Abstract:
An apparatus includes a network of switchable coils suspended in a magnetic field, wherein a topology of the network of switchable coils may be configured to change at least one characteristic of a sensor, and an optical detector to detect displacement of the coil in response to a stimulus. The apparatus further includes a feedback circuit coupled to the optical detector and to the network of switchable coils.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is related to the following patent applications: 
         [0002]    U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Programmable Gain and Dynamic Range and Associated Methods,” Attorney Docket No. SIAU002; 
         [0003]    U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Coil Constant and Associated Methods,” Attorney Docket No. SIAU003; 
         [0004]    U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Communication Port for Configuring Sensor Characteristics and Associated Methods,” Attorney Docket No. SIAU004; 
         [0005]    U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Improved Power Consumption and Associated Methods,” Attorney Docket No. SIAU005; 
         [0006]    U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Damping and Associated Methods,” Attorney Docket No. SIAU007; and 
         [0007]    International Application No. PCT/US2013/032584, filed on Mar. 15, 2013, titled “Closed Loop Control Techniques for Displacement Sensors with Optical Readout.” The foregoing applications are incorporated by reference in their entireties for all purposes. 
         [0008]    Furthermore, the present patent application is a continuation-in-part of International Application No. PCT/US2013/032584, filed on Mar. 15, 2013, titled “Closed Loop Control Techniques for Displacement Sensors with Optical Readout,” which claims priority to: (1) Provisional U.S. Patent Application No. 61/712,652, filed on Oct. 11, 2012; and (2) Provisional U.S. Patent Application No. 61/721,903, filed on Nov. 2, 2012. The foregoing applications are incorporated by reference in their entireties for all purposes. 
     
