A CMOS Hybrid Magnetic Field Sensor for Real-Time Speed Monitoring

In this article, we present a CMOS hybrid magnetic field sensor for real-time motor speed monitoring for smart energy-efficient autonomous systems. The sensor system consists of a micro Hall effect sensor (
$\mu $
HES) and a micro search coil magnetometer (
$\mu $
SCM) using Taiwan Semiconductor Manufacturing Company (TSMC) 0.18-
$\mu \text{m}$
1P6M CMOS process with a die size of
$1.5\times2$
mm. The hybrid sensor is realized completely by the CMOS process without postprocessing. A wide range of rotation speeds can be measured by the presented passive
$\mu $
SCM without signal amplification (>600 r/min) and the combination of the
$\mu $
SCM and
$\mu $
HES on the same chip allows the low rotation speed range measurement (< 600 r/min). Furthermore, the
$\mu $
SCM has zero offset and very low-temperature dependency. The magnetic field of a permanent magnet on the rotating shaft of the motor is measured by the
$\mu $
SCM and
$\mu $
HES to determine the rotation speed. The sensitivity of the
$\mu $
HES (at 5-V bias voltage) and the
$\mu $
SCM inside a uniform magnetic field are 113.6 and
$11.3 \mu \text{V}$
/mT at 1 Hz without amplification, respectively. The noise equivalent magnetic induction (NEMI) of the
$\mu $
SCM was calculated and verified experimentally by utilizing a zero-drift instrumentation amplifier. Furthermore, a simplified equivalent circuit model for the
$\mu $
SCM is presented and verified experimentally. According to the equivalent circuit model, the linear frequency response region of the
$\mu $
SCM is up to 20 kHz, which suits the controlling motors in smart autonomous systems and other low-frequency applications.