what is transistors switches fuse crystal and hardware components ICs, ICs families, MOS families memory CPU|

transistors

At the most basic level, transistor may seem simple. the bipolar junction transistor was the first solid-state amplifier element and started the solid-state electronics revolution. bardeen. brattain and shockley at the bell laboratories invented it in1948 as part of a post-war effort to replace vaccum tubes with solid-state devices.their work led them first to the point-contact transistor and then to the bipolar junction transistor.the first transistors used germanium as the semi-conductor of choice because it was possible to obtain high purity meterial. since then, the technology has progressed rapidly. transistors are the main components of microprocessors. microprocessors are essential to many of the products we use everyday such as TVs , car radios, home appliance and of course, computers . the common graphic cards today contain millions of transistors on a single board 

switches 

A switches is an electrical device having two state: on , or closed; and o, or open. ideally a switch offers a zero impedance to a current when it is closed, and it offers infinite impedance when mechanical switches, which operate by moving contains together  and apart, are often classified by the number of connections they can make or break at once and the number of closed positions in which they can be placed. there are many types of mechanical switches. they are knobs. toggle, push buttons, DIP, rocker, and rotary. these are the general idea but not limited to these. A switch can be done at the electronic level also but those generally go along the lines of integrated circuits themselves.

Connectors 

Let us provide the connectors you're looking foe. whether you need a hard-to-find PCB  connector or a specialized fiber optic connector, here is a list of the most popular kinds of connectors, including :

PCB connectors.

BNC connectors.

fiber optic connectors. tyco connectors. and more.

not sure which one you need ? lets take a look at the different types of connectors available :

Wire and fiber optic connectors most often join transmission media to equipment or cross connects. A fiber optic connector is thin, lightweight and flexible. printed circuit boards that perform separated functions need a PCB  connector to be joined together. BNC  connectors are common among networking hardware. they are commonly used for coaxial  cables,although there are many different types connectors that are employed by coaxial cable polarized headers  are idea for power supply and programmer connectors. they make good contacts and connectors are the mainstay of telecommunications. A standard phone line uses modular type connectors,as do LAN  cable.

Fuse

A fuse is a safety device used to protect an electronic circuit against an excessive current. A fuse consists essentially of a strip of low-melting alloy enclosed in suitable housing. it is connected in series with the circuit it is to protect. because of its electrical resistance, the alloy strip in the fuse in heated by an electri current; if the current exceeds the safe value for which the fuse was designed, the strip melts, opening the circuit and stopping the current. the fuse housing is designed to resist the pressure generated if the over-current vaporizs the alloy carry a small overload for a short time without opening the  circuit, while others are designed to open very rapidly if the rated current is exceeded. the choice of one type or the other depends on the ruggedness of the equipment to be protected and whether large pulses of current often occur in the circuit. A slow-blow fuse is usually used to protect motors, and a fast-blow fuse to protect electronic equipment.

Crystal 

A crystal is an electronic device that uses the mechanical resonance of a physical crystal of piezoelectric material to create an electrical signal with a very precise frequency. it is an especially accurate form of an electronic oscillator. the crystal is usually made of quartz wrist watches, to provide a stable clock for digital circuits, and to stabilize frequencies for radio transmitters. crystal oscillators are the most common source of time and frequency signals. the crystal is sometimes called a timing crystal they can be embedded in integrated circuits.

A regular timing crystal contains two electric plates , with a crystal sandwiched between them. the circuitry around the crystal then applies an AC signal to it, and the crystal will start oscillating in this frequency. however, because lets assume in this situation that this is so the natural frequency of the crystal is different than the applied frequency, it won't get a large amplitude. this is because when the crystal is pushed forward and the crystals natural frequency makes it go back at the same moment, the forces are working in opposite directions and we're not getting anywhere. this is called a forced frequency or resonance.

When the external logic notices this , it can adjust its frequency when the frequency gets closer to the natural frequency is suddenly almost no resistance at all , and that the current frequency is very close to the natural frequency of the crystal. this is usually done by micro controllers , which can be optimized for system on chip-like situations of the use of crystals, the generated clock can be extremely accurate, making it useful for timing systems at high speed. more than two billion quartz oscillators are manufactured annually. most are small devices built for wrist watches, clocks, and electronic circuits. however, quartz oscillators are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

A  quartz crystal inside the oscillator is the resonator. it could be made of either natural or synthetic quartz, but all modern devices use synthetic quartz. the crystal strains when an electrical voltage is applied . when the voltage is reversed, the train is reversed. this is known as the piezoelectric effect.