    
     TECHNICAL FIELD 
       [0009]    The disclosure relates generally to sensors, such as acceleration, speed, and displacement sensors and, more particularly, to apparatus for such sensors with configurable coils, and associated methods. 
       BACKGROUND 
       [0010]    With advances in electronics, a variety of sensors have been developed to sense physical quantities. The sensors may use a variety of technologies, such as electrical, mechanical, optical, and micro-electromechanical systems (MEMS), or combinations of such technologies. More particularly, some sensors can sense displacement, velocity, or acceleration. Sensors that can sense displacement, velocity, or acceleration find use in a variety of fields, such as ground or earth exploration, for instance, reflection seismology. 
         [0011]    As an example, devices known as geophones use a magnet and a coil that move relative to each other in response to ground movement. Waves sent into the earth generate reflected energy waves. In response to reflected energy waves, geophones generate electrical signals that may be used to locate underground objects, such as natural resources. 
         [0012]      FIG. 1  illustrates a conceptual diagram  10  of a geophone, which includes a magnet  16  coupled to an anchor point  12  (e.g., housing) and spring  14 , and coil  18  with mass m. In response to a stimulus, such as the energy waves described above, coil  18  moves in relation to magnet  16 . As a result, an electrical output signal is generated by coil  18 . 
         [0013]    The coil-spring assembly form a physical system that responds non-uniformly as the frequency of the stimulus is varied. Assuming that spring  14  has a spring constant k, the coil-spring assembly, with mass m (i.e., a negligible spring mass), has a natural frequency of oscillation of 
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         [0000]      FIG. 2  illustrates a frequency response curve  20  of the geophone of  FIG. 1  to physical stimuli. Frequency response curve  20  has a peak  23  at the frequency f N . Thus, geophone  10  has better response (higher output signal level) at frequencies near or equal to f N . 
         [0014]    Note that the description in this section and the corresponding figures are included as background information material. The materials in this section should not be considered as an admission that such materials constitute prior art to the present patent application. 
       SUMMARY 
       [0015]    According to an exemplary embodiment, an apparatus includes a network of switchable coils suspended in a magnetic field, wherein a topology of the network of switchable coils may be configured to change at least one characteristic of a sensor, and an optical detector to detect displacement of the coil in response to a stimulus. The apparatus further includes a feedback circuit coupled to the optical detector and to the network of switchable coils. 
         [0016]    According to another exemplary embodiment, a system includes a sensor. The sensor includes a plurality of switchable coils suspended in a magnetic field, and an optical detector to detect displacement of the plurality of switchable coils in response to a stimulus, and a feedback circuit coupled to the optical detector and to the coil. The sensor further includes a controller coupled to the plurality of switchable coils to couple the plurality of coils in a series configuration or in a parallel configuration. 
         [0017]    According to another exemplary embodiment, a method of operating a sensor is disclosed. The sensor includes a network of switchable coils suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, and a feedback circuit coupled to the detector and to the network of switchable coils. The method includes configuring a topology of the network of switchable coils to change at least one characteristic of the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The appended drawings illustrate only exemplary embodiments and therefore should not be considered as limiting the scope of the application or the claims. Persons of ordinary skill in the art appreciate that the disclosed concepts lend themselves to other equally effective embodiments. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks. 
           [0019]      FIG. 1  illustrates a conceptual diagram of a geophone. 
           [0020]      FIG. 2  depicts the frequency response of a geophone in response to physical stimuli. 
           [0021]      FIG. 3  shows a sensor according to an exemplary embodiment. 
           [0022]      FIG. 4  depicts forces operating in a sensor according to an exemplary embodiment. 
           [0023]      FIG. 5  illustrates a virtual spring caused by use of negative feedback in an exemplary embodiment. 
           [0024]      FIG. 6  depicts a cross-section of a sensor according to an exemplary embodiment. 
           [0025]      FIG. 7  illustrates a cross-section of a sensor according to an exemplary embodiment. 
           [0026]      FIG. 8  shows a schematic diagram of a sensor according to an exemplary embodiment. 
           [0027]      FIG. 9  illustrates a schematic diagram of a sensor according to an exemplary embodiment. 
           [0028]      FIG. 10  depicts an output signal of a trans-impedance amplifier (TIA) in an exemplary embodiment. 
           [0029]      FIG. 11  shows a flow diagram for a method of operating a sensor according to an exemplary embodiment. 
           [0030]      FIG. 12  illustrates a block diagram of a sensor communicating with another device or component according to an exemplary embodiment. 
           [0031]      FIG. 13  depicts a circuit arrangement for a sensor with a plurality of coils coupled in a series configuration according to an exemplary embodiment. 
           [0032]      FIG. 14  illustrates a circuit arrangement for the embodiment of  FIG. 13  with the plurality of coils coupled in a parallel configuration. 
           [0033]      FIG. 15  shows a circuit arrangement for a sensor with a network of switchable coils according to an exemplary embodiment. 
           [0034]      FIG. 16  depicts a network of switchable coils according to an exemplary embodiment. 
           [0035]      FIG. 17  illustrates a network of switchable coils according to another exemplary embodiment. 
           [0036]      FIG. 18  shows a network of switchable coils according to another exemplary embodiment. 
           [0037]      FIG. 19  depicts a network of switchable coils according to yet another exemplary embodiment. 
           [0038]      FIG. 20  illustrates a network of switchable coils according to yet another exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The disclosed concepts relate generally to sensors, such as acceleration, speed, and displacement sensors. More specifically, the disclosed concepts provide systems, apparatus, and methods for sensors with configurable coils, such as coils that may be configured in series or in parallel, etc. 
         [0040]    Sensors according to exemplary embodiments can sense acceleration, velocity, and/or displacement. As persons of ordinary skill in the art understand, acceleration, velocity, and displacement are governed by mathematical relationships. Thus, one may sense one of acceleration, velocity, and displacement, and derive the others from it. 
         [0041]    For example, if acceleration, a, is sensed, velocity, v, and displacement, x, may be derived from a. More specifically: 
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         [0042]    Sensors according to exemplary embodiments include a combination of electrical, optical, and mechanical components.  FIG. 3  illustrates a conceptual diagram of a sensor  100  according to an exemplary embodiment. 
         [0043]    Referring to  FIG. 3 , sensor  100  includes a spring  106  attached (e.g., at one end) to an acceleration reference frame or plane  103 . Spring  106  has a spring constant k s . Spring  106  is also attached (e.g., at another end) to coil  109 . Coil  109  and its corresponding assembly (not shown), e.g., a bobbin, have a mass m, also known as proof mass. 
         [0044]    A magnet  112  is positioned near or proximately to coil  109 . A magnetic field  112 A is established between the north and south poles of magnet  112 . Thus, coil  109  is completely or partially suspended within magnetic field  112 A. By virtue of spring  106 , coil  109  may move in relation to magnet  112  and, thus, in relation to magnetic field  112 A. 
         [0045]    More specifically, in response to a physical stimuli, such as a force that causes displacement x of coil  109 , coil  109  moves in relation to magnet  112  and magnetic field  112 A. As persons of ordinary skill in the art understand, movement of a conductor, such as coil  109 , in a magnetic field, such as magnetic field  112 A, induces a current in the coil. Thus, in response to the stimuli, coil  109  produces a current. 
         [0046]    Optical position sensor  115  detects the movement of coil  109  in response to the stimuli. More specifically, as described below in detail, optical position sensor  115  generates an output signal, for example, a current, in response to the movement of coil  109 . 
         [0047]    Note that in some embodiments, rather than generating a current, optical position sensor  115  may generate a voltage signal. For example, optical position sensor  115  may include a mechanism, such as an amplifier or converter, to convert a current produced by the electro-optical components of optical position sensor  115  to an output voltage. In either case, optical position sensor  115  provides an output signal  115 - 1  to amplifier  118 . 
