3-Input AND from Transistors

CSIS

CSIS 4381

3
-
Input AND from Transistors

•
Illustrates basic use of IDL
-
800

•
Illustrates construction of gates

•
Illustrates the “transistor bleed
-
through” problem
that affects the AND circuit.


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CSIS 4381

Transistors in Series

A

B

Out

C

V+

•
Construction of 3
-
Input (A,B,C)
AND from transistors.

•
Note the resistor and output are at the
“bottom”.

•
Three inputs (from switches)

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CSIS 4381

Connection to Power

Next slide shows the connection to power.

+ 5 volt power supply.

Connects to top transistor

A

B

Out

C

V+

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CSIS 4381

Connection to Ground

A

B

Out

C

V+

After output.

Through the current
-
limiting
resistor.

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CSIS 4381

Connection to Logic Switches

A

B

Out

C

V+

Switches connect to each
transitor.

Switches are either:

0
-
off, no voltage,

or 1
-
On, +5 volts

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CSIS 4381

Measuring Output with the Meter

A

B

Out

C

V+

2.13

•
Digital Volt Meter connects
to output, and to the ground.

•
It measures the voltage
differential between those
two points.

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CSIS 4381

Measuring Output with a LED

The output can be connected to a Light Emitting Diode
(LED) rather than to the DVM.

A voltage of around 2.5 and greater will cause the LED to
light.

The LED is already wired on one end to the ground.

A current limiting resistor ensure that the LED does not
receive too great a voltage and current.

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CSIS 4381

Voltage
–

1 input on

A

B

Out

C

V+

2.13

Illustrates the “transistor
bleed
-
through” effect.

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CSIS 4381

Voltage
–

2 inputs on

A

B

Out

C

V+

2.84

Illustrates the “transistor
bleed
-
through” effect.

Two transistors, larger
voltage detected.

This voltage is large
enough to be detected as a
“1” by the LED.

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CSIS 4381

Voltage 3 inputs on

A

B

Out

C

V+

4.07

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CSIS 4381

“Bleed
-
Through” voltage can light an LED,
and be detected as a “1”

A

B

Out

C

V+

2.83

Illustrates the “transistor
bleed
-
through” effect.

Two transistors, larger
voltage detected.

This voltage is large
enough to be detected as a
“1” by the LED.

CSIS

CSIS 4381

Use NANDs or NORs

•
Need to support AND, OR and NOT as Boolean
operations

•
Manufacturing cost:

–
Single silicon layering

•
don’t need to support two places (layers) to
connect resistors, or measure output

•
AND/OR different layer from NOT

–
Complete set of operations
–

NAND or NOR can be
wired for any logic

•
Fabricate a chip with one type of gate

•
Avoids AND “transistor bleed
-
through” problem

•
Actual modern logic implementations will vary as
technologies evolve