Editing Hall effect sensor (section)

== Principles ==
[[File:Common Hall Sensor Symbol.png|thumb|Hall element circuit symbol|97x97px]]{{Main article|Hall effect#Theory}}
In a Hall sensor, a fixed [[DC current|DC]] bias current<ref name=":0">{{Cite web |title=Hall Effect Sensor {{!}} Applications Guide |url=https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/hall-effect-ic-applications-guide |access-date=2023-12-28 |website=www.allegromicro.com}}</ref> is applied along one axis across a thin strip of metal called the Hall element [[transducer]]. Sensing electrodes on opposite sides of the Hall element along ''another'' axis measure the difference in [[electric potential]] ([[voltage]]) across the axis of the electrodes. The current's charge carriers are deflected by the [[Lorentz force]] in the presence of a magnetic field perpendicular to their flow. The sensing electrodes measure the potential difference (the Hall voltage) proportional to the axial component of the magnetic field that is perpendicular to ''both'' the current's axis and the sensing electrodes' axis.<ref>{{cite book |title= Hall effect devices |first= R. S.|last=Popović |edition= 2, illustrated |publisher= [[CRC Press]] |year= 2004 |isbn= 978-0-7503-0855-7 |url= https://books.google.com/books?id=_H5n-5sO5BAC&q=hall+effect+sensor&pg=PA1 }}</ref>

Hall effect sensors respond both to static magnetic fields and to changing ones. ([[Inductive sensor|Inductive sensors]], in contrast, only respond to changes in fields.)

=== Amplification ===
Hall effect devices produce a very low signal level and thus require amplification. The [[vacuum tube]] [[amplifier]] technology available in the first half of the 20th century was too large, expensive, and power-consuming for everyday Hall effect sensor applications, which were limited to laboratory instruments. Even early generation [[transistor]] technology was unsuited; it was only with the development of the low-cost [[silicon chip]]-based [[integrated circuit]] (IC) micro-technology that the Hall effect sensor became suitable for mass application. Devices sold as Hall sensors nowadays contain both the sensor as described above and a high gain IC amplifier in a single package. These Hall sensor ICs may add a stable [[voltage regulator]] in addition to the amplifier to allow operation over a wide range of [[voltage source|supply voltage]] and boost the Hall voltage for a convenient analog signal output proportional to the magnetic field component.<ref name=":0" /> In some cases, the linear circuit may cancel the offset voltage of Hall sensors. Moreover, AC modulation of the driving current may also reduce the influence of this offset voltage.

Hall sensors are called ''linear'' if their output is proportional to the incident magnetic field strength. This output signal can be an [[Analog signal|analog]] voltage, a [[pulse-width modulation]] (PWM) signal, or be [[Digital communication|communicated digitally]] over a modern [[Bus (computing)#Examples of internal computer buses|bus protocol]].<ref>{{Cite web |title=Linear Hall Sensors (product category) |url=https://product.tdk.com/en/products/sensor/linear/linear-hall/index.html |url-status=live |archive-url=https://web.archive.org/web/20230205002539/https://product.tdk.com/en/products/sensor/linear/linear-hall/index.html |archive-date=2023-02-05 |access-date=2024-01-02 |website=[[TDK]]}}</ref> Hall sensors may also be ''ratiometric'' if their sensitivity is also proportional to their supply voltage. With no magnetic field applied, their ''quiescent output voltage'' is typically half of the supply voltage.<ref>{{Cite web |last1=Gilbert |first1=Joe |last2=Dewey |first2=Ray |date=2022-05-05 |title=AN27702: Linear Hall-Effect Sensor ICs |url=https://www.allegromicro.com/-/media/files/application-notes/an27702-linear-hall-effect-sensor-ics.pdf |url-status=live |archive-url=https://web.archive.org/web/20231104000208/https://www.allegromicro.com/-/media/files/application-notes/an27702-linear-hall-effect-sensor-ics.pdf |archive-date=2023-11-04 |access-date=2024-01-02 |website=[[Allegro MicroSystems]]}}</ref> They may have [[Rail-to-rail opamp|rail-to-rail]] output (e.g., A1302).<ref>{{cite web|url=https://www.jameco.com/Jameco/Products/ProdDS/2135881.pdf|title=A1301 & A1302 - Continuous-Time Ratiometric Linear Hall Effect Sensor ICs|publisher=Allegro MicroSystems|website=www.jameco.com|archive-url=https://web.archive.org/web/20240103012358/https://www.jameco.com/Jameco/Products/ProdDS/2135881.pdf|archive-date=3 January 2024|url-status=live}}</ref>

=== Hall switch ===
While the Hall element is an [[analog device]], ''Hall switch'' ICs often additionally incorporate [[Threshold detector|threshold detection]] circuitry to form an [[electronic switch]] which has two states (on and off) that output a binary [[digital signal]].

