USOO92941 OOB2
`
`(12) United States Patent
`Van Zyl
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 9.294,100 B2
`Mar. 22, 2016
`
`(54)
`
`(71)
`
`(72)
`(73)
`
`(*)
`
`(21)
`(22)
`(65)
`
`(60)
`
`(51)
`
`(52)
`
`(58)
`
`FREQUENCY TUNING SYSTEMAND
`METHOD FOR FINDING A GLOBAL
`OPTIMUM
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`Applicant: Advanced Energy Industries, Inc., Fort
`Collins, CO (US)
`Inventor: Gideon Van Zyl. Fort Collins, CO (US)
`Assignee: Advanced Energy Industries, Inc., Fort
`Collins, CO (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 66 days.
`Appl. No.: 14/094,520
`
`Notice:
`
`Filed:
`
`Dec. 2, 2013
`
`Prior Publication Data
`US 2014/O1550O8 A1
`Jun. 5, 2014
`
`Related U.S. Application Data
`Provisional application No. 61/733,397, filed on Dec.
`4, 2012.
`
`(2006.01)
`(2006.01)
`
`Int. C.
`H04B I/04
`HO3L I/00
`U.S. C.
`CPC ........................................ H03L I/00 (2013.01)
`Field of Classification Search
`CPC ......................................................... HO4B 1/04
`USPC .................................. 455/120, 121, 122, 125
`See application file for complete search history.
`
`2, 2000 Wilbur
`6,020,794. A
`7,839.223 B2 * 1 1/2010 Van Zyl et al. ................. 331/35
`RE42,917 E * 1 1/2011 Hauer et al. .......
`315, 111.21
`2011/0148303 A1* 6/2011 Van Zyl et al. .......... 315/111.21
`2012/0152914 A1* 6, 2012 Matsuura ................. 219,121.42
`OTHER PUBLICATIONS
`
`Mitrovic, Bayer, “International Search Report and Written Opinion
`re Application No. PCT/US2013/072748, Feb. 25, 2014, p. 9, Pub
`lished in: AU.
`Nickitas-Etienne, “International Preliminary Report on Patentability
`re Application No. PCT/US2013/072748, Jun. 18, 2015, p. 6, Pub
`lished in: CH.
`
`* cited by examiner
`Primary Examiner — Sanh Phu
`(74) Attorney, Agent, or Firm — Neugeboren O'Dowd PC
`
`ABSTRACT
`(57)
`A generator and method for tuning the generator are dis
`closed. The method includes setting the frequency of power
`applied by the generator to a current best frequency and
`sensing a characteristic of the power applied by the generator.
`A current best error based upon the characteristic of the power
`is determined, and the frequency of the power at the current
`best frequency is maintained for a main-time-period. The
`frequency of the power is then changed to a probe frequency
`and maintained at the probe frequency for a probe-time
`period, which is less than the main-time-period. The current
`best frequency is set to the probe frequency if the error at the
`probe frequency is less than the error at the current best
`frequency.
`
`15 Claims, 9 Drawing Sheets
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`RENO EXHIBIT 2020
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`
`

`

`U.S. Patent
`U.S. Patent
`
`Mar. 22, 2016
`Mar.22, 2016
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`Sheet 1 of 9
`Sheet 1 of 9
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`US 9.294,100 B2
`US 9,294,100 B2
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`U.S. Patent
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`Mar. 22, 2016
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`Sheet 2 of 9
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`U.S. Patent
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`Mar. 22, 2016
`
`Sheet 3 of 9
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`US 9.294,100 B2
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`U.S. Patent
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`Mar. 22, 2016
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`Sheet 4 of 9
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`US 9.294,100 B2
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`U.S. Patent
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`Mar. 22, 2016
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`Sheet 5 Of 9
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`U.S. Patent
`U.S. Patent
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`Mar. 22, 2016
`Mar.22, 2016
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`Sheet 6 of 9
`Sheet 6 of 9
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`US 9.294,100 B2
`US 9,294,100 B2
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`U.S. Patent
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`Mar.22, 2016
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`Mar. 22, 2016
`Mar.22, 2016
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`Sheet 8 of 9
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`Mar. 22, 2016
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`Sheet 9 Of 9
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`US 9.294,100 B2
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`US 9,294,100 B2
`
`1.
