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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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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).
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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
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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
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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
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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
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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.