A CMOS smart rotary encoder using magnetic sensor arrays

This paper presents a new concept of small magnetic rotary encoders. The magnetic field induced by a rotatable magnet is detected by integrated CMOS magnetic sensors (MAGFETs) arranged in a square form. This magnetic sensor array is integrated on a CMOS chip with angle detection circuits, leading to the realization of a small-size and cost-effective rotary encoder. Commonly-used magnetic encoders using MR or Hall devices combined with a multi-pole magnet are difficult to meet the requirements of small-size, high-resolution, and absolute angle detection. The measurement result of a prototype sensor chip shows that the detected error angle is less than 0.36 [deg.]. This demonstrates for the first time that a CMOS small-size rotary encoder can achieve the resolution of 10 bits per rotation.