Patent Description:
The present invention relates generally to monitoring power, and more particularly, to a method and apparatus for monitoring current provided to a load.

Monitoring current is important in many contexts. For example, electrostatic chucks are used to support workpieces (e.g., wafers) in a variety of processing systems. In a deposition system, for example, an electrostatic chuck may be used to clamp a wafer in place while a thin film is deposited on the wafer. In an etch system, as another example, an electrostatic chuck may be used to clamp a wafer in place while material is being chemically etched from the wafer.

Electrostatic chucks use electrostatic force to hold the workpiece in place. An electrostatic chuck has electrodes that are energized with a clamping voltage, which electrostatically clamps the workpiece to the surface of the electrostatic chuck. The electrodes in the electrostatic chuck are coupled to an electrostatic power supply and a controller. The electrostatic power supply receives the control signal from the controller and generates a clamping voltage adapted to clamp the substrate with a clamping force.

Proper positioning of the workpiece relative to the electrostatic chuck is important at various times before, during, and after typical workpiece processes. For example, it is important to ensure that a workpiece is properly loaded onto the electrostatic chuck before applying the clamping voltage. As another example, it may be desirable to determine whether the workpiece is clamped or unclamped at certain times.

The electrostatic power supply may include a direct current (DC) voltage generator configured to generate a DC clamping voltage for the clamping electrode assembly of the electrostatic chuck and an alternating current (AC) voltage generator configured to generate an AC signal. The position of the workpiece may be detected by monitoring a capacitance of a combination of the workpiece and the electrostatic chuck. For example, when the workpiece is properly positioned on the electrostatic chuck, the sensed capacitance may be higher than when the workpiece is not properly positioned.

The varying level of current provided to the electrostatic chuck (in response to the application of the AC voltage) enables the capacitance of the electrostatic chuck to be monitored, and as a consequence, the position of the workpiece may be monitored by monitoring the current provided to the electrostatic chuck.

Prior art approaches to monitoring current typically utilize a shunt resistor on a return side (between the electrostatic chuck and ground) of the electrostatic chuck power supply because the output side needs to operate in the range of thousands of volts. Low side sensing avoids the problems of isolating the high voltage from the measurement output but often at the expense of noise. High side current sensing avoids the problem of noise but requires a means of isolation. Isolation amplifiers are available that can separate the high voltage output of the electrostatic chuck power supply from the measured signal, but unfortunately, isolation amplifiers typically have a lot of electrical noise that limits the lowest possible resolution of the system.

As processing techniques continue to move to higher power amplifiers with higher output currents, there is need to scale current measurement systems to fit a larger signal by reducing gain. When the current monitor is also used for capacitance sensing, reducing gain drives the relatively small capacitance signal below the noise floor. This causes an unacceptable reduction in the resolution of capacitance measurement abilities. Prior art documents <CIT> and <CIT> describe drive/ current sensing arrangements for electrostatic chucks for wafers, <CIT> general purpose frequency tunable current sensor, none of which splitting up a current sense signal into different frequency band signals, to which different gains are applied, to provide an adjusted signal to an isolation amplifier.

An aspect may be characterized as a current monitor that includes a high-voltage side configured to obtain a signal indicative of current through a conductor and apply different levels of gain to different frequency bands of the signal to produce an adjusted signal, using a high-pass filter and a low-pass filter.

A low-voltage side is electrically isolated from the high-voltage side and configured to split the adjusted signal to produce a plurality of output signals wherein each of the plurality of output signals is indicative of a level of current at one of the different frequency bands. An isolation amplifier is configured to communicate the adjusted signal from the high-voltage side to the low-voltage side while electrically isolating the high-voltage side from the low-voltage side.

Another aspect is a method for monitoring current that comprises obtaining a signal indicative of current through a conductor, splitting the signal into at least two frequency bands to obtain at least two high-voltage-side signals, and separately applying gain to each of the at least two high-voltage-side signals. The at least two high-voltage-side signals are combined to produce an adjusted signal that is communicated to a low-voltage-side via a galvanically isolated path. The adjusted signal is split on the low-voltage-side into at least two frequency bands to obtain at least two output signals, and one or more of the at least two output signals is used to monitor the current in the conductor.

