Patent Publication Number: US-2023147661-A1

Title: Optical time synchronization

Description:
FIELD OF THE INVENTION 
     The present application relates to a system and method for synchronizing time between devices, and particularly toward synchronizing time between devices in a low cost, precise manner. 
     BACKGROUND 
     There are many applications that require precise timing synchronization. This is often accomplished by using expensive coax cable and circuitry. Further, such conventional systems are often susceptible to interference, such as fast switching circuitry and RF communications. 
     Precision clocks are often used as a foundation for measurements obtained in real-time location systems. A conventional real-time location system, however, includes multiple devices disposed at different areas of an object with each device operating in accordance with its own clock. Although these clocks may be considered precise on an individual basis, there are frequency deviations among the clocks. Such deviations may be the result of inherent differences between the clock circuitry including tolerance differences between oscillators that are the same type (e.g., the same part number). Deviations may occur during operation as well—for example, a particular type of oscillator may be specified with a frequency stability of 10 parts per million (PPM). This means that, given an oscillator having an output frequency of 1 MHz, the frequency of the oscillator may vary by 5 Hz. With multiple oscillators in a real-time system, the actual frequencies of the oscillators are likely different from each other. These differences can adversely affect analysis of measurements in the real-time location system for determining a location of a device relative to an object. 
     SUMMARY 
     A system and method are provided for substantially locking an oscillator output to a reference oscillator output. In one embodiment the frequency of the oscillator output may be substantially locked to the frequency of the reference oscillator output via transmission of light energy corresponding to the reference oscillation output. 
     In general, one innovative aspect of the subject matter described herein can be a system for generating a clock signal in a device. The system may include an optical receiver configured to receive light energy corresponding to a reference oscillation signal, where the optical receiver may be operable to generate a receiver output based on the light energy. The system may include an oscillator configured to generate an oscillating signal, where the oscillator may be operably coupled to the receiver output of the optical receiver. The oscillating signal of the oscillator may be substantially locked to the reference oscillation signal received via the optical receiver. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. 
     In some embodiments, the system may include an amplifier operably coupled to the oscillator, where the amplifier may be configured to generate the clock signal based on the oscillating signal generated by the oscillator. 
     In some embodiments, the amplifier may include a first amplifier stage directly connected to the oscillator and configured to generate a first amplifier output based on the oscillating signal. The amplifier may include a second amplifier stage coupled to the first amplifier stage and configured to generate a second amplifier output based on the first amplifier output such that the second amplifier output is based on the oscillating signal. 
     In some embodiments, the oscillator and the amplifier may form a super-regenerative receiver with respect to the receiver output that is based on the reference oscillation signal. 
     In some embodiments, the oscillator may be a crystal oscillator. 
     In some embodiments, a mechanical vibration of the crystal oscillator may be varied based on the receiver output such that the mechanical vibration of the crystal oscillator is locked to the reference oscillation signal. 
     In some embodiments, the system may include a reference oscillator may be operable to generate the reference oscillation signal. The system may include an optical transmitter operably coupled to the reference oscillator, where the optical transmitter may be arranged to generate the light energy corresponding to the reference oscillation signal. The optical receiver and the oscillator may be disposed in the device, and the reference oscillator and the optical transmitter may be disposed in a remote device that is remote from the device, the optical receiver, and the oscillator. 
     In some embodiments, the system may include a fiber medium operably coupled between the optical transmitter and the optical receiver. 
     In some embodiments, the oscillating signal of the oscillator may be substantially locked to the reference oscillation signal in an open loop manner such that the reference oscillator is unaffected by operation of the oscillator. 
     In some embodiments, the system may include a slave device including the optical receiver and the oscillator, and where the system may include a plurality of such slave devices each capable of locking with the reference oscillation signal. 
     In general, one innovative aspect of the subject matter described herein can be embodied in a slave device that is remote from a master device. The slave device may include an optical receiver configured to receive light energy corresponding to a reference oscillation signal generated by the master device. The optical receiver may be operable to generate a receiver output based on the light energy. The slave device may include an oscillator configured to generate an oscillating signal, where the oscillator may be operably coupled to the receiver output of the optical receiver. The oscillating signal of the oscillator may be substantially locked to the reference oscillation signal received via the optical receiver and generated remotely from the optical receiver. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. 
     In some embodiments, the slave device may include an amplifier operably coupled to the oscillator. The amplifier may be configured to generate a clock signal based on the oscillating signal generated by the oscillator. 
     In some embodiments, the amplifier may include a first amplifier stage directly connected to the oscillator and configured to generate a first amplifier output based on the oscillating signal. The amplifier may include a second amplifier stage coupled to the first amplifier stage and configured to generate a second amplifier output based on the first amplifier output such that the second amplifier output is based on the oscillating signal. 
