The Hall EffectThe Hall-Effect principle is named for physicist Edwin Hall. In
1879 he discovered that when a conductor or semiconductor
with current flowing in one direction was introduced perpendicular
to a magnetic field a voltage could be measured at right angle
to the current path.
The Hall voltage can be calculated from V Hall = oB where:
V HalI = emf in volts
o = sensitivity in Volts/Gauss
B = applied field in Gauss
I = bias currentThe initial use of this discovery was for the classification of
chemical samples.
The development of indium arsenide semiconductor compounds
in the 1950's led to the first useful Hall effect magnetic
instruments. Hall effect sensors allowed the measurement of
DC or static magnetic fields with requiring motion of the sensor.
In the 1960's the popularization of silicon semiconductors led to
the first combinations of Hall elements and integrated amplifiers.
This resulted in the now classic digital output Hall switch.
The continuing evolution of Hall transducers technology saw
a progression from single element devices to dual orthogonally
arranged elements. This was done to minimize offsets at the
Hall voltage terminals. The next progression brought on the
quadratic of 4 element transducers. These used 4 elements
orthogonally arranged in a bridge configuration. All of these
silicon sensors were built from bipolar junction semiconductor
processes.A switch to CMOS processes allowed the implementation of
chopper stabilization to the amplifier portion of the circuit.
This helped reduce errors by reducing the input offset errors
at the op amp. All errors in the circuit non chopper stabilized
circuit result in errors of switch point for the digital or offset
and gain errors in the linear output sensors. The current
generation of CMOS Hall sensors also include, a scheme that
actively switched the direction of current through the hall
elements.
This scheme eliminates the offset errors typical of semi-
conductor Hall elements. It also actively compensates for
temperature and strain induced offset errors.
The overall effect of active plate switching and chopper
stabilization yields llall Effect sensors with an order of
magnitude improvement in drift of switch points or gain
and offset errors.
Melexis uses the CMOS process exclusively, for best
performance and smallest chip size. The developments
to Hall-Effect sensor technology can be credited mostly
to the integration of sophisticated signal conditioning
circuits to the Hall IC.
Recently Melexis introduced the world's first programmable
linear Hall IC, which offered a glimpse of future technology.
Future sensors will programmable and have integrated
microcontroller cores to make an even "smarter" sensor.How does it work ?
A Hall IC switch is OFF with no magnetic field and ON in
the presence of a magnetic field, as seen in above diagram.
1. The Earth's field will not operate a Hall IC Switch, but
a common refrigerator magnet will provide sufficient strength
to actuate the sensor.
_________________________________________For more information, contact Melexis...
Tel: +32 13 670495 Fax: +32 13 670770
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