sensors Article

A Distance Detector with a Strip Magnetic MOSFET and Readout Circuit Guo-Ming Sung *, Wen-Sheng Lin and Hsing-Kuang Wang Department of Electrical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan; [email protected] (W.-S.L.); [email protected] (H.-K.W.) * Correspondence: [email protected]; Tel.: +886-2-2771-2171 (ext. 2121); Fax: +886-2-2731-7187 Academic Editors: Nian X. Sun, Ming Liu and Menghui Li Received: 17 November 2016; Accepted: 4 January 2017; Published: 10 January 2017

Abstract: This paper presents a distance detector composed of two separated metal-oxide semiconductor field-effect transistors (MOSFETs), a differential polysilicon cross-shaped Hall plate (CSHP), and a readout circuit. The distance detector was fabricated using 0.18 µm 1P6M Complementary Metal-Oxide Semiconductor (CMOS) technology to sense the magnetic induction perpendicular to the chip surface. The differential polysilicon CSHP enabled the magnetic device to not only increase the magnetosensitivity but also eliminate the offset voltage generated because of device mismatch and Lorentz force. Two MOSFETs generated two drain currents with a quadratic function of the differential Hall voltages at CSHP. A readout circuit—composed of a current-to-voltage converter, a low-pass filter, and a difference amplifier—was designed to amplify the current difference between two drains of MOSFETs. Measurements revealed that the electrostatic discharge (ESD) could be eliminated from the distance sensor by grounding it to earth; however, the sensor could be desensitized by ESD in the absence of grounding. The magnetic influence can be ignored if the magnetic body (human) stays far from the magnetic sensor, and the measuring system is grounded to earth by using the ESD wrist strap (Strap E-GND). Both ‘no grounding’ and ‘grounding to power supply’ conditions were unsuitable for measuring the induced Hall voltage. Keywords: distance detector; Hall effect; strip MAGFET; polysilicon cross-shaped Hall plate; magnetic sensor; readout circuit; difference amplifier; instrumentation amplifier

1. Introduction The Hall plate is a major magnetic sensor, which is fabricated using CMOS technology, for sensing the magnetic induction perpendicular to the Hall plate surface and converting it into a corresponding electrical signals such as voltage, current, and frequency [1–3]. To enhance the linear characteristics of a current-mode Hall sensor, various compensated techniques have been developed [4–6]. The Hall plate performs with low-voltage-related magnetosensitivity compared with a magnetotransistor or magnetic MOSFET (MAGFET) [7]. A split-drain MAGFET is widely used as a Hall sensor for sensing the magnetic induction perpendicular to the MAGFET plane, in which a current difference is obtained between two adjacent drains of the MAGFET [8]. The relative sensitivity depends on the primary geometric parameters and biasing conditions of the applied magnetic device [9,10]. A symmetrical and differential structure performs with effective sensitivity [8]. In addition, the strip approach is considered to transmit a biasing current of up to 500 mA, whereas in the coil approach, the biasing current is limited to 20 mA [11]. The strip MAGFET with two sources is superior to that with a shared source in terms of the biasing current. In the present study, CSHP was used to detect the applied magnetic induction and to induce the differential Hall voltages, which was connected to two gates of two separated MOSFETs and generated two separated drain currents. An output voltage was obtained using a readout circuit. Notably, the magnetosensitivity was enhanced because the drain current of the Sensors 2017, 17, 126; doi:10.3390/s17010126

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MOSFET was a quadratic equation of the induced Hall voltage, which was equal to the gate voltage of the MOSFET, and the offset voltage will be effectively eliminated by the differential topology of the CSHP [12]. Magnets and magnetic induction sensing devices are often attractive in instrumentation because they can be operated in noncontacting conditions and are small in size [13]. However, the magnetic induction decays with distance according to the power–law relationship. A magnetic induction sensing device with a high sensitivity to small magnetic induction and linear response to human motion should be selected [13]. Notably, the magnetic induction strength is in the order of tens of Gauss. The proposed device in [13] could be useful in situations that require noncontacting displacement measurements. In addition, a linear bidirectional moving-magnet actuator with elastic magnetic force was presented in [14], which is an arrangement of two linear radiometric Hall sensors and a small permanent magnet disc attached to the mobile actuator’s rod that moves between the two fixed sensors. An open-loop method, proposed by Arcire [14], uses an analog flux density transducer based on the Hall effect with a microcontroller board for acquiring and processing the analog data delivered by the transducer. The determination of the displacement around a neutral equilibrium position is easy. Moreover, Netzer described two linear methods for noncontacting position measurement based on a relative movement between a Hall-element magnetic sensor and contact gradient static magnetic induction [15]. The induction intensity at the edges of the linear range was approximately ±300 G, and the maximum error due to the earth’s magnetic induction of ±0.3 G was approximately 0.1%. In addition, a new position detecting system by using the magnetic flux of the magnet on the mover was proposed, in which a Hall element was considered in a flux sensor for a synchronous motor [16]. Moreover, an intelligent odometer was studied using the Hall effect to avoid the mechanical odometer defect. The speed and mileage were measured using the Hall sensor through the pulse detection method [17]. For distance detection, an unconventional method was proposed to identify the lane markings on a road surface through laser measurement system. This method was achieved using the reflection of the laser beam [18]. Fall detection in elderly residents was performed using an infrared distance sensor [19]. Furthermore, the Poisson distance image was acquired by solving the two-dimensional Poisson equations defined on the spatial–temporal accumulative image, and the action descriptors were fed into the nearest neighbor classifier to recognize daily actions, particularly to detect the abnormal fall action [20]. In addition, an advanced driver assistance was presented to complete the measurement of the distance between a vehicle and the detected object. Particular attention has been given to the vision-based technique because it is considered one of the most accurate systems for identifying targets and measuring the distance from the target to the vehicle [21]. In brief, distance measurement can be completed using techniques such as laser beam, infrared sensor, visual-based fall detection, and vision-based technique. However, both laser beam and infrared sensor are oriental sensors, and the visual-based fall detection and vision-based technique operate in a bright environment. The object to be measured cannot be detected if it is located in the dark or has diverged from the oriental range even when it is considerably closer to the sensor. To resolve these faults, the current study proposes a distance detecting method by using the strip MAGFET, which includes two separated MOSFETs, a differential polysilicon CSHP, and a readout circuit. The proposed distance detector could detect the distance from the magnetic body (human) to the magnetic sensor by sensing the magnetic induction of the magnetic body perpendicular to the chip surface. The strip MAGFET not only increased the magnetosensitivity but also eliminated the offset voltage which is generated because of the device mismatch and Lorentz force [22]. Moreover, a commercial instrumentation amplifier (IA) INA333 was applied to amplify the output voltage of the readout circuit and increase the detecting distance. The remainder of this paper is organized as follows. Section 2 describes the operational principles of the proposed distance detector. Section 3 presents the readout circuit for the distance detector. Section 4 presents some simulated and measured results. Section 5 presents discussion followed by conclusions.

