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The authors have presented a pulse frequency modulation (PFM) amorphous wire CMOS IC magneto-impedance (MI) sensor for the purpose of omitting the A/D converter in the electronic compass for mobile phone application by counting the output square wave voltage width with the number of timing pulses of the microprocessor. Elimination of A/D converters is useful for downsizing, speed up and cost cutting in the mobile phone electronic compass. However, output stability of the PFM-MI sensor should be improved by canceling the fluctuation of sensor circuit parameter (R, C) with temperature variation. They recently constructed a pulsewidth modulation (PWM) amorphous wire CMOS IC MI sensor on the basis of the PFM-MI sensor detecting the pulse duty ratio proportional to the applied magnetic field strength, in which the sensor circuit parameter (R, C) are canceled in the sensor output equation for the improvement of the magnetic field sensing stability to temperature variation.