Piece-wise-linear amplitude regulation for oscillator with wide range tail current in inductive position sensors

The variation of oscillator amplitude in inductive position sensors causes a change of noise level on receiving coils, restricting the feasibility of off-line calibration. A method of piece-wise-linear amplitude regulation, realized by adjusting a 7-bit control word n<6:0>, is proposed for oscillators with a wide-range tail current. The n<6:0> is divided into 6 segments, and tail current is made to change exponentially with n<6:0> from segment to segment. This ensures a constant relative amplitude step across all segments, enabling both fast and accurate amplitude regulation. An oscillator with tail current ranged from 0.168 mA to 10.4 mA was designed in a 0.18 μm CMOS process. Simulation results show the maximum amplitude variation at all segments is no more than 70 mV and settling time is the duration of n<6:0>’s monotonic transition from its initial to its final value, in which the affection of amplitude variation upon position accuracy is negligible.