Abstract:
A magnetoresistive audio pickup comprises an audio detection circuit. The audio detection circuit comprises at least one linear magnetoresistive sensor, a coupling capacitance, an AC amplifier, and a signal processing circuit comprising an additional amplifier. The linear magnetoresistive sensor comprises at least one single-axis linear magnetoresistive sensor unit. The linear magnetoresistive sensors are placed in a measurement plane above a speaker&#39;s voice coil, the signal output end of each single-axis linear magnetoresistive sensor unit is capacitively coupled to the AC amplifier which provides AC signals through electrical connection to the amplifier, these signals are combined within the signal processing unit into an audio signal, and the audio signal is output from the circuit; each single-axis linear sensor unit is located in the linear response area of the measurement plane. The present invention detects a speaker&#39;s audio signals via magnetic field coupling between a speaker and a linear magnetoresistive sensor. The magnetoresistive audio pickup&#39;s structure is simple and it also provides low power consumption.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of magnetic sensor technologies, and in particular, to a magnetoresistive audio pickup. 
       BACKGROUND ART 
       [0002]    An audio pickup is a device that picks up audio electromagnetic signals of a speaker on a smartphone, a tablet computer or other smart electronic devices via a sensor, and plays on another speaker. 
         [0003]    At present, a coil or transformer type audio pickup is mainly employed. That is, a voice coil of a speaker is used as a primary coil of audio electromagnetic field transmitting signals, a receiving coil is used as a secondary coil to receive audio electromagnetic signals in the voice coil through the electromagnetic induction effect, of which the principle is similar to that of the transformer, and then the received signals are reconverted to sound signals in another speaker via a signal processing circuit. In this way, an audio play function of wireless connection is achieved between the speaker and the audio pickup. Such a coil-type audio pickup has the following problems: 
         [0004]    1) The amplitude of the voltage output by the receiving coil is related to the number of turns and the area of the coil, and thus, only by increasing the number of turns and the area of the coil can a large receiving voltage signal and high sensitivity be obtained; as a result, the volume and the size are larger. 
         [0005]    2) The electromagnetic field signals generated by the voice coil of the speaker are mainly surround spatial regions near the voice coil and attenuate quickly with the increase of the distance, and thus the receiving coil has to be located in regions near the voice coil as much as possible; as a result, the spatial flexibility of the coil is reduced. 
       SUMMARY OF THE INVENTION 
       [0006]    An objective of the present invention is to provide a magnetoresistive audio pickup for solving the problems such as a great volume of the existing audio pickup. 
         [0007]    To this end, the present invention provides a magnetoresistive audio pickup for converting an electromagnetic signal of a speaker to an audio signal, the speaker having a measurement plane above a voice coil surface, and the measurement plane having an single-axis working area; the single component working area being an intersection formed by a linear magnetic field measurement area, an alternating current (AC) magnetic field measurement area and a signal-to-noise ratio (SNR) measurement area of the measurement plane, wherein the magnetoresistive audio pickup includes an audio pickup circuit including at least one linear magnetoresistive sensor, a coupling capacitor, an AC amplifier, an amplifier and a signal processing circuit; the linear magnetoresistive sensor includes at least one single-axis linear magnetoresistive sensor unit sensing signals from the linear magnetic field measurement area. Each of the single-axis linear magnetoresistive sensor units has a power input end and a signal output end separately, the signal output end of each of the single-axis linear magnetoresistive sensor units is connected to the AC amplifier via the coupling capacitor, respectively, to output AC signals, and then is connected to the amplifier to combine the signals into one signal, which is then output as an audio signal via the signal processing circuit. 
         [0008]    Preferably, the magnetoresistive audio pickup according to the present invention further includes a linear magnetic field measurement area control circuit for detecting whether each of the single-axis linear magnetoresistive sensor units is located on the measurement plane or not, the control circuit being a magnetic switch type control circuit or a direct current (DC) output type control circuit or both. 
         [0009]    The magnetic switch type control circuit includes a magnetic switch sensor having at least one single-axis magnetic switch sensor unit, a comparator and a controller, the single-axis magnetic switch sensor units and the detected single-axis linear magnetoresistive sensor units have the same directions of sensitive axes for detecting magnetic fields of the directions of sensitive axes on the measurement plane, a signal output end of the single-axis magnetic switch sensor unit is connected to the comparator, and the comparator compares a signal of the single-axis linear magnetoresistive sensor unit detected by the single-axis magnetic switch sensor unit with a reference voltage stored by the comparator to obtain a comparison signal, and inputs the comparison signal into the controller, in order that the controller controls the audio pickup circuit according to the comparison signal; the DC output type control circuit includes a filter, a prepositive/differential amplifier, a comparator and a controller, the signal output end of each of the detected single-axis linear magnetoresistive sensor units is connected to the amplifier via the filter to obtain a DC output signal, the DC output signal is compared with the reference voltage of the comparator to obtain a comparison signal, and the comparator inputs the comparison signal into the controller, in order that the controller controls the audio pickup circuit according to the comparison signal. 
         [0010]    The magnetic switch sensor is a combination of discrete elements of at least two single-axis magnetic switch sensor units or a single chip element integrating at least two single-axis magnetic switch sensor units. 
         [0011]    Each of the single-axis magnetic switch sensor units is an X-, Y- or Z-axis magnetic switch sensor. 
         [0012]    Each of the single-axis switch sensor units is an all-pole type magnetic switch sensor. 
         [0013]    The single-axis linear magnetoresistive sensor unit is a half-bridge structure, and the signal output end of the single-axis linear magnetoresistive sensor unit is connected to the prepositive amplifier via the filter; 
         [0014]    or 
         [0015]    the single-axis linear magnetoresistive sensor unit is a full-bridge structure, and two signal output ends of the single-axis linear magnetoresistive sensor unit are connected to the differential amplifier via the filter, respectively. 
         [0016]    Upper and lower limits of linear magnetic fields and upper and lower limits of saturation magnetic fields of each of the single-axis linear magnetoresistive sensor units are values of operating magnetic fields and restoring magnetic fields of each of the single-axis switch sensor units or reference signals of a comparator of a DC voltage type control circuit. 
         [0017]    The control circuit is further used for outputting multiple control signals to respectively control the detected single-axis linear magnetoresistive sensor unit to switch to DC power supply or pulsed power supply, and to turn on or turn off any one or more of the power of the AC amplifier, the power of the amplifier, the power of the signal processing circuit and magnetically labeled signals. 
         [0018]    The linear magnetoresistive sensor is a combination of discrete elements of at least two single-axis linear magnetoresistive sensor units or a single chip element integrating at least two single-axis linear magnetoresistive sensor units. 
         [0019]    Each of the single-axis linear magnetoresistive sensor units is an X-, Y- or Z-axis sensor. 
