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Tanssion > blog > transistors > What is a transistor?

What is a transistor?

Author: Tanssion Date: 2023-08-15 Hits: 0

Ⅰ. History of transistor development
Ⅱ. Advantages of transistors
Ⅲ. Main parameters of transistors
Ⅳ. The Importance of Transistors
Ⅴ. Classification of transistors
Ⅵ. Application of transistor

A transistor is a semiconductor device used to amplify or switch electrical signals and power. Transistors are one of the basic building blocks of modern electronics. It consists of semiconductor material and usually has at least three terminals for connecting to electronic circuits. A voltage or current applied to one pair of terminals of a transistor controls the current through the other pair of terminals. Since the controlled (output) power can be higher than the controlled (input) power, the transistor can amplify the signal. Some transistors are individually packaged, but many more are embedded in integrated circuits.

What is a transistor

Transistors are composed of semiconductor materials and have at least three external terminals called poles. Taking a bipolar junction transistor as an example, there are base (B), collector (C), and emitter (E), where the base (B) is the control electrode, and the volt-ampere characteristic relationship between the other two terminals is controlled by the non-linear resistance relationship of the pole. The current or voltage input by the controlled pole of the transistor changes the impedance of the output terminal, thereby controlling the current passing through the output terminal, so the transistor can be used as a current switch, and because the power of the transistor output signal can be greater than the power of the input signal, the transistor can be used as an electronic amplifier.

A transistor is a semiconductor device, commonly used in amplifiers or electrically controlled switches. Transistors are the fundamental building blocks that regulate the operation of computers, cell phones, and all other modern electronic circuits.

Because of their fast response and high accuracy, transistors are used in a wide variety of digital and analog functions, including amplification, switching, voltage regulation, signal modulation, and oscillators. Transistors can be packaged individually or as part of an integrated circuit that can accommodate 100 million or more transistors in a very small area.

Most transistors are made of very pure silicon, some are made of germanium, but certain other semiconductor materials are sometimes used as well. Transistors may have only one charge carrier in field effect transistors, or two charge carriers in bipolar junction transistor devices. Transistors are generally smaller and require less power to operate than vacuum tubes. Certain vacuum tubes outperform transistors at very high operating frequencies or high operating voltages. Many types of transistors are made by multiple manufacturers to standardized specifications.

Ⅰ. History of transistor development

Austro-Hungarian physicist Julius Edgar Lilienfeld conceived the field-effect transistor in 1926, but at the time it was impossible to actually build a working device.

The first working device to be built was the point-contact transistor invented by American physicists John Bardeen and Walter Brattain in 1947 while working under William Shockley at Bell Laboratories. The trio shared the 1956 Nobel Prize in Physics for their achievement.

The transistor type is the Metal Oxide Semiconductor Field Effect Transistor (MOSFET), invented in 1959 by Mohamed Atalla and Dawon Kahng at Bell Labs. Smaller and cheaper radios, calculators and computers, etc.

Ⅱ. Advantages of transistors

1. Strong and reliable

Shock resistance and vibration resistance are the advantages of transistors. In addition, the volume of transistors is only one-tenth to one-hundredth of that of electronic tubes, and they emit little heat, which can be used to design small, complex and reliable circuits. Although the manufacturing process of transistors is precise, the process is simple, which is conducive to improving the mounting density of components.

A semiconductor triode is a semiconductor device that contains two PN junctions inside and usually three lead-out electrodes on the outside. It has the functions of amplifying and switching electrical signals, and is widely used. Both the input stage and the output stage use transistor logic circuits, which are called transistor-transistor logic circuits. They are referred to as TTL circuits in books and practical applications. The TTL NAND gate is a circuit system composed of several transistors and resistance elements, which is manufactured on a small silicon chip and packaged into an independent component.
Since Fleming invented the vacuum diode in 1904 and De Forest invented the vacuum triode in 1906, electronics has developed rapidly as a new discipline. But the real rapid progress of electronics should start after the invention of the transistor. In particular, the emergence of PN junction transistors has opened up a new era of electronic devices and caused a revolution in electronic technology.

2. Components are not consumed

No matter how good the electron tube is, it will gradually deteriorate due to the change of cathode atoms and chronic air leakage. For technical reasons, the same problem existed at the beginning of transistor production. With the advancement of materials and various improvements, the life of transistors is generally 100 to 1000 times longer than that of electron tubes.

3. No preheating required

It works as soon as it is turned on. For example, a transistor radio rings as soon as it is turned on, and a transistor TV set appears quickly when it is turned on. Tube equipment cannot do this. After turning on the machine, it takes a while to hear the sound and see the picture. Obviously, transistors are very advantageous in military affairs, measurement, recording, etc.

