Offset Suppression in a Micromachined Lorentz Force Magnetic Sensor by Current Chopping

We present a method to reduce offset in micromachined Lorentz force magnetic sensors by chopping the Lorentz force bias current. By switching the polarity of this current, the sensitivity of the magnetic sensor alternates its sign, whereas the offset remains the same. A residual offset of 31 μT is obtained from the initial offset of 25 mT. The proposed method significantly reduces the long-term drift of the magnetic sensor at the same time. A 9-h measurement shows the maximum drift error is reduced from ±500 μT to ±1 μT. Allan deviation measurements demonstrate that the longterm drift is reduced by a factor of 120. With 0.9 mA_rms bias current the white noise is 400 nT/rt-Hz, limited by the thermal-mechanical noise.