Introduction to Digital Electronics: The Integrated Circuit

In digital devices, there re only two values, usually referred to as 0 and 1. 1 - there is a voltage (usually 5 volts) 0 – means there is no voltage or 0 volts.

Integrated Circuits (IC) an electrical lay-out etched on thin, small, layers of semiconductor materials, incorporating or integrating various components inside, with the result of having a single device perform a particular function. The IC cannot be seen as it is completely covered by the package, except in certain types of chips called EPROMs, where there is a small circular opening or window and what you will see is a very small rectangular shaped shiny object- with very, very thin wires around it, that is the integrated circuit.

ADVANTAGES OF INTEGRATED CIRCUITS Integrated Circuits have low power consumptions. Video cameras can survive on small amounts of power because of their multi-function capabilities, miniature size and its semiconductor properties. ICs operate even on currents as low as a few milliamperes.

Integrated circuits incorporate several functions and circuitry in one small, thin rectangular-shaped object. Using the theories of doping, it was possible to incorporate diode as well as transistor circuits in a very small area. Instead of using all of these components, you just need a single IC and minimizing your worry about design problems. See how video cameras become smaller and smaller nowadays? Or how computers become faster? This is because some ICs manufactured nowadays have incorporated functions of several older ICs. Imagine an old computer as big as a large office room, being outperformed by today’s powerful notebook size computers.

DISADVANTAGES OF INTEGRATED CIRCUITS When an IC is damaged, you cannot repair it. You have to replace it. Since all the components are integrated. The sensitivity of the IC makes it important to provide the proper packaging and storing for it. The IC is also a device created under a clean environment, having just enough impurities to operate properly. Exposure to the outside world might cause damage to the IC.

ICs that are sensitive to static electricity can easily be damaged by it. We are one source of static electricity. Yes we can destroy an IC by just holding it in the pins. Why is this so? We carry static electricity, which had been accumulated, for one thing, by rubbing with other objects. So when you touch an IC pin, a static electricity is discharged, transferring current into the IC through the pins. An IC is a current-sensitive device and a large amount of current passing through any of the pins might destroy the chip.

FAMILIES OF INTEGRATED CIRCUITS Number of components Packaging Purpose

Types of ICs According to the Number of Components This implies the number of miniaturized parts an integrated circuit has. SSI (Small Scale Integration) – For ICs with only a few transistorized components , mostly less than twenty. MSI (Medium Scale Integration) – This group includes ICs with 20 to a few hundred transistorized components.

LSI (Large Scale Integration) – This involves ICs which have components numbering in the thousands. One LSI chip is equivalent to several MSI components or several hundreds or thousands of SSI components. VLSI (Very Large Scale Integration) – This comprises about 100,000 to as high as several million miniaturized components in one chip. This implies many functions that can be performed by a VLSI chip.

Types of ICs According to Packaging SIP (Single In-Line Package) – As the name suggests, Single In-Line Package contain pins aligned only one side, as seen in this type of package can only accommodate a few pins, since having to many pins using an SIP would make the chip longer. This type only has a few applications, an example of which is a resistor pack.

DIP (Dual In-Line Package) – The pins are arranged only on two sides of the package and are arranged in a single line. Small ICs and the first microprocessors are DIPs. QIP (Quad In-Line Package) – The pins are arranged on all four sides of the package, which has a square shape. PGA (Pin Grid Array) – This is similar to QIP but it runs several layers deep. TSOP (Thin-Small-Outline Package) – A special quad package, but for smaller ICs like memory components.

Types of ICs According to Function General Purpose Integrated Circuits – some ICs were designed for ordinary use. Hybrid Integrated Circuits – created by some who would like to combine functions of several general ICs and put them into a single IC. Application Specific Integrated Circuits – this is more complex than the hybrid as the entire purpose of the device will be placed in one chip.

BASIC LOGIC GATES In studying digital integrated circuits, one must start with the simplest group of circuits, the SSIs. Since these devices contain only a maximum of 10 transistorized components inside, these chips normally contain a function used in boolean algebra. Switching functions using boolean algebra is the simplest operation used in digital circuits, since it only involves a zero (0) and a one(1), much like the false (if zero) and true (if one) signals of boolean algebra.

THE NOT GATE  an inverter or NOT gate is a logic gate which implements logical negation. The truth table is shown In equation form Y=A INPUT OUTPUT A NOT A 1

THE AND GATE  is a basic digital logic gate that implements logical conjunction - it behaves according to the truth table. This implies the statement if any among the list is false, then the expression is false. Y=AB INPUT OUTPUT A B Q 1

THE OR GATE This type of gate has two or more inputs, and if we follow simple logic, this implies the statement if any among the list is true, then the expression is true. Y=A+B Y INPUT OUTPUT A B Y 1

THE NAND GATE This type of gate has two or more inputs, and it does the opposite of the And gate. That is why it is called NAND-Negative AND. Y=AB Y INPUT OUTPUT A B Y 1

THE NOR GATE This type of gate has two or more inputs, and it does the opposite of OR – Negative OR. Y=A+B Y INPUT OUTPUT A B Y 1

THE XOR GATE This type of gate has two or more inputs, and it follows the exclusive OR Logic. This means if the inputs are similar, the output is ‘0’. If the inputs are not similar then the output is ‘1’. Y=A+ B where + is the symbol for XOR. Y INPUT OUTPUT A B Y 1

PACKAGING LOGIC GATES Most of today’s SSIs are cased in DIPs, or dual-in-line packages. Each pin corresponds to a number, with pin number 1 can be as found in the drawing. This part of the IC is indicated by the half crescent found on the IC, or by just looking at the IC label, where pin no.1 is found on the lower left as shown. The numbering of the pins are also shown, following a U-shaped pattern.

Each boolean function in the IC corresponds to a code number Each boolean function in the IC corresponds to a code number. Usually for TTL or Transistor-Transistor Logic Integrated Circuits, the SSIs have such code names as 7404s for inverters, 7408s for AND gates and 7432s for OR Gates

Single-input SSIs in Dual-In-Line Packages The numbers 1 to 14 are called pin numbers Ai denotes input of logic gate i Yi denotes output of logic gate i +Vcc A6 Y6 A5 Y5 A4 Y4 14 13 12 11 10 9 8 1 2 3 4 5 6 7 A1 Y1 A2 Y2 A3 Y3 Vss

Example of Single-input SSI +Vcc A6 Y6 A5 Y5 A4 Y4 INPUT OUTPUT A1 Y1 A2 Y2 A3 Y3 A4 Y4 A5 Y5 A6 Y6 A1 Y1 A2 Y2 A3 Y3 Vss

Two-input SSIs in Dual-In-Line Packages The numbers 1 to 14 are called pin numbers Ai denotes input 1 of logic gate I Bi denotes input 1 of logic gate i. Yi denotes output of logic gate i