`FREQUENCY TUNING SYSTEMAND
`METHOD FOR FINDING A GLOBAL
`OPTIMUM
`
`PRIORITY
`
`The present application for patent claims priority to Provi
`sional Application No. 61/733,397 entitled “STEALTHY
`FREQUENCY TUNING ALGORITHM CAPABLE OF
`FINDING A GLOBAL OPTIMUM filed Dec. 4, 2012, and
`assigned to the assignee hereof and hereby expressly incor
`porated by reference herein.
`
`FIELD OF THE INVENTION
`
`10
`
`15
`
`This invention relates generally to power Supplies for
`plasma processing applications, and more particularly to sys
`tems and methods for frequency tuning power Supplies.
`
`BACKGROUND OF THE INVENTION
`
`Frequency tuning in RF generators is often used to reduce
`reflected power. A typical set-up is shown in FIG. 1. Typi
`cally, but not always, Some type of matching network is used
`to match the load to the generator. By correct design of the
`matching network (either internal to the generator or external
`as shown in FIG. 1), it is possible to transform the impedance
`of the load to a value close to the desired load impedance of
`the generator (either at the RF output connector, typically
`50C2, or at the active devices internal to the generator, typi
`cally some low complex impedance such as 8+3S2) at some
`frequency in the range of frequencies that the generator can
`produce. The measure of how close the load impedance is to
`the desired impedance can take many forms, but typically it is
`expressed as a reflection coefficient
`
`25
`
`30
`
`35
`
`40
`
`where p is the reflection coefficient of the impedance Z with
`respect to the desired impedance Zo and X* means the com
`plex conjugate of X. The magnitude of the reflection coeffi
`cient, p, is a very convenient way of expressing how close
`45
`the impedance Z is to the desired impedance Z. Both Zand
`Zo are in general complex numbers.
`Frequency tuning algorithms and methods try to find the
`optimal frequency of operation. Optimality is often defined as
`the frequency where the magnitude of the reflection coeffi
`cient with respect to the desired impedance is the Smallest.
`Other measures may be minimum reflected power, maximum
`delivered power, stable operation etc. On a time-invariant
`linear load, many algorithms will work well, but on time
`varying and/or nonlinear loads special techniques are
`required to ensure reliable operation of the tuning algorithm.
`Assuming that the optimum frequency of operation is the
`frequency at which the load reflection coefficient magnitude
`is at its minimum, it is noted that the relationship between the
`controlled variable (frequency) and the erroris frequently not
`monotonic and furthermore the optimum point of operation is
`generally at a point where the gain (change in error/change
`in frequency) is Zero. To add to the challenges it is also
`possible that local minima may exist in which any control
`algorithm can get trapped. FIG. 2A shows a plot of load
`reflection coefficient on a load reflection coefficient chart
`(Smith chart) at the top, and FIG. 2B shows the magnitude of
`
`50
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`55
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`2
`the load reflection coefficient used as the error as a function of
`frequency. This plot demonstrates the problems described
`above with a local minimum at f separated from the global
`optimum at f by a region of high load reflection coefficient
`around f, and (as is invariably the case) Zero slope of the error
`function at the global optimum frequency f.
`Two common problems on plasma loads are the nonlinear
`nature of the load (the load impedance is a function of power
`level) and that the load impedance changes over time (e.g.,
`because of changing chemistry, pressure, temperature etc.
`over time). Another problem that is unique to plasma (or
`plasma-like) loads is that the plasma can extinguish if the
`delivered power to the plasma falls below some value for a
`long enough time. The frequency-tuning algorithm can there
`fore not dwell at a frequency where enough power cannot be
`delivered for very long or the plasma may extinguish.
