CS 3510 Comp&Net Arch - Kennesaw State Universityksuweb.kennesaw.edu/~khoganso/CS4490_SpecTop_F16/...CS 3510 Comp&Net Arch Transistors & Gates Dr. Ken Hoganson © 2010. CS 3510 Comp&Net

CS 3510 CS 3510 Comp&NetComp&Net ArchArch

Transistors & Gates

Dr. Ken Hoganson © 2010

CS 3510 CS 3510 Comp&NetComp&Net Arch. Dr. Ken Hoganson, Copyright Arch. Dr. Ken Hoganson, Copyright ©© 20102010

3-Input AND from Transistors

Illustrates construction of gatesIllustrates the “transistor bleed-through” problem that affects the AND circuit.Illustrates basic use of IDL-800


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)



Connection to Power

+ 5 volt power supply.

Connects to top transistor

Next slide shows the connection to power.

A

B

Out

C

V+



Connection to Ground

A

B

Out

C

V+

After the output.

Through the current-limiting resistor.



Connection to Logic Switches

A

B

Out

C

V+

Switches connect to each transistor.

Switches are either:

0-off, no voltage,

or

1-On, +5 volts



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.



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.



Voltage – 1 input on

A

B

Out

C

V+

2.13

Illustrates the “transistor bleed-through” effect.



Voltage – 2 inputs on

A

B

Out

C

V+

2.84


Two transistors, larger voltage detected.

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



Voltage 3 inputs on

A

B

Out

C

V+

4.07



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

A

B

Out

C

V+

2.83


Two transistors, larger voltage detected.

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



Use NANDs or NORsNeed to support AND, OR and NOT as Boolean operationsManufacturing cost: Single silicon layering

don’t need to support two places (layers) to connect resistors, or measure outputAND/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 gateAvoids AND “transistor bleed-through”problemActual modern logic implementations will vary


NAND gateChanging the location for sampling output voltage reverses the operation.Relocate the current limiting resistor.

A

B

Out

C

V+

Out

A

B

C

V+AND NAND



Close-up of transistors in series, with:

• Output ahead of the transistors• Current-limiting resistor• Three input wires from switches


Close-up of switches

•One switch for each transistor base


Connection to DVM and LED

•Note, that the output is high (4.69v)

•And, the LED is “ON”


No problem with “Transistor Bleed-Though”

•Note that two switches are ON.

•With the AND, this produces a 2.8v output.

CS 3510 CS 3510 Comp&NetComp&Net Arch. Dr. Ken Hoganson, Copyright Arch. Dr. Ken Hoganson, Copyright ©© 20102010No problem with “Transistor Bleed-Though”

•Note that two switches are ON.

•With the AND, this produces a 2.8v output, or an incorrect “1” for the AND.

•Here, it produces a clear “1” at 4.7v, and lights the LED, correct for a NAND.


•Note that all three switches are now ON.


•Note that all three switches are now ON.

•With the NAND, the output is a “0”, at 0.06v, and the LED is OFF.

•Note the large voltage difference between a “0” at 0.06v, and a “1” at 4.69v: a differential of 4.63v

•The voltage differential for the AND is only 4.07-2.87=1.2v!

CS 3510 CS 3510 Comp&NetComp&Net Arch. Dr. Ken Hoganson, Copyright Arch. Dr. Ken Hoganson, Copyright ©© 20102010Caution!!Do not connect inputs A, B, or C directly

to the 5v power supply, as there is no current-limiting resistor between the inputs and ground.

The logic switches on the IDL-800 are “conditioned” to control their response.

In actuality, the inputs to a logic gate, are generally other logic devices, and are NOT directly connected to the power supply (see diagram).

Note that there are now other implementations of logic gates, using different technologies, using less current, lower voltages, and switching faster. This is the early “classic”technology.

Out

A

B

C

V+V+

CS 3510 CS 3510 Comp&NetComp&Net Arch. Dr. Ken Hoganson, Copyright Arch. Dr. Ken Hoganson, Copyright ©© 20102010End of LectureEnd of Lecture

End Of

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CS 3510 Comp&Net Arch - Kennesaw State Universityksuweb.kennesaw.edu/~khoganso/CS4490_SpecTop_F16/...CS 3510 Comp&Net Arch Transistors & Gates Dr. Ken Hoganson © 2010. CS 3510 Comp&Net