         [0048]    Without loss of generality, in exemplary embodiments, amplifier  118  constitutes a TIA. TIA  118  generates an output voltage in response to an input current. Thus, in the case where optical position sensor  115  provides an output current (rather than an output voltage)  115 - 1 , TIA  118  converts the current to a voltage signal. 
         [0049]    In some embodiments, depending on a number of factors, TIA  118  may include circuitry for driving coil  109 , such as a coil driver (not shown). Such factors include design and performance specifications for a given implementation, for example, the amount of drive specified for coil  109 , etc., as persons of ordinary skill in the art will understand. 
         [0050]    TIA  118  (or other amplifier circuitry, as noted above) provides an output signal  118 - 1  to coil  109 . The polarity of output signal  118 - 1  is selected such that output signal  118 - 1  counteracts the current induced in coil  109  in response to the physical stimuli. In other words, optical position sensor  115  and TIA  118  couple to coil  109  so as to form a negative-feedback loop. 
         [0051]    The feedback or driving signal, i.e., signal  118 - 1 , causes a force to act on coil  109 . In exemplary embodiments, the force is proportional to the displacement x. Thus, a force exerted by spring  106  and a force exerted by coil  109  (by virtue of negative feedback and driving signal  118 - 1 ) cooperate with each other against the force created by acceleration of coil  109  (the proof mass).  FIG. 4  illustrates the two forces. 
         [0052]    More specifically,  FIG. 4  shows a force vector  121  that corresponds to force F s  exerted by spring  106 .  FIG. 4  also depicts a force vector  124  that corresponds to force F c  exerted by virtue of the acceleration of coil  109 . According to Hook&#39;s law, force F s  relates to displacement x, specifically F s =−k s ·x, where, as noted above, k s  represents the spring constant of spring  106 . In effect, spring  106  resists the displacement in proportion to k s . 
         [0053]    Furthermore, according to Newton&#39;s second law (ignoring any relativistic effects), force F c  relates to the mass of coil  109  (including any physical components, such as a bobbin), and to the acceleration that coil  109  experiences as a result of the external stimuli (e.g., the source that causes displacement x to occur). Specifically, F c =m c ·a, where m c  represents the mass of coil  109 , and a denotes the acceleration that coil  109  experiences. 
         [0054]    As noted above, negative feedback is employed in sensor  100  (see  FIG. 5 ) so as to cause the mass m c  to come to equilibrium. Mathematically stated, the feedback causes the mass m c  to come to equilibrium when F s  equals F c . Thus, sensor  100  may be viewed as operating according to a force-balance principle, i.e., F s =F c  at equilibrium. 
         [0055]    Stated another way, force-balance occurs when −k s ·x=m c ·a. One may readily determine the spring constant k s  and the mass of coil  109 , m c  (e.g., by consulting data sheets or controlling manufacturing processes, etc.). Using the values of k s  and m c  in the above equation, one may determine the acceleration of coil  109  in response to the stimulus, i.e.: 
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         [0056]    In other words, output signal  118 - 1  of TIA  118  is proportional to acceleration a. Given acceleration a, velocity v, and displacement x may be determined, by using the mathematical relations described above. (Note also that optical position sensor  115  may also determine displacement x). Thus, sensor  100  may be used to determine displacement (position), velocity, and/or acceleration, as desired. 
         [0057]    Using negative feedback provides a number of benefits. First, it flattens or tends to flatten the response of sensor  100  to the stimuli. Second, feedback increases the frequency response of sensor  100 , i.e., sensor  100  has more of a broadband response because of the use of feedback. 
         [0058]    Third, negative feedback reduces the amount of displacement that results in a desired output signal level. In effect, negative feedback acts as a virtual spring coupled in parallel with spring  106 , a concept that  FIG. 5  illustrates. More specifically, the negative-feedback signal applied to coil  109  causes virtual spring  130  to counteract force F c , which is exerted because of the acceleration of coil  109 , as described above. Thus, spring  106  and virtual spring  130  work as additive forces to reach force equilibrium in opposition to the force created by acceleration of the coil mass (proof mass). Virtual spring  130  is controlled electronically, e.g., by TIA  118  in  FIG. 3 . 
         [0059]    Referring again to  FIG. 5 , because of the use of negative feedback, virtual spring  130  has a larger spring constant, k v , than does spring  106 . Use of virtual spring  130  results in sensor  100  creating a given output in response to a smaller stimulus. Put another way, virtual spring  130  acts as a stiff spring. Thus, compared to an open-loop arrangement, sensor  100  has a reduced total displacement for a desired level of output signal. Also, force applied to a sensor that uses an open-loop arrangement (e.g., a geophone), causes the mass suspended by the spring to wobble more, which limits the upper response limit of the sensor. 
         [0060]    As noted, use of negative feedback flattens or tends to flatten the sensor frequency response, and also reduces the sensitivity of the force-balance system to the value of spring constant k s  of spring  106 , since the spring constant of virtual spring  130  dominates. A benefit of the foregoing is to allow the use of a stiffer spring suspension  106 , which in turn facilitates sensor operation at any orientation with respect to Earth&#39;s gravity. Additionally, an increase in loop gain results in a stiffer virtual spring constant  130 , which in turn allows a larger full scale stimulus range. 
         [0061]    Note that a variety of embodiments of sensors according to the disclosure are contemplated. For example, in some embodiments, the position of coil  109  and magnet  112  may be reversed or switched (see  FIG. 3 ). Thus, coil  109  may be stationary, while magnet  112  may be suspended by spring  106 . 
         [0062]    As another example, in some embodiments, more than one magnet  112  may be used, as desired. As yet another example, in some embodiments, more than one coil  109  may be used, e.g., two coils in parallel or series, as desired. Other arrangements are possible, depending on factors such as design and performance specifications, cost, available technology, etc., as persons of ordinary skill in the art will understand. 
         [0063]      FIG. 6  depicts a cross-section of a sensor  200  according to an exemplary embodiment. Sensor  200  includes a housing, frame, or enclosure  205  to provide physical support for various components of sensor  200 . In the embodiment shown, housing  205  has sides  205 A,  205 B,  205 C, and  205 D, for example, a top, a right side or wall, a bottom, and a left side or wall. Other housing, frames, or enclosures are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0064]    Magnet  112  is arranged with magnet caps  215 A and  215 B. In the embodiment shown, magnet  112  is disposed between magnet caps  215 A and  215 B. A variety of types and shapes of magnets may be used, as desired. Examples include neodymium-iron-boron (NIB) or aluminum nickel cobalt (ALNICO) alloy magnets, but other materials, such as alloys with appropriate properties, may be used. Other arrangements of the magnet and magnet caps or support are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0065]    Coil  109  is wound on a bobbin  220 . In the embodiment shown, coil  109  and bobbin  220  together form the proof mass (neglecting the mass of spring  106 ). In the embodiment shown, coil  109  is wound in two sections on bobbin  220 , although other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0066]    The proof mass is suspended by spring  106 , which for illustration purposes is shown as four sections labeled  106 A- 106 D. In exemplary embodiments, spring  106  may include one, two, or more springs, such as flat, leaf, or spider springs, as desired. Other types and/or arrangements of spring  106  are possible and contemplated, as persons of ordinary skill in the art will understand. A variety of materials and techniques may be used to fabricate spring  106 . Some examples include etching or die cutting. Beryllium copper may be used as one example of spring material, but other materials with appropriate spring properties (e.g., having relatively low temperature coefficient) may be used, as desired. 
         [0067]    In exemplary embodiments, such as the embodiment of  FIG. 6 , spring  106  may have a relatively low spring constant. More specifically, spring  106  may have sufficient stiffness to suspend and support the proof mass. As noted above, a virtual spring (not shown) having a relatively high spring constant (i.e., higher than the spring constant of spring  106 ) operates in conjunction with spring  106 . Thus, spring  106  may provide just enough stiffness to physically support the proof mass. 
         [0068]    In the embodiment shown in  FIG. 6 , spring  106  (shown as sections or portions  106 A- 106 D) suspend the proof mass with respect to magnet  112  (and magnet caps  215 A- 215 B, if used). In other words, a stimulus, such as force, applied to sensor  200  causes the proof mass to move or experience a displacement with respect to magnet  112  (and magnet caps  215 A- 215 B). Other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. For example, spring  106  may attach to housing  205 , rather than magnet caps  215 A- 215 B. 
