Patent ID: 12228607

DETAILED DESCRIPTION

An optically isolated measurement system communicates over an optical domain and acts as an isolation barrier preventing electricity from the DUT side of the barrier from affecting the oscilloscope. A transmitter on the DUT side comprising a heterodyne modulating mixer with a local oscillator (LO) and Electrical-to-Optical (E/O) converter. The transmitter transmits the optical signal over an optical fiber to a receiver. The receiver comprises an Optical-to-Electrical (O/E) converter and heterodyne demodulating mixer with a phase recovered local oscillator. The fundamental frequency generated by the LO is recovered by a phase-locked loop and in-phase (I) and in-quadrature (Q) demodulation.

Temperature changes create significant measurement errors. First, the E/O and O/E converters' gains drift with temperature changes which causes the DUT signal to drift with temperature. The local oscillator cannot be used to recover the gain, because after mixing with the signal from the DUT, it is modulated by an unknown signal to be measured. The local oscillator frequency cannot be used to recover the phase because the polarity of the DUT signal is unknown. The DUT signal is a first signal.

A secondary tone, or pilot tone, can be created to recover the phase. The secondary tone is a second signal. The polarity of the secondary tone can be determined through factory calibration. The phase of the DUT signal also drifts with temperature. If the pilot tone and local oscillator are at different frequencies, the phase of the pilot tone compared to the local oscillator will drift with respect to each other, resulting in an unoptimized IQ vector for that given temperature, which results in measurement gain and distortion errors.

A pilot tone which is out of the bandwidth of the heterodyne mixed band of the instrument can be used to recover the gain and relative phase as the pilot tone's magnitude and phase drifts with the DUT signal due to temperature. The pilot tone is in the passband of the E/O and O/E devices and separated enough from the modulated DUT signal band such that the pilot tone can be filtered out of an acquisition measurement and tapped off combined signal lines to later recover the gain and phase information. This signal is to be summed into the same conductor before E/O conversion such that it shares the same gain change as the DUT signal, and therefore can be used to recover correct gain.

In the receiver after the O/E conversion, both the pilot tone and the modulated DUT signal are passed through a magnitude correction circuit. The pilot tone is then tapped off and sent to a gain/attenuation and phase recovery circuit. The DUT (first) signal is sent to a mixer to be demodulated.

In one aspect, gain/attenuation recovery is achieved with a feedback loop designed fully in hardware. The pilot tone tap can include the necessary bandpass filtering and amplification or attenuation stages to achieve cleanliness and voltage levels. The secondary tone is then passed through a limiting amplifier with a received signal strength indicator (RSSI) output. This stage gains up the pilot tone to the point of saturation, creating a square wave which will then be sent to the IQ demodulator for phase recovery. The RSSI is an analog output proportional to the amplitude of the received pilot tone. This signal is then fed back through an inverting integrator to control the gain or attenuation of the magnitude correction circuit. The DUT signal band gain is modulated by the same amount as the pilot tone, thus correcting both signals for the temperature effects through the optical converter link. Any difference in temperature dependence between the DUT signal band and the frequency of the pilot tone will result in a residual error after correction. Characterizing the system and selecting the appropriate frequency bands influences the accuracy of this system.

Other elements that influence the accuracy of this system are the amplitude and signal fidelity of the pilot tone. It is desirable to have the pilot tone be as small as possible in the optical converter link to minimize intermodulation distortion between the pilot tone and DUT signal. In one aspect, the pilot tone can be selected to be large enough such that after tapping it off after the magnitude correction circuit the signal is large enough that noise on the line or noise contributions from the limiting amplifier do not affect the feedback loop or introduce low frequency noise on the DUT signal. The integrator and other filtering limits the band to minimize the impact of this noise. The signal is linear over the entire range of necessary amplitudes to account for the full range of variation of the gain of the optical converters. Distortion of this signal would create error in gain correction.

To recover the phase for the demodulation, the saturated output of the limiting amplifier of the pilot tone is sent to an IQ demodulator. The IQ vector is swept and optimized during factory calibration for peak gain, correct phase (either inverting or non-inverting can be chosen) and distortion. The relative phase of the pilot tone and the modulation frequency tone drifts with temperature, and therefore for optimal performance the IQ vector also should change with temperature.

