csc 225 Lecture notes.pdf

WELLSPRING UNIVERSITY BENIN CITY COLLEGE OF SCIENCE AND COMPUTING COURSE CODE: CSC 225 COURSE TITLE: COMPUTER HARDWARE  UNIT 1 Introduction to Computer Hardware A computer is an electronic device, operating under the co...

WELLSPRING UNIVERSITY BENIN CITY COLLEGE OF SCIENCE AND COMPUTING COURSE CODE: CSC 225 COURSE TITLE: COMPUTER HARDWARE  UNIT 1 Introduction to Computer Hardware A computer is an electronic device, operating under the control of instructions stored in its own memory that can accept data (input), process the data according to specified rules, produce information (output), and store the information for future use. Characteristics of a Computer High Speed Computer is a very fast device. It is capable of performing calculation of very large amount of data. The computer has units of speed in microsecond, nanosecond, and even the picosecond. It can perform millions of calculations in a few seconds as compared to man who will spend many months to perform the same task. Accuracy In addition to being very fast, computers are very accurate. The calculations are 100% error free. Computers perform all jobs with 100% accuracy provided that the input is correct. Storage Capability Memory is a very important characteristic of computers. A computer has much more storage capacity than human beings. It can store large amount of data. It can store any type of data such as images, videos, text, audio, etc. Diligence Unlike human beings, a computer is free from monotony, tiredness, and lack of concentration. It can work continuously without any error and boredom. It can perform repeated tasks with the same speed and accuracy. Versatility A computer is a very versatile machine. A computer is very flexible in performing the jobs to be done. This machine can be used to solve the problems related to various fields. At one instance, it may be solving a complex scientific problem and the very next moment it may be playing a card game. 2 Reliability A computer is a reliable machine. Modern electronic components have long lives. Computers are designed to make maintenance easy. Automation Computer is an automatic machine. Automation is the ability to perform a given task automatically. Once the computer receives a program i.e., the program is stored in the computer memory, then the program and instruction can control the program execution without human interaction. Reduction in Paper Work and Cost The use of computers for data processing in an organization leads to reduction in paper work and results in speeding up the process. As data in electronic files can be retrieved as and when required, the problem of maintenance of large number of paper files gets reduced. Though the initial investment for installing a computer is high, it substantially reduces the cost of each of its transaction. FUNCTIONALITIES OF A COMPUTER Step 1 − Takes data as input. Step 2 − Stores the data/instructions in its memory and uses them as required. Step 3 − Processes the data and converts it into useful information. Step 4 − Generates the output. Step 5 − Controls all the above four steps. Applications of Computers A computer has high speed of calculation, diligence, accuracy, reliability, or versatility which has made it an integrated part in all business organizations. Computer is used in business organizations for − 3  The process of entering data and instructions into the computer 1 Take Input system. Saving data and instructions so that they are available for 2 Store Data processing as and when required. Performing arithmetic, and logical operations on data in order to 3 Processing Data convert them into useful information. Output The process of producing useful information or results for the user, 4 Informatio such as a printed report or visual display. n Control the Directs the manner and sequence in which all of the above 5 workflow operations are performed. 10 Input Unit This unit contains devices with the help of which we enter data into the computer. This unit creates a link between the user and the computer. The input devices translate the information into a form understandable by the computer. Following are some of the important input devices which are used in a computer − Keyboard Mouse Joy Stick Light pen Track Ball Scanner Graphic Tablet Microphone Magnetic Ink Card Reader(MICR) 11  Optical Character Reader(OCR) Bar Code Reader Optical Mark Reader(OMR) Keyboard Keyboard is the most common and very popular input device which helps to input data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions. Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet. The keys on the keyboard are as follows − 12  S.No Keys & Description Typing Keys 1 These keys include the letter keys (A-Z) and digit keys (09) which generally give the same layout as that of typewriters. Numeric Keypad 2 It is used to enter the numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators. Function Keys 3 The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has a unique meaning and is used for some specific purpose. Control keys 4 These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc). Special Purpose Keys 5 Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen. Mouse Mouse is the most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base, which senses the movement of the mouse and sends corresponding signals to the CPU when the mouse buttons are pressed. Generally, it has two buttons called the left and the right button and a wheel is present between the buttons. A mouse can be used to 13 control the position of the cursor on the screen, but it cannot be used to enter text into the computer. Advantages Easy to use Not very expensive Moves the cursor faster than the arrow keys of the keyboard. Joystick Joystick is also a pointing device, which is used to move the cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.The function of the joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games. Light Pen Light pen is a pointing device similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is moved over the monitor screen and the pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU. Track Ball Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the pointer can be moved. Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button, or a square. Scanner Scanner is an input device, which works more like a photocopy machine. It is used when some information is available on paper and it is to be transferred to the hard disk of the computer for further manipulation. Scanner captures images from the source which are then converted into a digital form that can be stored on the disk. These images can be edited before they are printed. Microphone Microphone is an input device to input sound that is then stored in a digital form. The microphone is used for various applications such as adding sound to a multimedia presentation or for mixing music. Magnetic Ink Card Reader (MICR) MICR input device is generally used in banks as there are large number of cheques to be processed every day. The bank's code number 14 and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable. This reading process is called Magnetic Ink Character Recognition (MICR). The main advantages of MICR is that it is fast and less error prone. Bar Code Readers Bar Code Reader is a device used for reading bar coded data (data in the form of light and dark lines). Bar coded data is generally used in labelling goods, numbering the books, etc. It may be a handheld scanner or may be embedded in a stationary scanner. Bar Code Reader scans a bar code image, converts it into an alphanumeric value, which is then fed to the computer that the bar code reader is connected to. Central Processing Unit (CPU) consists of the following features − CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results, and instructions (program). It controls the operation of all parts of the computer. CPU itself has following three components. Memory or Storage Unit Control Unit ALU(Arithmetic Logic Unit) Memory or Storage Unit This unit can store instructions, data, and intermediate results. This unit supplies information to other units of the computer when needed. It is also known as internal storage unit or the main memory or the primary storage or Random Access Memory (RAM). Its size affects speed, power, and capability. Primary memory and secondary memory are two types of memories in the computer. Functions of the memory unit are − It stores all the data and the instructions required for processing. It stores intermediate results of processing. It stores the final results of processing before these results are released to an output device. 15 DIODE, DIODE ARRAYS AND PERIPHERAL INTERFACE ADAPTERS (PIAs) Lecture Objectives At the end of this lesson the students would be able to: 1. Identify and know the uses of diodes 2. Enumerate the uses of diode arrays 3. Explain the use of the Peripheral Interface Adapters (PIAs) Diode A diode is an electronic component that conducts current in one direction and blocks current from flowing in the other direction. The diode symbol is Diode symbol How to Connect a Diode How diodes work - right direction  In the circuit above the diode is connected in the right direction. This means current can flow through it so that the LED (Light Emitting diode) will light up. How diodes work - wrong direction In this second circuit the diode is connected the wrong way. This means that no current will flow in the circuit and the LED will be turned OFF. The diode is created from a PN junction. A PN junction can be produced by taking negative doped and positive doped semiconductor material and putting it together. At the intersection of these two materials a “depletion region” appears. This depletion region acts as an insulator and refuses to let any current pass. When you apply a positive voltage from the positive side to the negative side, the “depletion layer” between the two materials disappears and the current can flow from the positive to the negative side. When you apply a voltage in the other direction, from the negative to the positive side, the depletion region expands and resists any current flowing. Uses of the Diode 1. Diodes are used as rectifiers The most common and important application of a diode is the rectification of AC power to DC power. Using the diodes, we can construct different types of rectifier circuits. The basic types of these rectifier circuits are half wave, full wave center tapped and full bridge rectifiers 2. Diodes are used in performing logic gates operations Computers operate in binary. The binary decision trees in computing are based on logic gates enabled by diodes that control whether a switch is on ("1") or off ("0"). Although hundreds of millions of diodes appear in modern processors, they're functionally the same as the diodes you buy at the electronics store it is just that they are much smaller. 