Sensitive and quick response micro magnetic sensor using amorphous wire MI element Colpitts oscillator

A new high performance micro magnetic sensor using an amorphous wire MI element (30 /spl mu/m diameter, 1/spl sim/3 mm length) is presented. The MI element works as an inductive element in the Colpitts oscillator circuit with an oscillation frequency of about 50/spl sim/100 MHz and changes its voltage amplitude with about 100%/Oe. The amplitude modulation-demodulation type field sensor circuit having a negative feedback loop shows sensing performances with a high linearity of 0.1%/FS (/spl plusmn/1 Oe), quick response at a cut off frequency of about 300 kHz, and a temperature stability of about 0.06%//spl deg/C (RT/spl sim/70/spl deg/C). The weak surface field of about 0.1 Oe of a densely magnetized ring magnet with 19 mm diameter and 1,000 poles for an accurate rotary encoder was detected using the MI sensor.