Improvement of the (mu)-Hall magnetic sensor sensitivity at low frequency

We have developed a configuration for precision magnetic measurements associating a (mu)-Hall sensor, a modulated ferromagnetic antenna, and an analog electronic circuitry. This association is not only able to remove the 1/f noise of the Hall sensor, but also to achieve an ultimate noise level even lower than thermal white noise of the Hall sensor. The system main characteristics are the following: bandwidth 645 Hz, noise level white and lower than 10 nT/(radical)Hz above 0.1 Hz, slew rate 10/sup -1/ T/s and system dynamic 84 dB in a 1-Hz bandwidth. The performances of the modulated sensor are compared to those of a dc operated sensor.