`
`SUMMARY
`
`Illustrative embodiments of the present disclosure that are
`shown in the drawings are Summarized below. These and
`other embodiments are more fully described in the Detailed
`Description section. It is to be understood, however, that there
`is no intention to limit the disclosure to the forms described in
`this Summary or in the Detailed Description. One skilled in
`the art can recognize that there are numerous modifications,
`equivalents, and alternative constructions that fall within the
`spirit and scope of the disclosure as expressed in the claims.
`According to one aspect, a method fortuning a generator is
`provided. The method includes setting the frequency of
`power applied by the generator to a current best frequency
`and sensing a characteristic of the power applied by the gen
`erator. A current best error is then determined based upon the
`characteristic of the power, and the frequency of the power is
`maintained at the current best frequency for a main-time
`period. The frequency of the power is changed to a probe
`frequency and maintained at the probe frequency for a probe
`time-period, which is less than the main-time-period. The
`current best frequency is set to the probe frequency if the error
`at the probe frequency is less than the error at the current best
`frequency.
`According to another aspect, a generator is provided. The
`generator may include a controllable signal generator to gen
`erate a frequency in response to a frequency control signal
`and a power amplifier to generate power at the generated
`frequency. An output line of the generator is coupled to the
`power amplifier, and a sensor is coupled to the power ampli
`fier to provide an output signal indicative of an impedance
`presented to the power amplifier. A controller provides the
`frequency control signal to the controllable signal generator
`in response to the output signal from the sensor, and the
`controller includes a processor and a non-transitory, tangible
`computer readable storage medium encoded with processor
`readable instructions for adjusting the frequency control sig
`nal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a system schematic showing generator delivering
`power to a load through a matching network;
`FIGS. 2A and 2B depict general behavior of load reflection
`coefficient as a function of frequency;
`FIGS. 3A and 3B depict general behavior of load reflection
`coefficient as a function of frequency overlaid with open loop
`constant power contours of a typical RF generator,
`
`

`

`US 9,294,100 B2
`
`3
`FIGS. 4A and 4B depict general behavior of load reflection
`coefficient as a function of frequency overlaid with open loop
`constant power contours of a RF generator with matched
`Source impedance;
`FIG. 5 is a flowchart depicting an exemplary method that
`may be traversed in connection with the embodiments dis
`closed herein;
`FIG. 6 includes graphs depicting exemplary frequencies
`that may be probed in connection with the method described
`with reference to FIG. 5 and corresponding error values:
`FIG. 7 is a diagram depicting an embodiment of a genera
`tor;
`FIG. 8 is a diagram depicting an exemplary embodiment of
`the balanced amplifiers shown in FIG. 7; and
`FIG. 9 is a diagram depicting a control system that may be
`utilized to realize the controller depicted in FIG. 7.
`
`10
`
`15
`
`4
`(e.g., as described in U.S. Pat. No. 7,839,223, which is incor
`porated herein by reference) is difficult because each candi
`date frequency may have to be visited multiple times until the
`load reflection coefficient is measured at the desired power
`level. The reason why the load reflection coefficient must be
`measured at the correct power level is due to the nonlinear
`nature of the load and can be understood by referring to FIGS.
`3A and 3B.
`Referring to FIGS. 3A and 3B, if the generator is operating
`at 700 W at a frequency f. and probes the frequency space
`with the control to the power amplifier remaining at the cur
`rent setting, the generator would find the apparent best reflec
`tion coefficientata frequency f. However, as FIG.3B shows,
`the actual best operating frequency is f. More damaging, if
`the generator were to change its operating frequency to f,
`then once the control system adjusts the power back to the
`desired setpoint (presumably 700 W or higher), the load
`reflection coefficient may be higher than at the original fre
`quency, f. Moreover, for the generator to be operating at f at
`700 W generally means that either the setpoint for the gen
`erator is 700 W and the generator is capable of meeting the
`setpoint while applying power into the mismatched load
`impedance, or the setpoint for the generatoris higher than 700
`W but the generator can only deliver 700 W into the mis
`matched load. In either case, once the frequency is changed to
`f, it is likely that the generator will only be capable of
`delivering less power than what it could deliver at f. This can
`result in the plasma extinguishing if the frequency is changed
`to f. Thus it may be concluded that for a typical generator
`where, for a fixed control input to the power amplifier, maxi
`mum power is delivered to an impedance other than a
`matched load (typically 502), the procedure described in
`U.S. Pat. No. 7,839,223 is advisable.
