Radio frequency power management and optimization

Abstract

Apparatuses, systems, and methods are disclosed to generate and transmit radio frequency (RF) energy by a first device that may be captured by a second device. The captured RF energy may be used to power the second device. The first device may determine a resonant frequency of a variable tank circuit configured to radiate RF energy. In addition, apparatuses, systems, and methods are disclosed to encode communication data onto the transmitted RF energy, optimizing for data pattern sensitivity and device to device variability. These apparatuses and methods may be configured for use with an implant (e.g., nerve stimulation implant).

Description

RADIO FREQUENCY POWER MANAGEMENT AND OPTIMIZATIONCLAIM OF PRIORITY

[0001] This patent application claim priority to U.S. provisional patent application no. 63 / 481,601, titled “RADIO FREQUENCY POWER MANAGEMENT AND OPTIMIZATION,” filed on January 25, 2023, herein incorporated by reference in its entirety.INCORPORATION BY REFERENCE

[0002] All publications and patent applications mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.BACKGROUND

[0003] Wireless charging has become universally adopted for use with mobile devices. Wireless charging enables the transfer of energy through the generation, transmission, and reception of radio frequency (RF) energy. RF energy for wireless charging is typically generated in a range of between 80 and 300 KHz, although other frequencies may be used.

[0004] Some wireless charging systems, particularly those with well-controlled physical characteristics (such as element shapes and / or separation distance between transmitters and receivers) may be easily optimized for efficient power transfer. However, some devices with changing or variable geometries may not have a fixed or stable RF transmitter / receiver relationship. These changing physical characteristics may cause an associated wireless charging system to have a varying or changing efficiency with respect to power transfer.

[0005] In some systems, the transmitted RF power that is used to provide power or charge batteries may also be used as a carrier for communication signals. Changing physical characteristics may also affect transmitted and received data based on transmitted RF power.SUMMARY OF THE DISCLOSURE

[0006] Described herein are apparatuses (e.g., systems and device, including hardware, software and firmware) and methods to transmit RF energy and data. In particular, these methods and apparatuses may be used as part of an implantable apparatus for delivering pulsed stimulation to a patient as part of a treatment. Any of the apparatuses and systems may include an inverter configured to deliver an RF drive signal to a variable tank circuit. The variable tank circuit may radiate RF energy to other devices. In general, any of these methodsand apparatuses may be part of, or may include an implant including the pulse generator and power control circuit (which may optionally include a power source, such as a battery, capacitor, etc.), and an external device for communicating with and delivering power to the implant. The implant may include (and may optionally be referred to herein as a microregulator). The external device may be optionally referred to as an energizer. One or more additional external (e.g., outside of the body) device may communicate with and / or may include assist in control, storage and / or communication (e.g., distributing processing and / or control) with one or more other external devices.

[0007] For example, described herein are methods for determining a resonant frequency of a variable tank circuit. Any of the methods may include generating plurality of pulse width modulated (PWM) signals that, in turn, may be used to generate and provide RF signals to the variable tank circuit. An envelope voltage may be monitored while the PWM signals are delivered to the variable tank circuit. A relative peak may indicate a PWM signal frequency near the resonant frequency of the variable tank circuit. In this manner, any of the apparatuses, systems, and methods may track changes in the resonant frequency of a tank circuit and modify the PWM signals accordingly.

[0008] Described herein are apparatuses, systems, and methods for calibrating transmit power of a communication and / or charging system. Example methods described herein can iteratively determine an envelope voltage associated with a radiated RF signal, which may be based on a PWM signal. A duty cycle of the PWM signal may be modified by one or more calibration factors based on the determined envelop voltage.

[0009] Described herein are apparatuses, systems, and methods for transmitting data using RF signals. In some examples, transmit power levels may be based on previous transmit power levels. In this manner, latency effects which may slow a data transfer rate may be overcome.

[0010] Any of the methods described herein may determine a resonant frequency of a variable tank circuit. Any of the methods may include generating a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency, generating, with a variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals, determining, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals, and determining a resonant frequency of the variable tank circuit based on the peak voltage.

[0011] Any of the methods for determining a resonant frequency may further include coupling RF signals from the variable tank circuit to the envelope detector. Any of themethods for determining a resonant frequency may include rectifying, by the envelope detector, the RF signals from the variable tank circuit.

[0012] In any of the methods for determining a resonant frequency, the variable tank circuit may include an inductor and a capacitor configured to radiate RF signals. Any of these apparatuses and methods may include an adjustable capacitance circuit. For example, any of these apparatuses and methods may include a firmware-tunable capacitor (e.g., as part of an RLC circuit) for dynamically tuning the resonant frequency. In any of the methods, the variable tank circuit may include a flexible inductor configured to radiate RF signals. In any of the methods described herein, the variable tank circuit may include a flexible inductor configured to be worn next to a human body.

[0013] Any of the methods for determining a resonant frequency may include generating and / or adjusting a plurality of PWM signals with coarse and / or fine PWM frequency differences. In any of the methods, the envelope detector may determine a peak voltage associated with the coarse PWM signals and the fine PWM signals. In any of the methods described herein, determining the resonant frequency of the variable tank circuit may include determining an association between the peak voltage and the frequency of the associated PWM signal.

[0014] Any of the devices described herein may include a variable tank circuit, one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the communication device to generate a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency, generate, with the variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals, determine, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals, and determine a resonant frequency of the variable tank circuit based on the peak voltage.

[0015] A processor may include hardware that runs the computer program code. Specifically, the term ‘processor’ may include a controller and may encompass not only computers having different architectures such as single / multi-processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other devices.

[0016] Any of the non-transitory computer-readable storage mediums described herein may store instructions that, when executed by one or more processors of a communication device, cause the communication to generate a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency, generate,with a variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals, determine, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals, and determine a resonant frequency of the variable tank circuit based on the peak voltage.

[0017] Any of the methods described herein may calibrate transmission power of a radio frequency (RF) signal generator and may include generating a first pulse width modulated (PWM) signal, transmitting, by a variable tank circuit, a first RF signal based on the PWM signal, determining, with an envelope detector, a first voltage based on a strength of the first RF signal, and generating a first modified PWM signal based, at least in part, on the first voltage.

[0018] Any of the methods may further include transmitting a second RF signal based on the first modified PWM signal. In any of the methods described herein generating the first modified PWM signal may include determining a first proportional adjustment factor based on the first voltage and generating the first modified PWM signal based on the first proportional adjustment factor. In addition to proportional adjustment, these methods and apparatuses may include additional adjustment types (e.g., integral, derivative). Furthermore, the methods may include determining a transmit (TX) scale factor based on the first proportional adjustment factor, wherein the TX scale factor modifies a pulse width of the first PWM signal. Additionally, or alternatively, any of the methods may include determining whether the first proportional adjustment factor is within a predetermined threshold of a constant value and generating a second modified PWM signal when the first proportional adjustment factor is not within the predetermined threshold of the constant value.

[0019] In any of the methods described herein, generating the second modified PWM signal may include generating a second PWM signal based on first modified PWM signal, transmitting a third RF signal based on the second PWM signal, determining a second voltage based on a strength of the third RF signal, and generating a second modified PWM signal based, at least in part, on the second voltage. Furthermore, generating the second modified PWM signal is repeatedly performed for not more than a predetermined number of times.

[0020] In any of the methods described herein, the first RF signal may be generated with an inverter receiving the first PWM signal.

[0021] Any of the communication devices described herein may include a variable tank circuit, one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the communication device to generate a first pulse width modulated (PWM) signal, transmit, by the variable tank circuit, a first RF signal based on the PWM signal, determine, with an envelope detector, a first voltage based on a strength of thefirst RF signal, generate a first modified PWM signal based, at least in part, on the first voltage.

[0022] Any of the non-transitory computer-readable storage mediums described herein may store instructions that, when executed by one or more processors of a communication device, cause the communication to generate a first pulse width modulated (PWM) signal, transmit, by a variable tank circuit, a first RF signal based on the PWM signal, determine, with an envelope detector, a first voltage based on a strength of the first RF signal, and generate a first modified PWM signal based, at least in part, on the first voltage.

[0023] Any of the methods of determining pulse width modulation (PWM) duty cycles to transmit a plurality of data bits described herein may include generating a first steady state voltage associated with a first data bit, wherein the first data bit is associated with a first PWM duty cycle, transmitting a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit, measuring a first transitional voltage associated with the first data bit within the first transitional bit pattern, and determining a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

[0024] In any of the methods described herein the first data bit may be ‘0b’ and the first transitional bit pattern may be ‘ 101 lb. Additionally or alternatively, the first data bit may be ‘ lb’ and the first transitional bit pattern may be ‘0100b.

[0025] In any of the methods described herein, generating the first steady state voltage may include generating a radio frequency (RF) signal with a PWM signal having the first PWM duty cycle. In any of the methods described herein, the first PWM duty cycle is associated with a ‘0b’ data bit.

[0026] In any of the methods described herein, the first steady state voltage and the second transitional voltage may be voltages proportional to a generated radio frequency (RF) signal. Furthermore, in any of the methods described herein, the RF signal may be based on the first and second PWM duty cycles.

[0027] In any of the methods described herein, determining the PWM duty cycles may include generating a second steady state voltage associated with a second data bit, wherein the second data bit is associated with a third PWM duty cycle, transmitting a second transitional bit pattern, wherein the second transitional bit pattern includes the second data bit, measuring a third transitional voltage associated with the second data bit within the second transitional bit pattern, and determining a fourth PWM duty cycle to generate a fourth transitional voltage near the second steady state voltage for the second data bit during thesecond transitional bit pattern, wherein the fourth transitional voltage is within a predetermined threshold of the second steady state voltage.

