chapter1 - Chapter 1 Introduction What is digital design ?...

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Unformatted text preview: Chapter 1 Introduction What is digital design ? Analog v. Digital Digital Devices Digital Abstraction Slide 3 Analog Versus Digital Analog devices process signal that can assume any value across a continuous range and produce results that are also in continuous form. Examples of continuous signal include voltage, current, force, etc.. Digital devices process signals that take on only two discrete values such as 0 and 1 and produces output that can be represented by 0 and 1. de 1 What is Digital Design ? Also referred to as logic design, digital design is concerned with designing digital circuits, devices or systems such as computers. Slide 4 Examples Analog Devices: solid-state devices TV (except for digital TV), telephone, etc. Digital Devices: Computer, CD player, digital TV, digital cellular phone, electronic calculator, DVD, and digital camera. de 2 Advantages of Digital Systems Reproducibility Easy of design via logic design Programmability-digital devices can be reprogrammed Robust to noise and perturbations Slide 7 Gates (cont'd) AND gate OR gate NOT gate de 5 Digital Devices: Gates The most fundamental building blocks of a digital system are gates. A digital system (a chip) consists of many, many gates. They have one or more digital inputs and one digital output. Gates are digital devices that perform various basic logic operations. See Figure 1-1 Slide 8 AND gate Performs the AND logic operation on its inputs and outputs its result. Input output de 6 de 9 Characteristics of 2-Input AND gate Four possible input combinations lead to two di erent outputs. Slide 11 Characteristics of 2-Input OR gate Four possible input combinations lead to two di erent outputs. OR gate Performs the OR logic operation on its inputs and outputs its result. Input output NOT gate Slide 12 e 10 Also referred to as inverter, produces an output value that is the opposite of the input value. Input output Flip-Flop A ip- op (FF) is a device that stores a value of either 0 or 1. The state (stored value) of a ip- op depends on its current clock input. Flip- op can be constructed from gates. It is often used in sequential circuit since it remembers. Memory is made up of FFs. Slide 15 Digital Abstraction Alternatively, high and low are often used to represent 1 and 0 while discussing electronic logic. Outputs Voltage Logic 1 Noise Margin Inputs Logic 1 High 3,5 V Invalid 1.5 V Logic 0 Logic 0 Low e 13 Digital Abstraction Digital circuit deals with analog voltages and currents. Digital abstraction allows analog behavior to be ignored. This can be accomplished by associating a range of voltages with each logic value. For example, the signals in a digital system might be restricted to two levels -5 and + 5 volts, corresponding to two discrete values of 0 and 1. It is necessary to understand the operating environment (e.g., voltage, temperature, loading, ..) under which the digital abstraction can be guaranteed. e 14 Slide 16 Software is widely used in digital design. It can signi cantly reduce design time, design cost, and improve design quality. It has been mainly used for drawing schematic diagrams circuit simulation and modeling testing and debugging timing analysis Software for simulation (e.g. LogicWorks) and programming language (e.g. VHDL) for programming Software for Digital Design Integrated Circuits (cont'd) logic devices. Slide 19 e 17 Based on the size (number of gates) of an IC, it can be classi ed as small-scale integration (SSI), medium-scale integration (MSI), large-scale integration (LSI), and very large-scale integration (VLSI). SSI usually contains less than 20 gates, MSI about 20-200 gates, LSI about 200 to 200,000 gates, and VLSI up to 1 million gates. The latest VLSI has 5 million gates. Integrated Circuits (cont'd) Integrated Circuits A collection of one or more gates fabricated on a single silicon chip to achieve a speci c function is called an integrated circuit or IC for short. Slide 20 e 18 An IC usually consists of \legs", referred to as pins or DIPs (Dual in line). Pins are input/output connectors. The functionality or purpose of each pin can be obtained from the pin diagram or data sheet. e 21 Slide 23 An IC is normally mounted a breadboard, often referred to as printed circuit board (PCB), to connect it with other ICs on the board. IC components are attached to the PCB using surface mount technology (SMT). Printed Circuit Boards Programmable Logic Devices Most digital devices can be programmed or reprogrammed for di erent functionalities without physically replacing or rewiring the devices Programmable Logic Arrays (PLA) Programmable Array of Logic (PAL) e 22 ...
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