At each temperature, a compromise is made between optimizing distortion and maximizing gain. From the fundamental frequency generated by a hardware implemented local oscillator, a new fundamental is generated by hardware multiplying the I (in-phase) and Q (in-quadrature) components by signed constants produced by two programmable digital-to-analog converters (DACs). The I multiplier and Q multiplier, together, form an IQ vector whose length and direction/phase can be programmed. The gain and distortion can be changed both by changing the phase of the IQ vector and/or its length; whereas the effect of changing the length of the IQ vector is generally minor, the phase effect is drastic—the amplitude can go from a local maximum to zero just by changing the angle by 45 degrees, and the harmonic distortion also changes very quickly with this phase.

Generally, what maximizes amplitude also minimizes distortion, but sometimes what is best for amplitude is not best for distortion, and vice-versa. The “distance” between the extrema is sometimes up to 10 degrees. When optimizing phase (and length), the two objectives are given weights so that there is not too much amplitude (which will hinder the signal to noise (SNR) performance) lost nor is there too much distortion (which will hinder the total harmonic distortion (THD) performance). In practice, achieving the optimal compromise is done by giving a weight to each summand in the optimization function. In addition, the ideal IQ phase changes with temperature

In one aspect, the method was to measure the best phase ϕRM(minimizing distortion and maximizing amplitude, each with a weight in the optimizing function) at room temperature. The exact temperature TRMpresent at this time is stored. The probe is then put in a miniature refrigerator. The same optimization is performed there, giving ϕFRat TFR, Finally, while in operation, the IQ vector is rotated by an angle (ϕFR−ϕRM) (T−TRM)/(TFR−TRM). This rotation is performed via integer arithmetic calculation, performing an integer number of infinitesimal rotations of the IQ vector (approximately one such small rotation per degree Celsius). During operation, the temperature is measured on board with a thermal sensor. As temperature changes, the onboard microcontroller adjusts the IQ vector on the fly according to the equation.

Characterizing the resulting performance across the device operating temperature for many units determines if the temperature coefficient is consistent enough that the same coefficient can be used for each unit. If the median ideal coefficient produces errors too large to achieve the desired specifications, each unit is measured during factory calibration to optimize each unit for its own drift characteristics.

Turning now to the Figures,FIG.1is one aspect of a receiver100comprising a magnitude correction circuit according to an exemplary aspect of the disclosure. The receiver100is coupled to a fiber optic cable102and an oscilloscope (not shown). The receiver100receives an optical signal from the fiber optic cable102. The receiver100comprises an optical to electrical converter106to convert the optical signal into an electrical signal. The electrical signal is defined by a phase and amplitude. The electrical signal is a combined electrical signal comprising a first signal and a second signal. In one aspect, the first signal is a device under test signal and the second signal is a pilot tone/signal or secondary tone/signal. For example, the device under test signal is a signal from a device detected by a probe to be measured by the oscilloscope. The pilot tone is a secondary tone to recover a gain/attenuation and a phase of the first signal. In one aspect, the second signal is out of the pass band of the first signal.

The receiver100further comprises a magnitude correction circuit110(an automatic gain/attenuation control block or correction circuit) to receive the electrical signal and to determine a gain or attenuation of the electrical signal. The gain or attenuation of the electrical signal is based on the drift of the electrical signal caused by a change in temperature. The gain or attenuation is used to determine the amplitude of the electrical signal before it was sent through the fiber optic cable102.

The magnitude correction circuit110determines an amplification or attenuation of the second signal. The magnitude correction circuit110comprises a detector118coupled to the variable gain amplifier108. The detector118generates a control signal proportional to received power of the second signal. The input received power is the voltage and current of the second signal. In one aspect, the detector118converts the second signal from an AC signal to a DC signal. In one aspect, the detector118is a rectifier. An error amplifier112is coupled to the detector118to compare a reference voltage114against an output of the detector118to generate a signal proportional to the difference between the reference voltage and the output of the detector to determine an amplification or attenuation of the second signal. The amplification or attenuation of the second signal varies based on a drift of the electrical signal due to temperature. In one aspect, the detector118is coupled to the output of a variable gain amplifier108. In one aspect, the error amplifier112is an inverting amplifier.

