TIẾNG ANH CHUYÊN NGÀNH CÔNG NGHỆ THÔNG TIN

Definition In electronics, a transistor is a semi-conductor device commonly used to amplify or switch electronic signals.. Or, the transistor can be used to turn current on or off in a

UNIT 1

TRANSISTOR

1 Definition

In electronics, a transistor is a

semi-conductor device commonly used to

amplify or switch electronic signals A

transistor is made of a solid piece of a

semiconductor material, with at least three

terminals for connection to an external

circuit A voltage or current applied to one

pair of the transistor's terminals changes

the current flowing through another pair of

terminals Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal

2 History

The first patent for the field-effect transistor principle was filed in Canada

by Austrian-Hungarian physicist, Julius Edgar Lilienfeld on 22 October

1925 But Lilienfeld did not publish any research articles about his devices

In 1934 German physicist Dr Oskar Heil patented another field-effect transistor

On 17 November 1947 John Bardeen and Walter Brattain, at AT&T Bell Labs, observed that when electrical contacts were applied to a crystal

of germanium, the output power was larger than the input William Shockley saw the potential in this and worked over the next few months

Fig 1 Some types of transistor

greatly expanding the knowledge of

semiconductors and could be described

as the father of the transistor, a legal

papers from the Bell Labs patent show

that William Shockley and Gerald

Pearson had built operational versions

from Lilienfeld's patents

The first silicon transistor was produced by Texas Instruments in

1954 This was the work of Gordon Teal, an expert in growing crystals of high purity, who had previously worked at Bell Labs The first MOS transistor actually built was by Kahng and Atalla at Bell Labs in 1960

The transistor is considered by many to be the greatest invention of the twentieth-century, and some consider it is one of the most important technological breakthroughs in human history It is the key active component in practically all modern electronics and is the fundamental building block of modern electronic devices like radio, telephone, computer etc Its importance in today's society rests on its ability to be mass produced using a highly automated process (in fabrication) that achieves astonishingly low per-transistor costs Some transistors are packaged individually but most are found in integrated circuits

Although several companies each produce over a billion individually

packaged (known as discrete) transistors every year, the vast majority of

transistors produced are in integrated circuits (often shortened to IC, microchips or simply chips) along with diodes, resistors, capacitors and

other electronic components to produce complete electronic circuits A logic gate consists of up to about twenty transistors whereas an advanced

Fig 2 Transistor in Lilienfeld’s

experience

microprocessor, as of 2006, can use as many as 1.7 billion transistors (MOSFETs) "About 60 million transistors were built this year [2002], for [each] man, woman, and child on Earth."

The transistor's low cost, flexibility, and reliability have made it a ubiquitous device Transistorized mechatronic circuits have replaced electromechanical devices in controlling appliances and machinery It is often easier and cheaper to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical control function

3 Applications

The bipolar junction transistor, or BJT, was the most commonly used transistor in the 1960s and 70s, after MOSFETs became widely available, the BJT remained the transistor of choice for many analog circuits such as simple amplifiers because of their greater linearity and ease of manufacture Desirable properties of MOSFETs, such as their utility in low-power devices, usually in the CMOS configuration, allowed them to capture nearly all market share for digital circuits; more recently MOSFETs have captured most analog and power applications as well, including modern clocked analog circuits, voltage regulators, amplifiers, power transmitters, motor drivers, etc

The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals This property is called gain A transistor can control its output in proportion to the input signal, that is, can act as an amplifier Or, the transistor can be used to turn current on or off in

a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements

The two types of transistors have slight differences in how they are

used in a circuit A bipolar transistor has terminals labeled base, collector, and emitter A small current at the base terminal (that is, flowing from the

base to the emitter) can control or switch a much larger current between the collector and emitter terminals For a field-effect transistor, the terminals

are labeled gate, source, and drain, and a voltage at the gate can control a

current between source and drain

The fig 3 represents a typical

bipolar transistor in a circuit Charge

will flow between emitter and

collector terminals depending on the

current in the base Since internally the

base and emitter connections behave

like a semiconductor diode, a voltage drop develops between base and emitter while the base current exists The size of this voltage depends on

the material the transistor is made from, and is referred to as VBE

3.1 Transistor as a switch

Transistors are commonly used as electronic switches, for both high power applications including switched-mode power supplies and low power applications such as logic gates

Using the simple transistor circuit it can be seen from the graph, from point A to point B, as the base voltage rises the base and collector current rise exponentially (the A-B segment should be curved), but the collector voltage simultaneously drops because of the collector resistor Relevant equations:

Fig 3 Typical circuit of transistor

Following the Kirhoff laws, one can write expression:

VRC = IC × RC

VRC + VCE = VCC

If VCE could fall to 0 (perfect closed switch) then Ic could go no higher than VCC / RC, even with higher base voltage and current The transistor is then said to be saturated In actuality VCE drops to roughly VBE

÷ 2, rising with higher collector currents Hence, values of input voltage can be chosen such that the output is either completely off, or completely

on The transistor is acting as a switch, and this type of operation is common in digital circuits where only "on" and "off" values are relevant

3.2 Transistor as an amplifier

The above common emitter amplifier is designed so that a small

change in voltage in (Vin) changes the small current through the base of the transistor and the transistor's current amplification combined with the

properties of the circuit mean that small swings in Vin produce large

changes in Vout

It is important that the operating parameters of the transistor are chosen and the circuit designed such that as far as possible the transistor operates within a linear portion of the graph, such as that shown between A and B, otherwise the output signal will suffer distortion

Fig 4 The transistor works as a switch

A

B

V B

I BC

Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both

From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing The first discrete transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive Some musical instrument amplifier manufacturers mix transistors and vacuum tubes in the same circuit, as some believe tubes have a distinctive sound

- Highly automated manufacturing processes, resulting in low per-unit cost

- Lower possible operating voltages, making transistors suitable for small, battery-powered applications

- No warm-up period for cathode heaters required after power application

- Lower power dissipation and generally greater energy efficiency

- Higher reliability and greater physical ruggedness

- Extremely long life Some transistorized devices have been in service for more than 30 years

- Complementary devices available, facilitating the design of tary symmetry circuits, something not possible with vacuum tubes

complemen Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications

5 Disadvantages

- Silicon transistors do not operate at voltages higher than about 1,000 volts (SiC devices can be operated as high as 3,000 volts) In contrast, electron tubes have been developed that can be operated at tens of thousands volts

- High power, high frequency operation, such as used in over-the-air television broadcasting, is better achieved in electron tubes due to improved electron mobility in a vacuum

- On average, a higher degree of amplification linearity can be achieved in electron tubes as compared to equivalent solid state devices, a characteristic that may be important in high fidelity audio reproduction

- Silicon transistors are much more sensitive than electron tubes to an electromagnetic pulse, such as generated by an atmospheric nuclear explosion

Exercise 1: Answer the question following the text:

1 What is a transistor?

2 What are the transistors made of?

3 Why can transistors provide amplification of a signal?

4 Where are transistors used?

5 Which type of transistor was used in 1960s-1970s

6 What does MOSFET stand for?

7.Why is transistor used for amplifying signal?

8 What are the terminals of BJT ?

9 What are the terminals of FET?

11.When was the first MOS transistor built?

12 How many transistors are in the advanced microprocessor in 2006?

Exercise 2: Identify the statements are True or False:

1 A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit

2 The transistor is the fundamental building block of modern electronic

devices like radio, telephone, computer and other electronic systems

3 The transistor is considered as one of the most important technological breakthroughs in human history

4 Transistorized mechatronic circuits couldn’t replace electromechanical devices in controlling appliances and machinery

5 Transistors operating at high voltage not suitable for small, powered applications

battery-6 Silicon transistors are much more sensitive than electron tubes to an electromagnetic pulse

Exercise 3: Translate the text and summery in short paragraph

UNIT 2

SENSOR

1 Definition

A sensor is a device that measures a physical quantity and converts

it into a signal which can be read by an observer or by an instrument For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube A thermocouple converts temperature to an output voltage which can be read by a voltmeter For accuracy, all sensors need to be calibrated against known standards

Sensors are used in everyday

objects such as touch-sensitive elevator

buttons and lamps which dim or

brighten by touching the base There are

also innumerable applications for

sensors of which most people are never

aware Applications include cars,

machines, aerospace, medicine,

manu-facturing and robotics

A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes For instance, if the mercury

in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C Sensors that measure very small changes must have very high sensitivities Sensors also have an impact on what they measure;

Fig 5 Humidity sensor

for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer

Sensors need to be designed to have a

small effect on what is measured; making the

sensor smaller often improves this and may

introduce other advantages Technological

progress allows more and more sensors to be

manufactured on a microscopic scale as

microsensors using MEMS (Micro Electro

Mechanical Systems) technology In most

cases, a microsensor reaches a significantly higher speed and sensitivity compared with macroscopic approaches A good sensor obeys the following rules:

 Is sensitive to the measured property

 Is insensitive to any other property

 Does not influence the measured property

Ideal sensors are designed to be linear The output signal of such a sensor is linearly proportional to the value of the measured property The sensitivity is then defined as the ratio between output signal and measured property For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/C]; this sensor is linear because the ratio is constant at all points of measurement If the sensor is not ideal, several types of deviations can be observed:

 The sensitivity may in practice differ from the value specified This

is called a sensitivity error, but the sensor is still linear

 Since the range of the output signal is always limited, the output signal will eventually reach a minimum or maximum when the measured

Fig 6 Thermometer

property exceeds the limits The full scale range defines the maximum and minimum values of the measured property

 If the output signal is not zero when the measured property is zero, the sensor has an offset or bias This is defined as the output of the sensor at zero input

 If the sensitivity is not constant over the range of the sensor, this is called nonlinearity Usually this is defined by the amount the output differs from ideal behavior over the full range of the sensor, often noted

as a percentage of the full range

 If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error Often, this behaviour is described with a bode plot showing sensitivity error and phase shift as function of the frequency of a periodic input signal

 If the output signal slowly changes independent of the measured property, this is defined as drift

 Long term drift usually indicates a slow degradation of sensor properties over a long period of time

 Noise is a random deviation of the signal that varies in time

 Hysteresis is an error caused by when the measured property reverses direction, but there is some finite lag in time for the sensor to respond, creating a different offset error in one direction than in the other

 If the sensor has a digital output, the output is essentially an approximation of the measured property The approximation error is also called digitization error

 If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic error

 The sensor may to some extent be sensitive to properties other than the property being measured For example, most sensors are influenced

by the temperature of their environment

 All these deviations can be classified as systematic errors or random errors Systematic errors can sometimes be compensated for by means of some kind of calibration strategy Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behavior of the sensor

2 Resolution

The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved The resolution is related to the precision with which the

measurement is made For example, a scanning tunneling probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules

All living organisms contain biological sensors with functions

similar to those of the mechanical devices described Most of these are specialized cells that are sensitive to:

 Light, motion, temperature, magnetic fields, gravity, humidity,

vibration, pressure, electrical fields, sound, and other physical aspects of the external environment

 Physical aspects of the internal environment, such as stretch, motion

of the organism, and position of appendages (proprioception)

 Environmental molecules, including toxins, nutrients, and

pheromones

 Estimation of biomolecules interaction and some kinetics parameters

 Internal metabolic milieu, such as glucose level, oxygen level, or osmolality

 Internal signal molecules, such as hormones, neurotransmitters, and cytokines

 Differences between proteins of the organism itself and of the ronment or alien creatures

envi-Artificial sensors that mimic biological sensors by using a biological sensitive component are called biosensors

Exercise 1: Answer the question following the text:

1 What is a sensor?

2 Where are sensors used?

3 What thing should be considered when making the sensors?

4 What properties the good sensors have

5 What is sensitivity error?

6 What does “linearity” means in term range of sensor?

7 What does “nonlinearity” means in term range of sensor?

8 What is a drift?

9 What causes the hysteresis in sensor?

10 What causes the digitization error?

11 What is the dynamic error?

12 What is the sensor resolution?

Exercise 2: Identify the statements are True or False:

1 Thermometer is one type of sensor

2 The application of sensor is not much

3 Sensors that measure very small changes must have very high

insensitivities

4 Technological progress allows more and more sensors to be

manufactured on a microscopic scale

5 If the sensitivity is not constant over the range of the sensor, this is called nonlinearity

6 Biological sensors have functions similar to those of the mechanical devices

7 The resolution is related to the precision of the measurement

8 Noise is a random error that can be reduced by signal processing

Exercise 3:

- Design a simple sensor, and then describe its working rule

- Summarizing the text of sensor in short paragraph (5-7 lines)

UNIT 3

ACTUATOR

1 Definition

An actuator is a mechanical device for moving or controlling a

mechanism or system An actuator typically is a mechanical device that takes energy, usually created by air, electricity, or liquid, and converts that into some kind of motion The typical actuator types are called switches