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2. Operational Operational Principles Principles of of the the Distance Distance Detector Detector 2. Figure 11 presents presents aa strip strip MAGFET, MAGFET, which which is is composed composed of of two two separated separated MOSFETs, M1 and and M2, M2, Figure MOSFETs, M1 and aa differential differential polysilicon polysilicon CSHP, CSHP,for forsensing sensingthe themagnetic magneticinduction inductionBBZZ perpendicular perpendicular to to the the chip chip and surface. The distance from the magnetic body (human) to the magnetic device (strip MAGFET) can surface. The distance from the magnetic body (human) to the magnetic device (strip MAGFET) can be easily detected using the proposed magnetic sensor. I bias is the biasing current in the y-direction be easily detected using the proposed magnetic sensor. Ibias is the biasing current in the y-direction and FF−−XXisisthe not only only effectively effectively and theLorentz Lorentzforce forcein inthe thex-direction, x-direction,reversely. reversely. The The differential differential topology topology not cancels the offset but also doubly enhances the magnetosensitivity. A polysilicon CSHP is located on on cancels the offset but also doubly enhances the magnetosensitivity. A polysilicon CSHP is located two identical identical MOSFETs MOSFETs to the absence of two to establish establish aa strip strip MAGFET MAGFETwith withhigh highbiasing biasingcurrent current[8]. [8].InIn the absence thethe applied magnetic induction BZB , two drain currents, I D1I and I D2,I are the same at D 1 D and D 2 of the of applied magnetic induction , two drain currents, and , are the same at and D of 1 2 Z D1 D2 MOSFETs, M1 M and M2, respectively. After passing through the readout circuit, which includes a the MOSFETs, 1 and M2 , respectively. After passing through the readout circuit, which includes a current-to-voltage(I-to-V) (I-to-V)converter, converter, a low-pass (LPF), a difference amplifier (DA), the current-to-voltage a low-pass filterfilter (LPF), and aand difference amplifier (DA), the output output voltage V OUT of the DA is constant. That is, ∆V OUT = 0. By contrast, the output voltage V OUT is voltage VOUT of the DA is constant. That is, ∆VOUT = 0. By contrast, the output voltage VOUT is aa function of of the the bias bias current currentversus versusapplied appliedmagnetic magneticinduction. induction. function

Figure with twotwo separated MOSFETs and aand differential polysilicon CSHP. The Lorentz Figure1.1.Strip StripMAGFET MAGFET with separated MOSFETs a differential polysilicon CSHP. The force FL not only positive ⊕ to the left left side of the not onlythe pushes thecharge positive charge  to gather the leftattothe gather at the left polysilicon side of the Lorentz force FL pushes CSHP, but also injects electron into the right side the of the polysilicon CSHP to reduce the polysilicon CSHP, butthe also injects current the electron current  into right side of the polysilicon CSHP drain current the first MOSFET (ID1 ).MOSFET (ID1). to reduce the of drain current of the first

In general, general,the thevoltage-mode voltage-mode Hall devices be biased two modes: and In Hall devices can can be biased in twoinmodes: voltagevoltage biasing biasing and current current biasing. In the current mode, the current-related sensitivity SRI is calculated as follows biasing. In the current biasing biasing mode, the current-related sensitivity SRI is calculated as follows [23]: [23]: 1 ∆VOUT SRI ( B) = (1) VOUT 1 ∆B Ibias S RI B  (1)

 

I

B

bias where the unit of SRI bias represents the supply bias current, ∆B represents the change in the applied induction, ∆VOUT represents a variation in the∆B DA output voltage [23]. V·A−1·T−1,and Ibias represents the supply bias current, represents the change where the unitmagnetic of SRI(B) is However, the proposed MAGFET detects the distance ∆D between sensor [23]. and in the applied magnetic strip induction, and ∆V OUT represents a variation in thethe DAmagnetic output voltage magnetic body. Thus, the current-related sensitivity should be redefined as follows: However, the proposed strip MAGFET detects the distance ∆D between the magnetic sensor and

(B) is V·A−1 ·T−1 , I

magnetic body. Thus, the current-related sensitivity should be redefined as follows: 1 ∆VOUT SRI ( D ) = Ibias V 1 ∆D

S RI D  

OUT

I bias D where the unit of SRI (D) is V·A−1 ·m−1 . In addition, the nonlinearity error (NLE) is defined as the nonlinearity error (NLE) is defined as where the unit of SRI(D) is V·A−1·m−1. In addition, (0) ∆V OUT − ∆VOUT NLE = × 100% V ∆V (0)V ( 0 ) OUT OUT OUT

NLE 

( 0) VOUT

 100%

(2)

(2)

(3)

(3)

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where the unit of NLE is % and ∆V (0) OUT represents the calculated output voltage difference based on the slope of the straight line obtained from the best fit to the output characteristic [24]. The operational principle of the strip MAGFET is described below. As shown in Figure 1, two identical MOSFETs, M1 and M2 , are operated in the saturation mode. If a magnetic induction BZ and a bias current Ibias are applied to the polysilicon CSHP, the positive and negative Hall voltages, VH (+) and VH (−), are generated by Lorentz force FL in the x-direction reversely and x-direction, respectively. In other words, the gate voltage of M2 is larger than that of M1 . By grounding two sources, S1 and S2 , two drain currents, ID1 and ID2 , can be expressed as follows: (

2 ID1 = 12 µn Cox W L (VGS1 − VTH ) 2 ID2 = 12 µn Cox W L (VGS2 − VTH )

(4)

and VGS2 − VGS1 = VH (+) − VH (−) = VH

(5)

VGS1 + VGS2 = VGS 2

(6)

where µn , Cox , W, L, and VTH represent the mobility of electrons, parasitic capacitance per unit gate area, width, length, and threshold voltage, respectively. VGS1 and VGS2 represent the differential gate-to-source voltages of M1 and M2, respectively, with magnetic induction, whereas VGS represents the gate-to-source voltage without magnetic induction. Subsequently, the induced Hall voltage VH is derived from the Lorentz force. VH = G R H Ibias BZ /t (7) where R H = −µ∗n /σn = −rn /nq represents the Hall coefficient, Ibias represents the bias current in the y-direction, BZ represents the magnetic induction in the z-direction, and t and G represent the polysilicon thickness and geometrical correction factor, respectively [24]. Thus, the current difference between ID1 and ID2 can be expressed as follows: ∆ID = ID2 − ID1

    1 VGS1 + VGS2 W = µn Cox 2 − VTH (VGS1 − VGS2 ) 2 L 2

(8)