     In some embodiments, the oscillator and the amplifier may form a super-regenerative receiver with respect to the receiver output that is based on the reference oscillation signal. 
     In some embodiments, the oscillator may be a crystal oscillator. 
     In some embodiments, a mechanical vibration of the crystal oscillator is varied based on the receiver output such that the mechanical vibration of the crystal oscillator is locked to the reference oscillation signal. 
     In some embodiments, the optical receiver may be operably coupled to a fiber medium to receive the light energy transmitted by the master device. 
     In some embodiments, the oscillating signal of the oscillator may be substantially locked to the reference oscillation signal in an open loop manner such that the reference oscillation signal is unaffected by operation of the oscillator. 
     In general, one innovative aspect of the subject matter described herein can be embodied in a method of synchronizing an oscillation signal to a reference oscillation signal that is generated remotely from the oscillation signal. The method may include receiving light energy corresponding to the reference oscillation signal, and generating a receiver output based on the light energy. The method may include substantially locking an oscillator signal to the reference oscillation signal. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. 
     In some embodiments, the method may include amplifying the oscillator signal to yield a clock signal. 
     In some embodiments, the method may include generating the oscillator signal via a crystal oscillator. 
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited to the details of operation or to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention may be implemented in various other embodiments and of being practiced or being carried out in alternative ways not expressly disclosed herein. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. Further, enumeration may be used in the description of various embodiments. Unless otherwise expressly stated, the use of enumeration should not be construed as limiting the invention to any specific order or number of components. Nor should the use of enumeration be construed as excluding from the scope of the invention any additional steps or components that might be combined with or into the enumerated steps or components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a system in accordance with one embodiment. 
         FIG.  2    shows a plurality of amplifier stages for a system in accordance with one embodiment. 
         FIG.  3    shows an alternative system in accordance with one embodiment. 
         FIG.  4    shows a system for determining a location of a portable device in accordance with one embodiment. 
         FIG.  5    shows a representative view of a system for determining a location of a portable device in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, a system and method for synchronizing clocks is provided. The system may include a master device having a reference clock and slave devices whose clocks may be synchronized with the reference clock. The master device may drive a light transmitter (e.g., LED) to produce a light pulse with each clock cycle of the reference clock. The light pluses may be distributed by a transmissive medium, such as a low cost optical fiber. In the slave device, a light receiver (e.g., a photo diode) may be used to convert the light pluses into current pulses. These current pluses may be feed into an oscillator of the slave device (e.g., a crystal oscillator), which is configured to operate as a super-regenerative receiver that locks the oscillator onto the incoming signal that corresponds to the reference clock. 
     One embodiment according to the present disclosure may provide a very low cost method to keep the reference clocks of two different circuits in sync at a distance by using light pluses through low cost fiber optic cable, with a minimum or reduced level circuitry. In one embodiment, a frequency of multiple oscillators may be substantially aligned despite the oscillators having inherent differences that would otherwise yield a degree of misalignment. As an example, two 10 PPM oscillators may be aligned in accordance with one embodiment of the present disclosure to achieve a degree of frequency alignment that is not available in a conventional separate oscillator system without two much more expensive and bulky oscillators, each having a much better frequency stability of at least 1 parts per billion (PPB). 10 PPM oscillators are significantly more compact and less expensive relative to 1 PPB oscillators. 
     I. Optical Synchronization System 
     A system for substantially locking an oscillator output to a reference oscillator output is shown in the illustrated embodiment of  FIG.  1    and is generally designated  200 . In the illustrated embodiment, the frequency of an oscillator output may be substantially locked to the frequency of a reference oscillator output via transmission of light energy corresponding to the reference oscillation output. 
     The system  200  in the illustrated embodiment includes a master device  210  and a slave device  220 . The master device  210  may be configured to transmit light energy based on a reference oscillation signal generated by an oscillator  212 . The slave device  220  may be operable to receive the light energy transmitted from the master device  210 . The master device  210  may include a light transmitter  214 , such as a laser diode operable to transmit light energy in accordance with the reference oscillation signal output from the reference oscillator  212 . The light transmitter  214  and illustrated embodiment is biased to the DC power supply via a pull-up resistor  216 , with the reference oscillator  212  configured to sink current from the DC power supply through the light transmitter  214  in accordance with the reference oscillation signal output from the reference oscillator  212 . It is to be understood that the present disclosure is not limited to this configuration for generating light energy in accordance with the reference oscillation signal. For instance, the reference oscillator  212  may be operable to source current from the DC power supply to the light transmitter  214  for generation of light energy therefrom. In the illustrated embodiment, the reference oscillator  212  may be a 24 MHz oscillator with a frequency stability of about 10 ppm. It is to be understood that the frequency of the reference oscillator  212  or the frequency stability of the reference oscillator  212 , or both, may vary depending on the application. 
