Page 39 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes
2.2.4 Gate Fan-out Example
Figure 2.30: Gate Fan-out

Fan-out is the output driving capability or output current capability of a logic gate giving greater
power amplification of the signal. It may be necessary to connect more than just one logic gate to
the output of another or to switch a high current load such as an LED, then a Gate will allow us
to do just that by having a high fan-out rating of up to 50.
Beware while connecting a variable DC voltage source to the NAND gate,
input must always stay in the range 0 to +5 V otherwise the circuit will
be destroyed.

Digital Logic Circuit

inary logic was first proposed by 19th-century British logician and mathematician
George Boole, who in 1847 invented a two-valued system of algebra that represented
Blogical relationships and operations. This system of algebra, called Boolean algebra,
was used by German engineer Konrad Zuse in the 1930s for his Z1 calculating machine. It was
also used in the design of the first digital computer in the late 1930s by American physicist
John Atanasoff and his graduate student Clifford Berry. During 1944–1945 Hungarian-born
American mathematician John von Neumann suggested using the binary arithmetic system
for storing programs in computers. In the 1930s and 1940s British mathematician Alan Turing
and American mathematician Claude Shannon also recognized how binary logic was well
suited to the development of digital computers.
Functions Performed by Logic Circuits
“True” can be represented by a 1 and “false” by a 0, and in logic circuits the numerals appear
as signals of two different voltages. Logic circuits are used to make specific true-false decisions
based on the presence of multiple true-false signals at the inputs. The signals may be generated
by mechanical switches or by solid-state transducers. Once the input signal has been accepted
and conditioned (to remove unwanted electrical signals, or “noise”), it is processed by the
digital logic circuits. The various families of digital logic devices, usually integrated circuits,
perform a variety of logic functions through logic gates, including “OR”, “AND”, and “NOT”,
and combinations of these (such as “NOR”, which includes both OR and NOT).
Contd...

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