3. They are used for high voltage protection Diodes also function well as protection devices for sensitive electronic components. When used as voltage protection devices, the diodes that are conducting current under normal operating conditions immediately short any high-voltage spike to ground where it cannot harm an integrated circuit. Specialized diodes called transient voltage suppressors are designed specifically for over-voltage protection and can handle very large power. Similarly, a diode can regulate voltage by serving as a clipper or a limiter—a specialized purpose that caps the voltage that can pass through it at a certain point. 4. They are used for stirring current The basic application of diodes is to steer current and make sure it only flows in the proper direction. One area where the current steering capability of diodes is used to good effect is in switching from power coming from a power supply to power running from a battery. When a device is plugged in and charging—for example, a cell phone or uninterruptible power supply—the device should be drawing power only from the external power supply and not the battery, and while the device is plugged in the battery should be drawing power and recharging. As soon as the power source is removed, the battery should power the device so that no interruption is noticed by the user. 5. They are used as a source of light. An LED flashlight is just a flashlight whose illumination is sourced from a light-emitting diode. In the presence of positive voltage, LEDs glow. A photodiode, by contrast, accepts light through a collector (like a mini solar panel) and converts that light into a small amount of current. 6. They are used for the Modulation/Demodulation of Signals The most common use of diodes is to remove the negative component of an AC signal. Because the negative portion of an AC waveform is usually identical to the positive half, very little information is effectively lost in this process of stripping it away, leading to more efficient signal processing. Signal demodulation is commonly used in radios as part of the filtering system to help extract the radio signal from the carrier wave. DIODE ARRAYS Diode arrays are composed of multiple discrete (usually unconnected) diodes on a single silicon chip. Diode array 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. In general, the term diode array implies four or more diodes in a single package. The most efficient packaging scheme is typically 8 diodes or more in a dual inline package, a DIP. Other packages are the SIP, a single inline package, the flat pack, and even a surface mount diode array. Linear diode arrays are used for digitizing x- ray images. 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 1. Computer and peripheral I/O ports, 2. Core driver switching, 3. High frequency data lines 4. Interface networks,  5. LAN and WAN networks, 6. Steering diode applications. The diagram of the Diode Array THE PERIPHERAL INTERFACE ADAPTER The Peripheral Interface Adapter (PIA) is a means used to interface peripheral equipment with the micro processing unit (MPU). It is a peripheral integrated circuit providing parallel I/O interfacing for microprocessor systems. The PIA communicates with the MPU via an eight bit bi-directional data bus, three chip selects, two register selects, two interrupt request lines, one read/write line, an enable line, and a reset line. Each PIA has two eight bit bi-directional peripheral data buses for interfacing with peripheral equipment as shown in figure below. Common PIAs include the Motorola MC6820 and MC6821, and the MOS Technology MCS6520, all of which are functionally identical but have slightly different electrical characteristics. The PIA is most commonly packaged in a 40 pin DIP package.  PRIMARY MEMORY The primary memory also called main memory or temporary memory is the internal memory of the computer. It is called the primary memory because it is the memory that the processor accesses first. It holds the data and instructions on which the processor is currently working on. The instructions dictate the action to be taken on the data. Primary memory is volatile in nature which means when power is switched off it loses its content (data). Once the computer is put on, the primary memory loads all running applications, including the base operating system (OS), user interface and any user-installed and running software utility. A program/application that is opened in primary memory interacts with the system processor to perform all application-specific tasks. TYPES OF PRIMARY MEMORY RAM (RANDOM ACCESS MEMORY) The RAM is known in full as Random Access Memory or Read /Write memory. It is generally referred to as main memory of the computer. The information stored in this memory is lost as power supply to the computer is switched off. That is why it is called ‘’volatile memory”. RAM is the place in a computing device where the operating system, application programs and data in current used are kept so they can quickly be reached by the processor. It is faster to read from or write to than other kinds of storage device like the hard disk (HDD). That is, it allows data items to be read or written in almost at the same amount of time irrespective of the physical location of data inside the memory. In contrast with other direct access data storage media like hard disk, The time required to read and write data item varies significantly depending on their physical locations on those devices due to the mechanical limitations such as media rotation speed and arm movement. TYPES OF RANDOM ACCESS MEMORY (RAM) MAGNETIC CORE MEMORY The Magnetic Core memory was a common form of computer Random Access Memory (RAM) for 20years between 1955 and 1975, and it was developed at Massachusetts Institute of Technology (MIT) in 1951. The memory made use of magnetic rings called cores that had wires passing through them for selecting and detecting the contents of the cores. With the introduction of semiconductor memories the core memory is now obsolete but the Random Access Memory of the computer can also be referred to as the core memory. The function of core memory was based on hysteresis of the magnetic material used to make the rings. Each core in the core memory was used to store one bit of information. The cores can be magnetized through clockwise and anticlockwise direction. The value stored in the core depended upon the direction of magnetization. Access to core memory involved read and write cycles. The read cycle would cause the memory contents to be lost, whereas the write cycle would restore the contents of the memory location. A read cycle must be followed by a write cycle. Another feature of core memory is non-volatility, meaning its contents are not lost once power is removed. Special logic was included in the memory controller to ensure the memory contents were not altered. The magnetic core memory The common sense/inhibit line for each bit, is used to alter or detect the contents of a memory location. Every memory access involves a read/write cycle. A read cycle is always destructive, meaning that the memory contents is lost after the location is read. A read cycle must be followed by a write cycle to restore the contents of the memory location. Advantages  1. Non-volatility was one of the biggest advantages with core memory in the early years of memory development. Disadvantages 1. It was fairly slow and initially expensive to fabricate. 2. Due to its magnetic nature, it was vulnerable to the effects of interference. Adjustments with respect to sense levels, drive currents and memory timing were required. 3. Time-consuming applications were required to diagnose hardware problems in core memory. SEMICONDUCTOR MEMORIES Semiconductor memories are digital electronic data storage devices usually used as computer memory they are designed on semiconductor electronic circuit (IC). Most types of semiconductor memory have the random access property, which means that it takes the same amount of time to access any memory location, so data can be efficiently accessed in any random order. This is in contrasts with data storage media such as Hard Disks (HDD) and Compact Disks (CDs) which read and write data consecutively and therefore the data can only be accessed in the same sequence it was written. Semiconductor memory also has faster access times than other types of data storage. A byte of data can be written to or read from semiconductor memory within a few nanoseconds, while access time for rotating storage such as hard disks is in the range of milliseconds. For these reasons it is used for main computer memory (primary storage), to hold data the computer is currently working on. Shift registers, processor registers, data buffers and other small digital registers that have no memory address decoding mechanism are not considered as memory although they also store digital data. STATIC RAM: Static RAM is also known as SRAM are commonly used in devices like Digital cameras, routers, printers, LCD screens. It retains stored information as long as power supply is ON. SRAM need a constant power flow in order to function. Because of the continuous power, SRAM do not need to be ‘refreshed’ (constant electric charge) in order to remember the data being stored. This is why SRAM is called ‘static’. That is no change or action (e.g. refreshing) is needed to keep data intact. However, SRAM is a volatile memory, which means that it loses is data content once the power is out. The advantages of using SRAM over DRAM are lower power consumption and faster access speeds. The disadvantages of using SRAM over DRAM are lesser memory capacities and higher costs of manufacturing (they are very expensive). Because of these characteristics, SRAM is typically used in processor cache memory (e.g. L1, L2, and L3), hard drive buffer/cache and Digital-to-analog converters (DACs) on video cards. DYNAMIC RAM: Dynamic RAM is also known as DRAM. It stores information in a very short time a few milliseconds even if the power supply is on. It is constantly restoring whatever information is being held in the memory. In other words, DRAM requires a periodic ‘refresh’ of power in order to function. This is so because the capacitors that store data in DRAM gradually discharge energy which will lead to lose of energy, hence data will be lost. DRAM refreshes the data by sending millions of pulse per second to the memory cells. This is why DRAM is called ‘dynamic’ – constant change or action (e.g. refreshing) is needed to keep data intact. DRAM is also a volatile memory, which means that all the stored data becomes lost once the power is cut off. The advantages of using DRAM over SRAM are lower costs of manufacturing (they are very cheap) and greater memory capacities. The disadvantages of using DRAM over SRAM are slower access speeds and higher power consumption. Because of these characteristics, DRAM is typically used as computer System memory and Video graphics memory. They are popularly used in Video game consoles and networking hardware. TYPES OF DYNAMIC RANDOM ACCESS MEMORY FPM DRAM – It stands for Fast Page Mode Dynamic Random Access Memory. This memory is little faster in comparison to the conventional DRAM. The access time is improved for this memory as it sends row address only once for accessing the neighboring locations in memory. Despite of its name, it is still one of the slowest RAMS used today. This memory is not considered good for high speed memory buses over 66 MHz.  FPM DRAMS EDO DRAM – It stands for Extended Data Output Dynamic Random Access Memory. It can be seen as an improved version of FPM, as it can retain data valid for a longer period than FPM. Due to this feature, it is known as the extended out. It started replacing FPM DRAM in 1993. It stores 265 bytes of data information into laches and these latches hold next same amount of information. This arrangement makes it possible for programs to be executed sequentially without any delay. EDO DRAM SDRAM – It stands for Synchronous Dynamic Random access memory. The word synchronized refers to its synchronization feature with the system bus. It requires a startup sequence just like DRAM, however signal generation is not that difficult in this as in DRAM. It is twice as faster as EDO DRAM. One of the major disadvantages of using SDRAM is that it works in Single Data Rate which allows it to carry out only a single task per clock cycle. Due to this disadvantage of SDRAM, Double Data Rate SDRAM was introduced later. Single Data Rate Synchronous Dynamic RAM (SDR SDRAM): it has been in the market since 1993 till date is used for Computer memory and video game consoles SDR SDRAM is the expanded term for SDRAM – the two types are one and the same, but most frequently referred to as just SDRAM. The ‘single data rate’ indicates how the memory processes one read and one write instruction per clock cycle. This labeling helps to clarify comparisons between SDR SDRAM and DDR SDRAM: DDR SDRAM is essentially the second generation development of SDR SDRAM SDR SDRAM Double Data Rate Synchronous Dynamic RAM (DDR SDRAM): it has been in the market since 2000 till date. It is popularly used as Computer memory. DDR SDRAM operates like SDR SDRAM, only twice as fast. DDR SDRAM is capable of processing two read and two write instructions per clock cycle (hence the ‘double’). Although similar in function, DDR SDRAM has physical differences (184 pins and a single notch on the connector) versus SDR SDRAM (168 pins and two notches on the connector). DDR SDRAM also works at a lower standard voltage (2.5 V from 3.3 V), preventing backwards compatibility with SDR SDRAM. DDR SDRAM  DDR2 SDRAM is the evolutionary upgrade to DDR SDRAM. While still double data rate (processing two read and two write instructions per clock cycle), DDR2 SDRAM is faster because it can run at higher clock speeds. Standard (not overclocked) DDR memory modules top out at 200 MHz, whereas standard DDR2 memory modules top out at 533 MHz. DDR2 SDRAM runs at a lower voltage (1.8 V) with more pins (240), which prevents backwards compatibility.  DDR2 SDRAM  DDR3 SDRAM improves performance over DDR2 SDRAM through advanced signal processing (reliability), greater memory capacity, lower power consumption (1.5 V), and higher standard clock speeds (up to 800 Mhz). Although DDR3 SDRAM shares the same number of pins as DDR2 SDRAM (240), all other aspects prevent backwards compatibility. DDR3 SDRAM  DDR4 SDRAM improves performance over DDR3 SDRAM through more advanced signal processing (reliability), even greater memory capacity, even lower power consumption (1.2 V), and higher standard clock speeds (up to 1600 MHz). DDR4 SDRAM uses a 288-pin configuration, which also prevents backwards compatibility. DDR4 SDRAM Graphics Double Data Rate Synchronous Dynamic RAM (GDDR SDRAM): it has been in the market since 2003 till date. It is popularly used in Video graphics cards, some tablets. GDDR SDRAM is a type of DDR SDRAM that is specifically designed for video graphics rendering, typically in conjunction with a dedicated GPU (graphics processing unit) on a video card. Modern PC games are known to push the envelope with incredibly realistic high-definition environments, often requiring hefty system specs and the best video card hardware in order to play (especially when using 720p or 1080p (pixels) high resolution displays).  GDDR SDRSM Similar to DDR SDRAM, GDDR SDRAM has its own evolutionary line (improving performance and lowering power consumption): GDDR2 SDRAM, GDDR3 SDRAM, GDDR4 SDRAM, and GDDR5 SDRAM. Despite sharing very similar characteristics with DDR SDRAM, GDDR SDRAM is not exactly the same. There are notable differences with the way GDDR SDRAM operates, particularly regarding how bandwidth is favored over latency. GDDR SDRAM is expected to process massive amounts of data (bandwidth), but not necessarily at the fastest speeds (latency) – think of a 16-lane highway set at 55 MPH. Comparatively, DDR SDRAM is expected to have low latency to immediately respond to the CPU – think of a 2-lane highway set at 85 MPH. Flash Memory: it has been in the market since 1984 till date. It is popularly used in Digital cameras, smartphones/tablets, handheld gaming systems/toys. Flash memory is a type of non-volatile storage medium that retains all data after power has been cut off. Despite the name, flash memory is closer in form and operation (i.e. storage and data transfer) to solid state drives than the aforementioned types of RAM. Flash memory is most commonly used in: USB flash drives, Printers, Portable media players, Memory cards ,Small electronics/toys, PDAs  FLASH MEMORY CACHE MEMORY The Cache Memory (Pronounced as "cash" memory) is the volatile computer memory which is very nearest to the processor (CPU), for this reason it is also called CPU memory. Cache memory is not directly accessible by the computer programmer. All the Recent Instructions are Stored into the Cache Memory. It is the fastest memory that provides high-speed data access to a computer microprocessor. Cache meaning is that it is used for storing the input which is given by the user and which is necessary for the computer microprocessor to perform a Task. The Capacity of the Cache Memory is too low as compare to Memory (random access memory (RAM)) and Hard Disk. Diagram showing the way the cache memory works IMPORTANCE OF CACHE MEMORY The cache memory lies in the path between the processor and the memory. The cache memory therefore, has lesser access time than memory and is faster than the main memory. A cache memory have an access time of 100ns, while the main memory may have an access time of 700ns (Nano seconds) but cache memory is very expensive and hence is limited in capacity. Earlier cache memories were available separately but the microprocessors contain the cache memory on the chip itself. The need for the cache memory is due to the disparity between the speeds of the main memory and the CPU. The CPU clock is very fast, whereas the main memory access time is when compared to the CPU clock is slower. Hence, no matter how fast the processor is, the processing speed depends more on the speed (access time) of the main memory. It is because of this reason that a cache memory having access time closer to the processor speed is introduced. The cache memory stores the program (or part of the program) currently being executed or which may be executed within a short period of time. The cache memory also stores temporary data that the CPU may frequently require for manipulation. The cache memory works according to various algorithms, which decide what information it has to store. These algorithms work out the probability to decide which data would be most frequently needed. This probability is worked out on the basis of past observations. It acts as a high speed buffer between CPU and main memory and is used to temporary store very active data and action during processing since the cache memory is faster than main memory, the processing speed is increased by making the data and instructions needed in current processing available in cache. The cache memory is very expensive and hence is limited in capacity. Cache memory improves the speed of the CPU, but it is expensive. TYPE OR LEVELS OF CACHE MEMORY Level 