         [0069]    Sensor  200  includes an optical interferometer to generate an electrical signal in response to displacement of coil  109  in relation to magnet  112  or housing  205 . The electrical signal constitutes the output of the optical interferometer. The electrical signal may be provided to an amplifier, e.g., TIA  118  in  FIG. 3 . 
         [0070]    Referring again to  FIG. 6 , in the embodiment shown, the optical interferometer includes a light source  225 , such as a vertical cavity surface-emitting laser (VCSEL). The light output of light source  225  is reflected by a mirror  222 , and is diffracted by diffraction grating  235 . The resulting optical signals are detected by optical detectors  230 A,  230 B, and  230 C. 
         [0071]    A mechanical or physical stimulus applied to sensor  200  causes a change in the detected light, and thus causes optical detectors  230 A- 230 C to provide an electrical output signal. The electrical output signal, e.g., a current signal, may be used in a feedback loop, as discussed above. 
         [0072]    Note that, if desired, the electrical output signal may be used in an open-loop configuration, rather than in a closed-loop (negative feedback) configuration. As noted above, closed-loop configuration provides some advantages over open-loop configuration. In some situations, however, operating sensor  200  in an open-loop configuration may be desired, for instance, on a temporary basis. 
         [0073]      FIG. 7  depicts a cross-section of a sensor  250  according to an exemplary embodiment. Sensor  250  includes a housing, frame, or enclosure  205  to provide physical support for various components of sensor  250 . In the embodiment shown, housing  205  has sides  205 A,  205 B and  205 C, for example, a right side or wall, a bottom, and a left side or wall. Other housing, frames, or enclosures are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0074]    Magnet  112  is arranged with magnet caps  215 A,  215 B, and  215 C. In the embodiment shown, magnet  112  is attached to magnet cap  215 B, which is disposed against or in contact with magnet caps  215 A and  215 C. A variety of types and shapes of magnets may be used, as desired. As noted, examples include neodymium-iron-boron (NIB) or aluminum nickel cobalt (ALNICO) alloy magnets, but other materials, such as alloys, with appropriate properties can be used. In some embodiments, magnet  112  may extend to a cavity in bobbin  220  (described below). Other arrangements of the magnet and magnet caps or support are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0075]    Coil  109  is wound on a bobbin  220 . In the embodiment shown, coil  109  and bobbin  220  together form the proof mass (neglecting the mass of spring  106 ). In the embodiment shown, coil  109  is wound around bobbin  220 , although other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. 
         [0076]    The proof mass is suspended by spring  106 , which for illustration purposes is shown as four sections labeled  106 A- 106 D. In exemplary embodiments, spring  106  may include one, two, or more springs, such as flat, leaf, or spider springs, as desired. Other types and/or arrangements of spring  106  are possible and contemplated, as persons of ordinary skill in the art will understand. As noted above, a variety of materials and techniques may be used to fabricate spring  106 . Some examples include etching or die cutting. Beryllium copper may be used as one example of spring material, but other materials with appropriate spring properties (e.g., having relatively low temperature coefficient) may be used, as desired. 
         [0077]    In exemplary embodiments, such as the embodiment of  FIG. 7 , spring  106  may have a relatively low spring constant. More specifically, spring  106  may have sufficient stiffness to suspend and support the proof mass. As noted above, a virtual spring (not shown), having a relatively high spring constant (i.e., higher than the spring constant of spring  106 ) operates in conjunction with spring  106 . Thus, spring  106  may provide just enough stiffness to physically support the proof mass. 
         [0078]    In the embodiment shown in  FIG. 7 , spring  106  (shown as sections or portions  106 A- 106 D) suspend the proof mass with respect to magnet  112  (and magnet caps  215 A- 215 C, if used). In other words, a stimulus, such as force, applied to sensor  250  causes the proof mass to move or experience a displacement with respect to magnet  112  (and magnet caps  215 A- 215 C). Other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. For example, spring  106  may attach to magnet caps  215 A and  215 C, rather than housing  205 . 
         [0079]    Sensor  250  includes an optical interferometer to generate an electrical signal in response to displacement of coil  109  in relation to magnet  112  or housing  205 . The electrical signal constitutes the output of the optical interferometer. The electrical signal may be provided to an amplifier, e.g., TIA  118  in  FIG. 3 . 
         [0080]    Referring again to  FIG. 7 , in the embodiment shown, the optical interferometer includes a light source  225 , such as a VCSEL. The light output of light source  225  is reflected by a mirror  222 , and is diffracted by diffraction grating  235 . The resulting optical signals are detected by optical detectors  230 A,  230 B, and  230 C. 
         [0081]    A stimulus applied to sensor  250  causes a change in the detected light, and thus causes optical detectors  230 A- 230 C to provide an electrical output signal. The electrical output signal, e.g., a current signal, may be used in a feedback loop, as discussed above. 
         [0082]    Note that, if desired, the electrical output signal may be used in an open-loop configuration, rather than in a closed-loop (negative feedback) configuration. As noted above, closed-loop configuration provides some advantages over open-loop configuration. In some situations, however, operating sensor  250  in an open-loop configuration may be desired, for instance, on a temporary basis. 
         [0083]      FIG. 8  shows a schematic diagram or circuit arrangement  300 A for a sensor according to an exemplary embodiment, for instance sensors  200  and  250  in  FIGS. 6 and 7 , respectively. Referring to  FIG. 8 , as described above, optical detectors  230 A- 230 C (photodiodes in the embodiment shown) provide an output signal to TIA  118 . A bias source, labeled V BIAS , for example, ground or zero potential, provides an appropriate bias signal to detectors  230 A- 230 C. In the embodiment of  FIG. 8 , the output signal of optical detectors  230 A- 230 C is provided to TIA  118  as a differential signal. 
         [0084]    Note that  FIG. 8  omits light source  225  for the sake of clarity of presentation. Light source  225 , e.g., a VCSEL, may be powered by an appropriate circuit (not shown). Examples include a voltage regulator, a reference source, etc., as desired. Also, in some embodiments, MCU  310  may control or program the light level that light source  225  emits, depending on various factors, such as power consumption, desired sensor parameters and performance, etc. 
         [0085]    In the embodiment shown in  FIG. 8 , TIA  118  includes two individual TIA circuits or amplifiers,  118 A and  118 B, to accommodate the differential input signal. TIA  118  includes resistors  305 A- 305 B to adjust (or calibrate or set or program or configure) the gain of TIAs  118 A- 118 B, respectively. 
         [0086]    Thus, by adjusting resistor  305 A, the gain of amplifier  118 A may be adjusted. Similarly, by adjusting resistor  305 B, the gain of amplifier  118 B may be adjusted. A controller, such as a microcontroller unit (MCU)  310  in the exemplary embodiment shown, adjusts the values of resistors  305 A- 305 B. 
         [0087]    Typically, given the differential nature of the input signal of TIA  118 , MCU  310  adjusts resistors  305 A- 305 B to the same resistance value so as to increase or improve the common-mode rejection ration (CMRR) of TIA  118 . Put another way, the two branches of TIA  118 , i.e., the branches containing amplifiers  118 A and  118 B, respectively, are typically matched by adjusting resistors  305 A- 305 B to the same resistance value. In some situations, however, resistors  305 A- 305 B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc. 
         [0088]    Note that adjusting the gains of amplifiers  118 A- 118 B does not set the full-scale range of the sensor. Rather, the gains of amplifiers  118 A- 118 B determine the overload point of the sensor, i.e., the peak overload point of the sensor in response to a stimulus. Furthermore, the coil constant of coil  109  determines the magnitude of the output signal of the sensor in response to a given amount of acceleration in response to a stimulus, such as force. The coil constant is defined in units of Newtons per Ampere. Increasing the coil constant increases the full-scale range of the sensor for a given available or applied coil current. For fixed values of resistors  320 A and  320 B, the effect of increasing coil constant is a decrease in the sensor&#39;s scale factor in terms of Volts per unit of stimulus (e.g., acceleration (g)), as force-balance equilibrium will be reached at a lower coil current (and hence output voltage) for a given stimulus value. 
         [0089]    The output of amplifier  118 A feeds one end or terminal of coil  109  via resistors  315 A and  320 A. Conversely, the output of amplifier  118 B feeds the other end of coil  109  via resistors  315 B and  320 B. Thus, amplifiers  118 A- 118 B provide a drive signal for coil  109  via resistors  315 A- 315 B and  320 A- 320 B. 
         [0090]    MCU  310  may adjust (or calibrate or set or program or configure) the values of resistors  320 A- 320 B. Similar to resistors  305 A- 305 B, typically, given the differential nature of the output signal of the sensor, MCU  310  adjusts resistors  320 A- 320 B to the same resistance value. In some situations, however, resistors  320 A- 320 B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc. 