The receiver100comprises a variable gain amplifier108coupled to the magnitude correction circuit110and the fiber optic cable102. The variable gain amplifier108generates a compensated electrical signal based on the amplification or attenuation of the second signal determined by the magnitude correction circuit110. The variable gain amplifier108amplifies or attenuates the electrical signal by the gain or attenuation determined by the error amplifier112. The magnitude correction circuit110coupled to the variable gain amplifier creates a negative feedback to adjust the variable gain or attenuation of the electrical signal and maintain a constant feedback with changing temperature. The variable gain amplifier outputs a compensated electrical signal.

The receiver100further comprises a de-modulating mixer116coupled to the magnitude correction circuit110. The output of the variable gain amplifier108is coupled to the de-modulating mixer116to mix a phase compensated signal and the compensated electrical signal. In one aspect, the phase compensated signal is determined by a phase recovered clock. The mixer116outputs a signal with a corrected amplitude such that the amplitude is equal to the amplitude of the first signal before it was sent by the transmitter.

FIG.2is one aspect of a receiver200comprising a phase correction circuit according to an exemplary aspect of the disclosure. The receiver200is coupled to a fiber optic cable202and an oscilloscope (not shown). The receiver200receives an optical signal. The receiver200comprises an optical to electrical converter206and a phase correction circuit224. The optical to electrical converter206converts the received optical signal into an electrical signal. The electrical signal, defined by an amplitude and a phase, is a combined signal comprising a first and second signal. The output of the optical to electrical converter206is coupled to the phase correction circuit224which receives the electrical signal. The receiver200further comprises a limiting amplifier222coupled to the optical to electrical converter206to normalize the gain of the second signal before the second signal is sent to the phase correction circuit.

The phase correction circuit224, coupled to the limiting amplifier222, comprises a modulator circuit226. The output of the phase correction circuit224is coupled to a mixer228. The modulator circuit226is coupled to a temperature sensor220and receives a temperature dependent phase compensated signal. The temperature dependent phase compensated signal is based on the temperature measured by the temperature sensor220. The temperature sensor220is to output a value indicative of a phase shift of the electrical signal based on the temperature. The modulator circuit226is coupled to the mixer228. The mixer228is also coupled to the limiting amplifier222to receive a reference signal defined by the phase of the electrical signal. The limiting amplifier222determines the reference signal defined by the phase of the electrical signal.

The phase correction circuit224outputs a phase compensated modulated signal. The phase compensated signal is a phase shifted second signal that compensates for the phase shift due to temperature variations. The receiver200comprises a mixer216coupled to the phase correction circuit224. In one aspect, the mixer216is a de-modulating mixer. The mixer216mixes the phase compensated modulated signal from the phase correction circuit224and a compensated first signal. In one aspect, the compensated first signal is the output of the optical to electrical converter206. In another aspect, the compensated first signal is a gain or attenuation of the first signal. The mixer216outputs a signal with a corrected phase such that the signal has the same phase as the signal before it was sent by a transmitter.

FIG.3is one aspect of a receiver300comprising a magnitude correction circuit and a phase correction circuit according to an exemplary aspect of the disclosure. The receiver300is coupled to a fiber optic cable302and an oscilloscope (not shown). The receiver300comprises an optical to electrical converter306coupled to the fiber optical cable302to convert the optical signal into an electrical signal. The electrical signal is a combined electrical signal comprising a first signal and a second signal. In one aspect, the second signal is outside the passband of the first signal. The optical to electrical converter306is coupled to a variable gain amplifier308. The receiver300further comprises a magnitude correction circuit310coupled to a phase correction circuit324and a de-modulating mixer316and a temperature sensor320. In one aspect, the temperature sensor320is coupled to a microcontroller338.