Rewriting Equation (8), we have ∆ID = µn Cox

W W × (VGS − VTH )VH = µn Cox L L



 GR H Ibias BZ (VGS − VTH ) t

(9)

As shown in Equation (9), the current difference ∆ID is directly proportional to the bias current Ibias and the magnetic induction BZ . If the bias current Ibias is set as constant, the larger the magnetic induction BZ is, the higher the drain current difference ∆ID is. The physical mechanism may be that the Lorentz force FL pushes the positive charge to the left to gather at the left side of the polysilicon CSHP, which is connected to the gate terminal G2 of the second MOSFET (M2 ). Moreover, the electron current is directly injected into the right side of the polysilicon CSHP, which is connected to the gate node G1 of the first MOSFET (M1 ), to reduce the drain current of the first MOSFET (ID1 ). By applying a magnetic induction (~mT) to the magnetic sensor, an output voltage VOUT is acquired at the output node of the readout circuit by multiplying the drain current difference ∆ID with a resistor RD in the I-to-V converter and then multiplying approximately 16 times by RA = 100 kΩ and RB = 6.2 kΩ. 3. Readout Circuit Two drain currents, ID1 and ID2 , obtained at two separated drains of two MAGFETs over the considered magnetic induction range, are of the order of few milliamperes (mA). By passing through the I-to-V converter with resistor RD and LPF with resistor R1 and capacitor C1 , the high-frequency noise will be filtered out before the entering the DA. Figure 2 presents the readout circuit of the

 1  sR C  R 1 1  B  where VREF represents a constant reference voltage, which is used to adjust the output level. ∆ID (= ID1 − ID2) is defined as the drain current difference between the first and second drains of the MAGFET. For a DC magnetic induction, s = 0, the small-signal output voltage vout is given by Sensors 2017, 17, 126

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RA (12) RB proposed distance detector, which includes the I-to-V converter, LPF, and DA. Notably, the offset v out   I D  R D 

voltage can be effectively removed using the DA, and the single output VOUT obtained is easy to use.

Figure 2. Readout circuit of the proposed distance detector comprising an I-to-V converter, low-pass Figure 2. Readout circuit of the proposed distance detector comprising an I-to-V converter, low-pass filter (LPF), and difference amplifier (DA). filter (LPF), and difference amplifier (DA).

As shown in Figure 2, an I-to-V convertercascaded was selected to convert the induced Figure 3 presents a low-voltage two-stage operational amplifier (opamp)drain withcurrent, Miller obtained from the proposed strip MAGFET, into a Hall voltage with drain resistor R . Two output D compensation and compact class-AB output stage, which is composed of two common-sourcevoltages, V VO2 , of theMI-to-V can be expressed as follows: O1 and connected output transistors, 19 and converter M20 [25]. To make the quiescent current of the output transistors ( the floating current source should have the same supply insensitive to supply voltage variations, VO1 =The VDDvalue − ID1of×the R D current source is set using two bias voltage dependency as the class-AB control. (10) V = V − I × R loaded with the drain currents of the voltages, Vb5 and Vb6. The mirrors, M7–MO2 10 and DD M15–MD2 18, are D where VDD represents the power supply. The output voltage of the DA, VOUT , passing through the LPF with resistor R1 and capacitor C1 , is given by VOUT = VREF − ∆ID × R D ×



1 1 + sR1 C1



×

RA RB

(11)

where VREF represents a constant reference voltage, which is used to adjust the output level. ∆ID (= ID1 − ID2 ) is defined as the drain current difference between the first and second drains of the MAGFET. For a DC magnetic induction, s = 0, the small-signal output voltage vout is given by vout = −∆ID × R D ×

RA RB

(12)

Figure 3 presents a low-voltage two-stage cascaded operational amplifier (opamp) with Miller compensation and compact class-AB output stage, which is composed of two common-source-connected output transistors, M19 and M20 [25]. To make the quiescent current of the output transistors insensitive to supply voltage variations, the floating current source should have the same supply voltage dependency as the class-AB control. The value of the current source is set using two bias voltages, Vb5 and Vb6 . The mirrors, M7 –M10 and M15 –M18 , are loaded with the drain currents of the input pairs M2 –M3 and M5 –M6 , respectively. These drain currents and the gate–source voltages of M7 and M17 change the common-mode input voltage. By adjusting two input bias currents with two bias voltages, Vb1 and Vb2 , the common-mode input voltage approaches the positive supply rail or the negative supply rail. The opamp is compensated by using the conventional Miller technique

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input pairs M2–M3 and M5–M6, respectively. These drain currents and the gate–source voltages of M7 and M17 change the common-mode input voltage. By adjusting two input bias currents with two bias voltages, Vb1 and Vb2, the common-mode input voltage approaches the positive supply rail or the Sensors 2017, supply 17, 126 rail. The opamp is compensated by using the conventional Miller technique 6 of 15 negative including the cascode stages, M12 and M14, in the Miller loops. This compensation technique shifts the output pole to a frequency of approximately [25]. including the cascode stages, M12 and M14 , in the Miller loops. This compensation technique shifts the output pole to a frequency of approximately [25].C g out  M  m0 (13) CGS C C M,out gm0 L (13) ωout = × CGS,out CL where gm0 represents the transconductance of the output transistors and CL represents the load where gm0 Crepresents therepresent transconductance of thecapacitor output transistors and CL represents the load capacitor. M and CGS,out the total Miller and the total gate–source capacitance of capacitor. C and C represent the total Miller capacitor and the total gate–source capacitance of GS,out the output M transistor, respectively. the output transistor, respectively.

Figure 3. Low-voltage two-stage cascaded operational amplifier with Miller compensation and compact Figure 3.output Low-voltage class-AB stage. two-stage cascaded operational amplifier with Miller compensation and compact class-AB output stage.

