Apparatus and method for real-time resonance adaptation for a power receiver

Abstract

Providing real-time resonance adaptation for a power receiver SOLUTION: Wireless powered receiver systems and sensors are described. In an embodiment, a power receiver system includes an inductive coil for receiving wireless power from an external transmitter, a capacitor bank for optimizing power transfer to an energy harvesting device, and a power receiving front end RF-DC rectifier with a periodically enabled closed feedback loop that adapts the settings of the capacitor bank in real time to adapt to changes on the inductive coil and maximize power transfer efficiency.SELECTED DRAWING: None

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to real-time resonance adaptation for power receivers, and more specifically to a system-on-chip solution for inductive power reception for implantable medical devices (IMDs) and other energy harvesting devices in the power range of a few microwatts to hundreds of microwatts. [Background technology]

[0002] (background) Wireless power transfer has been widely used for medical implants. Real-time regulated power transfer for implantable medical devices (IMDs) has mainly addressed scenarios where the power consumption of the IMD is in the mW-W range. At the same time, IMDs with lower power consumption and associated invasiveness have been attracting attention. Summary of the Invention [Means for solving the problem]

[0003] (Summary of the Invention) Many embodiments of the present invention are directed to a power receiver system for maximizing power transfer efficiency. One embodiment includes a power receiver system including an induction coil that receives wireless power from an external transmitter, a capacitor bank that optimizes power transfer to an energy harvesting device, and a power receiving front-end RF-DC rectifier with a periodically enabled closed feedback loop that adapts the capacitor bank settings in real time to match changes on the induction coil and maximize power transfer efficiency.

[0004] In another embodiment, the capacitor bank includes a binary weighted capacitor bank implemented in parallel with a Dickson stage passive rectifier.

[0005] In a further embodiment, the closed feedback loop mitigates resonance variations due to at least one of different dielectric environments, loading conditions, and processing mismatches.

[0006] In yet another embodiment, the capacitor bank is a 6-bit capacitor bank that is periodically tuned using a successive approximation resonant tuning process.

[0007] In a further embodiment, the closed feedback loop includes detecting and sampling swings on two hold capacitors, respectively, corresponding to two successive capacitor bank selections.

[0008] In yet another embodiment, the impedance of the induction coil is approximately symmetrical with respect to the offset of the resonant capacitor.

[0009] In a further embodiment, the power receiver includes a transmitter that transmits information to an external controller.

[0010] In another additional embodiment, the transmitter is an ultra-wideband impulse radio (IR-UWB) transmitter with back telemetry for output voltage adjustment, and the output voltage from the IR-UWB transmitter is adjusted based on the back telemetry transmitting real-time collected voltage readings.

[0011] In a further additional embodiment, operation is heavy duty cycled to reduce power consumption.

[0012] In a further embodiment, the power receiver system includes a coarse bandgap reference (BGR-Coarse) and a local low dropout regulator (LDO) that generates a voltage supply for internal circuitry, and a fine bandgap reference (BGR-Fine) that generates a stable voltage reference.

[0013] Another embodiment includes an induction coil that receives wireless power from an external transmitter, a capacitor bank that defines different settings for different external environments around the sensor chip, a power-receiving front-end RF-DC rectifier with a periodically enabled closed feedback loop that adapts the capacitor bank settings in real time to suit the surrounding environment, and a transmitter that transmits information related to the capacitor settings and voltage readings to an external controller.

[0014] In a further embodiment, the capacitor setting is used to determine the type of material in the surrounding environment.

[0015] In a further embodiment, changes to the impedance of the induction coil result in changes to the capacitor setting and are used to detect near-field changes in the surrounding environment.

[0016] In a further embodiment, changes to the voltage readings without changes to the capacitor settings are used to detect the far field in the surrounding environment.

[0017] In a further embodiment, the capacitor bank comprises a binary weighted capacitor bank implemented in parallel with a Dickson stage passive rectifier.

[0018] In a further embodiment, the closed feedback loop mitigates resonance variations due to at least one of different dielectric environments, loading conditions, and processing mismatches.

[0019] In a further embodiment, the capacitor bank is a 6-bit capacitor bank that is periodically tuned using a successive approximation resonant tuning process.

[0020] In a further embodiment, the closed feedback loop includes detecting and sampling swings on two hold capacitors, respectively, corresponding to two successive capacitor bank selections.

[0021] In a further embodiment, the impedance of the induction coil is approximately symmetrical with respect to the offset of the resonant capacitor.