The variable gain amplifier308is coupled to the magnitude correction circuit310. The magnitude correction circuit310comprises a bandpass filter332coupled to a limiting amplifier334. The bandpass filter332filters the second signal from the electrical signal. The limiting amplifier334receives the second signal from the bandpass filter332. The limiting amplifier334comprises a first output and a second output. The first output is coupled to the phase correction circuit324and provides a reference signal defined by the phase of the electrical signal. The second output is coupled to an error amplifier312and provides a received signal strength indicator of the second signal to the error amplifier312. In one aspect, the error amplifier312is an inverting amplifier. The received signal strength indicator is an analog output proportional to the amplitude of the second signal. An example of a limiting amplifier is Texas Instruments ONET4251PA.

The error amplifier312also is coupled to a reference voltage314. In one aspect, the reference voltage314is a digital to analog converter output programmed by the microcontroller338. The microcontroller338calibrates the gain of the system at room temperature such that the reference voltage314has a calibrated gain at room temperature (the reference temperature). The error amplifier acts as an integrator to output a gain or attenuation of the second signal. The gain or attenuation of the second signal is the same gain or attenuation of the first signal. The error amplifier312comprises an output coupled to the variable gain amplifier. The gain or attenuation of the second signal can then be used to determine a compensated first signal which is indicative of the first signal before a gain or attenuation drift with temperature due to the system of an electrical to optical converter in a transmitter, the fiber optic cable302, and the optical to electrical converter306. The error amplifier312provides the value to amplify or attenuate the electrical signal to the variable gain amplifier308. The variable gain amplifier308amplifies or attenuates the electrical signal by the value determined by the error amplifier312. The output of the variable gain amplifier308is coupled to the bandpass filter330to filter out the attenuated or amplified second signal. The variable gain amplifier308is coupled to the de-modulating mixer316. In one aspect, the bandpass filter330is coupled between the de-modulating mixer316and the variable gain amplifier308. In one aspect, the magnitude correction circuit310is a feedback loop to adjust the gain based on the temperature drift.

The magnitude correction circuit310is coupled to the phase correction circuit324. The phase correction circuit324receives the first output from the limiting amplifier334. The first output is a saturated signal, the saturated signal gains up the first signal to the point of saturation. The phase correction circuit324comprises a modulator circuit336. The modulator circuit336receives a reference signal defined by the phase of the electrical signal and a temperature dependent phase compensated signal. The reference signal is the first output of the limiting amplifier of the magnitude correction circuit310. The temperature dependent phase compensated signal is based on the temperature measured by the temperature sensor320.

In one aspect, the modulator circuit336comprises an IQ modulator. The IQ modulator comprises an in-phase input to receive an in-phase signal that is temperature dependent and an in-quadrature input to receive an in-quadrature signal that is temperature dependent. The temperature sensor320coupled to the modulator circuit336generates the temperature dependent phase compensated signal based on temperature measured by the temperature sensor320. The temperature dependent phase compensated signal comprises the in-phase signal and the in-quadrature signal. The IQ modulator also receives the reference signal from the magnitude correction circuit310. The IQ modulator modulates the reference signal with the temperature dependent phase compensated signal. The IQ modulator outputs a phase compensated signal. For example, the IQ modulator can be Texas Instruments TRF370315.

The temperature sensor320can be located on the receiver300, or proximate to the receiver300. In one aspect, the temperature sensor320is proximate to the optical to electrical converter306in the receiver300. The microcontroller338tracks the temperature in comparison to the reference temperature. The temperature sensor320is coupled to a microcontroller338. In one aspect, the microcontroller338continuously polls the temperature sensor320. In one aspect, the microcontroller338calculates the in phase and in quadrature signals based on the temperature measured by the temperature sensor. In another aspect, the microcontroller has a look up table of temperatures and corresponding temperature measurements. The microcontroller338is connected to a first and second digital to analog converter340,342. The microcontroller338controls the in phase and in quadrature values that are output to the first and second DACs. In one aspect, the first digital to analog converter340is coupled to the in phase input of the IQ modulator and the second digital to analog converter342is coupled to the quadrature input of the IQ modulator. The temperature sensor320measures temperature and outputs a value indicative of a phase shift of the electrical signal based on the temperature. In one aspect, the in phase and in quadrature signals are temperature dependent.

