HNC EEE DigiHistory ElectroTech007

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BTEC HNC ELECTRICAL / ELECTRONICENGINEERING

UNIT: Digital & Analogue Devices & Circuits

A Short History of DigitalElectronics

ElectroTech007

04-01-10


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HNC EEE A Short History of Digital Electronics ElectroTech007

Digital Electronics

What is Digital Electronics?

The use of the term digital in electronic systems indicates the use of digital signals. A

digital signal is where two voltage levels are represented by binary logic levels (1s &

0s) to produce two states (1 = true or 0 = false) (Fig.1).

Fig.1 Example of digital waveform, 1 = (low level/false), 2 = (high level/true), 3 = (rising edge), 4 = (falling edge)

Digital electronics circuits are representations of Boolean algebra first developed by

George Boole (Fig.2) in the 1830s and later documented in his book An

investigation of the laws of thought 1854.

Fig.2 George Boole mathematician & creator of Boolean algebra

What is Boolean algebra?

Boolean algebra is the algebra of two values namely 1 and 0, or as also termed true

and false; which represent logical operations and relationships. This gave birth to the

term binary logic (1s & 0s).
http://upload.wikimedia.org/wikipedia/commons/6/6c/George_Boole.jpghttp://upload.wikimedia.org/wikipedia/commons/5/53/S_digital.PNG


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In 1936 a German engineer Konrad Zuse (Fig.3) used Boolean algebra to create a

mechanical arithmetic unit based on the binary system which he called the Z1

calculating machine (Fig.4). This machine was mainly mechanical in nature except

for a small electrical engine used to create a clock signal of 1 Hz.

Fig.3 Konrad Zuse digital computer pioneer

Fig. 4 Konrad Zuse with the Z1 calculating machine
http://www.informatik.uni-hamburg.de/Info/ueber_uns/Zuse.gif


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In 1937 an American electronic engineer and mathematician Claude Elwood

Shannon (Fig.5) produced his masters thesis A symbolic analysis of relay and

switching circuits (Fig.6) where he implemented Boolean algebra and binary

arithmetic using electronic switches and relays, the first of an electrical nature in

history.

Fig.5 Claude Elwood Shannon responsible for the first electrical representation of a computer using binary arithmetic

Fig.6 Cover page of Claudes masters thesis entitled A Symbolic Analysis of Relay and Switching Circuits


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Later in 1937 George Stibitz (Fig.7) a researcher at Bell Labs created a relay based

computer which he named Model K (Fig.8) which implemented Boolean logic and

could be used for binary addition; this was the forerunner to the bell labs complexnumber calculator (Fig.9) in 1939.

Fig.7 George Stibitz

Fig.8 Model K

Fig.9 Complex number calculator 1939
http://images.google.co.uk/imgres?imgurl=http://www.kerryr.net/images/pioneers/gallery/stibitz3_lg.jpg&imgrefurl=http://www.kerryr.net/pioneers/gallery/ns_stibitz3.htm&usg=__JH21Xy7NO2GrpO6BaLgdHCT2FOs=&h=452&w=316&sz=18&hl=en&start=1&um=1&tbnid=rKcjKWmqm4J8pM:&tbnh=127&tbnw=89&prev=/images?q=George+Stibitz&hl=en&sa=N&um=1


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On January the 15th 1941 the first digital computer was announced which made use

of binary arithmetic and Boolean logic; it was called the ABC (Fig.10) and was the

brainchild of John Vincent Atanasoff (electrical engineer and school teacher) (Fig.11)

and his graduate assistant Clifford Berry. This was the first truly digital electronic

computer; it consisted of over 300 vacuum tubes and was capable of computing

complicated algebraic equations.

Fig.10 ABC digital computer (first truly digital computer)

Fig.11 John Vincent Atanasoff
http://en.wikipedia.org/wiki/File:John_Atanasoff.pnghttp://upload.wikimedia.org/wikipedia/commons/9/90/Atanasoff-Berry_Computer.jpg


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Logic Gates

What is a logic gate?

A logic gate is a device that performs logical operations on multiple binary inputs (1s

& 0s) to produce a single binary output.

History

The first logic gate named the analytical engine (Fig.12) was a mechanical device

designed by Charles Babbage (Fig.13) around 1837; it made use of mechanical

gearing to perform operations.

Fig.12 Analytical Engine first logic gate

Fig.13 Charles Babbage
http://en.wikipedia.org/wiki/File:CharlesBabbage.jpghttp://upload.wikimedia.org/wikipedia/commons/0/09/050114_2529_difference.jpg


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With various advancements in technology then came logic gates utilising

electromagnetic relays, vacuum tubes and then discrete components such as

transistors and diodes.

