Measuring and reporting of charge level information from communication devices

Abstract

There is provided a communication device for conveying charge level information. The communication device comprises an energy harvester arranged to harvest energy by receiving a first input signal from an energy source. The communication device comprises an energy storage comprising an energy storage component for storing the harvested energy and for supplying power to the communication device. The communication device comprises at least one voltage detector configured to determine a charge level of the communication device by is arranged to measure a voltage over the energy storage component. The communication device comprises a backscatter module configured to generate an information sequence representative of the voltage, and to use backscatter modulation of a wirelessly received second input signal for backscattering the information sequence. The information sequence conveys information about the charge level.

Description

[0001] MEASURING AND REPORTING OF CHARGE LEVEL INFORMATION FROM COMMUNICATION DEVICES

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a communication device, a computer program, and a computer program product for conveying charge level information of the communication device.

[0004] BACKGROUND

[0005] A radio communication protocol, such used in Long-Term Evolution (LTE), New Radio (NR), or other types of third-generation partnership project (3GPP) compliant telecommunication systems or wireless local area networks, such as IEEE 802.11 based protocols defined by IEEE, typically assumes that a communication device is capable for communication, such as reachable for paging signals or similar, at predefined time intervals when being in idle mode and camping on the network, and even more so if being in a connected mode (e.g., in radio resource control (RRC) connected state in 3GPP).

[0006] Communication devices can be powered by means of different types of energy sources. Some non-limiting examples, of power sources for communication devices are lithium-ion batteries, nickel-metal hydride batteries, solar panels, supercapacitors, piezoelectric energy harvesters, thermoelectric generators, and radio-frequency (RF) energy harvesting systems.

[0007] WO2O24199624A1 relates to configuration of energy harvesting devices in a wireless communication network. Proposals for radio communication protocol enhancements are proposed, enabling a communication device which has energy available for data generation to be actively communicating an energy harvesting profile to a network node. Such energy harvesting profile may include one or more of an energy harvesting source type of the communication device, an energy harvesting rate, an energy harvesting schedule, an energy harvesting time duration, an energy storage amount, and an energy storage capacity of the communication device. For example, the energy harvesting profile may state that the communication device is able to continuously harvest a certain amount of energy per time unit. Further, the communication device may indicate that it is capable of a first harvesting method(e.g., solar power-based energy harvesting), a second harvesting method (e.g., vibrational power-based energy harvesting), and so on, and also to indicate the amount of potential harvesting energy per harvesting method. Further the energy profile may include an energy consumption profile. Information of the energy profile maybe transmitted via RRC signaling, physical random access channel (PRACH) signaling, Layer 1 signaling, Layer 2 signaling, or physical uplink control channel (PUCCH) signaling. Thus, the signaling is based on existing protocols for radio signaling. However, such signaling consumes power in the communication device.

[0008] A potentially more energy-efficient way to convey information from a communication device is to use backscatter modulation. Accordingly, an incident electromagnetic wave is reflected and modulated to transmit information. In W02024130585A1 is disclosed using backscatter modulation to transmit harvesting information from a communication device to a network. Here, the harvesting information may include different aspects such as current RF harvesting efficiency or indicate a state of charge of energy storage in the device.

[0009] However, a communication device utilizing one or more energy harvesting sources maybe somewhat limited in the communication availability, depending on the state of harvesting. As example, a communication device may require a certain state of charge (SOC) of an energy storage, such as a capacitor or similar, for a signal transmission from the communication device to be successful. In other words, contrary to the expectations assumed in W02024130585A1, a communication device whose power source is based on energy harvesting may not always be enabled for communication, although the communication device is registered in the network.

[0010] Specifically, even if a basic energy harvesting profile would be available at the network, e.g. as proposed in WO2O24199624A1, or via a more detailed state of charge indication via backscattering as in W02024130585A1 the challenge of how to measure the SOC in an energy efficient manner still remains.

[0011] Hence, there is still a need for energy efficient measurements of the SOC in communication devices.SUMMARY

[0012] An object of embodiments disclosed herein is to address the above issues, enabling energy efficient measurements of the SOC to be made in communication devices.

[0013] A particular object of embodiments disclosed herein is to provide a measuring and reporting function of the SOC of a communication device, consuming so little power that the energy harvesting in the communication device is barely impacted, preferably below nW level.

[0014] According to a first aspect there is presented a communication device for conveying charge level information. The communication device comprises an energy harvester arranged to harvest energy by receiving a first input signal from an energy source. The communication device comprises an energy storage comprising an energy storage component for storing the harvested energy and for supplying power to the communication device. The communication device comprises at least one voltage detector configured to determine a charge level of the communication device by is arranged to measure a voltage over the energy storage component. The communication device comprises a backscatter module configured to generate an information sequence representative of the voltage, and to use backscatter modulation of a wirelessly received second input signal for backscattering the information sequence. The information sequence conveys information about the charge level.