[0028] Any of the communication devices described herein may include a variable tank circuit configured to transmit a radio frequency signal, an envelope detector configured to generate a voltage based on the transmitted radio frequency signal, one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the communication device to generate, with the envelope detector, a first steady state voltage associated a first data bit, wherein the first data bit is associated with a first PWM duty cycle, transmit a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit, measure a first transitional voltage associated with the first data bit within the first transitional bit pattern, and determine a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

[0029] Any of the non-transitory computer-readable storage mediums described herein may store instructions that, when executed by one or more processors of a communication device, cause the communication to generate, with an envelope detector, a first steady state voltage associated a first data bit, wherein the first data bit is associated with a first PWM duty cycle, transmit a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit, measure a first transitional voltage associated with the first data bit within the first transitional bit pattern, and determine a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

[0030] Any of the methods of pattern dependent power modulation described herein may include determining a binary data value for a first data bit, determining a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit, and selecting a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

[0031] In any of the methods described herein, selecting the PWM duty cycle may include selecting one of four predetermined PWM duty cycles. In any of the methods described herein, selecting the PWM duty cycle may include selecting the PWM duty cycle from a look-up table.

[0032] In any of the methods described herein, the selected PWM duty cycle increases a rate of change of an envelope voltage when the binary data value for the first data bit is different from the binary data value for the second data bit relative to a rate of change of the envelope voltage when the binary data value for the first data bit is the same as the binary data value for the second data bit. Furthermore, the envelope voltage may be proportional to the power of a transmitted RF signal. In any of the methods described herein may further include transmitting the second data bit.

[0033] Any of the communication devices described herein may include a variable tank circuit configured to transmit a radio frequency signal, one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the communication device to determine a binary data value for a first data bit, determine a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit, and select a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

[0034] Any of the non-transitory computer-readable storage mediums described herein may store instructions that, when executed by one or more processors of a communication device, cause the communication to determine a binary data value for a first data bit, determine a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit, and select a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

[0035] All of the methods and apparatuses described herein, in any combination, are herein contemplated and can be used to achieve the benefits as described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] A better understanding of the features and advantages of the methods and apparatuses described herein will be obtained by reference to the following detailed description that sets forth illustrative embodiments, and the accompanying drawings of which:

[0037] FIG. 1 is an example of an apparatus (e.g., system) for radio frequency charging and communication including an internal (e.g., implant with microregulator) and external (e.g., energizer, prescription pad) components.

[0038] FIG. 2 shows an example block diagram of an energizer.

[0039] FIG. 3 is a graph highlighting example signals and waveforms associated with the energizer of FIG. 2.

[0040] FIG. 4 is a flowchart showing an example method for dynamically tuning a radio frequency system having a variable tank circuit.

[0041] FIG. 5 shows a graph illustrating possible signals corresponding to the method of FIG. 4.

[0042] FIG. 6 shows an example block diagram of a firmware stack for controlling RF output power.

[0043] FIG. 7 is a flowchart showing an example method for dynamically scaling RF output power.

[0044] FIG. 8 shows a graph illustrating a relationship between a pulse-width modulated duty cycle and RF output power.

[0045] FIG. 9 shows a graph illustrating an example of bit-pattern dependent hysteresis associated with the energizer of FIG. 2.

[0046] FIG. 10 is a flowchart showing an example method for a progressive data modulation scheme.

[0047] FIG. 11 shows a graph illustrating an example envelope voltage signal associated with the energizer of FIG. 2.

[0048] FIG. 12 is a flowchart showing an example method for determining high and low calibration factors.

[0049] FIG. 13 shows a graph 1300 illustrating the method for determining very high and very low calibration factors.

[0050] FIG. 14 shows a block diagram of a device that may be one example of the energizer of FIG. 1 or the energizer of FIG. 2.DETAILED DESCRIPTION

[0051] The apparatuses (device and systems) and methods described herein may be used to help regulate operation of one or more implants that are configured to apply energy to a region of a subject’s body, such as a nerve (e.g., Vagus nerve). FIG. 1 is an example of an apparatus comprising a system 100 for radio frequency charging and communication. The system 100 may include a controller 110, an energizer 120, and a charge-powered device 130. The charge-powered device 130 may be any feasible device that can store a charge. In particular, the charge-powered device may be an implant, such as an implant for insertion and implantation into the body (e.g., to communicate with and deliver energy to one or more nerves). For example, the charge-powered device 130 may be an electronic pulse generatorconfigured to deliver electrical pulses of stimulation to a patient, including one or more of a patient’s nerves. In some variations, the charge-powered device 130 may be implanted within a patient. In some cases, the charge-powered device 130 may include memory, one or more processors, circuits and devices to generate the electrical pulses. For example, an included processor may generate one or more electrical pulses, each electrical pulse having a particular duration (pulse width), intensity (pulse voltage and / or pulse current), and / or duty cycle. The charge-powered device 130 may include an energy storage device (not shown) such as a battery, capacitor, super-capacitor, or the like. In some examples the apparatus is configured as a batteryless apparatus. The charge-powered device 130 may also include a radio frequency (RF) communication and a charge capturing module (not shown). The RF communication and charge capturing module may transmit and receive communication data through an RF signal. In addition, the RF communication and charge capturing module may also receive and convert RF signals into a charge that may be used to charge the included charge storage device.

[0052] The implant may be covered by a holder or pod, e.g., in some cases the implant may be implanted into a holder that is positioned around the nerve and may hold the implant in position.

[0053] The controller 110, which may be any feasible processing device such as a tablet computer, laptop computer, smart phone, or the like, can control the charge-powered device 130. For example, the controller 110 may instruct the charge-powered device 130 to deliver a specific arrangement of electrical pulses to the patient. That is, the controller 110 may cause the charge-powered device 130 to deliver electrical pulses to the patient with any particular duration, intensity, and / or duty cycle. The controller 110 may include a Bluetooth transceiver to enable Bluetooth communications.

[0054] The energizer 120 may perform at least two operations within the system 100. A first operation may be providing / generating RF energy (e.g., inductive RF charging) to the charge-powered device 130. For example, the energizer 120 may include a RF generation and communication module (not shown) that generates RF signals. In this manner, the generated RF signals may be captured and converted into a charge for the energy storage device within the charge-powered device 130. The energizer 120 may perform a second operation to facilitate communications with the charge-powered device 130. For example, the energizer 120 may include a Bluetooth transceiver to enable Bluetooth communications with the controller 110. Furthermore, the RF generation and communication module can modulate the generated RF signal with data for the charge-powered device 130 (e.g., inductive RF communication). In some embodiments, the energizer 120 may include one or moreprocessors, microcontrollers, state machines, memory and the like that can pass Bluetooth data from the controller 110 to the charge-powered device 130. That is, the energizer 120 can receive Bluetooth data from the controller 110, and convert it into a modulated RF signal for the charge-powered device 130. In some variations, the energizer 120 can also receive a modulated RF signal from the charge-powered device 130 and convert it into Bluetooth data (e.g., Bluetooth pass-through). Thus, the energizer 120 may be a communication device communicating with modulated RF signals and / or Bluetooth signals.

[0055] In some variations, the energizer 120 may be a wearable device. For example, the patient may wear the energizer 120 to provide RF signals to deliver charge to the charge- powered device 130, which may be implanted within the patient. The energizer 120 may include a flexible inductor to generate and radiate the RF signals. The flexible inductor may be part of an inductive / capacitive (LC) tank circuit. However, since the inductor may flex and move, the inductive / capacitive (LC) tank circuit may have a variable resonant frequency based, at least in part, on interactions between the inductor and the physical environment adjacent to the energizer 120.

[0056] In general, the energizer (e.g., external device) may be configured to be worn outside of the body, including worn over the implant. For example, the energizer, including the variable tank circuit, may be configured as a garmentjewelry, bandage, etc. In some cases the energizer may be configured to be worn adjacent to and / or against the subject’s skin over the region of the body (e.g., neck, chest, etc.). In some cases the energizer may include or be integrated with a frame. In some case the energizer may be part of a necklace, belt, strap, patch, etc.

[0057] FIG. 2 shows an example block diagram of an energizer 200. The energizer 200 may be an example of the energizer 120 of FIG. 1. The energizer 200 may include a microcontroller 210, an inverter 220, a tank circuit 230, and an envelope detector 240. Although described as a microcontroller, the microcontroller 210 may be or include a processor, state machine, virtual machine, or any other module, device, or machine capable of performing any of the operations described herein. In some examples, the microcontroller 210 may include a microcontroller with an ARM® core. The microcontroller 210 may generate a pulse- width modulation (PWM) signal 211 and include an analog-to-digital converter (ADC) input to read (sample) an envelope voltage signal 212.

[0058] The inverter 220, coupled to the microcontroller 210, may receive the PWM signal 211 and generate an RF drive signal 221. In some examples, the inverter 220 may include a half-bridge field effect transistor (FET) driver 222 that may be coupled to one or more FETs. In some variations, the inverter 220 may include more, fewer, or othercomponents. The half-bridge FET driver 222 may selectively control the one or more FETs to generate an oscillating RF voltage and / or current based on the PWM signal 211. The oscillating RF voltage and / or current from the one or more FETs may be output as the RF drive signal 221. The characteristics of the RF drive signal 221 may be based, at least in part, on signal characteristics (frequency, duty cycle, and the like) of the PWM signal 211.