The development of the first integrated circuit by Jack Kilby (Fig.15) of Texas

Instruments in 1958 opened the doors for the new generation of digital logic

integrated circuit.

Fig.14 Jack Kilby with first integrated circuit (IC)

In 1962 Orville Baker (Fig.14) from Signetics developed a class of digital logic IC

built using bipolar transistors, diodes and resistors called diode transistor logic

(DTL). Fig.15 shows an example of a DTL NAND gate. The signetics SE100 series

proved popular until it was overtaken in 1964 by Fairchilds 930 series which had

better noise immunity and lower cost.

Fig.15 DTL NAND gate
http://en.wikipedia.org/wiki/File:DTL_NAND_Gate.svg


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Around the same time as the DTL series of logic had been created James Buie of

Pacific Semiconductor had created what was to become one of the most popular

logic families; transistor transistor logic (TTL) by using transistors and resistors.

In 1963 Thomas Longo (Fig.16) who worked for Sylvania developed the first TTL

family called the Sylvania Universal High Level Logic (SUHL) (Fig.18), this was a

high profile design taken by the military to be used in the phoenix AIM missile

(Fig.17); the United States only long range air to air radar guided missile capable of

multiple launch against more than one target.

Fig.16 Thomas Longo

Fig.17 Phoenix missile (AIM-54) Fig.18 Sylvania (SUHL) Logic IC
http://en.wikipedia.org/wiki/File:AIM-54_Phoenix_cropped.jpg


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Around 1964 Texas Instruments who were impressed by the success of Sylvanias

SUHL TTL family decided to strike back with the creation of a TTL family aimed at

the high specification military/space market; the SN5400 series was born. The SN

series was designed with a wide temperature tolerance for extreme conditions. An

example of the flat pack packaging of the device can be seen in Fig.19 below.

Fig.19 SN5400 Series logic IC from Texas Instruments

Texas instruments then introduced a low cost plastic packaged industrial version

called the SN7400 series (Fig.20) which was aimed at the electronics industry, the

success of which gave Texas Instruments more than a 50% share of the logic

market.

Fig.20 SN7400 Series from Texas Instruments

By 1968 technological advances meant that even more bipolar transistors could be

integrated onto a chip, eager to win a greater percentage of TTL market share a host

of semiconductor manufacturers started producing variations on the original designs.

For example the Fairchild 9300 series and Signetics 8200 series were pioneering the

design of TTL-MSI, where hundreds of logic gates per chip where possible.


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Battle for Supremacy (TTL vs. CMOS)

At the same time as the fledgling TTL was being developed; a contender that was to

become one of the most popular logic types of the 21st century was being created.

This contender was complementary metal-oxide semiconductor (CMOS).

Complementary Metal-Oxide Semiconductor (CMOS)

CMOS was invented in 1963 by Frank Wanlass (Fig.21) of Fairchild Semiconductor.

While working in Fairchilds R&D laboratory, Frank produced a paper detailing that

logic circuits containing p-channel and n-channel MOS (metal-oxide semiconductor)

transistors in a symmetrical circuit configuration drew almost zero power in standbymode. This concept was patented by Frank in 1967 and came to be known as

CMOS technology (Fig.22).

Fig.21 Frank Wanlass

Fig.22 CMOS device structure


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The technologies name; complementary metal oxide semiconductor gives a good

indication of what the technology consists of.

The word complementary refers to the fact that it uses a pair of transistors for logic

functions, only one of which is switched on at any time.

The words metal-oxide semiconductor refers to the manufacturing process originally

used for CMOS ICs which was responsible for the creation of field effect transistors

(FET) that had a metal gate electrodes made of aluminium placed on top of an oxide

insulator which in turn was placed on top of a semiconductor. Todays CMOS chips

dont use metal gate electrodes but instead use an electrode of polysilicon.

The first CMOS integrated circuits known as COSMOS 4000 series weremanufactured by RCA around 1968 (Fig.23).

Fig.23 RCA 4000 series CMOS IC

These first CMOS logic ICs by definition drew much less power than TTL but were

not as fast; and therefore were suited to items that required longer battery life e.g.

digital watches.

Modern CMOS logic circuits have become the predominant technology for integrated

digital circuits due to their low power dissipation, energy efficiency, increasing

operating speeds, and simplicity which allows ever increasing chip densities

compared with bipolar transistors used in TTL chips.

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