Download ch02 - Docjava.com

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
• 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
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 2-1
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
• Periodic clock waveform
– repetitive form
– specific time interval
– successive pulses identical
• Period
• Frequency
• 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.
Engineering Notation
•
•
•
•
•
•
•
•
See Table 2-1
giga
mega
kilo
milli
micro
nano
pico
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
– one bit for each clock period
– telephone lines, intracomputer
• COM ports
• Plug-in cards
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
• COM - 115 kbps
• USB - 12 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.
Parallel Representation
• LPT1
– 8-bit parallel
– 115 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.
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
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.
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
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 2-17
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.
A Diode as a Switch
• Analogous to a water check valve
• Not a perfect short
– See Figure 2-24
• 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 2-24
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 of 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
–
–
–
–
–
–
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
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
–
–
–
–
negative voltage base to emitter
ON
positive voltage or 0 V from base to emitter
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.
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
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 pins
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.
The TTL Integrated Circuit
• DIP - dual-in-line package
– NC - not physically or electrically connected
• Pin Configuration
– see 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 2-39
William Kleitz
Digital Electronics with VHDL, Quartus®
II Version
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
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
• PLCC (plastic leaded chip carrier)
– square with leads on all four sides
– J-bend configuration
– more complex logic
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 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.
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.