[0059] In some examples, the frequency of the RF drive signal 221 may be related to a system clock frequency. For example, the microcontroller 210 may drive or control the PWM signal 211 with respect to a number of system clock cycles. If a system clock is 80 MHz, then one clock cycle corresponds to 12.5 ns. A PWM signal 211 based on a clock cycle count of 615 would have a frequency of about 130 MHz (615 * 12.5 ns). Through any feasible PWM signal 211, the half-bridge FET driver 222 can drive the one or more FETs to generate the RF drive signal 221 with a frequency of about 130 MHz.

[0060] The RF drive signal 221 may be coupled to the tank circuit 230. The tank circuit 230 may include an inductor 231 and a capacitor 232. In some variations, the tank circuit 230 may include more, fewer, or different components. For example, the tank circuit 230 may include additional discrete or parasitic resistance components not shown here. Thus, the tank circuit 230 may be referred to as an LC (inductive / capacitive) tank circuit or an RLC (resistive / inductive / capacitive) tank circuit.

[0061] The tank circuit 230 may transmit (radiate) RF energy provided by the RF drive signal 221. In some examples, as described above, the radiated RF energy may be received by the charge-powered device 130 of FIG. 1. The tank circuit 230 may have a characteristic resonant frequency. (The tank circuit 230 may be a resonant tank circuit.) A resonant frequency refers to the frequency that reactance values associated with the inductor 231 and the capacitor 232 are minimized. When the frequency of the RF drive signal 221, is at or near the resonant frequency of the tank circuit 230, then the tank circuit 230 can operate at or near peak efficiency and generate (radiate) the highest power output.

[0062] The resonant frequency of the tank circuit 230 may be controlled by actual inductance and capacitance values of the inductor 231 and the capacitor 232, respectively. However, the energizer 200 may be flexible and worn by a user causing variable inductance and / or capacitance values. Thus, a fixed PWM signal 211 may not be the correct frequency to allow the tank circuit 230 to operate at or near peak efficiency.

[0063] In some variations, an operating efficiency of the tank circuit 230 may be determined by measuring an envelope voltage signal associated with the tank circuit 230. Typically, the larger the envelope voltage signal, the more RF energy is radiated by the tankcircuit 230. Relatively higher voltages may therefore reflect relatively higher operating efficiencies.

[0064] The envelope detector 240 may be coupled to the tank circuit 230 through an RF sense voltage 233. A portion of the RF energy radiated by the tank circuit 230 may be coupled to the RF sense voltage 233. The envelope detector 240 can convert the RF energy in the RF sense voltage 233 into the envelope voltage signal 212 that may be detected (e.g., sampled) by an ADC included with the microcontroller 210. In some examples, the envelope detector 240 may rectify and smooth the RF signal from the tank circuit 230. To adjust operating efficiency, the microcontroller 210 can modify characteristics of the PWM signal 211 and thereby alter the RF drive signal 221. In some variations, the microcontroller 210 may iteratively sample the envelope voltage signal 212 and adjust the PWM signal 211 to “tune” the efficiency of the tank circuit 230.

[0065] FIG. 3 is a graph 300 highlighting example signals and waveforms associated with the energizer 200 of FIG. 2. The microcontroller 210 may generate a periodic PWM signal 310. The PWM signal 310 may be coupled to an inverter (such as the inverter 220). In turn, the inverter can generate an RF drive signal 320. The RF drive signal 320 may be coupled to a tank circuit (such as the tank circuit 230). Alternatively, 320 may refer to the RF drive signal from the inverter and 320 the resultant signal within the tank circuit (and also the RF sense voltage 233).

[0066] An envelope detector (such as the envelope detector 240) can receive a signal from the tank circuit and generate an envelope voltage signal 330. An ADC of the microcontroller can sample the envelope voltage signal 330 at various times to obtain a measure of RF output of the tank circuit 230.

[0067] In some examples, the system 100 of FIG. 1 and / or the energizer 200 of FIG. 2 may perform a series of operations to generate a PWM signal 211 that enables the tank circuit 230 to efficiently radiate a strong RF field (e.g., operate the tank circuit 230 near an associated resonant frequency).

[0068] FIG. 4 is a flowchart showing an example method 400 for dynamically tuning an RF system having a variable tank circuit. Some examples may perform the operations described herein with additional operations, fewer operations, operations in a different order, operations in parallel, and some operations differently. The method 400 is described below with respect to the energizer 200 of FIG. 2, however, the method 400 may be performed by any other suitable system or device.

[0069] The method 400 begins in block 402 as the microcontroller 210 generates a plurality of coarse PWM signals within a frequency range. Operation of the energizer 200may generally be limited to a frequency range bracketed by a minimum and a maximum operating frequency. In block 402, the microcontroller 210 may generate a plurality of coarse PWM signals, where each of the generated signals has a frequency between the minimum and maximum operating frequencies. As described with respect to FIG. 2, the microcontroller 210 may generate PWM signals based on a system clock. The coarse PWM signals may be “spaced” or separated by an integer interval of system clocks. For example, the frequency of each coarse PWM signal may be generated by adding five system clock periods to the period of the generated signal. In addition, the duty cycle of each of the coarse PWM signals may be the same with respect to each other. For example, the duty cycle of each of the coarse PWM signals may be 50% (or any other feasible fixed amount). In this manner, a full bandwidth of frequencies between the minimum and maximum operating frequencies may be generated without having to generate each possible PWM signal frequency.

[0070] Next, in block 404 the microcontroller 210 measures an envelope voltage associated with each of the coarse PWM signals. The coarse PWM signals generated by the microcontroller may be coupled to the inverter 220 which generates a related RF drive signal 221. The tank circuit 230, which receives the RF drive signal 221, can radiate RF energy . An RF sense voltage 233 from the tank circuit 230 may be converted to an envelope voltage signal 212 by the envelope detector 240 that, in turn, may be sampled by an ADC included with the microcontroller 210. Each envelope voltage measurement may be indicative of the RF output power provided by the tank circuit 230.

[0071] Next, in block 406 the microcontroller 210 determines the frequency of the coarse PWM signal having the largest envelope voltage. Since the microcontroller 210 has measured each envelope voltage associated with each coarse PWM signal, the microcontroller 210 can determine the largest envelope voltage and the frequency of the associated coarse PWM signal. Although the frequency of the coarse PWM signal may provide an improved RF output power, the RF output power based on other frequencies near the frequency of the coarse PWM signal also may be checked to fine tune the PWM signal.

[0072] Next, in block 408 the microcontroller 210 generates a plurality of fine PWM signals near the determined frequency of the coarse PWM signal. For example, the microcontroller 210 may generate PWM signals having slightly higher and slightly lower frequencies than the frequency of the coarse PWM signal. In cases where the generated PWM signal is based on a number of system clock cycles, the fine PWM signals may be based on slightly more and slightly fewer system clock cycles than the number of system clock cycles associated with the frequency of the determined coarse PWM signal. For example, if the coarse PWM signal is based on n system clock cycles, then the fine PWM signals may bewithin 4 system clock cycles of n. That is, the microcontroller 210 may generate up to 9 fine PWM signals (w-4, n-3, ...n, ...n+3, n+4). Although + / - 4 system clocks is described herein, in other embodiments, the fine PWM signals may be within any feasible number of system clock cycles.

[0073] Next, in block 410 the microcontroller 210 measures an envelope voltage associated with each of the fine PWM signals. For example, the RF sense voltage 233 from the tank circuit 230 may be converted to an envelope voltage signal by the envelope detector 240 that, in turn, may be sampled by an ADC included with the microcontroller 210. Each envelope voltage signal measurement may be indicative of the RF output power provided by the tank circuit 230.

[0074] Next, in block 412 the microcontroller 210 determines the frequency of the fine PWM signal having the largest envelope voltage signal. Since the envelope voltage signal may be an indicator as to the RF output power, the largest envelope voltage may indicate that settings of the energizer 200 may be “tuned” to provide the largest amount of RF output power. In other words, the frequency of the fine PWM signal may be the resonant frequency of the tank circuit 230.

[0075] FIG. 5 shows a graph 500 illustrating possible signals corresponding to the method 400 of FIG. 4. In particular, the graph 500 shows possible envelope voltages (envelope voltage signals) corresponding to different frequencies of a generated PWM signal. For example, the graph 500 shows envelope voltages 510 in relation to different PWM signals.

[0076] The graph 500 includes a coarse frequency sweep section 520 corresponding to blocks 402, 404, and 406 of FIG. 4. The coarse frequency sweep section 520 shows envelope voltages associated with a plurality of coarse PWM signals. Although eleven coarse PWM signals are shown here, in other embodiments, the coarse frequency sweep section may include any number of coarse PWM signals.

[0077] The coarse frequency sweep section 520 shows a relative peak of envelope voltage at approximately 129.7 KHz. The frequency of 129.7 KHz may be associated with 617 system clock cycles. Referring back to the discussion of FIG. 4, the number n = 617.

[0078] The graph 500 includes a fine frequency sweep section 530 corresponding to blocks 408, 410, and 412 of FIG. 4. The fine frequency sweep section 530 indicates envelope voltages associated with a plurality of fine PWM signals. Although nine coarse PWM signals are indicated here, in other embodiments, the coarse frequency sweep section may include any number of fine PWM signals.