`However, when the frequency-probing algorithm is com
`bined with a power amplifier with a source impedance
`matched to the nominal load impedance (typically 50C2) the
`algorithm can be simplified. To understand why, reference is
`made to FIG. 4. Assuming that the generator is operating at
`frequency f. at a power level of 300 W. If the probing algo
`rithm finds a frequency, f, at which the reflection coeffi
`cient is lower than at f it also means that if the generator were
`to simply stay at this frequency, f, the output power from
`the generator will be higher than the power at f, until the
`control loop of the generator adjusts the power back down to
`the setpoint. This is so because for a matched source imped
`ance generator, output power increases if the control input to
`the power amplifier of the generator is held constant and the
`load reflection coefficient is decreased. Thus, in the case of a
`generator with a matched source impedance, there is no need
`to do multiple probes of the same frequency, each time adjust
`ing the control input to the power amplifier. Instead of build
`ing a table, the generator can simply Switch to operation at the
`probed frequency when the load reflection coefficient at the
`probed frequency is lower than the current frequency since
`the generator can deliver at least as much power at the new
`frequency as at the old.
`To describe the algorithm the following variables are
`defined:
`f: start frequency
`f: minimum frequency
`f: maximum frequency
`e
`error at current best frequency
`f: current best frequency
`t: time that the generator stays at current best frequency
`time that the generator takes to probe a frequency
`to at a
`probe
`probe frequency
`probe
`
`faipa
`
`DETAILED DESCRIPTION
`
`30
`
`35
`
`40
`
`45
`
`The word “exemplary' is used herein to mean “serving as
`an example, instance, or illustration.” Any embodiment
`described herein as “exemplary' is not necessarily to be con
`Strued as preferred or advantageous over other embodiments.
`Embodiments of the current invention solve the problem of
`finding a global optimum to the tuning problem without extin
`25
`guishing a plasma load. The problem can be understood by
`referring to FIGS. 2A and 2B. As is evident from FIGS. 2A
`and 2B, any algorithm that searches for a local minimum of
`the load reflection coefficient will move towards the mini
`mum frequency, f, if the current frequency is between f and
`the frequency where the load reflection coefficient is highest,
`f. This situation, where the current frequency will move
`towards a local minimum, which is not the desired operating
`frequency, is quite common. In plasma systems in particular,
`the plasma chamber without a lit (ignited) plasma has a very
`different behavior than the chamber with a lit plasma. If the
`frequency where the plasma can be ignited is between f and
`f, then the initial frequency will be between f and f. Once
`the plasma is lit, the problem becomes how to find the global
`best frequency, f, starting from a frequency between f and
`f. Unlike other loads, simply Sweeping the frequency from fo
`to f until the globally optimum frequency, f is found is not
`an option. The problem is that when the frequency is in the
`vicinity off, almost no power can be delivered to the plasma
`and the plasma will very likely extinguish. If the plasma
`extinguishes, the Sweep will then continue with an unlit
`plasma with completely different characteristics and the glo
`ball optimum f, will not be found unless the plasma Somehow
`reignites in the vicinity off. Even if the plasma somehow
`reignites and the Sweep is thus successful, the very act of
`allowing the plasma to extinguish during the Sweep is unac
`ceptable in most applications.
