A CMOS OTA-C low-pass notch filter for EEG application is described. The pass-band covers four bands of brain wave and provides more than 65 dB attenuation for the 50 Hz power line interference. The OTA works in the weak inversion region and a low transconductance of 3 nA/V is achieved. The low transconductance enables using small capacitors in the OTA-C filter so that the filter is suitable for the multi-channel EEG integrated circuits. The measured results show the good performance of the filter for filtering the noise in acquired EEG signals.

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A design of orthogonal fluxgate sensor is presented, in which the sensing element consists of multiple number of cores of soft ferromagnetic thin wires closely packed together. An orthogonal fluxgate sensor with the sensing element formed by a glass-coated amorphous wire of 16μm in diameter and another orthogonal fluxgate sensor with the sensing element formed by 16 closely packed glass-coated amorphous wires of 16μm in diameter were constructed and tested. In the tests, the excitation currents passing through the sensing elements for both sensors were set in such a way that each of the amorphous wires in the sensing elements was driven by a current of equal magnitude. The current excitation frequency for each sensing element was determined such that the sensor gave the maximum sensing output. The results showed that under the excitation current of optimum frequencies the sensitivity of the 16-core sensor was 65 times higher than that of the single-core sensor, in a trend of increasing exponentially against the increase of the number of cores in the sensing element.