1 (L1) cache or Primary Cache L1 is the primary type cache memory. The Size of the L1 cache very small when compared to others. It is between 2KB to 64KB, it depends on computer processor. It is an embedded register in the computer microprocessor (CPU).The Instructions that are required by the CPU that are firstly searched in L1 Cache. Example of registers are accumulator, address register, Program counter etc. Level 2 (L2) cache or Secondary Cache L2 is secondary type cache memory. The Size of the L2 cache has higher storage capacity than L1. The size is between 256KB to 512KB.L2 cache is Located on computer microprocessor. After the processor searches for instructions in L1 Cache, if not found then it searches L2 cache. The high-speed system bus interconnects the cache to the microprocessor. Level 3 (L3) cache The L3 cache is larger in size but also slower in speed than L1 and L2, its size is between 1MB to 8MB.In Multicore processors, each core may have separate L1 and L2, but all core share a common L3 cache. L3 cache double speed than the RAM. Diagram showing the levels of Cache Memory THE COMPLEMENTRY METAL - OXIDE SEMICONDUCTOR (CMOS) The full meaning of CMOS (pronounced ‘see-moss’) is Complementary Metal- Oxide Semiconductor which is also known as Real-Time Clock (RTC), CMOS RAM, Non-Volatile RAM (NVRAM), Non-Volatile BIOS memory, or complementary- symmetry metal-oxide-semiconductor (COS-MOS). It is a computer RAM chip located on the motherboard. Which means it would normally lose the content (settings) it is storing when the computer is shut down. However, the CMOS battery is used to provide constant power to the chip there by making the RAM non-volatile. The BIOS is a computer chip on the motherboard like CMOS except that its purpose is to communicate between the processor and other hardware components like the hard drive, USB ports, sound card, video card, and more. A computer without a BIOS wouldn't understand how these pieces of the computer work together. When the computer boots up, BIOS pulls information from the CMOS chip to understand the hardware settings, time etc. that is stored in it. CMOS need a little power (a millionth amp of electricity) to hold on to its contents which are the BIOS settings (configuration data), system date and time for a long time (in years). CMOS battery is a lithium or dry cell battery located on the motherboard and can be replaced at any time when the battery becomes dead. Incorrect or slow system date\time and loss of BIOS settings are major signs of a dead or dying CMOS battery. The Diagram Of CMOS And CMOS Battery ROM (READ ONLY MEMORY) ROM stands for Read Only Memory and it is a permanent type of memory. ROM contains the programming that allows the computer to be "booted up" or regenerated each time it is turned on. Its content are not lost when power supply is switched off. Content of ROM is decided by the computer manufacturer and are permanently stored at the time of manufacturing. ROM cannot be overwritten by the computer and because of its ability to retain data even after power outage, it is called ‘’Non-Volatile Memory’’ used in calculations.  ROM (Read Only Memory) TYPES OF ROM (READ ONLY MEMORY) PROM (Programmable Read Only Memory): It is a programmable ROM, It is a nonvolatile memory that is programmed once and read from many times. Once the PROM Chip has been programmed, the recorded information cannot be changed. THE PROM EPROM (Erasable Programmable Read Only Memory): EPROM Chip can be programmed times and again by erasing the information stored earlier in it. EPROM is erased by exposure to ultraviolent light for at least 20minites. It is more expensive than PROM.  THE EPROM EEPROM (Electrically Erasable Programmable Read Only Memory): The EEPROM has the following characteristics:  It is programmed and erased by special electrical waves in milliseconds.  A single byte of a data or the entire content of the device can be erased at any time. That is any part of the ERRPROM can be written into anytime. This is called the byte level writing.  Writing takes much longer than reading.  It is more expensive  Less densed than EPROM THE EEPROM DIFFERENCE BETWEEN RAM AND ROM RAM ROM DATA The data is not permanent The data is permanent. It and it can be altered any can be altered but only a number of times. limited number of times  that too at slow speed SPEED It is high speed memory It is slower than the RAM PROCESSOR The CPU can access the CPU cannot access the INTERACTION data stored on it data stored on it. In order to do so, the data is first copied to the RAM. SIZE AND Large size with higher Small size with less CAPACITY capacity capacity. USAGE They are used as the main Firmware like BIOS or memory of computers UEFI. Medical devices, (DRAM) and CPU Cache and at places where a (SRAM). small and permanent memory solution is required. COST It is expensive It is cheaper than RAM The ROM is cheap and can hold data permanently but it has its limitations. On the other hand, RAM is quite useful than ROM but it is expensive. The ROM is not totally incompetent because the Flash memory on removable storage media like Solid State Drives, USB drives, SD cards, etc. is an advanced implementation of the EEPROM type of read-only memory. They provide faster storage alternative than the hard drives but the number of read/write operations is also a bottleneck. MEMORY ENHANCEMENT The processor works at a very high speed when compared to the time it takes for an instruction to be fetched from memory and executed (fetch execute cycle) by the processor. There is therefore the need to enhance memory. The following are methods of memory enhancement. 1. Wide Path Memory Access: This has to do with the increase in memory access through a wider data path so as to read or write as many byte or words of data between the processor and memory with each access. 2. Memory interleaving: This has to do with dividing memory into parts so that each part has its own data and address register. The memory parts can be accessed separately and simultaneously. 3. Cache memory: This has to do with the use of high speed memory to increase the rate at which data is processed. The processor has direct and fast access to the cache memory. Copies of data and instructions from the memory are stored in the cache there by making processor to easily access the data and instruction for processing. SECONDARY MEMORY The Secondary memory is also known as Auxiliary Memory, Permanent Memory or external memory. It is non-volatile memory because it retains stored programs and information permanently even when power is switched off. Programs and information can also be deleted at any time. It is called auxiliary memory because it serves as a backup memory to the primary memory. They are also used for off- line storage and achieving. The secondary storage devices have large storage capacity ranging from megabytes to terabytes of storage space within a single memory but they have slower access time when compared to the primary memory. They are also less expensive than the primary memory. That is, the cost per bit is low hence the increases in the storage capacity of the secondary memory. The processor does not have direct access to the secondary memory. Therefore, during operations, programs and information are transferred to the main memory for the processor to use and the output of processed data (information) are stored in the secondary memory. Examples of secondary storage device are floppy disk, magnetic storage devices (hard disk and floppy disk), optical disk (CD, DVD) and pen drives (flash drive). MAGNETIC DISKS A magnetic disk is made up of one or more circular platters made of glass, metal or plastic coated with a magnetic substance. Areas on the platters are magnetically polarized in directions and electromagnetic read/write heads are used to distinguish between 1s and 0s using magnetic polarization. A motor drive rotates the disk platters about its central axis. A read/write head is connected to the end of an arm. The arm moves radially in and out across the surface of the disk. A head motor controls exactly the position of the arm on the disk. Most hard disk drives have several platter, all mounted on the same axis with heads on each surface of platters. Each arm has two read/write heads that move in a way that the heads are at the same point on the platters. The head of the arms service both surface of the platter except for the top and button of the entire arrangement of platters. The heads trace out circles known as Tracks on the disk as the disk rotate. The set of tracks of all the surface of the disk form a Cylinder because they are held to by the arms in a cylindrical shape. The internal structure of the Magnetic Disk Drive The tracks on the disks platter contain blocks of data. The disk platter is divided into equally sized pie shaped segment called sectors. Each sector on a track contains one block of data usually 512 bytes which represent the smallest unit that can be read and written. A technique called constant angular velocity that has the advantages of simplicity and fast access assumes that the same angle is swept when a sector is accessed; therefore the transfer time is kept constant with the motor rotating at a fixed speed regardless of the tracks. Another technique called constant linear velocity CLV adjusts the motor speed such that the speed along the track would be constant regardless of the position of the head. The capacity of a CLV disk with the same diameter and bit density is approximately double that of an equivalent CAV disk. CLV technology is commonly used in DVDs and CDs but it’s really used for hard disks. Modern disk divides disks into a number of zones typically sixteen. The cylinder in different zones has different number of sectors. The number of sector within a particular is constant. A technique known as multi zone recording or zone bid recording (ZBK) or Zone CAU recording ( Z-CAU) which involves the disk controller buffering the data rate so that the data rate to I/O interface is constant despite variable data rate between the controller and the disk. A typical hard disk rotates at 5400 revolution per minute (RPM), 7200 RPM or 10800 RPM. The assembly of the disk platters and heads is tightly packed to prevent dust as it could lead to the crash of the hard disk. The heads rest in a parked position on the edge of the drive when the disk is stationary. The arm moves the head from is present track to the desired track. The time required to move from one track to another track is known as seek time. Average seek time is used as a specification for hard disk. Since the distance between tracks is a factor that affects seek time of a disk. Once the track that is desired is located the read/write operation waits for the disk to rotate to the beginning of the correct sector. The time for this to occur is called rotational latency time or rotational delay or latency time. Average latency = 1 1 2 * Rotational speed The time taken to transfer a block of data is known as transfer time which is defined by the number of sector on a track. 