Yet another aspect is a system for current monitoring comprising a power supply configured to apply a voltage to an electrostatic chuck that includes a direct current (DC) component and an alternating current (AC) component. The system also comprises a current monitor that comprises means for obtaining a signal indicative of current through a conductor that couples the power supply to the electrostatic chuck. The system also comprises means for splitting the signal into at least two frequency bands to obtain at least two high-voltage-side signals, means for separately applying gain to each of the at least two high-voltage-side signals, and means for combining the at least two high-voltage-side signals to produce an adjusted signal. In addition, the system comprises means for communicating the adjusted signal to a low-voltage-side via a galvanically isolated path, and the low-voltage-side comprises means for splitting the adjusted signal on the low-voltage-side into at least two frequency bands to obtain at least two output signals. The system also comprises means for using one or more of the at least two output signals to monitor the current in the conductor.

Referring first to <FIG>, shown is an exemplary electrostatic chucking system <NUM>, which is one environment in which embodiments of high side current monitors disclosed herein may be utilized. As depicted, the electrostatic chucking system <NUM> includes an electrostatic chuck power supply <NUM>, a high side current monitor <NUM>, and an electrostatic chuck <NUM>. As shown, the electrostatic chuck <NUM> is positioned within a plasma processing chamber <NUM>, and a workpiece <NUM> is shown clamped to the electrostatic chuck <NUM>. Also shown is a workpiece position module <NUM> that is configured to provide an indication of a position of the workpiece <NUM> based upon current measured by the high side current monitor <NUM>.

In this exemplary application, the plasma processing chamber <NUM> may be realized by chambers of substantially conventional construction (e.g., including a vacuum enclosure which is evacuated by a pump or pumps (not shown)). And, as one of ordinary skill in the art will appreciate, the plasma excitation in the plasma processing chamber <NUM> may be achieved by any one of a variety of sources including, for example, a helicon type plasma source, which includes magnetic coil and antenna to ignite and sustain a plasma <NUM> in the reactor, and a gas inlet may be provided for introduction of a gas into the plasma processing chamber <NUM>.

As depicted, the workpiece <NUM> to be treated (e.g., a semiconductor wafer), is supported at least in part by the electrostatic chuck <NUM>, and power is applied to the electrostatic chuck <NUM> via one or more conductors (e.g., cables). For simplicity only a single conductor <NUM> is shown coupled the electrostatic chuck <NUM>, but it should be recognized that aspects described herein are applicable to monopolar chucks and multipolar chucks. As an example, those of ordinary skill in the art will appreciate that six power lines and six corresponding high side current monitors may be employed in connection with a hexapolar electrostatic chuck.

The electrostatic chuck power supply <NUM> may be realized by any of a variety of known, or yet to be developed, power supplies that are capable of applying a voltage that includes DC and AC components. For example, the electrostatic chuck power supply <NUM> may be capable of applying <NUM> volts DC and <NUM> to <NUM> volts AC (peak-to-peak) at <NUM>, but these voltages and frequency are exemplary only and may vary depending upon the many factors. As discussed above, the DC voltage effectuates a DC clamping voltage at the electrostatic chuck <NUM> that draws the workpiece <NUM> to the electrostatic chuck while the AC voltage may be utilized to detect a position of the workpiece <NUM> relative to the electrostatic chuck <NUM>.

Referring next to <FIG>, shown is an exemplary high side current monitor <NUM> that may be used to realize the high side current monitor <NUM> shown in <FIG>. As shown, a shunt impedance, Z, is disposed along a conduction path that includes a conductor <NUM> that couples a power source such as the electrostatic chuck power supply <NUM> to a node, v1, on one side of the shunt impedance, Z. The conduction path also includes the shunt impedance, Z, and another portion of the conductor <NUM> that couples another side of the shunt impedance, Z, at node v2 to the electrostatic chuck <NUM>. Thus, the shunt impedance, Z, is disposed in a current path from a power source (e.g., the electrostatic chuck power supply <NUM>) to a load (e.g., the electrostatic chuck <NUM>). As a consequence, the voltage across the shunt impedance, Z, (between nodes v1 and v2) varies with the current provided to the electrostatic chuck <NUM>; thus, the voltage between nodes v1 and v2 may be used as a signal that is indicative of the current provided to the electrical load (e.g., the electrostatic chuck <NUM>). As shown, a first lead <NUM> is coupled to the node v1 and a second lead <NUM> is coupled to the node v2. Thus, the signal (indicative of the current) in obtained in the embodiment of <FIG> by coupling the leads <NUM>, <NUM> across the shunt impedance, Z, positioned in a current path of the conductor <NUM>. As discussed above, the voltage applied to v1 may be about <NUM> VDC and the voltage at v2 is a floating ground, which is a local reference that varies with the output voltage of a power source (such as the electrostatic chuck power supply <NUM>). For example, the floating ground at v2 may be about <NUM> volt different than the voltage applied at node v1.

