AN OFFSET-TRIMMABLE ARRAY OF MAGNETIC-FIELD-SENSITIVE MOS-TRANSISTORS(MAGFETS)

Magnetic-held sensors can be implemented by the use of a magnetic-fiel d-sensitive MOSFET structure, commonly referred to as a MAGFET. The MA GFET is a split-drain MOSFET where the difference between the drain cu rrents is dependent on the magnetic field applied to the MAGFET. Unfor tunately, the sensitivity of the MAGFET is rather small and the inhere nt offset between the drain currents (at zero magnetic field) may well be of the same magnitude as the field-dependent current difference, e ven for fields of about 0.1 T. Hence, it is often necessary to introdu ce some sort of offset compensation. In this paper we present a new co mbination of an offset compensating circuit and a MAGFET cascade circu it with increased sensitivity. The offset compensation utilizes a digi tally trimmable current mirror implemented by a multiple-gate MOS tran sistor structure. A prototype circuit has been fabricated in a 2.4 mu m n-well CMOS technology. The measured results show that the offset is reduced by more than one order of magnitude.