The A1425 ac-coupled Hall-effect sensor is a monolithic integrated circuit that switches in response to changing differential magnetic fields created by rotating ring magnets or, when coupled with a magnet, by ferrous targets. The device is a true zero-crossing detector: the output switches precisely when the difference in magnetic field strength between the two Hall elements is zero. A unique dualcomparator scheme provides for accurate switching during zero-crossing, both when the sensed field is increasing in strength and when it is decreasing, while utilizing hysteresis to prevent false switching. The zero-crossing nature of this device provides excellent repeatability for crankshaft applications. Changes in field strength at the device face caused by a moving target are sensed by the two integrated Hall transducers, generating signals that are differentially amplified by on-chip electronics. This differential sensing design provides immunity to radial vibration within the operating air gap range of the A1425, by rejection of the common mode signal. Steady-state magnet and system offsets are eliminated using an on-chip differential band-pass filter. This filter also provides relative immunity to interference from electromagnetic sources. The device utilizes advanced temperature compensation for the high-pass filter, sensitivity, and the Schmitt trigger switchpoints, guaranteeing optimal operation to low frequencies over a wide range of air gaps and temperatures.