The ATS640JSB Hall-effect gear-tooth sensor is a peak detecting device that uses internal gain control to provide extremely stable duty cycles down to zero speed. Each sensor subassembly consists of a high-temperature plastic shell that holds together a samarium-cobalt magnet, a pole piece, and a true zero-speed BiCMOS differential Hall-effect gear-tooth sensor IC that has been optimized to the magnetic circuit. This small package can be easily assembled and used in conjunction with a wide variety of gear shapes and sizes.