COMPUTER HARDWARE

CMP 206

COURSE OUTLINE
Computer Circuits; Diode Arrays, PLAs etc.
Integrated Circuits Fabrication Processes.
Use of MSI, LSI and VLSI IC Hardware Design.
Primary and Secondary Memories; Core Memory etc.
Magnetic Devices; Disks, Tapes, Video Disks etc.
Peripheral Devices; Printers, CRTs, Keyboards, Character Recognition.
Operational Amplifiers; AD and DA Converters.
Analog Computers.

SECTION 1
Introduction
A computer is a programmable machine designed to perform arithmetic and logical operations
automatically and sequentially on the input given by the user and gives the desired output after
processing. Computer components are divided into two major categories namely hardware and
software.
Hardware is the machine itself and its connects devices such as monitor, keyboard, mouse etc.
Software are the set of programs that make use of hardware for performing various functions.
1.1 Features of a Computer System:
A computer system is made up of many components which collectively make it possible to work
efficiently and effectively. The working of a computer is characterised by the following features:

Figure 2: Features of a Computer System

i. Speed: The processing speed of a computer is very high; it can perform millions of instructions
in a fraction of a second. The work that used to take several days to be completed by humans can
now be done in a few minutes with the help of computers. They can handle large quantity of data
simultaneously for multiple processing. Different types of computers work at different speed
(depending upon their hardware capability) ranging from high to very high. The speed of
computer is calculated in Million Instructions per Second (MIPS) or Million Floating Point
Operations Per Second (MFLOPS). The processing speed of computers is measured MHz which
is in micro second (10-6 part of second) or Nano second (10 -9 part of second) and Pico second (10 -
12
part of second).
ii. Accuracy: Computers work at a very high level of accuracy and correctness. The chances of a
computer giving wrong results are least and very rare. They work on GIGO principle
i.e. Garbage In Garbage Out. The errors in output may be the results of human errors in
providing inaccurate input, wrong instructions, user negligence and poor design of hardware and
software. If the programs are not correct, then the results may give errors. Errors are seldom
attributed to the computers.

iii. Storage: Computers have large storage capacity and can store large quantity of data and
instructions. This large capacity of computers is attributed to secondary storage devices like
compact disk, DVDs, hard disk etc. Information on secondary storage can be stored for a number
of years and can be retrieved any time. The storage capacity can be measured in kilobytes,
megabytes, gigabytes and terabytes (KB, MB, GB, TB).

iv. Versatility: Computers are versatile machines and can be used in different kinds of
applications simultaneously. The same computer can be used for scientific, mathematical,
financial, managerial and other types of functions. The various applications depend on the
programs uploaded in the memory of computer. User can use computer to type a document, send
an email, prepare pay slips, maintain accounts, play music or print a document.

v. Automation: Computer is an automatic machine. Once a task is assigned to it, it may execute
the operations without any intervention from the user.

vi. Diligence: A computer doesn’t have human traits like tiredness, lack of concentration, fatigue
etc. They can handle millions of transactions with the same speed and zeal without fatigue or
lethargy. They can continue to work repeatedly with same speed and accurately for hours and
days without getting tired. Due to this ability computer has now replaced human beings in
tedious, routine and repetitive jobs.

vii. Reliability: Reliability in computers comes naturally as a result of accuracy. A computer is

capable of giving standardised results every time without failure. Computers have built in
problem solving and diagnostic capabilities, which help in continuous checking of the system.

viii. Convenience: Now a days, carrying a computer is very convenient. They are available in
pocket size also. Mobiles are the best examples of convenient computing device.

ix. Resource Sharing: In the initial stages of computer evolution, they used to be lonely
machines. With the tremendous growth of technology, today computers are no longer isolated
machines they can now be connected with each other using wires and internet. This advancement
has made sharing of resources possible between computers. Now two or more computers can be
connected to a single printer. Data and information sharing can be made possible among
computers, thereby creating a large information and knowledge base.

1.2 CHARACTERISTICS OF COMPUTERS

The characteristics of computers that have made them so powerful and universally useful are
speed, accuracy, diligence, versatility and storage capacity. Let us discuss them briefly.
Speed: Computers work at an incredible speed. A powerful computer is capable of performing
about 3-4 million simple instructions per second.

Accuracy In addition to being fast, computers are also accurate. Errors that may occur can
almost always be attributed to human error (inaccurate data, poorly designed system or faulty
instructions/programs written by the programmer)

Diligence Unlike human beings, computers are highly consistent. They do not suffer from
human traits of boredom and tiredness resulting in lack of concentration. Computers, therefore,
are better than human beings in performing voluminous and repetitive jobs.

Versatility Computers are versatile machines and are capable of performing any task as long as
it can be broken down into a series of logical steps. The presence of computers can be seen in
almost every sphere – Railway/Air reservation, Banks, Hotels, Weather forecasting and many
more.

Storage Capacity Today’s computers can store large volumes of data. A piece of information
once recorded (or stored) in the computer, can never be forgotten and can be retrieved almost
instantaneously.