Their outputs may be [[open collector]] [[NPN transistor|NPN transistors]] (or open drain n-type [[MOSFETs]]) for compatibility with ICs that use different supply voltages.<ref name=":0" /> Rather than a voltage being produced at the Hall sensor signal output wire, an output transistor is turned on, providing a circuit to ground through the signal output wire.

==== Hysteresis ====
[[Schmitt trigger]] filtering may be applied (or integrated into the IC) to provide a clean digital output that is [[Robustness|robust]] against sensor noise. The [[hysteresis]] thresholds for switching (specified as B{{Sub|OP}} and B{{Sub|RP}}) categorize digital Hall ICs as either unipolar switches,<ref>{{Cite web |title=Unipolar Hall-Effect Sensor IC Basics |url=https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/unipolar-hall-effect-sensor-ic-basics |access-date=2023-12-28 |website=www.allegromicro.com}}</ref> omnipolar switches,<ref>{{Cite web |title=Omnipolar Switch Hall-Effect IC Basics {{!}} Allegro MicroSystems |url=https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/omnipolar-switch-hall-effect-ic-basics |access-date=2023-12-28 |website=www.allegromicro.com}}</ref> or bipolar switches,<ref>{{Cite web |title=Bipolar Switch Hall-Effect ICs |url=https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/bipolar-switch-hall-effect-ics |access-date=2023-12-28 |website=www.allegromicro.com}}</ref> which may sometimes be called latches.<ref>{{Cite web |title=AN296067: Hall Effect Switch {{!}} Latching Switch Basics |url=https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/latching-switch-hall-effect-ic-basics |url-status=live |archive-url=https://web.archive.org/web/20230927181352/https://www.allegromicro.com/en/insights-and-innovations/technical-documents/hall-effect-sensor-ic-publications/latching-switch-hall-effect-ic-basics |archive-date=2023-09-27 |access-date=2023-12-28 |website=www.allegromicro.com}}</ref> Unipolar (e.g., A3144)<ref>{{cite web|url=https://www.elecrow.com/download/A3141-2-3-4-Datasheet.pdf|title=A1341, A1342, A3143, and A3144 - Sensitive Hall Effect Switches for High-Temperature Operation|publisher=Allegro MicroSystems|website=www.elecrow.com|archive-url=https://web.archive.org/web/20250322183337/https://www.elecrow.com/download/A3141-2-3-4-Datasheet.pdf|archive-date=22 March 2025|url-status=live}}</ref> refers to having switching thresholds in only one polarity of the magnetic field. Omnipolar switches have two sets of switching thresholds, for both positive and negative polarities, and so operate alternatively with a strong positive or a strong negative magnetic field.

Bipolar switches have a positive B{{Sub|OP}} and a negative B{{Sub|RP}} (and thus require both positive and negative magnetic fields to operate). The difference between B{{Sub|OP}} and B{{Sub|RP}} tends to be greater for bipolar switches described as latches, which remain in one state much longer (i.e. they latch onto their last value) and require a greater field strength to change states than bipolar switches require. The naming distinction between "bipolar" and "latch" may be a little arbitrary, for instance, the datasheet for the [[Honeywell]] SS41F describes it as "bipolar", while another manufacturer describes their SS41F<ref>{{cite web|url=https://www.elecrow.com/download/A3141-2-3-4-Datasheet.pdf|title=SS41F - Hall Latch Position Sensor|publisher=SEC Electronics|website=radiolux.com.ua|date=1 November 2013|archive-url=https://web.archive.org/web/20240602175226/https://radiolux.com.ua/files/pdf/SS41F.pdf|archive-date=2 June 2024|url-status=live}}</ref> with comparable specifications as a "latch".