4. Very little power consumption

It is only one tenth or a few tenths of the electron tube. It does not require a heated filament to generate free electrons like a tube. A transistor radio can be listened to for half a year with only a few dry batteries, which is difficult for a tube radio. Transistors can operate at lower voltages, reducing energy consumption. Transistor types such as MOSFETs dissipate very little energy switching, which is especially important in mobile devices and battery-powered applications.

5. Small size and miniaturization

Transistors can be made very small, and as technology develops, they get smaller and smaller, allowing integrated circuits (ICs) to hold more transistors and electronic components. This miniaturization increases device functionality, performance and efficiency.

6. Reliability and stability

Transistors generally have a long lifetime and stability, and can operate at relatively high temperatures and environmental conditions, making them suitable for a variety of operating environments.

7. High speed and fast switching characteristics

Transistors switch very fast, being able to switch from the off state to the on state extremely quickly, which makes them suitable for high frequency applications such as communication equipment, microprocessors, etc.

8. Integration and scalability

Transistors can be highly integrated in integrated circuits, integrating millions or even billions of transistors on a single chip. This integration allows complex functions and circuits to be implemented on a small chip, saving space and improving efficiency.

What is a transistor

Ⅲ. Main parameters of transistors

The main parameters of the transistor are power dissipation, current amplification factor, maximum collector current, reverse current, maximum reverse voltage, frequency characteristics, etc.

1. Dissipated power

Dissipated power is also called the maximum allowable collector dissipated power PCM, which refers to the maximum collector dissipated power when the transistor parameter changes do not exceed the specified allowable value. Dissipated power is closely related to the highest allowable junction temperature and maximum collector current of the transistor. When the transistor is in use, its actual power consumption is not allowed to exceed the PCM value, otherwise the transistor will be damaged due to overload.

Usually, transistors with power dissipation PCM less than 1W are called low-power transistors, transistors with PCM equal to or greater than 1W and less than 5W are called medium-power transistors, and transistors with PCM equal to or greater than 5W are called high-power transistors.

2. Current amplification factor

The DC current amplification factor is also called the static current amplification factor or the DC amplification factor. It refers to the ratio of the transistor collector current IC to the base current IB when there is no static signal input. It is generally represented by hFE or β.

3. Maximum collector current

Collector maximum current (ICM) refers to the maximum current allowed to pass through the transistor collector. When the collector current IC of the transistor exceeds ICM, the parameters such as the β value of the transistor will change significantly, which will affect its normal operation and even be damaged.

4. Reverse current

5. Maximum reverse voltage

The maximum reverse voltage refers to the highest operating voltage that the transistor is allowed to apply when it is working. It includes collector-emitter reverse breakdown voltage, collector-base reverse breakdown voltage and emitter-base reverse breakdown voltage.

6. Frequency characteristics

The highest oscillation frequency is the frequency at which the power gain of the transistor drops to 1. Generally, the highest oscillation frequency of a high-frequency transistor is lower than the common base cut-off frequency fα, while the characteristic frequency fT is higher than the common base cut-off frequency fα and lower than the common-collector cut-off frequency fβ.

Ⅳ. The Importance of Transistors

The transistor is considered one of the greatest inventions in modern history, possibly the most important invention of the twentieth century, allowing radios, calculators, computers, and related electronics to become smaller and cheaper.

It is comparable in importance to inventions such as printing, the automobile and the telephone. Transistors are key active devices in all modern appliances. Transistors are so important in today's society largely because of their ability to be mass-produced using highly automated processes, and thus reach incredibly low unit costs. The invention of the transistor by Bell Laboratories in 1947 has been listed on the IEEE Milestone List.

Although millions of individual transistors are still in use, the vast majority of transistors are assembled on microchips along with diodes, resistors, and capacitors to make complete circuits. May be analog, digital, or mixed on-chip. The cost of designing and developing complex chips is quite high, but when spread over millions of production units, it has little effect on the price of each chip. A logic gate contains 20 transistors, and in 2012 an advanced microprocessor used 1.4 billion transistors.

The cost, flexibility and reliability of transistors make them general-purpose devices for non-mechanical tasks, such as digital computing. Transistor circuits are also replacing electromechanical devices in controlling appliances and machinery because it is generally cheaper and more efficient. With electronic control, one can use standard integrated circuits and write a computer program to accomplish the same task as a machine control.

Because of the low cost of transistors and later electronic computers, a wave of digitizing information began. Since computers provide the ability to quickly find, sort and process digital information, more and more effort is being devoted to the digitization of information.

Much of today's media is distributed electronically and ultimately converted and presented in analog form by computers. Fields affected by the digital revolution include television, radio and newspapers.

