Couplers,
also known as "isolators" because they electrically isolate as well
as transmit data, are widely used in industrial and factory networks, instruments,
and telecommunications. Every one knows the problems with optocouplers. They take
up a lot of space, are slow, optocouplers age and their temperature range is quite
limited. For years, optical couplers were the only option. Over the years, most
of the components used to build instrumentation circuits have become ever smaller.
Optocoupler technology, however, hasn't kept up. Existing coupler technologies
look like dinosaurs on modern circuit boards.
Magnetic
couplers are analogous to optocouplers in a number of ways. Design engineers,
especially in instrumentation technology, will welcome a galvanically-isolated
data coupler with integrated signal conversion in a single IC. My report will
give a detailed study about 'ISOLOOP MAGNETIC COUPLERS'. GROUND LOOPS When
equipment using different power supplies is tied together (with a common ground
connection) there is a potential for ground loop currents to exist. This is an
induced current in the common ground line as a result of a difference in ground
potentials at each piece of equipment.
Normally
all grounds are not in the same potential. Widespread electrical and communications
networks often have nodes with different ground domains. The potential difference
between these grounds can be AC or DC, and can contain various noise components.
Grounds connected by cable shielding or logic line ground can create a ground
loop-unwanted current flow in the cable. Ground-loop currents can degrade data
signals, produce excessive EMI, damage components, and, if the current is large
enough, present a shock hazard.
Galvanic
isolation between circuits or nodes in different ground domains eliminates these
problems, seamlessly passing signal information while isolating ground potential
differences and common-mode transients. Adding isolation components to a circuit
or network is considered good design practice and is often mandated by industry
standards. Isolation is frequently used in modems, LAN and industrial network
interfaces (e.g., network hubs, routers, and switches), telephones, printers,
fax machines, and switched-mode power supplies.
Giant
Magnetoresistive (GMR): Large magnetic field dependent changes in resistance
are possible in thin film ferromagnet/nonmagnetic metallic multilayers. The phenomenon
was first observed in France in 1988, when changes in resistance with magnetic
field of up to 70% were seen. Compared to the small percent change in resistance
observed in anisotropic magnetoresistance, this phenomenon was truly 'giant' magnetoresistance.
The spin of electrons in
a magnet is aligned to produce a magnetic moment. Magnetic layers with opposing
spins (magnetic moments) impede the progress of the electrons (higher scattering)
through a sandwiched conductive layer. This arrangement causes the conductor to
have a higher resistance to current flow.
An
external magnetic field can realign all of the layers into a single magnetic moment.
When this happens, electron flow will be less effected (lower scattering) by the
uniform spins of the adjacent ferromagnetic layers. This causes the conduction
layer to have a lower resistance to current flow. Note that these phenomenon takes
places only when the conduction layer is thin enough (less than 5 nm) for the
ferromagnetic layer's electron spins to affect the conductive layer's electron's
path.