[0022] In a further embodiment, the transmitter is an ultra-wideband impulse radio (IR-UWB) transmitter with back telemetry for output voltage adjustment, and the output voltage from the IR-UWB transmitter is adjusted based on back telemetry transmitting real-time collected voltage readings. The present invention provides, for example, the following items. (Item 1) 1. A power receiver system comprising: an induction coil that receives wireless power from an external transmitter; a capacitor bank for optimizing power transfer to the energy harvesting device; a power receiving front-end RF-DC rectifier with a periodically enabled closed feedback loop that adapts the capacitor bank settings in real time to match changes on the induction coil and maximize power transfer efficiency; 1. A power receiver system comprising: (Item 2) Item 1. The power receiver system of item 1, wherein the capacitor bank comprises a binary-weighted capacitor bank implemented in parallel with a Dickson stage passive rectifier. (Item 3) Item 10. The power receiver system of item 1, wherein the closed feedback loop mitigates resonance variations due to at least one of different dielectric environments, loading conditions, and processing mismatches. (Item 4) Item 2. The power receiver system of item 1, wherein the capacitor bank is a 6-bit capacitor bank that is periodically tuned using a successive approximation resonant tuning process. (Item 5) Item 10. The power receiver system of item 1, wherein the closed feedback loop includes detecting and sampling swings on two hold capacitors, respectively, corresponding to two successive capacitor bank selections. (Item 6) Item 6. The power receiver system of item 5, wherein the impedance of the induction coil is approximately symmetrical with respect to the offset of the resonant capacitor. (Item 7) Item 10. The power receiver system of item 1, further comprising a transmitter that transmits information to an external controller. (Item 8) 8. The power receiver system of item 7, wherein the transmitter is an ultra-wideband impulse radio (IR-UWB) transmitter as back telemetry for output voltage adjustment, and the output voltage from the IR-UWB transmitter is adjusted based on back telemetry transmitting real-time collected voltage readings. (Item 9) Item 14. The power receiver system of item 1, wherein operation is heavy-duty cycled to reduce power consumption. (Item 10) a coarse bandgap reference (BGR-Coarse) and a local low dropout regulator (LDO) to generate a voltage supply for the internal circuitry; A narrow bandgap reference (BGR-thin) that generates a stable voltage reference Item 1. The power receiver system of item 1, further comprising: (Item 11) A wireless power supply sensor chip, an induction coil that receives wireless power from an external transmitter; a capacitor bank defining different settings for different external environments around the sensor chip; a power receiving front-end RF-DC rectifier with a periodically enabled closed feedback loop that adapts the capacitor bank settings in real time to suit the ambient environment; a transmitter for transmitting information relating to said capacitor settings and voltage readings to an external controller; A wireless power supply sensor chip comprising: (Item 12) Item 12. The wirelessly powered sensor chip of item 11, wherein the capacitor setting is used to determine a type of substance in the surrounding environment. (Item 13) Item 12. The wirelessly powered sensor chip of item 11, wherein a change to the impedance of the induction coil results in a change to the capacitor setting and is used to detect changes in the near field in the surrounding environment. (Item 14) Item 12. The wirelessly powered sensor chip of item 11, wherein changes to voltage readings without changes to the capacitor settings are used to detect the far field in the surrounding environment. (Item 15) Item 16. The wirelessly powered sensor chip of item 11, wherein the capacitor bank comprises a binary-weighted capacitor bank implemented in parallel with a Dickson stage passive rectifier. Item 12. The wirelessly powered sensor chip of item 11, wherein the closed feedback loop mitigates resonance variations due to at least one of different dielectric environments, loading conditions, and processing mismatches. (Item 17) Item 12. The wirelessly powered sensor chip of item 11, wherein the capacitor bank is a 6-bit capacitor bank that is periodically tuned using a successive approximation resonant tuning process. (Item 18) Item 12. The wirelessly powered sensor chip of item 11, wherein the closed feedback loop includes detecting and sampling swings on two hold capacitors, respectively, corresponding to two successive capacitor bank selections. (Item 19) Item 12. The wirelessly powered sensor chip according to item 11, wherein the impedance of the induction coil is approximately symmetrical with respect to the offset of the resonant capacitor. (Item 20) Item 12. The wireless power sensor chip of item 11, wherein the transmitter is an ultra-wideband impulse radio (IR-UWB) transmitter as back telemetry for output voltage adjustment, and the output voltage from the IR-UWB transmitter is adjusted based on the back telemetry transmitting real-time collected voltage readings. [Brief explanation of the drawings]

[0023] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 illustrates the circuit architecture of an inductive power receiver according to an embodiment of the present invention.

[0024] [Figure 2] FIG. 2 illustrates a system opportunistic selection schedule for duty cycling, according to an embodiment of the present invention.

[0025] [Figure 3] FIG. 3 illustrates a circuit schematic of a power receiving front end with a SART according to an embodiment of the present invention.

[0026] [Figure 4] FIG. 4 illustrates the successive approximation process in a 4-bit scenario according to an embodiment of the present invention.

[0027] [Figure 5] FIG. 5 illustrates a logic flow process for adaptation of a 6-bit SART in accordance with an embodiment of the present invention.

[0028] [Figure 6] FIG. 6 illustrates the efficiency of a rectifier for different ILOADs at a VOUT of 3V according to an embodiment of the present invention.

[0029] [Figure 7]FIG. 7 illustrates the efficiency of a rectifier at different VOUT for ILOAD of 1 μA, 3 μA, 10 μA, and 30 μA, respectively, in accordance with an embodiment of the present invention.

[0030] [Figure 8] FIG. 8 illustrates (a) a circuit schematic of each switched capacitor unit and (b) a layout of a 6-bit switched capacitor bank array according to an embodiment of the present invention.

[0031] [Figure 9] FIG. 9 illustrates Tx and Rx coils according to an embodiment of the present invention.

[0032] [Figure 10] FIG. 10 illustrates normalized link efficiency versus resonant capacitor offset in the Rx coil, in accordance with an embodiment of the present invention.

[0033] [Figure 11] FIG. 11 illustrates a circuit schematic diagram of a bottom-sampling SAR ADC according to an embodiment of the present invention.

[0034] [Figure 12] FIG. 12 illustrates a circuit schematic diagram of an IR-UWB transmitter according to an embodiment of the present invention.

[0035] [Figure 13] FIG. 13 illustrates S21 of an on-chip UWB filter according to an embodiment of the present invention.

[0036] [Figure 14] FIG. 14 illustrates (a) the transient waveform and (b) the frequency spectrum of a UWB impulse according to an embodiment of the present invention.

[0037] [Figure 15] FIG. 15 illustrates a photomicrograph of a power receiver IC according to an embodiment of the present invention.

[0038] [Figure 16] FIG. 16 illustrates a power breakdown according to an embodiment of the present invention.