         [0020]    The single-axis linear magnetoresistive sensor unit is a half-bridge structure, and the signal output end of the single-axis linear magnetoresistive sensor unit is connected to a prepositive AC amplifier via the coupling capacitor; 
         [0021]    or 
         [0022]    the single-axis linear magnetoresistive sensor unit is a full-bridge structure, and two signal output ends of the single-axis linear magnetoresistive sensor unit are connected to a differential AC amplifier via the coupling capacitor, respectively. 
         [0023]    At least one single-axis linear magnetoresistive sensor, two-axis and three-axis linear magnetoresistive sensors are each located in an intersection or union of single-axis working areas of each of the corresponding single-axis linear magnetoresistive sensor units respectively. 
         [0024]    The linear magnetoresistive sensor is one of AMR, Hall, GMR and TMR sensor. 
         [0025]    The measurement plane is at a distance in a range of 0 mm to 10 mm from the voice coil surface of the speaker. 
         [0026]    The directions of sensitive axes of the single-axis linear magnetoresistive sensor units are perpendicular to or parallel to the measurement plane. 
         [0027]    The linear magnetoresistive sensor is located on a measurement plane parallel to the voice coil surface of the speaker, and at least one of the single-axis linear magnetoresistive sensor units is located in a linear magnetic field measurement area on the measurement plane. 
         [0028]    Each of the single-axis linear magnetoresistive sensor units is located in the corresponding single component working area on the measurement plane; on the measurement plane, a linear magnetic field measurement area, a non-linear magnetic field measurement area and a saturation magnetic field measurement area of an DC magnetic field of a permanent magnetic circuit correspond to a linear magnetic field characteristic area, a non-linear magnetic field characteristic area and a saturation magnetic field characteristic area of each of the single-axis linear magnetoresistive sensor units, respectively; on the measurement plane, regions in which amplitudes of various AC magnetic field components produced by the voice coil of the speaker are greater than 1 mG are AC magnetic field measurement areas, and regions in which the amplitudes are less than 1 mG are AC magnetic field non-measurement areas; on the measurement plane, when a frequency band is 15 kHz, regions in which SNRs of AC audio signals output by each of the single-axis linear magnetoresistive sensor units to thermal noise are greater than 1 are SNR measurement areas, and regions in which the SNRs are less than 1 are SNR non-measurement areas. 
         [0029]    The audio pickup is suitable for speakers having circular, racetrack-shaped or rectangular voice coils. 
         [0030]    The audio pickup is suitable for external magnetic or internal magnetic speakers. 
         [0031]    The magnetoresistive audio pickup provided in the present invention uses a high-sensitivity linear magnetoresistive sensor to directly convert AC electromagnetic field signals of a voice coil to AC voltage signals for output, which successfully solves the above shortcomings. The linear magnetoresistive sensor only responds to magnetic field signals at the location thereof, the spatial position occupied by it only depends on the size of the linear magnetoresistive sensor itself, and the size of the linear magnetoresistive sensor is much less than that of a pickup coil; therefore, the linear magnetoresistive sensor pickup will have a greater measureable range and a greater spatial flexibility, and its mounting size required will also be reduced greatly; in addition, as the linear magnetoresistive sensor has higher magnetic field sensitivity, an output voltage signal greater than that of the pickup coil can be obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a schematic view of positions of a smartphone and a speaker of the smartphone; 
           [0033]      FIG. 2  is a two-dimensional schematic structural view of an internal magnetic speaker; 
           [0034]      FIG. 3  is a two-dimensional schematic structural view of an external magnetic speaker; 
           [0035]      FIG. 4  is a schematic view of a geometrical shape of a voice coil of a speaker; 
           [0036]      FIG. 5  is a characteristic curve of output voltage vs. external magnetic field of a linear magnetoresistive sensor; 
           [0037]      FIG. 6  is a characteristic curve of output resistance vs. external magnetic field of the linear magnetoresistive sensor; 
           [0038]      FIG. 7  is a distribution plot of two-dimensional magnetic force lines of DC magnetic fields of an internal magnetic speaker; 
           [0039]      FIG. 8  is a distribution plot of two-dimensional DC magnetic fields on a measurement plane of the internal magnetic speaker; 
           [0040]      FIGS. 9-11  are respectively profiles of measurement areas of DC magnetic fields Bx, By and Bz on a measurement plane of an internal magnetic rectangular speaker; 
           [0041]      FIGS. 12-14  are respectively profiles of measurement areas of DC magnetic fields Bx, By and Bz on a measurement plane of an internal magnetic circular speaker; 
           [0042]      FIG. 15  is a distribution plot of two-dimensional magnetic force lines of DC magnetic fields of an external magnetic speaker; 
           [0043]      FIG. 16  is a distribution plot of two-dimensional DC magnetic fields on a measurement plane of an external magnetic speaker; 
           [0044]      FIGS. 17-19  are respectively profiles of measurement areas of DC magnetic fields Bx, By and Bz on a measurement plane of an external magnetic rectangular speaker; 
           [0045]      FIGS. 20-22  are respectively profiles of measurement areas of DC magnetic fields Bx, By and Bz on a measurement plane of an external magnetic circular speaker; 
           [0046]      FIG. 23  is a distribution plot of two-dimensional AC magnetic force lines of a voice coil of a speaker; 
           [0047]      FIG. 24  is a distribution plot of two-dimensional AC magnetic fields on a measurement plane; 
           [0048]      FIGS. 25-27  are respectively equipotential views of AC magnetic fields bx, by and bz on a measurement plane of a rectangular voice coil; 
           [0049]      FIGS. 28-30  are respectively equipotential views of AC magnetic fields bx, by and bz on a measurement plane of a circular voice coil; 
           [0050]      FIGS. 31-33  are respectively contour plots of the SNRs of magnetic field components detected by a linear magnetoresistive sensor in a measurement plane of a rectangular internal magnetic speaker in X, Y and Z directions; 
           [0051]      FIGS. 34-36  are respectively contour plots of SNRs of magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a circular internal magnetic speaker in X, Y and Z directions; 
           [0052]      FIGS. 37-39  are respectively contour plots of SNRs of magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a rectangular external magnetic speaker in X, Y and Z directions; 
           [0053]      FIGS. 40-42  are respectively contour plots of SNRs of magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a circular external magnetic speaker in X, Y and Z directions; 
           [0054]      FIGS. 43-45  are respectively distribution plots of measurement areas of magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a rectangular external magnetic speaker in X, Y and Z directions; 
           [0055]      FIGS. 46-48  are respectively distribution plots of measurement areas of magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a circular external magnetic speaker in X, Y and Z directions; 
           [0056]      FIGS. 49-51  are respectively distribution plots of measurement areas magnetic field components detected by of a linear magnetoresistive sensor on a measurement plane of a rectangular internal magnetic speaker in X, Y and Z directions; 
           [0057]      FIGS. 52-54  are respectively distribution plots of measurement areas magnetic field components detected by a linear magnetoresistive sensor on a measurement plane of a circular internal magnetic speaker in X, Y and Z directions; 
           [0058]      FIGS. 55-57  are respectively schematic views of full-bridge, half-bridge and push-pull full-bridge linear magnetoresistive sensors; 
           [0059]      FIG. 58  is a view of an audio pickup system of a single-axis linear magnetoresistive sensor of a DC output type control circuit; 
           [0060]      FIG. 59  is a view of an audio pickup system of a single-axis linear magnetoresistive sensor of a magnetic switch type control circuit; 
           [0061]      FIG. 60  is a characteristic curve of external magnetic field vs. output voltage of a magnetic switch sensor; 
           [0062]      FIGS. 61-62  are respectively profiles of audio pickup systems of two-axis and three-axis linear magnetoresistive sensors; and 
           [0063]      FIGS. 63-65  are respectively tables of logic control signals of audio pickup systems of single-axis, two-axis and three-axis linear magnetoresistive sensors. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0064]    The present invention is described below in detail with reference to the drawings and embodiments. 
