US20150042981A1

US20150042981A1 - Apparatus for Sensor with Programmable Gain and Dynamic Range and Associated Methods

Info

Publication number: US20150042981A1
Application number: US14/520,735
Authority: US
Inventors: Abidin Guclu Onaran; Charles D. Thompson
Original assignee: Silicon Audio Seismic LLC
Current assignee: Silicon Audio Seismic LLC
Priority date: 2012-10-11
Filing date: 2014-10-22
Publication date: 2015-02-12
Also published as: US20150036123A1; WO2014058472A1; CN104884915A; US20150042359A1; US20150036124A1; RU2015112966A; CA2890298A1; US9702992B2; EP2906916A1; EP2906916A4; US20150293243A1; US20150035544A1

Abstract

An apparatus includes a coil suspended in a magnetic field and an optical detector to detect displacement of the coil in response to a stimulus. The apparatus further includes a feedback circuit to program a gain of the sensor, wherein the feedback circuit is coupled to the optical detector and to the coil.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to the following patent applications:
U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Coil Constant and Associated Methods,” Attorney Docket No. SIAU003;
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;
U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Improved Power Consumption and Associated Methods,” Attorney Docket No. SIAU005;
U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Coil and Associated Methods,” Attorney Docket No. SIAU006;
U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Damping and Associated Methods,” Attorney Docket No. SIAU007; and
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.
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

The disclosure relates generally to sensors, such as acceleration, speed, and displacement sensors and, more particularly, to apparatus for such sensors with programmable gain and dynamic range, and associated methods.

BACKGROUND

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.
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.
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.
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
$f_{N} = \sqrt{\frac{k}{m}} .$
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.
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

According to one exemplary embodiment, an apparatus includes a coil suspended in a magnetic field and an optical detector to detect displacement of the coil in response to a stimulus. The apparatus further includes a feedback circuit to program a gain of the sensor, wherein the feedback circuit is coupled to the optical detector and to the coil.
According to another exemplary embodiment, a method is disclosed for operating a sensor. The sensor includes a coil suspended in a magnetic field and an optical detector to detect displacement of the coil in response to a stimulus. The method includes programming a gain of the sensor by using a feedback circuit that is coupled to the optical detector and to the coil.
According to another exemplary embodiment, a sensor includes a magnet, having an associated magnetic field; a coil suspended by a spring in the magnetic field of the magnet; and an optical detector to detect displacement of the coil in response to a stimulus applied to the sensor. The sensor further includes a feedback circuit coupled to the optical detector and to the coil, the feedback circuit to program a gain of the sensor by using at least one nonlinear transfer function.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1 illustrates a conceptual diagram of a geophone.

FIG. 2 depicts the frequency response of a geophone in response to physical stimuli.

FIG. 3 shows a sensor according to an exemplary embodiment.

FIG. 4 depicts forces operating in a sensor according to an exemplary embodiment.

FIG. 5 illustrates a virtual spring caused by use of negative feedback in an exemplary embodiment.

FIG. 6 depicts a cross-section of a sensor according to an exemplary embodiment.

FIG. 7 illustrates a cross-section of a sensor according to an exemplary embodiment.

FIG. 8 shows a schematic diagram of a sensor according to an exemplary embodiment.

FIG. 9 illustrates a schematic diagram of a sensor according to an exemplary embodiment.

FIG. 10 depicts an output signal of a trans-impedance amplifier (TIA) in an exemplary embodiment.

FIG. 11 shows a flow diagram for a method of operating a sensor according to an exemplary embodiment.

FIG. 12 illustrates a block diagram of a sensor communicating with another device or component according to an exemplary embodiment.

FIG. 13 depicts a nonlinear transfer function used to modify the gain and dynamic range of a sensor according to an exemplary embodiment.

FIG. 14 shows a nonlinear transfer function used to modify the gain and dynamic range of a sensor according to another exemplary embodiment.

FIG. 15 illustrates a number of nonlinear transfer functions that may be used in a sensor according to an exemplary embodiment.

FIG. 16 depicts a block diagram of a circuit arrangement for a sensor having programmable gain and dynamic range according to an exemplary embodiment.