[0039] [Figure 17] FIG. 17 illustrates a measurement setup according to an embodiment of the present invention.

[0040] [Figure 18] FIG. 18 illustrates wireless measurement ADC output code versus sampled voltage in accordance with an embodiment of the present invention.

[0041] [Figure 19] FIG. 19 illustrates the INL of an ADC according to an embodiment of the present invention.

[0042] [Figure 20] FIG. 20 illustrates photographs of samples (a) #A and (b) #B with sample (b) #B incorporating an additional 10-pF parallel capacitor, according to an embodiment of the present invention, where #A and #B conform to capacitor bank codes “100100” and “001010,” respectively.

[0043] [Figure 21] FIG. 21 illustrates a transient waveform of an IR-UWB signal "1001100" according to an embodiment of the present invention.

[0044] [Figure 22] FIG. 22 illustrates the end-to-end efficiency at different Tx-Rx distances for samples #A and #B, and the predicted results without SART, according to an embodiment of the present invention.

[0045] [Figure 23] Figure 23 illustrates the power breakdown in a 2cm power transfer link assuming a Tx power of 186.2μW.

[0046] [Figure 24] FIG. 24 illustrates an in vitro experiment using a piece of pork loin covering a power receiver in accordance with an embodiment of the present invention, (a) before and (b) after the pork loin covers the device, and the corresponding transient waveforms of the IR-UWB signal are shown in (c, e) and (d, f), respectively, and the IR-UWB data remains the same with or without the pork loin.

[0047] [Figure 25] FIG. 25 illustrates resonance-compensated logic waveforms measured during fitting, according to an embodiment of the present invention.

[0048] [Figure 26] FIG. 26 illustrates a power receiver incorporating a digitally controlled capacitor in the energy harvesting front end according to an embodiment of the present invention, where (a) is a photograph of the printed circuit board housing the proposed IC, Rx coil, and digitally controlled capacitor NCD2100, and (b) is the overall setup where a microcontroller is used to program the capacitor and read data from the IC.

[0049] [Figure 27] FIG. 27 illustrates an output voltage waveform in response to a transient resonant capacitor offset, according to an embodiment of the present invention.

[0050] [Figure 28] FIG. 28 illustrates the IC's compensation capacitor being matched to the capacitance of NCD2100 in accordance with an embodiment of the present invention, with the inset showing the capacitance of NCD2100 as a function of control code according to its datasheet.

[0051] [Figure 29] FIG. 29 illustrates the output voltages generated at each control code of the NCD 2100 in accordance with an embodiment of the present invention.

[0052] [Figure 30] FIG. 30 illustrates a comparison of resonance compensation techniques in a power receiving front end, according to an embodiment of the present invention.

[0053] [Figure 31] FIG. 31 illustrates a comparison of a prior art inductive power receiver for low power IMD, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0054] Detailed Description of the Drawings Turning now to the drawings, systems and methods are illustrated for an inductive power receiver system-on-chip for powering energy harvesting devices, including, for example, implantable medical devices (IMDs), oil and gas sensors, and infrastructure sensors, among many other wirelessly powered devices, in accordance with embodiments of the present invention. In particular, implantable medical devices (IMDs) with low power consumption and minimal invasiveness are described. In particular, many embodiments provide an inductive power receiver system-on-chip for powering such IMDs. In many embodiments, the power receiver is a 13.56 MHz inductive power receiver system-on-chip. In many embodiments, the power receiver can achieve an input sensitivity of approximately −25 dBm (3.41 μW) and an efficiency of 45.7% while driving a 10-μA @ 3-V load. In one embodiment, the power receiver can include an ultra-wideband impulse radio (IR-UWB) transmitter for back-transmission telemetry. A regulated output voltage of 1.7V to 3.3V can be achieved from the transmitter via ultra-wideband impulse radio (IR-UWB) back telemetry, which carries real-time collected voltage readings. Furthermore, because resonant power transfer improves transmission efficiency, IMD power receivers generally suffer from resonance variations due to different dielectric environments and loading conditions. Therefore, many embodiments provide a real-time resonance adaptation scheme to address this. Furthermore, changes in resonance variations can be used to sense the surrounding environment (e.g., air, oil, gas) and / or detect changes in the surrounding environment (e.g., bleeding patients, changes occurring in oil / gas pipelines, among many other applications).

[0055] In particular, many embodiments include a capacitor bank including switched capacitor units, and the particular settings used for the capacitor bank can be adapted and / or optimized using a closed-loop feedback process to maximize power transfer. In many embodiments, the feedback process adapts the optimal settings for the capacitor bank in real time to maintain proper resonance, thereby reducing V dd,Harv is kept at a maximum to maintain good resonance, resolve mismatches, and deliver higher power to the sensor or other energy harvesting device.

[0056] In many embodiments, the logic for tuning the capacitor bank is periodically enabled successive approximation resonant tuning (SART) logic. In many embodiments, the capacitor bank is a 6-bit capacitor bank with identical switched capacitor units.

[0057] In many embodiments, information related to the changed settings of the capacitor bank can be used to sense the surrounding environment and / or detect changes in the environment. In particular, in many embodiments, the capacitor bank value and / or voltage readings can be digitized and transmitted to an external controller, and this information can be used to determine various properties of the environment around the sensor chip, particularly the environment around the induction coil of the receiving antenna. In many embodiments, the system can measure the rectified voltage and report the readings back using a transmitter, which can be useful for various sensing applications.

[0058] In this manner, the chip can be used as a sensor device for a variety of different applications. In many embodiments, the sensor device can detect the dielectric constant of the surrounding environment, which can be useful for a broad spectrum of different applications (e.g., oil / gas / water infrastructure applications, implantable medical devices, 3D imaging applications, among others). For example, the sensor chip can be implanted near a patient's surgical site and used to measure blood activity or detect bleeding in the patient after surgery.

