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Philips Magnetoresistive Sensor manual

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Table of contents for the manual

  • Page 1

    2000 Sep 06 DISCRETE SEMICONDUCT ORS General Magnetoresistive sensors for magnetic field measurement[...]

  • Page 2

    2000 Sep 06 2 Philips Semiconductors Magnetoresistive sensor s for magnetic field measurement General CONTENTS General field measurement • Operating principles • Philips magnetoresistive sensors • Flipping • Effect of temperature on behaviour • Using magnetoresistive sensors • Further information for advanced users • Appendix 1: The[...]

  • Page 3

    2000 Sep 06 3 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General The KMZ range of magnetoresistive sensors is characterized by high sensitivity in the detection of magnetic fields, a wide operating temperature range, a low and stable offset and low sensitivity to mechanical stress. They therefore provide an exc[...]

  • Page 4

    2000 Sep 06 4 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General In this basic form, the MR effect can be used effectively for angular measurement and some rotational speed measurements, which do not require linearization of the sensor characteristic. In the KMZ series of sensors, four permalloy strips are arra[...]

  • Page 5

    2000 Sep 06 5 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Two further resistors, R T , are included, as shown in Fig.5. These are for trimming sensor offset down to (almost) zero during the production process. For some applications however, the MR effect can be used to its best advantage when the sensor [...]

  • Page 6

    2000 Sep 06 6 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Flipping The internal magnetization of the sensor strips has two stable positions. So, if for any reason the sensor is influenced by a powerful magnetic field opposing the internal aligning field, the magnetization may flip from one position to th[...]

  • Page 7

    2000 Sep 06 7 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Figure 7 also shows that the flipping itself is not instantaneous, because not all the permalloy strips flip at the same rate. In addition, it illustrates the hysteresis effect exhibited by the sensor. For more information on sensor flipping, see [...]

  • Page 8

    2000 Sep 06 8 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Fig.9 Output voltage ‘V o ’ as a fraction of the supply voltage of a KMZ10B sensor as a function of transverse field ‘H y ’ for several temperatures. handbook, full pagewidth 3 0 15 32 2 MLC134 5 10 10 5 15 0 1 1 H (kA/m) y V O (mV/V) T = [...]

  • Page 9

    2000 Sep 06 9 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Figure 10 is similar to Fig.9, but with the sensor powered by a constant current supply. Figure 10 shows that, in this case, the temperature dependency of sensitivity is significantly reduced. This is a direct result of the increase in bridge resi[...]

  • Page 10

    2000 Sep 06 10 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Using magnetoresistive sensors The excellent properties of the KMZ magnetoresistive sensors, including their high sensitivity, low and stable offset, wide operating temperature and frequency ranges and ruggedness, make them highly suitable for us[...]

  • Page 11

    2000 Sep 06 11 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Further information for ad vanced users T HE MR EFFECT In sensors employing the MR effect, the resistance of the sensor under the influence of a magnetic field changes as it is moved through an angle α as given by: (2) It can be shown that (3) a[...]

  • Page 12

    2000 Sep 06 12 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General For sensors using Barber poles arranged at an angle of +45 ° to the strip axis, the following expression for the sensor characteristic can be derived (see Appendix 1 on the MR effect): (7) The equation is linear where H/H o = 0, as shown in Fig.[...]

  • Page 13

    2000 Sep 06 13 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General The following general recommendations for operating the KMZ10 can be applied: • To ensure stable operation, avoid operating the sensor in an environment where it is likely to be subjected to negative external fields (‘ − H x ’). Preferabl[...]

  • Page 14

    2000 Sep 06 14 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Fig.16 KMZ10B application circuit with instrumentation amplifier. handbook, full pagewidth MLC145 KMZ10B offset R2 V O V S R1 R3 OP2 R7 R4 R6 R KTY82-110 R5 R9 R10 R12 R11 R13 R14 OP1 OP3 T R A R B The amplification of the input stage (‘OP1’ [...]

  • Page 15

    2000 Sep 06 15 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General APPENDIX 1: THE MA GNET ORESISTIVE EFFECT Magnetoresistive sensors mak e use of the fact that the electrical resistance ρ of cer tain ferromagnetic allo ys is influenced by e xter nal fields. This solid-state magnetoresistive eff ect, or aniso[...]