FIGS. 17-18 show circuit arrangements that may be used for programming a feedback network of a sensor according to an exemplary embodiment.

DETAILED DESCRIPTION

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 programmable gain and dynamic range/dynamic range compression.
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.
For example, if acceleration, a, is sensed, velocity, v, and displacement, x, may be derived from a. More specifically:
$a = \frac{\partial v}{\partial t} \Rightarrow v = \int a \cdot \partial t$ $v = \frac{\partial x}{\partial t} \Rightarrow x = \int v \cdot \partial t$
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.
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.
A magnet 112 is positioned near or proximately to coil 109. A magnetic field 112A is established between the north and south poles of magnet 112. Thus, coil 109 is completely or partially suspended within magnetic field 112A. By virtue of spring 106, coil 109 may move in relation to magnet 112 and, thus, in relation to magnetic field 112A.
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 112A. 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 112A, induces a current in the coil. Thus, in response to the stimuli, coil 109 produces a current.
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.
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.
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.
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.
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 or circuit.
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.
More specifically, FIG. 4 shows a force vector 121 that corresponds to force F_sexerted 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's law, force F_srelates to displacement x, specifically F_s=−k_s·x, where, as noted above, k_srepresents the spring constant of spring 106. In effect, spring 106 resists the displacement in proportion to k_s.
Furthermore, according to Newton's second law (ignoring any relativistic effects), force F_crelates 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_crepresents the mass of coil 109, and a denotes the acceleration that coil 109 experiences.
As noted above, negative feedback is employed in sensor 100 (see FIG. 5) so as to cause the mass m_cto come to equilibrium. Mathematically stated, the feedback causes the mass m_cto come to equilibrium when F_sequals F_c. Thus, sensor 100 may be viewed as operating according to a force-balance principle, i.e., F_s=F_cat equilibrium.
Stated another way, force-balance occurs when −k_s·x=m_c·a. One may readily determine the spring constant k_sand the mass of coil 109, m_c(e.g., by consulting data sheets or controlling manufacturing processes, etc.). Using the values of k_sand m_cin the above equation, one may determine the acceleration of coil 109 in response to the stimulus, i.e.:
$a = \frac{- k_{s} \cdot x}{m_{c}} .$
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.
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.
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.
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.
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_sof 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'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.
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.
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.
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 205A, 205B, 205C, and 205D, 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.
Magnet 112 is arranged with magnet caps 215A and 215B. In the embodiment shown, magnet 112 is disposed between magnet caps 215A and 215B. 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.
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.
The proof mass is suspended by spring 106, which for illustration purposes is shown as four sections labeled 106A-106D. 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.
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.
In the embodiment shown in FIG. 6, spring 106 (shown as sections or portions 106A-106D) suspend the proof mass with respect to magnet 112 (and magnet caps 215A-215B, 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 215A-215B). 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 215A-215B.
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.
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 minor 222, and is diffracted by diffraction grating 235. The resulting optical signals are detected by optical detectors 230A, 230B, and 230C.
A mechanical or physical stimulus applied to sensor 200 causes a change in the detected light, and thus causes optical detectors 230A-230C 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.
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.
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 205A, 205B and 205C, 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.
Magnet 112 is arranged with magnet caps 215A, 215B, and 215C. In the embodiment shown, magnet 112 is attached to magnet cap 215B, which is disposed against or in contact with magnet caps 215A and 215C. 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, may 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.
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.
