Introduction
This application note presents basic information about Hall-effect sensors. It also introduces magnetic fundamentals and the added value of programmable sensors and sensor interfaces.
Solid-state switching and automotive use
Solid-state switches have been used for many years. In various applications, Hall-effect sensors (Hall ICs) have progressively replaced mechanical contact switches. In the mid-1980s, Hall ICs replaced contact points in automotive ignition systems. The automotive market consumes more than 40 million Hall ICs annually.
Hall effect
The Hall effect is named after physicist Edwin Hall. In 1879 he discovered that when a conductor or semiconductor carrying a unidirectional current is placed in a magnetic field perpendicular to the current, a voltage appears at right angles to the current path.
Early instruments and digital switches
This discovery was initially applied to the analysis of chemical samples. In the 1950s, the development of indium arsenide semiconductor compounds led to useful Hall-effect magnetic instruments. Hall-effect sensors permit measurement of DC or static magnetic fields without requiring sensor motion. In the 1960s, the widespread adoption of silicon semiconductors enabled the first combinations of Hall elements and integrated amplifiers, producing the classic digital-output Hall switch.
Sensor technology development
Hall sensor technology evolved from single-element devices to dual orthogonally arranged elements to minimize Hall voltage terminal offset. Subsequent developments produced four-element sensors using four elements arranged orthogonally in a bridge configuration. These silicon sensors were manufactured using bipolar-junction semiconductor processes. Transitioning the amplifier portion to CMOS processes enabled chopper stabilization, which reduces error by lowering amplifier input offset. Errors in non-chopper-stabilized circuits result in switch-point drift or offset and gain errors in linear-output sensors.
Modern CMOS Hall sensors
Current-generation CMOS Hall sensors often include active schemes that alternate the direction of current through the Hall element. This approach eliminates the typical offset of semiconductor Hall elements and actively compensates for temperature- and stress-induced offset. The combination of active switching and chopper stabilization yields roughly an order-of-magnitude improvement in switch-point drift and in gain and offset errors.
Integration and programmability
Melexis uses CMOS processes to optimize performance and chip size. The development of Hall sensor technology has been driven mainly by integrating complex signal-conditioning circuits into Hall ICs. Recently, Melexis introduced one of the first programmable linear Hall ICs. Future sensors are expected to be programmable and to incorporate integrated microcontroller cores, enabling more intelligent sensor functions.
