I. Introduction Touch screen technology enables direct interaction with devices through touch. Using either capacitive or resistive methods, these screens detect user input, translating it into commands. Widely used in smartphones, tablets, and kiosks, touch screens offer intuitive navigation, eliminating the need for physical buttons and enhancing user experience across various applications. Understanding how touch screens work is crucial for users and developers alike. It enhances user experience by ensuring effective interaction, informs choices in device selection, and guides troubleshooting. For developers, knowledge of touch technology is vital for creating intuitive applications and improving interface design, ultimately leading to greater user satisfaction. This blog aims to explore why touch screens predominantly respond to fingers, delving into the science behind touch sensitivity. By examining the principles of capacitive and resistive technology, we will uncover the
What is a transistor?
A
transistor is a semiconductor device which is used for switching electrical signals. In
other words it is also considered as electrical switch. It is one of the basic
components of modern electronics. Now a days wide range of transistors are available
for various purposes like amplifying signal, switching, putting logic to a
circuit etc. Transistors are either available as discrete devices or within the
integrated circuits (ICs).
History of transistor
In early 1900s thermionic valve or vacuum tube
technology was introduced, but these devices were expensive, bulky and also
required powering by a battery. Soon afterwards the Cat's Whisker detector was
discovered which is known today as semiconductors. To replace vacuum tube
technology, the point contact transistor was introduced which can amplify or
switch electrical signals. Bell Labs was the first recognized organization to
work on alternatives of vacuum tube technology.
On December 16, 1947, Bardeen and
Brattain had built the first point-contact transistor which was made from
strips of gold foil on a plastic triangle, pushed down into the contact with a
slab of germanium.
Why is transistor called transistor?
We may break
the word transistor as a combination of transfer and resistance. This is
because it transfers the resistance from one end of the device to the
other end. Hence, the name transistor. Transistors have very high I/P and very low O/P resistance.
How does a transistor work?
The
transistor is a device that consists of three different layers and each layer
is a terminal. Two of the layers are doped to give one type of semiconductor
and the other one is the opposite type i.e. two may be n-type and one p-type (NPN),
or two may be p-type and one may be n-type (PNP). They are arranged in such a
way that the two similar layers of the transistor sandwich the layer of the
opposite type. As a result these semiconductor devices are designated as either
PNP transistors or NPN transistors according to the way they are made up.
The names for the three electrodes or terminals found in transistor are understood differently as below:
The names for the three electrodes or terminals found in transistor are understood differently as below:
- Base: In the earliest point contact transistors, there were two point contacts placed onto the base material. This base material formed the base connection and hence the name stuck.
- Emitter: As the name emitter says, it emits the charge carriers.
- Collector: As the name emitter says, it collects the charge carriers.
How to identify the terminals in a transistor?
Normally
transistors have three pins. We generally get confused in identifying the pins.
The one side of the body of the transistor is found flat. To identify the pins,
keep the flat side facing you and find the middle one which is base, pin in the
right is emitter and the pin in left is collector.
Why NPN transistors are used more than PNP transistors?
What is the difference between PNP & NPN transistor?
Based on the arrangement
of the semiconductor layers, the transistors are of two types as −
·
NPN Transistor:
· PNP Transistor: Conversely a PNP transistor is formed when a thin layer of N-type semiconductor material is sandwiched between two layers of P-type semiconductor material. In a PNP transistor, the emitter and collector are made of P-type material, while the base is constructed from N-type material. The circuit symbol for a PNP transistor is represented as shown in the figure below.
Differences between NPN & PNP transistors:
1. In NPN transistor,
current flows from collector region to emitter region where as In PNP transistor;
the direction of current is from emitter to collector.
2. In NPN transistors,
Electrons are the majority charge carriers and hole is the minority charge
carrier whereas in PNP transistors, Holes are the majority charge carriers and
electrons are the minority charge carriers.
3. Switching of NPN
transistor is faster due to high drift velocity of electrons, whereas Switching
speed of PNP transistor is low due to low drift velocity of holes.
4. The switching time of
NPN transistor is small and the switching time of PNP transistor is large.
5. In NPN transistor, the
base current flows from base to emitter but In PNP transistor, the base current
flows from emitter to base.
In actual applications, NPN transistors are far more popular than PNP
transistors.
There are several reasons for
this:
·
Carrier mobility: In NPN transistors,
electrons are the majority carriers rather than holes that are the majority
carriers in PNP transistors. As holes move far more easily within the crystal lattice
than electrons, which means they have a higher mobility, they can operate
faster, sensitive and provides much better level of performance.
·
Negative grounding: Over the years, a
negative ground has become standard, e.g. within automotive vehicles, it is
negatively grounded because of ease in grounding and safety reasons, and the
polarity of NPN transistors means that the basic transistor configurations
operate with a negative ground.
