Technology Park Malaysia

MODULE TITLE : ANALOGUE ELECTRONICS

(EE001-3-5-2-AE)

ASSIGNMENT TITLE : INDIVIDUAL ASSIGNMENT (AUDIO AMPLIFIER)

STUDENT NAME : GURSHEN SINGH A/L GURUCHARAN SINGH

STUDENT ID : TP017639

INTAKE : UC2F1001 EE

SUBMISSION DATE : 17/5/2010

LECTURER”S NAME : MR. SARVESWAREN KARUNANITHI

ACKNOWLEDGEMENT

First of all, I would like to thank and present my gratitude to the supreme God for

giving me the strength to complete this assignment. The assignment includes contribution

from numerous people for their kind cooperation in providing the necessary information and

support that I need for completing this assignment. I really appreciate their ideas and

suggestions and it’s helped me a lot by physically and mentally in completing this assignment

both directly and indirectly.

Special thanks to my lecturer, Mr. Sarveswaren Karunanithi for helping me to

enhance the contents found for this assignment. He have given me a lot of guidance by

reviewing the progress of my assignment from time to time and also motivating and

supporting me to ensure that I will be able to come out with quality content in this

assignment.

Last but not least, I owe a big thanks to the people around me especially my friends,

who have been working together with me and supporting me throughout this assignment.

Thanks to all of you for your valuable support.

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TABLE OF CONTENTS

INTRODUCTION......................................................................................................................4

OBJECTIVE..............................................................................................................................4

WORK PROGRAM...................................................................................................................5

ANALYSIS TECHNIQUES......................................................................................................5

THE DESIGN............................................................................................................................6

-BIPOLAR JUNCTION TRANSISTOR...............................................................................6

-TRANSISTOR CONFIGURATIONS..................................................................................9

-STATE OF TRANSISTOR.................................................................................................11

-COMMON BASE CONFIGURATIONS...........................................................................13

-α AND β RELATIONSHIPS..............................................................................................15

OVERALL CIRCUIT DESIGN..............................................................................................16

ANALYSIS OF CIRCUIT.......................................................................................................16

CALCULATIONS...................................................................................................................17

-DC ANALYSIS..................................................................................................................17

-AC ANALYSIS..................................................................................................................19

MULTISIM STIMULATIONS...............................................................................................25

DISCUSSION AND CONCLUSION......................................................................................26

REFERENCES.........................................................................................................................29

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INTRODUCTION

An audio amplifier is an electronic amplifier that amplifies low-power audio signals

of signals composed primarily of frequencies between 20 hertz to 20,000 hertz, the human

range of hearing to a level which suitable for driving loudspeakers and is the final stage in a

typical audio playback chain. This audio amplifier amplifies audio signals with the help of

many electronics component which are made up to produce such signals such as transistors,

capacitors, resistors and many more. The famous and commonly use device is

BJTs (bipolar junction transistors). The invention of the bipolar transistor in

1948 ushered in a revolution in electronics. Technical feats previously

requiring relatively large, mechanically fragile, power-hungry vacuum

tubes were suddenly achievable with tiny, mechanically rugged, power-

thrifty specks of crystalline silicon. This revolution made possible the

design and manufacture of lightweight, inexpensive electronic devices

that we now take for granted. Understanding how transistors function is of

paramount importance to anyone interested in understanding modern

electronics.

In this assignment, we are required to design a low cost audio amplification circuit

using a bipolar junction transistor with the specification of output and input voltage for the

used in the budget segment of high fidelity (hifi) sets. Herein, I have included my complete

research as well as the requirements which are needed for this assignment. I have also

simulated the circuit using multisim software..Finally,I construct the circuit and test it in the

lab.

OBJECTIVE

The objective of this assignment is to design and construct a low cost audio

amplification circuit for use in the budget segment of high fidelity (hifi) sets.

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WORK PROGRAM

Develop a low cost audio amplification circuit using only bipolar junction transistor

(BJT). The audio amplification specifications are input voltage, V i = 200 mVp-p and output

voltage, Vo = 20 Vp-p with 0° phase offset (noninverting).

ANALYSIS TECHNIQUES

The audio amplifier specifications are as follows:

i) Input: 200 mVp-p

ii) Output: 20 Vp-p

iii) Phase offset: 0 (non-inverting)

In order to solve this problem, it is advisable to use the appropriate hybrid pi model and refer

to the BJT data sheet to find out the early voltage of the transistor. Perform simulations using

Multisim to assess how the circuit would perform under nominal conditions.

Methodology:

a. Voltage gain, Av calculation based on the given specification.

b. Draw the hybrid pi model.

c. Design the circuit using both DC and AC analysis.

d. Ensure that the resistance values used is nominal standard resistance values.

e. Verify the design circuit by using Multisim.

f. Construct the circuit in the lab to calculate the voltage gain and to display both input

and output waveforms.