Oscillation is sustained by taking a voltage signal from the resonator, amplifying it, and feeding it back to the resonator. the rate of expansion and contraction is the resonance frequency, and is determined by the cut size of the crystal. many crystals are often represented in letters such as XO,TCXO,XTA,VCO  and so on.

Hardware components and ICs 

The microprocessor and other LSIs  together cannot build a complete PC . in addition to these, we also need a good number of ICs of SSI  and MSI  . A discussion of these IC s is the primary objective of this chapter. As a preparation for the reader a review of the relevant concepts of digital electronics and integrated circuits is presented. it is impossible to cover all the aspects in details, the objective is to present essential topics in simple terms.

Hardware components: discrete and integrated 

The different components used in the figure 4.1 . the integrated circuit chip is single package  consist of more than one component of the same or different types forming a circuit. in short , IC  means a circuit fabricated on a piece of semiconductor material. there are variety of IC chips each one offering a different function such as AND,OR,INVERT,NAND,NOR etc. ICs offering such basic functions are know as  GATES  or LOGIC GATES

A gate is difined as a logic circuit with one or more input lines but only one output line. A signal IC may also contain multiple gates of the same type. An IC may contain a complex circuit formed by gates.
classification of IC's are classified into SSI, MSI,LSL and VLSI according to the relative number of basic gates necessary to build a circuit to achive the same logic function . table 4.2 defines the SSI,MSI , and  LSI  types with sample functions achived at these levels.

Pulse circuits and wave forms

The main functions of pulse circuits are as follows:

1. Generation of pulse waveforms
2. Amplification of pulse waveforms
3. Shaping of pulse waveforms
4. Storage of digital information
5. Switching
6. Gating

Positive and negative logic 

The terms positive and negative logic specify the way logic 1 and logic 0 are defined . in a positive logic, the higher level is denoted as logic 1 and the lower level as logic 0. in negative logic, the higher level is denoted as logic 0 and the lower level as logic 1. negative logic is very rarely followed in pc , it is used only in the RS232c communication interface. 

Special gates

There are some gates which do not perform any logic function. they are used merely for one of the following special functions:

• Wave shaping.
• increasing signal driving capacity.
• Removing noise on a singnal
• Shifting signal levels.
• Interfacing between different IC  families.
• Isolating an IC from its loads.
• Establishing bi-directional communication.
• Forming bus.

These IC's are called by different names, such as BUFFERS, DRIVERS, LEVEL CONVERTER, LINE DIVERS, SCHMITT TRIGGERS etc. depending on the applications.

IC Families 

Several types of IC's have been developed over the year. popular IC  families are listed below:

• Resistor-transistor logic (RTL)
• Diode-transistor logic (DTL)
• Transistor-transistor logic (TTL)
• Emitter-coupled logic (ECL) 
• High - threshold logic (HTL).
• Metal oxide semiconductor logic(MOS).
• Complementary metal oxide semiconductor logic (CMOS)
• Integrated injection logic(HL)

These IC  families differ in their characteristics 

• Speed.
• Power dissipation.
• Cost.
• Operating temperature ranges.
• Noise margins(noise immunity)
• Packaging density 
• Loading and driving limits 
• Ease of interfacing 
• Operating supply voltage.
• Ease of handling.

MOS Families 

MOS IC s are popular because of three reasons:

• Low power dissipation.
• Large functions in very little chip area.
• Good noise immunity.

Generally MOS  logic ICs are LSIs such as microprocessors, 1/0 controllers, memories, shift register and ALUs. however even SSIs and MSIs are available as MOS ICs to limited extent. the popular MOS  logic families are PMOS, NOMS, CMOS, SMOS, HMOS ,VMOS and SOSMOS.

The  MOS ICs in the IBM PC and clones are limited thought the functions performed by these IC s are very significant and varied. some of the MOS ICs used in a PC are listed below.

• 8259 A Programmable interrupt controller (PIC)
• 8253 A Programmable interval timer (PIT)
• 8255 A-5 programmable Peripheral Interface (PPI) 
• 8237 A-5 Programmable DMA controller.
• MC 6845 CRT Controller.