       Embodiment 1 
       [0065]      FIG. 1  is a schematic view of the position of a speaker in a smart electronic device, such as a smartphone; the speaker  2  is located in a position below the screen of the smartphone  1 .  FIG. 2  and  FIG. 3  are structural views of the speaker, the speaker includes two parts: a permanent magnetic circuit  4  or  4 ( 1 ) and a voice coil  3 , the permanent magnetic circuit  4  or  4 ( 1 ) includes a permanent magnet  5  or  5 ( 1 ) and soft magnets  6  or  6 ( 1 ) and  7  or  7 ( 1 ) and an air gap  8  or  8 ( 1 ), and the voice coil  3  is located at the air gap  8  or  8 ( 1 ); as the permanent magnetic circuit  4  or  4 ( 1 ) produces a strong static magnetic field in the air gap  8  or  8 ( 1 ), when an audio AC signal passes through the voice coil  3 , the voice coil  3  produces Lorentz force under the action of the static magnetic field in the air gap  8  or  8 ( 1 ) to drive a vibrating diaphragm to sound. According to different arrangements of the permanent magnet  5  or  5 ( 1 ) and the soft magnets  6  or  6 ( 1 ) and  7  or  7 ( 1 ) in the permanent magnetic circuit  4  or  4 ( 1 ), the speaker  2  may be divided into an internal magnetic type and an external magnetic type, for the former, as in  FIG. 2 , the permanent magnet  5  is located inside the voice coil  3 , and for the latter, as in  FIG. 3 , the permanent magnet  5 ( 1 ) is located on the periphery of the voice coil  3 . The voice coil  3  and the permanent magnetic circuit  4  or  4 ( 1 ) have similar geometrical shapes, which are generally the rectangle  12  or the circle  11  as shown in  FIG. 4 . Therefore, the speaker  2  may be divided into four typical structures: an external magnetic circle, an external magnetic rectangle, an internal magnetic circle and an internal magnetic rectangle, according to different geometrical shapes and types of permanent magnetic circuits. 
         [0066]    The linear magnetoresistive sensor  10  in  FIG. 2  and  FIG. 3  is placed on a measurement plane  9  parallel to surfaces of the voice coil  3  and the permanent magnetic circuit  4 . 
         [0067]    Preferably, the measurement plane is located at a distance in a range of 0 mm to 10 mm from a voice coil surface of the speaker. 
       Embodiment 2 
       [0068]    Magnetic fields of the speaker  2  include two parts, that is, DC static magnetic fields from the permanent magnetic circuit  4  or  4 ( 1 ) and AC audio magnetic fields from the voice coil  3 . Therefore, for the linear magnetoresistive sensor  10  placed on the measurement plane  9 , a biased DC static magnetic field H is present, and under this condition, measurement on an AC audio magnetic field h is implemented, wherein, for a mobile phone&#39;s speaker, the amplitude of H is much greater than that of h. 
         [0069]      FIG. 5  and  FIG. 6  are respectively characteristic curves of resistance vs. magnetic field and output signal voltage vs. magnetic field of the linear magnetoresistive sensor  10 , from which it can be seen that the linear magnetoresistive sensor  10  has three characteristic areas in the whole magnetic field range, that is, a linear magnetic field characteristic area  13 , a non-linear magnetic field characteristic area  14  and a saturation magnetic field characteristic area  15 , and only when the DC static magnetic field H is in the linear magnetic field characteristic area  13  can an AC audio magnetic field signal h be correctly converted to a voltage signal of the linear magnetoresistive sensor  10 . Corresponding to the measurement plane  9 , the DC static magnetic field H thereon may also be divided into three magnetic field measurement areas, that is, a linear magnetic field measurement area, a non-linear magnetic field measurement area and a saturation magnetic field measurement area. 
         [0070]    In addition, for the linear magnetoresistive sensor  10 , only by requiring the amplitude of the AC audio magnetic field h to be greater than 1 mG can measurement requirements be met; for smaller magnetic fields, in the presence of resolution and noise, it is difficult to implement measurements, and no signal will be output at this point. 
         [0071]    On this basis, distributions of DC output signals and audio output signal voltages of the linear magnetoresistive sensor  10  in the linear magnetic field measurement area are determined respectively according to the characteristic curve of output signal voltage vs. magnetic field of the linear magnetoresistive sensor  10  and distribution values of the DC static magnetic field H and the AC audio magnetic field h on the measurement plane  9  in the three magnetic field measurement areas. Further, in order to determine distributions of ratios of audio output signals of the linear magnetoresistive sensor  10  to Johnson thermal noise, distributions of Johnson noise voltages in the three magnetic field measurement areas are determined according to the curve of resistance vs. magnetic field of the linear magnetoresistive sensor  10  and spatial distribution of the DC static magnetic field H, and ratios of the distributions to distribution values of the audio output signal voltages are calculated. 
