A magnetic sensor array including magnetoresistive sensor elements having outputs combined by frequency division multiplexing (FDM) is provided. Each sensor element provides an input to a mixer which provides a distinct frequency shift. Preferably, time division multiplexing is also used to combine sensor element outputs. Each sensor element is typically in proximity to a corresponding sample. The sensor elements are preferably subarrays having row and column addressable sensor element pixels. This arrangement provides multiple sensor pixels for each sample under test. Multiplexing of sensor element outputs advantageously reduces readout time. A modulated external magnetic field is preferably applied during operation, to reduce the effect of 1/f noise on the sensor element signals. The effect of electromagnetic interference (EMI) induced by the magnetic field on sensor element signals is advantageously reduced by the mixing required for FDM.