Patent ID: 7138793

Claim:
Apparatus for detecting passing magnetic articles and providing a detector output signal indicative of the passing magnetic articles comprising: a magnetic field sensor providing a magnetic field signal proportional to an ambient magnetic field; an offset adjustment circuit responsive to the magnetic field signal for adjusting an offset of the magnetic field signal based on a dynamically adjustable offset threshold signal to provide an offset-adjusted signal; a Positive Digital-to-Analog converter (PDAC) operative to provide a PDAC signal that tracks positive peaks of the offset-adjusted signal; a Negative Digital-to-Analog converter (NDAC) operative to provide an NDAC signal that tracks negative peaks of the offset-adjusted signal; and a comparator responsive to the offset-adjusted signal and a switching threshold signal to provide the detector output signal, wherein the switching threshold signal is a percentage of the difference between the PDAC signal and the NDAC signal.