Transistors are the basic building blocks inside computers, they perform logic operations, store and transfer data in processors. The improvement of computing speed and performance of computers is closely related to the development of transistor technology. It plays a vital role in communications equipment, including wireless communications, mobile phones, satellite communications, and fiber optic communications. They are used to amplify signals and modulate signals to make communication more stable and efficient.

Ⅴ. Classification of transistors

There are two common types of JFETs: N-channel (N-channel) and P-channel (P-channel). These two types of JFETs have some differences in structure, but the basic working principle is similar.

The working principle of JFET involves controlling the flow of current between source and drain, similar to MOSFET, but JFET is controlled differently than MOSFET.

N-Channel JFET: In N-channel JFET, there is an N-type semiconductor channel between the source and drain. When a negative voltage is applied between the gate and source, a depletion region is formed that reduces the channel's ability to conduct electricity, limiting current flow. And when the gate voltage is zero or negative, the conductivity of the channel is enhanced, the current can flow from the source to the drain, and the JFET is turned on.

P-Channel JFET: In P-channel JFET, there is a P-type semiconductor channel between the source and drain. When a positive voltage is applied between the gate and source, a depletion region is formed that reduces the channel's ability to conduct electricity, limiting current flow. And when the gate voltage is zero or positive, the conductivity of the channel is enhanced, the current can flow from the source to the drain, and the JFET is turned on.

The on-state of the JFET is controlled by the polarity of the gate voltage, and unlike the MOSFET, no charge needs to be applied between the gate and the source, so the control current of the JFET is simpler.

An IGBT is a semiconductor device that integrates the characteristics of a MOSFET and a bipolar junction transistor (BJT). The structure of IGBT combines the characteristics of MOSFET and BJT, and has three main areas: Collector, Emitter, and Gate.

Compared to MOSFETs, IGBTs have a higher current carrying capability, similar to BJTs. This makes IGBTs suitable for high current and high power applications such as power conversion, motor drive, etc.

The control current (gate current) of the IGBT is relatively low, and a large current flow can be controlled by a small current, thereby reducing energy consumption.

Compared to conventional BJTs, IGBTs switch faster, making them suitable for applications that require frequent switching.

Bipolar transistors are primarily used to amplify and control current. Bipolar transistors are divided into NPN type and PNP type.

1.NPN type:

Amplified region (Active region): When a sufficient forward bias voltage is applied between the base-emitter, the emitter-base junction is broken down, causing current to flow from the emitter to the base, and then from the base to the collector electrode. This area is called the magnification or active area. A small change in the base current can lead to a large change in the collector current, enabling current amplification.

Cut-off region (Off state): When there is no forward bias voltage between the base-emitter, that is, not enough current is provided to break down the PN junction of the emitter-base junction, the BJT is in the cut-off state. In this case, no current flows between the emitter and base, and no current flows between the collector-base.

Saturation region: When the voltage between the base-emitter is high enough, the BJT enters the saturation region, the base-emitter junction is completely broken down, and the current flow is maximized. In the saturation region, the BJT is no longer able to amplify the signal, but acts as a switch.

2.PNP type:

The PNP-type BJT consists of three main areas: P-type Emitter, N-type Base, and P-type Collector. An NP junction is formed between the emitter and base, and a PN junction is formed between the base and collector.

Bipolar transistors use both the majority and minority carriers in the semiconductor to conduct, hence the name. The bipolar transistor is the first mass-produced transistor. It is composed of two diodes with different junctions. Its structure can be divided into two layers of N-type semiconductors sandwiching a layer of P-type semiconductor NPN transistors, and two-layer P-type A PNP transistor with a layer of N-type semiconductor sandwiched between semiconductors. Therefore, there will be two PN junctions, namely the base-emitter junction and the base-collector junction, separated by a layer of semiconductor, which is the base.

Bipolar transistors differ from field effect transistors in that bipolar transistors are low input impedance devices. When the base-collector voltage increases, the collector-emitter current will increase exponentially according to the Shokky model and the Ebbers-Moore model. Therefore bipolar transistors have a higher transconductance than FETs.

Bipolar transistors can also be designed to conduct when exposed to light, because the base absorbs photons to generate photocurrent, and its effect is similar to that of the base current, and the collector current is generally β times the photocurrent. The package has a transparent window called a phototransistor.

Field-effect transistors conduct current using either electrons (N-channel FETs) or holes (P-channel FETs). Field effect transistors have three poles of gate, drain, and source. If it is not a junction field effect transistor, there will be one pole called body. In most field effect transistors, the body will be connected to the source.

FET is a type of transistor commonly used in radio frequency circuits, and MOSFET is an important subclass of FET, especially playing an important role in RF circuits.

