Patent ID: 8405385

Claim:
A magnetoresistive sensor apparatus comprising: a) a magnetoresistive sensor; b) a magnetic field source that provides a tickling magnetic field having a modulation frequency of f f , wherein said magnetoresistive sensor is disposed in said tickling magnetic field; c) an electrical source configured to provide an excitation to said magnetoresistive sensor having a modulation frequency of f c , wherein f f and f c , are distinct, and wherein an output spectrum of said sensor includes a carrier tone (CT) at frequency f c and side tones (STs) at frequencies f c ±f f , wherein the carrier tone has a CT amplitude and the side tones have an ST amplitude; and d) a processor configured to determine a baseline relation between the CT amplitude and the ST amplitude in said output spectrum; wherein operation of said apparatus includes measuring corresponding CT and ST amplitudes when a sample is present to provide an input CT measurement and an input ST measurement; wherein said apparatus is configured to correct the input ST measurement using said baseline relation and the input CT measurement to provide a corrected ST measurement as an output.