Figure Figure44presents presentsthe theexperimental experimentalsetup setupof ofthe thedistance distancedetector detectorcomposed composed of ofaadevice deviceunder under test (DUT), an IA (INA333, Texas Instruments, Dallas, TX, USA) printed circuit board (PCB), a digital test (DUT), an IA (INA333, Texas Instruments, Dallas, TX, USA) printed circuit board (PCB), a digital multimeter Santa Clara, CA, USA), a magnetic body (human), and a power multimeter(Agilent (Agilent34405A, 34405A, Santa Clara, CA, USA), a magnetic body (human), and regulator a power with a 9-V battery. The DUT included the strip MAGFET and readout circuit, and the magnetic body regulator with a 9-V battery. The DUT included the strip MAGFET and readout circuit, and the was actually a human weighing approximately kg. The distance was defined from thedefined chip center magnetic body was actually a human weighing65 approximately 65 kg. The distance was from of DUT to the weight of the magnetic body. Notably, theNotably, proposed detecting thethe chip center of the DUT center to the weight center of the magnetic body. thedistance proposed distance method is not only a universal detection method but also operates in dark conditions away detecting method is not only a universal detection method but also operates in dark conditions from away light To enhance the sensitivity of the distance detection and totoincrease fromemission. light emission. To enhance the sensitivity of the distance detection and increasethe thedetecting detecting distance, distance,aacommercial commercialIA IA(INA333) (INA333)was wasapplied appliedto to amplify amplify the the output output voltage voltage of of the the readout readout circuit. circuit. Figure 5 presents the applied PCB that includes two commercial IAs, two bias voltages for IAs, two Figure 5 presents the applied PCB that includes two commercial IAs, two bias voltages for IAs,bias two voltages for thefor proposed strip MAGFET, and resistors, RC and R . By adjusting the variable resistor bias voltages the proposed strip MAGFET, and resistors, RD C and RD. By adjusting the variable Rresistor power ofpower IA1 was set to 43 set dB to (approximately 150 times). D , the magnifying RD, the magnifying of IA1 was 43 dB (approximately 150 times). Figures 6 and 7 present the measured equipment that includes a magnetic induction generator, a commercial IA (INA333) PCB, and a display monitor. As shown in Figure 6, only the offset voltage was displayed on the monitor and not the magnetic body. When the magnetic body contacts with the distance detector, Hall voltage evidently appeared on the monitor, as shown in Figure 7. A quality analysis of the measured Hall voltage is presented in Figure 7. To avoid bias, a digital multimeter (Agilent 34405A) was used for the quantity analysis of the distance detector that included a strip MAGFET, readout circuit, and IA PCB (INA333).

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Figure 4. Experimental setup of distance detection.

Figure setup ofdistance distancedetection. detection. Figure 4.Experimental Experimentalsetup setupof of distance Figure 4.4.Experimental detection.

Figure 5. Applied PCB with two commercial instrumentation amplifiers (INA333).

Figures 6 and 7 present the measured equipment that includes a magnetic induction generator, a commercial IA (INA333) PCB, and a display monitor. As shown in Figure 6, only the offset voltage was displayed on the monitor and not the magnetic body. When the magnetic body contacts with the distance detector, Hall voltage evidently appeared on the monitor, as shown in Figure 7. A quality analysis of the measured Hall voltage is presented in Figure 7. To avoid bias, a digital multimeter (Agilent 34405A) was used for the quantity analysis of the distance detector that included a strip MAGFET, readout circuit, and IA PCB (INA333). amplifiers Figure Applied PCB with two commercial instrumentation amplifiers (INA333). Figure 5. Applied PCB with twocommercial commercial instrumentation (INA333). Figure 5.5.Applied PCB with two instrumentation amplifiers (INA333). Figures66and and77present presentthe themeasured measuredequipment equipmentthat thatincludes includesaamagnetic magneticinduction inductiongenerator, generator, Figures commercialIA IA(INA333) (INA333)PCB, PCB,and andaadisplay displaymonitor. monitor.As Asshown shownininFigure Figure6,6,only onlythe theoffset offsetvoltage voltage aacommercial was displayed on the monitor and not the magnetic body. When the magnetic body contacts with the was displayed on the monitor and not the magnetic body. When the magnetic body contacts with the distancedetector, detector,Hall Hallvoltage voltageevidently evidentlyappeared appearedon onthe themonitor, monitor,asasshown shownininFigure Figure7.7.AA distance qualityanalysis analysisofofthe themeasured measuredHall Hallvoltage voltageisispresented presentedininFigure Figure7.7.To Toavoid avoidbias, bias,aadigital digital quality multimeter (Agilent (Agilent 34405A) 34405A) was was used used for for the the quantity quantityanalysis analysisofofthe thedistance distancedetector detectorthat that multimeter included a strip MAGFET, readout circuit, and IA PCB (INA333). included a strip MAGFET, readout circuit, and IA PCB (INA333).

Figure 6.Figure Offset6. voltage (right(right circle) displayed ononthe withouta amagnetic magnetic body Offset voltage circle) displayed themonitor monitor without body and and DUTDUT (Device (Device under in theinduction magnetic induction generator. under test) placed intest) the placed magnetic generator.

Figure 6. Offset voltage (right circle) displayed on the monitor without a magnetic body and DUT (Device

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Figure 7. Hall voltage appears on the monitor evidently when the magnetic body comes in contact Figure 7. Hall voltage appears on the monitor evidently when the magnetic body comes in contact with the distance distance detector. detector. with the

4. Simulated and Measured Results 4. Simulated and Measured Results This paper presents a low-voltage two-stage cascaded opamp with Miller compensation and This paper presents a low-voltage two-stage cascaded opamp with Miller compensation and compact class-AB output stage based on 0.18 μm CMOS technology for distance detection [25]. The compact class-AB output stage based on 0.18 µm CMOS technology for distance detection [25]. simulated results demonstrated that the designed two-stage cascaded opamp had an open-loop gain The simulated results demonstrated that the designed two-stage cascaded opamp had an open-loop of 75.3 dB, a phase margin of 54.9°, a common-mode rejection ratio (CMRR) of 123 dB, a slew rate of gain of 75.3 dB, a phase margin of 54.9◦ , a common-mode rejection ratio (CMRR) of 123 dB, a slew rate 0.07 V/μs, an input common-mode range (ICMR) of 0.9 V, a power supply rejection ratio (PSRR) of of 0.07 V/µs, an input common-mode range (ICMR) of 0.9 V, a power supply rejection ratio (PSRR) 119 dB, an output swing of 1.70 V, power consumption of 179 μW for a power supply of 1.8 volts, of 119 dB, an output swing of 1.70 V, power consumption of 179 µW for a power supply of 1.8 volts, and a load capacitor of 10 pF. and a load capacitor of 10 pF. Figure 8 presents a measured open-loop gain of 67.7 dB and phase of 74° with respect to Figure 8 presents a measured open-loop gain of 67.7 dB and phase of 74◦ with respect to frequency. frequency. The measured open-loop gain was lower than that obtained through simulation, but the The measured open-loop gain was lower than that obtained through simulation, but the measured measured phase was higher than that obtained through simulation. Figures 9 and 10 present the phase was higher than that obtained through simulation. Figures 9 and 10 present the measured CMRR measured CMRR and PSRR, respectively, which were approximately equal to the relative simulated and PSRR, respectively, which were approximately equal to the relative simulated results. Furthermore, results. Furthermore, Figure 11 presents a measured slew rate of 0.07 V/μs, rise time of 19.73 μs, and Figure 11 presents a measured slew rate of 0.07 V/µs, rise time of 19.73 µs, and fall time of 6.67 µs at an fall time of 6.67 μs at an operating frequency of 1 kHz. The simulated and measured results compared operating frequency of 1 kHz. The simulated and measured results compared with those of previous with those of previous studies are tabulated in Table 1. Measured results of voltage gain, phase studies are tabulated in Table 1. Measured results of voltage gain, phase margin, CMRR, slew rate, margin, CMRR, slew rate, ICMR, PSRR, and output swing, were more favorable than those obtained ICMR, PSRR, and output swing, were more favorable than those obtained in previous studies [26,27]. in previous studies [26,27]. Although these previous studies have not proved the efficiency, the Although these previous studies have not proved the efficiency, the measured data in the present measured data in the present study verified that the designed opamp worked as intended. Figure 12 study verified that the designed opamp worked as intended. Figure 12 presents the microphotograph presents the microphotograph of the designed opamp without external resistors and capacitors. of the designed opamp without external resistors and capacitors. Notably, an output voltage VOUT Notably, an output voltage VOUT was acquired at the output node of the DA by multiplying the drain was acquired at the output node of the DA by multiplying the drain current difference ∆ID with current difference ∆ID with external resistors, RA = 100 kΩ and RB = 6.2 kΩ. That is, the voltage gain of external resistors, RA = 100 kΩ and RB = 6.2 kΩ. That is, the voltage gain of the DA was approximately the DA was approximately 17 times greater. 17 times greater.