SECTION 2
COMPUTER ARCHITECTURE
A computer system consists of mainly four basic units; namely input unit, storage unit, central
processing unit and output unit. Central Processing unit further includes Arithmetic logic unit
and control unit,
A computer performs five major operations or functions irrespective of its size and make.
These are:

 it accepts data or instructions as input,

 it stores data and instruction

 it processes data as per the instructions,

 it controls all operations inside a computer, and

 it gives results in the form of output.

4.1 Functional Units:

a. Input Unit: This unit is used for entering data and programs into the computer system by
the user for processing
b. Storage Unit: The storage unit is used for storing data and instructions before and after
processing.

c. Output Unit: The output unit is used for storing the result as output produced by the
computer after processing.

d. Processing: The task of performing operations like arithmetic and logical operations is
called processing.
The Central Processing Unit (CPU) takes data and instructions from the storage unit and
makes all sorts of calculations based on the instructions given and the type of data provided. It is
then sent back to the storage unit. CPU includes Arithmetic logic unit (ALU) and control unit
(CU)
 Arithmetic Logic Unit: All calculations and comparisons, based on the instructions
provided, are carried out within the ALU. It performs arithmetic functions like
addition, subtraction, multiplication, division and also logical operations like greater than,
less than and equal to etc.
 Control unit: Controlling of all operations like input, processing and output are performed
by control unit. It takes care of step by step processing of all operations inside the
computer.

SECTION 3
Computer Memory
Memory is major part of computers that is categorized into several types. Memory is best storage
part to the computer users to save information, programs and etc, The computer memory offer
several kinds of storage media some of them can store data temporarily and some stores data
permanently. Memory consists of instructions and the data saved into computer through Central
Processing Unit (CPU).

3.1 Types of Computer Memory:

Memory is the best essential element of a computer because computer can’t perform simple tasks
without Memory. The performance of computer mainly based on memory and CPU.

Memory is internal storage media of computer that has and majorly categorized into two types,
namely: Primary memory and Secondary memory.

1. Primary Memory / Volatile Memory.

2. Secondary Memory / Non Volatile Memory.

1. Primary Memory / Volatile Memory:

The primary storage is referred to as random access memory (RAM) due to the random selection
of memory locations. It performs both read and write operations on memory. If power failures
happened in systems during memory access then you will lose your data permanently. So, RAM
is volatile memory. RAM categorized into following types.

 DRAM
 SRAM
  DRDRAM

Primary Memory can be further classified as RAM and ROM.

 RAM or Random Access Memory is the unit in a computer system. It is the place in a
computer where the operating system, application programs and the data in current use
are kept temporarily so that they can be accessed by the computer’s processor. It is
said to be ‘volatile’ since its contents are accessible only as long as the computer is on.
The contents of RAM are no more available once the computer is turned off.
 ROM or Read Only Memory is a special type of memory which can only be read and
contents of which are not lost even when the computer is switched off. It typically
contains manufacturer’s instructions. Among other things, ROM also stores an initial
program called the ‘bootstrap loader’ whose function is to start the operation of computer
system once the power is turned on.

2. Secondary Memory / Non Volatile Memory:

Secondary memory is external and permanent memory that is useful to store the external storage
media such as floppy disk, magnetic disks, magnetic tapes and etc cache devices. Secondary
memory deals with following types of components.

Read Only Memory (ROM):

ROM is permanent memory location that offer huge types of standards to save data. But it work
with read only operation. No data lose happen whenever power failure occur during the ROM
memory work in computers.

Secondary storage devices are of two types; magnetic and optical.

Magnetic devices include hard disks and optical storage devices are CDs, DVDs, Pen drive, Zip
drive etc

3.2 Magnetic Disk (Hard Disk Drive)

Hard disks are made up of rigid material and are usually a stack of metal disks sealed in a box.
The hard disk and the hard disk drive exist together as a unit and is a permanent part of
the computer where data and programs are saved. These disks have storage capacities ranging
from 1GB to 80 GB and more. Hard disks are rewritable.
3.3 Optical Disk

Compact Disk (CD) is portable disk having data storage capacity between 650-700 MB. It can
hold large amount of information such as music, full-motion videos, and text etc. CDs can be
either read only or read write type.
Digital Video Disk (DVD) is similar to a CD but has larger storage capacity and enormous
clarity. Depending upon the disk type it can store several Gigabytes of data. DVDs are primarily
used to store music or movies and can be played back on your television or the computer too.
These are not rewritable.
ROM memory has several models such names are following.

1. PROM: Programmable Read Only Memory (PROM) maintains large storage media but can’t
offer the erase features in ROM. This type of ROM maintains PROM chips to write data once
and read many. The programs or instructions designed in PROM can’t be erased by other
programs.
2. EPROM : Erasable Programmable Read Only Memory designed to recover the problems of
PROM and ROM. Users can delete the data of EPROM thorough pass on ultraviolet light and it
erases programs and reprograms.
3. EEPROM: Electrically Erasable Programmable Read Only Memory similar to the EPROM
but it uses electrical beam to erase the data of ROM.