         [0072]      FIG. 7  is a distribution plot of two-dimensional DC magnetic fields of a permanent magnetic circuit  4  of an internal magnetic speaker, from which it can be seen that magnetic force lines have axisymmetric characteristics, and start from the permanent magnet  7 , cross the air gap  8  and pass through the soft magnets  6  and  5  to return to the permanent magnet  7 .  FIG. 8  is a distribution plot of two-dimensional DC static magnetic fields, that is, magnetic fields Bx and By, on the measurement plane  9  above the internal magnetic circuit  4  along an X direction, from which it can be seen that Bx has antisymmetric distribution characteristics relative to the magnetic field  0  in the center, while By has symmetric distribution characteristics relative to the center. In addition, from the distribution of the linear magnetic field characteristic area  13  of the linear magnetoresistive sensor  10 , there are three linear magnetic field measurement areas for Bx, that is, a region  16  near the magnetic field  0  in the center and two magnetic field attenuation regions  17  and  18  located on two ends. There are four linear magnetic field measurement areas for By, that is, regions  19  and  20  near two magnetic fields  0  on the left and the right and magnetic field attenuation regions  21  and  22  on two ends; the magnetic field attenuation regions are caused by cubic attenuation with the increase of the distance occurring when a magnetic field is away from a magnet. 
         [0073]      FIGS. 9, 10 and 11  are respectively distribution plots of isoline regions of three-dimensional magnetic fields Bx, By and Bz on a measurement plane  9  of a rectangular internal magnetic speaker, wherein two marked isolines represent magnetic field limit values between a linear magnetic field characteristic area  13  and a non-linear magnetic field characteristic area  14  and between the non-linear magnetic field characteristic area  14  and a saturation magnetic field characteristic area  15  respectively; only a quarter of the distribution plots of isolines of the magnetic fields are drawn due to axisymmetric characteristics of X and Y axes. A saturation magnetic field measurement area  23 , a non-linear magnetic field measurement area  24  and a saturation magnetic field measurement area  25  of Bx and a saturation magnetic field measurement area  26 , a non-linear magnetic field measurement area  27  and a saturation magnetic field measurement area  28  of By on the measurement plane  9  can be seen, and it can be seen in combination with the distribution plot of the two-dimensional magnetic field Bx that three regions corresponding to the two-dimensional linear magnetic field measurement areas  16 ,  17  and  18  shown in  FIG. 8  are actually connected into a region  25  or  28  on the measurement plane  9 . In addition, it can be seen that, in the distribution plots of three-dimensional isoline regions, Bx in  FIG. 9  and By in  FIG. 10  have similar isoline distribution characteristics, but their phases rotate 90 degrees relatively. For Bz in  FIG. 11 , it has two linear magnetic field measurement areas, one  32  is located at an edge of the voice coil  3  and the other one  33  is located outside the voice coil, of which the saturation area  29  only occupies a small part and located at a corner of the voice coil, other regions, for example,  30  and  31 , are non-linear magnetic field measurement areas, and compared with  FIG. 8 , the two-dimensional linear magnetic field measurement areas  19  and  20  are the three-dimensional linear magnetic field measurement area  32 , and  21  and  22  are  33 . 
         [0074]      FIGS. 12, 13 and 14  are respectively distribution plots of isoline regions of three-dimensional magnetic fields Bx, By and Bz on a measurement plane  9  of a circular internal magnetic speaker, from which it can be seen that distribution positions of linear magnetic field measurement areas  36  and  39  in  FIG. 12  and  FIG. 13  are similar to those in the distribution plots of regions of the rectangular internal magnetic speaker, and one difference lies in that the regions are arc-shaped regions; in addition, non-linear magnetic field measurement areas  35  and  38  and saturation magnetic field measurement areas  34  and  37  are also arc-shaped, for Bz in  FIG. 14 , evidently different from the distribution plot of isolines of the corresponding rectangular internal magnetic speaker in  FIG. 11 , it has three linear magnetic field measurement areas  44 ,  43  and  42 , corresponding to the distribution plot of the two-dimensional magnetic field By in  FIG. 8 , it can be found that a newly-added region is located in a magnetic field low value area in a nearby region of the magnetic field  0 , the value of the magnetic field is specifically related to the size of the permanent magnetic circuit  4  and the magnetization intensity of the permanent magnet  5 , the newly-added region may be located in a non-linear magnetic field measurement area or a linear magnetic field measurement area, in the rectangular internal magnetic speaker, the value thereof is only reduced to the non-linear magnetic field measurement area, while in the circular internal magnetic speaker, the value thereof is reduced to the linear magnetic field measurement area. The other difference lies in that there is no saturation magnetic field measurement area in  FIG. 14 . 
       Embodiment 3 
       [0075]      FIG. 15  is a distribution plot of two-dimensional magnetic force lines of a permanent magnetic circuit  4 ( 1 ) of an external magnetic speaker, from which it can be seen that the magnetic force lines start from the permanent magnet  5 ( 1 ) on the periphery of the voice coil, pass through the soft magnet  7 ( 1 ) and cross the air gap  8 ( 1 ), and pass through the soft magnet  6 ( 1 ) to return to the permanent magnet  5 ( 1 ); similarly, the distribution of magnetic fields thereof have axisymmetric characteristics.  FIG. 16  is a distribution plot of two dimensional magnetic fields Bx and By on the measurement plane  9  along an X direction, from which it can be seen that Bx still has antisymmetric characteristics, while By has symmetric characteristics; for Bx, as two ends of the curve thereof directly cross Point  0 , two linear magnetic field measurement areas  46  and  47  are added relative to the internal magnetic permanent magnetic circuit, in addition to the linear magnetic field measurement areas  45 ,  48  and  49 . For By, the number of the linear magnetic field measurement areas remains the same, which are  50 ,  51 ,  52  and  53 . 
         [0076]      FIGS. 17, 18 and 19  are respectively distribution plots of isoline regions of three-dimensional magnetic fields Bx, By and Bz on the measurement plane, from which it can be seen that, different from the internal magnetic permanent magnetic circuit, in addition to the non-linear magnetic field measurement area  55 , a non-linear magnetic field measurement area  56  is added, and peripheries of  55  and  56  correspond to the non-linear magnetic field measurement areas; seen from the distribution curve of the two-dimensional magnetic field Bx vs. the magnetic field X, the added regions  46  and  47  are actually regions located between  56  and  55 ; in a three-dimensional view, the linear magnetic field measurement area  57  is actually a whole, although the number of the linear magnetic field measurement areas is increased in terms of the distribution of the two-dimensional magnetic field, the number of the actual linear magnetic field measurement areas is decreased in terms of the distribution of the three-dimensional magnetic field. 
         [0077]    Similarly, By in  FIG. 18  also has similar characteristics, which include a linear magnetic field measurement area  61 , a saturation magnetic field measurement area  58 , and non-linear magnetic field measurement areas  59  and  60 . 
         [0078]    For Bz in  FIG. 19 , there is a saturation magnetic field measurement area  62  which is located at a corner of the voice coil, linear magnetic field measurement areas thereof are  65  and  66 , wherein  65  is a narrow region in the voice coil, and  64  and  63  are non-linear magnetic field measurement areas. 
