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# 3-Input AND from Transistors PowerPoint PPT Presentation

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. V+. A. B. C. Out. Transistors in Series. Construction of 3-Input (A,B,C) AND from transistors.

3-Input AND from Transistors

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### 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.

V+

A

B

C

Out

### Transistors in Series

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

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

• Three inputs (from switches)

V+

A

B

C

Out

### Connection to Power

Next slide shows the connection to power.

+ 5 volt power supply.

Connects to top transistor

V+

A

B

C

Out

### Connection to Ground

After output.

Through the current-limiting resistor.

V+

A

B

C

Out

### Connection to Logic Switches

• Switches connect to each transitor.

• Switches are either:

• 0-off, no voltage,

• or 1-On, +5 volts

V+

A

B

C

Out

2.13

### Measuring Output with the Meter

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

• It measures the voltage differential between those two points.

### 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.

V+

A

B

C

Out

2.13

### Voltage – 1 input on

Illustrates the “transistor bleed-through” effect.

V+

A

B

C

Out

2.84

### Voltage – 2 inputs on

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.

V+

A

B

C

Out

4.07

V+

A

B

C

Out

2.83

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

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.

### 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