Transcript Chapter 2
Chapter 2 Digital Electronic Signals and Switches William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Digital Signals • Made up of a series of 1’s and 0’s • Timing Diagram – voltage versus time – shows logic state • If not exactly 0V or 5V – Still interpreted as a 0 or a 1 • Use Oscilloscope to view William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Clock Waveform Timing • Precise timing • Periodic clock waveform – repetitive form – specific time interval – successive pulses identical William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. • Period – Length of time between rising or falling edges – Basic unit is seconds • Frequency – The reciprocal of the period – Basic unit is hertz • f = 1/tp and tp = 1/f William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Serial Representation • Single electrical conductor • Slow (relative) – one bit for each clock period – telephone lines, intra-computer William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–5 Serial communication between computers. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Serial Representation • Several standards – V.90, ISDN, T1, T2, T3, USB, Ethernet, 10baseT, 100baseT, cable, DSL, RS-232 • COM - 115 kbps • USB – USB 1.1 12 Mbps – USB 2.0 480 Mbps William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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) William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–7 Parallel communication between a computer and a printer. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Parallel Representation • LPT1 – 8-bit parallel – 115 kBps = 115 kBps x 8 bits/byte = 920 Kbps • SCSI – 16-bit parallel – 160 MBps • Bps - BYTES per second William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–8 Parallel representation of the binary number 01101100. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Basic Electricity • Current – Charged particles which flow from the voltage source through conductive material to a ground – Basic unit - Amp • Voltage – The difference in electrical potential between 2 points of a circuit – Basic unit - Volt • Resistance – The opposition that a material body offers to the passage of an electric current – Basic unit - Ohm Ohm’s Law • Defines the relationship between voltage, current, and resistance • Voltage = Current x Resistance • V = I x R, I = V / R Analogy to Water • Voltage is analogous to pressure • Current is analogous to water flow • Resistance is analogous to flow restrictor Switches in Electronic Circuits • Make and break a connection • Manual Switches - Ideal resistances – ON - 0 ohms – OFF - infinite William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–14 Physical representation of an electromechanical relay: (a) normally closed (NC) relay; (b) normally open (NO) relay; (c) photograph of actual relays. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–14 (continued) Physical representation of an electromechanical relay: (a) normally closed (NC) relay; (b) normally open (NO) relay; (c) photograph of actual relays. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A Relay as a Switch • Disadvantages – several milliamperes of current to operate – slower - several milliseconds vs. micro or nano – Mechanical movement • Less reliable than an electronic component • Advantage – Switch higher currents William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–22 Diode in a series circuit: (a) forward biased; (b) reverse biased. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A Diode as a Switch • Analogous to a water check valve • Not a perfect short – Silicon Diode – 0.7 volts • 0.7 V across its terminals William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–25 Forward-biased diode in an electric circuit: (a) original circuit; (b) equivalent circuit showing the diode voltage drop and Vout = 5 – 0.7 = 4.3 V. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A Transistor as a Switch • Bipolar transistor – input signal at one terminal – two other terminals become short or open • Types – NPN – PNP William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A Transistor as a Switch • NPN – ON • positive voltage from base to emitter • collector-to-emitter junction short – OFF • negative voltage or 0 V from base to emitter • collector-to-emitter junction open William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A Transistor as a Switch • PNP – ON • negative voltage base to emitter • collector-to-emitter junction short – OFF • positive voltage or 0 V from base to emitter • collector-to-emitter junction open William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–28 NPN transistor switch: (a) transistor ON; (b) transistor OFF. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–31 Equivalent circuits: (a) transistor OFF; (b) transistor ON. The TTL Integrated Circuit • Transistor-transistor logic – Most widely used of IC technology • Transistor Saturation (Vin = 5V) • Transistor Cutoff (Vin = 0V) • Inverter – takes digital level input – complements it to the output William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The TTL Integrated Circuit • 7404 – – – – – hex inverter six complete logic circuits single silicon chip 14 pin DIP (Dual Inline Package) 7 on a side William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2-39 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–37 Schematic of a TTL inverter circuit. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–40 Photograph of three commonly used ICs: the 74HC00, 74ACT244, and 74150. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. The CMOS Integrated Circuit • Complementary Metal Oxide Semiconductor – – – – low power consumption battery-powered devices slower switching speed than TTL sensitive to electrostatic charges William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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 William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Surface-Mounted Devices • SO (small outline) – – – – dual-in-line package gull-wing format lower-complexity logic 30% to 50% less space then DIP • PLCC (plastic leaded chip carrier) – – – – square with leads on all four sides J-bend configuration more complex logic requires less space than SO package William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–42 Typical surface-mount devices (SMDs) and their footprints: (a) small outline (SO); (b) plastic leaded chip carrier (PLCC); (c) photograph of actual SMDs; (d) photograph of SMDs mounted on a printed-circuit board. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Figure 2–42 (continued) Typical surface-mount devices (SMDs) and their footprints: (a) small outline (SO); (b) plastic leaded chip carrier (PLCC); (c) photograph of actual SMDs; (d) photograph of SMDs mounted on a printedcircuit board. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Summary • The frequency of a clock waveform is equal to the reciprocal of the waveform’s time • 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. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 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. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Summary • SMD-style ICs are gaining popularity over the through-hole style DIP ICs because of their smaller size and reduced manufacturing costs. William Kleitz Digital Electronics with VHDL, Quartus® II Version Copyright ©2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.