The proof mass is suspended by spring 106, which for illustration purposes is shown as four sections labeled 106A-106D. 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.
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.
In the embodiment shown in FIG. 7, spring 106 (shown as sections or portions 106A-106D) suspend the proof mass with respect to magnet 112 (and magnet caps 215A-215C, 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 215A-215C). 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 215A and 215C, rather than housing 205.
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.
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 230A, 230B, and 230C.
A stimulus applied to sensor 250 causes a change in the detected light, and thus causes optical detectors 230A-230C 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.
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.
FIG. 8 shows a schematic diagram or circuit arrangement 300A 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 230A-230C (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 230A-230C. In the embodiment of FIG. 8, the output signal of optical detectors 230A-230C is provided to TIA 118 as a differential signal.
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.
In the embodiment shown in FIG. 8, TIA 118 includes two individual TIA circuits or amplifiers, 118A and 118B, to accommodate the differential input signal. TIA 118 includes resistors 305A-305B to adjust (or calibrate or set or program or configure) the gain of TIAs 118A-118B, respectively.
Thus, by adjusting resistor 305A, the gain of amplifier 118A may be adjusted. Similarly, by adjusting resistor 305B, the gain of amplifier 118B may be adjusted. A controller, such as a microcontroller unit (MCU) 310 in the exemplary embodiment shown, adjusts the values of resistors 305A-305B.
Typically, given the differential nature of the input signal of TIA 118, MCU 310 adjusts resistors 305A-305B 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 118A and 118B, respectively, are typically matched by adjusting resistors 305A-305B to the same resistance value. In some situations, however, resistors 305A-305B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc.
Note that adjusting the gains of amplifiers 118A-118B does not set the full-scale range of the sensor. Rather, the gains of amplifiers 118A-118B 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 320A and 320B, the effect of increasing coil constant is a decrease in the sensor'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.
The output of amplifier 118A feeds one end or terminal of coil 109 via resistors 315A and 320A. Conversely, the output of amplifier 118B feeds the other end of coil 109 via resistors 315B and 320B. Thus, amplifiers 118A-118B provide a drive signal for coil 109 via resistors 315A-315B and 320A-320B.
MCU 310 may adjust (or calibrate or set or program or configure) the values of resistors 320A-320B. Similar to resistors 305A-305B, typically, given the differential nature of the output signal of the sensor, MCU 310 adjusts resistors 320A-320B to the same resistance value. In some situations, however, resistors 320A-320B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc.
Note that the values of resistors 320A-320B affect the gain or scale factor of the sensor. In other words, the values of resistors 320A-320B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus.
Nodes 325A and 325B provide the differential output signal of the sensor. In the embodiment shown, node 325A provides the positive output signal, whereas node 325B 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.
In some embodiments, MCU 310 may include circuitry to receive and process the output signal provided at nodes 325A-325B. For example, MCU 310 may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes 325A-325B 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.
FIG. 9 shows a schematic diagram or circuit arrangement 300B 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 230A-230C (photodiodes in the embodiment shown) provide an output signal to TIA 118. In the example shown, V_BIASis ground potential although, as noted above, other appropriate values may be used. In the embodiment of FIG. 9, the output signal of optical detectors 230A-230C is provided to TIA 118 as a single-ended signal.
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.
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.
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.
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.
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 320A and 320B determine the output scale factor in Volts per unit of stimulus, e.g., g of acceleration.
The output of amplifier 345 feeds one end or terminal of coil 109 via resistors 315A and 320A. Conversely, the output of amplifier 355 feeds the other end of coil 109 via resistors 315B and 320B. Thus, amplifiers 345 and 355 provide a drive signal for coil 109 via resistors 315A-315B and 320A-320B.
MCU 310 may adjust (or calibrate or set or program or configure) the values of resistors 320A-320B. Note that the values of resistors 320A-320B affect the gain or scale factor of the sensor. In other words, the values of resistors 320A-320B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus.