A biased switch is one

containing a spring that returns the

actuator to a certain position The

"on-off" notation can be modified

by placing parentheses around all

positions other than the resting

position For example, an

(on)-off-(on) switch can be switched on by

moving the contact in either

direction away from the centre, but return to the central off position when the contact is released The momentary push-button switch is a type of biased switch The most common type is a "push-to-make" (or normally-open or NO) switch, which makes contact when the button is pressed and breaks when the button is released Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch A "push-to-break" (or normally-closed or NC) switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released An example of a

Fig 7 Three pushbutton switches

push-to-break switch is a button used to release a door held open by an electromagnet

2 Some types of Actuator

-Knife switch: Knife switches are unique; the electrical contacts are

exposed, mounted on an insulating plastic or porcelain plate, unlike modern switches in which the working parts are enclosed in an insulating plastic or rubber housing to protect users from contact with hazardous voltages The

"knife", a flat metal swinging arm, is moved by the user between two or more gripping contacts of springy metal The knife and contacts are typically formed of copper, steel, or brass, depending on the application

The primary advantage of a

knife switch is the extremely high

current capability inherent to the

design The amount of surface area

on the "knife" that shorts the

contacts is also extremely high,

allowing a wide range of high vol-

tage or high amperage applications with no circuit degradation, choke, or arcing during switch throw Thicker components need only be accompanied by wider contacts to conduct higher currents, which allow the design to scale extremely well with size Its disadvantage is that to operate

it, a user has to grasp the knife's insulated handle near the exposed contacts and knife blade, causing a great risk of electric shock Although knife switches are inferior to traditional switches in applications where user safety is paramount, they are still commonly employed in everyday high-voltage applications such as building transformers, large power relays, and air-conditioning units

Fig 8 The symbol of witches

in diagram

-An electronic switch: is an electrical component that can break an

electrical circuit, interrupting the current or diverting it from one conductor

to another The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting Since the advent of digital logic in the 1950s, the term has spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between two logic levels or connect different signal lines, and even computers, network switches, whose function is to provide connections between different ports in a computer network The term 'switched' is also applied to telecommunications networks, and signifies a network that is circuit switched, providing dedicated circuits for communication between end nodes, such as the public switched telephone network The common feature of all these usages is they refer to devices

that control a binary state: they are either on or off, closed or open, connected or not connected

-Mercury tilt switch: The mercury switch consists of a drop of mercury

inside a glass bulb with 2 contacts The two contacts pass through the glass, and are connected by the mercury when the bulb is tilted to make the mercury roll on to them This type of switch performs much better than the ball tilt switch, as the liquid metal connection is unaffected by dirt, debris and oxidation, it wets the contacts ensuring a very low resistance bounce-free connection, and movement and vibration do not produce a poor contact These types can be used for precision works It can also be used where arcing is dangerous (such as in the presence of explosive vapour) as

the entire unit is sealed A simple semiconductor switch is a transistor Other types of switch include:

In the simplest case, a switch has two pieces of metal called contacts

that touch to make a circuit, and separate to break the circuit The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity Sometimes the contacts are plated with noble metals They may be designed to wipe against each other to clean off any contamination Nonmetallic conductors, such as conductive plastic, are sometimes used

A pair of contacts is said to be 'closed' when there is no space between them, allowing electricity to flow from one to the other When the contacts are separated by an insulating air gap, an air space, they are said to

be 'open', and no electricity can flow at typical voltages

Some contacts are normally open (Abbreviated "n.o." or "no") until closed by operation of the switch, while others are normally closed ("n.c

or "nc") and opened by the switch action, where the abbreviations given are

commonly used on electronics diagrams for clarity of operation in assembly, analysis or troubleshooting They serve to synchronize meaning with possible mistakes in wiring assembly, where wiring part of switch one way and part another (usually opposite) way will pretty much guarantee things won't work as designed

Exercise 1: Answer the question following the text:

1 What is an actuator?

2 What is the normally close switch?

3 What is the normally open switch?

4 What is the function of “knife” portion in electric switch?

5 What is knife made of?

6 What are advantages, disadvantages of a knife switch?

7 What is electronic switch?

8 What is a mercury tilt switch?

9 What are the advantages of mercury tilt switch?

10 Where is mercury tilt switches used?

11 What are criterions of chosen material for making switch contact?

12 What is a contact?

Exercise 2: Identify the statements are True or False:

1 An on-off switch can be switched on by moving the contact in either direction away from the centre, but return to the central off position

2 An NC switch makes contact when the button is pressed and breaks

when the button is released

3 The knife and contacts are typically made of copper, steel, or brass,