         [0079]      FIGS. 20, 21 and 22  are respectively distribution plots of isoline regions of three-dimensional magnetic fields Bx, By and Bz on a measurement plane  9  of a permanent magnetic circuit of a circular external magnetic speaker, from which it can be seen that, in addition to the arc-shaped distribution characteristics, linear magnetic field measurement areas  70  and  71 , non-linear magnetic field measurement areas  68  and  69  and  72 ,  73  and saturation magnetic field measurement areas  67  and  71  thereof are very similar to those of the rectangular external magnetic permanent magnetic circuit. For Bz in  FIG. 22 , compared with the rectangular permanent magnetic circuit, there are no saturation magnetic field measurement areas, a linear magnetic field measurement area  77  is added in addition to the linear magnetic field measurement areas  79  and  78 , and non-linear magnetic field measurement areas thereof are  76  and  75 . This is very similar to the distribution characteristics of magnetic fields on the measurement plane  9  of the circular internal magnetic permanent magnetic circuit. 
       Embodiment 4 
       [0080]      FIG. 23  is a distribution plot of two-dimensional AC magnetic force lines of the voice coil  3  of the speaker, in which the magnetic force lines start from the center, and cross the edge of the voice coil to return to the center, to form a closed loop.  FIG. 24  is a distribution plot of two-dimensional AC magnetic fields bx and bz on the measurement plane  9 , from which it can be seen that bx has antisymmetric distribution characteristics, while Bz has symmetric distribution characteristics. 
         [0081]    Only by requiring the amplitude range of the AC magnetic fields to be greater than 1 mG, can sufficient signal response be generated; it can be seen from  FIG. 24  that, for bx, there is an AC magnetic field non-measurement area  80  near a magnetic field  0  in the central region, and in addition, AC magnetic field non-measurement areas  81  and  82  are present in magnetic field attenuation regions on two ends respectively; while for bz, two AC magnetic field non-measurement areas  83  and  84  are present near two magnetic fields  0  on two ends, and in addition, two AC magnetic field non-measurement areas  85  and  86  are also present in magnetic field attenuation regions on two ends. As the value of 1 mG is very small, it can be seen that the AC magnetic field non-measurement areas thereof are very narrow. 
         [0082]      FIGS. 25, 26 and 27  are distribution plots of isolines of three-dimensional AC magnetic fields bx, by and bz on a measurement plane of a rectangular voice coil, from which it can be seen that, for bx, there are two isolines  87  of 1 mG, respectively located near a symmetry axis X and in a magnetic field attenuation area, which is identical with the result of the two-dimensional AC magnetic fields, and thus AC magnetic field measurement areas thereof are regions between them. For by, the result is also similar, and the isolines of 1 mG are  88 , for bz, the isolines of 1 mG are  89  located in a narrow region near the isoline of the magnetic field  0  illustrated and in a magnetic field attenuation area; therefore, AC magnetic field measurement areas thereof are located in two regions of an equipotential line surrounding area of the magnetic field  0  and the region between the magnetic field  0  and  89 .  FIGS. 28, 29 and 30  are respectively distribution plots of isolines of three-dimensional AC magnetic fields bx, by and bz on a measurement plane  9  of a circular voice coil, isolines  90  and  91  of 1 mG are respectively located in regions near the isoline of the magnetic field  0 , to form a closed shape, and AC magnetic field measurement areas thereof are located inside a closed curve; for bz shown in  FIG. 30 , there are a long and narrow region  92  near the magnetic field  0  and an isoline  93  of 1 mG near an attenuation magnetic field  0  beyond the edge; therefore, the AC magnetic field measurement areas are classified into two parts, respectively located between  92  and  93  and inside  92 . 
       Embodiment 5 
       [0083]      FIGS. 31, 32 and 33  are distribution plots of isolines of ratios of AC audio signals to Johnson thermal noise signals when magnetic field components of the corresponding linear magnetoresistive sensor  10  on a measurement plane  9  of an internal magnetic rectangular speaker are along directions X, Y and Z respectively; as effective signal detection can be implemented only when the SNR is greater than 1, it can be seen from  FIGS. 31 and 32  that  94  and  95  are isolines with the SNR of 1 in X and Y directions respectively, wherein the surrounded regions are SNR measurement areas, and in addition, it can be seen from  FIG. 33  that there are two regions in which the isolines are 1, one is located in a peripheral magnetic field attenuation area  96 , and the other is near the value  0  of  97 , which corresponds to two SNR measurement areas with one between  96  and  97 , and the other within  97 . 
         [0084]      FIGS. 34, 35 and 36  are respectively distribution plots of SNR isolines of sensitive axes of the linear magnetoresistive sensor  10  on a measurement plane  9  of a corresponding internal magnetic circular speaker along directions X, Y and Z; it can be seen from  FIGS. 34 and 35  that isolines  102  and  103  of which the SNR is 1 are near the magnetic field  0 , and regions surrounded therein are SNR measurement areas; in  FIG. 36 , there are two regions in which the SNR of the isoline is 1, that is,  104  and  105  which is on the periphery, and thus the SNR measurement areas thereof are classified into two parts, one is located between  104  and  105 , and the other is located in  104 . 
       Embodiment 6 
       [0085]      FIGS. 37, 38 and 39  are distribution plots of SNR isolines when sensitive magnetic fields of the linear magnetoresistive sensor  10  on a measurement plane  9  of a corresponding external magnetic rectangular speaker are along directions X, Y and Z, from which it can be seen that  106  and  107  are respectively profiles of isolines of which the values are 1, and regions surrounded by them are SNR measurement areas. For the Z-direction SNR view, there are two isolines of which the values are 1, being  108  and  109  respectively,  108  is located in an attenuation area, and thus there are two SNR measurement areas within the region  109  and between  109  and  108 . 
         [0086]      FIGS. 40, 41 and 42  are respectively distribution plots of SNRs when magnetic field components detected by the linear magnetoresistive sensor  10  on a measurement plane  9  of a corresponding external magnetic circular speaker are along directions X, Y and Z, from which it can be seen that regions surrounded by isolines  110  and  111  of which the X- and Y-direction SNRs are 1 are SNR measurement areas on a corresponding external magnetic circular detection plane  9 . For the Z direction, isolines  112  and  113  of which the SNRs are 1 form two SNR measurement areas, one is the region internal to  112 , the other is a region between  112  and  113 , and  113  is located in the magnetic field attenuation area. 
