Research On Key Technologies Of Low-power Magnetic Switching Based On AMR

Magnetic sensor has the characteristics of anti-vibration,anti-noise ability,high sensitivity,and has been widely used in modern human production and life.Magnetic switch is an important member of magnetic sensor,which is controlled by magnetic signal and plays an important role in all kinds of non-contact control systems.In this thesis based on the 0.18μm BCD process of a foundry and the magnetic characteristics of AMR Wheatstone bridge,a low-power magnetic switch chip based on AMR is designed and completed.It can sense changes in external magnetic field,convert magnetic signal into electrical signal,and compare the potential of this signal with the set threshold voltage through the circuit.The result obtained is Open-Drain output.This thesis mainly focuses on the low power consumption and high precision detection of magnetic field,and does the following research work:1.The working principle of AMR effect and Wheatstone bridge based on AMR effect is studied in this thesis and the relevant key parameters are derived in detail.Based on the current mainstream magnetic switch chip architecture and related performance parameters,the chip index parameters and chip design scheme designed in this thesis are proposed from the perspective of low power consumption and high precision magnetic field detection.2.In order to realize low power detection of external magnetic field,the magnetic switch chip designed in this thesis uses the enable control of low power clock and timer to periodically wake up and sleep: in the wake up state,each circuit module in the chip is enabled to work,detect the external magnetic field,refresh the magnetic field detection results and send them to the OUT pin.Each circuit module is closed during sleep,and only the built-in low power clock and timer work.3.In order to realize the high precision detection of external magnetic field,this thesis has designed and completed the temperature compensation scheme and AMR Wheatstone bridge imbalance voltage calibration scheme,eliminate the interference of AMR Wheatstone bridge non-ideal factors.4.Cadence platform is used to design and simulate each important sub-module circuit.The working principle,design process and simulation results of low power clock circuit,timer,low imbalance comparator,threshold reference circuit,over temperature protection circuit and under voltage protection circuit are introduced in detail.5.The simulation results show that the average current of the designed magnetic switch is 0.5μA under the typical working period(25ms),14.1μA under the fastest working period(250μs),the residual deviation of the offset voltage after calibration is40μV,and the maximum error of the magnetic field detection accuracy of the circuit is not more than 6.5%.Compared with similar foreign magnetic switch products,it has obvious advantages in power consumption and speed.The overall layout area of chip is600μm×580μm.