[0079] The fine frequency sweep section 530 shows a relative peak of envelope voltage at approximately 129.2 KHz. The frequency of 129.2 KHz may be associated with 619 system clock cycles. Thus, the microcontroller 210 would select the PWM signal associated with 619 system clock cycles to generate RF energy through the tank circuit 230. The combination of coarse and fine frequency sweeps shown here may enable the energizer 200 to quickly determine an optimum operating frequency, despite changes to resistance, inductance, or capacitance associated with the tank circuit 230. In some example, performing the operations of the method 400 (illustrated in the graph 500) may only take approximately 10 - 20 milliseconds. Therefore, the method 400 may be performed before each time that the energizer 120 of FIG. 1 generates an RF signal for the charge-powered device 130. This examples illustrates a “full" frequency sweep which may be performed, e.g., when the RF is initially turned on. Any of the apparatuses and methods described herein may also or alternatively performs a “quick” frequency sweep which consists of a fine frequency range surrounding the current (and recently determined) RF frequency. Thus, these methods and apparatuses may include one or more combinations of course + fine and / or fine-only adjustment methods.

[0080] In some variations, the system 100 of FIG. 1 may transmit data between the controller 110 and the charge-powered device 130 through the energizer 120. For example, the controller 110 and the energizer 120 may communicate through Bluetooth or any other feasible wireless or wired communication protocol. The energizer 120 and the charge- powered device 130 may communicate using modulated RF energy. The modulated RF energy may also be used to transmit energy from the energizer 120 to the charge-powered device 130. In some examples, the energizer 120 may “pass through” Bluetooth data from the controller 110 to the charge-powered device 130 by converting the Bluetooth data to modulated RF energy.

[0081] Modulation of RF energy by the energizer 120 may include modulating the amplitude of the RF energy generated by the energizer 120. Accurate data transfer may therefore be reliant on an accurate control of generated RF energy. As described above with respect to FIGS. 2-5, a PWM signal may be used to generate RF energy. In some variations, different duty cycles of the PWM signal may generate and accurately control the amount of RF energy generated by the energizer 120.

[0082] FIG. 6 shows an example block diagram of a firmware stack 600 for controlling RF output power. In some examples, the energizer 120 of FIG. 1 may use a TX parameter to control RF output power. In some examples, the TX value may not change for different data bit types. Instead, a fixed coefficient (e.g., the y value in equations 5, 6, 7 and 8, below) maybe applied to the TX value to generate the steady state PWM signals associated with 1 and 0 bits. For example, a 1 bit might be (TX * 150%) and a 0 bit might be (TX * 50%), assuming y=0.5. Thus, the TX parameter may be provided to an upper level 610 of the firmware stack 600. In a lower level 620 of the firmware stack 600, the TX parameter may be converted to a duty cycle. The duty cycle may be applied to the PWM signal generated by the energizer 120. In some examples, a lower duty cycle may be associated with a lower RF output power and a higher duty cycle may be associated with a higher RF output power. In some cases, a dynamic control of the RF output power may be desired to provide a more accurate and consistent control of RF output power.

[0083] An example relationship between the TX parameter and the RF output power is described below in equation 1 :Where: TX is a transmit power parameter (e.g., an unsigned 8 bit value);Coil Voltage is a measured RF sense voltage; and 250 is a constant.In some examples, the coil voltage may correspond to the measured envelope voltage signal 212 of FIG. 2.

[0084] In some examples, a TX scale factor k may be used to help dynamically adjust the RF output power. An example of using the TX scale factor k is expressed below in equation 2:Where: Pulse Width is a pulse width of the PWM signal; k is a TX scale factor (0 < k < 1);TX is the TX transmit power parameter;Pulse WidthMAx is a maximum pulse width of the PWM signal; and TXMAX is a maximum transmit power.

[0085] In some examples, the TX scale factor k may be adjusted to maintain the relationship described with equation 1. The TX scale factor k may be determined throughiterative measurements and adjustments. An example procedure to determine the scale factor k may be expressed below using equations 3 and 4.Where: p is a proportional adjustment factor;TX is the transmit power parameter;RF Frequency is the frequency of the PWM signal Coil Voltage is the envelope voltage signal; and 250 is a constant.Where: k’ is the new value of the TX scale factor (for use in eq. 2); p is the proportional adjustment factor of eq. 3; and k is the previous value of k’.

[0086] FIG. 7 is a flowchart showing an example method 700 for dynamically scaling RF output power. The method 700 is described below with respect to the energizer 200 of FIG. 2, however, the method 700 may be performed by any other suitable system or device. The method 700 may apply the equations 1-4 to dynamically scale RF output power.

[0087] The method begins in block 702 as the microcontroller 210 determines a pulse width of the PWM signal and generates an RF signal. The microcontroller 210 may determine the pulse width using equation 2. During an initial or first time that operations from block 702 are performed, the TX scale factor k may be 1. For example, using the determined pulse width, the microcontroller 210 can generate the PWM signal 211. Then, using the PWM signal 211, the inverter 220 may generate the RF drive signal 221 thereby enabling the tank circuit 230 to generate an RF signal.

[0088] Next, in block 704 the microcontroller 210 measures an envelope voltage signal associated with the tank circuit 230. For example, the microcontroller 210 may include an ADC coupled to the envelope detector 240 to measure a voltage from the tank circuit 230. In measuring the envelope voltage, the microcontroller 210 may determine the strength of RF energy radiated by the tank circuit 230.

[0089] Next, in block 706 the microcontroller 210 calculates the proportional adjustment factor p and the TX scale factor k. For example, the microcontroller 210 can determine an updated value of the proportional adjustment factor p using the determined envelope voltage as the “coil voltage” in equation 3. Then, using the updated proportional adjustment factor / ;, the microcontroller 210 may determine a new value for the TX scale factor k using equation 4. Note that in some examples, the equation 4 may reduce the proportional adjustment factor p by approximately 25% to avoid overcompensation. In this manner the TX scale factor k and the proportional adjustment factor p are updated.

[0090] Next in block 708, the microcontroller 210 determines whether a number of performed calculations exceeds a predetermined number. For example, the microcontroller 210 can track the number of times the operations associated with block 706 have been performed. In this manner, the microcontroller 210 can control how many iterations through the method 700 can occur. In some variations, the predetermined number may be three. If the number of calculations exceeds the predetermined number, then the method 700 ends. On the other hand, if the number of performed calculations does not exceed the predetermined number, then the method proceeds to block 710.

[0091] In block 710, the microcontroller 210 determines whether the calculated value of the proportional adjustment factor p is sufficiently close to a constant value. In some examples, the constant value is 1. If the proportional adjustment factor p is sufficiently close to 1 (for example, if p is within a threshold amount or predetermined amount of 1), then the method 700 ends. On the other hand, if the proportional adjustment factor p is not sufficiently close to 1, then the method returns to block 702.

[0092] As described above, data may be transmitted from the energizer 120 to the charge- powered device 130 of FIG. 1 by changing (modulating) the amount of radiated or transmitted RF power. For example, a first RF output power (e.g., a first power level) may be associated with a first binary value (e.g., a data bit) and a second RF output power (a second power level) may be associated with a second binary value. In some examples, the first binary value may be a ‘0’ and the second binary value may be a ‘ 1’. In some other examples, the first binary value may be a ‘ 1’ and the second binary value may be a ‘O’. The duty cycle of the PWM signal may control the RF output power levels. Thus, a first duty cycle may generate the first RF power output level to transmit a first binary value and a second duty cycle may generate the second RF output power level to transmit a second binary value. However, the speed with which a change in RF output power can be induced (e.g., can cause a change in the output signal) may affect the accuracy and speed of data transmission.

[0093] FIG. 8 shows a graph 800 illustrating a relationship between PWM duty cycle and RF output power. The graph 800 includes a line representing the envelope voltage signal 802 plotted with respect to time. The envelope voltage signal 802 may be another example of the envelope voltage signal 212 of FIG. 2. During the first time period 810, the envelope voltage signal 802 is shown as stable and at a first value. The value of the envelope voltage signal 802 during the first time period 810 may be associated with a 25% duty cycle of the PWM signal. The 25% duty cycle described here is exemplary and not limiting. Any other feasible duty cycle may be used.

[0094] During a second time period 820, the PWM signal changes to have a 50% duty cycle and accordingly, the envelope voltage signal 802 increases. The 50% duty cycle described here is exemplary and not limiting. Any other feasible duty cycle may be used. In this example, increasing the duty cycle results in a related increase in the envelope voltage signal 802. In another example, increasing the duty cycle may result in a related decrease in the envelope voltage signal 802. Notably, the envelope voltage signal 802 does not increase instantaneously, but instead increases gradually during a “ring up” period. In some examples, the ring up period may be based on a quality factor (Q) of the inductor 231 in the tank circuit 230 as well as the envelope voltage signal 802 voltage change.

[0095] During a third time period 830, the envelope voltage signal 802 reaches a steady state and becomes stable. The time delay denoting the period beginning when the PWM duty cycle increases and ending when the envelope voltage signal 802 reaches the steady state is referred to as a ring-up latency period.

[0096] During a fourth time period 840, the PWM signal changes to have a 25% duty cycle and the envelope voltage signal 802 decreases. Due to the quality factor of the inductor 231, the envelope voltage signal 802 decreases gradually during a “ring down” period. The time delay denoting the period beginning when the PWM duty cycle decreases to when the envelope voltage signal 802 reaches a steady state is referred to as a ring down latency period.

