Design On A High Accuracy CMOS Hall-effect Switch

Among the various sensing technologies used to detect magnetic field,the Hall-effect transducer is the most widespread and commonly used.Hall-effect transducers have replaced mechanical contact switchescompletely in some occasions. Hundreds of millions of these devices areproduced every year in the global world for use in a wide variety ofapplications such as computers, automobiles, industrial controls andconsumer device.This paper designs an omnipolar Hall-effect switch designed in BCDfab’s mixed signal1.0u CMOS process. Either sufficient south or northpole magnetic field strength will turn the output on. If the magnetic fluxdensity is larger than operating point (BOP), the output will be turned on; ifit is less than releasing point (BRP), the output will be turned off. Theoutput structure is open-drain type. Such output allows simple connectivitywith TTL or CMOS logic by using a pull-up resistor tied between a pull-upvoltage and the device output. Moreover, a sleep-awake logic controls theIC in sleep time or awake time. This function will reduce the powerdissipation of the IC.The device integrates a voltage regulator, Hall sensor with dynamicoffset cancellation system, Schmitt trigger and an open-drain output driver,all in a SOT23-3package.The chopper-stabilized amplifier uses switched capacitor technique tosuppress the offset generally observed with Hall sensors and amplifiers.The CMOS technology makes this advanced technique possible andcontributes to smaller chip size and lower current consumption thanbipolar technology. The small chip size is also an important factor to minimize the effect of physical stress. This combination results in morestable magnetic characteristics and enables faster and more precise design.