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of simulated and measured results of amplifier with results of previous designs.9 of 15 SensorsTable 2017, 1. 17,Comparison 126 Table 1. Comparison of simulated and measured results of amplifier with results of previous designs.

This Work [26] [27] Specifications This Work [26] [27] Simulation Simulation Simulation Table 1. Comparison of simulated and measured Measurement results of amplifier with results of previous designs. Specifications Simulation Measurement Simulation Simulation Technology 0.18 μm 0.18 μm 0.18 μm 0.5 μm Technology 0.18 μmThis Work 0.18 μm 0.18 μm 0.5 μm [26] [27] Voltage gain (dB) 75.3 67.7 67.7 45 Specifications Voltage gain (dB) 75.3 67.7 67.7 45 Phase margin (°) 54.9 74 Simulation Measurement Simulation Simulation Phase margin (°) 54.9 74 CMRR (dB) 123 122 92 75 Technology 0.18 µm 0.18 µm 0.18 µm 0.5 µm CMRR (dB) 123 122 92 Slew rategain (V/μs) 0.07 0.07 Voltage (dB) 75.3 67.7 67.7 4575 ◦) Slew rate (V/μs) 0.07 0.07 Phase margin ( 54.9 74 - -ICMR (VPP) 0.9 0.744 CMRR(V(dB) 123 122 92 75 ICMR PP) (kHz) 0.9 0.744 Gain bandwidth 1.85 0.225 1.75 5.8 Slew rate (V/µs) 0.07 0.07 -5.8 Gain bandwidth (kHz) 1.85 0.225 1.75 UGB (MHz) 7.85 91.33 ICMR (VPP ) 0.9 0.744 - UGB (MHz) 7.85 91.33 PSRR(+) (dB)(kHz) 119 123 Gain bandwidth 1.85 0.225 1.75 5.8-PSRR(+) (dB)(V) 119 123 -UGBswing (MHz) 7.85 91.33 - -Output 1.70 1.32 PSRR(+) (dB) 119 123 Output swing (V) 1.70 1.32 Power dissipation (μW) 179 274 263 280 Output swing (V) 1.70 1.32 Power dissipation (μW) 179 274 263 280 Chip area (mm2) 0.0153 0.0153 1.49 Power dissipation 2(µW) 179 274 263 280 Chip area (mm 2) 0.0153 0.0153 1.49 Chip area (mm )

0.0153

0.0153

1.49

-

Figure of 74° Figure 8. 8. Measured Measured open-loop open-loop gain gain of of 67.7 67.7 dB dB and and phase phase of 74◦ versus versus frequency frequency (Hz). (Hz). Figure 8. Measured open-loop gain of 67.7 dB and phase of 74° versus frequency (Hz).

Figure 9. 9. Measured Measured common-mode common-mode rejection rejection ratio ratio (CMRR) (CMRR) of of the the designed Figure designed opamp. opamp. Figure 9. Measured common-mode rejection ratio (CMRR) of the designed opamp.

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Figure 10. Measured Measuredpower power supply rejection ratio (PSRR) of designed the designed opamp respect to Figure 10. supply rejection ratio (PSRR) of the opamp with with respect to frequency frequency (Hz). (Hz).

Figure 11. 11.Measured Measuredslew slewrate rateofof 0.07 V/μs,rise rise time 19.73 time of 6.67 an operating Figure 0.07 V/µs, time of of 19.73 µs,μs, andand fallfall time of 6.67 µs atμs anatoperating frequency of 1 kHz. frequency of 1 kHz.

To elucidate the detection mechanism, the experimental setup can be divided into three To elucidate the detection mechanism, the experimental setup can be divided into three categories: categories: direct measurement without grounding (direct), grounding to earth with electrostatic direct measurement without grounding (direct), grounding to earth with electrostatic discharge (ESD) discharge (ESD) wrist strap (Strap E-GND), and grounding to power supply with ESD wrist strap wrist strap (Strap E-GND), and grounding to power supply with ESD wrist strap (Strap S-GND). (Strap S-GND). The first category elucidates the influence of ESD without grounding. Next, ESD will The first category elucidates the influence of ESD without grounding. Next, ESD will be eliminated be eliminated from the magnetic sensor by grounding it to earth. Finally, in the third category, the from the magnetic sensor by grounding it to earth. Finally, in the third category, the ESD wrist strap ESD wrist strap is grounded to the power supply, and not to earth. This connection will enable the is grounded to the power supply, and not to earth. This connection will enable the removal of ESD removal of ESD from the magnetic sensor to the power supply; however, ESD always exists between from the magnetic sensor to the power supply; however, ESD always exists between the power supply the power supply and earth. and earth.

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Figure Microphotograph of designed the designed low-voltage two-stage cascaded without Figure 12. 12. Microphotograph of the low-voltage two-stage cascaded opampopamp without external external resistors and capacitors. resistors Figureand 12.capacitors. Microphotograph of the designed low-voltage two-stage cascaded opamp without external resistors and capacitors.

