4.1 Digital IC

Digital ICs are a collection of resistors, diodes, and transistors fabricated on a single piece of semiconductor material, usually silicon called substrate which is commonly referred to as a "chip". The chip is enclosed in a protective plastic or ceramic package from which in extend for connecting IC to other devices,

An integrated circuit, may it be analog or digital, offers many advantages over discrete components. Its small size and weight, low power consumption, high reliability, and improved performance contributes much to circuit miniaturization and more powerful features of digital systems.

The pictures included in this chapter show some applications for digital ICs.

Microprocessors, also called silicon chips, are typically embedded in a protective casing. The wires radiating from the silicon chip connect to short metal legs that are soldered into integrated circuit boards.

Part 4.1.1 Integrated Circuit of a Computer

An integrated circuit (IC) consists of many circuit elements such as transistors and resistors fabricated on a single piece of silicon or other semiconducting material. The tiny microprocessor shown here is the heart of the personal computer (PC). Such devices may contain several million transistors and be able to execute over 100 million instructions per second. The rows of leglike metal pins are used to connect the microprocessor to a circuit board.

Figure 1. Example of a Digital IC, what is inside, and the function it performs.

Digital Logic and NOR Gate Circuitry

This circuit uses 4 NOR gates, each of which makes the decision "neither A nor B." The NOR operation yields an output of 0 whenever one or more of the input values is 1. The table shows input values (A, B) and output value (F) for the NOR gate. A circuit map (bottom) shows the layout of a NOR gate and its components, indicating voltage values when the inputs are 0,0 and the output is 1.

Part 4.1.2 Computer Circuit Board

Integrated circuits (ICs) make the microcomputer possible; without them, individual circuits and their components would take up far too much space for a compact computer design. Also called a chip, the typical IC consists of elements such as resistors, capacitors, and transistors packed on a single piece of silicon. In smaller, more densely-packed ICs, circuit elements may be only a few atoms in size, which makes it possible to create sophisticated computers the size of notebooks, A typical computer circuit board features many integrated circuits connected together.

Part 4.1.3 IC Packages

Digital ICs come in several types of packaging, the most common of which is the DIP (dual-in-line package). Other types include the ceramic flat pack, surface mounted L and J-lead packages.

Figure 2 Comparison of DIP (in the left) and J-lead (in the right)

Part 4.1.3 IC Numbering

ICs are identified by the code top-marked on its surface. Aside from the manufacturer's code, ICs are numbered based on the given format:

Shown in the table below are examples of common TTL ICs

Table 1. Example of common TTL ICs

Device Number	Description	Number of Gates
7400	Quadruple 2-input NAND gates	4
7402	Quadruple 2-input NAND gates	4
7404	Quadruple 2-input NAND gates	6
7408	Quadruple 2-input NAND gates	4
7410	Quadruple 2-input NAND gates	3
7420	Quadruple 2-input NAND gates	2
74138	Quadruple 2-input NAND gates	>25

Part 4.1.4 IC Schematic Symbols Showing Pin Designations

Logic gates are available in IC forms; they are fabricated the same way as analog ICs are made. Below are some examples of SSI logic ICs showing the pin assignments and another set of examples shows the type of gate each IC represents.

Figure 3. Example of SSI Logic ICs

The examples below identifies the ICs to what it contain and it would be a guide in wiring gates but what appears in an actual logic diagram, are gates drawn, connected and labeled properly as will be shown in the example below.

Figure 4. Pinouts of Various SSI Logic ICs (source: bucknell.edu)

Shown below are example of ICs used in most logic diagram, these are standard symbols with inputs shown on the left and output on the right side of the gate.

Figure 5 Common Standard symbol of Logic Gates

The diagram below shows a part of a circuit utilizing quadruple 2-input NOR gates (MC14001IC - CMOS). Note how the gates are connected and labeled.

Figure 6. Sample of circuit utilizing quadruple 2-input NOR gates (MC14001IC - CMOS).

There are rules and standards to follow in the use of electronic components to have an effective and efficient circuit. Reference data sheet and IC cookbooks are made available to facilitate the choice and placement of ICs. The important parameters will be covered in the next sections.