In general, the shunt impedance, Z, is a complex quantity that includes resistive and reactive components, but in many implementations, the shunt impedance, Z, may be implemented as a resistor with a reactance that is substantially zero. As an example, without limitation, the shunt impedance, Z, may be realized by a <NUM>-ohm resistor, and a full-scale current through the shunt impedance, Z, may be <NUM> milliamps. As a consequence, the voltage across the shunt impedance, Z, may be about <NUM> volt or less. Because the voltage differential between v1 and v2 is due to the current, a positive voltage at v1 relative to v2 indicates current is going into the electrostatic chuck <NUM>.

It should be recognized that the shunt impedance, Z, is only one way to sense and obtain a signal indicative of current through the conductor <NUM> and that there are several other ways to sense current such as, for example, Hall effect sensors, fluxgate sensors, and transformers.

As shown, the node, v1, is coupled to a high-voltage-side band splitter <NUM> via the lead <NUM>, and the high-voltage-side band splitter <NUM> is coupled to a gain component <NUM>, which is coupled to a summer <NUM>. The output of the summer <NUM> is coupled to a high-voltage side of an isolation amplifier <NUM>, and a low-voltage side of the isolation amplifier <NUM> is coupled to a low-voltage-side band splitter <NUM>, which provides a plurality of output signals including first output signal <NUM> and a second output signal <NUM>. It should be recognized that the depicted components are intended to convey logical functions and that the functions may be implemented by common underlying physical components or effectuated by a distribution of physical components. For example, a filter and gain amplifier may be implemented by a common operational amplifier (op-amp) or may be implemented by separate physical components. It should also be recognized that the depicted functions may be implemented by hardware or a combination of hardware and software.

In general, the isolation amplifier <NUM> functions to galvanically isolate the high-voltage side of the current monitor <NUM> from the low-voltage side of the current monitor <NUM> while allowing signal information to be passed across a barrier without any ohmic path between input and output.

Isolation can be implemented using an all-analog isolation amplifier. Alternatively, a subcircuit comprised of a non-isolated amplifier followed by an analog-to-digital converter and isolator (which may use optical, capacitive, magnetic principles) may be utilized. An isolated power supply that is independent of the electrostatic chuck power supply <NUM> may be used to power the components of the isolation amplifier. As a specific example, the isolation amplifier <NUM> may be realized by an isolation amplifier identified by part No. ISO224ADWVR sold by Texas Instruments, Inc, which may be powered by an isolated power supply identified by part No. NMS0515C sold by Murata Manufacturing Co. , but it should be recognized that other parts from other sources may be utilized to realize, and provide power to, the isolation amplifier <NUM>.

While referring to <FIG>, simultaneous reference is made to <FIG>, which is a flowchart depicting an exemplary method that may be traversed in connection with the embodiment depicted in <FIG>. In operation, when a power source, such as the electrostatic chuck power supply <NUM>, applies power to a load, such as the electrostatic chuck <NUM> (Block <NUM>), the current through the shunt impedance, Z, will create a voltage signal at the v1 node, which is indicative of the level of current flowing through the shunt impedance, Z (Block <NUM>). The voltage signal (also referred to herein more simply as a signal) is provided to the high-voltage-side band splitter <NUM> and then split into at least two frequency bands by the high-voltage-side band splitter <NUM> to obtain at least two high-voltage-side signals (Block <NUM>). As depicted, the high-voltage-side band splitter <NUM> may include two or more filters and the gain component <NUM> may include the same number of gain amplifiers to produce two or more signals that are summed by the summer <NUM> to produce an adjusted voltage signal that is applied at the high voltage side of the isolation amplifier <NUM>.