[0059] In particular, different substances in the environment have different dielectric constants (e.g., air is 1, water is 90.2, benzene is 2.3), and based on the particular environment around the chip, including the parasitic capacitance of the induction coil, the settings of the capacitive bank can be modified accordingly using a closed-loop process, and these settings can be used to sense the nature of the surrounding environment (e.g., whether the chip is surrounded by water, air, gas, oil, etc., changes in the environment such as bleeding in a patient after surgery, intravenous bleeding, proximity to the heart, etc.).

[0060] Additionally, the system can be used as a sensor chip capable of sensing changes in the surrounding environment in both the near field and the far field. The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering away from the object. Non-radiative "near field" behavior dominates near the antenna or scattering object, while the "far field" behavior of electromagnetic radiation dominates at greater distances.

[0061] In particular, in many embodiments, the sensors can detect various properties of the surrounding environment, including where events are occurring (near-field vs. far-field). In particular, near-field changes can be sensed as they change the impedance of the induction coil, and thus affect both the setting of the capacitive bank and the voltage sampled. Similarly, far-field changes can be sensed in a way that may not affect the impedance of the induction coil and therefore not change the setting of the capacitive bank; however, far-field events may change (e.g., increase or decrease) the voltage sampled, and thus the quality of the lossy channel can be monitored. Thus, by monitoring these settings over time, the system can determine whether and where changes in the environment are occurring.

[0062] For example, multiple sensor chips can be installed throughout a location, and information can be collected across different sensor chips to detect properties of the surrounding environment. For example, if a person moves between the transmitter and receiver coil, this may reduce the signal strength, and thus a voltage is measured, so that the person's movement within a location can be sensed based on changes in the measured voltage. This information can be collected from a collection of different sensors placed at various locations in a particular location to explore and monitor 3D locations and / or movements and / or objects within the particular location.

[0063] Thus, systems according to many embodiments can be used in a variety of different applications, including as a power harvesting system to optimize power transfer to energy harvesting devices and / or sensor chips that may be used to sense and / or monitor the surrounding environment.

[0064] In many embodiments, the system can adapt the capacitor bank to optimize power transfer based on the resonance variation of the induction coil. In particular, the circuit can converge to the optimal resonant capacitor within a few clock cycles (e.g., 12 clock cycles) at minimal power dissipation cost. In many embodiments, the system can be fabricated in an 180 nm CMOS process, and the system features an overall current dissipation of 900 nA. In many embodiments, the system is insensitive to resonant capacitor offsets with precise compensation accuracy. For example, at a distance of 2 cm, end-to-end efficiency can be equal to 14.8% regardless of an artificially induced 10-pF offset while driving a 30 μW load. Such resonant matching improves power link efficiency by orders of magnitude with respect to realistic IMD, depending on the specific load.

[0065] As mentioned, wireless power transfer has been widely used for medical implants. Prior art implementations of real-time, regulated power transfer for implantable medical devices (IMDs) have primarily addressed scenarios where the IMD's power consumption is in the mW-W range. At the same time, IMDs with lower power consumption and associated invasiveness have become one of the recent paradigms. Because the IMD's power consumption can be reduced to tens of μW or less, the power link can be significantly extended with modest Tx power and thus can be widely used for many therapeutic applications. These IMDs can also form distributed sensing and actuation systems instead of their traditional centralized counterparts. A cardiac sensing and pacing network based on wirelessly powered microdevices implanted directly within the heart is an example of such a system. In particular, continuous mobility may require frequent and periodic adaptation of the energy harvesting front end.

[0066] The sophisticated design of wireless power transfer systems with power ratings from a few μW to hundreds of μW has been largely undiscussed in the prior art. These systems should prioritize sensitivity and de-emphasize power transfer efficiency, which tends to be higher for heavier loads. Therefore, in terms of rectification topology, active rectifiers consisting of power-hungry high-speed comparators can be replaced with optimally designed passive rectifiers.

[0067] As mentioned above, a challenge with energy harvesting IMD is its vulnerability to resonance variations, which can be induced, for example, from process mismatches, different implantation sites, movement, scar tissue accumulation, and varying loading conditions, among many other reasons. In particular, actuation devices can produce different equivalent input capacitances of the rectifier depending on the stimulation intensity and on / off status. One approach has been to intentionally lower the quality factor in tradeoff for wider bandwidth, but this naturally sacrifices optimal efficiency. Therefore, many embodiments of the system provide an active compensation method in which a capacitor bank is adaptively tuned to compensate for resonance variations. Therefore, many embodiments provide implementations of such circuits that can rapidly converge to an optimal solution and incur negligible power consumption overhead that would otherwise hinder system sensitivity.

[0068] Another challenge can be output voltage regulation. Techniques that have been used to regulate harvested power can be a cascaded two-step approach, such as RF-DC rectification and DC regulation, with corresponding two-step losses. To combine the two stages, a resonant regulated rectification method has been adopted, in which the rectifier operation is duty-cycled to stabilize the output voltage. However, the high-speed comparator in the active rectifier creates challenges with low-power IMD. The method is also associated with excessive output voltage fluctuations.