     The system  200  may include a light transmissive medium  202  configured to enable transmission of light energy from the master device  210  to a slave device  220 . The light transmissive medium  202  in the illustrated embodiment is a light transmissive fiber (e.g., optical fiber) capable of enabling transmission of light energy from the light transmitter  214  to a light receiver  224  of the slave device  220 . The light transmissive medium  202  may vary depending on the application, and is not limited to a fiber construction. For instance, the light transmissive medium may correspond to a gas, such as atmospheric air disposed between the master device  210  and the slave device  220 . 
     As described herein, the system  200  is not limited to transmission of light energy from the master device  210  to a single slave device  220 . In other words, although the system  200  is depicted in illustrated embodiment of  FIG.  1    as transmitting light energy from the master device  210  to a single slave device  220 , the system  200  is not so limited. The system  200  may be configured to enable transmission of light energy from the master device  210  to a plurality of slave devices  220 . 
     In one embodiment, the light transmissive medium  202  may be shared by the plurality of slave devices  220 . For instance, all of the plurality of slave devices  220  may receive light energy transmitted from the master device  210  via a light transmissive medium  202  in the form of atmospheric air. Alternatively, the light transmissive medium  202  may be an optical fiber routed from the master device  210  to each of the plurality of slave devices  220 , with one or more of the plurality of slave devices  220  having an optical tap coupled to the optical fiber to receive light energy therefrom. 
     In one embodiment, the master device  210  may be configured to transmit light energy to each of a plurality of slave devices  220  via separate respective light transmissive medium  202 . For instance, a first slave device  220  may receive light energy via a first light transmissive medium  202 , and a second slave device  220  may receive light energy via a second light transmissive medium  202 . Optionally, the first light transmissive medium  202  may be operable to facilitate transmission of light energy to the first slave device  220  and one or more additional slave devices  220  in a shared manner as described herein. Likewise, additionally or alternatively, the second light transmissive medium  202  may be operable to facilitate transmission of light energy to the second slave device  220  and one or more other slave devices  220  in a shared manner as described herein. 
     The slave device  220  and the illustrated embodiment of  FIG.  1    includes a light receiver  224  operable to receive light energy transmitted from the master device  210  via the light transmissive medium  202 . The light receiver  224  in the illustrated embodiment is provided as a PIN diode photodetector operable to convert optical signals into an electrical signal (e.g., an optical signal corresponding to the light energy transmitted from the light transmitter  214  to a current). The light receiver  224  in the illustrated embodiment is biased toward a DC power supply of the slave device  220  via a pull-up resistor  226 , and is configured to conduct current in response to light energy received via the light transmissive medium  202 . Current conducted through the pull-up resistor  226  may facilitate injection of a timing signal into an oscillation circuit  221  as described herein to facilitate substantially locking a frequency of the oscillation circuit  221  to a frequency of the reference oscillation signal. For instance, a voltage signal present between the light receiver  224  and the pull-up resistor  226  may be supplied to the oscillation circuit  221  via a decoupling capacitor  228 . It is to be understood that the light receiver  224  may be configured in a different manner for facilitating injection of the timing signal into the oscillation circuit  221 , including, for example, an output of the light receiver  224  being directly coupled to the decoupling capacitor  228  for injection of the timing signal into the oscillation circuit  221 . 
     The timing signal generated by the light receiver  224  may correspond to the light energy received by the light receiver  224  and transmitted by the light transmitter  214 . In this way, the timing signal may correspond to the reference oscillation signal output from the reference oscillator  212 . 
     The oscillation circuit  221  in the illustrated embodiment includes an oscillator  230 , first and second tuning capacitors  236 ,  238 , and amplifier  232 , and a feedback resistor  234  for the amplifier  232 . The oscillation circuit  221  may be configured to generate a clock signal CS based on an oscillation signal generated by the oscillator  230 . The amplifier  232  may be configured for operation in a gain limited mode in an inverted configuration. The amplifier  232  and oscillator  230 , in conjunction with the timing signal injected by the light receiver  224 , may be configured as a super-regenerative circuit capable of locking the oscillator  230  to the incoming signal received from the reference oscillator  212  via the transmissive medium  202 . 