In the embodiment depicted in <FIG>, the high-voltage side band splitter <NUM> includes two filters: a high pass filter <NUM> to pass frequencies of the signal above a first frequency (to obtain a first signal <NUM> for a first frequency band) and a low pass filter <NUM> to pass frequencies of the signal below a second frequency to obtain a second signal <NUM> for a second frequency band. In addition, the current monitor <NUM> depicted in <FIG> includes a first gain amplifier <NUM> to apply a first gain level to the first signal <NUM> and a second gain amplifier <NUM> to apply a second gain level to the second signal <NUM>. As shown, the summer <NUM> is positioned and configured to combine the gain-adjusted first signal and the gain-adjusted second signal to produce an adjusted signal that is applied to the isolation amplifier <NUM>.

In some implementations, the low pass filter <NUM> may pass DC information below <NUM> and the high pass filter <NUM> may pass AC information above <NUM>. In many implementations, the filtering is performed in the analog domain by any of a variety of analog filtering techniques such as Sallen-Key filtering, but other types of active filtering and/or passive filtering may be used. In some implementations, the high pass filter <NUM> and associated first gain amplifier <NUM> (gain = x amplifier) may be implemented as a single op-amp circuit and the low pass filter <NUM> and associated second gain amplifier <NUM> (gain = y amplifier) may be implemented as another op-amp circuit. It is also contemplated that the voltage signal at v <NUM> may be converted to a digital signal and then filtered, digitally amplified, and summed in the digital domain. In other words, the high pass filter <NUM>, the low pass filter <NUM>, the first gain amplifier <NUM>, the second gain amplifier <NUM>, and the summer <NUM> may be realized by digital components.

Referring again to <FIG>, gain is separately applied to the at least two highside-voltage signals (Block <NUM>). In the implementation depicted in <FIG>, the first gain amplifier <NUM> that applies a gain equal to x is coupled to the high pass filter <NUM>, and a second gain amplifier <NUM> with a gain equal to y is coupled to the low pass filter <NUM> (where x may be equal, or inequal, to y); thus, the DC information (e.g., below <NUM>) and the AC information (e.g., above <NUM>) may be separately amplified with different gain values.

In the context of the electrostatic chucking system <NUM>, the separate amplification beneficially allows the higher-frequency band information (also referred to as AC current information) to be amplified to a much higher level to more accurately detect changes in AC current (which are indicative of changes in the capacitance of the workpiece <NUM> and electrostatic chuck <NUM>). Moreover, the amplification of the constituent components of the voltage signal is beneficially performed before the isolation amplifier <NUM> so that gain in subsequent stages is not required and any noise produced by the isolation amplifier <NUM> is not amplified further.

As shown, the at least two high-voltage-side signals are combined by the summer <NUM> to produce an adjusted signal (Block <NUM>). In the analog domain, the summer <NUM> may also be implemented as an op-amp as one of ordinary skill in the art will appreciate. The isolation amplifier <NUM> is then used to communicate the adjusted signal from the high-voltage side to the low-voltage side while electrically isolating the high-voltage side from the low-voltage side (Block <NUM>). The isolation amplifier <NUM> operates to separate the low-voltage side from the high-voltage side by creating galvanic isolation as is known in the art. Beneficially, the isolation amplifier <NUM> separates the high-voltage-side of the current monitor <NUM> (operating with the floating ground) from the low-voltage side of the current monitor <NUM> (that operates with reference to earth ground); thus, protecting the low-voltage-side from damage.

As shown, the adjusted voltage signal on the low-voltage side (also referred to as a low-voltage-side combined signal) is split by the low-voltage-side band splitter <NUM> to obtain at least two low-voltage-side output signals (Block <NUM>). The low-voltage-side band splitter <NUM> may mirror the high-voltage-side band splitter <NUM> with respect to the number of frequency bands that are used. As shown in <FIG>, the low-voltage-side band splitter <NUM> includes a high pass filter <NUM> and a low pass filter <NUM>, which may have the same frequency response as the high pass filter <NUM> and low pass filter <NUM>, respectively, of the high-voltage-side band splitter <NUM>. In addition, the high pass filter <NUM> and the low pass filter <NUM> on the low voltage side may, or may not, be implemented using the same technology as the high pass filter <NUM> and a low pass filter <NUM> on the high-voltage-filter side. Referring again to <FIG>, the one or more of the at least two low-voltage-side output signals may be used to monitor the current through the conductor <NUM> (Block <NUM>). And in the context of the electrostatic chucking system <NUM>, the monitored higher frequency current (as indicated by the first output signal <NUM>) may be used by the workpiece position module <NUM> to assess a position of the workpiece <NUM>, and the monitored lower frequency current (as indicated by the second output signal) may be used to assess leakage current in the electrostatic chuck <NUM>.