Nodes 325A and 325B provide the differential output signal of the sensor. In the embodiment shown, node 325A provides the positive output signal, whereas node 325B 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.
In some embodiments, MCU 310 may include circuitry to receive and process the output signal provided at nodes 325A-325B. For example, MCU 310 may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes 325A-325B 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.
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.
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.
Thus, in the example shown, in response to a displacement x₁, 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.
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.
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's power-up.
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.
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.
At 510, MCU 310 adjusts one or more resistors (e.g., resistors 305A-305B 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.
At 515, MCU 310 adjusts resistors (e.g., resistors 320A-320B 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 320A-320B 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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
One aspect of the disclosure relates to sensors with programmable gain and dynamic range/dynamic range compression. As noted above, typically the output signal of a sensor according to an exemplary embodiment (see, for example, FIGS. 8-9), is provided to follow-on circuitry for further signal processing, such as to an ADC, an amplifier, etc. (whether included in MCU 310, discrete circuitry, or other arrangement).
Typically, the dynamic range of the sensor exceeds that of the follow-on circuitry. Put another way, the follow-on circuitry typically has more noise than does the sensor, which limits the dynamic range of the overall circuit. In exemplary embodiments, a nonlinear transfer function may be used to modify the dynamic range of the sensor, and match the sensor's dynamic range to the dynamic range of the follow-on circuitry.
The nonlinear transfer function may be added to sensors according to various embodiments in a number of ways. In some embodiments, the nonlinear transfer function may be implanted by modifying the feedback network or circuit of the sensor, such as the circuitry around TIA 118 or other circuitry, such as amplifier 345 or amplifier 355 (see FIGS. 8, 9). In some embodiments, TIA 118 and/or other circuitry, such as amplifier 345 and/or amplifier 355, may be modified to have a logarithmic response, as desired.
In other embodiments, the nonlinear transfer function may be implemented by adding a circuit, a feedback network, in the negative feedback loop or circuit that includes TIA 118 and coil 109. For example, a feedback network or circuit with a nonlinear transfer function may be added at the output of TIA 118, the output of amplifier 345, and/or the output of amplifier 355. An example of such a circuit includes a logarithmic amplifier or circuit.
FIG. 13 depicts a nonlinear transfer function 700 used to modify the dynamic range of a sensor according to an exemplary embodiment. Transfer function 700 has a linear or nearly linear portion 703. In response to input stimuli, the output voltage of the sensor varies linearly or nearly linearly in this portion. In other words, as the input stimulus varies from P₁to P₂(approximately, because of the “soft” corner in the transfer function), corresponding to the output levels labeled −V_sc(soft-clip voltage) and +V_sc, the output voltage varies linearly (or nearly linearly), with a slope m₁. (Note that for stimulus values near P₁and P₂, the output voltage exhibits some nonlinear behavior.)
Transfer function 700 has another linear or nearly linear portion 706. For input stimulus below P₁or above P₂, portion 706 governs the output voltage. As the input stimulus goes below P₁or above P₂(approximately), portion 706, with a slope m₂, determines the level of the output signal. Thus, points P₁and P₂constitute inflection points, at or near which the gain and dynamic range of the sensor are modified in a nonlinear fashion, i.e., a change from slope m₁to slope m₂and vice-versa, depending on the direction of change in the input stimulus.
Note that slope m₁is larger than slope m₂. In other words, for input stimulus levels below P₁or above P₂(approximately), the sensor exhibits less overall gain and smaller dynamic range than it does for stimulus levels between P₁and P₂(approximately). By programming (or modifying or setting or configuring) slopes m₁and m₂and/or levels P₁and P₂, the gain and dynamic range (or dynamic range compression) of the sensor may be modified, for example, to desired levels or characteristics.
Note further that the transition from portion 703 to portion 706 (or vice-versa) of the transfer function occurs smoothly. Put another way, the first-order derivative of transfer function 700 varies continuously as the response of the sensor makes a transition from portion 703 to portion 706 (or vice-versa).