·
Production costs: The manufacture of
silicon based semiconductor components is most economically undertaken using
large N type silicon wafers. Whilst it is possible to manufacture PNP
transistors which requires 3 times more surface area of the wafer, and this
significantly increases the costs. As the wafer costs form a major part of the
overall component cost, this increases production costs significantly for PNP
transistors.
Different types of transistor
There are many different types
of transistors in use. Each transistor has its own advantage in its
application. The main classification is as follows.
Bipolar Junction Transistor:
A Bipolar junction
transistor (BJT) is called so as it has two PN junctions for its
function. This BJT is nothing but a normal transistor controlled by current. It
may be two types of configurations NPN or PNP.
Usually NPN transistor is preferred for the sake of convenience. The following
image shows how a practical BJT looks like.
Field Effect Transistor(FET)
A unipolar
semiconductor device with three terminals, the field-effect transistor (FET) is
distinguished by its composition of either P-type or N-type materials,
rendering it unipolar. This property enables current conduction through either
electrons or holes. Unlike a bipolar junction transistor, the FET operates as a
voltage-controlled device. Its chief benefit lies in its exceptionally high
input impedance, typically measured in megaohms. FETs offer various advantages,
including minimal heat dissipation, low power consumption, and high efficiency.
The image below illustrates the physical appearance of a practical FET.
Features of FET: The Field Effect Transistor (FET) possesses several distinctive features, which are as follows.
1.Unipolar: The FET is categorized as a unipolar device since it conducts
current through either holes or electrons.
2. High input
impedance: Due to reverse biasing, the FET exhibits high input impedance,
allowing the flow of input current.
3. Voltage
controlled device: The gate input voltage governs the output voltage of the
FET, making it a voltage-controlled device.
4. Low
noise: The absence of junctions along the conduction path in FETs results in
lower noise compared to Bipolar Junction Transistors (BJTs).
5. Transconductance
gain: The gain of FETs is characterized by transconductance, which represents
the ratio of the change in output current (Ic) to the change in input voltage(V).
Advantages
of FET: There are several advantages of using FETs over BJTs, which set them
apart. Here are some differentiating advantages of FETs:
1. Unipolar
device: FETs, such as JFETs, operate as unipolar devices, while BJTs are
bipolar devices.
2. Voltage-driven:
FETs are driven by voltage, whereas BJTs are driven by current.
3. High
input impedance: FETs exhibit high input impedance, whereas BJTs have low input
impedance.
4. Better
thermal stability: FETs offer improved thermal stability compared to BJTs,
which have relatively less thermal stability.
5. Transconductance-based
gain: In FETs, gain is characterized by transconductance, whereas in BJTs, it
is characterized by voltage gain.
FET Terminals: Similar to BJTs, FETs are
three-terminal devices, but the terminal names differ. In FETs, the terminals
are known as Gate, Source, and Drain. The Source terminal corresponds to the
Emitter in BJTs, the Gate is analogous to the Base, and the Drain is equivalent
to the Collector.
The symbols of a FET are shown in below image
Types of FET
Mainly there are two types of FETS. They are JFET and MOSFET. The
figure below is the classification.
JFET (Junction Gate Field-Effect Transistor):
Junction Field-Effect Transistors (JFETs) are a type of field-effect transistor with three terminals. They find numerous applications, including use as switches, amplifiers, and more. JFETs are classified into two categories: N-Channel JFETs and P-Channel JFETs.
MOSFET (Metal–Oxide–Semiconductor Field-Effect
Transistor):
The MOSFET (Metal-Oxide-Semiconductor Field-Effect
Transistor) is a type of field-effect transistor with four terminals: source
(S), gate (G), drain (D), and body (B). It is classified into two basic
configurations: Depletion Mode MOSFET and Enhancement Mode MOSFET.
What is the latest technology in transistors?
The latest technology in transistors is the production of
3-nanometer chips based on new transistor technology by Samsung. According to
Samsung, these chips offer 45% better power efficiency compared to current
five-nanometer silicon. It has been reported that Samsung intends to introduce
an enhanced version of this new process in 2023.
Nomenclature of transistors
Transistors have information displayed as a code on their
front body. In the European system of coding, this code consists of two
alphabets preceding the number. The first alphabet represents the type of
semiconductor material used in the transistor, while the second alphabet
specifies the intended application or use of the transistor.
For example, BC548 is Silicon Audio frequency Amplifier.
B – Silicon C – Audio frequency amplifier –
Below is the details of the codes.
First letter
A – Germanium
B – Silicon
C – Gallium Arsenide
D – Indium Antimide
Second letter
C – Audio frequency Amplifier
D – Audio frequency power amplifier
F – Low power Radio frequency amplifier
P – High power Radio frequency amplifier
According to the
American system, the code begins with 2N followed by a
number that indicates the time of design. A higher number indicates recent
design.
Eg. 2N 2222A
Quiz for you.
Comment the details of
the transistors.
1. BD 140
2. AD 140
AC 187
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