1. Principles & Applications
Digital Electronics
Principles & Applications
Fifth Edition
Roger L. Tokheim
Chapter 1
Digital Electronics
© Glencoe/McGraw-Hill

2. CHAPTER 1 PREVIEW 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

3. 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:
Digital
HIGH or 1
LOW or 0
Time

4. 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.

5. 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.

6. GENERATING A DIGITAL SIGNAL (WITH SWITCH)
0 V
time
HIGH
undefined
LOW
+5 V
Note: signal goes H, L, H,
UNDEFINED, and finally HIGH.
CAUTION:
Switch bounce
may cause problems.
Debounced Switch
Debouncing
Latch
time
HIGH
LOW

7. 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.

8. PRODUCING A DIGITAL PULSE
One-shot
multivibrator
The output pulse width is determined by the multivibrator and not how long the button is pressed.

9. Note: This can also be called a clock.
A free-running multivibrator produces a continuous string of digital pulses.
Free-running
multivibrator
Note: This can also be called a clock.

10. TEST
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 free-running 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 one-shot MV __________
monostable
(Left click mouse for next question or answer)

11. 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.
CAUTION: Input voltages in the UNDEFINED region may yield
unpredictable results.
TTL
family of ICs
CMOS
family of ICs
HIGH
100%
90%
80%
70%
60%
50%
40%
30%
20%
10% 0%
HIGH
Voltage
Undefined
Undefined
LOW
LOW

12. TEST 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 __________
HIGH
5. An input voltage of +1.5V to a TTL IC (+5V supply) would be
considered a ___ (H, L, undefined) logic level __________
undefined

13. TESTING FOR A DIGITAL SIGNAL
LED output indicators
Logic probe
DMM or VOM
Oscilloscope
Logic Analyzer

14. TRANSISTOR-DRIVEN LED OUTPUT INDICATOR
150 W
10 kW
+5 V

15. LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS
TTL
CMOS
100%
90%
80%
HIGH
70%
HIGH
60%
50%
40%
30%
20%
10%
LOW
LOW 0%
The logic LOW
indicator lights.

16. LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS
TTL
CMOS
100%
90%
HIGH
80%
70%
HIGH
60%
50%
40%
30%
20%
LOW
LOW
10% 0%
The logic HIGH
indicator lights.

17. LOGIC PROBE BEHAVIOR VERSUS LOGIC LEVELS
TTL
CMOS
100%
90%
HIGH
80%
70%
HIGH
60%
50%
40%
30%
20%
LOW
LOW
10%
The FLOATING
indicator lights. 0%
Note: This response varies with the design of the Logic Probe.

18. LOGIC PROBE DYNAMIC RESPONSE
The probe toggles
between HIGH
and LOW.

19. LOGIC PROBE DYNAMIC RESPONSE
Probes stretch narrow pulses so they are not missed.
The probe toggles
between HIGH
and LOW.

20. LOGIC PROBE DYNAMIC RESPONSE
Pulse stretching also allows high frequencies to be displayed.
The probe toggles
between HIGH
and LOW.

21. MOUNTING ICs: INSERTION TECHNOLOGY
Device leads pass through holes in the circuit board.
Solder

22. SURFACE MOUNT TECHNOLOGY
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