1. CHAPTER 2
Logic Gates

2. Contents









Boolean Variables & Truth Tables
OR Operation
AND Operation
NOT Operation
NOR Operation
NAND Operation
The Exclusive- OR Gate
The Exclusive-NOR Gate
INTEGRATED CIRCUIT LOGIC FAMILIES
2

3. Boolean Variables & Truth Tables
LOGIC 0
False
Off
Low
No
Open Switch
LOGIC 1
True
On
High
Yes
Close Switch
3

4. OR Operation
4

5. Timing Diagrams of OR gates
5

6. An application: Alarm System
6

7. AND Operation
7

8. Timing Diagrams of AND gates
8

9. An application: A Seat Belt Alarm
System
-1
-I
9

10. NOT Operation
10

11. NOR Operation
11

12. Negative AND equivalent of a NOR
gate
12

13. An application: An aircraft landing
indicator
13

14. NAND Operation
14

15. Negative OR Equivalent Operation
of the NAND Gate
15

16. An application: A Manufacturing
Plant Tank Indicator
The sensors produce a 5 V level when
the tanks are more than onequarter full.
16

17. The Exclusive- OR Gate
Inputs
A
0
0
1
1
output
B
0
1
0
1
X
0
1
1
0
17

18. The Exclusive-NOR Gate
Inputs
•
equivalence 0
coincidence
X-NOR
to
A
0
0
1
1
output
B
0
1
0
1
X
1
0
0
1
18

19. Timing diagram
19

20. INTEGRATED CIRCUIT LOGIC
FAMILIES
Diode Logic (DL)
 Resistor-Transistor Logic (RTL)
 Diode-Transistor Logic (DTL)
 Transistor-Transistor Logic (TTL)
 Emitter-Coupled Logic (ECL)
 CMOS Logic

20

21. Fan-in & Fan-out

Fan-in


The number of standard loads drawn by an
input to ensure reliable operation. Most inputs
have a fan-in of 1.
Fan-out

The number of standard loads that can be
reliably driven by an output, without causing
the output voltage to shift out of its legal range
of values.
21

22. Comparison of performance characteristics of
CMOS, TTL and ECL logic gates.
Technology
Device
series
Power
dissipation:
Static
At 100 kHz
Propagation
delay time
Fan-out
CMOS
(silicon
gate)
74HC
Std : standard
Schottky
TTL
std
TTL
LS
TTL
S
TTL
ALS
TTL
AS
ECL
74
74LS
74S
74ALS
74AS
10KH
1 uW
0.17
mW
8 ns
CMOS
(metal
gate)
4000B
10
mW
10
mW
10
ns
10
2
mW
2
mW
10 ns
19
mW
19
mW
3 ns
1 mW
25
mW
25
mW
1 ns
20
20
20
8.5
mW
8.5
mW
1.5
ns
40
0.1
mW
50 ns
LS: Low power Schottky
ALS: Advanced Low power Schottky
Schottky
1 mW
4 ns
S:
AS: Advanced
22