Magnetic relaxation detector for microbead labels in biomedical assays

A Hall-effect biosensor based on magnetic label detection is implemented in 0.18 μm CMOS. No external magnet, reference sensor or calibration is required. The sensor offset is suppressed to sub-μV by a mixed-signal feedback loop and correlated double sampling (CDS). Flicker noise and thermal noise are rejected by CDS and averaging. A single 4.5 μm bead is detected in 16 ms with a probability of error <;0.1%.