[0069] Thus, many embodiments provide an inductive power (e.g., 13.56 MHz inductive power) receiver system-on-chip for IMD in the power range of a few μW to hundreds of μW. Many embodiments of the inductive power receiver achieve input power sensitivity of a few μW (e.g., 2.88 μW) and are capable of adjusting the output voltage within a range (e.g., 1.7 V to 3.3 V with adjustments of over 40 dB). In many embodiments, ultra-wideband impulse radio (IR-UWB) back-transmission telemetry can be employed to transmit the digitized output voltage. Many embodiments of the power receiver can address resonance variations, which have been a problem with power reception IMD, by using a successive approximation resonant tuning (SART) technique, which can provide a compensation dynamic range (e.g., 6 bits of compensation dynamic range) and can make power consumption overhead negligible. For example, targeting a 30 μW load at a 2 cm link distance, a system according to one embodiment of the present invention is able to achieve an end-to-end efficiency of 16.1%, regardless of an artificially induced 10-pF resonant capacitor offset. Resonant matching techniques according to many embodiments improve power transfer efficiency by an order of magnitude with respect to realistic IMD.

[0070] The overall power receiver architecture, implementation of the adaptive resonance process including SART, rectifier optimization, magnetic link, implementation of ADC and IR-UWB back telemetry for voltage regulation from the transmitter, as well as measurement results and comparisons according to many embodiments of the present invention are described in detail.

[0071] (System Overview) A complete block diagram of an inductive power receiver according to an embodiment of the present invention is shown in Figure 1. The circuit shown in Figure 1 can include, among other circuitry, an induction coil, a capacitor bank, a rectifier, a transmitter, and a closed feedback loop for optimizing the capacitor bank setting based on changes in the resonant frequency of the induction coil. In many embodiments, the IC circuitry includes an RF-to-DC rectifier with a SART and a sampled voltage V DD,HARVThe SART may include a SAR ADC (e.g., a 7-bit SAR ADC) for digitizing the SART signal and an IR-UWB transmitter for back telemetry. In many embodiments, these operations may be heavily duty-cycled to reduce power consumption, as shown in the timeline map of FIG. 2 according to an embodiment of the present invention. The clock signal according to many embodiments may be generated by a relaxation oscillator (e.g., a relaxation oscillator running at approximately 5 kHz). Each SART execution may last less than a percentage of the system cycle (e.g., 0.5% of the system cycle) and thus may not interfere with power reception efficiency. The system cycle including the SART, voltage digitization, and back telemetry operations may be executed at a specific Hz (e.g., approximately 2 Hz) to accommodate constantly changing dielectric environments and loading conditions.

[0072] In many embodiments, a coarse bandgap reference (BGR-coarse) and a local low-dropout regulator (LDO) implemented in a 3.3V process can generate a voltage supply for internal circuitry at approximately 1.6V. Another fine bandgap reference (BGR-fine) can create a stable voltage reference with a power supply rejection ratio (PSRR) of over 60dB. In many embodiments, the ADC can be designed with seven effective bits to provide 42dB adjustment of the output voltage. The IR-UWB transmitter can be implemented as back telemetry due to its low power consumption and potential sharing with other bioelectrical sensing functions. In many embodiments, for example, an n-bit header (e.g., a 4-bit header) and an n-bit ADC (e.g., a 7-bit ADC output) forming 11 bits can be serially streamed to the transmitter. While FIG. 1 illustrates a specific circuit architecture for an inductive power receiver, any of a variety of circuit architectures for inductive power receivers and / or sensors can be utilized as suited to the requirements of a particular application according to embodiments of the present invention.

[0073] (Power receiving front end with successive approximation resonant tuning) Parallel capacitor C P A tuner is typically required to tune the resonant frequency of the receiving coil, which can increase the voltage swing and improve power transfer efficiency. Research has focused on actively compensating for any resonant variations by tuning the resonant capacitor. Some prior art designs employ thermometer-coded capacitors based on PMOS varactors to achieve a 3-bit dynamic range, while others implement a binary-weighted capacitor bank at the rectifier input. On-chip optimization logic has been implemented as a hill-climbing algorithm, where each step of operation only matches adjacent codes. Thus, convergence time increases exponentially with dynamic range. Some prior art implementations propose a gradient descent algorithm, which has concerns about logic complexity and associated power consumption. This work also monitors the rectified output voltage, which requires excessive time before stabilization. Note that for most IMDs, resonant compensation is not simply required as a one-time calibration, since the dielectric environment and loading conditions can change over time.

[0074] To address these challenges, in many embodiments, the inductive power receiver provides an algorithm (e.g., a SART logic network) that can accurately and timely compensate for any resonant capacitor offset. To address constantly changing resonance fluctuations, the SART can be run periodically, while a rectifier can continuously harvest inductive power. These techniques, according to many embodiments, can be applied to a variety of energy-harvesting IMDs.

[0075] (Architecture and Compensation Logic) A circuit schematic of a power receiver front end with a SART according to an embodiment of the present invention is shown in FIG. 3. In many embodiments, the capacitor bank can be implemented with a rectifier. In one embodiment, a 6-bit binary-weighted capacitor bank can be implemented in parallel with a Dickson stage passive rectifier. Each capacitor bank selection can lead to a variation in the amplitude of the RF signal. In many embodiments, the swings corresponding to two successive capacitor bank selections can be detected and sampled on two hold capacitors, respectively. A comparison of the two can be performed by a zero-static power StrongARM latch comparator as input to the SART logic. While FIG. 3 illustrates a specific circuit schematic of a power receiver front end with a SART, any of a variety of circuit designs can be specified as meeting the requirements of a particular application according to embodiments of the present invention.

[0076] In many embodiments, the impedance of the coil may be approximately symmetrical with respect to the offset of the resonant capacitor. Higher impedance may lead to larger voltage swings. Therefore, many embodiments of the power receiver provide a resonant compensation algorithm that adapts to the capacitor bank to achieve maximum voltage swing. The SART process according to an embodiment of the present invention is illustrated in FIG. 4 for a 4-bit scenario. The process begins by comparing one-quarter and three-quarters of the full dynamic range, e.g., "0100" and "1100," and the result may be updated as the MSB. The process then compares the remaining one-quarter and three-quarters of the range, e.g., "MSB, 010" and "MSB, 110," and the result may be updated as the second significant bit, etc.