`To understand the problem, note that in order not to extin
`guish the plasma, the time spent probing a frequency can
`typically be no longer than a few tens of microseconds. If the
`load reflection coefficient at the frequency being probed is
`high and more than a few tens of microseconds are spent at
`that frequency, the plasma can extinguish. At the same time,
`the time that it takes the power control system of the generator
`to adjust to the desired power level is typically on the order of
`a few hundreds of microseconds, so for all practical purposes
`the reflection coefficient of the load is measured at the same
`power control input to the power amplifier with the actual
`power determined by the load impedance.
`In the prior art it is known that a table of frequencies and
`associated reflection coefficients is compiled by probing to
`find the best operating frequency. Compiling Such a table
`
`50
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`

`US 9,294,100 B2
`
`10
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`15
`
`5
`Referring next to FIG. 5, it is a flowchart depicting a
`method for frequency tuning. While referring to FIG. 5,
`simultaneous reference is made to FIG. 6, which includes
`graphs depicting exemplary frequencies (and corresponding
`error values) that may be probed in connection with the
`method described with reference to FIG. 5. As depicted, the
`frequency of the generator is initially set to a start frequency,
`f, which is a frequency at which the plasma may be ignited
`(Block 500). An error is then determined. (Block 502), and
`the current best frequency (e.g., f) is initially set to the
`start frequency (f) while the error at the current best fre
`quency (e.g., e) is set to the error determined at Block
`502. In several embodiments, the error is a measure of how
`close the impedance presented to the generator is to a desired
`impedance (e.g., 5092). For example, the error may be calcu
`lated as a load reflection coefficient magnitude, Voltage stand
`ing wave ratio, reflected power, and a deviation from maxi
`mum delivered power. And in other embodiments, the error
`may be a value representative of an instability. It is contem
`plated that other values may be calculated or measured and
`utilized as an error value.
`As depicted in FIG. 5, the generator then stays at the
`current best frequency (e.g., f) for a main-time-period
`t
`(Block 504) before Switching to a probe frequency (e.g.,
`f) (Block 506), and the generator remains at the probe
`frequency for a probe-time-period (ta) (Block 508). In
`some embodiments, the probe-time-period (t) at Block
`508 is less than 100 microseconds, and in other embodiments
`the probe time period(t) is less than 10% of time that the
`generator stays at current best frequency (t) at Block 504.
`If the probe error (e.g., etc.) at the probe frequency (e.g.,
`f) is lower than the current best error (e.g., e,,)
`(Block 510), the generator sets the current best frequency
`(f) to the probe frequency (fi) (Block 512). The cur
`rent best error (e) is then determined at the new current
`best frequency (f) (Block 502) and the process is then
`repeated. As depicted, if the probe error (e.g., etc.) at the
`probe frequency (e.g., f) is not less than the current best
`error (e.g., e) (Block 510), the generator frequency is set
`again to the current best frequency (e.g., f) (Block 514),
`and the process is then repeated. FIG. 6 depicts exemplary
`behavior in which two probe frequencies (f,
`and f2)
`are attempted (at times t and t) before the probe error (e-
`robes at time ta) is lower than the current best error, and then
`the error is reduced again at time t at a new probe frequency
`fia that becomes and remains the current best frequency
`through two subsequent frequency probes (fs and fo)
`that result in corresponding errors (es and etc.) that are
`greater than the error (e) at the current best frequency
`f probe4
`The choice of probe frequencies depends on the applica
`tion, but to ensure that the entire frequency range is evaluated,
`an initial Sweep should cover the entire frequency range of the
`generator in frequency steps Small enough to ensure that
`minima in the error are not missed by jumping over areas of
`minimum error. After an initial Sweep a smaller range around
`f, can be probed to refine the tuning. Refining of the range
`can be repeated until the best operating frequency is deter
`mined with Sufficient accuracy.
`The tuning algorithm may be augmented by conditions for
`starting and stopping the tuning algorithm. For example, a
`lower and upper target for the error as well as a time to get to
`the lower target is typically set. The tuning algorithm will
`then attempt to get to the lower target in the allotted time. If it
`reaches the lower target the algorithm stops, and if the allotted
`time is exceeded, the algorithm stops if the error is less than
`the upper target. Once the algorithm is stopped, it is generally
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`re-started when the upper target is exceeded. If the algorithm
`fails to reach the upper or lower targets, errors and warnings
`may be issued to the system controller.
