CMOS magnetic field to frequency converter

A CMOS magnetic field to frequency converter with high resolution is presented. It is composed of two voltage-controlled ring oscillators whose output frequency differences linearly vary with the magnetic field perpendicular to the chip surface. The prototype circuit has been fabricated in a 0.5-μm CMOS process and operated at a 5-V supply voltage. The measured sensitivity is 24 kHz/mT and the power consumption is 5.1 mW. The small equivalent resolution of at least 20 μT can be achieved. The frequency offset is 42 kHz when no magnetic field applied. Its nonlinearity within ±120 mT is smaller than 0.56%.