The Research Of Offset And Noise Cancellation Technology On The Magnetic Hall Sensor

Magnetic Hall sensor, using CMOS or BiCMOS technology, which is a magnetoelectricity conversion components based on hall effect. It has lots of advantage, such as Simple structure, small volume, low cost, easy installation, work supply voltage range wide, long service life, high accuracy and the characteristics of preventing dust and oil, it has been widely applied to industrial frequency conversion control, transportation, health systems, consumer electronics and all kinds of intelligent instruments. However, hall sensor is easlly affected by manufacturing technology, the outside temperature and mechanical stress, they make the output signal of high offset voltage and low frequency noise, thus seriously affect the detection of faint hall signal.At present, there are a lot of circuits which can elimination the offset voltage and low frequency noise. In the overall, it includes two phase or four phase rotation current control circuit, the chopper modulation circuit, auto-zero circuit and dual-related sampling circuit. Among them, the characteristics of rotating current control circuit is simple structure, which can effectively amplification faint hall signal and dynamically eliminate offset voltage. However, auto-zero and dual-related sampling circuits need the process of sampling and keeping, so the input signal will introduce larger residual offset, it only applies to data sampling system for low demand; And the chopper modulation circuit of lower residual offset, which can be applied in continuous signal processing system.In this paper, the modulation circuit is not only to enlarge the weak hall signal, but also eliminate the offset voltage and low frequency noise. First of all, in order to enlarge the hall signal, it must use the operational amplifier, and bandgap reference voltage source can supply the bias of the op-amp, so, they are the design emphasis of this paper. In addition, in order to eliminate the offset voltage, it must use the two phase rotation current control circuit, which needs RC oscillator for supplying the clock signal. The high-pass filter of the modulation circuit can also filter the flashing noise in the useful signals.The main work of the paper is to design a regulate circuit which is based on the magnetic Hall sensor in order to eliminate the offset voltage and low frequency noise. It includes magnetic Hall sensors, rotary current control circuit, instrument amplifier, bandgap reference voltage source, comparator, Schmitt trigger and RC oscillators. Firstly, through the rotating current control circuit, hall sensor can output polarity cyclical change hall signal and polarity constant offset signal. And then, through the processing of the instrument amplifiers, sampling, keeping and adding circuit, it can output the digital hall signal. The regulate circuit can not only effectively amplification faint hall signal, but also dynamically eliminate the offset voltage. Firstly, This thesis introduces the design process and simulation test of the regulate circuit, and then optimize them. Secondly, we must complete the overall layout design and post layout simulation tests. In CSMC 0.5 um CMOS technology, the simulation results show that the circuit can work properly under 2V-4V power supply voltage. The open-loop gain and phase margin of the instrument amplifier are 72 dB and 60. Temperature drift of the bandgap reference voltage source is 3.125 ppm/℃, and PSRR is 59 dB, and static power consumption is 32.7 uW, the frequency of RC oscillator is 0.58 MHz. These parameters can meet the index requirements of the regulate circuit. And, when the magnetic Hall sensor detect the additional magnetic field signal for 1 kHz and 5 mT, at this time, the total circuit can eliminate the biggest 14 mV offset voltage; When the offset voltage is up to 10 mV, the magnetic field signal needs at least 4.34 mT in order to eliminate fundamentally the offset voltage and low frequency noise. Finally, through the subsequent layout design and simulation, we know that post layout simulation results of the regulate circuit is basically the same as before, so, it can satisfy the chip requirements of offset and noise cancellation circuit.