       Embodiment 7 
       [0087]      FIGS. 43, 44 and 45  are respectively distribution plots of measurement areas when magnetic field components detected by the linear magnetoresistive sensor  10  on a measurement plane  9  of an internal magnetic rectangular speaker are along directions X, Y and Z respectively, wherein  114  is a linear magnetic field measurement area boundary,  115  is an AC magnetic field measurement area boundary,  116  is a SNR measurement area boundary, wherein an AC magnetic field measurement area boundary  118  is located inside a SNR measurement area boundary  119 , therefore, an X-axis working area is located in a region formed by  118  and  117 . Similarly, a Y-axis working area is within a boundary region formed by the linear magnetic field measurement area boundary  117  and the AC magnetic field measurement area boundary  118 . A Z-axis working area is divided as follows: a first region located between a linear magnetic field measurement area boundary  121  and an AC magnetic field measurement area boundary  124  of an attenuation area, a second region located between a linear magnetic field measurement area boundary  120  and an AC magnetic field measurement area boundary  122 , and a third region located between a linear magnetic field measurement area boundary  123  and the AC magnetic field measurement area boundary  122 , and the region where  122  is located is very narrow. 
         [0088]      FIGS. 46, 47 and 48  are respectively distribution plots of measurement areas when magnetic field components detected by the linear magnetoresistive sensor  10  on a measurement plane  9  of an internal magnetic rectangular speaker are along directions X, Y and Z respectively; similarly, an X-axis working area is a region located between a linear magnetic field measurement area boundary  125  and an AC magnetic field measurement area boundary  126 , and a SNR measurement area boundary  127  is located outside  126 . A Y-axis working area is a region located between a linear magnetic field measurement area boundary  128  and an AC magnetic field measurement area boundary  129 , and a SNR measurement area boundary  130  is located outside  129 . A Z-axis working area is also divided into four parts, the first one is located between a linear magnetic field measurement area boundary  131  and an AC magnetic field measurement area boundary  136 , the second one is located between a linear magnetic field measurement area boundary  135  and an AC magnetic field measurement area  132 , the third one is located between  135  and a linear magnetic field measurement area boundary  133 , and the fourth one is located within a linear magnetic field measurement area boundary  134 . 
         [0089]      FIGS. 49, 50 and 51  are respectively distribution plots of measurement areas when magnetic field components detected by the linear magnetoresistive sensor  10  on a measurement plane  9  of an external magnetic rectangular speaker are along directions X, Y and Z respectively; an X-axis working area is a region located between linear magnetic field measurement area boundaries  137 ,  138  and an AC magnetic field measurement area boundary  139 , and  140  is a SNR measurement area boundary which is located outside  139 . A Y-axis working area is a region located between linear magnetic field measurement area boundaries  141 ,  142  and an AC magnetic field measurement area boundary  143 , and  144  is a SNR measurement area boundary which is located outside  143 . A Z-axis working area includes three regions, the first one is located between a linear magnetic field measurement area boundary  145  and an AC magnetic field measurement area boundary  149 , the second one is located between a linear magnetic field measurement area boundary  146  and an AC magnetic field measurement area boundary  146 , and the third one is located between an AC magnetic field measurement area boundary  146  and a linear magnetic field measurement area boundary  148 . 
         [0090]      FIGS. 52, 53 and 54  are respectively distribution plots of measurement areas when magnetic field components detected by the linear magnetoresistive sensor  10  on a measurement plane  9  of an external magnetic circular speaker are along directions X, Y and Z respectively; an X-axis working area is a region located between linear magnetic field measurement area boundaries  150 ,  151  and an AC magnetic field measurement area boundary  152 , and  153  is a SNR measurement area boundary which is located outside  152 . A Y-axis working area is a region located between linear magnetic field measurement area boundaries  154 ,  155  and an AC magnetic field measurement area boundary  156 , and  157  is a SNR measurement area boundary which is located outside  156 . A Z-axis working area includes three regions, the first one is located between a linear magnetic field measurement area boundary  158  and an AC magnetic field measurement area boundary  163 , the second one is located between a linear magnetic field measurement area boundary  160  and an AC magnetic field measurement area  161 , wherein the AC magnetic field measurement area boundary is outside the measurement region, and the third one is located within a linear magnetic field measurement area boundary  162 . 
       Embodiment 8 
       [0091]      FIGS. 55, 56 and 57  are structural views of the linear magnetoresistive sensor  10 ,  FIG. 55  shows a full-bridge structure  1101  which includes four magnetoresistive sensor units R 1 , R 2 , R 4  and R 5 , wherein R 2  and R 4  are reference units, while R 1  and R 5  are sensitive units and have the same directions of sensitive axes.  FIG. 56  shows a half-bridge structure  1102  which includes two magnetoresistive units R 1  and R 2 , wherein R 2  is a reference unit, R 1  is a sensitive unit, and signals are output from the middle of the half bridge.  FIG. 57  shows a push-pull full-bridge structure  1103 , two adjacent magnetoresistive sensor units R 6 , R 7  and R 8 , R 9  in the same bridge arm have opposite directions of magnetic field sensitive axes, and two opposite magnetoresistive sensors R 6 , R 8  and R 7 , R 9  in two bridge arms have opposite directions of magnetic field sensitive axes. The magnetoresistive sensor units may be one of Hall, AMR, GMR or TMR sensor; in addition, the full-bridge structure  1101 , the half-bridge structure  1102  and the push-pull full-bridge structure  1103  of the linear magnetoresistive sensor  10  may be linear magnetoresistive sensor structures whose magnetic field sensitive directions are along an X, Y or Z direction. 
       Embodiment 9 
       [0092]    An embodiment of the present invention further provides a magnetoresistive audio pickup, specifically, a control circuit is disposed in the audio pickup, to detect whether each of the single-axis linear magnetoresistive sensor units is located in a linear magnetic field measurement area on the measurement plane or not, and when it is detected that the single-axis linear magnetoresistive sensor unit is in a linear magnetic field working area, output multiple control signals to perform some or all of the following operations: for example, controlling the detected single-axis linear magnetoresistive sensor unit to switch to DC power supply, turning on the power of the AC amplifier, turning on the power of the amplifier, turning on the power of the signal processing circuit, and turning on magnetically labeled signals; when it is detected that the single-axis linear magnetoresistive sensor is not in the linear magnetic field working area, outputting multiple control signals to control some or all of the following operations: for example, switching the detected single-axis linear magnetoresistive sensor unit to pulsed power supply, turning off the power of the AC amplifier, turning off the power of the amplifier, turning off the power of the signal processing circuit, and turning off the magnetically labeled signals. 
         [0093]      FIGS. 58 and 59  are respectively schematic views of circuit systems of a single-axis audio pickup of two different control circuit types, that is, DC output type and magnetic switch type, which may be a circuit diagram of a smart audio pickup system of a single-axis linear magnetoresistive sensor, and may also be a circuit diagram of each single-axis linear magnetoresistive sensor in an audio pickup system of a two-axis or three-axis linear magnetoresistive sensor, wherein the two-axis or three-axis linear magnetoresistive sensor is a combination of discrete elements of multiple single-axis linear magnetoresistive sensor units or a single chip element integrating multiple single-axis linear magnetoresistive sensor units; it should be noted that, for a single-axis, two-axis or three-axis linear magnetoresistive sensor, each axial direction corresponding thereto may include at least one linear magnetoresistive sensor unit in the same axial direction. 