  • Page 16

    2000 Sep 06 16 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General sin φ= (6) where |H y | ≤ |H 0 +H x | and H x and H y are the components of the e xternal field. In the simplest case H x = 0, the volt- ages U x and U y become: U x =ρ ⊥ l (7) U y =ρ ⊥ l (8) (Note: if H x = 0, then H 0 must be replaced[...]

  • Page 17

    2000 Sep 06 17 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General B ARBER - POLE SENSORS A number of Philips’ magnetoresistiv e sensors use a ‘barber-pole’ constr uction to linear ize the R-H relationship, incor porating slanted strips of a good conductor to rotate the current. This type of sensor has the[...]

  • Page 18

    2000 Sep 06 18 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General This definition relates DU to a unit operating v oltage. The highest (H G ) and lowest (H min ) fields detectab le by the sensor are also of significance. The measuring range H G is restricted by non-linearity - if this is assumed at 5%, an ap[...]

  • Page 19

    2000 Sep 06 19 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General this also considerab ly enlarges H k . If a small temperature coefficient of ∆ρ is required, NiCo allo ys are pref erab le. The amor phous allo y CoFeB has a low ∆ρ/ρ , high H k and slightly worse thermal stability but due to the absence [...]

  • Page 20

    2000 Sep 06 20 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Fig.23 Sensor output ‘V o ’ as a function of the transv erse field H y . handbook, full pagewidth MLC132 0 24 68 1 0 1 2 O (mV) H (kA/m) y H = 4 kA/m x 2 kA/m 1 kA/m 0 V 100 150 50 A Saf e Operating ARea (SO AR) can be deter mined f or magne[...]

  • Page 21

    2000 Sep 06 21 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General APPENDIX 3: SENSOR LA Y OUT In Philips’ magnetoresistive sensors , the per malloy strips are formed into a meander patter n on the silicon substrate. With the KMZ10 (see Fig 25) and KMZ51 series, f our barber-pole permalloy strips are used whil[...]

  • Page 22

    2000 Sep 06 22 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General In one pair of diagonally opposed elements the barber-poles are at +45˚ to the strip axis, with the second pair at − 45˚. A resistance increase in one pair of elements due to an e xter nal magnetic field is matched b y an equal decrease in r[...]

  • Page 23

    2000 Sep 06 23 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General WEAK FIELD MEASUREMENT Contents • Fundamental measurement techniques • Application note AN00022: Electronic compass design using KMZ51 and KMZ52 • Application circuit: signal conditioning unit for compass • Example 1: Earth geomagnetic fi[...]

  • Page 24

    2000 Sep 06 24 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Flipping causes a change in the polarity of the sensor output signal and this can be used to separate the offset signal from the measured signal. Essentially, the unknown field in the ‘normal’ positive direction (plus the offset) is measured [...]

  • Page 25

    2000 Sep 06 25 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General Fig.30 Timing diagram for flipping circuit (a) output voltage; (b) filtered output voltage; (c) output voltage filtered and demodulated. handbook, full pagewidth MBH618 offset internal magnetization flipping current I F V O T time time V O time V[...]

  • Page 26

    2000 Sep 06 26 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General S ENSOR TEMPERA TURE DRIFT The sensitivity of MR sensors is also temperature dependent, with sensitivity decreasing as temperature increases (Fig.31).The effect on sensor output is certainly not negligible, as it can produce a difference of a fac[...]

  • Page 27

    2000 Sep 06 27 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General The simplest form of temperature compensation is to use a current source to supply to the sensor instead of a voltage source. In this case, the resulting reduction in sensitivity due to temperature is partially compensated by a corresponding incr[...]

  • Page 28

    2000 Sep 06 28 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General The optimal method of compensating for temperature dependent sensitivity differences in MR measurements of weak fields uses electro-magnetic feedback. As can be seen from the sensor characteristics in Figs 31 and 32, sensor output is completely i[...]

  • Page 29

    2000 Sep 06 29 Philips Semiconductors Magnetoresistiv e sensors for magnetic field measurement General The influence of other disturbing fields can also be eliminated provided they are well known, by adding a second current source to the compensating coil. Such fields might be those arising from the set-up housing, ferromagnetic components placed [...]