RMS-to-DC Converter for GMI Magnetic Sensor

In a giant magnetoimpedance (GMI) magnetic sensor, the magnetic field is measured by the voltage amplitude across the sensing element, the GMI wire. Most often, the amplitude of the high-frequency signal is measured by a peak detector, i.e., a diode-capacitor system. A new measurement technique has been developed, by measuring the root mean square (rms) value of the signal. For any signal, the rms value can be used to obtain information on the signal amplitude. In the frequency domain, this type of measurement is mainly well-suited and dedicated for the high-accuracy measurement of static or low frequency magnetic field. In the amplitude domain, rms-to-dc converters can be used for relatively low-amplitude signals, up to 1 V. The rms-to-dc converter has been used with a GMI sensor. Operation in open and closed loop has been tested. The closed loop allows obtaining a very good linearity, and a better bandwidth. Alternative magnetic field at 240 Hz can be measured.