1 Transfer time = Number of sector * Rotational speed A typical modern computer requires 20 to 25 milliseconds to access a disk block and its CPU can execute millions of instructions in nanoseconds. This indicates that the processor has to be other things while waiting which is a bottleneck to the processing time of the CPU. A inter block gap separate the block from neighboring blocks. Formatting the disk is the process of establishing track position, blocks and heads. This must be done before the disk can be used. The figure illustrating the seek time, latency time and transfer time. DISK ARRAY The grouping of two or more disk drive is called disk array or drive array. Disk array are commonly used in large computing environment to provide program and data storage facility in a network. They are used to: 1. Reduce data access time by sharing data among multiple disks. 2. Increase system reliability by providing storage redundancy. RAID which stands for Redundant Array of Inexpensive Disk or Redundant Array Independent Disk is a type of disk array. There are two standard methods of implementing a disk array. Which are: 1. Mirrored Array: This consists of two or more disk drives that store the same data. During read operation, data blocks are read from individual disk and later combined to form a complete data. The access time is reduced by the number of disk drive from which the data were read from. If a failure occurs in a read operation from the drive, the data is read from another drive and the block is marked bad to prevent future use of the block thereby increasing system reliability. In critical application, data can be read from two or more drives and compared with data in other drive thereby increasing reliability. Furthermore, in a situation where errors are not detected from a read operation a method known as majority logic is used to detect error. This method is used in highly reliable computer system known as Fault Tolerant computers. Majority logic has to do with computing data read from disk to determine the integrity of the data. If the data is same for the drives then the data is accepted but if it is same for majority of the drives, the drives that has a different data is flagged as an error. 2. The Stripped Array: In stripped array a file segment to be stored, is divided into blocks. Different blocks are written and stored in different disk drives simultaneously. This increases throughput rate by the number of data disk in the array. In stripped array, disk drives is reserved for error checking during a write operation, the system creates a block of words from each group of data blocks and store them in the reserved disk, during reading operation. The parity data is used to check the original data.  Redundant Array of Independent Disk(RAID) OPTICAL DISK STORAGE Optical disk storage includes Compact Disks (CDs) and Digital Versatile Disks (DVDs) in read only, write once and read / write form that are alternative to the magnetic disk storage. Optical disk is portable and has the ability to pack large amount of data. For example, CD-ROM (12cm in diameter) store approximately 650 MB, Blue-Ray DVD (Same size as the CD- ROM) store up to 50GB and HVD for holographic Disk can store up to 1.6TB although it is expensive. Optical disk are used for off-site or off-line archiving as well as program and file distribution (until the growth of the internet) unlike magnetic disks drives that are used to store, read and write data for current use. CD ROM – Data are stored in blocks on disk. The blocks are arranged in file with a directory structure similar to the magnetic disk. CD-ROM store data on a single track that is approximately three miles long which spiral from inside to outside unlike the centric tracks of the magnetic disk drives. Data is stored in linear blocks along the tracks unlike sector in magnetic drives. CD-ROM was originally designed for audio files where data access is sequential from start to finish hence the spiral track is a good decision. CD-ROM typically stores 270,000 blocks of data. Each block is 2352 bytes long and stores 2048 bytes of data. It can store both audio and video data. The data on CD-ROM is the sometimes called Large Frames. Data is stored on disk in form of pits and lands that are burned into the surface of the master disk with high powered leaser. The disk is mechanically produced using a stamping process unlike the bit by bit process of disk drives. The disk is protected with a clear coasting. A laser beam is reflected off the pitted surface at the disk as in motor rotates the disk. The reflection is used to differentiate between the pit and lands and translated into bits. Difference between the tracks in the optical disk and the magnetic disk drive. The disk are read using constant linear velocity (CLV) and a variable speed motor to keep transfer rate constants. DVD: DVD is similar in size to the CD-ROM. It uses shorter light wave length (visible reds) instead of infrared which allows tighter packing of the disk. The laser can be focused in such a way that two layers of data placed on the same side of disk can be focused on disk. A different manufacturing technique allows the use of both sides. Each layer of DVD can hold approximately 4.7 GB. If both layers of both sides are used, the DVD capacity of storage is approximately 17GB. The use of blue ray leaser can increase to the capacity to approximately 50 GB WORM: Write once read many times is an inexpensive way of archiving data. It provides high capacity storage with the convenience of compact size, reasonable cost and removability. Worm is written once. Once written into, the data block cannot be rewritten. This is suitable to store business data of legal purpose that does not require frequent change. If there is an update, the file is written in another data block which makes auditing easy. When the disk is filed, the disk is stored away and a new one is used. Worm works similarly to a CD or DVD but the major different is that it is made up of a material that can be blustered by a medium power laser. The disk is smooth initially, but when written on, the medium power laser creates tiny blurters on the location of the disk. These corresponds to the pits in the CD-ROM. The WORM is read with a low power laser in the same way as a CD-ROM. The blister technology is used in CD and DVD called CD-R, DVD-R and DVD+R. But there is rewritable version of this technology CD-RW, DVD-RW, DVD-RAM and DVD+RAMBD-RE although there are compatibility issues where some drives can read some format while others can read all formats. MAGNETIC TAPE Magnetic tapes are used for backup and archives in large computer system. They are nonvolatile and can store data indefinitely. The data on magnetic tapes are accessed sequentially and can be used for offsite storage for as long as possible. Most magnetic tapes are cartridge based and when it is on a tape drive for operation, it is said to be mounted. It has the capacity of storing 1.6TB of compressed data. Advantages 1. Convenience 2. Ease of use 3. It can be mounted and unmounted. 4. Small and easy to store Categories 1. Linear tape open format (LTO): it is used to represent linear recording cartridges. It folds up to 820 meters in 1 ½ inches wide tape that is in 102mm x 105mm x 21.5mm cartridge. The techniques use in storing and retrieving data is called Data Streaming. The cartridge tapes are divided into tracks that are as many as 886. The tapes write and read in bits longitudinally. Data are stored in the tape  starting from the center tracks. At the end, the tape reversed, for the rest group of track to be written or read into. 2. Helical scan cartridge: Designed for video tapes originally, data on HSC are packed tightly using a read/write head that rotate at a high speed. The tracks at the HSC are diagonal across the width of tapes. The magnetic Tape FLASH MEMORY Flash memory is also called the solid state memory. It is nonvolatile electronic integrated circuit memory that is very similar to ROMs but different in technology in the sense that ROM are read, erased and written in large block of addresses, while Flash memories can be read, written into and erased in bits or small blocks (). This enables the flash memory to be used for applications that require random access (especially where more access are reads).They are considered impractical to be used as RAMs because: 1. It requires block erasure and write accesses require additional steps that writes the unchanged data back to block 2. The erase and rewrite operation is very slow compared to read access. Due to its small size, flash memory are used as secondary storage in cell phones, music players and digital also as flash USB thumb drives. Advantages of solid state drives are:  Long term storage with less weight  Low power consumption  Small size  Immunity to failure due to physical shock and Vibration (no moving part)  Generate little heat with less noise The Flash Memory DIFFERENCE BETWEEN PRIMARY AND SECONDARY MEMORY PRIMARY MEMORY SECONDARY MEMORY 1 Primary memory stores data temporally. It stores data permanent. 