[0077] For an N-bit dynamic range, the process may require N such comparisons, or 2N clock cycles, to achieve an optimal selection code. The convergence time of a SART may be proportional to the dynamic range, while prior art techniques exhibit an exponential relationship. A complete logic flow diagram for adapting a 6-bit capacitor bank in accordance with an embodiment of the present invention is shown in FIG. 5. While FIG. 5 illustrates a specific process for a 6-bit SART, any of a variety of processes may be utilized as suited to the requirements of a particular application in accordance with an embodiment of the present invention.

[0078] (rectifier) In many embodiments, the passive rectifier may include N stages (N=5) and employ native transistors to increase rectification efficiency. LOAD may be a design target, which represents a typical IMD dissipation. In one embodiment, the width of each transistor may be sized to 5 μm, while the gate length is kept to a minimum of 0.5 μm. LOAD The simulated rectification efficiency for I is shown in Figure 6. It is shown for I from 0.6 μA to 10 μA. LOAD For high power regimes, the active rectifier may result in better efficiency, while optimal gate sizing for other load ratings may be achieved by proportionally scaling the transistor width. OUT The rectification efficiency versus load is plotted in FIG. 7, demonstrating stable performance for the targeted load.

[0079] (switched capacitor bank) Switched capacitors in binary weighting for a resonant-compensated front end can easily suffer from nonlinearity problems due to processing mismatch. Therefore, many embodiments of the power receiver implement the capacitor bank as identical unit cells with metal-insulator-metal capacitors and NMOS switches. In many embodiments, the capacitor bank can be implemented as 63 identical unit cells, each with a 400-fF metal-insulator-metal capacitor and an NMOS switch with W / L=24 μm / 0.18 μm, as shown in item (a) of FIG. 8 according to an embodiment of the present invention, which can contribute a sufficient high quality factor of approximately 1,000 or a dissipation factor of 1 / 1,000 according to circuit simulations (note that this is only the quality factor or dissipation factor of the switched capacitor unit, not the Rx tank). Due to the parasitic capacitance of the switches, the unit cell can exhibit an equivalent capacitance of approximately 20 fF in the off state. Therefore, the tuning resolution can be 380 fF, and the total range is equal to 24 pF. The layout of the capacitor banks is illustrated in Figure 8(b), which illustrates the layout of a 6-bit switched capacitor bank array in accordance with an embodiment of the present invention. While Figure 8 illustrates a specific circuit schematic of each switched capacitor unit and the layout of a 6-bit switched capacitor bank array, any of a variety of circuit designs may be defined as suited to the requirements of a particular application in accordance with an embodiment of the present invention.

[0080] (magnetic coupling link) The design of the Tx and Rx coils according to an embodiment of the present invention is illustrated in FIG. 9, and Table I of FIG. 9 demonstrates certain important parameters. The Rx coil can be designed with a small diameter (e.g., 12 mm) to fit a small IMD. The inductances of the Tx and Rx coils can be simulated to be 5.76 μH and 6.36 μH, respectively. A 21.7-pF parallel capacitor C Pmay be required to resonate the Rx coil at 13.56 MHz, and the Tx coil may employ an additional L matching section to match the 50 Ω power source.

[0081] C P , C ΔP Offsets of up to 10 pF can affect voltage swing and therefore power transfer efficiency. ΔP are considered, which mimics a realistic situation where the Rx coil is placed in a different dielectric medium, for example, underwater, which is significantly different from air. ΔP The power transfer efficiency with respect to may be normalized as shown in Figure 10. As expected, systems with higher quality factors may be more vulnerable to offsets. While Figure 9 illustrates a specific design of Tx and Rx coils with certain important parameters, any of a variety of Tx and Rx designs may be defined as meeting the requirements of a particular application according to embodiments of the present invention.

[0082] (Voltage regulation and UWB telemetry) Previous wireless power receivers typically employ a separate LDO to regulate the rectified voltage. The two-step conversion introduces additional inefficiencies. Also, two large decoupling capacitors are typically required before and after regulation to reduce ripple in the sampled voltage and stabilize the regulation feedback. Resonant regulation rectification schemes are associated with comparator time-selection-induced losses. To address this issue, a power-hungry high-speed comparator can be used, or the system complexity can be significantly increased with the adoption of a delay compensation scheme.

[0083] Therefore, many embodiments of the power receiver regulate the voltage sampled from the transmitter via on-chip voltage digitization and back telemetry. In many embodiments, a 7-bit ADC provides a regulation ratio of approximately 42 dB. Similarly, an IR-UWB transmitter with negligible power consumption can be implemented for potential sharing with other sensing functions.

[0084] (SAR ADC) In many embodiments, a bottom-plate sampling SAR ADC can be implemented. FIG. 11 illustrates a bottom-plate sampling SAR ADC with 7-bit dynamic range in accordance with embodiments of the present invention. In many embodiments, all sample and hold buffers can be power-gated only for the duration of operation, as shown in FIG. 3, to minimize power consumption. The 7-bit ADC output can be serialized and packetized using a "0101" header for back telemetry transmission. While FIG. 11 illustrates a specific circuit schematic of a bottom-plate sampling SAR ADC, any of a variety of circuit schematics can be defined as suited to the requirements of a particular application in accordance with embodiments of the present invention.

