Digital Electronics
Principles & Applications
Seventh Edition
Roger L. Tokheim
Chapter 1
Digital Electronics
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
INTRODUCTION
• Analog vs. Digital
• Why Digital or Analog?
• Generating a Digital Signal
• Multivibrators
• Defining Logic Levels
• Testing for Digital Signals
• Using a Logic Probe
• Mounting ICs
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Analog vs. Digital
Analog signal- one whose output varies continuously in
step with the input.
Example:
Analog
Digital signal- one whose output varies at discrete voltage levels
commonly called HIGH or LOW (1 or 0).
Example:
HIGH or 1
Digital
LOW or 0
Time
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1. A(n) __________ signal is one whose output
varies at discrete voltage levels commonly
referred to as HIGH or LOW (1 or 0).
digital
2. A(n) __________ signal is one whose
output varies continuously in step with
the input.
analog
3. A sine wave (sinusoidal waveform) is
an example of a(n) __________ signal.
analog
4. A square wave is an example of a(n)
__________ signal.
digital
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Why Digital?
• Data can be stored (memory characteristic
of digital).
• Data can be used in calculations.
• Compatible with display technologies.
• Compatible with computer technologies.
• Systems can be programmed.
• Digital IC families make design easier.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Why Analog?
• Most “real-world” events are analog
in nature.
• Analog processing is usually simpler.
• Analog processing is usually faster.
• Traditional electronic systems were
mostly analog in nature.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1. Most “real world” measurements (like
temperature, speed, pressure, etc.) are
__________ (analog, digital) in nature.
analog
2. Electronic circuits that store information
and make calculations are probably
__________ (analog, digital) in nature.
digital
3. Electronic devices that can be
programmed and have alphanumeric
displays probably contain __________
(analog, digital) circuitry.
4. Traditional circuitry (as in TVs) was
probably __________ (analog, digital)
in nature.
digital
analog
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Generating a Digital Signal (with Switch)
+5 V
0V
HIGH
undefined
LOW
CAUTION:
Note: signal
goes H, L, H,
Switch
bounce
UNDEFINED,
and
finally HIGH.
may cause problems.
time
Debounced Switch
NOTICE– no switch bounce!!
Debouncing
Latch
HIGH
LOW
time
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Multivibrators
One-shot (monostable) - an electronic device that
emits a single pulse when triggered.
Free-running (astable) - an electronic device that
oscillates between two stable states (HIGH and
LOW). Commonly called a clock in digital
systems.
Latch (bistable) - an electronic device that has two
stable states (HIGH and LOW) and must be
triggered to jump from one to the other. Commonly
called a flip-flop. Commonly used as temporary
memory.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Producing a Digital Pulse
One-shot
multivibrator
The PULSE WIDTH is determined
by the design of the multivibrator
and NOT how long the
input pushbutton is pressed.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
A free-running multivibrator produces
a continuous string of digital pulses.
Free-running
multivibrator
Note: This can also be called a clock.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1. A(n) __________ (astable, monostable)
multivibrator is an electronic device that
generates a continuous string of digital pulses.
It may also be called a clock or a freerunning MV.
astable
2. A(n) __________ (astable, monostable) multivibrator
is an electronic device that generates a single digital
pulse when triggered.
monostable
3. A(n) __________ (bistable, monostable) multivibrator
is an electronic device that has two stable states. It is
also called a flip-flop and is used as a latch to hold
data.
bistable
4. A(n) __________ (astable, monostable) multivibrator
is an electronic device that is sometimes called a oneshot MV.
monostable
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Defining Logic Levels
• Logic devices interpret input voltages as either HIGH or LOW.
• TTL or CMOS IC families have their unique voltage profiles.
• Both TTL and CMOS IC input voltage profiles are shown below.
TTL
Family of ICs
CAUTION:
100%
90%
HIGH
HIGH
80%
70%
60%
50%
Undefined
40%
Undefined
30%
20%
LOW
10%
0%
LOW
Voltage
Input voltages in the
UNDEFINED region
may yield unpredictable
results.
CMOS
Family of ICs
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1. An input voltage of +3.5V to a TTL IC (+5V supply) would
be considered a __________ (H, L, undefined) logic level.
HIGH
2. An input voltage of +0.5V to a TTL IC (+5V supply) would
be considered a __________ (H, L, undefined) logic level.
LOW
3. An input voltage of +1V to a CMOS IC (+10V supply) would
be considered a __________ (H, L, undefined) logic level.
LOW
4. An input voltage of +9V to a CMOS IC (+10V supply)
would be considered a __________ (H, L, undefined) logic
level.
5. An input voltage of +1.5V to a TTL IC (+5V supply) would
be considered a __________ (H, L, undefined) logic level.
HIGH
undefined
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Testing for a Digital Signal
• LED Output Indicators
• Logic Probe
• DMM or VOM
• Oscilloscope
• Logic Analyzer
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
+5 V
Transistor-Driven
LED Output Indicator
150 W
Activate
input
Switch
(mouse click)
Positive voltage
at base
of transistor
10 kW
+5 V
Turns on Q1
and LED lights
Q1
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Behavior Versus Logic Levels
TTL
HIGH
LOW
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
CMOS
HIGH
LOW
The logic LOW
indicator lights.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Behavior Versus Logic Levels
TTL
HIGH
LOW
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
CMOS
HIGH
LOW
The logic HIGH
indicator lights.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Behavior Versus Logic Levels
TTL
HIGH
LOW
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
CMOS
HIGH
LOW
The FLOATING
indicator lights.
Note: This response varies with the design of the Logic Probe.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Dynamic Response
The probe toggles
between HIGH
and LOW.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Dynamic Response
Probes stretch narrow
pulses so they are not
missed.
The probe toggles
between HIGH
and LOW.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Logic Probe Dynamic Response
Pulse stretching also
allows high frequencies
to be displayed.
The probe toggles
between HIGH
and LOW.
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
QUIZ
1.
A simple handheld instrument for detecting HIGH,
LOW, and Undefined digital logic levels is called a
__________ (logic analyzer, logic probe).
2. In the lab, a simple LED indicator circuit can be
built using a __________ (transistor, voltage
comparator) to drive the LED.
logic probe
transistor
3. In CMOS (using a 10V power supply), a voltage of
9V would light the __________ (HIGH, LOW,
Undefined) indicator on a logic probe.
HIGH
4. In TTL (using a 5V power supply), a voltage of
0.2V would light the __________ (HIGH,
LOW, Undefined) indicator on a logic probe.
LOW
5. If the input to a logic probe is 50Hz square wave,
the output would __________ (read HIGH, toggle
between HIGH and LOW).
toggle between
HIGH and LOW
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Mounting ICs:
Insertion Technology
Device leads pass through holes in the circuit board.
Solder
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
Mounting ICs:
Surface Mount Technology
Solder
•
•
•
•
•
Devices placed by automatic equipment
Circuit boards cost less (fewer holes)
Higher connection density
Smaller and less expensive products
Difficult to repair
©2008 The McGraw-Hill Companies, Inc. All rights reserved.
REVIEW
• Analog vs. Digital
• Why Digital or Analog?
• Generating a Digital Signal
• Multivibrators
• Defining Logic Levels
• Testing for Digital Signals
• Using a Logic Probe
• Mounting ICs
©2008 The McGraw-Hill Companies, Inc. All rights reserved.