[0097] During a fifth time period 850, envelope voltage signal 802 again reaches a steady state. Because two distinct RF output power levels (based on two PWM signals) may be used to convey two different data bits (logic states), reducing ring up latency and ring down latency may improve data transfer rates. However, in some examples, a previous data bit may affect the ring up or ring down latency time. This bit-pattern dependent envelope voltage signal hysteresis is described in more detail in conjunction with FIG. 9.

[0098] FIG. 9 shows a graph 900 illustrating an example of bit-pattern dependent hysteresis associated with the energizer 200 of FIG. 2. The graph 900 includes a linerepresenting an envelope voltage signal 902 plotted with respect to time. Different RF output power levels may be used to transmit different data bits. The graph 900 also includes transmitted data bits associated with the envelope voltage signal 902. As described above, two different RF output power levels may be used to transmit two different data bits.

[0099] When the energizer 200 transitions from transmitting a first data bit to a different second data bit (e.g., transmit a ‘ 1’ followed by a ‘O’, or transmit a ‘0’ followed by a ‘ 1’), the ring up latency and ring down latency described with respect to FIG. 8 may cause a delay for the envelope voltage signal to reach a steady state. On the other hand, when the energizer 200 transmits two or more identical data bits (e.g., transmit a ‘ 1’ followed by a ‘ 1’, or transmit a ‘0’ followed by a ‘0’), the envelope voltage signal can more easily reach steady state. This behavior is described below.

[0100] For example, in region 910 two consecutive ‘ 1 ’ data bits are transmitted by increasing or setting the PWM duty cycle to 50%. (The 50% duty cycle is merely demonstrative and not limiting.) However due to the ring up latency, the envelope voltage signal 902 may not reach steady state immediately after the first ‘ 1’ data bit is transmitted. As shown, after the second ‘ 1’ bit is transmitted, the envelope voltage signal 902 can more easily reach a steady state voltage that may be associated with a ‘ 1’ data bit.

[0101] In a similar fashion, in region 920 two consecutive ‘0’ data bits are transmitted by decreasing or setting the PWM duty cycle to 25%. Due to the ring down latency, the envelope voltage signal 902 may not become stable after the first ‘0’ bit is transmitted. After the second ‘0’ bit is transmitted, the envelope voltage signal 902 can more easily reach a steady state voltage that may be associated with a ‘0’ data bit.

[0102] In region 930, the PWM duty cycle is decreased from 50% to 25% so that a ‘0’ data bit is transmitted after a ‘ 1’ data bit. Because of ring down latency, the envelope voltage signal 902 may not reach the same steady state voltage as compared to the region 920. In some cases, when envelope voltage signal 902 has not reached the correct level, a data transmission error may occur.

[0103] In region 940, the PWM duty cycle has increased from 25% to 50% so that a ‘ 1’ data bit is transmitted after a ‘0’ data bit. Because of ring up latency, the envelope voltage signal 902 may not reach the same steady state voltage as compared to the region 910. Again, an incorrect envelope voltage signal 902 may cause a data transmission error to occur.

[0104] In some embodiments, a progressive data modulation algorithm may be used to adjust the RF output power based on current and past (previously) transmitted data bits. The progressive data modulation algorithm may use different PWM duty cycles to transmitdifferent data bits, based on previously transmitted data bits. An example method is described in FIG. 10.

[0105] FIG. 10 is a flowchart showing an example method 1000 for a progressive data modulation scheme. The method 1000 is described below with respect to the energizer 200 of FIG. 2, however, the method 1000 may be performed by any other suitable system or device. The method 1000 is described below with reference to a data bit ‘0’ being associated with a lower envelope voltage signal compared to a data bit ‘ 1.’ Persons skilled in the art will recognize that the method 1000 may be modified to accommodate any feasible voltage level / data bit association.

[0106] The method 1000 begins in block 1002 as the microcontroller 210 determines whether a previously transmitted data bit is a ‘0.’ If the previously transmitted data bit is a ‘O’, then in block 1004 the microcontroller 210 determines whether the current data bit to be transmitted is a ‘0.’ If the current data bit to be transmitted is a ‘O’, then two consecutive ‘0’ data bits are to be transmitted. In this case, since the previous data bit and the current data bit are the same, the microcontroller 210 does not need to overcome a large ring down latency. As a result, in block 1006 the microcontroller 210 sets the PWM signal to a duty cycle referred herein to as a “low duty cycle”. With the low duty cycle, PWM signal 211 drives the inverter 220 and the tank circuit 230 to generate envelope voltage signal associated with the ‘0’ data bit. The method returns to block 1002.

[0107] Returning to block 1004, if the data bit is not a ‘O’, then in block 1008, the microcontroller 210 sets the PWM signal to a duty cycle referred to herein as a “very high duty cycle”. Since the previous data bit was a ‘O’, and the next data bit to be transmitted is a ‘ 1’, a relatively large ring up voltage change may be required. Thus, the very high duty cycle may attempt to drive the envelope voltage to a voltage much higher than a voltage level typically associated with the ‘ 1’ data bit. In other words, the very high duty cycle may increase the rate of change of the envelope voltage signal. The method returns to block 1002.

[0108] Returning to block 1002, if the microcontroller 210 has determined that the previous data bit is not a ‘0’ (e.g., the previous data bit is a ‘ 1’), the method 1000 proceeds to block 1010. In block 1010, the microcontroller 210 determines whether the next data bit to be transmitted is a “0”. If the next data bit to be transmitted is a “0” and since the previous data bit is a ‘ 1’, then a relatively large ring down voltage change may be required. Thus, in block 1012, the microcontroller 210 sets the PWM signal to a duty cycle referred to here as a “very low duty cycle”. The very low duty cycle may attempt to drive the envelop voltage signal to a voltage much lower than a voltage level typically associated with the ‘0’ data bit. In otherwords, the very low duty cycle may increase the rate of change of the envelope voltage signal. The method returns to block 1002.

[0109] Returning to block 1010, if the microcontroller 210 determines that the next data bit to be transmitted is not a “0” (e.g., the current transmitted data bit is a ‘ 1 ’), then in block 1014 the microcontroller sets the PWM signal to a duty cycle referred to herein as a “high duty cycle”. The high duty cycle may attempt to drive the RF sense voltage to a voltage associated with the ‘ 1’ data bit. The method returns to block 1002.

[0110] The association between logic states, binary data, and RF power output can be arbitrary. For example, a first logic state may be associated with a “0” data bit or a “1” data bit. In a similar manner, a high RF power output may be associated with any logic state or binary value. Persons skilled in the art will recognize that any logic state or binary data may be associated with any RF power output.[OHl] The operations of the method 1000 may be illustrated in table 1, shown below:Notably, in some examples, operations of the method 1000 may be stored, accessed, and / or executed through a look-up table stored within a memory.

[0112] FIG. 11 shows a graph 1100 illustrating an example envelope voltage signal associated with the energizer 200 of FIG. 2 after performing the method 1000 for applying a progressive data modulation scheme. The graph 1100 includes a line representing an envelope voltage signal 1102 plotted with respect to time. Different PWM duty cycles (which determine different RF output power levels) may be used to transmit different data bits. The graph 1100 also shows transmitted data bits. The envelope voltage signal 1102 shows the results of the progressive data modulation scheme.

[0113] In region 1110, a previous data bit is a ‘ T and the current data bit is also a ‘ 1’ . In this region there is no large ring up voltage (e.g., no large positive voltage change).Therefore, the high duty cycle as described herein may be used to transmit the current databit. In a similar manner, in region 1120, the previous and current data bits are both ‘0.’ In this region there is no large ring down voltage (e.g., no large negative voltage change). Therefore the low duty cycle as described herein may be used to transmit the current data bit.

[0114] In region 1130, the previous data bit is a ‘ 1 ’ and the current data bit is a ‘0’ . Accordingly, there is a large ring down voltage (e.g., a large negative voltage change). In region 1130 a very low duty cycle may be used for the PWM signal. The very low duty cycle may help the envelope voltage signal 1102 overcome any ring down latency. In region 1140, the previous data bit is a ‘0’ and the current data bit is a ‘ I .’ Accordingly, there is a large ring up voltage (e.g., a large positive voltage change). Thus, in region 1140 the very high duty cycle may be used for the PWM signal. The very high duty cycle may help the envelope voltage signal 1102 overcome any ring up latency.

[0115] Definition and determination of pulse widths associated with the high, low, very high, and very low duty cycles are described below with respect to equations 5-8.

[0116] For any given frequency, the pulse width may be used to express and / or specify an associated duty cycle. Any of the duty cycles discussed herein may be expressed with an equation. Equation 5 below may express a pulse width for the high duty cycle:Where: y is a fixed modulation coefficient; k is the TX scale factor (see eq. 2 and 4 above);TX is a desired output transmit power;Pulse WidthMAx is a maximum pulse width of the PWM signal; and TXMAX is a maximum transmit power.

[0117] Equation 6 below may express a pulse width for the low duty cycle:Where: y is the fixed modulation coefficient; k is the TX scale factor (see eq. 2 and 4 above);TX is a desired output transmit power;Pulse WidthMAx is a maximum pulse width of the PWM signal; and TXMAX is a maximum transmit power.

