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Integrated Circuits

Integrated circuits enable us to not have to construct circuits with lots of individual discrete components such as transistors, diodes and resistors.  With an integrated circuit it is possible to fabricate a large number of the equivalent discrete components onto a tiny piece of silicon.  The resulting equivalent arrangement is far more compact than if all the components were separate and it is also considerably cheaper and much more reliable.  In books it is suggested that it is not necessary to have a detailed understanding of the internal circuitry of an IC in order to make effective use of it.  Instead I have to be aware of some basic rules concerning the supply voltage rails and input and output requirements.  A measure of the number of individual semiconductor devices within the chip is given by referring to its ‘scale of integration’ with the following terminology usually applied:

Scale of integration Abbreviation Number of logic gates or circuitry of equivalent complexity
Small SSI 1-10
Medium MSI 10-100
Large LSI 100-1000
Very large VLSI 1000-10000
Super large SLSI 10000-100000

 With the exception of only a few circuits, the availability of low cost integrated circuits has made discrete circuitry obsolete.  Integrated circuits hold a number of advantages of a discrete component circuit that is designed to fulfill the same job.

  •  They have a higher reliability despite their complexity
  •  They cost less than the equivalent discrete circuitry
  •  They have a much smaller space requirement, typically about 10% in comparison to discrete component circuit.
  •  They have an easier circuit layout.  Because they are designed to use a minimal number of external connections the layout is simplified.
  •  They have a matched performance.  The semi-conductor devices fabricated using IC technology usually have closely matched characteristics and tend to have a more assured performance than there would be with the number of variations in discrete component characteristics.

 The disadvantages of using an IC could be that they lack flexibility as it is not generally possible to modify the parameters within which an integrated circuit will operate as easily as it is to modify the performance of discrete circuitry.

 They may also have performance limitations where high currents, voltages, power levels, frequency signals and very low level signals are involved.

 IC’s are divided into two general classes which are linear (analogue) or digital.  Digital integrated circuits are comprised of logic gates.

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Categories: Integrated Circuits
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