         [0091]    Note that the values of resistors  320 A- 320 B affect the gain or scale factor of the sensor. In other words, the values of resistors  320 A- 320 B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus. 
         [0092]    Nodes  325 A and  325 B provide the differential output signal of the sensor. In the embodiment shown, node  325 A provides the positive output signal, whereas node  325 B provides the negative output signal. Together, the positive and negative output signals provide a differential output signal that is proportional to acceleration, a, experienced by the proof mass in response to the stimulus (e.g., force), as discussed above. 
         [0093]    In some embodiments, MCU  310  may include circuitry to receive and process the output signal provided at nodes  325 A- 325 B. For example, MCU  310  may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes  325 A- 325 B to a digital quantity. MCU  310  may communicate the resulting digital quantity to another circuit or component, for example, via link  370 , as desired. Furthermore, MCU  310  may receive power (to supply the various components in the sensor) or other information, for example, parameters related to adjusting various resistor values, as described above, via link  370 . 
         [0094]      FIG. 9  shows a schematic diagram or circuit arrangement  300 B for a sensor according to an exemplary embodiment, for instance sensors  200  and  250  in  FIGS. 6 and 7 , respectively. Referring to  FIG. 9 , as described above, optical detectors  230 A- 230 C (photodiodes in the embodiment shown) provide an output signal to TIA  118 . In the example shown, V BIAS  is ground potential although, as noted above, other appropriate values may be used. In the embodiment of  FIG. 9 , the output signal of optical detectors  230 A- 230 C is provided to TIA  118  as a single-ended signal. 
         [0095]    Note that  FIG. 9  omits light source  225  for the sake of clarity of presentation. Light source  225 , e.g., a VCSEL, may be powered by an appropriate circuit (not shown). Examples include a voltage regulator, a reference source, etc., as desired. Also, in some embodiments, MCU  310  may control or program the light level that light source  225  emits, depending on various factors, such as power consumption, desired sensor parameters and performance, etc. 
         [0096]    The gain of TIA  118  may be adjusted by adjusting (or calibrating or setting or programming or configuring) resistor  305 . In the embodiment shown, MCU  310  adjusts the values of resistor  305 . In other embodiments, other arrangements may be used, as desired, for example, use of a host or controller coupled to the sensor, described below. 
         [0097]    The output of TIA  118  drives an input of amplifier  345  via resistor  335 . A feedback resistor  340  couples the output of amplifier  345  to resistor  335  (input of amplifier  345 ). If desired, the gain of amplifier  345  may be adjusted by adjusting resistor  340  (more specifically, the ratio of resistors  340  and  335 ). In the embodiment shown, MCU  310  may adjust the value of resistor  345 . 
         [0098]    The output of amplifier  345  drives an input of amplifier  355  via resistor  350 . A feedback resistor  360  couples the output of amplifier  355  to resistor  350  (input of amplifier  355 ). If desired, the gain of amplifier  355  may be adjusted by adjusting resistor  360  (more specifically, the ratio of resistors  360  and  350 ). In the embodiment shown, MCU  310  may adjust the value of resistor  360 . 
         [0099]    Note that adjusting the gain of TIA  118  (and optionally the gains of amplifiers  345  and  355 ) does not set the full-scale range of the sensor. Rather, the gain of TIA  118  (and optionally the gains of amplifiers  345  and  355 ) determines the overload point of the sensor, i.e., the peak overload point of the sensor in response to a stimulus. Furthermore, the coil constant of coil  109  determines the magnitude of the output signal of the sensor in response to a given amount of acceleration in response to a stimulus, such as force. More specifically, the coil constant of coil  109  in conjunction with the values of  320 A and  320 B determine the output scale factor in Volts per unit of stimulus, e.g., g of acceleration. 
         [0100]    The output of amplifier  345  feeds one end or terminal of coil  109  via resistors  315 A and  320 A. Conversely, the output of amplifier  355  feeds the other end of coil  109  via resistors  315 B and  320 B. Thus, amplifiers  345  and  355  provide a drive signal for coil  109  via resistors  315 A- 315 B and  320 A- 320 B. 
         [0101]    MCU  310  may adjust (or calibrate or set or program or configure) the values of resistors  320 A- 320 B. Note that the values of resistors  320 A- 320 B affect the gain or scale factor of the sensor. In other words, the values of resistors  320 A- 320 B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus. 
         [0102]    Nodes  325 A and  325 B provide the differential output signal of the sensor. In the embodiment shown, node  325 A provides the positive output signal, whereas node  325 B provides the negative output signal. Together, the positive and negative output signals provide a differential output signal that is proportional to acceleration, a, experienced by the proof mass in response to the stimulus (e.g., force), as discussed above. 
         [0103]    In some embodiments, MCU  310  may include circuitry to receive and process the output signal provided at nodes  325 A- 325 B. For example, MCU  310  may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes  325 A- 325 B to a digital quantity. MCU  310  may communicate the resulting digital quantity to another circuit or component, for example, via link  370 , as desired. Furthermore, MCU  310  may receive power (to supply the various components in the sensor) or other information, for example, parameters related to adjusting various resistor values, as described above, via link  370 . 
         [0104]    Note that although the exemplary embodiments of  FIGS. 8-9  show MCU  310  as the controller, other possibilities exist and are contemplated. For example, a processor (e.g., a central processing unit (CPU) or other type of processor), a logic circuit, a finite-state machine, etc., may be used to control the values of the various resistors. The choice of the controller used depends on factors such as design and performance specifications, the degree of flexibility and programmability desired, the available technology, cost, etc., as persons of ordinary skill in the art will understand. 
         [0105]      FIG. 10  illustrates the output signal  400  of a TIA  118  in an exemplary embodiment, for example, one of the embodiments of FIGS.  3  and  6 - 9 . Output signal  400  shows how the output signal  400  (measured in Volts) of TIA  118  varies as a function of displacement, x (measured in meters). The output signal  400  shows a variation around a reference point  405  in response to displacement. 
         [0106]    Thus, in the example shown, in response to a displacement x 1 , having, for example, an absolute value of 100 nm around reference point  405  (say, ±100 nm), the output signal  400  varies from −V to +V, for example, by ±2 volts. The output signal  400  is a function of the gain of TIA  118 . As noted above, the gain of TIA  118  determines the peak response or overload point of TIA  118 . 
         [0107]    Note that the output signal  400  of TIA  118  may be periodic (e.g., a cyclical interference fringe condition) in response to displacement, as persons of ordinary skill in the art will understand.  FIG. 10  shows merely a portion of output signal  400  for the sake of discussion. 
         [0108]      FIG. 11  shows a flow diagram  500  for a method of operating a sensor according to an exemplary embodiment. More specifically, the figure illustrates the actions that a controller, such as MCU  310 , described above, may take, starting with the sensor&#39;s power-up. 
         [0109]    After power-up, at  505  MCU  310  is reset. The reset of MCU  310  may be accomplished in a variety of ways. For example, a resistor-capacitor combination may hold the reset input of MCU  310  for a sufficiently long time to reset MCU  310 . As another example, a power-on reset circuit external to MCU  310  may cause MCU  310  to reset. As another example, MCU  310  may be reset according to commands or control signals from a host. 
         [0110]    After reset, MCU  310  begins executing firmware or user program instructions. The firmware or user program instructions may be included in a storage circuit within MCU  310  (e.g., internal flash memory) or in a storage circuit external to MCU  310  (e.g., an external flash memory). In any event, MCU  310  takes various actions in response to the firmware or user program instructions. 
         [0111]    At  510 , MCU  310  adjusts one or more resistors (e.g., resistors  305 A- 305 B in  FIG. 8  or resistor  305  in  FIG. 9 ) to calibrate the gain of TIA  118  (see, for example,  FIGS. 8 and 9 ). As described above in detail, the gain of TIA  118  affects certain attributes of the sensor. 
         [0112]    At  515 , MCU  310  adjusts resistors (e.g., resistors  320 A- 320 B in  FIGS. 8 and 9 ) in the signal path that drives coil  109  (see, for example,  FIGS. 8 and 9 ). As described above in detail, the values of resistors  320 A- 320 B affects certain attributes of the sensor, such as gain or scale of the sensor. Optionally, MCU  310  may make other adjustments or calibrations, for example, it may adjust the values of resistors  340  and  360  (see  FIG. 9 ). 
