The Hall Effect The 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 current The 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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