In some embodiments, the nonlinear transfer function may have a piecewise-linear shape. FIG. 14 shows a transfer function 720 with a piecewise-linear (nonlinear, overall) characteristic. Transfer function 720 has a linear or nearly linear portion 723. In response to input stimuli, the output voltage of the sensor varies linearly or nearly linearly in this portion. In other words, as the input stimulus varies from P₁to P₂, corresponding to the output levels labeled −V_sc(soft-clip voltage) and +V_sc, the output voltage varies linearly (or nearly linearly), with a slope m₁.
Transfer function 720 has another linear or nearly linear portion 726. For input stimulus below P₁or above P₂, portion 726 governs the output voltage. As the input stimulus goes below P₁or above P₂, portion 726, with a slope m₂, determines the level of the output signal. Thus, points P₁and P₂constitute inflection points, at (or near) which the gain and dynamic range of the sensor are modified in a nonlinear fashion, i.e., a change from slope m₁to slope m₂and vice-versa, depending on the direction of change in the input stimulus.
Note that slope m₁is larger than slope m₂. In other words, for input stimulus levels below P₁or above P₂), the sensor exhibits less overall gain and smaller dynamic range than it does for stimulus levels between P₁and P₂. By programming (or modifying or setting or configuring) slopes m₁and m₂and/or levels P₁and P₂, the gain and dynamic range (or dynamic range compression) of the sensor may be modified, for example, to desired levels or characteristics.
Note further that the transition from portion 723 to portion 726 (or vice-versa) of the transfer function occurs relatively abruptly (e.g., compared to transfer function 700 of FIG. 13). Put another way, referring back to FIG. 14, the first-order derivative of transfer function 720 as a discontinuity (at −V_scand +V_sc) as the response of the sensor makes a transition from portion 723 to portion 726 (or vice-versa).
In some embodiments, the gain and dynamic range of the sensor may be programmed (or modified, set, configured, etc.) to provide a family, set, or a number of profiles of characteristics. In other words, the sensor's characteristics (gain, dynamic range) may be programmed by selecting one of a number of nonlinear transfer functions (e.g., feedback networks or circuits) to be included in the feedback network. The selected nonlinear transfer function may subsequently be changed to another nonlinear transfer function, as desired. In this manner, sensors with flexible, programmable properties, such as gain and dynamic range profiles, may be provided.
FIG. 15 illustrates a set or family of nonlinear transfer functions 730A-730C that may be used in a sensor according to an exemplary embodiment. The set of nonlinear transfer functions shown in the figure includes three nonlinear transfer functions, although fewer or more nonlinear transfer functions may be used, as desired. Furthermore, although piecewise-linear nonlinear transfer functions are shown in the figure, other types of nonlinear transfer function may be used, for example, the nonlinear transfer function shown in FIG. 13.
Referring again to FIG. 15, transfer functions 730A each have a linear or nearly linear portion 733A-733C, respectively. Similar to the nonlinear transfer function of FIG. 14, in response to input stimuli, the output voltage of the sensor varies linearly or nearly linearly in portions 733A-733C. In other words, as the input stimulus varies in a range corresponding to the output levels labeled −V_scand +V_sc, the output voltage varies linearly (or nearly linearly).
Transfer functions 730A-730C each have another linear or nearly linear portion 736A-736C, respectively. For input stimulus below or above the range that results in output voltages of −V_scto +V_sc, respectively, portions 736A-736C govern the output voltage. Similar to the transfer function shown in FIG. 14, the two respective portions of transfer functions 730A-730C have differing slopes, which result in the gain and dynamic range of the sensor to vary in a nonlinear fashion, i.e., according to a change from one slope level to another slope level and vice-versa, depending on the direction of change in the input stimulus.
Note that although FIG. 15 shows a set of piecewise-linear transfer functions, other types or curves or functions may be used. For example, some or all of the transfer functions in FIG. 15 may be replaced with the type of nonlinear function shown in FIG. 13, as desired.
As noted above, the nonlinear transfer functions may be implemented in a variety of ways in sensors according to exemplary embodiments. More particularly, various attributes of the sensor, such as gain, sensitivity, and dynamic range, may be programmed by selecting a desired nonlinear transfer function for inclusion in the feedback path of the sensor.
Selection of nonlinear transfer function may be made by coupling or uncoupling one or more circuits, e.g., feedback networks, as part of the overall feedback network of the sensor. FIG. 16 shows a circuit arrangement 750 that uses this scheme.
Circuit arrangement 750 includes TIA 118, switches 753A-753D coupled to feedback networks 756A-756D. Feedback networks 756A-756D are coupled to drive coil 106, for example, via coil driver 762. Note that, depending on the specific components and circuitry used (e.g., drive strengths), coil driver 762 may be omitted, or an amplifier in the sensor may be used to drive coil 106.