     The oscillator  230  may be a crystal oscillator configured to generate an oscillation signal based on mechanical vibration of the crystal oscillator. As described herein, the timing signal injected into the oscillation circuit  221  may facilitate aligning a frequency of the mechanical vibration to the reference oscillation signal. For instance, injection of the timing signal into the oscillation circuit  221  may facilitate locking the frequency of the mechanical vibration to the reference oscillation signal of the reference oscillator  212 , which is received via transmission of light energy from the master device  210  in the illustrated embodiment. 
     The first and second tuning capacitors  236 ,  238  may be specified by the manufacturer of the oscillator  230 . However, as described herein, the timing signal injected oscillation circuit  221  may facilitate tuning the oscillator  230  to operate substantially at the same frequency as the reference oscillation signal output from the reference oscillator  212 . As a result, adjustment or selection of the first and second tuning capacitors may be implemented to coarsely align with or approximate a frequency of the reference oscillator  212 , with fine alignment or substantial locking with the reference oscillation signal being achieved via injection of the timing signal. 
     In one embodiment, the first and second tuning capacitors  236 ,  238  may be variable, such that a controller (not shown) may adjust a capacitance of one or both of the first and second tuning capacitors  236 ,  238  during operation. As described herein, because an oscillation output of the oscillator  230  may correspond substantially to the reference oscillation signal via injection of the timing signal, adjustment of the first and second tuning capacitors  236 ,  238  may have little to no effect on a frequency of the oscillator  230 . However, adjustment of the first and second tuning capacitors  236 ,  238  may be utilized to adjust a phase of the oscillation output of the oscillator  230 . For instance, the phase of the oscillation output may be varied in one embodiment in order to align a phase of the oscillation output with a phase of the reference oscillator output. 
     In the illustrated embodiment of  FIG.  1   , the timing signal injected into the oscillator output of the oscillator  230  is depicted in further detail relative to the oscillator output. The oscillator output in the illustrated embodiments is gained limited by the amplifier  232 . As described herein, because the oscillator output is gained limited, injection of the timing signal may initiate a transition of the oscillation signal sooner or later than would otherwise occur, pushing or pulling the oscillation signal toward substantial alignment with the reference oscillation signal. 
     As can be seen in the illustrated embodiment, the timing signal may be injected into the oscillation output of the oscillator  230 . Transitions of the timing signal are depicted occurring sooner than the oscillation signal respective durations T 1 , T 2 . The oscillation signal is depicted in the illustrated embodiment as moving toward alignment with the timing signal injected into the oscillation circuit  221  by the light receiver  224 . For purposes of disclosure, alignment between the injected timing signal and the oscillation output of the oscillator  230  is shown over three periods. In practice, alignment may occur over many more periods. It is to be understood that injection of the timing signal into the oscillation circuit  221  may continuously push or pull the oscillation output of the oscillator  230  toward substantial alignment with the reference oscillation signal. In this way, the oscillation output of the oscillator  230  may be substantially locked in frequency with the reference oscillator  212  via continuous injection of the timing signal into the oscillator circuit  221 . The frequency lock may be achieved in an open loop manner such that adjustment of the oscillation signal of the oscillator  230  may occur without affecting the reference oscillation signal output from the reference oscillator  212  and without actively controlling the reference oscillation signal output from the reference oscillator  212 . 
     The peak value (e.g., peak voltage) of the timing signal injected into the oscillation circuit  221  may be determined as a function of a peak output of the oscillator signal and a frequency stability of the oscillator  230 . In the illustrated embodiment, the peak value of the timing signal injected into the oscillation circuit corresponds to the peak output of the oscillator signal multiplied times the frequency stability in parts per million (PPM). As an example, for a 100 mV peak oscillator output and a 10 PPM oscillator  230 , the peak value of the timing signal injected into the oscillation circuit  221  that is sufficient to achieve a frequency lock is 1 μV. 
     In one embodiment, the slave device  220  may be operated in a low-power or sleep mode while the master device  210  continues to transmit light energy via the light medium  202 . In a low-power mode, the slave device  220  may provide power to the light receiver  224  and the oscillation circuitry  221  such that the clock signal CS output from the oscillation circuitry  221  is substantially locked in frequency to the reference oscillator  212 , despite other components of the slave device being unpowered. 