`Referring next to FIG. 7, it is a block diagram depicting
`components of an exemplary embodiment of a generator. As
`shown, the generator includes one or more DC power Supplies
`702 that receive AC power and produce DC power to power a
`radio frequency (RF) power amplifier 704 and a controller
`706. The controller 706 in this embodiment includes a fre
`quency tuning component 708 that provides, responsive to an
`output signal 714 from a sensor 716 that is indicative of an
`impedance presented to the power amplifier 704, a frequency
`control signal 710 to signal generator 712. In response, the
`signal generator 712 generates a particular frequency (e.g.,
`the current best frequency (f) and probe frequencies
`(f)) corresponding to the frequency control signal 710,
`and the power amplifier 704 amplifies the output of the signal
`generator 712 to generate output power 718 at the particular
`frequency.
`FIG. 8 depicts an exemplary balanced amplifier that may
`be utilized in connection with realizing the balanced ampli
`fiers depicted in FIG. 7.
`Referring next to FIG. 9, it depicts an exemplary control
`system 900 that may be utilized to implement the controller
`706 and user interfaces described with reference to FIG. 7.
`But the components in FIG. 9 are examples only and do not
`limit the scope of use or functionality of any hardware, soft
`ware, firmware, embedded logic component, or a combina
`tion of two or more Such components implementing particu
`lar embodiments of this disclosure.
`Control system 900 in this embodiment includes at least a
`processor 901 such as a central processing unit (CPU) or an
`FPGA to name two non-limiting examples. The control sys
`tem 900 may also comprise a memory 903 and storage 908,
`both communicating with each other, and with other compo
`nents, via a bus 940. The bus 94.0 may also linka display 932,
`one or more input devices 933 (which may, for example,
`include a keypad, a keyboard, a mouse, a stylus, etc.), one or
`more output devices 934, one or more storage devices 935,
`and various non-transitory, tangible processor-readable stor
`age media 936 with each other and with one or more of the
`processor 901, the memory 903, and the storage 908. All of
`these elements may interface directly or via one or more
`interfaces or adaptors to the bus 940. For instance, the various
`non-transitory, tangible processor-readable storage media
`936 can interface with the bus 940 via storage medium inter
`face 926. Control system 900 may have any suitable physical
`form, including but not limited to one or more integrated
`circuits (ICs), printed circuitboards (PCBs), mobile handheld
`devices, laptop or notebook computers, distributed computer
`systems, computing grids, or servers.
`Processor(s) 901 (or central processing unit(s) (CPU(s)))
`optionally contains a cache memory unit 902 for temporary
`local storage of instructions, data, or processor addresses.
`Processor(s) 901 are configured to assist in execution of non
`transitory processor-readable instructions stored on at least
`one non-transitory, tangible processor-readable storage
`medium. Control system 900 may provide functionality as a
`result of the processor(s) 901 executing instructions embod
`ied in one or more non-transitory, tangible processor-readable
`storage media, such as memory 903, storage 908, storage
`devices 935, and/or storage medium 936 (e.g., read only
`memory (ROM)). For instance, instructions to effectuate one
`or more steps of the method described with reference to FIG.
`5 may be embodied in one or more non-transitory, tangible
`processor-readable storage media and processor(s) 901 may
`execute the instructions. Memory 903 may read the instruc
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`US 9,294,100 B2
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`tions from one or more other non-transitory, tangible proces
`sor-readable storage media (Such as mass storage device(s)
`935, 936) or from one or more other sources through a suit
`able interface, such as network interface 920. Carrying out
`Such processes or steps may include defining data structures
`stored in memory 903 and modifying the data structures as
`directed by the software.