Feedback networks 756A-756D may correspond to a set of nonlinear transfer functions, such as transfer functions 730A-730C of FIG. 15. Thus, in this example, feedback networks 756A-756C provide a gain that corresponds to the slope of portions 733A-733C of transfer functions 730A-730C.
Referring again to FIG. 16, feedback network 756D corresponds to portions 736A-736C of transfer functions 730A-730C. In portions 736A-736C, the soft-clip portions, feedback network 756D provides a gain that corresponds to a lower slope than the slope of portions 733A-733C. The slope in the soft-clip portions may be fixed or might be different among the transfer functions, as desired, depending on the particular circuitry of feedback network 756D.
By selectively closing one of switches 753A-753D, the corresponding one of feedback networks 756A-756D is coupled in the feedback loop or circuit of the sensor. For example, closing switch 756A (while leaving switches 756B-756D open) couples feedback network 756A in the overall feedback loop or circuit of the sensor, and so on. Thus, the gain and dynamic range of the sensor may be programmed by selectively closing switches 753A-753D.
Switches 753A-753D are closed depending on the output voltage of the sensor. One of switches 753A-753C is closed when the absolute value of the output voltage of the sensor is below V_sc(the output level of source 759). In this scenario, a gain corresponding to portions 736A-736C of transfer functions 730A-730C is provided in the feedback loop or circuit of the sensor.
Conversely, switches 753A-753C are open when the absolute value of the output voltage of the sensor is above V_sc. In this situation, switch 753D is closed, which causes a gain corresponding to the slope of portions 736A-736C of transfer functions 730A-730C to be provided in the feedback loop or circuit of the sensor. More specifically, when the absolute value of the output voltage of the sensor is above V_sc, diode 760 conducts, and feedback network 756D is coupled in the overall feedback loop or circuit of the sensor. Note that in practice, a non-ideal diode has a finite forward-conduction voltage. In exemplary embodiments, the conduction voltage of diode 760 is taken into account when setting the value of V_sc.
Referring to FIG. 16, in some embodiments, MCU 310 may be used to control switches 753A-753D. By programming MCU 310, one may select the desired transfer function for the feedback loop or circuit of the sensor. More specifically, MCU 310 may be programmed to close one of switches 756A-756C or switch 756D, depending on the level of the output voltage of the sensor, as described above. MCU 310 may do so by comparing the output voltage of the sensor with a value corresponding to V_sc, and providing appropriate signals to switches 753A-753D.
Note that other arrangements and alternatives are contemplated, for example, using a remote host (see FIG. 12) to control switches 753A-753D. As another example, a controller in the sensor may be used to control switches 753A-753D, for example, by comparing the output voltage of the sensor with a value corresponding to V_sc, and providing appropriate signals to switches 753A-753D.
Note that although FIG. 16 shows separate blocks for feedback networks 756A-756D, in some embodiments, one or more components in a circuit may be varied to provide a feedback network with programmable characteristics. For example, one or more resistors in the feedback network may be programmed (e.g., varied or modified or set) to implement a desired transfer function in the feedback loop or circuit of the sensor. As another example, by virtue of using diode 760, described above, a soft-clip function is provided where the scale factor of the sensor is instantaneously (or nearly instantaneously) reduced when the absolute value of the output voltage of the sensor exceeds V_sc.
FIG. 17 depicts a circuit arrangement 770 that may be used for programming a feedback network of a sensor according to an exemplary embodiment. More specifically, circuit arrangement provides a mechanism for programming the value of a resistor 773, which may be resistor 320A, resistor 320B, resistor 305A, resistor 305B, resistor 305, resistor 340, and or resistor 360 (see FIGS. 8-9) and, consequently, the gain or full-scale range of the sensor. Thus, by varying or programming the resistance of one or more resistors in the feedback circuit of the sensor, such as the sensors in FIGS. 8-9, attributes of the sensor, such as gain, sensitivity, and dynamic range may be programmed.
Referring to FIG. 17, resistor 773 includes a string or cascade of N resistors or resistance sections 773A-773N, where N denotes a positive integer larger than unity. Circuit arrangement 770 includes a set of N switches 780A-780N, with the switches coupled across a corresponding resistor in the set of N resistors 773A-773N.
When a switch in the set of switches 780A-780N is open, the corresponding resistor in the set of resistors 773A-773N is included in the overall value of resistor 773. Conversely, when a switch in the set of switches 780A-780N is closed, it effectively shorts the corresponding resistor in the set of resistors 773A-773N. Thus, the corresponding resistor in the set of resistors 773A-773N is excluded from the overall value of resistor 773.
