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).