         [0094]      FIG. 58  and  FIG. 59  both include two parts: an audio pickup circuit and a control circuit, wherein the audio pickup circuit includes a single-axis linear magnetoresistive sensor unit  1206 , a coupling capacitor  1207 , a prepositive/differential AC amplifier  1208 , a prepositive/summing amplifier  1209  and a signal processing circuit  1210 . The signal output end of the single-axis linear magnetoresistive sensor  1206  removes DC output signals via the coupling capacitor  1207 , to obtain AC output signals, if  1206  is the half-bridge structure  1102 , the signal output end of one end thereof is amplified with the prepositive amplifier  1209 , if  1206  is the full-bridge structure  1101  or the push-pull structure  1103 , two signal output ends are connected to two input ends of the differential amplifier  1208  via the coupling capacitor  1207  respectively, the output signal end of the prepositive/differential AC amplifier  1208  is connected to the input end of the prepositive/summing amplifier  1209 , if the single-axis linear magnetoresistive sensor  1206  is a single-axis linear magnetoresistive sensor audio pickup system,  1208  is directly connected to the input end of the prepositive amplifier  1209 , if  1206  is any single-axis linear magnetoresistive sensor of the two-axis or three-axis linear magnetoresistive sensors,  1208  is connected to one input end of the summing amplifier  1209 , and the signal output end of the prepositive/summing amplifier  1209  is connected to the signal processing circuit  1210 , which then outputs audio signals. 
         [0095]    The control circuit is divided into two types, one is the DC output type shown in  FIG. 58 , and the other is the magnetic switch type shown in  FIG. 59 ;  FIG. 58  includes a filter  1212 , a prepositive/differential amplifier  1213 , a comparator  1214  and a controller  1204 . If  1206  is the half-bridge structure  1102 , the signal output end of one end thereof is connected to the prepositive amplifier  1213  via the filter  1212  to obtain DC output signals which are then compared with a reference voltage signal of the comparator  1214 , a reference voltage is corresponding to a linear magnetic field characteristic area limit of  1206 , the comparator outputs a logic signal I/O to correspondingly judge whether the detected single-axis linear magnetoresistive sensor unit  1206  is in a linear magnetic field characteristic area or not, the logic signal is input to the controller  1204 , the controller outputs signals to control switching of DC power/pulse power of the single-axis linear magnetoresistive sensor unit  1206 , turn-on and turn-off of the power of the AC prepositive/differential amplifier  1208 , turn-on and turn-off of the power of the prepositive/summing amplifier  1209  and the signal processing circuit  1210 , and turn-on and turn-off of the magnetically labeled signals. 
         [0096]      FIG. 59  includes a single-axis magnetic switch sensor  1304 , of which the sensitive direction is identical with that of the detected single-axis linear magnetoresistive sensor unit  1206 , and a single-axis magnetic switch sensor is an all-pole switch, the corresponding magnetic field output characteristic curve is as shown in  FIG. 60 , an operating magnetic field and a restoring magnetic field corresponding thereto are limit values of a linear magnetic field and a saturation magnetic field of each of the single-axis linear magnetoresistive sensor units, a reference voltage passing through the comparator  1305  corresponds to an output characteristic voltage of the magnetic switch sensor, so as to judge whether the detected single-axis linear magnetoresistive sensor unit  1206  is in the single component working area or not to convert the reference voltage to a logic signal I/O which is input into the controller  1204 , the controller outputs signals to control switching of DC power/pulse power of the single-axis linear magnetoresistive sensor unit  1206 , turn-on and turn-off of the power of the AC prepositive/differential amplifier  1208 , turn-on and turn-off of the power of the prepositive/summing amplifier  1209  and the signal processing circuit  1210 , and turn-on and turn-off of the magnetically labeled signals. The magnetic switch sensor may be a single-axis, two-axis or three-axis magnetic switch sensor, and the two-axis or three-axis magnetic switch sensor is a combination of discrete elements of multiple single-axis magnetic switch sensor units or a single chip element integrating multiple single-axis magnetic switch sensor units; each of the single-axis magnetic switch sensor units is an X-, Y- or 
         [0097]    Z-axis magnetic switch sensor. 
         [0098]    The single-axis linear magnetoresistive sensor is located in a single component working area corresponding to the corresponding single-axis linear magnetoresistive sensor. The two-axis or three-axis linear magnetoresistive sensor is located in an intersection of single-axis working areas corresponding to each of the single-axis linear magnetoresistive sensor units, and may also be located in a union of the single-axis working areas. When the two-axis or three-axis linear magnetoresistive sensor is located in the intersection, multiple single-axis linear magnetoresistive sensors transmit audio signals at the same time, and thus output audio signals are the sum of the audio signals of each of the linear magnetoresistive sensors; when the two-axis or three-axis linear magnetoresistive sensor is located in the union, the control circuit judges whether each of the single-axis linear magnetoresistive sensors is in the single-axis working areas or not and turns on the linear magnetoresistive sensors in the single-axis working areas, so that the working range of the measurement plane can be expanded. 
         [0099]    In order to simplify the description about the circuit structure of the audio pickup system of the two-axis or three-axis linear magnetoresistive sensor, in  FIG. 58  and  FIG. 59 , an audio pickup circuit and a control circuit are divided into two block structures, wherein two block diagrams corresponding to  FIG. 58  are  1300  and  1350 , and two block diagrams corresponding to  FIG. 59  are  1400  and  1350 , wherein  1350  is a common part of two structures, in addition, the corresponding controller, the pulse power/DC power of the single-axis linear magnetoresistive sensor, the power of the AC prepositive/differential signal amplifier, and the power of the prepositive/summing amplifier are also common parts. 
         [0100]      FIG. 63  is a view of input and output of logic signals of the controller of the single-axis linear magnetoresistive sensor audio pickup corresponding to  FIG. 58 or 59 . The input end of the controller is  1218 , the output ends are  1219 ,  1220 ,  1221 ,  1222  and  1223 , when  1218  is 0, that is, the control circuit monitors that the single-axis linear magnetoresistive sensor is not in a linear working area,  1220  is 1 at this point, that is, it is still pulsed power supply, and at this point,  1221 ,  1222 ,  1223  and  1219  are all 0, the power circuit of the AC prepositive/differential amplifier, the power of the prepositive/differential amplifier and the power of the signal processing circuit are all turned off; on the contrary, when  1218  is 1, that is, the control circuit monitors that the single-axis linear magnetoresistive sensor is in the linear working area, at this point,  1220  is 0, that is, it is switched to DC power supply at this point,  1221 ,  1222 ,  1223  and  1219  are all 1 at this point, and the power circuit of the AC prepositive/differential amplifier, the power of the prepositive/differential amplifier and the power of the signal processing circuit  1708 ,  1710  are all turned on at this point, and audio signals are output. The input end of the controller of the audio pickup system of the single-axis linear magnetoresistive sensor has two combinations, and the output end has two bits and also has two combinations. 
