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.
CSIS 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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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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Connection to Ground
A
B
Out
C
V+After output.
Through the current-limiting resistor.
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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
CSIS 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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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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Voltage – 1 input on
A
B
Out
C
V+
2.13
Illustrates the “transistor bleed-through” effect.
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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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Voltage 3 inputs on
A
B
Out
C
V+
4.07
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“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.
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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