In one aspect, the microcontroller338stores factory calibration data to adjust the gain. In another aspect, the microcontroller338stores factory calibration of phase temperature adjustment parameters. In one aspect, factory calibrating comprises the microcontroller338measuring the best phase ϕRM(minimizing distortion and maximizing amplitude, each with a weight in the optimizing function) at room temperature. The exact temperature TRMpresent at this time is stored. The probe is then put in a temperature chamber that creates a temperature variation from room temperature to measure the drift associated with temperature, such as a miniature refrigerator or an oven. In one aspect, the transmitter drift is measured in the temperature chamber. In another aspect, the receiver drift is measured in the temperature chamber. The transmitter drift and receiver drift are measured separately, such that when the receiver is in a temperature chamber the transmitter is at room temperature and vice versa. In one aspect, the transmitter drift is calculated when the transmitter is in the temperature chamber to form a transmitter temperature curve. The receiver drift is calculated when the receiver is in the temperature chamber to form a receiver temperature curve. The transmitter temperature curve and the receiver temperature curve may be different curves. The same optimization is performed there, giving ϕFRat TFR, Finally, while in operation, the IQ vector is rotated by an angle (ϕFR−ϕRM) (T−TRM)/(TFR−TRM). This rotation is performed via integer arithmetic calculation, performing an integer number of infinitesimal rotations of the IQ vector (approximately one such small rotation per degree Celsius). During operation, the temperature is measured on board with a thermal sensor (temperature sensor320). As temperature changes, the onboard microcontroller338adjusts the IQ vector on the fly according to the equation.

The modulator circuit336outputs a phase compensated modulated signal based on a phase drift of the electrical signal. The modulator circuit336is coupled to a phase-locked loop circuit. The phase-locked loop comprises a multiplier344to receive the phase compensated modulated signal from the modulator circuit336. The phase lock loop circuit comprises a voltage controlled oscillator346and a multiplier348coupled to the voltage controlled oscillator346. In one aspect, the multiplier348is a frequency multiplier. The multiplier344creates two outputs of the phase compensated modulated signal. The first output of the phase compensated electrical signal is sent to a voltage controlled oscillator (VCO)346. The second is sent to a multiplier348. The multiplier multiples the output of the VCO346and the phase modulated electrical signal. A bandpass filter350is coupled to the multiplier348in order to output the phase compensated modulated signal. The phase-locked loop circuit synchronizes the output of the phase compensated modulated signal and normalizes the amplitude of the phase compensated modulated signal.

The output of the variable gain amplifier308is coupled to a bandpass filter330and outputs a compensated first signal. The phase correction circuit324outputs a phase compensated modulated signal. The mixer316mixes the compensated first signal with a phase compensated modulated signal. In one aspect, the mixer316is a heterodyne de-modulating mixer. The mixer316then outputs the signal to be measured by the oscilloscope with a phase and gain/attenuation compensation. The signal recovers the phase and amplitude of the electrical signal sent by a transmitter. The mixer316is coupled to a filter352to filter the signal to be measured by the oscilloscope.

In one aspect, the receiver300is coupled to a digital communication fiber optic cable. The digital communication fiber optic cable is coupled to the microcontroller338of the receiver300to receive temperature measurements of the transmitter. The microcontroller338adjusts the IQ signals based on a potential different transmitter temperature environment.

FIG.4is one aspect of a transmitter460according to an exemplary aspect of the disclosure. The transmitter460is coupled to a device under test462. For example, the device under test462is a device with a voltage and frequency to be detected by a probe and sent to an oscilloscope to be measured. The transmitter460receives a device under test signal indicative of the voltage and frequency of the device. The device under test signal is also referred to as the first signal. The transmitter460comprises a reference clock464. The reference clock464outputs a second signal. The transmitter460comprises a mixer466coupled to the device under test462and the reference clock464to receive the first signal and second signal. The mixer466modulates the first signal with the second signal to output a modulated first signal. The transmitter460further comprises a summation circuit468(also referred to as a summing node) that combines the modulated first signal and the second signal into a combined electrical signal. The summation circuit468is coupled to an electrical to optical converter470. The combined electrical signal is sent to the electrical to optical converter420to convert the combined electrical signal into an optical signal. The optical signal is then sent down the fiber optic cable402to a receiver (shown inFIG.3). The receiver de-modulates the signal for the oscilloscope to measure.