Figure 13 presents the measured output Hall voltages as a function of the distance, from 0 cm to presents the at measured Hall (I voltages as a function of the distance, from 0 cm to 120Figure cm in 13 steps of 10 cm, a CSHP output bias current bias) of 12 mA. In the first category, the measured Figure 13 presents the measured output Hall voltages as a function of the distance, from 0 cm to 120output cm in stepsvoltage of 10 cm, at afrom CSHP biastocurrent (IbiasThe ) of voltage 12 mA. variation In the first category, the measured 58.35 59.00 mA. approximately 0.65 120 cm Hall in steps of 10varied cm, at a CSHP bias current (Ibias) of 12 mA. In the firstwas category, the measured output Hall voltage varied from 58.35 to 59.00 mA. The voltage variation was approximately 0.65 mV. mV. In the second category, the variation in the measured output Hall voltage was approximately output Hall voltage varied from 58.35 to 59.00 mA. The voltage variation was approximately 0.65 In 5.04 the second category, the62.58 variation inthe the third measured output Hall voltage wasmeasured approximately from 57.54category, to mV.variation In category, theoutput variation involtage the output5.04 HallmV, mV. mV, In the second the in the measured Hall was approximately from 57.54was to 62.58 mV. In the third category, the variation in the measured output Hall voltage was voltage approximately 3.12 mV,In from 60.58 to 63.70 mV. voltage, 5.04 mV, from 57.54 to 62.58 mV. the third category, theAccording variation to in the themeasured measuredHall output Hall approximately 3.12 mV, from 60.58 to 63.70 mV. According to the measured Hall voltage, the second the second category performed with a more efficient sensitivity than the other two, and the first voltage was approximately 3.12 mV, from 60.58 to 63.70 mV. According to the measured Hall voltage, category performed a morewith efficient sensitivity than the other two, and the and firstthe category category performed with minimum sensitivity of nearlysensitivity zero. That is, ESD could betwo, eliminated from the second categorywith performed a more efficient than the other first the magnetic sensor by grounding it to earth; however, ESD will cancel the sensitivity out when thethe performed with minimum sensitivity of nearly zero. That is, ESD could be eliminated from category performed with minimum sensitivity of nearly zero. That is, ESD could be eliminated from sensor is not grounded. Notably, saturation was observed in the second category. This result indicates magnetic sensor by grounding it to earth; however, ESD will cancel the sensitivity out when the sensor the magnetic sensor by grounding it to earth; however, ESD will cancel the sensitivity out when the that theis magnetic influence cansaturation be was ignored if observed theinhuman stayed farcategory. fromThis theThis DUT, which was is not grounded. Notably, saturation observed theinsecond category. result indicates that sensor not grounded. Notably, was the second result indicates grounded to earth by using the ESD wrist strap (Strap E-GND). However, the first and third thethat magnetic influence can be ignored if the human fromfar thefrom DUT,the which grounded the magnetic influence can be ignored if the stayed human far stayed DUT,was which was were still by the magnetic body(Strap (human). Both grounding’ ‘grounding to categories earth by using the influenced ESD wristthe strap (Strap However, the‘no first and third categories were grounded to earth by using ESD wristE-GND). strap E-GND). However, the and first and third to power supply’ were unsuitable for measuring the induced Hall voltage although the magnetic were influencedbody by the magneticBoth body (human). Bothand ‘no grounding’ ‘grounding stillcategories influenced by still the magnetic (human). ‘no grounding’ ‘groundingand to power supply’ body was far and away the designed DUT. to unsuitable power supply’ were from unsuitable for measuring the induced voltage although thefarmagnetic were for measuring the induced Hall voltage althoughHall the magnetic body was and away body far andDUT. away from the designed DUT. from thewas designed

Figure 13. Measured output Hall voltages as a function of the distance, from 0 to 120 cm in steps of 10 cm, at a bias13. current of 12 output mA forHall the proposed strip MAGFET with readoutfrom circuit IA PCB (INA333). Figure Measured voltages of the distance, 0 toand 120 in cm steps 10 cm, Figure 13. Measured output Hall voltagesasasa afunction function of the distance, from 0 tocm 120 inofsteps at a bias current of 12 mA for the proposed strip MAGFET with readout circuit and IA PCB (INA333). of 10 cm, at a bias current of 12 mA for the proposed strip MAGFET with readout circuit and

IA PCB (INA333).

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Figure from 0 to 120120 cmcm in steps of 10 Figure 14 14 presents presents the themeasured measuredNLE NLEasasa afunction functionofofdistance, distance, from 0 to in steps of cm, and various categories forfor thethe designed strip MAGFET 10 cm, and various categories designed strip MAGFETwith witha areadout readoutcircuit circuitand andan anIA IA PCB. PCB. The variation in inNLE NLEwas waslarge largewhen whenthe theMAGFET MAGFET was operated category 2 conditions in which The variation was operated in in category 2 conditions in which the the measurement is completed by grounding the sensor to earth with an ESD wrist strap (Strap Emeasurement is completed by grounding the sensor to earth with an ESD wrist strap (Strap E-GND). GND). NLEnearly was nearly constant the measurement finished without grounding. The The sensor NLE was constant whenwhen the measurement waswas finished without grounding. sensor performed with a linear characteristic when operated in category 1, but yielded a quadratic curve performed with a linear characteristic when operated in category 1, but yielded a quadratic curve in in categories zero at at two two distances, distances, 20 20 and and 100 100 cm. cm. The measured categories 22 and and 3. 3. Notably, Notably, NLE NLE was was equal equal to to zero The measured (0) on the output was equal to the calculated output voltage difference ∆V(0)OUT output voltage voltage difference difference ∆V ∆VOUT OUT was equal to the calculated output voltage difference ∆V OUT on basis of the slope of the straight line obtained from the best fit to the output characteristic [24]. the basis of the slope of the straight line obtained from the best fit to the output characteristic [24].

14. Measured Measured nonlinearity errors (NLE) in categories 1, 2,3,and 3, against the distance, Figure 14. nonlinearity errors (NLE) in categories 1, 2, and against the distance, from 0 from to in 120steps cm in steps cm, for the proposed strip with MAGFET with circuit a readout and to 1200cm of 10 cm,offor10the proposed strip MAGFET a readout and circuit an IA PCB an IA PCB (INA333). (INA333).

Table summarizes the of the Table 22 summarizes the measured measured results results of the proposed proposed strip strip MAGFET MAGFET with with aa readout readout circuit circuit and an IA PCB (INA333). The average nonlinearity NLE ave and the maximum nonlinearity NLEmax max and an IA PCB (INA333). The average nonlinearity NLEave and the maximum nonlinearity NLE were proportional to to the the measured measured Hall Hall voltage voltage difference difference ∆V ∆VH H and current-related sensitivity were proportional and the the current-related sensitivity S RI (D) with a bias current of 12 mA. The maximum current-related magnetosensitivity was 0.35 SRI (D) with a bias current of 12 mA. The maximum current-related magnetosensitivity was 0.35 V/A ·m V/A·m at an output Hall voltage of 5.04 mV and a distance of 0 cm (i.e., the magnetic body contacts at an output Hall voltage of 5.04 mV and a distance of 0 cm (i.e., the magnetic body contacts with with The measured demonstrated the proposed strip MAGFET was an effective DUT).DUT). The measured resultsresults demonstrated that thethat proposed strip MAGFET was an effective distance distance sensor; however, it presented poor linearity. Figure 15 presents a microphotograph of the sensor; however, it presented poor linearity. Figure 15 presents a microphotograph of the proposed 2 2 proposed strip with MAGFET chip area of approximately 100. × 220 μm . strip MAGFET a chipwith areaaof approximately 100 × 220 µm Table Hall voltages. voltages, Table 2. 2. Measurements Measurements of of maximum maximum output output Hall

