045 1000 1244.444444
800000 0.05 0.098 0.000048 1000 1041.666667
1000000 0.031 0.084 0.000053 1000 584.9056604
1200000 0.028 0.07 0.000042 1000 666.6666667
2000000 0.025 0.08 0.000055 1000 454.5454545
2500000 0.02 0.07 0.00005 1000 400
3000000 0.01 0.06 0.00005 1000 200
Table 11: Common-Emitter Output Impedance
Page 31 of 32
Laboratory Computation
Common-Emitter Gain
Input/output Impedance
Page 32 of 32
Conclusions:
Experiment 5:
In conclusion the BJT was needed to operate in the active region where
0<VCE<VCC. This operation ensured that the DC currents and DC voltages of the BJT
was approximately acceptable for VCE > 300 millivolts, IB = 0 amps, IC = IE. Other
regions that were found from the transfer characteristic graph shown in Figure 5 are
saturation and cutoff. Again saturation was found to be when VCE < 300 millivolts and
the cutoff was when VCE = VCC. The DC current gain was measured and found to
approximately 100 and or greater than 100. A measured DC current gain of 100 or greater
was found to ensure that the BJT was in the active region.
Experiment 6:
In conclusion the BJT was constructed in three different configurations, common-
emitter, common-base and common-collector. From the data results the common-emitter
and common-base had approximately same midband voltage gain and bandwidth. The
common-collector was found to have a higher lower cutoff frequency. The common-
collector had the largest of bandwidth and the smallest midband voltage gain. Common-
collector had the smallest gain due the restriction on the emitter of the BJT. Since there
was no capacitance on the emitter of the common-collector the midband voltage gain was
changed by a factor of the DC current gain times the resister in the emitter.
Experiment 7:
In conclusion a common-emitter BJT circuit was constructed in the lab to
demonstrate the input and output impedance. The output and input impedance were found
to have about the same value impedance. Comparing the lab results to P-spice, the lab
results were in about the same manner as P-spice found the input and output impedance.
As a result the calculated values for the impedance did vary a lot. In general an amplifier
needed to have a high input impedance to make sure that the preceding current does not
change. Again the output impedance needed to be low in a similar matter as the input
impedance.
List of Attachments:
QN3904 Datasheet
References: [5] Lab Handout “BJT Basics”
[6] Lab Handout “BJT Amplifier Configurations”
[7] Lab Handout “BJT Amplifier Input/Output Impedances”
This report was submitted in compliance with UNCC POLICY STATEMENT #105
THE CODE OF STUDENT ACADEMIC INTEGRITY, Revised August 24, 2008
(http://www.legal.uncc.edu/policies/ps-105.html) (ECM).
Recommended