[0118] Equation 7 below may express a pulse width for the very high duty cycle:Where: y is the fixed modulation coefficient; b is a very high calibration factor; k is the TX scale factor (see eq. 2 and 4 above);TX is the desired output transmit power;Pulse WidthMAx is a maximum pulse width of the PWM signal; and TXMAX is a maximum transmit power.

[0119] Equation 8 below may express a pulse width for the very low duty cycle:Where: y is the fixed modulation coefficient; c is a very low calibration factor; k is TX scale factor (see eq. 2 and 4 above);TX is the desired output transmit power;Pulse WidthMAx is a maximum pulse width of the PWM signal; and TXMAX is a maximum transmit power.

[0120] The modulation coefficient can be any feasible number. In some examples, the modulation coefficient y can be 40% (0.4). Essentially, the modulation coefficient sets the difference in duty cycle between the low and high RF output levels. Determination of the b and c calibration factors can be accomplished by placing the energizer 200 into predetermined operating conditions, sampling envelope voltage signals, and iteratively applying approximated b and c calibration factors. An example method is described below in conjunction with FIG. 12.

[0121] FIG. 12 is a flowchart showing an example method 1200 for determining high and low calibration factors. The method 1200 is described below with respect to the energizer 200 of FIG. 2, however, the method 1200 may be performed by any other suitable system or device.

[0122] The method 1200 begins in block 1202 as the microcontroller 210 determines the TX scale factor. For example, the microcontroller 210 may perform one or more operations described with respect to the method 700 of FIG. 7 to determine a PWM signal (e.g., a PWM signal frequency) and a TX scale factor k suitable for the tank circuit 230.

[0123] Next, in block 1204 the microcontroller 210 generates a constant RF output. For example, using the PWM signal and the TX scale factor k determined in block 1202, the microcontroller 210 may cause the inverter 220 and the tank circuit 230 to output a constant RF signal. In some examples, the microcontroller 210 may use equation 5 or 6 as described herein after setting the modulation coefficient to zero (y = 0).

[0124] Next, in block 1206, the microcontroller 210 generates an RF signal associated with a “high” level using a first PWM duty cycle. For example, the microcontroller 210 may generate the PWM signal according to equation 5, however, in this case the modulation coefficient y may be non-zero. The PWM signal, in turn, may generate an RF signal using inverters, tuned circuits, and the like. In some variations, the modulation coefficient may be 40% (0.40). The microcontroller 210 may generate the PWM signal for a sufficient amount of time to allow the envelope voltage signal 212 to reach a high steady state voltage associated with the high level.

[0125] Next, in block 1208 the microcontroller 210 samples (with an ADC, for example) the envelope voltage signal 212 to determine a “high” target voltage. The high target voltage sample enables the microcontroller 210 to learn the steady state envelope voltage associated with the high RF output power.

[0126] Next, in block 1210, the microcontroller 210 generates an RF signal associated with a “low” level using a second PWM duty cycle. For example, the microcontroller 210 may generate the PWM signal according to equation 6 with the modulation coefficient set in a similar manner as for block 1206. The PWM signal, in turn, may generate an RF signal using inverters, turned circuits, and the like. The microcontroller 210 may generate the PWM signal for a sufficient amount of time to allow the envelope voltage signal 212 to reach a low steady state voltage associated with the low level.

[0127] Next, in block 1212 the microcontroller 210 samples the envelope voltage signal 212 to determine a “low” target voltage. The low target voltage sample enables the microcontroller 210 to learn the steady state envelope voltage associated with the low RF output power.

[0128] Next, in block 1214 the microcontroller 210 determines a first calibration factor. In some examples, the determined calibration factor may be a very high calibration factor b as described in equation 7. The very high calibration factor b enables the energizer 200 tomodify the pulse width of the PWM signal to drive the envelope voltage signal to the high steady state voltage faster, and thereby reduce response latency of the envelope voltage signal.

[0129] One example approach to determining the very high calibration factor b may include generating a first estimate of the very high calibration factor / >, transmitting a first transitional bit pattern, and then sampling the envelope voltage to determine if the sampled envelope voltage is close to the high steady state voltage. The microcontroller 210 may then update the estimate of the very high calibration factor b. The microcontroller 210 may iterate the estimation, transmitting, and sampling steps a predetermined number of times or until the sampled envelope voltage is sufficiently close to the high steady state voltage. In some variations, the microcontroller 210 may iterate up to three times. In other embodiments, the microcontroller 210 may iterate any other feasible number of times.

[0130] The first transitional bit pattern may be a bit pattern designed to test transitioning from a low level to a high level and thereby testing the energizer’s ring up time latency. In some examples, the first bit pattern may include 0100b (e.g., a “zero” bit, followed by a “one” bit, followed by two more “zero” bits). This particular bit pattern may enable the microcontroller 210 to determine the envelope voltage associated with the “high” output level when preceded by “low” output level.

[0131] Next, in block 1216 the microcontroller 210 determines a second calibration factor. In some examples, the determined calibration factor may be a very low calibration factor c as described in equation 8. The very low calibration factor c enables the energizer 200 to modify the pulse width of the PWM signal to drive the envelope voltage signal to the low steady state voltage faster, and thereby reduce response latency of the envelope voltage signal.

[0132] One example approach to determining the very low calibration factor c may include generating a first estimate of the very low calibration factor c, transmitting a second transitional bit pattern, and then sampling the envelope voltage to determine if the sampled envelope voltage is close to the low steady state voltage. The microcontroller 210 may then update the estimate of the very low calibration factor c. The microcontroller 210 may iterate the estimation, transmitting, and sampling steps a predetermined number of times or until the sampled envelope voltage is sufficiently close to the low steady state voltage. In some variations, the microcontroller 210 may iterate up to three times. In other embodiments, the microcontroller 210 may iterate any other feasible number of times.

[0133] The second transitional bit pattern may be a bit pattern designed to test transitioning from a high level to a low level and thereby testing the energizer’s ring downtime latency. In some examples, the second transitional bit pattern may include 1011b (e.g., a "one" bit, followed by a “zero” bit, followed by two more “one” bits). This particular bit pattern may enable the microcontroller 210 to determine the envelope voltage associated with the “low” output level when preceded by an extended “high” output level.

[0134] FIG. 13 shows a graph 1300 illustrating the method 1200 for determining very high and very low calibration factors. The graph 1300 includes a line representing an envelope voltage signal 1302 plotted with respect to time. During a first time period 1310, the envelope voltage signal 1302 is allowed to reach a high steady state voltage, for example as described in block 1206 of FIG. 12. Toward the end of the first time period 1310, the microcontroller 210 of FIG. 2 can sample the envelope voltage signal 1302 to determine a high target voltage, for example as described in block 1208.

[0135] Next, in a second time period 1315, the envelope voltage signal 1302 is allowed to reach a low steady state voltage, for example as described in block 1210. Toward the end of the second time period 1315, the microcontroller 210 can sample the envelope voltage signal 1302 to determine a low target voltage, for example as described in block 1212.

[0136] Next, in a third time period 1320, the microcontroller 210 may transmit a first transitional bit pattern. The microcontroller 210 may then sample the envelope voltage signal 1302 to determine a high envelope voltage (after a low envelope voltage). As shown, the high envelope voltage during the first transitional bit pattern is less than the high steady state voltage included in the first time period 1310. Accordingly, the microcontroller 210 may determine a very high calibration factor b that may be used to increase the envelope voltage during these transitions.

[0137] Next, in a fourth time period 1325, the microcontroller 210 may transmit the first transitional bit pattern using a new or updated very high calibration factor b and determine whether the high envelope voltage is near the high steady state voltage. The operations described in the third time period 1320 and the fourth time period 1325 may correspond to the block 1214.

[0138] Next, in a fifth time period 1330, the microcontroller 210 may transmit a second transitional bit pattern. The microcontroller 210 may then sample the envelope voltage signal 1302 to determine a low envelope voltage (after a high envelope voltage). As shown, the low envelope voltage is greater than the low steady state voltage that is included in the second time period 1315. Accordingly, the microcontroller 210 may determine a very low calibration factor c that may be used to decrease the envelope voltage during these transitions.

[0139] Next, in a sixth time period 1335, the microcontroller 210 may transmit the second transitional bit pattern using a new or updated very low calibration factor c anddetermine whether the transitional low voltage is near the low steady state. The operations described in the fifth time period 1330 and the sixth time period 1335 may correspond to the block 1216.

[0140] FIG. 14 shows a block diagram of a device 1400 that may be one example of the energizer 120 of FIG. 1 or the energizer 200 of FIG. 2. The device 1400 may include an inverter 1410, a variable tank circuit 1420, an envelope detector 1425, a processor 1430, and a memory 1440.

[0141] The variable tank circuit 1420, which is coupled to the inverter 1410 and the envelope detector 1425, may be used to radiate and / or transmit RF signals. In some examples, the variable tank circuit 1420 includes an inductor and a capacitor and may be another example of the tank circuit 230 of FIG. 2. In some examples, the variable tank circuit 1420 may be flexible thereby enabling it to be worn by a patient. Flexibility of the variable tank circuit 1420 may change the inductance and / or capacitance of any included components causing a related resonant frequency to change.

[0142] The inverter 1410 may be coupled to the processor 1430 and the variable tank circuit 1420. In some examples, the processor 1430 may generate or provide a PWM signal 1431. The inverter 1410 may receive the PWM signal 1431 and generate a corresponding RF signal 1411 that is coupled to the variable tank circuit 1420. The variable tank circuit 1420 can radiate RF energy that may be used to deliver charge or may be used to transmit data with other devices. In some cases, the other devices may include other charge powered devices, such as the charge-powered device 130.