SECTION 4

CACHE MEMORY
Cache memory, also called CPU memory, is Random Access Memory (RAM) that a
computer microprocessor can access more quickly than it can access regular RAM. This
memory is typically integrated directly with the CPU chip or placed on a separate chip that has a
separate bus interconnect with the CPU.

The basic purpose of Cache Memory is to store program instructions that are frequently re-
referenced by software during operation. Fast access to these instructions increases the overall
speed of the software program.
As the microprocessor processes data, it looks first in the cache memory; if it finds the
instructions there (from a previous reading of data), it does not have to do a more time-
consuming reading of data from larger memory or other data storage devices.

SECTION 5
MAGNETIC-CORE MEMORY: This was the predominant form of Random-
Access Computer Memory for 20 years between about 1955 and 1975. Such memory is often
just called Core Memory, or, informally, Core.
Core uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and
read information. Each core represents one bit of information. The cores can be magnetized in
two different ways (Clockwise or Counterclockwise) and the bit stored in a core is zero or one
depending on that core's magnetization direction. The wires are arranged to allow an individual
core to be set to either a one or a zero and for its magnetization to be changed by sending
appropriate electric current pulses through selected wires. The process of reading the core causes
the core to be reset to a zero, thus erasing it. This is called destructive readout. When not being
read or written, the cores maintain the last value they had, even when power is turned off. This
makes them nonvolatile.

SECTION 6
PERIPHERAL DEVICES
A peripheral device is an internal or external device that connects directly to a computer but does
not contribute to the computer's primary function, such as computing. It helps end users access
and use the functionalities of a computer.
A peripheral device provides input/output (I/O) functions for a computer and serves as an
auxiliary computer device without computing-intensive functionality. Peripheral devices connect
with a computer through several I/O interfaces, such as communications (COM), Universal
Serial Bus (USB) and serial ports.
Peripheral devices include the following:

 Mouse
 Keyboard
 Printer
 Webcam
 Scanner
 External drives
 Graphics cards
 CD-ROM

A peripheral device may be classified as an internal or external peripheral device.

SECTION 7
VARIOUS COMPONENTS OF COMPUTER SYSTEM

The system unit is made up of various components which are listed below:

 Motherboard
 Microprocessor or Central Processing Unit (CPU)
 Memory (RAM and ROM)
 Power supply unit
 Disk drives
 Expansion Card

7.1 The Motherboard

The motherboard holds the microprocessor, memory chips (RAM and ROM), expansion slots,
power connectors and any other microchips required for the PC to function. It is the panel
through which other components on/in the computer system are directly connected to; it
determines the computational power of the computer. It was formally categorized based on
Pentium (PI, PII, PIII, PIV, PM) and later based on cores (Dual Cores, Core 2, Core i3, i5, i7).
Typical Motherboard

7.2 The Microprocessor

The microprocessor can be referred to as the brain of the computer. The microprocessor is also
known as the CPU (Central Processing Unit). The microprocessor does the following:

 Carries out commands to make the hardware components perform their task.
 Processes data. This involves:

- Performing logical instructions such as comparing

- Performing mathematical instructions such as adding and subtracting

Although the instructions performed by the CPU are relatively simple, the CPU can execute
many millions of instructions every second. This is what makes the PC such a powerful tool.

7.3 Power Supply

The power supply is responsible for converting the incoming electricity supply to the 5v and 12v
DC power that is required by the PC for it’s operation. The 5v supply is used to power the circuit
boards on the PC. The 12v supply is used to power motor-driven devices such as hard drives or
CD-ROMs. Many newer systems also require 3.3v or 2.8v, as current processors tend to use
lower voltages. Devices such as CD-ROMs and floppy drives are connected to the power supply
using molex or mini molex connectors. The motherboard connectors are known as P8 and P9.

7.4 Hard Disk Drives (HDD)

If data held in RAM is to be kept permanently, it should be saved to a Hard Disk Drive. HDD
are the storage area of a PC. A disk drive can be divided into logical areas called directories (or
folders). These directories are used to hold the files that
contain ones data.
The data is recorded as magnetic fields on the surface of the
disk. These fields are written in concentric circles (known as
tracks) as the disk turns. These tracks are divided into equal-
sized blocks called sectors. Each track and sector has a
number that is used to remember where each piece of data is.

7.5 The 3½" Floppy Disk

The floppy disk represent one of the most common data storage devices. Each side of a high-
density 3½" disk is divided into 80 concentric tracks, with each track divided into 18 equal
sectors. Each sector is used to store 512 bytes, or 0.5KB of information. Data is transferred from
the disk into the PC's memory (or from memory to disk) one sector at a time. The total capacity
of this disk is, therefore:
80 tracks x 18 sectors x 0.5 kilobytes x 2 sides = 1,440KB or
1.44MB.
The 3½" floppy disk drive is often described as a 1.44MB drive.
Floppy disks do not have a sealed covering like a hard disk (see below) and are not as strong.
They must be treated carefully, which means keeping them away from dust, magnetic fields and
high temperatures. The main advantage of floppy disks is that they are portable and can be used
for transferring data between PCs, and for storage of data away from the PC itself.