FIG.5is one aspect of a transmitter560according to an exemplary aspect of the disclosure. The transmitter560inFIG.5comprises all elements ofFIG.4. The transmitter560is coupled to an input lead572that measures the device under test462. For example, the input lead572facilitates making a physical connection with the device under test462to measure the device under test462. The transmitter560comprises a variable gain amplifier574coupled to the input lead. The variable gain amplifier574is coupled to the mixer466. The variable gain amplifier574amplifies or attenuates the first signal to send to the mixer466. The output of the mixer466is coupled to a bandpass filter576.

The transmitter560further comprises the reference clock464coupled to an amplifier578. The amplifier578is coupled to a multiplier and a bandpass filter586. The multiplier580coupled to a bandpass filter582which is coupled to an amplifier584. In one aspect, the multiplier580is a frequency multiplier. The reference clock is multiplied to create a phase-deterministic local oscillator. In one aspect, the multiplier580creates clock for modulation which is a distinct different band from the second signal. The bandpass filter582filters the reference clock signal. The amplifier584is coupled to the mixer466and amplifies the reference clock signal sent to the mixer466. In one aspect, the mixer466is a heterodyne modulation mixer. The mixer466mixes the first signal (device under test signal) with the output of the amplifier584, which is the phase deterministic local oscillator. The mixer466is coupled to a bandpass filter576to filter the modulated first signal. In one aspect, the bandpass filter576filters out anything other than the modulated input signal. The modulated input signal is the modulated device under test signal. The bandpass filter576is coupled to the summation circuit468.

The bandpass filter586is coupled to the summation circuit468and filters the reference clock signal sent to the summation circuit468. The summation circuit468combines the first signal and the second signal. The first signal is the signal from the mixer466and the second signal is the reference clock signal from bandpass filter586. The summation circuit468is coupled to the electrical to optical converter470where the electrical signal is converted to an optical signal to transmit the optical signal through the fiber optic cable402to a receiver (shown inFIGS.1,2, and3). The signal output from the summation circuit468is a combined signal because it comprises the first signal and the second signal.

The transmitter560further comprises a temperature sensor588coupled to a microcontroller590. The temperature sensor588can be located on the transmitter560, or proximate to the transmitter560. In one aspect, the temperature sensor588is proximate to the electrical to optical converter470. The temperature sensor588measures the temperature of the transmitter560in order to communicate through the optical fiber to a microcontroller in a receiver, such that the receiver could adjust the IQ correction based on a potential different transmitter temperature environment. The temperature signal is sent through a digital communication fiber optic cable. In one aspect, the microcontroller590tracks the temperature in comparison to the reference temperature.

In one aspect, the electrical to optical converters of transmitters ofFIGS.4and5and the optical to electrical converters ofFIGS.1-3both drift with temperature. For conciseness and clarity, when referring toFIG.3, all elements can be executed with either of the receivers fromFIG.1or2as well. In addition, when referring toFIG.5, all elements can be executed with the receiverFIG.4. In one aspect, when the transmitter560and receiver300are separated by a long fiber optical cable302, the transmitter560and receiver300may be at different temperatures. In one aspect, the phase correction is calculated based on the combination of both the transmitter and receiver temperatures. In one aspect, the phase correction uses the transmitter temperature curve and the receiver temperature curve. For example, the microcontroller590of the transmitter560communicates with the microcontroller338of the receiver300over the digital communication fiber optic cable. The microcontroller338calculates the weighted inputs for the temperatures from the temperature sensors of the transmitter560and receiver300. The magnitude correction inherently accounts for both drifts without this communication.