     In an alternative embodiment, the light receiver  224  and the oscillation circuitry  221  may be unpowered in a low-power or sleep mode for the slave device  220 . The master device  210  in this configuration may also continue to transmit light energy via the light medium  202 . However, the present disclosure is not so limited—the master device  210  may selectively transmit light energy via the light medium  202  in accordance with the reference oscillator output, such as while the slave device  220  is awake and not while the slave devices sleep. In an embodiment in which the oscillation circuitry  221  and the light receiver  224  are unpowered in a low-power or sleep mode, the slave device  220  may awake from the low-power or sleep mode to an active mode and begin supply power to the oscillation circuitry  221  and the light receiver  224 . The oscillation circuitry  221  may initially be operating at a frequency slightly different from the reference oscillator  212 ; however, as described herein, the oscillation circuitry  221  in conjunction with the light receiver  224  may substantially lock, over the course of a plurality of cycles, with the reference oscillator  212  via injection of the timing signal output from the light receiver  224  in response to light energy transmitted from the master device  210 . With this low-power mode of operation and the ability to substantially lock to the reference oscillator  212  after awakening from the low-power mode or a sleep state, the slave device  100  may avoid continuously powering the oscillation circuitry and/or the light receiver  224  in order to lock the oscillation circuitry to the frequency of the reference oscillator  212 . 
     Turning to the illustrated embodiment of  FIG.  2   , the slave device  220  may include one or more amplifier stages coupled to the oscillation circuit  221  and operable to generate a clock signal CLK, which can be supplied to one or more components of the slave device  220 . Alternatively, the slave device  222  may be absent one or more such amplifier stages such that the clock signal CS corresponds to the clock signal CLK supplied to one or more components of the slave device  220 . 
     The one or more amplifier stages of the slave device  220  in the illustrated embodiment may provide one or more layers of isolation between components of the slave device  220  and the oscillation circuitry  221 . It is noted that the oscillation circuitry  221  in the illustrated embodiment includes an amplifier directly coupled to the oscillator  230 . Accordingly, the amplifier stages described in conjunction with the illustrated embodiment of  FIG.  2   —although described as first and second stages—may be second and third stages relative to the amplifier stage of the oscillation circuitry  221 . 
     In this way, components of the slave device  220  that are coupled to the clock signal CLK can be substantially prevented from affecting operation of the oscillation circuitry  221 . In practice, the one or more amplifier stages may substantially limit impact oscillation circuitry  221  by components of the slave device  222  coupled to the clock signal CLK; however, it is to be understood, depending on the construction of the one or more amplifier stages, there is a potential for such components to have a trivial or minor impact on the oscillation circuitry  221 . Any such effects may be substantially negated by injecting the timing signal into the oscillation circuitry  221  as described herein, where the injected timing signal is based on light energy received from the master device  210 . 
     In the illustrated embodiment, the one or more amplifier stages includes a first amplifier stage  240  directly coupled to the oscillation circuitry  221  to receive the clock signal CS there from. The first amplifier stage  240  may be configured for linear mode operation or near linear mode operation. The first amplifier  240  may be operable to generate and output a clock signal based on the clock signal CS, where transitions of the clock signal output from the first amplifier  240  occur faster than the clock signal CS output from the oscillation circuitry  221 . In other words, the switching speed of the clock signal output from the first amplifier  240  is greater than the switching speed of the clock signal CS output from the oscillation circuitry  221 . 
     The first amplifier stage  240  in the illustrated embodiment includes a decoupling capacitor  244  and an amplifier  242  configured in an inverted mode. The decoupling capacitor  244  may provide DC isolation between the clock signal CS output from the oscillation circuitry  221  and the input to the amplifier  242 . 
     In the illustrated embodiment, the clock signal output from the first amplifier stage  240  may be supplied as an input to a second amplifier stage  250 . The second amplifier stage  250  may be configured for operation in non-linear mode, with a switching speed of the clock signal CLK output from the second amplifier stage  250  being equal to or faster than the clock signal output from the first amplifier stage  240 . The second amplifier stage  250  may include an amplifier  252  configured for nonlinear operation. 
     II. Alternative Embodiment 
     An alternative system in accordance with one embodiment is depicted in  FIG.  3    and generally designated  200 ′. The system  200 ′ is similar in many respects to the system  200 , including a master device  210 ′, a slave device  220 ′, oscillation circuitry  221 , and a light receiver  224  operable to inject a timing signal into the oscillation circuitry  221  in order to facilitate substantially aligning the frequency of the clock signal CS with the frequency of the oscillator  212 . For purposes of disclosure, the system  200 ′ includes several components identified by the same reference number as the system  200 . Such components of the system  200 ′ are substantially similar to the counterpart of the system  200 . 
     The system  200 ′ in the illustrated embodiment depicts a communication interface operable to transmit data between the master device  210 ′ and the slave device  220 ′. The communication interface may be utilized for transmitting data from the master device  210 ′ to the slave device  220 ′. Additionally, or alternatively, the communication interface may be utilized for transmitting data from the slave device  220 ′ to the master device  210 ′. The communication interface may facilitate transfer of data via the light transmissive media  202 , which may be similar to the light transmissive media described in conjunction with the system  200 ′. 