         [0113]    Referring again to  FIG. 11 , at  520  MCU  310  may optionally enter a sleep state. In the sleep state certain parts or blocks of MCU  310  may be disabled or powered down or placed in a low-power state (compared to when MCU  310  is powered up). Examples include placing the processor, input/output (I/O) circuits, signal processing circuits (e.g., ADC), and/or other circuits (e.g., arithmetic processing circuits) of MCU  310  in a sleep state. 
         [0114]    Placing some of the circuitry of MCU  310  in a sleep state lowers the power consumption of MCU  310 , in particular, and of the sensor, overall. Depending on the amount of power consumed in the sleep state and factors such as power-source capacity (e.g., the capacity of a battery used to power the sensor), MCU  310  may remain in the sleep state for relatively long periods of time, e.g., days, weeks, months, or even longer. Thus, the power savings because of the use of the sleep state provide a particular benefit in portable or remote applications where a battery may be used to power the sensor. 
         [0115]    Note that some circuitry in MCU  310  may be kept powered up, even during the sleep mode or state. For example, a real-time clock (RTC) circuit (or other timer circuitry) may be kept powered and operational so as to track the passage of time. As another example, interrupt circuitry of MCU  310  may be kept powered and operation so that MCU  310  may respond to interrupts. 
         [0116]    As part of entering the sleep state, the state of MCU  310  may be saved, for example, contents of registers, content of the program counter, etc. Saving the state of MCU  310  allows restoring MCU  310  later (e.g., when MCU  310  wakes up or resumes from the sleep state) to the same state as when it entered the sleep state. 
         [0117]    MCU  310  may leave the sleep mode or state (wake up) and enter the normal mode of operation (e.g., processing signals generated in the sensor in response to a stimulus), or resume from the sleep state. For instance, in some embodiments, MCU  310  (or a CPU or other processor or controller) remains in the sleep state until one or more conditions are met, for example, the output signal (Out+−Out−) exceeding a preset threshold or value, or a timer generating a signal after a preset amount of time has elapsed, etc. In some embodiments, once the condition(s) is/are met, an interrupt may be generated to cause MCU  310  to leave the sleep state. 
         [0118]    As part of the process of leaving the sleep state and entering the normal mode of operation, the state of MCU  310  may be restored (if the state was saved, as described above). Once MCU  310  leaves the sleep state, it can process signals generated in response to the stimuli, as described above. 
         [0119]    In some embodiments, the sensor may be self-contained. In other words, the sensor, e.g., MCU  310 , may include instructions for code that determine how the sensor responds to stimuli, how it processes the signals generated as a result of the application of the stimulus (e.g., log the signal values, and time/date information, as desired), etc. The sensor may also include a source of energy, such as a battery, to supply power to the various circuits of the sensor. Such embodiments may be suitable for operation in conditions where access to the sensor is limited or relatively difficult. 
         [0120]    In other embodiments, the sensor may communicate with another device, component, system, or circuit, such as a host.  FIG. 12  illustrates such an arrangement according to an exemplary embodiment. 
         [0121]    Specifically, a sensor, such as the sensors depicted in FIGS.  3  and  6 - 9 , includes a controller, such as MCU  310 . Circuit arrangement  600  in  FIG. 12  also includes a host (or device or component or system or circuit)  605 . The sensor, specifically, the controller (MCU  310 ) communicates with host  605  via link  370 . 
         [0122]    In exemplary embodiments, link  370  may include a number of conductors, and facilitate performing a number of functions. In some embodiments, link  370  may constitute a multi-conductor cable or other or similar means of coupling. In some embodiments, link  370  may constitute a bus. 
         [0123]    In some embodiments, link  370  may constitute a wireless link (e.g., the sensor and host  605  include receiver, transmitter, or transceiver circuitry that allow wireless communication via link  370  by using radio-frequency (RF) signals). Use of a wireless link provides the advantage of communication without using cumbersome electrical connections, and may allow arbitrary or desired locations for the sensor and host  605 . 
         [0124]    In some embodiments, link  370  may constitute an optical link. Use of an optical link allows for relatively low noise in link  370 . In such a situation, the sensor and host  605  may include optical sources and/or receivers or detectors, depending on whether unidirectional or bidirectional communication is desired. 
         [0125]    In some embodiments, link  370  provides a mechanism for supplying power to various parts of the sensor. The sensor may include one or more local regulators, as desired, to regulate or convert the power received from host  605  (or other source), for example, by changing the voltage level or increasing the load regulation, as desired. 
         [0126]    In some embodiments, link  370  provides a mechanism for the sensor and host  605  to communicate a variety of signals. Examples include data signals, control signals, status signals, and handshaking signals (e.g., as used in information exchange protocols). As an example, link  370  provides a flexible mechanism by which the sensor may receive information (e.g., calibration information) from host  605 . 
         [0127]    As another example, the sensor may provide information, such as data corresponding to or derived from a stimulus applied to the sensors. Examples of such data include information regarding displacement, velocity, and/or acceleration. Using this mechanism, host  605  may record a log of the data using desired intervals. 
         [0128]    In exemplary embodiments, link  370  provides a flexible communication channel by supporting a variety of types of signals, as desired. For example, in some embodiments, link  370  may be used to communicate analog signals. In other embodiments, link  370  may be used to communicate digital signals. In yet other embodiments, link  370  may be used to communicate mixed-signal information (both analog and digital signals). 
         [0129]    In some embodiments, host  605  may constitute or comprise an MCU (or other processor or controller) (not shown). In such scenarios, MCU  310  in the sensor may be omitted or may be moved to host  605 , as desired. As an alternative, in some embodiments, the MCU in host  605  may communicate with MCU  310  in the sensor. 
         [0130]    One aspect of the disclosure relates to sensors with configurable or switchable coils. More specifically, in exemplary embodiments, sensor include a network of switchable coils suspended in a magnetic field (e.g., produced by magnet  112 , as described above). As described below, the network of switchable coils includes a number of coils and a number of switches that may be switches in order to change the topology of the network of switchable coils. By doing so, one or more characteristics of the sensor may be configured (trimmed, programmed, varied, modified, adjusted, calibrated, etc.), as described below in detail. 
         [0131]      FIG. 13  depicts a circuit arrangement  650  for such a sensor. As described above, the sensor in  FIG. 13  includes coil  109  suspended in the magnetic field of one or more magnets  112 . Optical position sensor  115  detects the movement of coil  109  in response to stimuli, such as acceleration. As described above, optical position sensor  115  generates an output signal, for example, a current or voltage, in response to the movement of coil  109 . 
         [0132]    Signal processing circuit  655  is coupled to coil  109  and optical position sensor  115  to form a negative feedback circuit, as described above. Thus, signal processing circuit  655  receives the output signal of optical position sensor  115 , processes that signal, and then applies an output signal to coil  109 , as described above. 
         [0133]    Signal processing circuit  655  may include a variety of components, blocks, or circuits.  FIGS. 8-9  show examples according to two exemplary embodiments. Thus, signal processing circuit  655  may include one or more TIAs (not shown), resistors (not shown), amplifiers (not shown), filtering or feedback circuits/networks, etc. Generally, a variety of signal processing circuits  655  are contemplated, and are not limited to the examples shown in  FIGS. 8-9 , as persons of ordinary skill in the art will understand. 
         [0134]    An output of signal processing circuit  655  couples to and drives coil  109 . By virtue of the negative feedback in the circuit, coil  109  produces a force such that the sensor operates according to a force-balance principle, as described above. 
         [0135]    In the example shown, coil  109  includes two coils,  109 A and  109 B. Coils  109 A- 109 B may be coupled in series or in parallel by using a number of switches (the number of switches depends on a number of factors, such as the type of switch available, as described below). 
         [0136]    In the configuration shown in  FIG. 13 , coils  109 A and  109 B have been coupled in series (by using switches (not shown)). Given that the supply voltage of the sensor is finite (and typically limited, for example, to the voltage of a battery used in the field), the maximum available current (assuming negligible losses or voltage drops in other circuit components, such as transistors, amplifiers, etc.), I max , flowing through coil  109  is given by: 
         [0000]    
       