       Embodiment 10 
       [0101]    By means of the block structures shown in  FIG. 58  and  FIG. 59 ,  FIG. 61  is a view of an audio pickup system of a corresponding two-axis linear magnetoresistive sensor. In addition to peripheral circuits, for example, a pulse power circuit  1200 , a DC power circuit  1201 , an AC prepositive/differential amplifier power circuit  1202 , a prepositive/summing amplifier power circuit  1203  and a controller  1204 , three parts: a block diagram  1350  and block diagrams  1500  and  1600 , are further included, wherein  1500  and  1600  represent the audio pickup circuit and the control circuit of two single-axis linear magnetoresistive sensors corresponding to the two-axis linear magnetoresistive sensor respectively. According to the block structures in  FIG. 58  and  FIGS. 59, 1500 and 1600  may have the structure of  1300  or  1400 , and output signal ends  1520  and  1521  of the AC prepositive/differential amplifier corresponding to  1500  and  1600  are connected with the summing amplifier  1209  in  1350 ; for the two-axis linear magnetoresistive sensor, it is necessary to use the summing amplifier  1209  to calculate the sum of output signals of the single-axis linear magnetoresistive sensors  1500  and  1600  respectively. In addition, two logic signals generated by the control circuits in  1500  and  1600  are input to the input end of the controller respectively, control signals output by the controller respectively control switching of DC power/pulse power of the single-axis linear magnetoresistive sensors corresponding to  1500  and  1600  and turn-on and turn-off of the power of the AC prepositive/differential amplifier and the power of the summing amplifier and the signal processing circuit. 
         [0102]      FIG. 64  is a view of input and output logic signals of a controller of the two-axis linear magnetoresistive sensor audio pickup corresponding to FIG.  60 . Input ends of the control circuit are  1518  and  1519 , output ends of the control circuit are  1501 ,  1502 ,  1503 ,  1504 ,  1505 ,  1506 ,  1507  and  1509 , when the input ends  1518  and  1519  have two bits and four combinations, the output ends have five bits and four combinations. 
       Embodiment 11 
       [0103]      FIG. 61  is a view of an audio pickup system of the corresponding three-axis linear magnetoresistive sensor, which is also represented with the block structures corresponding to  FIG. 58  and  FIGS. 59, 1700, 1800 and 1900  respectively represent block diagrams of an audio pickup circuit and a control circuit corresponding to each single-axis linear magnetoresistive sensor,  1700 ,  1800  and  1900  may employ one of the block diagrams of  1300  and  1400 , which may employ a DC output control manner and may also employ a magnetic switch control manner, the input end of the AC prepositive/differential amplifier in the audio pickup circuit of each single-axis linear magnetoresistive sensor in  1700 ,  1800  and  1900  is connected with the summing amplifier in  1350 , and outputs audio signals via the signal processing circuit, three logic signals in  1700 ,  1800  and  1900  which monitor whether each single-axis linear magnetoresistive sensor works in a linear area or not are respectively input to the input end of the controller  1209 , and output control signals of the controller  1209  respectively control switching of DC power/pulse power of the single-axis linear magnetoresistive sensors in  1700 ,  1800  and  1900  and turn-on and turn-off of the power of the corresponding AC prepositive/differential amplifier and the power of the summing amplifier and the signal processing circuit. 
         [0104]      FIG. 65  is a view of input and output of logic signals of a controller of the three-axis linear magnetoresistive sensor audio pickup corresponding to  FIG. 61 . Input ends of the controller are  1811 ,  1812  and  1813 , output ends of the controller are  1701 ,  1702 ,  1703   1704 ,  1705 ,  1706 ,  1707 ,  1708 ,  1709 ,  1710  and  1713 . The input ends have a total of eight combinations, and the output ends have seven bits and eight combinations. 
         [0105]    To sum up, the present invention provides a magnetoresistive audio pickup, for converting an electromagnetic signal of a speaker to an audio signal, the speaker having a measurement plane above a voice coil surface, and the measurement plane having a single component working area thereon; the single component working area being an intersection formed by a linear magnetic field measurement area, an AC magnetic field measurement area and a SNR measurement area on the measurement plane, wherein the magnetoresistive audio pickup includes an audio pickup circuit including at least one linear magnetoresistive sensor, a coupling capacitor, an AC amplifier, an amplifier and a signal processing circuit; the linear magnetoresistive sensor includes at least one single-axis linear magnetoresistive sensor unit sensing signals from the linear magnetic field measurement area. 
         [0106]    It should be noted that, when each of the single-axis linear magnetoresistive sensor units is located in an AC magnetic field non-measurement area on the linear magnetic field measurement area of the measurement plane, no related signals can be measured, and thus no signals will be output at this point. 
         [0107]    Preferably, each of the single-axis linear magnetoresistive sensor units has a power input end and a signal output end separately, the signal output end of each of the single-axis linear magnetoresistive sensor units is connected to the AC amplifier via the coupling capacitor, respectively, to output AC signals, and then is connected to the amplifier to combine these signals into one signal, which is then output as an audio signal via the signal processing circuit. 
         [0108]    Preferably, a linear magnetic field measurement area control circuit for detecting whether each of the single-axis linear magnetoresistive sensor units is located on the measurement plane or not is further included, the control circuit being a magnetic switch type control circuit or a DC output type control circuit or both. 
         [0109]    Preferably, the magnetic switch type control circuit includes a magnetic switch sensor having at least one single-axis magnetic switch sensor unit, a comparator and a controller, the single-axis magnetic switch sensor units and the detected single-axis linear magnetoresistive sensor units have the same directions of sensitive axes; the DC output type control circuit includes a filter, a prepositive/differential amplifier, a comparator and a controller, the signal output end of each of the detected single-axis linear magnetoresistive sensor units is connected to the amplifier via the filter to obtain a DC output signal, the DC output signal is compared with the reference voltage of the comparator, to obtain a comparison signal, and the comparator inputs the comparison signal into the controller, in order that the controller controls the audio pickup circuit according to the comparison signal. 
         [0110]    Preferably, the control circuit is further used for outputting multiple control signals to respectively control the detected single-axis linear magnetoresistive sensor unit to switch to DC power supply or pulsed power supply, and to turn on or turn off any one or more of the power of the AC amplifier, the power of the amplifier, the power of the signal processing unit and magnetically labeled signals.