     The communication interface in the illustrated embodiment of  FIG.  3    includes data transmission circuitry  260 ′ operable to control transmission of light energy from a data transmitter  262 ′ (e.g., a laser diode similar to the light transmitter  214 ). The data transmitter  262 ′, similar to the light transmitter  214 , may be coupled to a pull-up resistor  264 ′ that biases the data transmitter  262  toward a supply side of a DC source. The data transmission circuitry  260 ′ may be configured to selectively sink current through the data transmitter  262 ′ in accordance with data to be transmitted via the transmissive medium  202 . The data transmission circuitry  260 ′ may be configured to encode data received for transmission from circuitry of the master device  210 ′ in a variety of ways depending on the application. For example, the data transmission circuitry  260 ′ may encode the data in accordance with non-return-to-zero (NRZ) serial data. 
     The master device  210 ′ may include a transmission interface  266 ′ operably coupled to the light transmitter  214  and the data transmitter  262 ′ to facilitate transmission of light energy to the transmissive medium  202  in a shared manner. In the illustrated embodiment, the light transmitter  214  and the data transmitter  262 ′ are operable to transmit light energy according to different spectrums (e.g., different colors). This way, the transmissive medium  202  may be shared for transmission of light energy in accordance with the reference oscillator  212  and in accordance with data transmitted by the data transmission circuitry  260 ′. 
     The slave device  220 ′ in the illustrated embodiment includes the oscillation circuitry  221  as described herein, as well as a data receiver  272 ′ and data reception circuitry  270 ′. The data receiver  272 ′ may be similar to the light receiver  224  (e.g., a PIN diode photodetector) such that the data receiver  272 ′ is operable to conduct current in response to light energy received from the data transmitter  262 ′ via the transmissive medium  202 . The data receiver  272 ′ may be biased toward a supply side of a DC source via a pull-up resistor  274 ′, similar in operation to the pull-up resistor  226 . The data receiver  272 ′ may be configured to conduct current source from the DC source via the pull-up resistor  274 ′ in response to receipt of light energy as described herein. 
     The slave device  220 ′ in the illustrated embodiment includes diffraction grating  276 ′ operable to facilitate separation of light energy received via the transmissive medium  202  into first and second light signals respectively directed to the light receiver  224  and the data receiver  272 ′. For instance, the data transmitter  262  may transmit light energy in accordance with a different spectrum from a spectrum utilized for transmission of light energy by the light transmitter  214 . The diffraction grating  276 ′ may separate these different spectrums of light energy and facilitate directing these different spectrums of light respectively to the light receiver  224  and the data receiver  272 ′. This way, by separating different spectrums of light with the diffraction grating  276 ′, light energy transmitted from the light transmitter  214  may be directed to the light receiver  224  separate from the light generated by the data transmitter  262 ′ Likewise, light energy transmitted by the data transmitter  262 ′ may be directed to the data receiver  272  separate from the light generated by the light transmitter  214 . 
     The data receiver circuitry  270 ′ in the illustrated embodiment may be operable to decode a data signal generated by the data receiver  272 ′ in accordance with light energy transmitted by the data transmitter  262 ′ and received via the transmissive medium  202 . It is to be understood that multiple types of data transmitters or data receivers, or both, may be incorporated into the master device  210  or the slave device  220 , or both. 
     III. Location System Overview 
     A system in accordance with one embodiment is shown in the illustrated embodiment of  FIG.  4    and generally designated  100 . The system  100  may include one or more system components as outlined herein. A system component may be a user or an electronic system component, which may be the remote device  20 , a sensor  40 , or an object device  50 , or a component including one or more aspects of these devices. Several aspects of the remote device  20 , the sensor  40 , and the object device  50  may be similar. The primary difference between the object device and the sensor pertains to the role of the device within the system  100 —e.g., the object device  50  may transmit data to and receive data from the sensor  40  via a communication link  130 . The object device  50  may direct operation of the sensor  40  by transmitting data to the sensor  40 . The object device  50  may obtain, via the communication link  130 , information from the sensor  40  indicative of a position of the remote device  20  relative to the sensor  40  and/or the object  10 . One or more or all features described in connection with the sensor  40  depicted in the illustrated embodiments may be incorporated into the remote device  20 . 
     In one embodiment, the sensor  40  and the object device  50  may form at least part of a system  100  disposed on an object  10 , such as a vehicle or a building. The object device  50  may be communicatively coupled to one or more systems of the object  10  to control operation of the object  10 , to transmit information to the one or more systems of the object  10 , or to receive information from the one or more systems of the object  10 , or a combination thereof. For instance, the object  10  may include an object controller  52  configured to control operation of the object  10 . The object  10  may include one or more communication networks, wired or wireless, that facilitate communication between the object controller  52  and the object device  50 . The communication network  54  for facilitating communications between the object device  50  and the object controller  52  may be a CAN bus; however, it is to be understood that the communication network is not so limited. The communication network  54  may be any type of network, including a wired or wireless network, or a combination of two or more types of networks. 