7.5 Monitors
There is a wide choice of monitors available for the PC, varying both in screen size and
technology. In general, monitors range in size from 14" to 21" and use Cathode Ray Tube
(CRT) or Liquid Crystal Display (LCD) technology. The most important factor in selecting a
monitor is to ensure it is compatible with the display adapter and that it will support its
maximum resolution. Other points to examine are the dot pitch and refresh rate of the screen. A
smaller dot pitch gives greater clarity. Monitors with refresh rates lower than 75Hz may flicker
causing headaches and eyestrain.

7.6 Keyboard
The keyboard is the main input device of the PC. It is used for giving commands to the PC or
typing documents. Although a computer keyboard is based on the old typewriter layout, there are
some major differences in the ways that keys are used. Computer keyboards also have additional
keys. Learning to use the unique keys and special functions of
the computer keyboard can save you time and make you more
comfortable with your computer. The keyboard is like a
typewriter but with special keys. You use these keys of
combinations of them for special functions. Below you can find
some of the most common ‘special’ commands of a keyboard:

7.7 Mouse

There are many, many things for the novice to learn so that they are
able to navigate Windows. The first thing that you should learn to do
is how to use the mouse to navigate Windows. The mouse is another
equally important input device, like the keyboard, very simple to use.
It is extremely useful for navigation in software environments and can
save much time and effort comparing to the keyboard for similar use.
Your mouse gives you the ability to point to, select, and move items
on the computer screen.

7.8 Modem
A modem is a device that translates the digital signals from your computer into analog signals
that can travel over a standard phone line. A modem on the other end of the line can understand
it and converts the sounds back into digital information. It is
the device that will connect you to the internet or allow you
to communicate with a friend. Modems come in different
speeds and are measured in bps or bits per second. A 28.8
Kbps modem transmits data at speeds up to 28,800 bits per
second. A 56 Kbps modem is twice as fast, sending and
receiving data at a rate of up to 56,000 bits per second. Most
modems today are 56 Kbps. In case modems come with your
PC as external devices they look like the device above. The other alternative is to have the
modem mounted on the motherboard so it appears as internal device of the computer.

SECTION 8

8.1 Computer Circuits

Most computer processors are fabricated from a few simple component circuits which have been
designed in such a manner as to make it easy for a designer to connect the outputs of one circuit
to the inputs of another circuit. This allows complex circuits to be built from simple components
in a sort of building blocks fashion.

The TTL (Transistor Transistor Logic) circuit family is one such circuit family. TTL circuits use
two voltage levels, 0 volts and +5 volts to represent the two binary digits 0 and 1 respectively.
This circuit family also has the property that, within certain reasonable limits, it is possible to
wire the outputs of one TTL circuit to the inputs of another TTL circuit and not have to be
concerned with such electrical engineering issues of voltage levels and current flows in the
circuit. Recently, circuit families with voltages lower than 5 volts have become widely used in
new designs.

Basic Logic Circuits

We introduce a digital circuit symbol notation for each of the basic circuit elements we wish to
use.
The first of these is the or circuit. The logic interpretation of the verb or is the same as its use in
ordinary language. For example, consider the compound sentence: The sky is blue or it is raining
outside. This sentence is true if one or the other or both of the sentences, The sky is blue., It is
raining outside. are true.
or | 0 | 1
---+---+---
0|0|1
---+---+---
1|1|1
That is, the conjunction or is 1 when one or the other or both are 1. The circuit symbol for or is:

The second of these is the and circuit. The logic interpretation of the verb and is the same as its
use in ordinary language. For example, consider the compound sentence: The sky is blue and it is
raining outside. This sentence is true when and only when both of the sentences, The sky is
blue. , It is raining outside. are true.

and| 0 | 1
---+---+---
0|0|0
---+---+---
1|0|1
That is, the conjunction and is 1 when and only when both inputs are 1. The circuit symbol for
and is:

The third is the not circuit. The logic interpretation of not is the same as its use in ordinary
language. That is, the sentence It is not raining outside. is false if it is raining outside.

not| 0 | 1
---+---+---
|1|0
That is, the not of 1 is 0 and not 0 is 1. The circuit symbol for not is:

Two other useful circuit elements are nand (not and) and nor (not or). The function table for
nand is:

nand| 0 | 1
----+---+---
0|1|1
----+---+---
1|1|0
The circuit symbol for nand is :
The function table for the circuit nor is:

nor| 0 | 1
---+---+---
0|1|0
---+---+---
1|0|0
The circuit symbol for nor is :

8.1 XOR

This function is known by another name, exclusive or. Exclusive or is 1 when one or the other
but not both arguments are 1. Otherwise the result is 0.

