Computer Technology
Transistor to computer gates
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
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Computer
Transistor
 Central Processor Unit or CPU
 Motherboard

`
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
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http://upload.wikimedia.org/wikipedia/commons/4/4e/Diopsis.jpg
The Transistor
Amplifier
 Remote controlled switch
 It is the basic element of the computer
 A modern computer core (CPU) can
have over 200,000,000 transistors (200
million).

©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
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Transistor in digital electronics
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

In modern electronics most transistors are
used as a switch that is controlled by an
input signal.

This is accomplished by giving the
transistor a large enough signal to snap it
on completely or…

giving it a small enough signal to turn it off.

Commonly these states (on/off) are
represented by a zero (off) or one (on).
Transistors
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Transistors:
common circuits for computers

Transistors are used to form many basic
circuits in computers.

These are the five basic circuits:
◦
◦
◦
◦
◦
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

Not
AND
NAND (Not AND)
OR
NOR (Not OR)
They are named after the logic function
they provide.
NOT gate
Also called a inverter
 It inverts the input

NOT gate
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
Output Q
0
1
1
0
Not gate using a NPN transistor
If Input A is off then the gate is off and VCC
supplies power to the Output Q.
NOT gate
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
Output Q
0
1
1
0
Not gate using a NPN transistor
If Input A is on then the gate is on and
Output Q is pulled down to ground.
NOT gate
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
Output Q
0
1
1
0
Transistor-AND gate
The basic AND gate has two inputs
 If both inputs are high, then the output is
high
 Otherwise the output is low

©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
AND gate
Input A Input B Output Q
0
0
0
0
1
0
1
0
0
1
1
1
The AND gate using PNP transistors
If Input A or Input
B are off then VCC
turns on the Q3
and grounds the
Output Q.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Q3
AND gate
Input A Input B Output Q
0
0
0
0
1
0
1
0
0
1
1
1
The AND gate using PNP transistors
If Input A AND
Input B are on
then Q3 is turned
off and Output Q is
pulled high.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Q3
AND gate
Input A Input B Output Q
0
0
0
0
1
0
1
0
0
1
1
1
Transistor-NAND gate
The basic NAND gate has two inputs
 If any inputs are high, then the output is
low
 Otherwise the output is high

©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
NAND gate
Input A Input B Output Q
0
0
1
0
1
1
1
0
1
1
1
0
The NAND gate using PNP transistors
If Input A and
Input B are on
then Output Q is
pulled to ground.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
NAND gate
Input A Input B Output Q
0
0
1
0
1
1
1
0
1
1
1
0
The NAND gate using PNP transistors
If Input A or Input B
are off then Output
Q is pulled high.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
NAND gate
Input A Input B Output Q
0
0
1
0
1
1
1
0
1
1
1
0
Transistor-OR gate
The basic OR gate has two inputs
 If either input is high, then the output is
high
 Otherwise the output is low

©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
0
0
1
1
OR gate
Input B Output Q
0
0
1
1
0
1
1
1
Transistor-OR gate with PNPs
If Input A or
Input B are on
then Output Q
is pulled high.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
0
0
1
1
OR gate
Input B Output Q
0
0
1
1
0
1
1
1
Transistor-OR gate with PNPs
If Input A and
Input B are OFF
then Output Q is
pulled low.
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Input A
0
0
1
1
OR gate
Input B Output Q
0
0
1
1
0
1
1
1
Transistor-NOR gate
The basic NOR gate has two inputs
 If either input is high, then the output is
low
 Otherwise the output is high

©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
NOR gate
Input A Input B Output Q
0
0
1
0
1
0
1
0
0
1
1
0
Transistor-NOR gate with PNPs
©2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
NOR gate
Input A Input B Output Q
0
0
1
0
1
0
1
0
0
1
1
0