Integrated Circuits
IC or Chip
Various gates are interconnected to form a circuit
14 to 64 pins for a typical IC
Levels of Integration
Small Scale Integration (SSI)
Less than 10 gates
Medium Scale Integration (MSI)
10 to 100 gates, adders, multiplexers
Large Scale Integration (LSI)
100 to few thousands of gates, processors
Very Large Scale Integration (VLSI)
Thousands of gates, complex computer Chips, memory arrays
Digital Logic Families
TTL (Transistor – Transistor Logic)
Widespread and this is the standard
Bipolar
ECL (Emitter Coupled Logic )
For high speed operation
Bipolar
MOS (Metal Oxide Semiconductors)
High component density
Unipolar
CMOS (Complementary Metal Oxide Semiconductors)
Useful where Low power consumption is needed
unipolar
Characteristics of digital logic families
Fan in
Number of inputs of an electronic gate
Physical logic gates with large fan in are slower compared to less fan in
The NAND gates have a fan in factor of 4
Fan out
Specifies the number of standard loads that the output of a gate can drive without impairing its normal operation.
Propagation Delay
Average transition delay time for the signal to propagate from input to output
A full adder has an overall gate delay of 3 logic gates from the inputs A and B to the carry output Cout shown in red
Power dissipation
Power consumed by the gate
Noise Margin
Minimum external noise voltage that causes an undesirable change in the circuit output
A full adder has an overall gate delay of 3 logic gates from the inputs A and B to the carry output Cout shown in red
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