Integrated Circuits

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

image

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

image

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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