Category

Category

1 1 22 33

∆VH ∆VH (mV) (mV) 0.65 0.65 5.04 5.04 3.12 3.12

SRI(D)

SRI (D) (V/A·M) (V/A·M)

0.045 0.045 0.350 0.350 0.217 0.217

NLEave NLEave (%) (%) 0.055 0.055 0.729 0.729 0.349 0.349

NLEmax NLEmax (%) (%) 0.112 0.112 1.426 1.426 0.732 0.732

Ibias Ibias (mA) (mA) 12 12 1212 1212

Distance Distance (cm) (cm) 120 120 120 120 120 120

Grounded Grounded Mode Mode Direct Direct Strap E-GND Strap E-GND Strap S-GND Strap S-GND

∆V∆V H; H optimum current-related magnetosensitivities, (D); average nonlinearity error, NLEave; ; optimum current-related magnetosensitivities, SRI (D);SRI average nonlinearity error, NLEave ; maximum nonlinearity error, NLE ; and maximum distance at a bias current of 12 mA for the proposed strip MAGFET max maximum nonlinearity error, NLEmax; and maximum distance at a bias current of 12 mA for the with a readout circuit and an IA PCB. proposed strip MAGFET with a readout circuit and an IA PCB.

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Figure 15. Microphotograph Microphotograph of the proposed proposed strip MAGFET comprising two separated separated MOSFETs and polysilicon cross-shaped cross-shaped Hall Hall plate plate (CSHP). (CSHP). a differential polysilicon

5. Conclusions 5. Conclusions In this this paper, paper, aa strip strip MAGFET MAGFET with with aa readout readout circuit circuit and and an an IA IA PCB PCB (INA333) (INA333) is is presented presented to to In measure the the distance distancefrom fromaamagnetic magneticbody body (human) DUT, which fabricated using measure (human) to to thethe DUT, which waswas fabricated using 0.180.18 µm μm 1P6M CMOS technology. The object to be measured cannot be detected using the proposed 1P6M CMOS technology. The object to be measured cannot be detected using the proposed magnetic magnetic sensor if the object is the dark or has from diverged from the oriental when sensor if the object is located in located the darkinor has diverged the oriental range evenrange wheneven the object theconsiderably object is considerably closer to theThe sensor. The physical mechanism underlying this phenomenon is closer to the sensor. physical mechanism underlying this phenomenon is that is that the Lorentz force pushes the positive charge to the left to gather at the left side of the polysilicon the Lorentz force pushes the positive charge to the left to gather at the left side of the polysilicon CSHP, which which is is connected connected to to the the gate gate terminal terminal of of the the second second MOSFET MOSFET (M (M22). ). The The current current difference difference CSHP, ∆IDD between the ∆I between the the two two drains drains will will be be amplified amplified linearly. linearly. After After passing passing through through the the readout readout circuit, circuit, the magnetosensitivity of the sensor will be improved effectively by amplifying the current difference magnetosensitivity of the sensor will be improved effectively by amplifying the current difference ∆IDD.. The by ∆I Theexperimental experimentalresults resultsrevealed revealed that that ESD ESD could could be be eliminated eliminated from from the the magnetic magnetic sensor sensor by grounding the sensor to earth; however, the magnetosensitivity is canceled out without grounding. grounding the sensor to earth; however, the magnetosensitivity is canceled out without grounding. Furthermore, the which is is Furthermore, the magnetic magnetic influence influence can can be be ignored ignored if if the the human human stays stays far far from from the the DUT, DUT, which grounded to to earth earth by by using using the the ESD ESD wrist wrist strap strap (Strap grounded (Strap E-GND). E-GND). Both Both ‘no ‘no grounding’ grounding’ and and ‘grounding ‘grounding to power supply’ were unsuitable for measuring the induced Hall voltage of the magnetic to power supply’ were unsuitable for measuring the induced Hall voltage of the magnetic body. body. Notably, the the NLE NLE was was nearly nearly constant constant when when the the measurement measurement was Notably, was completed completed without without grounding. grounding. The sensor yielded a quadratic curve in The sensor performed performed with withaalinear linearcharacteristic characteristicinincategory category1,1,whereas whereas yielded a quadratic curve categories 2 and 3. The maximum current-related magnetosensitivity of 0.35 V/A·m was obtained at in categories 2 and 3. The maximum current-related magnetosensitivity of 0.35 V/A·m was obtained anan output Hall voltage of 5.04 mVmV andand a distance of 0 of cm0 (i.e., the magnetic bodybody was in contact with at output Hall voltage of 5.04 a distance cm (i.e., the magnetic was in contact the DUT). According to the measured results, the proposed strip MAGFET with a readout circuit and with the DUT). According to the measured results, the proposed strip MAGFET with a readout circuit an IA PCB (INA333) is an efficient distance detector. Moreover, this study is unique because it and an IA PCB (INA333) is an efficient distance detector. Moreover, this study is unique because compensates forfor the distance it compensates thelack lackofofthe theresearch researchliterature literaturein in Open Open Access Access Publishing Publishing related related to to distance detection by using a magnetic sensor. detection by using a magnetic sensor. Acknowledgments: The Acknowledgments: The authors authors would would like like to thank the Ministry of Science and Technology, R.O.C., for financially supportingthis thisresearch researchunder under Contract No. MOST 103-2622-E-027-014-CC3. are grateful financially supporting Contract No. MOST 103-2622-E-027-014-CC3. They They are grateful to the to theImplementation Chip Implementation Taiwan, for fabricating thechip. test chip. Nicholson is appreciated for Chip CenterCenter (CIC),(CIC), Taiwan, for fabricating the test Jane Jane Nicholson is appreciated for her her editorial assistance. editorial assistance. Author Contributions: This study was completed with three contributors. G.-M.S. designed the magnetic device, Author Contributions: study was completed with three contributors. G.-M.S. the designed the magnetic completed the theoreticalThis analysis, and wrote the paper; W.-S.L. conceived and designed experiments; H.-K.W. device, completed thesurveyed theoretical analysis, and wrote the paper; W.-S.L. conceived and designed the analyzed the data and the references. experiments; H.-K.W.The analyzed thedeclare data and surveyed references. Conflicts of Interest: authors no conflict of the interest. Conflicts of Interest: The authors declare no conflict of interest.

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References 1. 2.

3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

15. 16.

17.

18.

19.

20.