Exclusive or function table:

xor | 0 | 1
---+---+---
0|0|1
---+---+---
1|1|0
Following is the circuit symbol for exclusive or:

We model the exclusive or circuit with the definition:

bitXor =: bitHalfAdder

8.2 Half Adder and Full Adder with Truth Table

An adder is a digital logic circuit in electronics that implements addition of numbers. In many
computers and other types of processors, adders are used to calculate addresses, similar
operations and table indices in the ALU and also in other parts of the processors. These can be
built for many numerical representations like excess-3 or binary coded decimal. Adders are
classified into two types: half adder and full adder. The half adder circuit has two inputs: A and
B, which add two input digits and generate a carry and sum. The full adder circuit has three
inputs: A, B and Cin, which add the three input numbers and generate a carry and sum. This
article gives brief information about half adder and full adder in tabular forms and circuit
diagrams.

Half Adder and Full Adder

8.2.1 Half Adder and Full Adder Circuit

An adder is a digital circuit that performs addition of numbers. The half adder adds two binary
digits called as augend and addend and produces two outputs as sum and carry; XOR is applied
to both inputs to produce sum and AND gate is applied to both inputs to produce carry. The full
adder adds 3 one bit numbers, where two can be referred to as operands and one can be referred
to as bit carried in. And produces 2-bit output, and these can be referred to as output carry and
sum.

8.3 Half Adder

By using half adder, you can design simple addition with the help of logic gates.

Let’s see an addition of single bits.

Half Adder
0+0 = 0
0+1 = 1
1+0 = 1
1+1 = 10

These are the least possible single-bit combinations. But the result for 1+1 is 10, the sum result
must be re-written as a 2-bit output. Thus, the equations can be written as
0+0 = 00
0+1 = 01
1+0 = 01
1+1 = 10

The output ‘1’of ‘10’ is carry-out. ‘SUM’ is the normal output and ‘CARRY’ is the carry-out.

Half Adder Truth Table

Half Adder Truth Table

X

Now it has been cleared that 1-bit adder can be easily implemented with the help of the XOR
Gate for the output ‘SUM’ and an AND Gate for the ‘Carry’. When we need to add, two 8-bit
bytes together, we can be done with the help of a full-adder logic. The half-adder is useful when
you want to add one binary digit quantities. A way to develop a two-binary digit adders would be
to make a truth table and reduce it. When you want to make a three binary digit adder, do it
again. When you decide to make a four digit adder, do it again. The circuits would be fast, but
development time is slow.
 Half Adder Logic Circuit
The simplest expression uses the exclusive OR function: Sum=AÅB. An equivalent expression
in terms of the basic AND, OR, and NOT is: SUM=A|.B+A.B’

8.4 Full Adder

This adder is difficult to implement than a half-adder. The difference between a half-adder and a
full-adder is that the full-adder has three inputs and two outputs, whereas half adder has only two
inputs and two outputs. The first two inputs are A and B and the third input is an input carry as
C-IN. When a full-adder logic is designed, you string eight of them together to create a byte-
wide adder and cascade the carry bit from one adder to the next.

Full Adder
The output carry is designated as C-OUT and the normal output is designated as S.

Full Adder Truth Table:

Full Adder Truth Table
With the truth-table, the full adder logic can be implemented. You can see that the output S is an
XOR between the input A and the half-adder, SUM output with B and C-IN inputs. We take C-
OUT will only be true if any of the two inputs out of the three are HIGH.

So, we can implement a full adder circuit with the help of two half adder circuits. At first, half
adder will be used to add A and B to produce a partial Sum and a second half adder logic can be
used to add C-IN to the Sum produced by the first half adder to get the final S output.

Full Adder Logic Circuit

If any of the half adder logic produces a carry, there will be an output carry. So, COUT will be
an OR function of the half-adder Carry outputs. Take a look at the implementation of the full
adder circuit shown below.

The implementation of larger logic diagrams is possible with the above full adder logic a simpler
symbol is mostly used to represent the operation. Given below is a simpler schematic
representation of a one-bit full adder.
Full Adder Design Using Half Adders
With this type of symbol, we can add two bits together, taking a carry from the next lower ord er
of magnitude, and sending a carry to the next higher order of magnitude. In a computer, for a
multi-bit operation, each bit must be represented by a full adder and must be added
simultaneously. Thus, to add two 8-bit numbers, you will need 8 full adders which can be formed
by cascading two of the 4-bit blocks.

8.5 Combinational Logic Circuit

Combinational circuit combines the different gates in the circuit for example encoder,
decoder, multiplexer and demultiplexer.
Characteristics of combinational circuits are as follows
 The output at any instant of time, depends only on the levels present at input terminals.
 It does not use any memory. The previous state of input does not have any effect on the
present state of the circuit.
 It can have a number of inputs and m number of outputs.
The relationship between the Full-Adder and the Half-Adder is half adder produces results and
full adder uses half adder to produce some other result. Similarly, while the Full-Adder is of two
Half-Adders, the Full-Adder is the actual block that we use to create the arithmetic circuits.