2 It is directly accessible to the processor It not directly accessible to the processor. 3 It is volatile in nature It is not volatile in nature. 4 More expensive than the secondary Less expensive than the primary memory storage. 5 They are semiconductor memory They are magnetic or optical memory. 6 Also known as main memory or internal Also known as auxiliary or external memory. 7 Examples: RAM, ROM, Caches memory, Examples: HDD, FDD, DVD, CD, Pen drive PROM, EPROM etc. etc. 8 Operations are electronic. Their operations are mostly mechanical except the flash memory.  Integrated Circuits 627 23 Integrated Circuits 23.1 Integrated Circuit 23.2 Advantages and Disadvantages of Integrated Circuits 23.3 Inside an IC Package 23.4 IC Classifications 23.5 Making Monolithic IC 23.6 Fabrication of Components on Monolithic IC 23.7 Simple Monolithic ICs 23.8 IC Packings 23.9 IC Symbols 23.10 Scale of Integration 23.11 Some Circuits Using ICs INTRODUCTION INTRODUCTION T he circuits discussed so far in the text consisted of separately manufactured components (e.g. resistors, capacitors, diodes, transistors etc.) joined by wires or plated conductors on printed boards. Such circuits are known as discrete circuits because each component added to the circuit is discrete (i.e. distinct or separate) from the others. Discrete circuits have two main disadvan- tages. Firstly, in a large circuit (e.g. TV circuit, computer circuit) there may be hundreds of compo- nents and consequently discrete assembly would occupy a large space. Secondly, there will be hun- dreds of soldered points posing a considerable problem of reliability. To meet these problems of space conservation and reliability, engineers started a drive for miniaturized circuits. This led to the development of microelectronics in the late 1950s. Microelectronics is the branch of electronics engineering which deals with micro-circuits. A micro-circuit is simply a miniature assembly of electronic components. One type of such circuit is the integrated circuit, generally abbreviated as IC. An integrated circuit has various components such as resistors, capacitors, diodes, transistors etc. fabricated on a small semiconductor chip. How circuits containing hundreds of components are fabricated on a small semiconductor chip to produce 628 Principles of Electronics an IC is a fascinating feat of microelectronics. This has not only fulfilled the everincreasing demand of industries for electronic equipment of smaller size, lighter weight and low power requirements, but it has also resulted in high degree of reliability. In this chapter, we shall focus our attention on the various aspects of integrated circuits. 23.1 Integrated Circuit An integrated circuit is one in which circuit components such as transistors, diodes, resistors, capacitors etc. are automatically part of a small semiconductor chip. An integrated circuit consists of a number of circuit components (e.g. transistors, diodes, resistors etc.) and their inter connections in a single small package to per- form a complete electronic function. These components are formed and connected within a small chip of semi- conductor material. The following points are worth not- ing about integrated circuits : Fig. 23.1 (i) In an IC, the various components are automati- cally part of a small semi-conductor chip and the individual components cannot be removed or re- placed. This is in contrast to discrete assembly in which individual components can be removed or replaced if necessary. (ii) The size of an *IC is extremely small. In fact, ICs are so small that you normally need a microscope to see the connections between the components. Fig. 23.1 shows a typical semi-conduc- tor chip having dimensions 0.2 mm × 0.2 mm × 0.001 mm. It is possible to produce circuits contain- ing many transistors, diodes, resistors etc. on the surface of this small chip. (iii) No components of an IC are seen to project above the surface of the chip. This is because all the components are formed within the chip. 23.2 Advantages and Disadvantages of Integrated Circuits Integrated circuits free the equipment designer from the need to construct circuits with individual discrete components such as transistors, diodes and resistors. With the exception of a few very simple circuits, the availability of a large number of low-cost integrated circuits have largely rendered discrete circuitry obsolete. It is, therefore, desir- able to mention the significant advantages of in- tegrated circuits over discrete circuits. However, integrated circuits have some disadvantages and continuous efforts are on to overcome them. Advantages : Integrated circuits possess the following advantages over discrete circuits : (i) Increased reliability due to lesser num- ber of connections. (ii) Extremely small size due to the fabrica- tion of various circuit elements in a single chip of semi-conductor material. Integrated circuits (iii) Lesser weight and **space requirement due to miniaturized circuit. ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * Since it combines both active (e.g., transistors, diodes etc.) and passive elements (e.g., resistors, capaci- tors etc.) in a monolithic structure, the complete unit is called an integrated circuit. ** Typically, this is about 10% of the space required by comparable discrete assembly.  Integrated Circuits 629 (iv) Low power requirements. (v) Greater ability to operate at extreme values of temperature. (vi) Low cost because of simultaneous production of hundreds of alike circuits on a small semi- conductor wafer. (vii) The circuit lay out is greatly simplified because integrated circuits are constrained to use minimum number of external connections. Disadvantages : The disadvantages of integrated circuits are : (i) If any component in an IC goes out of order, the whole IC has to be replaced by the new one. (ii) In an IC, it is neither convenient nor economical to fabricate capacitances exceeding 30 pF. Therefore, for high values of capacitance, discrete components exterior to IC chip are connected. (iii) It is not possible to fabricate inductors and transformers on the surface of semi-conductor chip. Therefore, these components are connected exterior to the semi-conductor chip. (iv) It is not possible to produce high power ICs (greater than 10 W). (v) There is a lack of flexibility in an IC i.e., it is generally not possible to modify the parameters within which an integrated circuit will operate. 23.3 Inside an IC Package The IC units are fast replacing the discrete components in all electronic equipment. These are similar to the discrete circuits that they replaced. However, there are some points to be noted. An integrated circuit (IC) usually contains only transistors, diodes and resistors. It is usually very difficult to form inductors in an IC. Also, only very small capacitors, in the picofarad range, can be included. When inductors and large values of C are needed, they are connected externally to an IC. The various components in an IC are so small that they cannot be seen with a naked eye. Therefore, individual components cannot be removed or replaced. If a single component within an IC fails, the complete IC is replaced. When studying circuits using ICs, we are more concerned with the external connections to the ICs than with what is actually going on inside. We cannot get into an IC to repair its internal circuitry. 23.4 IC Classifications Four basic types of constructions are employed in the manufacture of integrated circuits, namely ; (i) mono-lithic (ii) thin-film (iii) thick-film (iv) hybrid. Monolithic ICs are by far the most common type used in practice. Therefore, in this chapter we shall confine our attention to the construction of this type of ICs only. It may be worthwhile to mention here that regardless of the type of method used to fabricate active and passive components, the basic characteristics and circuit operation of an IC are the same as for any of their counterparts in a similar circuit using separate circuit components. 23.5 Making Monolithic IC A monolithic IC is one in which all circuit components and their inter-connections are formed on a single thin wafer called the substrate. The word monolithic is from Greek and means “one stone.” The word is appropriate because all the components are part of one chip. Although we are mainly interested in using ICs, yet it is profit- able to know something about their fabrication. The basic production processes for the monolithic ICs are as follow : (i) p-Substrate. This is the first step in the making of an IC. A cylindrical p-type *silicon crystal is grown having typical dimensions 25 cm long and 2.5 cm diameter [See Fig. 23.2 (i)]. The crystal is then cut by a diamond saw into many thin wafers like Fig. 23.2 (ii), the typical thickness of ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * Since silicon possesses characteristics which are best suited to IC manufacturing processes. 630 Principles of Electronics the wafer being 200 µm. One side of wafer is polished to get rid of surface imperfections. This wafer is called the substrate. The ICs are produced on this wafer. Fig. 23.2 (ii) Epitaxial n layer. The next step is to put the wafers in a diffusion furnace. A gas mixture of silicon atoms and pentavalent atoms is passed over the wafers. This forms a thin layer of n-type Fig. 23.3 semi-conductor on the heated surface of substrate [See Fig. 23.3 (i) ]. This thin layer is called the *epitaxial layer and is about 10 µm thick. It is in this layer that the whole integrated circuit is formed. (iii) Insulating layer. In order to prevent the contamination of the epitaxial layer, a thin SiO2 layer about 1µm thick is deposited over the entire surface as shown in Fig. 23.3 (ii). This is achieved by passing pure oxygen over the epitaxial layer. The oxygen atoms combine with silicon atoms to form a layer of silicon dioxide (SiO2). (iv) Producing components. By the process of **diffu- sion, appropriate materials are added to the substrate at specific locations to produce diodes, transistors, resistors and capacitors. The production of these components on the wafer is discussed in Art 23.6. (v) Etching. Before any impurity is added to the substrate, the oxide layer (i.e. SiO2 layer) is etched. The process of etching exposes the epitaxial layer and permits the production of desired components. The terminals are processed by etching the oxide layer at the desired locations. (vi) Chips. In practice, the wafer shown in Fig. 23.4 is di- vided into a large number of areas. Each of these areas will be a separate chip. The manufacturer produces hundreds of alike ICs Fig. 23.4 on the wafer over each area. To separate the individual ICs, the ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * The word “epitaxial” is derived from the Greek language and means arranged upon. ** In IC construction, diffusion is the process of deliberately adding controlled impurities at specific loca- tions of substrate by thermal processes.  