As an example of the overall method of the electrostatic chucking system <NUM>, assume the DC current through the shunt impedance, Z, is <NUM> milliamps and the impedance of the shunt impedance, Z, is <NUM> ohms (without any reactive component), to produce <NUM> volt across the shunt impedance, Z. Further assume that the gain of y is set to be equal to <NUM> and the gain of x is set to equal <NUM>. The low pass filter <NUM> will produce a voltage signal of <NUM> VDC and the corresponding second gain amplifier <NUM> will apply unity gain to produce <NUM> VDC. In turn, the isolation amplifier <NUM> will show <NUM> VDC as an output and the low pass filter <NUM> on the low-voltage-side will produce <NUM> VDC relative to earth ground.

With respect to the AC component (for calculating capacitance), assume a <NUM> signal is inserted (e.g., by the electrostatic chuck power supply <NUM>) to produce AC current of <NUM> across the shunt impedance, Z. If a <NUM> milliamp peak-to-peak current is produced, the high pass filter <NUM> is going to "see" <NUM> millivolts AC on top of <NUM> VDC and pass <NUM> millivolts AC, which is amplified by <NUM> by the second gain amplifier <NUM> to produce a signal of <NUM> volts peak-to-peak. Given the output of the isolation amplifier <NUM> is +/- <NUM> volts, the AC signal may be amplified to occupy a greater range of the isolation amplifier <NUM>. At the output of the low-voltage-side there may be two signals: a <NUM> volt DC signal and a <NUM> volt AC peak-to-peak signal. Beneficially, the gains of the high-pass and low pass processing chains may be set so that when a maximum capacitive load is observed with the maximum DC current, the rails of the isolation amplifier <NUM> do not exceed specifications of the isolation amplifier <NUM> (so clipping does not occur). This capability contrasts with prior art approaches that simply allow a setting of volts per amp. Moreover, prior art systems employ gain amplification after an isolation amplifier, which amplifies the inherent noise of the isolation amplifier.

To detect a position of the workpiece <NUM> in the context of the electrostatic chucking system <NUM>, the relationship between capacitance and positions of workpiece may be empirically determined, and threshold capacitances may be established that are indicative of, for example, the workpiece <NUM> in place or the workpiece <NUM> in clamp. The threshold capacitance values may be stored in nonvolatile memory in connection with workpiece position data to enable a mapping between capacitance values and workpiece position. The workpiece position module <NUM> may use the empirically obtained data in connection with the current measurements (e.g., higher frequency measurements obtained from the first output signal <NUM>) to obtain a capacitance seen at the electrostatic chuck <NUM>. As those of ordinary skill in the art readily appreciate, capacitance of a load may be determined based upon the time-varying AC voltage and current as follows: <MAT>.

Once the capacitance of the load (e.g., the combination of the electrostatic chuck <NUM> and the workpiece <NUM>) is obtained, the position of the workpiece <NUM> may be obtained from nonvolatile memory.

The second output signal <NUM> beneficially provides an indication of low frequency current through the conductor <NUM>, which typically provides an indication of a level of low frequency (e.g., below <NUM>) leakage current in the electrostatic chuck <NUM>. In many instances, the low frequency current (indicative of leakage current) may be below <NUM>.

As described above, the functions and methods described in connection with the embodiments disclosed herein may be effectuated utilizing hardware, in processor executable instructions encoded in non-transitory machine readable medium, or as a combination of the two. Referring to <FIG> for example, shown is a block diagram depicting physical components that may be utilized to realize one or more aspects of the high side current monitor <NUM> and its various embodiments (such as the current monitor <NUM>). Moreover, the multiple instances of the computing device depicted in <FIG> may be implemented in the systems described herein. As shown, in this embodiment a display <NUM> and nonvolatile memory <NUM> are coupled to a bus <NUM> that is also coupled to random access memory ("RAM") <NUM>, a processing portion (which includes N processing components) <NUM>, a field programmable gate array (FPGA) or microcontroller1127, and a transceiver component <NUM> that includes N transceivers. Although the components depicted in <FIG> represent physical components, <FIG> is not intended to be a detailed hardware diagram; thus, many of the components depicted in <FIG> may be realized by common constructs or distributed among additional physical components. Moreover, it is contemplated that other existing and yet-to-be developed physical components and architectures may be utilized to implement the functional components described with reference to <FIG>.

