Page 212 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Unit 11: Registers and Counters

Notes
MRAM
This is Magneto-resistive RAM, or Magnetic RAM. It is a non-volatile RAM memory technology
that uses magnetic charges to store data instead of electric charges. Unlike technologies including
DRAM, which require a constant flow of electricity to maintain the integrity of the data, MRAM
retains data even when the power is removed. An additional advantage is that it only requires
low power for active operation. As a result, this technology could become a major player in the
electronics industry now that production processes have been developed to enable it to be produced.

A device for storing digital information that is fabricated by using integrated
circuit technology. Also known as integrated-circuit memory; large-scale
integrated memory; memory chip; semiconductor storage; transistor memory.

Semiconductor History

emory chips have been called the crude oil of the twenty-first century. They are used
in a wide variety of electronic applications from children’s toys to sophisticated
Mcommunication satellites. The current generation of memory chip (64 Mb) is capable
of storing 3,355 pages of text on a piece of about the size of a dime.
What is a Semiconductor?

A number of elements are classified as semiconductors including silicon, zinc, and germanium.
These elements have the ability to conduct electrical current, and they can be regulated in the
amount of their conductivity. Silicon is the most widely used semiconductor material because
it is easily obtained.
Silicon is basically extracted from sand. It has been used for centuries to make cast iron,
bricks, and pottery. In ultra-pure form, the controlled addition of minute amounts of certain
impurities (called dopants) alters the atomic structure of the silicon. The silicon can then be
made to act as a conductor or a non-conductor, depending upon the polarity of an electrical
charge applied to it. Hence, the generic term semiconductor.
Early Developments

Semiconductor materials were studied in laboratories as early as 1830. The first materials
studied were a group of elements and compounds that were usually poor conductors if heated.
Shining light on some of them would generate an electrical current that could pass through
them in one direction only.

By 1874, electricity was being used not only to carry power, but to carry information. The
telegraph, telephone, and later the radio were the earliest devices in an industry that would
eventually be called electronics.
Radio receivers required a device called a rectifier to detect signals. Ferdinand Braun used the
rectifying properties of the galena crystal, a semiconductor material composed of lead sulfide,
to create the cat’s whisker diode for this purpose. Thus was born the first semiconductor device.

The Integrated Circuit
Until 1959, all electronic components were discrete: that is, they performed only one function,
and many of them had to be wired together to create a functional circuit. Although a great
number of identical discrete transistors could be fabricated on a single wafer, they then had
Contd...

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