Integrated Circuits 631 wafer is divided into small chips by a process similar to glass cutting. This is illustrated in Fig. 23.4. It may be seen that hundreds of alike ICs can be produced from a small wafer. This simultaneous mass production is the reason for the low cost of integrated circuits. After the chip is cut, it is bonded to its mounting and connections are made between the IC and external leads. The IC is then encapsulated to prevent it from becoming contaminated by the sur- rounding atmosphere. 23.6 Fabrication of Components on Monolithic IC The notable feature of an IC is that it comprises a number of circuit elements inseparably associated in a single small package to perform a complete electronic function. This differs from discrete assem- bly where separately manufactured components are joined by wires. We shall now see how various circuit elements (e.g. diodes, transistors, resistors etc.) can be constructed in an IC form. Fig. 23.5 (i) Diodes. One or more diodes are formed by diffusing one or more small n-type deposits at appropriate locations on the substrate. Fig. 23.5 shows how a diode is formed on a portion of sub- strate of a monolithic IC. Part of SiO2 layer is etched off, exposing the epitaxial layer as shown in Fig. 23.5 (i). The wafer is then put into a furnace and trivalent atoms are diffused into the epitaxial layer. The trivalent atoms change the exposed epitaxial layer from n-type semi-conductor to p-type. Thus we get an island of n-type material under the SiO2 layer as shown in Fig. 23.5 (ii). Next pure oxygen is passed over the wafer to form a complete SiO2 layer as shown in Fig. 23.5 (iii). A hole is then etched at the centre of this layer ; thus exposing the n-epitaxial layer [See Fig. 23.5 (iv)]. This hole in SiO2 layer is called a window. Now we pass trivalent atoms through the window. The trivalent atoms diffuse into the epitaxial layer to form an island of p-type material as shown in Fig. 23.5 (v). The SiO2 layer is again formed on the wafer by blowing pure oxygen over the wafer [See Fig. 23.5 (vi)]. Thus a p-n junction diode is formed on the substrate. The last step is to attach the terminals. For this purpose, we etch the SiO2 layer at the desired locations as shown in Fig 23.6 (i). By depositing metal at these locations, we make electrical contact with the anode and cathode of the integrated diode. Fig. 23.6 (ii) shows the electrical circuit of the diode. 632 Principles of Electronics Fig. 23.6 (ii) Transistors. Transistors are formed by using the same principle as for diodes. Fig. 23.7 shows how a transistor is formed on a portion of the substrate of a monolithic IC. For this purpose, the steps used for fabricating the diode are carried out upto the point where p island has been formed and sealed off [See Fig. 23.5 (vi) above]. This Fig. is repeated as Fig. 23.7 (i) and shall be taken as the starting point in order to avoid repetition. Fig. 23.7 A window is now formed at the centre of SiO2 layer, thus exposing the p-epitaxial layer as shown in Fig. 23.7(ii). Then we pass pentavalent atoms through the window. The pentavalent atoms diffuse into the epitaxial layer to form an island of n-type material as shown in Fig. 23.7 (iii). The SiO2 layer is re-formed over the wafer by passing pure oxygen [See Fig. 23.7 (iv)]. The terminals are processed by etching the SiO2 layer at appropriate locations and depositing the metal at these locations as shown in Fig. 23.7 (v). In this way, we get the integrated transistor. Fig. 23.7 (vi) shows the electrical circuit of a transistor. (iii) Resistors. Fig. 23.8 shows how a resistor is formed on a portion of the substrate of a monolithic IC. For this purpose, the steps used for fabricating diode are carried out upto the point where n island has been formed and sealed off [Refer back to Fig. 23.5 (iii)]. This figure is repeated as Fig. 23.8 (i) and shall be taken as the starting point in order to avoid repetition. A window is now formed at the centre of SiO2 layer, thus exposing the n-epitaxial layer as shown in Fig. 23.8 (ii). Then we diffuse a p-type material into the n-type area as shown in Fig. 23.8 (iii). The SiO2 layer is re-formed over the wafer by passing pure oxygen [See Fig. 23.8 (iv)]. The terminals are processed by etching SiO2 layer at two points above the p island and depositing the metal at these locations [See Fig. 23.8 (v)]. In this way, we get an integrated resistor. Fig. 23.8 (vi) shows the electrical circuit of a resistor.  Integrated Circuits 633 Fig. 23.8 The value of resistor is determined by the material, its length and area of cross-section. The high-resistance resistors are long and narrow while low-resistance resistors are short and of greater cross-section. Fig. 23.9 (iv) Capacitors. Fig. 23.9 shows the process of fabricating a capacitor in the monolithic IC. The first step is to diffuse an n-type material into the substrate which forms one plate of the capacitor as shown in Fig. 23.9 (i). Then SiO2 layer is re-formed over the wafer by passing pure oxygen as shown in Fig. 23.9 (ii). The SiO2 layer formed acts as the dielectric of the capacitor. The oxide layer is etched and terminal 1 is added as shown in Fig. 23.9 (iii). Next a large (compared to the electrode at terminal 1) metallic electrode is deposited on the SiO2 layer and forms the second plate of the capacitor. The oxide layer is etched and terminal 2 is added. This gives an integrated capacitor. The value of capacitor formed depends upon the dielectric constant of SiO2 layer, thickness of SiO2 layer and the area of cross-section of the smaller of the two electrodes. 23.7 Simple Monolithic ICs It has been seen above that individual components can be integrated in a monolithic IC. We shall now see how an electronic circuit comprising different components is produced in an IC form. The key point to keep in mind is that regardless of the complexity of the circuit, it is mainly a process of etching windows, forming p and n islands, and connecting the integrated components. 634 Principles of Electronics (i) Two-diode IC. Fig. 23.10 (i) shows a two-diode IC with a common anode whereas Fig. 23.10 (ii) shows a two-diode IC with individual anode. Two points are worth noting. Firstly, any circuit [ like the one shown in Fig 23.10 (i) or Fig 23.10 (ii)] is not integrated individually ; rather hundreds of alike circuits are simultaneously fabricated on a wafer. The wafer is then cut into chips so that each chip area represents one circuit. This is the key factor for low cost of ICs and is exerting considerable influence on electronics engineers to switch over to IC technology. Secondly, ICs are usually not as simple as shown in Fig. 23.10. In fact, actual ICs Monolithic IC contain a large number of components. Fig. 23.10 (ii) Another simple IC. Fig.23.11 shows an IC consisting of a capacitor, resistor, diode and transistor connected in series. The interconnection of the circuit elements is accomplished by extend- ing the metallic deposits from terminal to terminal of adjacent components. Fig. 23.11  Integrated Circuits 635 It is interesting to see that p substrate isolates the integrated components from each other. Thus referring to Fig. 23.11, depletion layers exist between p substrate and the four n islands touching it. As the depletion layers have virtually no current carriers, therefore, the integrated components are insulated from each other. 23.8 IC Packings In order to protect ICs from external environment and to provide mechanical protection, various forms of encapsulation are used for integrated circuits. Just as with semi-conductor devices, IC packages are of two types viz. Fig. 23.12 (i) hermatic (metal or ceramic with glass) (ii) non-hermatic (plastics) Plastics are cheaper than hermatic but are still not regarded as satisfactory in extremes of tem- perature and humidity. Although ICs appeared in the market several years ago, yet the standardisation of packages started only in the recent years. The three most popular types of IC packages are shown in Fig. 23.12. (i) Fig. 23.12 (i) shows TO-5 package* which resembles a small signal transistor in both ap- pearance and size but differs in that it has either 8, 10 or 12 pigtail-type leads. The close leads spacing and the difficulty of removal from a printed circuit board has diminished the popularity of this package with the users. (ii) Fig. 23.12 (ii) shows a flat pack container with 14 leads, seven on each side. (iii) Fig. 23.12 (iii) shows the dual-in-line (DIL) pack in 14-lead version. The 14-pin DIL is the ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * This was the earliest type of package and it was natural for the semi-conductor manufactures to use modified transistor cases. 636 Principles of Electronics most popular form and has seven connecting pairs per side. The pairs of pins of this pack are in line with one another, the pins being 2.5 mm apart to allow IC to be fitted directly into the standard printed circuit boards. 