FETs are a class of transistors whose operation is based on electric field effects to control the flow of current. FETs are widely used in the RF field mainly because of their high input impedance, low noise and high frequency characteristics.

In a field effect transistor, the source-drain current flows through the channel connecting the source and drain, and the degree of conduction depends on the electric field generated by the voltage between the gate and the source, so the gate-source can be used The voltage controls the source-drain current, acting as a simple switch.

Field effect transistors can be divided into two types: junction field effect transistors (JFETs) and insulated gate field effect transistors (IGFETs). The most common of the latter is metal oxide semiconductor field effect transistors (MOSFETs). It reflects its original structure consisting of metal (gate), oxide (insulating layer) and semiconductor. A junction field effect transistor forms a PN diode between the source and drain. Therefore, the N-channel JFET is similar to the triode of the vacuum tube. Both of them also operate in the depletion region, have high input impedance, and both use the input voltage to control the current.

1. Junction Field Effect Transistor (JFET)

The junction field effect transistor is the simplest type of unipolar field effect transistor. It can be divided into n-channel (n-channel) or p-channel (p-channel). In the following discussion, the n-channel junction field effect transistor is mainly taken as an example. In the p-channel junction field effect transistor, the n-region and p-region and all voltage positive and negative and current directions are just reversed.

N-channel JFETs consist of an n-type dopant surrounded by a p-type dopant. The drain and source are connected to the n-type doping. The stretch of semiconductor from source to drain is called an n-channel. The p region is connected with a gate. This pole is used to control the junction field effect transistor, which forms a pn diode with the n channel, so the junction field effect transistor is similar to the metal-oxide-semiconductor field effect transistor, except that in the metal-oxide-semiconductor field Instead of using a pn junction in the effect tube, a Schottky junction (junction between the metal and the semiconductor) is used. In principle, the junction field effect transistor is exactly the same as the metal-oxide-semiconductor field effect transistor.

2. Insulated Gate Field Effect Transistor (IGFET)

IGFETs use an insulated gate to control the flow of current in the channel and feature high input impedance, low power consumption, and fast switching speed.

Ⅵ. Application of transistor

Transistors generally have three poles, one of which is also an input and output terminal, (B) the base cannot be used for output, (C) the collector cannot be used for input, and the other two poles form an input and output pair. The reason why transistors are so versatile is their ability to amplify signals. When a small signal is applied to one pair of electrodes, it can control the other pair of extremely large signals. This characteristic is called gain.

When the transistor works linearly, the output signal is proportional to the input signal, and the transistor becomes an amplifier. This is a common approach in analog circuits such as RF amplifiers, electronic amplifiers, audio amplifiers, voltage regulator circuits.

A transistor is used as a switch when its output is either fully off or fully on. This approach is primarily used in digital circuits, such as logic gates, random access memory (RAM), and microprocessors.

Microprocessors and integrated circuits: The tiny size and high performance of transistors make them key building blocks in microprocessors and integrated circuits, which perform computing and control tasks.

Memory: Transistors are used to build various types of memory such as static and dynamic random access memory (SRAM and DRAM).

Logic gates and circuits: Transistors form logic gates, such as AND gates, OR gates, and NOT gates, which are used for logic operations in digital circuits.

RF Amplifiers and Mixers: Transistors are used to build RF amplifiers and mixers for signal amplification and frequency conversion in wireless communication systems.

What is a transistor

Transceiver: Transistors are used in transceivers to convert signals from digital to radio frequency, and to send and receive signals in wireless communications.

Solar Cell: Transistors are used in solar cells to convert light energy into electricity.
Industrial Automation: Transistors are used in industrial automation systems to control machinery, equipment, and processes.

Biosensors: Transistors are used as biosensors to monitor and detect biomolecules and signals.


Frequently Asked Questions

1、What is transistor in simple words?
A transistor is a type of semiconductor device that can be used to conduct and insulate electric current or voltage. A transistor basically acts as a switch and an amplifier. In simple words, we can say that a transistor is a miniature device that is used to control or regulate the flow of electronic signals.
2、Why is it called a transistor?
The word transistor is a combination of transfer and resistance. This is because it transfers the resistance from one end of the device to the other end or we can say, transfer of resistance. Hence, the name transistor. Transistors have very high input resistance and very low output resistance.
3、What is the difference between a chip and a transistor?
A microchip, also known as a computer chip, is a set of electronic circuits printed onto a small flat piece of silicon. Transistors act as miniature electrical switches on the chip that can turn a current on or off.
4、Is A transistor a switch?
A transistor is a three-terminal semiconductor device that can be used as a switch or amplifier. The transistor as a switch is used to turn ON or OFF a circuit. The transistor as an amplifier is used to amplify the voltage or current.

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