The transmitters ofFIG.4or5can be connected to the receivers ofFIG.1,2, or3. In one aspect, the reference clocks in the transmitter and receiver are of the same frequency. In one aspect, when the reference clock modulation signal in the transmitter is multiplied to create a phase deterministic local oscillator, the phase recovered clock is in receiver is multiplied by the same multiplier to create a de-modulated clock. For example, the system comprises a transmitter from any ofFIGS.4-5and a receiver from any ofFIGS.1-3. For conciseness and clarity, when referring toFIG.3, all elements can be executed with either of the receivers fromFIG.1or2as well. In addition, when referring toFIG.5, all elements can be executed with the receiverFIG.4. The transmitter560comprises a reference clock464with a reference clock signal, a mixer466coupled to the reference clock464to mix the reference clock signal with an input to the transmitter560to output a first signal, a summation circuit468coupled to the reference clock464and the mixer466to combine the first signal and the reference clock signal to form a combined electrical signal, and an electrical to optical converter470to convert the combined electrical signal into an optical signal. The receiver300comprising a temperature sensor320, an optical to electrical converter306to receive an optical signal and convert the optical signal to an electrical signal defined by a phase. The electrical signal is a combined electrical signal comprising the first signal and a second signal. The receiver300comprising a magnitude correction circuit310coupled to the optical to electrical converter306. The magnitude correction circuit310is to determine an amplification or attenuation of the second signal based on a drift of the electrical signal. The receiver300comprising a variable gain amplifier308coupled to the magnitude correction circuit310. The variable gain amplifier308is to generate a compensated electrical signal based on the amplification or attenuation of the second signal determined by the magnitude correction circuit310. The receiver300comprising a phase correction circuit324coupled to the magnitude correction circuit310. The phase correction circuit324is to output a phase compensated modulated signal. The receiver300comprising a bandpass filter330coupled to the variable gain amplifier308. The bandpass filter330to filter an amplified first signal from the compensated electrical signal. The receiver300comprising a de-modulating mixer316coupled to the bandpass filter330and the phase correction circuit324. The de-modulating mixer316to mix the phase compensated modulated signal from the phase correction circuit310and the amplified first signal.FIG.6is a logic flow diagram of a method600of operating a receiver and transmitter according to an exemplary aspect of the disclosure. With reference now toFIG.6together withFIGS.1-5, according to the method600, the receiver100,200,300receives602a combined electrical signal. For conciseness and clarity, the method600when referring toFIG.3can be executed with either of the receivers fromFIG.1or2as well. In addition, the method600can be executed with either transmitter fromFIG.4or5. For conciseness and clarityFIG.5will be used in reference to implementing the method600. The combined electrical signal comprises a first and second signal. The receiver300determines603a compensation type, wherein the compensation type comprises a gain or attenuation compensation. The magnitude correction circuit310determines604a gain or attenuation of the second signal. The variable gain amplifier calculates608a compensated first signal based on the gain or attenuation of the second signal. The mixer modulates612the compensated first signal with the phase compensated second signal.

In one aspect, the method600further comprises combining601the first signal and the second signal.

In one aspect, the compensation type further comprises phase compensation. The phase correction circuit324determines606a phase shift of the second signal. The modulator circuit336calculates610a phase compensated second signal based on the phase shift of the second signal.

In one aspect, the method600further comprises receiving a temperature from a temperature sensor320. In one aspect, the microcontroller338determines a temperature dependent signal indicative of the phase shift of the second signal based on the temperature.

In one aspect, the method600further comprises filtering, by the bandpass filter330, a compensated first signal from the compensated signal.

In one aspect, the method600further comprises receiving, by the receiver300, an optical signal. The optical to electrical converter306converts an optical signal into the electrical signal.

In one aspect, the method600further comprises filtering, by the bandpass filter332, the second signal from the electrical signal. The limiting amplifier334calculates a reference signal defined by the phase of the electrical signal and a received signal strength of the second signal.