The display <NUM> generally operates to provide a user interface for a user, and in several implementations, the display <NUM> is realized by a touchscreen display. For example, display <NUM> can be implemented as a part of the high side current monitor <NUM> to enable a user to control gain settings of the first gain amplifier <NUM> and second gain amplifier <NUM> and/or time constants of the high pass filter <NUM> and low pass filter <NUM>. The display <NUM> may also be utilized as a part of the workpiece position monitor to display information about the position of the workpiece <NUM>.

In general, the nonvolatile memory <NUM> is non-transitory memory that functions to store (e.g., persistently store) data and machine readable (e.g., processor executable) code (including executable code that is associated with effectuating the methods described herein). In some embodiments, for example, the nonvolatile memory <NUM> includes bootloader code, operating system code, file system code, and non-transitory processor-executable code to facilitate the execution of the methods described with reference to <FIG> described above. The nonvolatile memory <NUM> may also be used to store empirically obtained data that relates workpiece position to capacitance data.

In many implementations, the nonvolatile memory <NUM> is realized by flash memory (e.g., NAND or ONENAND memory), but it is contemplated that other memory types may also be utilized. Although it may be possible to execute the code from the nonvolatile memory <NUM>, the executable code in the nonvolatile memory is typically loaded into RAM <NUM> and executed by one or more of the N processing components in the processing portion <NUM>.

In operation, the N processing components in connection with RAM <NUM> may generally operate to execute the instructions stored in nonvolatile memory <NUM> to realize the functionality of one or more components of embodiments of the high side current monitor <NUM> and/or the workpiece position module <NUM>. As one of ordinary skill in the art will appreciate, the processing portion <NUM> may include a video processor, digital signal processor (DSP), graphics processing unit (GPU), and other processing components. In digital implementations, a DSP may be used to effectuate the high pass filter <NUM>, low pass filter <NUM>, first gain amplifier <NUM>, and second gain amplifier <NUM> depicted in <FIG>.

In addition, or in the alternative, the field programmable gate array (FPGA) <NUM> may be configured to effectuate one or more aspects of the functions and methodologies described herein. For example, non-transitory FPGA-configuration-instructions may be persistently stored in nonvolatile memory <NUM> and accessed by the FPGA <NUM> (e.g., during boot up) to configure the FPGA <NUM> to effectuate the functions of the current monitor <NUM>.

If the computing device <NUM> is implemented to realize the workpiece position module <NUM> (as a separate component from the high side current monitor <NUM>), the input component may operate to receive signals (e.g., from the high side current monitor <NUM>) that are indicative of the monitored current. The output component generally operates to provide one or more analog or digital signals to effectuate an operational aspect of components described herein. For example, if the computing device <NUM> is implemented as a part of the high side current monitor <NUM>, the output portion may transmit output signal(s) (e.g., first output signal <NUM> and second output signal <NUM>) indicative of current levels to the workpiece position module <NUM>.

The depicted transceiver component <NUM> includes N transceiver chains, which may be used for communicating with external devices via wireless or wireline networks. Each of the N transceiver chains may represent a transceiver associated with a particular communication scheme (e.g., WiFi, Ethernet, Profibus, etc.).

Claim 1:
A current monitor comprising:
a high-voltage side configured to obtain a signal indicative of current through a conductor (<NUM>) and apply (<NUM>) different levels of gain to different frequency bands (<NUM>, <NUM>) of the signal to produce an adjusted signal;
a low-voltage side electrically isolated from the high-voltage side and configured to split (<NUM>) the adjusted signal to produce a plurality of output signals (<NUM>, <NUM>), each of the plurality of output signals is indicative of a level of current at one of the different frequency bands; and
an isolation amplifier (<NUM>) configured to communicate the adjusted signal from the high-voltage side to the low-voltage side while electrically isolating the high-voltage side from the low-voltage side, wherein the high-voltage side comprises:
a high-pass filter (<NUM>) to pass frequencies of the signal indicative of current through the conductor above a first frequency to obtain a first signal for a first frequency band; and
a low pass filter (<NUM>) to pass frequencies of the signal indicative of current through the conductor below a second frequency to obtain a second signal for a second frequency band.