Design of fluxgate CMOS interface circuit

A novel CMOS interface circuit that has driving and detecting functions is presented to achieve the integration of interface circuit of fluxgate with three tips. The driving circuit adopts the switch network and negative feedback loop for fully differential drive in substitution for traditional centertapped transformer, balances the voltage signal on driving electrodes in real time and suppresses the influence of power supply drift and temperature variation. The detecting circuit uses switched demodulation based on the double frequency of driving signal to extract the second harmonics and adopts closed loop detection to improve the linearity of system. The whole circuitry is realized with 0.5 μm CMOS technology and its testing results show that this kind of miniature fluxgate magnetometer (the fluxgate with three tips and CMOS interface circuit) has a sensitivity of 30.8 μV/nT and a linearity error of 0.62%, in which the power supply is 10 V and the power consumption is 100 mW. The area of the chip is merely 15.54 mm².