[0143] The envelope detector 1425 may be coupled to the variable tank circuit 1420 and the processor 1430. The envelope detector 1425 may provide an envelope voltage signal 1426 to the processor 1430 that may vary in magnitude proportional to a strength of radiated or transmitted RF signals from the variable tank circuit 1420.

[0144] The processor 1430, which is also coupled to the memory 1440, may be any one or more suitable processors capable of executing scripts or instructions of one or more software programs stored in the device 1400 (such as within memory 1440).

[0145] The memory 1440 may include a non-transitory computer-readable storage medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that may store the following software modules: e.g., a resonant frequency detection software (SW) module 1442 to determine a resonant frequency of the variable tank circuit 1420; a transmit (TX) power calibration SW module 1443 to calibrate transmit power associated with the variable tank circuit 1420; a progressive data modulation SW module 1444 to adjust modulated RF power transmitted by the variable tank circuit 1420;a power calibration for progressive data modulation SW 1445; and / or a communication SW module 1446 to transmit and / or receive data. Each software module may include program instructions that, when executed by the processor 1430, may cause the device 1400 to perform the corresponding function(s). Thus, the non-transitory computer-readable storage medium of memory 1440 may include instructions for performing all or a portion of the operations described herein.

[0146] The processor 1430 may execute the resonant frequency detection SW module 1442 to determine the resonant frequency of any tank circuit, including the variable tank circuit 1420. Execution of the resonant frequency detection SW module 1442 may cause the processor 1430 to generate a plurality of fine and coarse PWM signals 1431 and detect corresponding envelope voltage signals 1426 to determine an appropriate resonant frequency of the variable tank circuit 1420. In some examples, the processor 1430 may perform one or more operations corresponding to the method 400 of FIG. 4.

[0147] The processor 1430 may execute the TX power calibration SW module 1443 to fine tune and control radiated RF energy from the variable tank circuit 1420. Execution of the TX power calibration SW module 1443 may cause the processor to modify the pulse width of the PWM signal 1431 in accordance with the envelope voltage signal 1426 and equations 1-4. In some examples, the processor 1430 may perform one or more operations corresponding to the method 700 of FIG. 7

[0148] The processor 1430 may execute the progressive data modulation SW module 1444 to modify the transmission of RF data by the inverter 1410 and the variable tank circuit 1420. Execution of the progressive data modulation SW module 1444 may cause the processor to modify the pulse width of the PWM signal 1431 based on previous and current data bits (e.g., previously transmitted data bits adjacent to a currently transmitted data bit). In some examples, the processor 1430 may perform one or more operations corresponding to the method 1000 of FIG. 10.

[0149] The processor 1430 may execute the power calibration for progressive modulation SW module 1445 to determine pulse width characteristics that may be associated with progressive data modulation. Execution of the power calibration for progressive modulation SW module 1445 may cause the processor 1430 to transmit known bit patterns and sample the envelope voltage signal 1426 from the envelope detector 1425 corresponding to the known bit patterns. The processor 1430 may then iteratively determine new pulse width duty cycles to overcome ring up and ring down latency. In some examples, the processor 1430 may perform one or more operations corresponding to the method 1200 of FIG. 12.

[0150] The processor 1430 may execute the communication SW module 1446 to transmit data to another device through the variable tank circuit 1420. Execution of the communication SW module 1446 may cause the processor 1430 to change the pulse width of the PWM signal 1431 to alter the amount of RF energy transmitted based on data to be transmitted.

[0151] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein and may be used to achieve the benefits described herein.

[0152] The process parameters and sequence of steps described and / or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and / or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed. The various example methods described and / or illustrated herein may also omit one or more of the steps described or illustrated herein or include additional steps in addition to those disclosed.

[0153] Any of the methods (including user interfaces) described herein may be implemented as software, hardware or firmware, and may be described as a non-transitory computer-readable storage medium storing a set of instructions capable of being executed by a processor (e.g., computer, tablet, smartphone, etc.), that when executed by the processor causes the processor to perform any of the steps, including but not limited to: displaying, communicating with the user, analyzing, modifying parameters (including timing, frequency, intensity, etc.), determining, alerting, or the like. For example, any of the methods described herein may be performed, at least in part, by an apparatus including one or more processors having a memory storing a non-transitory computer-readable storage medium storing a set of instructions for the process(es) of the method.

[0154] While various embodiments have been described and / or illustrated herein in the context of fully functional computing systems, one or more of these example embodiments may be distributed as a program product in a variety of forms, regardless of the particular type of computer-readable media used to actually carry out the distribution. The embodiments disclosed herein may also be implemented using software modules that perform certain tasks. These software modules may include script, batch, or other executable files that may be stored on a computer-readable storage medium or in a computing system. In some embodiments, these software modules may configure a computing system to perform one or more of the example embodiments disclosed herein.

[0155] As described herein, the computing devices and systems described and / or illustrated herein broadly represent any type or form of computing device or system capable of executing computer-readable instructions, such as those contained within the modules described herein. In their most basic configuration, these computing device(s) may each comprise at least one memory device and at least one physical processor.

[0156] The term “memory” or “memory device,” as used herein, generally represents any type or form of volatile or non-volatile storage device or medium capable of storing data and / or computer-readable instructions. In one example, a memory device may store, load, and / or maintain one or more of the modules described herein. Examples of memory devices comprise, without limitation, Random Access Memory (RAM), Read Only Memory (ROM), flash memory, Hard Disk Drives (HDDs), Solid-State Drives (SSDs), optical disk drives, caches, variations or combinations of one or more of the same, or any other suitable storage memory.

[0157] In addition, the term “processor” or “physical processor,” as used herein, generally refers to any type or form of hardware-implemented processing unit capable of interpreting and / or executing computer-readable instructions. In one example, a physical processor may access and / or modify one or more modules stored in the above-described memory device. Examples of physical processors comprise, without limitation, microprocessors, microcontrollers, Central Processing Units (CPUs), Field-Programmable Gate Arrays (FPGAs) that implement softcore processors, Application-Specific Integrated Circuits (ASICs), portions of one or more of the same, variations or combinations of one or more of the same, or any other suitable physical processor.

[0158] Although illustrated as separate elements, the method steps described and / or illustrated herein may represent portions of a single application. In addition, in some embodiments one or more of these steps may represent or correspond to one or more software applications or programs that, when executed by a computing device, may cause the computing device to perform one or more tasks, such as the method step.

[0159] In addition, one or more of the devices described herein may transform data, physical devices, and / or representations of physical devices from one form to another. Additionally or alternatively, one or more of the modules recited herein may transform a processor, volatile memory, non-volatile memory, and / or any other portion of a physical computing device from one form of computing device to another form of computing device by executing on the computing device, storing data on the computing device, and / or otherwise interacting with the computing device.

[0160] The term “computer-readable medium,” as used herein, generally refers to any form of device, carrier, or medium capable of storing or carrying computer-readable instructions. Examples of computer-readable media comprise, without limitation, transmission-type media, such as carrier waves, and non-transitory-type media, such as magnetic-storage media (e.g., hard disk drives, tape drives, and floppy disks), optical-storage media (e.g., Compact Disks (CDs), Digital Video Disks (DVDs), and BLU-RAY disks), electronic-storage media (e.g., solid-state drives and flash media), and other distribution systems.

[0161] A person of ordinary skill in the art will recognize that any process or method disclosed herein can be modified in many ways. The process parameters and sequence of the steps described and / or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and / or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed.

[0162] The various exemplary methods described and / or illustrated herein may also omit one or more of the steps described or illustrated herein or comprise additional steps in addition to those disclosed. Further, a step of any method as disclosed herein can be combined with any one or more steps of any other method as disclosed herein.

[0163] The processor as described herein can be configured to perform one or more steps of any method disclosed herein. Alternatively or in combination, the processor can be configured to combine one or more steps of one or more methods as disclosed herein.

[0164] Terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. For example, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ".

[0165] Although the terms “first” and “second” may be used herein to describe various features / elements (including steps), these features / elements should not be limited by these terms, unless the context indicates otherwise. These terms may be used to distinguish one feature / element from another feature / element. Thus, a first feature / element discussed below could be termed a second feature / element, and similarly, a second feature / element discussedbelow could be termed a first feature / element without departing from the teachings of the present invention.

[0166] Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising” means various components can be co-jointly employed in the methods and articles (e.g., compositions and apparatuses including device and methods). For example, the term “comprising” will be understood to imply the inclusion of any stated elements or steps but not the exclusion of any other elements or steps.

[0167] In general, any of the apparatuses and methods described herein should be understood to be inclusive, but all or a sub-set of the components and / or steps may alternatively be exclusive, and may be expressed as “consisting of’ or alternatively “consisting essentially of’ the various components, steps, sub-components or sub-steps.