To identify and IC by visual inspection the type number is printed on the top of the IC . in addition the following information is also printed on the IC  top.

• company name
• year of manufacture.
• week of manufactutre .

This section provides an overview of how computers inside . it identifies some of the major hardware  components of a computers system and  describes how they interact.

 A computer is a machine that performs calculations . most task that a computer performs therefore roughly follow these steps:

• Accept input data .
• Perform calculations on the input data .
• Output the result finish.

You maycompare the operation of a computer to that . of manufacturing factory . initially, the factory recieves the raw materials- the input data it will use to build the product . in the process, it will probably need to temporarily store either the raw materials or some intermediate products in its warehouse, where they can await further processing. when the produce is finished it is shipped - the result is output.

The von neumann model of the PC  

Computers have their roots 300 years back in history . mathematicians and philosophers like pascal, leibnitz, babbage and boole made the foundation with their theoretical works . only in the second half of this century was electronic science sufficient developed to make practical use of their theories.

The modern PC  has roots that go back to  the USA in the 1940s . among the many scientists, we like to remember john von neumann he was a mathematician, born in hungary. we can still use his computer design today. he broke computer hardware down in five primary parts:

1. CPU.
2. input
3. output
4. working memory
5. permanent memory

actually , von neumann was the first to design a computer with a working memory apply his mode to current PC s it will look like this:

inside a computer a very similar process take place. the computer  recieves input data - either directly from the user or by retrieving data that has previously been stored at some place- and build this input data into new data by performing certain calculations on it. depending on the complexity of the calculations involved , it may be necessary to temporarily stored some intermediate result in the computers memory the exact nature of the calculations, of course, depends the task at hand - in other words, on the software currently telling the computer what to do.





components in the central unity- the computer
                         
               the motherboard :CPU  , Ram, Cache,
               ROM chips with BIOS and star-up programs.
               Chip set (controllers) . ports, buses and expansion slots.
               Drives:Hard disk , floppy drives, DVD-CD , etc
                Expansion cards: graphics card (video adapter),
                network controller, SCSI controller.
                Sound card, video and TV  card.
                 Internal modem and ISDN card.

peripheral -Keyboard , and mouse , joystick, monitor,printer,scanner,Loudspeakers,External drives,External tape station External modem,
we subdevided the hardware of computer into the following components .
input-unit- you can think of this as the recieving section of the computer.
output-unit-this is the rapid access, relatively low-capacity warehouse section of the computer. intermediate parts of the product may be stored here temporarily
central processing unit (CPU) -this is the manufacturing section of the computer where the actual product is made.
Arithmetic and logic unit (AU)-this part of CPU the machinery used to carry of the manufacturing process .
secondary storage unit-this is the long-term high-capacity warehousing section of the computer. lets look at some of these components in more detail.

CPU

The central process unit is a microprocessor chip that is central to the entire computer. the CPU  performs the actual computations and in addition it controls all other hardware components for this reason it is often reffered to as the brain of the computer. central processing unit is a microprocessor chip that is central to the entire computer. the CPU  performs the actual computations and in addition it controls all other hardware components. for this reason it is often reffered to as the brain of the computer.

since the CPU  is incharge of the computer, software (also called a computer program) contains instructions that tell the CPU  what to do . these instructions come in a format called machine code and are contained in binary files . ( for example on a PC, programs can be recognized from their EXE  file extension).

some common  CPU  families that are used in different computers today include:

• Pentium I,II,III, and IV (used in PCs)
• AMD (used in PCs : a cheaper altranative to the pentium) 
• sparce  used in professional workstation and servers 

Each of these CPU families has its own machine code . CPU  s from one families are in general unable to understand machine code for any of the other families. (that is the reason  that you cannot , for example, use  PC  software on a Mac). 

with respect to processing power can perform and is expressed in hertz  1 hz equals one elementary operation per second. recent  CPU  have clock speeds as high as 2 GHz (=2*10 to the power 2 Hz);  in other words , such  CPU  s can  perform as many as two billion operations a signal second. even though the CPU , speed is an important factor of the overall speed of the computer after all , it determines the speed at which its a brain can handle operations it is common misconception that it is the only factor.

Some Advance Tips 

If you like this article so please share this post , and if you know to interest about RAM, ROM, and PC so visit my site : https://www.digitaltech.net.in