In other words, by selectively closing switches 780A-780N, a desired resistance value for resistor 773 may be programmed. As a result, a corresponding gain is provided in the feedback loop or circuit of the sensor.
FIG. 18 shows a circuit arrangement 820 that may be used for programming a feedback network of a sensor according to an exemplary embodiments. Similar to resistor 773 in FIG. 17, resistor 773 in FIG. 18 includes a string or cascade of N resistors or resistance sections 773A- 773 N. Circuit arrangement 820 further includes a switch 825, coupled to resistors 773A-773N.
Switch 825 has a number of positions that are coupled to corresponding nodes or taps in resistor 773. For example, the left-most position of switch 825 couples to the node between resistor 773A and resistor 773B. As another example, the second left-most position of switch 825 couples to the node between resistor 773B and resistor 773C, and so on. The right-most position of switch 825 couples to the end of resistor 773.
The wiper (or common node or terminal) of switch 825 selectively couples the various positions to point B. Depending on the position of the wiper of switch 825, a corresponding number of resistors and, hence, a total amount of resistance, is provided between points A and B. Thus, by changing the position of the wiper of switch 825, the effective resistance of resistor 773 may be configured.
For example, when the wiper is at the left-most position of switch 825, resistor 773A is included in resistor 773. As another example, when the wiper is at the second left-most position of switch 825, resistors 773A-773B are included in resistor 773, and so on. When the wiper is at the right-most position of switch 825, resistors 773A-773N are included in resistor 773, i.e., resistor 773 has maximum resistance.
Referring to FIGS. 17-18, the choice of the number of switches 780A-780N, number of positions of switch 825, and the number of resistors, i.e., N, affects the granularity with which the value of resistor 773 may be programmed. A tradeoff exists between that level of granularity and the complexity of the circuit. The appropriate number of switches/switch positions and resistors depends on factors such as desired performance specifications (e.g., the number of gain profiles), cost, complexity, space constraints, etc., as persons of ordinary skill in the art will understand.
In some embodiments, the resistance of resistors 773A-773N is equal or nearly equal, say, R ohms. In this situation, opening or closing one of switches 780A-780N or changing the wiper position of switch 825 changes the value of resistor 773 by R, i.e., uniform resistance-change steps. In other embodiments, different resistance values may be used for resistors 773A-773N. By using unequal resistance values, non-uniform resistance-change steps may be implemented, for instance in situations where relatively large changes in gain are desired.
In the embodiment shown, MCU 310 controls switches 780A-780N or switch 825. 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) may control switches 780A-780N or switch 825. As another example, the switches may be manually controlled by a user, e.g., by setting each switch to the desired position.
As another example, switches 780A-780N or switch 825 may be controlled by a memory. More specifically, bits (or bytes, etc.) in the memory may control corresponding switches 780A-780N or the wiper position of switch 825. For instance, a bit with a logic high stored in it might cause one of switches 780A-780N to turn on, whereas a bit with a logic low stored in it might cause one of switches 780A-780N to turn off.
In such a scheme, a variety of types and configurations of memory may be used. For example, a random access memory (RAM) or other type of volatile memory may be used in situations where the sensor's user desires the programming of the gain to remain valid (be in effect) while the memory is powered on. As another example, a non-volatile memory, such as read-only memory (ROM), electrically erasable programmable ROM (EEPROM), or flash memory, may be used where the programming of the gain is to remain valid or in effect even after the memory and/or sensor are powered off or put into the sleep state.
Switches 780A-780N may be implemented in a variety of ways, as desired, and as persons of ordinary skill in the art will understand. In some embodiments, switches 780A-780N may be implemented using transistors, such as metal oxide semiconductor (MOS) transistors. In other embodiments, switches 780A-780N may be implemented using analog transmission gates. In yet other embodiments, switches 780A-780N may be implemented using manually controlled switches, relays (e.g., reed relays), etc., as desired. Similarly, switch 825 may be implemented electronically, mechanically, or a combination of the two.
Although sensors according to exemplary embodiments have been described and illustrated in the accompanying drawings, a variety of other embodiments and arrangements are contemplated. By way of illustration, the following description provides some examples.
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.
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.
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.
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.
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.
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.