SECTION 9
DIODE ARRAYS INFORMATION
Diode: is a semiconductor device with two terminals, typically allowing the flow of current in
one direction only. Or A thermionic valve having two electrodes (an anode and a cathode).

Diode arrays are composed of multiple discrete (usually unconnected) diodes on a single silicon
chip. Diode arrays are important semiconductor products because they save assembly time and
improve reliability over individually packaged diodes. In general, diode arrays use four or more
diodes in a single package. The most efficient packaging scheme is typically eight diodes or
more in a dual inline package (DIP). Diode arrays have been used for many years in both digital
and linear circuits. Diode arrays are commonly used in such applications as computer and
 peripheral I/O ports, core driver switching, high frequency data lines, interface networks, LAN
and WAN networks, and steering diode applications.

9.1 Why Use Diode Arrays?

Diode arrays, such as a SIP diode array, are a single inline of system in package diode array. The
objective of SIP diode arrays is to merge many electronic requirements of a functional system or
a subsystem into one package. SIP diode arrays typically include chip-level interconnect
technology, such as a flip chip, wire bond, Tape Automated Bonding (TAB) diodes, or other
technology to interconnect directly to an Integrated Circuit (IC) chip. A SMT diode array is a
surface mount diode array that is used to connect passive components to other SMT-compatible
components, such as connectors to SIP substrates.

9.2 What is a Diode Array Detector?

A diode array detector is a detector that absorbs light within UV
or visible wavelength spectrums to perform spectroscopic
scanning and to obtain precise absorbance readings at a variety
of wavelengths. Diode array detectors are commonly used for
chromatography, which is a system for separating and analyzing
complex mixtures. Diode arrays may also use a photo diode array (PDA) detector to measure the
absorbance across a broad spectrum of wavelengths simultaneously. PDAs have some
advantages in that they allow measurement of a single selected wavelength at any point in a
chromatogram. High performance liquid chromatography (HPLC) uses diode array detectors to
detect material nanograms for impurity testing, degradant analysis, excipient characterization,
and analysis of non-chromophore materials.

9.3 CLASSES OF DIODE

 Current Limiting Diodes
Current limiting diodes (CLD) regulate current over a wide voltage range. There are several
types of current limiting diodes (CLD). Examples include a current regulator diode, constant
current diode, and current limit diodes.
 General Purpose Diodes
General-purpose diodes are electric components that conduct electric current in only one
direction, functioning similarly to a one-way valve.
 Gunn and IMPATT Diodes
Gunn diodes or transfer electron devices (TED) exhibit a negative resistance region. They are
used in high-frequency applications, often for building RF oscillators. Impact ionization
avalanche transit-time (IMPATT) diodes are designed to operate at very high frequency and
power. They are used as elements in RF and microwave devices.
 Rectifiers
 Rectifier diodes are designed for use in rectification circuits. Rectifiers are used to convert
AC to DC.
 Schottky Diodes
Schottky diodes in their simplest form consist of a metal layer that contacts a semiconductor
element. The metal / semiconductor junctions exhibit rectifying behavior (i.e., the current
passes through the structure more readily with one polarity than the other).
 Step Recovery Diodes
Step recovery diodes produce an abrupt turn-off (step) time by allowing a very fast release of
stored charge when switching from forward to reverse bias, and from reverse to forward bias.
 Zener Diodes
Zener diodes are PN junction devices that are designed to operate in the reverse-breakdown
region.
SECTION 10
PROGRAMMABLE LOGIC ARRAY (PLAS)
A programmable logic array (PLA) is a kind of programmable logic device used to implement
combinational logic circuits. The PLA has a set of programmable AND gate planes, which link
to a set of programmable OR gate planes, which can then be conditionally complemented to
produce an output

PLA Schematic Example

It has 2^N AND Gates for N input variables and for M outputs from PLA, there should be M OR
Gates, each with programmable inputs from all of the AND gates. This layout allows for a large
number of logic functions to be synthesized in the sum of products canonical forms.
PLAs differ from Programmable Array Logic devices (PALs and GALs) in that both the AND
and OR gate planes are programmable.

10.1 IMPLEMENTATION PROCEDURE OF PLAs

 1. Preparation in SOP (sum of products) form.
2. Obtain the minimum SOP form to reduce the number of product terms to a minimum.
3. Decide the input connection of the AND matrix for generating the required product term.
4. Then decide the input connections of OR matrix to generate the sum terms.
5. Decide the connections of invert matrix.
6. Program the PLA.