[0085] (UWB transmitter) IR-UWB has been widely used in IMD due to its low power consumption and small antenna form factor. Therefore, many embodiments of power receivers employ a filtering edge combining technique to generate an FCC standard UWB impulse. As shown in the schematic diagram of FIG. 12 according to an embodiment of the present invention, a monopulse can first be generated from a delay cell and then passed through an on-chip passive filter.

[0086] M1 may operate in Class C, and an upper cascode transistor M2 may be implemented to avoid voltage overshoot. In many embodiments, the values ​​of filter components C1, C2, L1, and L2 are equal to 981 fF, 444 fF, 614 nH, and 1.69 nH, respectively. As shown in FIG. 13, the estimated drain capacitance of M2 is equal to 221 fF and may be absorbed by C1 to determine the filtering characteristics. The transient waveform and corresponding frequency spectrum of each impulse emitted onto a 50 Ω load according to an embodiment of the present invention are shown in FIGS. 14(a) and 14(b), respectively. In particular, FIG. 14(a) illustrates the transient waveform of a UWB impulse, and FIG. 14(b) illustrates the frequency spectrum. In many embodiments, the system may only be required to transmit approximately 20 impulses per second, which easily complies with FCC emission masks.

[0087] In many embodiments, the transmitter is positive edge triggered, so the input symbols may first be converted to return-to-zero format.

[0088] Each logic "1" and logic "0" can be converted to a "10" and a "00", respectively. Therefore, the transmitter symbol rate can be half the clock frequency. Each impulse can be simulated to consume approximately 65.6 pJ (DC energy), and the emitted energy is approximately 2.7 pJ. Twenty emissions per second corresponds to a power dissipation of 1.3 nW.

[0089] (Measurement values) An IC according to many embodiments can be fabricated in a 180 nm CMOS process using a micrograph, as shown in Figure 15. The overall dimensions of the IC are approximately 1.7 mm. 2 Its current dissipation is measured to be 750 nA. In many embodiments, the IC has a minimum V DD,HARV, which may require an input power of 2.88 μW or approximately −25.4 dBm, which determines the sensitivity of the system. A power breakdown graph according to an embodiment of the present invention is shown in FIG.

[0090] Tx and Rx coils, such as those shown in Figure 9, can be fabricated on FR4 laminate. The Tx coil can be matched to a 50 Ω signal source at 13.56 MHz. The power receiver can incorporate a simple 12 mm long monopole antenna for IR-UWB back-telemetry. A horn antenna cascaded with a bandpass filter and low-noise amplifier, as shown in Figure 17 according to an embodiment of the present invention, can be positioned 30 cm away as a back-telemetry receiver.

[0091] As shown in Figure 18, according to an embodiment of the present invention, the ADC output versus the sampled voltage can be wirelessly measured with remarkable linearity. The results also demonstrate the proper design of auxiliary blocks such as the BGR and local LDO. The integral nonlinearity (INL) according to an embodiment of the present invention, e.g., the difference between the measured code and the ideal value (red line), is plotted in Figure 19, which rarely exceeds half an LSB.

[0092] As shown in FIG. 20 according to an embodiment of the present invention, two power receivers #A and #B can be assembled with #B incorporating an additional 10-pF parallel capacitor. They can be used to drive a 300 kΩ resistor, which typically exhibits tens of μW IMD. At wireless power onset, sample #A automatically adjusts SW5-SW0 to "100100," while #B adjusts them to "001010." Because each switched capacitor unit contributes 380 fF, the code difference is 26, which corresponds to 9.9 pF. This result is very close to the nominal value of the additional capacitor, 10 pF.

[0093] The power transfer efficiency as a function of Tx-Rx distance is investigated. The measurements are performed at distances of 2 cm, 3 cm, 5 cm, and 8 cm. As shown in FIG. 21 according to an embodiment of the present invention, the Tx power is adjusted until the wireless reading shows "1001100", indicating an output voltage of 3 V. The end-to-end efficiency (as shown in FIG. 22) can be calculated as the ratio between the load power of 30 μW and the Tx power. At 2 cm, the overall link efficiency reaches a high of 16.1%. The efficiencies for Samples #A and #B are very close, with a difference of less than 10%.

[0094] Since the rectification and loading efficiencies according to an embodiment of the present invention are equal to 49.9% and 93.02% (10 / 10.75), respectively, the inductive coupling efficiency as a theoretical power transfer limit can be estimated and plotted in Figure 22. The power breakdown for the 2 cm scenario assuming a Tx power of 186.2 μW according to an embodiment of the present invention is shown in Figure 23.

[0095] The rectifier input impedance can be simulated to incorporate a parallel resistor of 3.27 kΩ. Therefore, taking into account the inductance of the Rx coil, the quality factor of the front-end tank is approximately equal to 6. Without resonant compensation, a 10 pF capacitor offset degrades link efficiency by 89% according to the simulation of FIG. 10 in accordance with an embodiment of the present invention. Estimated results without SART in accordance with an embodiment of the present invention are also plotted in FIG. 22.

[0096] To demonstrate the operation of inductive coupling and an IR-UWB data link, as shown in FIG. 24 according to an embodiment of the present invention, a piece of 1.5 cm thick pork loin is used to completely cover the power receiver. Notably, the IR-UWB signal exhibits weakened swing due to tissue loss (FIG. 24(c-f)), while the power transfer link efficiency remains unchanged, as evidenced by the unchanged collected voltage, which is consistent with the nature of magnetic coupling. This feature was also verified in an in vivo experiment, where inductive-based power transfer was demonstrated through the chest of a pig model.