     The one or more sensors  40  may be disposed in a variety of positions on the object  10 , such as the positions described herein, including for instance, one or more sensors  40  in the door panel and one or more other sensors in the B pillar. 
     The object device  50  and the one or more sensors  40  may be powered via a power bus  120 . The power bus  120  may be daisy chained from one device to the next as depicted in the illustrated embodiment of  FIG.  5   . Alternatively, the power bus  120  may be provided in the form of a star connection with power being supplied from one location to multiple locations via separate connections. Power supply and architecture is not limited to any one type—for instance, power may be distributed via both daisy chain and star connection configurations. 
     The system  100  in the illustrated embodiment may be configured to determine location information in real-time with respect to the remote device  20 . In the illustrated embodiment of  FIGS.  4  and  5   , a user may carry the remote device  20  (e.g., a smartphone). The system  100  may facilitate locating the remote device  20  with respect to the object  10  (e.g., a vehicle) in real-time with sufficient precision to determine whether the user is located at a position at which access to the object  10  or permission for an object  10  command should be granted. 
     For instance, in an embodiment where the object  10  is a vehicle, the system  100  may facilitate determining whether the remote device  20  is outside the vehicle but in close proximity, such as within 5 feet, 3 feet, or 2 feet or less, to the driver-side door  15 . This determination may form the basis for identifying whether the system  100  should unlock the vehicle. On the other hand, if the system  100  determines the remote device  20  is outside the vehicle and not in close proximity to the driver-side door (e.g., outside the range of 2 feet, 3 feet, or 5 feet), the system  100  may determine to lock the driver-side door. As another example, if the system  100  determines the remote device  20  is in close proximity to the driver-side seat but not in proximity to the passenger seat or the rear seat, the system  100  may determine to enable mobilization of the vehicle. Conversely, if the remote device  20  is determined to be outside close proximity to the driver-side seat, the system  100  may determine to immobilize or maintain immobilization of the vehicle. 
     The object  10  may include multiple object devices  50  or a variant thereof, such as an object device  50  including a sensor  40  coupled to an antenna array, in accordance with one or more embodiments described herein. The object device  50  may be configured to communicate directly with one or more sensors  40  via the communication link  130 , which as described herein, may include one or more interfaces, such as the communication interface described herein with respect to the system  200 ′. The one or more interfaces may be established via one or more physical mediums. 
     In the illustrated embodiment of  FIG.  5   , the communication link  130  is distributed from one device to another and includes a terminator  132  at each end. The communication link  130  among the devices may be a shared link or a separate link for each device, or a combination thereof. For instance, the communication link  130  may be shared among two or more devices as depicted, and additionally or alternatively, the communication link  130  may be established separately from one device to another device. A device may communicate via more than one separate communications line  130 , and may be configured to relay communications from one communication link  130  to another communication link  130 . 
     In addition to or alternative to one or more location techniques described herein, micro-location of the remote device  20  may be determined in a variety of ways, such as using information obtained from a global positioning system, one or more signal characteristics of communications from the remote device  20 , and one or more sensors (e.g., a proximity sensor, a limit switch, or a visual sensor), or a combination thereof. An example of microlocation techniques for which the system  100  can be configured are disclosed in U.S. Nonprovisional patent application Ser. No. 15/488,136 to Raymond Michael Stitt et al., entitled SYSTEM AND METHOD FOR ESTABLISHING REAL-TIME LOCATION, filed Apr. 14, 2017—the disclosure of which is hereby incorporated by reference in its entirety. 
     In the illustrated embodiment of  FIGS.  4 - 5   , the object device  50  (e.g., a system control module (SCM)) and a plurality of sensors  40  (each coupled to an antenna array) may be disposed on or in a fixed position relative to the object  10 . Example use cases of the object  10  include the vehicle identified in the previous example, or a building for which access is controlled by the object device  50 . 
     The remote device  20  may communicate wirelessly with the object device  50  via a communication link  140 , such as a BLE communication link or an Ultra Wideband (UWB) communication link. The plurality of sensors  40  may be configured to sniff the communications of the communication link  140  between the remote device  20  and the object device  50  as shown in phantom lines  142 . Based on the sniffed communications, a sensor  40  may determine one or more signal characteristics of the communications as described herein, such as a signal strength, time of arrival, time of flight, angle of arrival, or a combination thereof. The determined signal characteristics may be communicated or analyzed and then communicated to the object device  50  via the communication link  130  separate from the communication link  140  between the remote device  20  and the object device  50 . 
