Chapter 2 Digital Electronic Signals and Switches Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Digital Signals See Figure 2-1(a) Timing Diagram –voltage versus time –shows logic state Interpretation if not exactly 0V or 5V Use the oscilloscope to view Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Figure 2-1 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Clock Waveform Timing Periodic clock waveform –repetitive form –specific time interval –successive pulses identical Period Frequency f = 1/t p and t p = 1/f Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Engineering Notation See Table 2-1 giga mega kilo milli micro nano pico Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Serial Representation Single electrical conductor Slow –one bit for each clock period –telephone lines, intracomputer COM ports Plug-in cards Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Serial Representation Several standards –V.90, ISDN, T1, T2, T3, USB, Ethernet, 10baseT, 100baseT, cable, DSL COM kbps USB - 12 Mbps Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Parallel Representation Separate electrical conductor for each bit Expensive Very fast Inside a computer External Devices –Centronics printer interface (LPT1) –SCSI (Small Computer Systems Interface) Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Parallel Representation LPT1 –8-bit parallel –115 kBps SCSI –16-bit parallel –160 MBps Bps - BYTES per second Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Switches in Electronic Circuits Make and break a connection Manual switch of electromechanical relay Semiconductor devices –diodes –transistors Manual Switches - Ideal resistances –ON - 0 ohms –OFF - infinite Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Relay as a Switch Electromechanical Relay –contacts –external voltage to operate –magnetic coil energizes NC - normally closed NO - normally open Total isolation –triggering source –output Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Relay as a Switch Disadvantages –several milliamperes of current to operate –slower - several milliseconds vs. micro or nano Energized relay coil Replace source with clock oscillator Timing diagrams See Figure 2-17 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Figure 2-17 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Diode as a Switch Semiconductor Current flow in one direction only Forward-biased –anode more positive than cathode –current flow Reverse-biased –anode equal or more negative than cathode –no current flow Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Diode as a Switch Analogous to a water check valve Not a perfect short –See Figure V across its terminals Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Figure 2-24 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Transistor as a Switch Bipolar transistor –input signal at one terminal –two other terminals become short of open Types –NPN –PNP Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Transistor as a Switch NPN –positive voltage from base to emitter –collector-to-emitter junction short –ON –negative voltage or 0 V from base to emitter –collector-to-emitter junction open –OFF Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

A Transistor as a Switch PNP –negative voltage base to emitter –ON –positive voltage or 0 V from base to emitter –OFF Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

The TTL Integrated Circuit Transistor-transistor logic Inverter –takes digital level input –complements it to the output Transistor Saturation Transistor Cutoff TTL Integrated Circuit –totem-pole output Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

The TTL Integrated Circuit 7404 –hex inverter –six complete logic circuits –single silicon chip –14 pins –7 on a side Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

The TTL Integrated Circuit DIP - dual-in-line package –NC - not physically or electrically connected Pin Configuration –see Figure 2-39 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Figure 2-39 Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

The CMOS Integrated Circuit Complementary Metal Oxide Semiconductor –low power consumption –battery-powered devices –slower switching speed than TTL –sensitive to electrostatic charges Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Surface-Mounted Devices SMD –reduced size and weight –lowered cost of manufacturing circuit boards –soldered directly to metalized footprint –special desoldering tools and techniques –chip densities increased –higher frequencies Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Surface-Mounted Devices SO (small outline) –dual-in-line package –gull-wing format –lower-complexity logic PLCC (plastic leaded chip carrier) –square with leads on all four sides –J-bend configuration –more complex logic Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Summary The digital level for 1 is commonly represented by a voltage of 5 V in digital systems. A voltage of 0 V is used for the 0 level. An oscilloscope can be used to observe the rapidly changing voltage-versus-time waveform in digital systems. Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Summary The frequency of a clock waveform is equal to the reciprocal of the waveform’s speed The transmission of binary data in the serial format requires only a single conductor with a ground reference. The parallel format requires several conductors but is much faster than serial. Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Summary Electromechanical relays are capable of forming shorts and opens in circuits requiring high current values but not high speed. Diodes are used in digital circuitry whenever there is a requirement for current to flow in one direction but not the other. Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Summary The transistor is the basic building block of the modern digital integrated circuit. It can be switched on or off by applying the appropriate voltage at its base connection. TTL and CMOS integrated circuits are formed by integrating thousands of transistors in a single package. They are the most popular ICs used in digital circuitry today. Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version

Summary SMD-style ICs are gaining popularity over the through-hole style DIP ICs because of their smaller size and reduced manufacturing costs. Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version