[0168] As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word "about" or “approximately,” even if the term does not expressly appear. The phrase “about” or “approximately” may be used when describing magnitude and / or position to indicate that the value and / or position described is within a reasonable expected range of values and / or positions. For example, a numeric value may have a value that is + / - 0.1% of the stated value (or range of values), + / - 1% of the stated value (or range of values), + / - 2% of the stated value (or range of values), + / - 5% of the stated value (or range of values), + / - 10% of the stated value (or range of values), etc. Any numerical values given herein should also be understood to include about or approximately that value unless the context indicates otherwise. For example, if the value " 10" is disclosed, then "about 10" is also disclosed. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. It is also understood that when a value is disclosed that "less than or equal to" the value, "greater than or equal to the value" and possible ranges between values are also disclosed, as appropriately understood by the skilled artisan. For example, if the value "X" is disclosed the "less than or equal to X" as well as "greater than or equal to X" (e.g., where X is a numerical value) is also disclosed. It is also understood that the throughout the application, data is provided in a number of different formats, and that this data, represents endpoints and starting points, and ranges for any combination of the data points. For example, if a particular data point “10” and a particular data point “15” are disclosed, it is understood that greater than, greater than or equal to, less than, less than or equal to, and equal to 10 and 15 are considered disclosed as well as between 10 and 15. It is also understood that each unit between two particular unitsare also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0169] Although various illustrative embodiments are described above, any of a number of changes may be made to various embodiments without departing from the scope of the invention as described by the claims. For example, the order in which various described method steps are performed may often be changed in alternative embodiments, and in other alternative embodiments one or more method steps may be skipped altogether. Optional features of various device and system embodiments may be included in some embodiments and not in others. Therefore, the foregoing description is provided primarily for exemplary purposes and should not be interpreted to limit the scope of the invention as it is set forth in the claims.

[0170] The examples and illustrations included herein show, by way of illustration and not of limitation, specific embodiments in which the subject matter may be practiced. As mentioned, other embodiments may be utilized and derived there from, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Such embodiments of the inventive subject matter may be referred to herein individually or collectively by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept, if more than one is, in fact, disclosed. Thus, although specific embodiments have been illustrated and described herein, any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

Claims

CLAIMSWhat is claimed is:

1. A method for determining a resonant frequency of a variable tank circuit, the method comprising: generating a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency; generating, with the variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals; determining, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals; and determining a resonant frequency of the variable tank circuit based on the peak voltage.

2. The method of claim 1, further comprising coupling RF signals from the variable tank circuit to the envelope detector.

3. The method of claim 1, wherein the envelope detector rectifies, at least in part, the RF signals from the variable tank circuit.

4. The method of claim 1, wherein the variable tank circuit includes an inductor and a capacitor configured to radiate RF signals.

5. The method of claim 1, wherein the variable tank circuit includes a flexible inductor configured to be worn next to a human body.

6. The method of claim 1, wherein the plurality of PWM signals include coarse PWM signals and fine PWM signals.

7. The method of claim 6, wherein the envelope detector determines a peak voltage associated with the coarse PWM signals and the fine PWM signals.

8. The method of claim 1, wherein determining the resonant frequency includes determining an association between the peak voltage and frequency of an associated PWM signal.

9. A communication device, comprising a variable tank circuit; one or more processors; and a memory storing instructions that, when executed by the one or more processors, cause the communication device to: generate a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency; generate, with the variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals; determine, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals; and determine a resonant frequency of the variable tank circuit based on the peak voltage.

10. A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors of a communication device, cause the communication device to: generate a plurality of pulse width modulated (PWM) signals, wherein each of the plurality of PWM signals have a different frequency; generate, with a variable tank circuit, a plurality of radio frequency (RF) signals based at least in part on the plurality of PWM signals; determine, through an envelope detector, a peak voltage from a plurality of voltages associated with each of the plurality of RF signals; and determine a resonant frequency of the variable tank circuit based on the peak voltage.

11. A method for calibrating transmission power of a radio frequency (RF) signal generator, the method comprising: generating a first pulse width modulated (PWM) signal; transmitting, by a variable tank circuit, a first RF signal based on the PWM signal; determining, with an envelope detector, a first voltage based on a strength of the first RF signal; and generating a first modified PWM signal based, at least in part, on the first voltage.

12. The method of claim 11, further comprising transmitting a second RF signal based on the first modified PWM signal.

13. The method of claim 11, wherein generating the first modified PWM signal comprises: determining a first proportional adjustment factor based on the first voltage; and generating the first modified PWM signal based on the first proportional adjustment factor.

14. The method of claim 13, further comprising determining a transmit (TX) scale factor based on the first proportional adjustment factor, wherein the TX scale factor modifies a pulse width of the first PWM signal.

15. The method of claim 13, further comprising: determining whether the first proportional adjustment factor is within a predetermined threshold of a constant value; and generating a second modified PWM signal when the first proportional adjustment factor is not within the predetermined threshold of the constant value.

16. The method of claim 15, wherein generating the second modified PWM signal comprises: generating a second PWM signal based on first modified PWM signal; transmitting a third RF signal based on the second PWM signal; determining a second voltage based on a strength of the third RF signal; and generating a second modified PWM signal based, at least in part, on the second voltage.

17. The method of claim 16, wherein generating the second modified PWM signal is repeatedly performed for not more than a predetermined number of times.

18. The method of claim 11, wherein the first RF signal is generated with an inverter receiving the first PWM signal.

19. A communication device, comprising a variable tank circuit;one or more processors; and a memory storing instructions that, when executed by the one or more processors, cause the communication device to: generate a first pulse width modulated (PWM) signal; transmit, by the variable tank circuit, a first RF signal based on the PWM signal; determine, with an envelope detector, a first voltage based on a strength of the first RF signal; and generate a first modified PWM signal based, at least in part, on the first voltage.

20. A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors of a communication device, cause the communication device to: generate a first pulse width modulated (PWM) signal; transmit, by a variable tank circuit, a first RF signal based on the PWM signal; determine, with an envelope detector, a first voltage based on a strength of the first RF signal; and generate a first modified PWM signal based, at least in part, on the first voltage.

21. A method of determining pulse width modulation (PWM) duty cycles to transmit a plurality of data bits, the method comprising: generating a first steady state voltage associated with a first data bit, wherein the first data bit is associated with a first PWM duty cycle; transmitting a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit; measuring a first transitional voltage associated with the first data bit within the first transitional bit pattern; and determining a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

22. The method of claim 21, wherein the first data bit is ‘Ob’ and the first transitional bit pattern is ‘ 1011b’.

23. The method of claim 21, wherein the first data bit is ‘ lb’ and the first transitional bit pattern is ‘0100b’.

24. The method of claim 21, wherein generating the first steady state voltage includes generating a radio frequency (RF) signal with a PWM signal having the first PWM duty cycle.

25. The method of claim 21, wherein the first PWM duty cycle is associated with a ‘Ob’ data bit.

26. The method of claim 21, wherein the first steady state voltage and the second transitional voltage are voltages proportional to a generated radio frequency (RF) signal.

27. The method of claim 26, wherein the RF signal is based on the first and second PWM duty cycles.

28. The method of claim 21, further comprising: generating a second steady state voltage associated with a second data bit, wherein the second data bit is associated with a third PWM duty cycle; transmitting a second transitional bit pattern, wherein the second transitional bit pattern includes the second data bit; measuring a third transitional voltage associated with the second data bit within the second transitional bit pattern; and determining a fourth PWM duty cycle to generate a fourth transitional voltage near the second steady state voltage for the second data bit during the second transitional bit pattern, wherein the fourth transitional voltage is within a predetermined threshold of the second steady state voltage.

29. A communication device, comprising a variable tank circuit configured to transmit a radio frequency signal; an envelope detector configured to generate a voltage based on the transmitted radio frequency signal; one or more processors; and a memory storing instructions that, when executed by the one or more processors, cause the communication device to:generate, with the envelope detector, a first steady state voltage associated a first data bit, wherein the first data bit is associated with a first PWM duty cycle; transmit a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit; measure a first transitional voltage associated with the first data bit within the first transitional bit pattern; and determine a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

30. A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors of a communication device, cause the communication device to: generate, with an envelope detector, a first steady state voltage associated a first data bit, wherein the first data bit is associated with a first PWM duty cycle; transmit a first transitional bit pattern, wherein the first transitional bit pattern includes the first data bit; measure a first transitional voltage associated with the first data bit within the first transitional bit pattern; and determine a second PWM duty cycle to generate a second transitional voltage near the first steady state voltage for the first data bit during the first transitional bit pattern, wherein the second transitional voltage is within a predetermined threshold of the first steady state voltage.

31. A method of pattern dependent transmit power modulation, the method comprising: determining a binary data value for a first data bit; determining a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit; and selecting a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

32. The method of claim 31, wherein selecting the PWM duty cycle includes selecting one of four predetermined PWM duty cycles.

33. The method of claim 31, wherein selecting the PWM duty cycle includes selecting the PWM duty cycle via a look-up table.

34. The method of claim 31, wherein the selected PWM duty cycle increases a rate of change of an envelope voltage when the binary data value for the first data bit is different from the binary data value for the second data bit relative to a rate of change of the envelope voltage when the binary data value for the first data bit is the same as the binary data value for the second data bit.

35. The method of claim 34, wherein the envelope voltage is proportional to power of a transmitted RF signal.

36. The method of claim 31, further comprising transmitting the second data bit.

37. A communication device, comprising a variable tank circuit configured to transmit a radio frequency signal; one or more processors; and a memory storing instructions that, when executed by the one or more processors, cause the communication device to: determine a binary data value for a first data bit; determine a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit; and select a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

38. A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors of a communication device, cause the communication device to: determine a binary data value for a first data bit; determine a binary data value for a second data bit to be transmitted immediately subsequent to the first data bit; andselect a pulse width modulation (PWM) duty cycle to generate a radio frequency (RF) signal to transmit the second data bit based on the binary data values of the first data bit and the second data bit.

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