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THE DESIGN

BIPOLAR JUNCTION TRANSISTOR

The invention of the bipolar transistor in 1948 ushered in a revolution in electronics.

Technical feats previously requiring relatively large, mechanically fragile, power-hungry

vacuum tubes were suddenly achievable with tiny, mechanically rugged, power-thrifty specks

of crystalline silicon. This revolution made possible the design and manufacture of

lightweight, inexpensive electronic devices that we now take for granted. Understanding how

transistors function is of paramount importance to anyone interested in understanding modern

electronics.

A bipolar transistor consists of a three-layer “sandwich” of doped (extrinsic) semiconductor

materials, either P-N-P or N-P-N. Each layer forming the transistor has a specific name, and

each layer is provided with a wire contact for connection to a circuit.

Figure 1: PNP & NPN transistor

The functional difference between a PNP transistor and an NPN transistor is the proper

biasing (polarity) of the junctions when operating. For any given state of operation, the

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current directions and voltage polarities for each kind of transistor are exactly opposite each

other.

Bipolar transistors work as current-controlled current regulators. In other words, transistors

restrict the amount of current passed according to a smaller, controlling current. The main

current that is controlled goes from collector to emitter, or from emitter to collector,

depending on the type of transistor it is (PNP or NPN, respectively). The small current that

controls the main current goes from base to emitter, or from emitter to base, once again

depending on the kind of transistor it is (PNP or NPN, respectively). According to the

standards of semiconductor symbology, the arrow always points against the direction of

electron flow as shown in the figure below;

Figure 2: PNP and NPN transistors and their p-n junctions

Small electron base current controls large collector electron current flowing against emitter arrow.

Bipolar transistors are called bipolar because the main flow of electrons through them takes

place in two types of semiconductor material: P and N, as the main current go from emitter to

collector (or vice versa). In other words, there are two types of charge carriers, electrons and

holes which comprise this main current through the transistor.

Thus, the controlling current and the controlled current always mesh together through the

emitter wire, and their electrons always flow against the direction of the transistor's arrow.

This is the first and foremost rule in the use of transistors: all currents must go in the proper

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directions for the device to work as a current regulator. The small, controlling current is

usually referred to simply as the base current because it is the only current that goes through

the base wire of the transistor. Conversely, the large, controlled current is referred to as the

collector current because it is the only current that goes through the collector wire. The

emitter current is the sum of the base and collector currents, in compliance with Kirchhoff's

Current Law.

No current through the base of the transistor, shuts it off like an open switch and prevents

current through the collector. A base current, turns the transistor on like a closed switch and

allows a proportional amount of current through the collector. Collector current is primarily

limited by the base current, regardless of the amount of voltage available to push it. Since a

transistor's collector current is proportionally limited by its base current, it can be used as a

sort of current-controlled switch. A relatively small flow of electrons sent through the base of

the transistor has the ability to exert control over a much larger flow of electrons through the

collector.

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TRANSISTOR CONFIGURATIONS

Transistors are mostly used for either amplifying or switching. In operation, the

transistor as mentioned before has three states which are the active region, cut off region and

the saturation region. Normally the switching function of transistor happens in saturation

region and cut off region. However the amplification happens in active region of transistor.

There are different transistor configurations which each of them has its own features such as

common emitter, common base, and common collector.

TRANSISTOR CONFIGURATION BY COMPARISON CHART

AMPLIFIER TYPE

COMMON

BASE

COMMON EMITTER

COMMON EMITTER

(Emitter Resistor)

COMMON COLLECTOR

(Emitter Follower)

INPUT/OUTPUT

PHASE RELATIONSHIP

0° 180° 180° 0°

VOLTAGE GAIN

HIGH MEDIUM MEDIUM LOW

CURRENT GAINLOW

MEDIUM MEDIUM

HIGH

POWER GAIN LOW HIGH HIGH MEDIUM

INPUT RESISTANCE

LOW MEDIUM MEDIUM HIGH

OUTPUT RESISTANCE

HIGH MEDIUM MEDIUM LOW

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Below are the transistor configurations comparison as well as the input and output waveform

of each transistor configuration;

Figure 3: Input and Output waveform of each transistor configuration

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STATE OF TRANSISTOR

We will focus on N-P-N transistors. Operation of a PNP transistor is analogous to that of a NPN transistor except that the role of majority charge carries is reversed.

BIAS STABILIZATION

The stability of a system is a measure of the sensitivity of a network to variations in its parameters. Below are states region of a transistors:

Active region:In active region, the base – emitter junction is forward biased while the base-collector region is reversed biased. This state is used for amplification function.

Cutoff region:In this region, both base-emitter junction and base-collector junction are reversed biased.