`The signal input component 950 generally operates to
`receive signals (e.g., digital and/or analog signals) that pro
`vide information about one or more aspects of the RF power
`output 718. For example, the RF sensor 716 may include
`Voltage and/or current sensors (e.g., VI sensors, directional
`couplers, simple Voltage sensors, or current transducers) that
`provide analog Voltage signals, which are received and con
`verted to digital signals by the signal input component 950.
`The signal output component 960 may include digital-to
`analog components known to those of ordinary skill in the art
`to generate the frequency control signal 710 to control the
`frequency of the signal generated by the signal generator 712,
`which may be implemented by any of a variety of signal
`generators known to those of skill in the art. For example, the
`frequency control signal 710 may be a voltage that is varied to
`effectuate (via the signal generator 712) the frequency
`changes that are made to tune the generator as described with
`reference to FIG. 5.
`The memory 903 may include various components (e.g.,
`non-transitory, tangible processor-readable storage media)
`including, but not limited to, a random access memory com
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`ponent (e.g., RAM 904) (e.g., a static RAM “SRAM, a
`dynamic RAM “DRAM, etc.), a read-only component (e.g.,
`ROM905), and any combinations thereof. ROM 905 may act
`to communicate data and instructions unidirectionally to pro
`cessor(s) 901, and RAM 904 may act to communicate data
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`and instructions bidirectionally with processor(s) 901. ROM
`905 and RAM 904 may include any suitable non-transitory,
`tangible processor-readable storage media described below.
`In some instances, ROM 905 and RAM 904 include non
`transitory, tangible processor-readable storage media for car
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`rying out the methods described herein.
`Fixed storage 908 is connected bidirectionally to pro
`cessor(s) 901, optionally through storage control unit 907.
`Fixed storage 908 provides additional data storage capacity
`and may also include any Suitable non-transitory, tangible
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`processor-readable media described herein. Storage 908 may
`be used to store operating system 009, EXECs 910 (ex
`ecutables), data 911, API applications 912 (application pro
`grams), and the like. Often, although not always, storage 908
`is a secondary storage medium (such as a hard disk) that is
`slower than primary storage (e.g., memory 903). Storage 908
`can also include an optical disk drive, a solid-state memory
`device (e.g., flash-based systems), or a combination of any of
`the above. Information in storage 908 may, in appropriate
`cases, be incorporated as virtual memory in memory 903.
`In one example, storage device(s) 935 may be removably
`interfaced with control system 900 (e.g., via an external port
`connector (not shown)) via a storage device interface 925.
`Particularly, storage device(s) 935 and an associated
`machine-readable medium may provide nonvolatile and/or
`Volatile storage of machine-readable instructions, data struc
`tures, program modules, and/or other data for the control
`system 900. In one example, software may reside, completely
`or partially, within a machine-readable medium on Storage
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`device(s)935. In another example, software may reside, com
`pletely or partially, within processor(s) 901.
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`Bus 940 connects a wide variety of subsystems. Herein,
`reference to a bus may encompass one or more digital signal
`lines serving a common function, where appropriate. Bus 940
`may be any of several types of bus structures including, but
`not limited to, a memory bus, a memory controller, a periph
`eral bus, a local bus, and any combinations thereof, using any
`of a variety of bus architectures. As an example and not by
`way of limitation, Such architectures include an Industry
`Standard Architecture (ISA) bus, an Enhanced ISA (EISA)
`bus, a Micro Channel Architecture (MCA) bus, a Video Elec
`tronics Standards Association local bus (VLB), a Peripheral
`Component Interconnect (PCI) bus, a PCI-Express (PCI-X)
`bus, an Accelerated Graphics Port (AGP) bus, HyperTrans
`port (HTX) bus, serial advanced technology attachment
`(SATA) bus, and any combinations thereof.
`Control system 900 may also include an input device 933.
`In one example, a user of control system 900 may enter
`commands and/or other information into control system 900
`via input device(s) 933. Examples of an input device(s) 933
`include, but are not limited to, a touch screen, an alpha
`numeric input device (e.g., a keyboard), a pointing device
`(e.g., a mouse or touchpad), a touchpad, a joyst