In one aspect, the method600comprises receiving, by the receiver300, a combined electrical signal wherein the combined electrical signal comprises a first signal and a second signal. The receiver300determines a compensation type, wherein the compensation type comprises a phase compensation. The phase correction circuit324determines a phase shift of the second signal. The modulator circuit336calculates a phase compensated second signal based on the phase shift of the second signal. The mixer316modulates a compensated first signal with the phase compensated second signal.

In one aspect, the method600further comprises combining601the first signal and the second signal.

In one aspect, the method600further comprises receiving a temperature from a temperature sensor320. In one aspect, the method600further comprises determining a temperature dependent signal, by the microcontroller338, indicative of the phase shift of the second signal based on the temperature.

In one aspect, the method600further comprises receiving, by the receiver300, an optical signal. The optical to electrical converter306converts an optical signal into the electrical signal.

In one aspect, the method600further comprises determining, by the microcontroller338, an in-phase value and in-quadrature value based on the temperature measured by the temperature sensor320. In one aspect, the modulator circuit336receives an in-quadrature signal based on the temperature, an in-phase signal based on temperature, and a reference signal defined by the phase of the electrical signal.

In one aspect, the method600comprises operating a transmitter560and receiver300of an optically isolated probe. The transmitter560sends an optical signal containing a combined electrical signal. The receiver300receives the combined electrical signal wherein the electrical signal comprises a first signal and a second signal. The receiver300determines a compensation type. The compensation type comprises at least one of a gain or attenuation compensation or a phase compensation. The magnitude correction circuit310determines a gain or attenuation of the second signal. The phase correction circuit324determines a phase shift of the second signal. The variable gain amplifier308calculates a compensated first signal based on the gain or attenuation of the second signal. The modulator circuit336calculates a phase compensated second signal based on the phase shift of the second signal. The mixer316modulating the compensated first signal with the phase compensated second signal.

In one aspect, the method600further comprises combining601the first signal and the second signal. In one aspect, the method600further comprises summing by the summation circuit468the first signal and the second signal into the electrical signal.

In one aspect, the method600further comprises the electrical to optical converter470converting the electrical signal to the optical signal.

In one aspect, the method600further comprises the optical to electrical converter306converting the optical signal to an electrical signal.

Having thus described several aspects and embodiments of the technology of this application, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those of ordinary skill in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described in the application. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described. In addition, any combination of two or more features, systems, articles, materials, and/or methods described herein, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.

In most embodiments, a processor may be a physical or virtual processor. In other embodiments, a virtual processor may be spread across one or more portions of one or more physical processors. In certain embodiments, one or more of the embodiments described herein may be embodied in hardware such as a Digital Signal Processor (DSP). In certain embodiments, one or more of the embodiments herein may be executed on a DSP. One or more of the embodiments herein may be programmed into a DSP. In some embodiments, a DSP may have one or more processors and one or more memories. In certain embodiments, a DSP may have one or more computer readable storages. In many embodiments, a DSP may be a custom designed ASIC chip. In other embodiments, one or more of the embodiments stored on a computer readable medium may be loaded into a processor and executed.

Also, as described, some aspects may be embodied as one or more methods. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified.

The terms “approximately” and “about” may be used to mean within +20% of a target value in some embodiments, within +10% of a target value in some embodiments, within +5% of a target value in some embodiments, and yet within +2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. The transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively.

Where a range or list of values is provided, each intervening value between the upper and lower limits of that range or list of values is individually contemplated and is encompassed within the disclosure as if each value were specifically enumerated herein. In addition, smaller ranges between and including the upper and lower limits of a given range are contemplated and encompassed within the disclosure. The listing of exemplary values or ranges is not a disclaimer of other values or ranges between and including the upper and lower limits of a given range.

The use of headings and sections in the application is not meant to limit the disclosure; each section can apply to any aspect, embodiment, or feature of the disclosure. Only those claims which use the words “means for” are intended to be interpreted under 35 USC 112 (f). Absent a recital of “means for” in the claims, such claims should not be construed under 35 USC 112. Limitations from the specification are not intended to be read into any claims, unless such limitations are expressly included in the claims.

Embodiments disclosed herein may be embodied as a system, method or computer program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module,” or “system.” Furthermore, embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.