         
           
             
               
                 I 
                 
                   ma 
                    
                   
                       
                   
                    
                   x 
                 
               
               = 
               
                 
                   V 
                   s 
                 
                 
                   R 
                   c 
                 
               
             
             , 
           
         
       
     
         [0000]    where V s  and R c  denote, respectively, the supply voltage of the sensor and the total coil resistance. 
         [0137]    By using two coils coupled in series (e.g., by breaking up a coil  109  into two coil sections and coupling them in series), the total resistance of the coil has a maximum value. More specifically, compared to coupling the two coils in parallel, series-coupled coils have a higher overall resistance. 
         [0138]    As noted above, given a supply voltage V s , the maximum value of coil current, I max  is limited by the overall coil resistance. Compared to a parallel configuration (described below in detail), the configuration shown in  FIG. 13  results in a smaller coil current. 
         [0139]    Assuming other parameters of the sensor (e.g., TIA gain, resistance values, etc.) are held constant, coupling coils  109 A and  109 B in series causes a number of characteristics of the sensor to change. For example, the sensor has higher sensitivity to stimuli, such as acceleration, and also higher scale factor (gain). 
         [0140]    As noted above, coils  109 A- 109 B may be switched into a parallel configuration.  FIG. 14  illustrates a circuit arrangement  670  for the embodiment of  FIG. 13  with the plurality of coils coupled in a parallel configuration (by using switches (not shown)). 
         [0141]    Using two coils coupled in parallel (e.g., by breaking up a coil  109  into two coil sections, as described above) and coupling them in parallel) decrease the overall resistance of the coil. Specifically, compared to coupling the two coils in series, parallel-coupled coils have a lower overall resistance. 
         [0142]    Given a supply voltage V s , the maximum value of coil current, I max , is limited by the overall coil resistance, as discussed above. Thus, compared to a series configuration (shown in  FIG. 13 ), the configuration in  FIG. 14  results in a larger coil current. 
         [0143]    Assuming other parameters of the sensor (e.g., TIA gain, resistance values, etc.) are held constant, coupling coils  109 A and  109 B in parallel causes a number of characteristics of the sensor to change. For example, the sensor has a higher total coil current and thus a higher full-scale range. 
         [0144]    As noted above, in exemplary embodiments, the topology of the overall coil (which may include two or more coils) of the sensor may be configured or changed (e.g., by changing the topology of a network of switchable coils). Given that the configuration of the coils affects sensor characteristics, as described above, changing the coil configuration allows configuration of the sensor characteristics. 
         [0145]    Furthermore, by changing the coil configuration, one or more sensor characteristics corresponding to a given coil configuration may be traded off with one or more sensor characteristics corresponding to another coil configuration. For instance, referring to the example shown in  FIGS. 13-14 , using series-coupled coils  109 A- 109 B provides a higher scale factor, compared to a higher full-scale range that results from using parallel-coupled coils  109 A- 109 B. Thus, the two characteristics, scale factor and full-scale range, may be traded off by changing the topology of the network of switchable coils from series-coupled to parallel-coupled. 
         [0146]    As noted above, in exemplary embodiments, two or more coils may be used. More specifically, a network of switchable coils may be used that includes two or more coils and a plurality of switches. By changing the topology of the network of switchable coils, the topology of the coil may be changed (the coil may be configured). 
         [0147]      FIG. 15  shows a circuit arrangement  680  for a sensor with a network of switchable coils according to an exemplary embodiment. Specifically, the sensor in  FIG. 15  includes coil switch network  690 , which includes a plurality of coils and a plurality of switches  690 . As such, coil switch network  690  constitutes a network of switchable coils. By changing the topology of coil switch network  690 , the topology of the overall coil (e.g., series-coupled coils, parallel-coupled coils) of the sensor may be configured. 
         [0148]    Similar to the embodiment in  FIGS. 13-14 , optical position sensor  115  detects the movement of the coil (as presented by coil switch network  690 ) in response to stimuli, such as acceleration. As described above, optical position sensor  115  generates an output signal, for example, a current or voltage, in response to the movement of the coil. 
         [0149]    Signal processing circuit  655  is coupled to coil switch network  690  and optical position sensor  115  to form a negative feedback circuit, as described above. Thus, signal processing circuit  655  receives the output signal of optical position sensor  115 , processes that signal, and then applies an output signal to the coils in coil switch network  690 . 
         [0150]    As noted above, signal processing circuit  655  may include a variety of components, blocks, or circuits, as desired. The output of signal processing circuit  655  couples to and the inputs or terminals of coil switch network  690  (denoted as A and B) to drive the coils in coil switch network  690 . By virtue of the negative feedback in the circuit, the coils in coil switch network  690  produces a force such that the sensor operates according to a force-balance principle, as described above. 
         [0151]    Coil switch network  690 , described in more detail below, includes a plurality of coils and switches. By using controller  660 , the switches in coil switch network  690  may be controlled. For example, by using controller  660 , some of the switches in coil switch network  690  may be opened. As another example, by using controller  660 , some of the switches in coil switch network  690  may be closed. As another example, by using controller  660 , some of the switches in coil switch network  690  may be opened, whereas some of the switches in coil switch network  690  may be closed. 
         [0152]    In some embodiments, the switches in coil switch network  690  are physically or mechanically switched (e.g., switched manually). In such embodiments, controller  660  may be omitted, and the user of the sensor may manually set the positions or state of the switches in coil switch network  69 . 
         [0153]    In some embodiments, the switches in coil switch network  690  are electronically controlled. In such embodiments, controller  660  controls the switches in coil switch network  690 . Examples of such switches include electromechanical switches (e.g., relays, reed relays) and transistors (e.g., such as metal oxide semiconductor (MOS) transistors, bipolar junction transistor (BJT), etc. 
         [0154]    In exemplary embodiments, coil switch network  690  may have a variety of topologies and arrangements.  FIGS. 16-20  provides some examples of coil switch network  690 . 
         [0155]    More specifically,  FIG. 16  depicts a coil switch network  690  with two coils  109 A and  109 B. Coil switch network  690  also includes switches SA and SB. Switches SA and SB are commonly controlled by controller  660 . In other worse, switches SA and SB are configured as double-pole double-throw (DPDT) switch. 
         [0156]    Coils  109 A- 109 B may be coupled in series or in parallel, as desired. To couple coils  109 A- 109 B in series, the wipers of switches SA and SB is placed (by controller  660 ) in the “up” position (i.e., the position shown in  FIG. 16 ). In that position, switch SB couples coil  109 A in series with coil  109 B between points A and B. Switch SA does not affect the coil configuration, as its wiper is coupled to a switch terminal that is not coupled to another part of the circuit. 
         [0157]    Conversely, cols  109 A- 109 B may be coupled in parallel. To do so, the wipers of switches SA and SB is placed (by controller  660 ) in the “down” position (i.e., the opposite of the position shown in  FIG. 16 ). In that position, switch SB couples coil  109 B to point A. Also, switch SA couples coil  109 A to point B. As a consequence, coils  109 A- 109 B are coupled in parallel between points A and B. 
         [0158]    Rather than using multi-throw switches, such as the switches in  FIG. 16 , other types of switch may be used, e.g., single-throw switches or single-pole single-throw (SPST) switches.  FIGS. 17-20  provide examples of coil switch network  690  that use alternative switches. 
         [0159]    Referring to  FIG. 17 , a coil switch network  690  according to an exemplary embodiment is illustrated. Coil switch network  690  includes coils  109 A- 109 B, and four switches S 1 A-S 1 B and S 2 A-S 2 B. Controller  660  (not shown) controls switches S 1 A-S 1 B and S 2 A-S 2 B in order to provide a desired topology of coil switch network  690  and, thus, a desired coil configuration, to points A and B. 
         [0160]    More specifically, by controlling switches S 1 A-S 1 B and S 2 A-S 2 B, coils  109 A- 109 B may be coupled in series or in parallel. Table 1 shows the topology of coil switch network  690  as a function of the status (i.e., open and closed) of switches S 1 A-S 1 B: 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Configuration 
                 S1A 
                 S1B 
                 S2A 
                 S2B 
               
               
                   
               
             
             
               
                 coil 109A in series with 
                 Open 
                 Closed 
                 Closed 
                 Open 
               