[0097] Example waveforms for SW5-SW0 adaptation according to an embodiment of the present invention are demonstrated in FIG. 25. When SART is performed, convergence takes only 12 clock cycles or 2.4 ms. The response of a power receiver to a transient resonant capacitor offset according to an embodiment of the present invention is measured with the aid of a commercially available digitally controlled capacitor, the IXYS NCD2100, connected in parallel at the front end, as shown in FIG. 26. The power receiver output node connects a 300 kΩ load resistor and a 47 μF decoupling capacitor. The capacitor offset according to an embodiment of the present invention is varied between 11 pF and 28 pF every 8 s, and the output waveform is shown in FIG. 27. While a voltage droop occurs at each switch, the output voltage resumes its approximate value. The recovery time depends on the decoupling capacitance.

[0098] The capacitance of the NCD2100 is swept across its entire range. 6.6 pF to 37.553 pF is covered by 10 control bits, including coarse and fine bits. According to its datasheet, the capacitance as a function of the control code is demonstrated in the inset of FIG. 28, according to an embodiment of the present invention. The dependency is not perfectly linear. As shown in FIG. 28, according to an embodiment of the present invention, measurements show that the IC accurately compensates for offsets within its entire dynamic range. As shown in FIG. 29, according to an embodiment of the present invention, the output voltage remains relatively stable for resonant capacitor offsets from 6.6 pF to approximately 29 pF, which corresponds to the self-resonant frequency of the Rx tank up to approximately 26.5 MHz. Because the system's operation is based on discrete compensation capacitance values, small variations exist. Only when the capacitor offset is outside the compensation range does the output voltage exhibit a dramatic drop.

[0099] As summarized in Table II of FIG. 30 and FIG. 31, resonance compensation techniques according to various embodiments of the system are compared with the prior art. The SART techniques according to various embodiments of the present invention are time- and energy-efficient, thus not only addressing one-time calibration but also providing real-time adaptability to constantly changing dielectric environments and loading conditions. Prior art inductive power receivers for low-power IMDs are further compared in Table III. Accordingly, various embodiments feature low input power sensitivity, making them particularly suitable for powering ultra-low-power IMDs. When driving a 30 μW load, an end-to-end efficiency of approximately 16% is achieved regardless of a 10-pF capacitor offset. Because high power transfer efficiency becomes increasingly challenging for lighter loads, efficiencies normalized to the corresponding loads are discussed.

[0100] Although specific implementations for inductive power receivers and sensors with real-time resonance adaptation and wireless voltage regulation are discussed above with respect to FIGS. 1-31 , any of a variety of implementations utilizing the techniques discussed above can be utilized for power receivers and / or sensors in accordance with embodiments of the present invention. While the above description includes many specific embodiments of the present invention, these should not be construed as limitations on the scope of the invention, but rather as an example of one embodiment thereof. It should therefore be understood that the invention may be practiced other than as specifically described without departing from the scope and spirit of the invention. Accordingly, the present embodiments should be considered in all respects as illustrative and not restrictive.

Claims

1. An implantable medical device, comprising: an induction coil having a resonant frequency that varies due to one or more of movement of the IMD, scar tissue accumulation, and loading conditions, the induction coil configured to receive power from an external transmitter; a power-receiving RF-DC rectifier; a capacitor bank having an input coupled to the induction coil and an output coupled to the power-receiving RF-DC rectifier, the capacitor bank comprising a plurality of capacitor units configured to be switched; a periodically enabled closed feedback loop comprising a resonance compensator coupled to the capacitor bank, the resonance compensator configured to sample measurements of the input of the capacitor bank and to adapt settings of the capacitor bank in real time based on the measurements to optimize power transfer to a load due to changes in the resonant frequency of the induction coil; An implantable medical device comprising:

2. The implantable medical device of claim 1, further comprising a transmitter configured to transmit real-time collected voltage readings from the power-receiving RF-DC rectifier to an external controller.

3. The implantable medical device of claim 2, further comprising an analog-to-digital converter (ADC) configured to digitize the real-time collected voltage readings.

4. A system cycle is executed at a specific frequency based on a clock signal, and the system cycle the sampling of measurements of the inputs of the capacitor bank and the adaption of settings of the capacitor bank by the periodically enabled closed feedback loop; the digitization of the real-time collected voltage readings by the ADC; and said transmitting said real-time collected voltage readings by said transmitter; 4. The implantable medical device of claim 3, comprising:

5. The implantable medical device of claim 1, wherein the capacitor bank is a 6-bit capacitor bank configured to be periodically adjusted using a successive approximation resonant tuning process (SART).

6. The implantable medical device of claim 1, further comprising a coarse bandgap reference (BGR-coarse) and a local low dropout regulator (LDO) that generate a voltage supply for the resonant compensator.

7. The implantable medical device of claim 4, further comprising a narrow bandgap reference (BGR-thin) coupled to the LDO and configured to generate a stable voltage reference.

8. An implantable medical device as described in claim 1, wherein the load includes an energy harvesting device.

9. An external controller; Implantable medical devices and wherein the implantable medical device comprises: an induction coil having a resonant frequency that varies due to one or more of movement of the IMD, scar tissue accumulation, and loading conditions, the induction coil configured to receive power from an external transmitter; a power-receiving RF-DC rectifier; a capacitor bank having an input coupled to the induction coil and an output coupled to the power-receiving RF-DC rectifier, the capacitor bank comprising a plurality of capacitor units configured to be switched; a periodically enabled closed feedback loop comprising a resonance compensator coupled to the capacitor bank, the resonance compensator configured to sample measurements of the input of the capacitor bank and to adapt settings of the capacitor bank in real time based on the measurements to optimize power transfer to a load due to changes in the resonant frequency of the induction coil; A system comprising:

10. The system of claim 9, further comprising a transmitter configured to transmit real-time collected voltage readings from the power-receiving RF-DC rectifier to the external controller.

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