23.9 IC Symbols In general, no standard symbols exist for ICs. Often the circuit diagram merely shows a block with numbered terminals. However, sometimes standard symbols are used for operational amplifiers or digital logic gates. Some of the symbols used with ICs are shown below. Fig. 23.13 Fig. 23.14 Fig. 23.13 shows the symbol of an IC r-f amplifier containing 3 transistors, 3 resistors and 8 terminals. Similarly, Fig. 23.14 shows an IC audio amplifier which contain 6 transistors, 2 diodes, 17 resistors and has 12 terminals. 23.10 Scale of Integration An IC chip may contain as large as 100,000 semiconductor devices or other components. The relative number of these components within the chip is given by referring to its scale of integration. The following terminology is commonly used. Scale of integration Abbreviation Number of components Small *SSI 1 to 20 Medium MSI 20 to 100 Large LSI 100 to 1000 Very large VLSI 1000 to 10,000 Super large SLSI 10,000 to 100,000 23.11 Some Circuits Using ICs Integrated circuits are fairly complex because they contain a large number of circuit components within a small semiconductor chip. While studying circuits using ICs, we are more concerned with the external connections to the IC rather than what is actually going on inside. (i) IC Fixed 5-volt Voltage Regulator. The IC voltage regulator is a device that is used to hold the output voltage from a dc power supply constant as the input voltage or load current changes. For example, LM 309 (fixed postive) provides a + 5 V d.c. output. This regulator is frequently used in digital circuits. Fig. 23.15 shows the circuit of the voltage regulator using LM 309. It is a three terminal device with terminals labelled as input, output and ground terminal. It provides a fixed 5 V between the output and ground terminals. ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * SSI stands for small scale integration.  Integrated Circuits 637 Fig. 23.15 The LM 309 has a number of advantages over the zener diode. First, it is much more accurate than the zener diode. Secondly, there is built-in overload protection. The LM 309 also has overheat- ing protection. If the internal temperature becomes excessive, it shuts off until the temperature is reduced, at which point it will start up again. (ii) IC Adjustable Voltage Regulator. Sometimes, we want a voltage regulator whose voltage we can vary. An example of such a voltage regulator is LM 317 whose schematic diagram is shown in Fig. 23.16. By varying the value of R2, the output voltage of the regulator can be adjusted. The following equation is used to determine the regulated d.c. output voltage for an LM 317 regulator circuit : ⎛R ⎞ Vout = 1.25 ⎜ 2 + 1 ⎟ R ⎝ 1 ⎠ Example 23.1. In LM 317 voltage regulator shown in Fig. 23.16, R2 is adjusted to 2.4 kΩ. If the value of R1 is 240 Ω, determine the regulated d.c. output voltage for the circuit. Fig. 23.16 ⎛ R2 ⎞ Solution. Vout = 1.25 ⎜ R + 1⎟ ⎝ 1 ⎠ ⎛ 2.4 kΩ ⎞ = 1.25 ⎜ + 1⎟ = 13.75 V ⎝ 240 Ω ⎠ (iii) The 555 Timer as monostable multivibrator. Fig. 23.17 shows the circuit of the 555 timer as a monostable multivibrator. The R and C are the external components whose values deter- mine the time T (in seconds) for which the circuit is on. This time is given by ; T = 1.1 RC 638 Principles of Electronics Fig. 23.17 Example 23.2. The monostable multivibrator like the one in Fig. 23.17 has the values of R = 1.2 kΩ and C = 0.1 μF. Determine the time T for which the circuit is on. Solution. The time T for which the circuit is on is given by ; 3 –6 T = 1.1 RC = 1.1(1.2 × 10 ) (0.1 × 10 ) –6 = 132 × 10 s = 132 μs (iv) The 555 Timer as astable multivibrator. Fig. 23.18 shows the 555 timer as an astable multibrator. Note that the circuit contains two resistors (R1 and R2) and one capacitor (C) and does not have an input from any other circuit. The lack of a triggering signal from an external source is the circuit recognition feature of the astable multivibrator. Fig. 23.18 The time T1 for which the output is ‘high’ is given by ; T1 = 0.694 (R1 + R2) C The time T2 for which the output is ‘low’ is given by ;  Integrated Circuits 639 T2 = 0.694 R2C ∴ Total period T for the oscillation is T = T1 + T2 = 0.694 (R1 + 2 R2) C The frequency f of the astable multivibrator is given by ; 1= 1 = 1.44 f = T 0.694 (R1 + 2R2 ) C (R1 + 2R2 ) C Note that f will be in Hz if resistance is in ohms and capacitance in farads. Example 23.3. Determine the frequency of the circuit shown in Fig. 23.18. Given that R1 = 3 kΩ ; R2 = 2.7 kΩ and C = 0.033 μF. Solution. The frequency of the circuit is given by ; 1.44 f = ( R + 2R ) C 1 2 3 Here R1 + 2R2 = 3 kΩ + 2 × 2.7 kΩ = 8.4 × 10 Ω ; C = 0.033 μF = 0.033 × 10– 6 F 1.44 ∴ f = (8 ⋅ 4 × 103) (0.033 × 10 − 6 ) = 5.19 × 103 Hz = 5.19 kHz (v) Op-Amp Half-wave Rectifier. Fig. 23.19 shows the half-wave rectifier using an *Op- Amp. The use of Op-Amp greatly reduces the effect of diode offset voltage and allows the circuit to be used in the millivolt region. Fig. 23.19 When the input signal goes positive, the output of Op-Amp goes positive and turns on the diode. The circuit then acts like a voltage follower and the positive half-cycle appears across the load resistor RL. On the other hand, when the input goes negative, the Op-Amp output goes negative and turns off the diode. Since the diode is open, no voltage appears across the load resistor RL. Therefore, the voltage across RL is almost a perfect half-wave signal. (vi) Logarithmic amplifier. A logarithmic amplifier produces an out- put voltage that is proportional to the logarithm of the input voltage. If you place a **diode in the feedback loop of an Op-Amp as shown in Fig. 23.20, you have a log amplifier. The output is limited to a maximum value of about 0.7V be- cause the diodes logarithmic character- istic is limited to voltages below 0.7V. Fig. 23.20 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ * Now-a-days, Op-Amp is produced as an IC. ** The forward characteristic of a diode is logarithmic upto a forward voltage of about 0.7V. 640 Principles of Electronics Also, the input must be positive when the diode is connected in the direction shown in Fig. 23.20. To handle negative inputs, you should reverse the direction of the diode. It can be shown that the output voltage of the circuit shown is given by ; ⎛ V ⎞ Vout = – (0.025 V) loge ⎜ in ⎟ ⎝ I R R1 ⎠ where IR = reverse leakage current of the diode For example, if Vin = + 2 V, R1 = 100 kΩ and IR = 50 nA, then, ⎛ 2V ⎞ Vout = – (0.025) loge ⎜ −9 3 ⎟ ⎝ (50 × 10 ) (100 × 10 ) ⎠ = – (0.025) loge (400) = – 0.15 V (vii) Constant-current source. A constant current source delivers a load current IL that re- mains constant when the load resistance RL changes. Fig. 23.21 shows the basic circuit of a constant current source. Since the inverting ( – ) input of the Op-Amp is at virtual ground (0V), the value of Ii is determined by Vin and Ri i.e. V Ii = in Ri Fig. 23.21 The internal impedance of Op-Amp is extremely high (ideally infinite) so that practically all of Ii flows through RL. Since Ii = IL, V ∴ IL = in Ri Note that load resistance RL does not appear in this equation. Therefore, the load current (IL) is independent of load resistance RL. If RL changes, IL remains constant as long as Vin and Ri are held constant. In other words, the load is driven by a constant current source. MULTIPLE-CHOICE QUESTIONS 1. An IC has................. size. 2. ICs are generally made of................. (i) very large (i) silicon (ii) germanium (ii) large (iii) copper (iv) none of the above (iii) extremely small 3............... ICs are the most commonly used. (iv) none of the above (i) thin film (ii) monolithic (iii) hybrid (iv) none of the above  Integrated Circuits 641 4. The most popular form of IC package is 10. ICs are used in.................................. (i) linear devices only (i) DIL (ii) flatpack (ii) digital devices only (iii) TO-5 (iv) none of the above (iii) both linear and digital devices 5.................. cannot be fabricated on an IC. (iv) none of the above (i) transistors (ii) diodes 11. A transistor takes................. inductor on a (iii) resistors silicon IC chip. (iv) large inductors and transformers (i) less space than 6. An audio amplifier is an example of.............. (ii) more space than (i) digital IC (ii) linear IC (iii) same space as (iv) none of the above (iii) both digitial and linear IC 12. The most popular types of ICs are................. (iv) none of the above (i) thin-film (ii) hybrid 7. The active components in an IC are............. (iii) thick-film (iv) monolithic (i) resistors (ii) capacitors 13. Digital ICs process................. (iii) transistors and diodes (i) linear signals only (iv) none of the above (ii) digital signals only 8. We use................. ICs in computers. (iii) both digital and linear signals (i) digital (ii) linear (iv) none of the above (iii) both digital and linear 14. Operational amplifiers use................. (iv) none of the above (i) linear ICs (ii) digital ICs 9. The SiO2 layer in an IC acts as................. (iii) both linear and digital ICs (i) a resistor (iv) none of the above (ii) an insulating layer 15. Which of the following is most difficult to (iii) mechanical output fabricate in an IC ? (iv) none of the above (i) diode (ii) transistor (iii) FET (iv) capacitor Answers to Multiple-Choice Questions 1. (iii) 2. (i) 3. (ii) 4. (ii) 5. (iv) 6. (ii) 7. (iii) 8. (i) 9. (ii) 10. (iii) 11. (i) 12. (iv) 13. (iii) 14. (ii) 15. (iv) Chapter Review Topics 1. What is an integrated circuit ? Discuss the relative advantages and disadvantages of ICs over discrete assembly. 2. How will you make a monolithic IC ? 3. Explain how (i) a diode (ii) a transistor (iii) a resistor and (iv) a capacitor can be constructed in a monolithic integrated circuit. 4. Explain how electronic circuit consisting of different components can be constructed in a monolithic IC. 5. Write short notes on the following : (i) Epitaxial layer (ii) IC packages (iii) IC symbols Discussion Questions 1. Why are ICs so cheap ? 2. Why do ICs require low power ? 3. Why cannot we produce ICs of greater power ? 4. Why are ICs more reliable than discrete assembly ? 5. Why is DIL IC package the most popular ?