     Additionally, or alternatively, the remote device  20  may establish a direct communication link with one or more of the sensors  40 , and the one or more signal characteristics may be determined based on this direct communication link. The direct communication link may be established according to the BLE protocol; however, the present disclosure is not so limited—the direct communication link may be any type of link or links, including Ultra Wideband (UWB). 
     It is to be understood that an object  10 , such as a vehicle, may include a number of sensors  40  that can be greater than or less than the number shown in the illustrated embodiments of  FIGS.  4  and  5   . Depending on the implementation, some number of sensors  40  may be integrated in a vehicle. 
     Additional or alternative types of signal characteristics may be obtained to facilitate determining position according to one or more algorithms, including a distance function, trilateration function, a triangulation function, a lateration function, a multilateration function, a fingerprinting function, a differential function, a time of flight function, a time of arrival function, a time difference of arrival function, an angle of departure function, a geometric function, or any combination thereof. 
     In the illustrated embodiments of  FIGS.  4  and  5   , a transmission medium  202  is provided between the object device  50  and one or more sensors  40 . The transmission medium  202  may enable transmission of light energy and may be substantially immune to electromagnetic interference generated by electrical components and of the object  10 , such as interference generated by fast switching of wired communication interfaces, radio frequency interference, and electromechanical components of the object  10  (e.g., an engine). 
     The object device  50  may correspond to the master device  210 , and the one or more sensors  40  may correspond to the slave device  220 . The system  200  described herein may be utilized to lock a frequency of a clock signal CLK utilized in the sensor  40  with a reference oscillator  212  provided in the object device  50 . This way, a clock signal utilized in the object device  50  may be substantially the same frequency as a clock signal utilized in the sensor  40 . The transmissive medium  202  may be utilized by the object device  50  to facilitate locking a frequency of a clock signal CLK in multiple sensors  40 , such that light energy transmitted from the light transmitter  214  may be received by multiple light receivers  224  in respective ones of the plurality of sensors  40 . 
     Alignment of the frequency being utilized by multiple devices in the system  100  may aid avoiding complex analysis and comparisons of the one or more signal characteristics detected by multiple sensors  40  in the system. For instance, measurements with respect to time of flight can be compared with little to no regard for deviations in the frequency of one device relative to another device. By having the frequency of multiple devices being substantially the same, algorithms operable to analyze signal characteristics measured by different sensors  40  can substantially ignore effects due to frequency deviations. In one embodiment, as described herein, the phase of the clock signals CLK in multiple devices may be adjusted for alignment with a phase of the reference oscillator  212  of the master device  210 . This phase alignment may further facilitate analysis and comparison of measurements obtained by sensors  40  located at different positions and operating separately from each other. 
     As described herein, one or more signal characteristics, such as a phase characteristic, a signal strength, time of arrival, time of flight, and angle of arrival may be analyzed to determine location information about the remote device  20  relative to the object  10 , an aspect of the object  10 , or the object device  50 , or a combination thereof. For instance, a phase rotation of a tone transmission, and optional re-transmission, or a phase characteristic indicative of a phase rotation may form the basis for determining a distance between an object device  50  or a sensor  40  and the remote device  20 . Additional examples of signal characteristics include time difference of arrival or the angle of arrival, or both, among the sensors  40  and the object device  50  may be processed to determine a relative position of the remote device  20 . The positions of the one or more antenna arrays  220  relative to the object device  50  may be known so that the relative position of the remote device  20  can be translated to an absolute position with respect to the antenna arrays  220  and the object device  50 . 
     The system  100  in one embodiment may incorporate aspects of the system  200 ′, such as data communication capabilities that share the transmission medium  202  utilized to facilitate aligning the frequencies of oscillators within the system  100 . The data communication capabilities may be provided in place of or in addition to the communication interface  130 . 
     It is further noted that, in one embodiment, the transmission medium  202  may be atmospheric gas. The slave device  220  may correspond to the portable device  20 , with the master device  210  being an object device  50  or sensor  40  disposed on the vehicle, and the light transmitter  214  transmitted light energy that is received by the portable device  20  and enables the portable device  20  to substantially align a clock signal CLK of the portable device  20  with a reference oscillator  212  of the object device  50  or sensor  40  disposed on the vehicle. 
     Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to any specific orientation(s). 
     The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular. Any reference to claim elements as “at least one of X, Y and Z” is meant to include any one of X, Y or Z individually, and any combination of X, Y and Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.