PLA block diagram:

2ND 3RD
1ST BLOCK 4TH BLOCK 5TH BLOCK
BLOCK BLOCK

INPUT AND OR INVERT/ NON FLIP FLOP OUTPUT

BUFFER MATRIX MATRIX INVERT MATRIX BUFFER

10.2 Advantages over Read-Only Memory

The desired outputs for each combination of inputs could be programmed into a read-only
memory, with the inputs being loaded onto the address bus and the outputs being read out as
data. However, that would require a separate memory location for every possible combination of
inputs, including combinations that are never supposed to occur, and also duplicating data for
"don't care" conditions (for example, logic like "if input A is 1, then, as far as output X is
concerned, we don't care what input B is": in a ROM this would have to be written out twice,
once for each possible value of B, and as more "don't care" inputs are added, the duplication
grows exponentially); therefore, a programmable logic array can often implement a piece of
logic using fewer transistors than the equivalent in read-only memory. This is particularly
valuable when it is part of a processing chip where transistors are scarce (for example, the
original 6502 chip contained a PLA to direct various operations of the processor

10.3 Applications PLA

One application of a PLA is to implement the control over a datapath. It defines various states in
an instruction set, and produces the next state (by conditional branching). [e.g. if the machine is
in state 2, and will go to state 4 if the instruction contains an immediate field; then the PLA
should define the actions of the control in state 2, will set the next state to be 4 if the instruction
contains an immediate field, and will define the actions of the control in state 4.
Programmable logic arrays should correspond to a state diagram for the system. Other commonly
used programmable logic devices are PAL, CPLD and FPGA.

An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or

a microchip) is a set of electronic circuits on one small flat piece (or "chip")
of semiconductor material, normally silicon.
Integrated circuits were made practical by mid-20th-century technology advancements
in semiconductor device fabrication.

ICs have two main advantages over discrete circuits: cost and performance. Cost is low because
the chips, with all their components, are printed as a unit by photolithography rather than being
constructed one transistor at a time. Furthermore, packaged ICs use much less material than
discrete circuits. Performance is high because the IC's components switch quickly and consume
comparatively little power because of their small size and close proximity. The main
disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This
high initial cost means ICs are only practical when high production volumes are anticipated.

SECTION 11

IC FABRICATION PROCESS STEPS

The fabrication of integrated circuits consists basically of the following process steps:

 Lithography: The process for pattern definition by applying thin uniform layer of
viscous liquid (photo-resist) on the wafer surface. The photo-resist is hardened by baking
and then selectively removed by projection of light through a reticle containing mask
information.
 Etching: Selectively removing unwanted material from the surface of the wafer. The
pattern of the photo-resist is transferred to the wafer by means of etching agents.
 Deposition: Films of the various materials are applied on the wafer. For this purpose
mostly two kinds of processes are used, physical vapor deposition (PVD) and chemical
vapor deposition (CVD).
 Chemical Mechanical Polishing: A planarization technique by applying chemical slurry
with etchant agents to the wafer surface.

 Oxidation: In the oxidation process oxygen (dry oxidation) or H O (wet oxidation)

molecules convert silicon layers on top of the wafer to silicon dioxide.
 Ion Implantation: Most widely used technique to introduce dopant impurities into
semiconductor. The ionized particles are accelerated through an electrical field and
targeted at the semiconductor wafer.
 Diffusion: A diffusion step following ion implantation is used to anneal bombardment-
induced lattice defects.

Models describing the steps used in fabricating ICs have also been incorporated into process
simulators. It is therefore quite possible today to ``build'' new semiconductor structures and
predict their performance using these computer tools. The state of the art in such simulators is
that they are indeed very useful, but cannot completely replace real laboratory experiments,
because the models used in the simulators are not complete in some cases, or are purely
empirical in other cases.

As the models are improved with ongoing research, the simulators will become more robust and
therefore more generally useful. There is great motivation to do this, because real laboratory
experiments are very expensive and very time consuming, especially as chip technology
continuates to advance.

