Research And Design Of High Precision Linear Hall Magnetic Sensor

Hall magnetic sensors have been widely used in industrial control,medical equipment,smart instrumentation,and automobiles owing to its small size,low cost,and other outstanding performance,which are used to detect current,speed,angle,position,and so on.However,the output signal of the Hall devices is generally weak and it is also accompanied by serious offset and temperature drift.In this thesis,a high-precision linear Hall magnetic sensor chip is designed and implemented in SMIC0.18 ?m CMOS technology.The linear amplification circuit of Hall signal,the offset cancellation and temperature drift compensation technique are studied in depth.The main research contents and results are as follows:(1)Design and realization of linear amplification and offset cancellation circuit for the Hall magnetic sensor.Different from the traditional one-time offset cancellation technology,twice cancellation operations are operated on the Hall offset voltage to obtain extremely low residual offset and excellent linearity.First,a modulation circuit is used to separate the Hall signal and the offset signal.Then,the modulated signal is linearly amplified by an instrumentation amplifier.After that,the Hall and offset signals are performed subtraction and addition functions by sample-and-hold subtractor and adder respectively to eliminate the offset voltage.Finally,the high-frequency interference signal is filtered through a low-pass filter,and the linear Hall voltage is obtained with a very low residual offset.The test results show that in the magnetic field range of-100 to 100 m T,the Hall voltage is changed linearly with the magnetic field,and the linearity is as high as 99.9%.The magnetic field sensitivity is 5.8 V/T,and the residual offset is as low as 62 ?T.(2)Design of a compensation circuit for sensitivity temperature drift for the Hall magnetic sensor.Unlike the traditional open-loop compensation method,the thesis adopts a closed-loop continuous calibration compensation method,which can not only compensate the temperature drift of sensitivity but also has a good compensation effect for the sensitivity drift caused by device aging and mechanical stress.A metal coil is used to generate a reference magnetic field inside the Hall magnetic sensor chip,which does not change with temperature.The reference magnetic field is induced by the Hall device and generates a reference voltage.When the variation of temperature,the output Hall voltage is compared with the reference voltage to compensate the temperature drift of sensitivity through a feedback loop.The simulation results show that after temperature compensation,the temperature drift coefficient of the Hall device sensitivity is as low as 53 ppm/? in the operating temperature range of-40 to 150 ?.(3)Design and realization of the system protection circuit for the Hall magnetic sensor,including under-voltage and over-temperature protection circuits.The circuit structure is simple and has a "hysteresis" function to avoid outputting useless rotation near the under-voltage threshold and overtemperature threshold.The hysteresis comparator structure is adopted to cut off power of the Hall magnetic sensor under the circumstances of under-voltage and over-temperature to protect itself.The simulation results show that the under-voltage protection circuit and the over-temperature protection circuit can start normally when the two pre-setting thresholds are reached,and the power supply is cut off to protect the chip.In addition,the test result of the under-voltage protection circuit shows that its basic function is normal and has the under-voltage protection function.