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Characteristics of dif ferent digital electronic devices

By Harry Morwood

Brief histor y of logic; Theory of combinational and sequential logic and hardware design; 1854 – George Boole, an investigation of the laws of thought. 1904 – E.V. Huntington, sets of independent postulates for the algebra of logic. 1936 – Alan Turning, on computable numbers. 1938 – C.E.Shannon, a symbolic analysis of relay and switching circuit. 1945 – John von Neumann, final draft of a report on the EDVAC (Eckert and Mauchly’s computer electronic discrete variable calculator at the university of Penn Moore school of engineering). 1955 – G.H. Mealy, method of synthesizing sequential logic circuits. 1956 – E.F. Moore, gedanken experiments on sequential machices

Brief histor y of logic; Technology (approximate dates); 1800 – Jaquard loom stored program concept. 1850’s – Charles Babbage analytical engine (mechanical computer) 1906 – De Forrest vacuum tube audio and electronics born. 1948 – Transistor invented at Bells lab. 1959 – Jack Kilby at Texas instruments and Robert Noyce at Intel: integrated circuit. 1965 – Gordon Moore at Intel proposes “Moore’s law” which stands to this day: doubling of transistors on a chip every 18-24 months. 1970 – UNIX and C developed at Bells lab. 1980 – Berkeley Software Distribution (BSD) UNIX includes TCP/IP and internet follows. 1982 – IBM “standardizes” the personal computer and Microsoft is created. 1985 – First public version of VHDL available, FPGA’s are also available. 1992 – Linux open source software becomes available.

Examples of logic devices used; PLA’s –

Programmable Logic Arrays

PAL’s –

Programmable Array Logic

GAL’s –

Genetic Array Logic

CPLD’s – Device

Complex Programmable Logic

PLA’s –

Programmable Logic Array’s ;

A programmable logic array is a kind of programmable logic device used to implement combinational logic circuits. The PLA has a set of programmable AND gate planes, which link to a set of programmable OR gate planes, which can then be conditionally complemented to produce an output, as show in the picture on the right. This layout allows for a large number of logic functions to be created in the sum of products canonical forms. PLA's differ from PALs and GALs in that both the AND and OR gate planes are programmable.

PAL’s -

Programmable Array Logic ;

Programmable Array Logic is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. MMI obtained a registered trademark on the term PAL for use in "Programmable Semiconductor Logic Circuits". PAL devices consisted of a small PROM (programmable read-only memory) core and additional output logic used to implement particular desired logic functions with few components. Using specialized machines, PAL devices were "field-programmable". Each PAL device was "one-time programmable" (OTP), meaning that it could not be updated and reused after its first programming.

GAL’s -

Generic Array Logic ;

The Generic Array Logic device was an innovation of the PAL and was invented by Lattice Semiconductor. The GAL was an improvement on the PAL because one device was able to take the place of many PAL devices or could even have functionality not covered by the original range. Its primary benefit was that it was erasable and reprogrammable making prototyping and design changes easier for engineers.

CPLD’s –

Co mplex Progra mmabl e l ogic


devic e A complex programmable logic device is a programmable logic device with complexity between that of PALs and FPGAs, and architectural features of both. The main building block of the CPLD is a macrocell, which contains logic implementing disjunctive normal form expressions and more specialized logic operations.

Possible uses for the previous devices; The most common use for the pervious devises listed are electric/electronic circuit boards like the one pictured top right of this slide. The circuit boards are then used in various appliances and devices like the ones pictured below.

Comparisons between two dif ferent families of devices; TTL stands for Transistor-Transistor Logic. It is a classification of integrated circuits. The name is derived from the use of two Bipolar Junction Transistors or BJTs in the design of each logic gate. CMOS (Complementary Metal Oxide Semiconductor) is also another classification of ICs that uses Field Effect Transistors in the design. The main differences are; 1.

TTL circuits utilize BJTs while CMOS circuits utilize FETs.


CMOS allows a much higher density of logic functions in a single chip compared to TTL.


TTL circuits consumes more power compared to CMOS circuits at rest.


CMOS chips are a lot more susceptible to static discharge compared to TTL chips.


There are CMOS chips that have TTL logic and are meant as replacements for TTL chips.

References; 

Digital Electronic Devices  

By Harry Morwood

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