SECTION 12

SSI: The first integrated circuits contained only a few transistors and so were called “Small-
Scale Integration (SSI). They used circuits containing transistors numbering in the tens. They
were very crucial in development of early computers.
MSI: SSI was followed by introduction of the devices which contained hundreds of transistors
on each chip, and so were called “Medium-Scale Integration (MSI). MSI were attractive
economically because which they cost little more systems to be produced using smaller circuit
boards, less assembly work, and a number of other advantages.
LSI: Next development was of Large Scale Integration (LSI)
The development of LSI was driven by economic factors and each chip comprised tens of
thousands of transistors. It was in 1970s, when LSI started getting manufactured in huge
quantities.
VLSI: LSI was followed by Very Large Scale Integration (VLSI) where hundreds of thousands
of transistors were used and still being developed. It was for the first time that a CPU was
fabricated on a single integrated circuit, to create a microprocessor. In 1986, with the
introduction of first one megabit RAM chips, more than one million transistors were integrated.
ULSI: Microprocessor chips produced in 1994 contained more than three million transistors.
ULSI refer to “Ultra-Large Scale Integration” and correspond to more than 1 million of
transistors. However there is no qualitative leap between VLSI and ULSI, hence normally in
technical texts the “VLSI” term cover ULSI
SECTION 13
An operational amplifier (often op-amp or opamp) is a DC-coupled high-gain electronic
voltage amplifier with a differential input and, usually, a single-ended output. In this
configuration, an op-amp produces an output potential (relative to circuit ground) that is typically
hundreds of thousands of times larger than the potential difference between its input terminals.
Operational amplifiers had their origins in analog computers, where they were used to perform
mathematical operations in many linear, non-linear, and frequency-dependent circuits.
The popularity of the op-amp as a building block in analog circuits is due to its versatility. By
using negative feedback, the characteristics of an op-amp circuit, its gain, input and output
impedance, bandwidth etc. are determined by external components and have little dependence on
temperature coefficients or manufacturing variations in the op-amp itself.
Op-amps are among the most widely used electronic devices today, being used in a vast array of
consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in
moderate production volume; however, some integrated or hybrid operational amplifiers with
special performance specifications may cost over US$100 in small quantities. Op-amps may be
packaged as components or used as elements of more complex integrated circuits.
The op-amp is one type of differential amplifier. Other types of differential amplifier include
the fully differential amplifier(similar to the op-amp, but with two outputs), the instrumentation
amplifier (usually built from three op-amps), the isolation amplifier (similar to the
instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an
ordinary op-amp), and negative-feedback amplifier (usually built from one or more op-amps and
a resistive feedback network).

SECTION 14
What are A/D and D/A converters?

D/A Converters

D/A converters convert digital signals into analog format.

Digital Data:
Evenly spaced discontinuous values
Temporally discrete, quantitatively discrete

Analog Data (Natural Phenomena):

Continuous range of values
Temporally continuous, quantitatively continuous

A/D Converters

An A/D converter is a device that converts analog signals (usually voltage) obtained from
environmental (physical) phenomena into digital format

Conversion involves a series of steps, including sampling, quantization, and coding.

A/D and D/A Requirements

Electrically sophisticated and high-speed processing are performed digitally in CPUs and DSPs.

Natural phenomena are converted to digital signals using an A/D converter for digital signal
processing, then converted back to analog signals via a D/A converter.

Advancements in Microfabrication Technology→Signal Processing Digitization

→A/D and D/A Converters Required
A/D Converter Applications

Digital Audio:
Digital audio workstations, sound recording, pulse-code modulation

Digital signal processing:

TV tuner cards, microcontrollers, digital storage oscilloscopes

Scientific instruments:
Digital imaging systems, radar systems, temperature sensors

D/A Converter Applications

Digital Audio：
CD, MD, 1-bit Audio

Digital Video：
DVD, Digital Still Camera

Communication Equipment：
Smartphones, FAX, ADSl equipment

PCs：
Audio, video cards

Measurement instruments：
Programmable power supplies, etc.

Basic Operation of a D/A Converter

A D/A converter takes a precise number (most commonly a fixed-point binary number) and
converts it into a physical quantity (example: voltage or pressure). D/A converters are often used
to convert finite-precision time series data to a continually varying physical signal.

An ideal D/A converter takes abstract numbers from a sequence of impulses that are then
processed by using a form of interpolation to fill in data between impulses. A conventional D/A
converter puts the numbers into a piecewise constant function made up of a sequence of
rectangular functions that is modeled with the zero-order hold.

A D/A converter reconstructs original signals so that its bandwidth meets certain requirements.
With digital sampling comes quantization errors that create low-level noise which gets added to
the reconstructed signal. The minimum analog signal amplitude that can bring about a change in
the digital signal is called the Least Significant Bit (LSB), while the (rounding) error that occurs
between the analog and digital signals is referred to as quantization error.

Basic Operation of an A/D Converter

Now, let's take a look at the basic operation of an A/D converter.

The A/D converter breaks up (samples) the amplitude of the analog signal at discrete intervals,
which are then converted into digital values. The resolution of an analog to digital converter
(indicating the number of discrete values it can produce over a range of analog values) is
typically expressed by the number of bits. In the above case of a 3bit A/D converter, the upper
value (b2) is referred to as the Most Significant Bit (MSB) and the lowest value (b0) the Least
Significant Bit (LSB).

The graph below shows the relationship between the analog input and digital output.

In addition, the first digital change point (000→001) below 0.5LSB is the zero scale, while the
last digital change point (110→111) is termed full scale and the interval from zero to full scale
referred to as the full scale range.
Analog Signal to Digital Signal Conversion Methods

Sampling:
Sampling is the process of taking amplitude values of the continuous analog signal at
discrete time intervals (sampling period Ts).
[Sampling Period Ts = 1/Fs (Sampling Frequency)]
Sampling is performed using a Sample and Hold (S&H) circuit.

Quantization:
Quantization involves assigning a numerical value to each sampled amplitude value from
a range of possible values covering the entire amplitude range (based on the number of
bits).
[Quantization error: Sampled Value - Quantized Value]

Coding:
Once the amplitude values have been quantized they are encoded into binary using an
Encoder.