Magnetic Relaxation Detector for Microbead Labels

A compact and robust magnetic label detector for biomedical assays is implemented in 0.18-mu m CMOS. Detection relies on the magnetic relaxation signature of a microbead label for improved tolerance to environmental variations and relaxed dynamic range requirement, eliminating the need for baseline calibration and reference sensors. The device includes embedded electromagnets to eliminate external magnets and reduce power dissipation. Correlated double sampling combined with offset servo loops and magnetic field modulation, suppresses the detector offset to sub-mu T. Single 4.5-m magnetic beads are detected in 16 ms with a probability of error <0.1%.