               
                 coil 109B 
                   
                   
                   
                   
               
               
                 coil 109A in parallel with  
                 Closed 
                 Closed 
                 Open 
                 Closed 
               
               
                 coil 109B 
               
               
                   
               
             
          
         
       
     
         [0161]      FIG. 18  depicts a coil switch network  690  according to another exemplary embodiment is illustrated. Coil switch network  690  includes coils  109 A- 109 B, and three switches S 1 A-S 1 C. Controller  660  (not shown) controls switches S 1 A-S 1 C in order to provide a desired topology of coil switch network  690  and, thus, a desired coil configuration, to points A and B. 
         [0162]    More specifically, by controlling switches S 1 A-S 1 C, coils  109 A- 109 B may be coupled in series or in parallel. Table 2 shows the topology of coil switch network  690  as a function of the status (i.e., open and closed) of switches S 1 A-S 1 B: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Configuration 
                 S1A 
                 S1B 
                 S1C 
               
               
                   
               
             
             
               
                 coil 109A in series with 
                 Open 
                 Open 
                 Closed 
               
               
                 coil 109B 
                   
                   
                   
               
               
                 coil 109A in parallel with 
                 Closed 
                 Closed 
                 Open 
               
               
                 coil 109B 
               
               
                   
               
             
          
         
       
     
         [0163]    The coil switch networks shown in  FIGS. 17-18  may be generalized to more than two coils, for example, N coils, where N represents a positive integer greater than two.  FIGS. 19-20  provide examples of coil switch networks  690  with N coils according to exemplary embodiments. 
         [0164]      FIG. 19  depicts a coil switch network  690  with N coils according to an exemplary embodiment. The coil switch network in  FIG. 19  is a more general version (N coils) of the coil switch network shown in  FIG. 17 . 
         [0165]    Coil switch network  690  includes coils  109 A- 109 N, and switches S 1 A-S 1 N and S 2 A-S 2 N. Controller  660  (not shown) controls switches S 1 A-S 1 N and S 2 A-S 2 N in order to provide a desired topology of coil switch network  690  and, thus, a desired coil configuration, to points A and B. 
         [0166]    By controlling switches S 1 A-S 1 N and S 2 A-S 2 , two or more of coils  109 A- 109 N may be coupled in series or in parallel. For example, to couple coils  109 A- 109 C in series, switches S 1 B, S 2 A, S 2 B, and SNB are closed, but switches S 1 A, S 2 B, and SNA are opened. As another example, to couple coils  109 B- 109 C in parallel, switches S 1 A, S 2 A, S 2 B, S 3 B, and SNB are closed, and switches S 1 B, S 3 A, and SNA are opened. A variety of other switch configurations and, thus, coil configurations presented at points A and B, are possible. 
         [0167]      FIG. 20  illustrates a coil switch network  690  with N coils according another exemplary embodiment. The coil switch network in  FIG. 20  is a more general version (N coils) of the coil switch network shown in  FIG. 18 . 
         [0168]    Also, the coil switch network in  FIG. 20  is similar to the coil switch network shown in  FIG. 19 , but adds switches S 1 C, S 2 C, etc. The additional switches (S 1 C, S 2 C, etc.) provide more flexibility in coupling two or more of coils  109 A- 109 N in series or parallel. 
         [0169]    Similar to  FIG. 19 , by controlling the switches in  FIG. 20 , two or more of coils  109 A- 109 N may be coupled in series or in parallel. For example, to couple coils  109 A and  109 C in series, switches S 1 C, S 2 A, S 2 B, and SNB are closed, but switches S 1 A, S 1 B, S 2 B, S 2 C, S 3 A, and SNA are opened. As another example, to couple coils  109 B- 109 C in parallel, switches S 1 A, S 2 A, S 2 B, S 3 B, and SNB are closed, and switches S 1 B, S 1 C, S 2 C, S 3 A, and SNA are opened. A variety of other switch configurations and, thus, coil configurations presented at points A and B, are possible. 
         [0170]    In the embodiments shown, controller  660  controls various switches. Other arrangements, however, are contemplated and may be used. For example, a controller, either in the sensor or in a remote location (e.g., a remote host, such as host  605  in  FIG. 12 ) may control the switches. As noted above, as another example, the switches may be manually controlled by a user, e.g., by setting each switch to the desired position. 
         [0171]    As yet another example, MCU  310  (see, for example,  FIGS. 8-9 ) may be used to control the states of the switches. In some embodiments, MCU  310  may include information, such as instructions or commands, to control the switch states. In some embodiments, MCU  310  may obtain information (e.g., from host  605  or another source), such as instructions or commands, to control the switch states. 
         [0172]    Although sensors according to exemplary embodiments have been described and illustrated in the accompanying drawings, a variety of other embodiments and arrangements are contemplated. The following description provides some examples. 
         [0173]    In some embodiments, MCU  310  may be omitted. Instead, a remote host, device, component, system, circuit, etc., may couple to circuitry in the sensor to perform various operations, e.g., adjust the values of the various resistors. The sensor may include circuitry to facilitate communication with the remote host. Analog, digital, or mixed-signal control communication signals may be used to adjust the resistor values, as desired. 
         [0174]    In some embodiments, the electrical components (e.g., MCU  310 , TIA  118 , etc.) and rest of the sensor components (e.g., coil, optical position sensor) reside in the same housing. In other embodiments, the electrical components and rest of the sensor components reside in different components (e.g., to allow easier access to some components, while protecting other components) of the same housing. 
         [0175]    In yet other embodiments, the electrical components and rest of the sensor components, for example, the coil and/or optical position sensor, reside in different or separate housings. The choice of configuration depends on a variety of factors, as persons of ordinary skill in the art will understand. Examples of such factors include design and performance specifications, the intended physical environment of the sensor, the level of access desired to various components, cost, complexity, etc. 
         [0176]    Sensors according to exemplary embodiments may be used in a variety of applications. For example, sensors according to some embodiments may be used for geological exploration. As another example, sensors according to some embodiments may be used for detecting seismic movement, i.e., in seismology. As another example, sensors according to some embodiments may be used for detecting and/or deriving various quantities related to navigation, i.e., in inertial navigations. Other applications include using the sensor as a reference sensor for motion stimulus testing of other components or sensors under test. 
         [0177]    Referring to the figures, persons of ordinary skill in the art will note that the various blocks shown might depict mainly the conceptual functions and signal flow. The actual circuit implementation might or might not contain separately identifiable hardware for the various functional blocks and might or might not use the particular circuitry shown. For example, one may combine the functionality of various blocks into one circuit block, as desired. Furthermore, one may realize the functionality of a single block in several circuit blocks, as desired. The choice of circuit implementation depends on various factors, such as particular design and performance specifications for a given implementation. Other modifications and alternative embodiments in addition to those described here will be apparent to persons of ordinary skill in the art. Accordingly, this description teaches those skilled in the art the manner of carrying out the disclosed concepts, and is to be construed as illustrative only. Where applicable, the figures might or might not be drawn to scale, as persons of ordinary skill in the art will understand. 
         [0178]    The forms and embodiments shown and described should be taken as illustrative embodiments. Persons skilled in the art may make various changes in the shape, size and arrangement of parts without departing from the scope of the disclosed concepts in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here. Moreover, persons skilled in the art may use certain features of the disclosed concepts independently of the use of other features, without departing from the scope of the disclosed concepts.