CMOS Logic Gate Technology

Implementation of Boolean logic in real world

Faculty of Electrical Engineering, Automatics, Computer Science and

Electronics

Paweł Zegartowski

The idea of Logic Gate

• What a logic gate is?

• A logic gate is a physical model of a Boolean function, that is,

it performs a logical operation on one or more logic inputs and

produces a single logic output.

• Example of logic gate – AND gate:

• AND gate performs operation of logic conniunction

INPUT

OUTPUT

A B A AND

B

0 0 0

0 1 0

1 0 0

1 1 1

Which operations can be implements using logic gates?

• Combinations of logic gates

• However single gate, can not execute every logic operations,

like NAND or NOR, there is a possibility to connect many simple

gates into more complicated one.

• Example of composed gate – NOR gate

• The NOR gate is a digital logic gate that implements logical

NOR - it behaves according to the truth table to the right. A

HIGH output (1) results if both the inputs to the gate are LOW

(0). If one or both input is HIGH (1), a LOW output (0) results.

NOR is the result of the negation of the OR operator.

INPUT A B

OUTPUT A NOR B

0 0 1

0 1 0

1 0 0

1 1 0

Other examples of logic gates I

Other examples of logic gates II

How to implement above functions in real electronic device?

• Several ways of logical computing

• Many early electromechanical digital computers, such as the

Harvard Mark I, were built from relay logic gates, using

electro-mechanical relays.

How to implement above functions in real electronic device?

• Logical operations in modern devices

• There are several logic families with different characteristics (

power consumption, speed, cost, size) such as: RDL (resistor-

diode logic), RTL (resistor-transistor logic), DTL (diode-

transistor logic), TTL (transistor-transistor logic) and CMOS

(complementary metal oxide semiconductor).

• As of 2008, most logic gates are made of CMOS transistors.

Often millions of logic gates are packaged in a single

integrated circuit.

What a CMOS is in fact? Integration of MOSFET transistors.

• Definition of CMOS

• Complementary metal–oxide–semiconductor (CMOS) is a

technology for constructing integrated circuits. CMOS

technology is used in microprocessors, microcontrollers, static

RAM, and other digital logic circuits. CMOS technology is also

used for several analog circuits such as image sensors, data

converters, and highly integrated transceivers for many types

of communication. Frank Wanlass patented CMOS in 1967.

• Advantages of CMOS

• Noise immunity

• Low, static power consumption

Metal-Oxide Semiconductor Field Effect Transistor - MOSFET

• What is a MOSFET?

• It is a device used for amplifying or switching electronic

signals. The basic principle of this kind of transistor was first

proposed by Julius Edgar Lilienfeld in 1925.

• Composition of MOSFET

• MOSFET transistor consists of a semi conductive body, drain,

source, and insulated gate. Usually the semiconductor of

choice is silicon, but some chip manufacturers, most notably

IBM and Intel, recently started using a chemical compound of

silicon and germanium (SiGe) in MOSFET channels.

Creation of conducting chanell in MOSFET transistor

• How a MOSFET works?

• In MOSFETs, a voltage on the oxide-insulated gate electrode

can induce a conducting channel between the two other

contacts called source and drain. The channel can be of n-type

or p-type, and is accordingly called an nMOSFET or a pMOSFET

(also commonly nMOS, pMOS).

Simulation result for formation of

inversion channel (electron density) and

attainment of threshold voltage (V) in a

nanowire MOSFET. Note that the

threshold voltage for this device lies

around 0.45V

INPUT OUTPUT

A NOT A

0 1

1 0

Example from real live: CMOS Inverter – simplest CMOS based gate

• Inverter – NOT Gate

• NOT gate performs operation of logical negation

• For this purpose inverter using two different MOSFETs (nMOS

+ pMOS)

• How it is looks like?

• Schematics and microphotography

Future of Logic Gates and CMOS technology

• What is a future of logic computing?

• During the last years main stream of development of logic

circuits was miniaturization, according to Moore’s law.

• New directions of research:

• Optical gates.

• Quantum gates and new proposition of logic.

Thank you for attention