Saturation region:In saturation region, both base-emitter junction and base-collector junction are forward bias. Saturation region and cut-off region are used for switching function.

Figure 3: States region circuit diagram of a transistor

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Figure 4: Transistor states

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For this assignment, the specification is more towards common base configurations.

COMMON BASE CONFIGURATIONS

Two voltages VBE and VCB are applied to the emitter, E and collector C, of the transistor with

respect to the common base, B as shown in the figure below.

Figure 5: An example of common base configuration circuit

In this configuration, base-emitter, BE junction is in forward biased due to the

negative voltage applied on emitter terminal. On the other hand, base-collector, BC junction

is in reversed biased due to positive voltage applied on collector terminal (positive voltage

source attracts the free electrons on n-type layer of n-p-n transistor).

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Moreover, the resistance across the base-emitter junction is smaller and is higher on the base-

collector due to reverse biased. On the other hand, collector current has almost same value as

emitter current, so it produced a high current across emitter terminal due to the small

resistance value as mentioned collector current is almost as same as emitter current.

Therefore, the product of collector current and collector resistance will result a high voltage

gain. Moreover, the voltage gain depends on the amount of DC power source on the input

signal. Furthermore, it also depends on the internal resistance between the base and emitter. It

varies with different levels of current through the emitter.

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α AND β RELATIONSHIPS

By combining the both parameters α and β, we can obtain two mathematical expressions that

give the relationship between the different currents flowing in the transistors shown above.

Figure 6: Levels of IC and IB

The range of IB current is in micro ampere, therefore in ideal transistor IC will be equal to IB.

Moreover, the value of alpha is always less than one.

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OVERALL CIRCUIT DESIGN

Figure 7: Multisim design of the circuit

ANALYSIS OF CIRCUIT

In the circuit design as shown above, the transistor used is 2N2222A NPN transistor. The

base of the transistor is grounded. The emitter terminal is connected to AC power source with

the value of 0.707V (RMS value) is connected in series with a 50uF capacitor. A 2kΩ resistor

is connected in series with a 5V DC power source. The collector terminal is connected to a

5.5kΩ resistor in series with a 25V DC power source. A 100uF capacitor is connected

parallel with the 5.5kΩ resistor and the 25V DC power source.

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Vo

CALCULATIONSThe calculation is done based on circuit design above. Assuming some nominal value of components, we can design the circuit which is suitable for our requirements. Furthermore, with the aid of the circuit diagram the DC and AC analysis with the calculation is done to prove that the average voltage, AV is 100.

DC ANALYSIS

For DC analysis, the capacitor becomes open circuit as shown in the figure below:

Figure 8: Circuit under DC analysis

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Vo

I

II

(I) KVL AT BE LOOP

V5 – IERE – VBE = 0

5 - IE (2×103) – 0.7 = 0

(2×103) IE = 4.3

IE = 2.15mA

β:

Minimum value : 100

Maximum value : 300

And measured by DMM : 157

The value chosen 157 which is near by the average value of Beta

To find IC;

I C=( ββ+1 ) I E

I C=( 157158 )×(2.15 × 10 x−3)

I C = 2.136mA

(II) KVL AT CE LOOP

V5 – IERE – VCE – ICRC + V6 = 0

5 – (2.15×10-3) (2 ×103) – VCE – ( 2.136 ×10-3) (5.5×103) + 25 = 0

5 – 4.3 – VCE – 11.748 + 5 = 0

VCE = 13.952V

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To find IB;

IC = β IB

IB = IC

β

= ( 2.136 × 10 -3 )

157

I B = 13.6 uA

AC ANALYSIS

For AC analysis, the capacitor and the DC source become open circuit as shown in the figure below;

Figure 9: Circuit under AC analysis

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Vo

Due to early voltage;

I C=I S eV BE

V T (1+V CE

V A

)

In order to find IS (saturation current) ,assumed VCE is equal to zero (where the saturation region VCE is equal to zero).

Therefore ICS:

I CS=V 3+V 2

(( ββ+1 )RE+RC)

I CS=30

(( 157158 )(2×10 x3 )+(5.5× 10 x3))

I CS=4.0 mA

Therefore;

V A=V CE

I C

I S ×eV BE

V T

−1

V A=13.952

2.136

4 ×e0.7

0.026

−1

V A=13.952V

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AC HYBRID-PI MODEL

Figure 10: AC Hybrid-pi model

The output resistance, ro:

rO=V A

I CQ

rO= 13.952

2.136 x 10−3

rO=6.53 kΩ

The base resistor,r π:

r π=β ×V T

I CQ

r π=157 × 0.026

2.136 x 10−3

r π=1.91kΩ

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The trans conductance,gm :

gm=I CQ

V T

gm=2.136 x 10−3

0.026

gm=82.15 x10−3 A/V

KCL at output node:

( gm × vπ )+(vo ×( 1rC

+ 1ro ))=0

vo=(−gm × vπ )

( 1rC

+ 1r o

)

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Relation between Vπ and VS from the hybrid-pi model (Vπ VS )

Note that VS and the voltage across the emitter resistor are in parallel. Therefore the total

voltage of VS and VRE:

V total=V S ×V ℜ

V S+V ℜ

Since VS = VRE

V total=V S ×V S

2V S

V total=V S

2

Therefore,

V π+V total=0

V π+V S

2=0

V π=−V S

2

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Therefore by substituting Vπ in equation derivate by KCL at output node:

vo=( gm × vS )

2( 1rC

+ 1ro

)AV =

vo

vS

=gm

2( 1rC

+ 1r o

)

AV =vo

vS

= 82.15 ×10−3

2( 15.5 ×103 + 1

6.53 × 103 )

AV =122.63

Hence the voltage gain of this amplifier is 122.63

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MULTISIM STIMULATIONSBased on the circuit design, the output voltage, Vo is 6.909V.This value is approximately same the output voltage 20Vp-p.I have also obtain the output the required output waveform as shown below:

Practical Output voltage, Vo = 6.909 × RMS

= 6.909 × 2 √ 2

= 19.54V

Figure 11: The complete stimulation of my circuit design

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Figure 12: Input waveform

Figure 12: Output waveform

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Input wave Output wave

Figure 13: Combination of Input and Output waveform

DISCUSSION AND CONCLUSION

The design required a specified input and output voltage as given in the

specifications. Comparison was done to compare the results of the

simulated circuit which is shown above with the practical design circuit

while testing it in the lab ,and there were some differences in the results

obtained:

(i) The simulation output voltage was somehow more than the one

which i got during practical circuit testing in the lab.

(ii) There are also some differences in the input and the output

waves .In the simulation using multisim, the waves were in phase

and compare with the practical design waves which were also in

phase but it was not that clear then the stimulation waves.

(iii) The voltage gain obtain from the theoretical part is 100 while the voltage gain

obtained from the calculation part is around 122.63.This is due to some

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assumption taken while calculating. The voltage gain of an amplifier is an

important factor to determine how much of incoming voltage has been amplified

at the output point. Once the voltages gain in known, it shows how much of sound

has been amplified.

The transistor is the key active component in practically all modern electronics, and is

considered by many to be one of the greatest inventions of the twentieth century. The

transistor's low cost, flexibility, and reliability have made it a ubiquitous device.

Herein, in conclusion, I have learnt about the bipolar junction transistors (BJT) and its

basic applications. Besides that, I have also understood the common base configuration and

its features and also its important factors which have effect on itself. Common base

configuration has no phase shift and it causes high voltage gain which is suitable to use for

audio amplifier. Furthermore, due to the DC power sources, emitter- base junction is in

forward bias and the collector-base junction is in reverse bias. Moreover, I have also learnt

about the effect and the important factors in AC analysis and amplification such as early

voltage, internal resistance as well as trans conductance.

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REFERENCES

Anonymous, Common Base Amplifier, online at

http://www.allaboutcircuits.com/vol_3/chpt_4/7.html, accessed on 5th May 2010.

Dr. Alaa El-Din Hussein,2008,Bjt transistors,(operations and characteristics),online at

http://opencourseware.kfupm.edu.sa/colleges/ces/ee/ee203/files%5C3-

Handouts_Handout_3a.pdf, accessed on 10th May 2010.

Electronic Devices and Circuits Engineering Sciences 154, 2001, Basic BJT Amplifier

Configurations, online at

http://people.seas.harvard.edu/~jones/es154/lectures/lecture_3/bjt_amps/bjt_amps.html,

accessed on 26th April 2010.

Electronics tutorial, 1998-2010, Bipolar Transistor, online at,http://www.electronics-

tutorials.ws/transistor/tran_1.html,accessed on 1st May 2010.

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ECE65 Lecture Notes (F. Najmabadi), Winter 2006, Bipolar-Junction (BJT) transistors,

online at http://aries.ucsd.edu/NAJMABADI/CLASS/ECE65/06-W/NOTES/BJT1.pdf,

accessed on 7th May 2010.

Integrate publishing, Electrical Engineering Training Series, Transistor configuration,

online at http://www.tpub.com/neets/book7/25f.htm, accessed on 3rd May 2010.

Kenneth R. Laker, 2008, Early Effect and BJT Biasing, online at

http://www.seas.upenn.edu/~ese319/Lecture_Notes/Lec_4_BJTBias1_08.pdf, accessed on

27th April 2010.

Kenneth R. Laker, 2008, ESE319 Introduction to Microelectronics, online at http://www.seas.upenn.edu/~ese319/Lecture_Notes/Lec_9_CCandCBDesigns_08.pdf, accessed on 25th April 2010.

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