Henriksen, D.; Dalslet, B.T.; Skieller, D.H.; Lee, K.H.; Okkels, F.; Hansen, M.F. Planar Hall effect bridge magnetic field sensors. Appl. Phys. Lett. 2010, 97. [CrossRef] Heidari, H.; Gatti, U.; Bonizzoni, E.; Maloberti, F. Low-noise low-offset current-mode Hall sensors. In Proceedings of the 9th Conference on Ph.D. Research in MicroElectronics and Electronics (PRIME 2013), Villach, Austria, 24–27 June 2013; pp. 325–328. Nathan, I.A.; Mckay, I.; Filanovsky, M.; Baltes, H.P. CMOS oscillator with magnetic-field frequency modulation. IEEE J. Solid State Circuits 1987, 22, 230–232. [CrossRef] Heidari, H.; Bonizzoni, E.; Gatti, U.; Maloberti, F. A 0.18-µm CMOS current-mode Hall magnetic sensor with very low bias current and high sensitive front-end. In Proceedings of the 2014 IEEE Sensors, Valencia, Spain, 2–5 November 2014; pp. 1467–1470. Ajbl, A.; Pastre, M.; Kayal, M. A fully integrated Hall sensor microsystem for contactless current measurement. IEEE Sens. J. 2013, 13, 2271–2278. [CrossRef] Pastre, M.; Kayal, M.; Blanchardl, H. A Hall sensor analog front end for current measurement with continuous gain calibration. IEEE Sens. J. 2007, 7, 860–867. [CrossRef] Min, Y.J.; Kwon, C.K.; Kim, H.K.; Kim, C.; Kim, S.W. A CMOS magnetic Hall sensor using a switched biasing amplifier. IEEE Sens. J. 2012, 12, 1195–1196. [CrossRef] Donoval, M.; Daricek, M.; Stopjakova, V.; Donoval, D. Magnetic FET-based on-chip current sensor for current testing of low-voltage circuits. J. Electr. Eng. 2008, 59, 122–130. Yunruo, Y.; Dazhong, Z.; Qing, G. Sector split-drain magnetic field effect transistor based on standard CMOS technology. Sens. Actuators A Phys. 2005, 121, 347–351. [CrossRef] Castaldo, F.C.; Mognon, V.R.; dos Reis Filho, C.A. Magnetically cupled current sensors using CMOS split-drain transistors. IEEE Trans. Power Electron. 2009, 24, 1733–1736. [CrossRef] Torres, R.R.; Dominguez, E.A.G.; Klima, R.; Selberherr, S. Analysis of split-drain MAGFETs. IEEE Trans. Electron Devices 2004, 51, 2237–2245. [CrossRef] Sung, G.M.; Yu, C.P. 2-dimensional differential folded vertical Hall device fabricated on a p-type substrate using CMOS technology. IEEE Sens. J. 2013, 13, 2253–2262. [CrossRef] Mccall, W.D.; Rohan, E.J. A linear position transducer using a magnet and Hall effect devices. IEEE Trans. Instrum. Meas. 1977, 26, 133–136. [CrossRef] Arcire, A.; Mihalache, G. Position control of a bidirectional moving magnet actuator based on contactless Hall-effect transducer. In Proceedings of the 9th International Symposium on Advanced Topics in Electrical Engineering, Bucharest, Romania, 7–9 May 2015; pp. 417–421. Netzer, Y. A very linear noncontact displacement with a Hall-element magnetic sensor. Proc. IEEE 1981, 69, 491–492. [CrossRef] Sugimoto, T.; Suzuki, K.; Dohmeki, H. A position detecting method using Hall element for discontinuous stator permanent magnet linear synchronous motor. In Proceedings of the XIX International Conference on Electrical Machines (ICEM 2010), Rome, Italy, 6–8 September 2010; pp. 1–6. Chen, B.; Lu, G.; Hao, R.; Hu, L.; Tian, X. Intelligent speed and mileage measurement system for vehicles based on Hall sensor. In Proceedings of the 2009 First International Workshop on Education Technology and Computer Science, Wuhan, China, 7–8 March 2009; pp. 272–274. Hernandez, D.C.; Filonenko, A.; Seo, D.; Jo, K.H. Laser scanner based heading angle and distance estimation. In Proceedings of the 2015 IEEE International Conference on Industrial Technology (ICIT), Seville, Spain, 17–19 March 2015; pp. 1718–1722. Jankowski, S.; Szymanski, Z.; Dziomin, U.; Mazurek, P.; Wagner, J. Deep learning classifier for fall detection based on IR distance sensor data. In Proceedings of the 2015 IEEE 8th International Conference on Intelligent Data Acquisition and Advanced Computing Systems, Technology and Applications (IDAACS), Warsaw, Poland, 24–26 September 2015; pp. 723–727. Qian, H.M.; Zhou, J.; Yuan, Y. Visual-based fall detection using histogram of oriented gradients of Poisson distance image. In Proceedings of the 2015 Chinese Automation Congress (CAC), Wuhan, China, 27–29 November 2015; pp. 657–662.

Sensors 2017, 17, 126

21.

22. 23. 24. 25.

26.

27.

15 of 15

Zhao, M.; Mammeri, A.; Boukerche, A. Distance measurement system for smart vehicles. In Proceedings of the 2015 7th International Conference on New Technologies, Mobility and Security (NTMS), Paris, France, 27–29 July 2015; pp. 1–5. Rezaei, N.; Dehghani, R.; Jalili, A.; Mosahebfard, A. CMOS magnetic sensor with MAGFET. In Proceedings of the 2013 21st Iranian Conference on Electrical Engineering (ICEE), Mashhad, Iran, 14–16 May 2013; pp. 1–5. Baltes, H.P.; Popovic, R.S. Integrated semiconductor magnetic field sensors. Proc. IEEE 1986, 74, 1107–1132. [CrossRef] Roumenin, C.S. Bipolar magnetotransistor sensors: An invited review. Sens. Actuators A Phys. 1990, 24, 83–105. [CrossRef] Hogervorst, R.; Tero, J.P.; Eschauzier, G.H.; Huijsing, J.H. A compact power-efficient 3 V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries. IEEE J. Solid State Circuits 1994, 29, 1505–1513. [CrossRef] Goel, A.; Singh, G. Novel high gain low noise CMOS instrumentation amplifier for biomedical applications. In Proceedings of the IEEE 2013 International Conference on Machine Intelligence and Research Advancement (ICMIRA), Jammu, India, 21–23 December 2013; pp. 392–396. Goswami, M.; Khanna, S. DC suppressed high gain active CMOS instrumentation amplifier for biomedical application. In Proceedings of the IEEE 2011 International Conference on Emerging Trends in Electrical and Computer Technology (ICETECT), Nagercoil, India, 23–24 March 2011; pp. 747–751. © 2017 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).