Offsets (short and long term) are significantly reduced in a Lorentz force magnetometer circuit. A modulated bias current supplied to the magnetometer is chopped by periodically switching its polarity. Magnetometer output is demodulated, then de-chopping performed to restore signal polarity output. Chopping of the bias current signal polarity modulates magnetic field signal to a frequency in which electrostatic force remains constant toward eliminating offset and long-term drift from said micromechanical resonator.