Claims

1. An apparatus, comprising:

a coil suspended in a magnetic field;

an optical detector to detect displacement of the coil in response to a stimulus; and

a feedback circuit to program a gain of the sensor, wherein the feedback circuit is coupled to the optical detector and to the coil.

2. The apparatus according to claim 1, wherein the feedback circuit varies the gain of the sensor in response to an output signal of the sensor.

3. The apparatus according to claim 1, wherein the feedback circuit includes a feedback network with a nonlinear transfer function.

4. The apparatus according to claim 2, wherein the nonlinear transfer function comprises a piecewise-linear transfer function.

5. The apparatus according to claim 4, wherein the piecewise-linear transfer function comprises a first linear portion having a first slope corresponding to a first gain value, and a second linear portion having a second slope corresponding to a second gain value, wherein the first slope is larger than the second slope.

6. The apparatus according to claim 5, wherein the gain of the sensor is varied by using the first gain or the second gain depending on an output signal of the sensor.

7. The apparatus according to claim 1, wherein the feedback circuit includes a plurality of feedback networks with a corresponding plurality of nonlinear transfer functions, and wherein the gain of the sensor is programmed by selecting a feedback network from the plurality of feedback networks.

8. The apparatus according to claim 7, wherein at least one of the plurality of nonlinear transfer functions comprises a piecewise-linear transfer function.

9. The apparatus according to claim 7, wherein the feedback circuit varies the gain of the sensor in response to an output signal of the sensor.

10. The apparatus according to claim 1, wherein the gain of the sensor is programmed by changing a resistance of at least one resistor in the feedback circuit.

11. A method of operating a sensor that includes a coil suspended in a magnetic field and an optical detector to detect displacement of the coil in response to a stimulus, the method comprising programming a gain of the sensor by using a feedback circuit that is coupled to the optical detector and to the coil.

12. The method according to claim 11, wherein programming a gain of the sensor further comprises varying the gain of the sensor in response to an output signal of the sensor.

13. The method according to claim 11, wherein the feedback circuit includes a feedback network with a nonlinear transfer function.

14. The method according to claim 13, wherein the nonlinear transfer function comprises a piecewise-linear transfer function.

15. The method according to claim 14, wherein the piecewise-linear transfer function comprises a first linear portion having a first slope corresponding to a first gain value, and a second linear portion having a second slope corresponding to a second gain value, wherein the first slope is larger than the second slope.

16. The method according to claim 11, wherein programming the gain of the sensor further comprises using the first gain or the second gain depending on an output signal of the sensor.

17. A sensor, comprising:

a magnet, having an associated magnetic field;

a coil suspended by a spring in the magnetic field of the magnet;

an optical detector to detect displacement of the coil in response to a stimulus applied to the sensor; and

a feedback circuit coupled to the optical detector and to the coil, the feedback circuit to program a gain of the sensor by using at least one nonlinear transfer function.

18. The sensor according to claim 17, wherein the stimulus comprises acceleration.

19. The sensor according to claim 17, wherein the at least one nonlinear transfer function comprises a piecewise-linear transfer function comprising a first linear portion having a first slope corresponding to a first sensor gain, and a second linear portion having a second slope corresponding to a second sensor gain, wherein the first sensor gain is larger than the second sensor gain.

20. The sensor according to claim 17, wherein depending on an output signal of the sensor a microcontroller unit (MCU) programs the gain of the sensor by causing the feedback circuit to use the first linear portion or the second linear portion of the at least one nonlinear transfer function.