[0015] According to a second aspect there is presented a method for conveying charge level information of a communication device. The method is performed by the communication device. The method comprises harvesting energy by receiving a first input signal from an energy source. The method comprises storing, in an energy storage comprising an energy storage component, the harvested energy and supplying power to the communication device. The method comprises determining, by at least one voltage detector arranged to measure a voltage over the energy storage component, a charge level of the communication device. The method comprises generating an information sequence representative of the voltage. The method comprises backscattering the information sequence using backscatter modulation of a wirelessly received second input signal. The information sequence conveys information about the charge level.According to a third aspect there is presented a computer program for conveying charge level information of a communication device. The computer program comprises computer code which, when run on processing circuitry of the communication device, causes the communication device to perform actions. One action comprises the communication device to harvest energy by receiving a first input signal from an energy source. One action comprises the communication device to store, in an energy storage comprising an energy storage component, the harvested energy and supplying power to the communication device. One action comprises the communication device to determine, by at least one voltage detector arranged to measure a voltage over the energy storage component, a charge level of the communication device. One action comprises the communication device to generate an information sequence representative of the voltage. One action comprises the communication device to One action comprises the communication device to backscatter the information sequence using backscatter modulation of a wirelessly received second input signal. The information sequence conveys information about the charge level.

[0016] According to a fourth aspect there is presented a computer program product comprising a computer program according to the third aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

[0017] Advantageously, these aspects enable energy efficient measurements of the SOC to be made in the communication device and reported to the network.

[0018] Advantageously, these aspects enable the communication device to consume so little power for the measuring and reporting function of the SOC that the energy harvesting in the communication device is barely impacted, and could be as little as below nW level.

[0019] Advantageously, these aspects thus yield extremely low energy consumption. In more detail, the disclosed communication device requires very little power for not only reporting the SOC but also for actually measuring the SOC, thereby minimizing its consumption from the energy storage. It is thus possible to obtain information about the charging state without significantly affecting it, which would otherwise offset theadvantages of performing the measurement. The expected total power consumption is in the range from a pW to a nW, depending on the supply voltage, thus making it feasible even for low-power communication devices.

[0020] Advantageously, these aspects enable network scheduling on high time granularity. In further detail, the network can be informed about the SOC of the communication device without draining the energy storage at the communication device, in turn enabling better scheduling of operations, such as reducing latency and / or improving network resource allocations and thereby system efficiency. The network can also better plan wireless charging of the communication device. The communication and charging of the communication device can also be from other devices, like a device acting as a reader that wirelessly powers another communication device and then communicates with it when sufficiently charged.

[0021] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0022] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0025] Fig. 1 is a schematic diagram illustrating a communication system according to embodiments;

[0026] Fig. 2 is a block diagram of a communication device according to an embodiment;

[0027] Fig. 3 is a block diagram of part of a communication device according to an

[0028] embodiment;Fig. 4 illustrates a digital state machine according to an embodiment;

[0029] Fig. 5 schematically illustrates a voltage detector according to an embodiment;

[0030] Fig. 6 is a flowchart of methods according to embodiments;

[0031] Fig. 7 is a schematic diagram showing structural units of a communication device according to an embodiment; and

[0032] Fig. 8 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

[0033] DETAILED DESCRIPTION

[0034] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0035] Fig. 1 is a schematic diagram illustrating a communication system 100 according to embodiments. A communication device no and a network node 150 are configured for communication with each other over a wireless link 160. The communication device 110 may be any of: a low-power Internet-of-Things (loT) device, an extended reality (XR) device, a smart sensor, a wearable device, a medical implant, a smart home device, a monitoring device. The communication device no is configured for energy harvesting from an energy source 120. In the illustrated embodiment, the energy source 120 is external to the communication device no. As illustrated in more detail in Fig. 1, the communication device no is configured for receiving a first input signal 130 from the energy source 120. The first input signal 130 maybe any of: a radio frequency signal, an acoustic signal, a light signal, a thermal signal, a mechanical signal, a magnetic signal, an electrostatic signal. As will be further disclosed below, e.g., with reference to Fig. 2, the first input signal 130 is received byan energy harvester in the communication device no. Further, information about the charge level of the communication device 110 is conveyed by means of second input signal 160 being backscattered 140 by the communication device 110. In the illustrative examples of Fig. 1, the second input signal 160 is represented by a downlink signal sent on the wireless link 160. The first input signal and the second input signal could be one and the same input signal (e.g., when the first input signal is an RF signal).

[0036] As noted above, there is still a need for energy efficient measurements of the SOC in communication devices.

[0037] In further detail, measuring the energy storage state, such as the voltage level of a capacitor or battery, in a communication device is an operation that, in itself, consumes power. This is because typically analogue-to-digital converters (ADCs) are used to measure the voltage at the energy storage and the communication device needs to activate the ADC, a clock and a reference voltage for the ADC to take the measurement, process the data, and then transmit or store the information to memory. This process can consume a significant amount of power relative to the overall energy budget typical of some low-energy communication devices, such as ambient loT devices.

[0038] At least some of the herein disclosed embodiments are therefore based not only on that the communication device communicates its charge level through backscattering, but also that the communication device measures the charge level in an energy-efficient manner. In particular, the communication device may communicate different backscattered sequences that represent different states of charge, where the different states of charge are determined through voltage measurements.

[0039] The embodiments disclosed herein in particular relate to techniques for conveying charge level information. In order to obtain such techniques, there is provided a communication device no, a method performed by the communication device 110, a computer program product comprising code, for example in the form of a computer program, that when run on a communication device no, causes the communication device 110 to perform the method.Reference is next made to the block diagram of Fig. 2 illustrating a communication device 200 for conveying charge level information according to an embodiment. The communication device 200 comprises an energy harvester 210. The energy harvester 210 is arranged to harvest energy by receiving a first input signal 130 from an energy source 120. In the illustrated embodiment, the energy source 120 is external to the communication device 200. The communication device 200 comprises an energy storage 220. The energy storage 220 comprises an energy storage component for storing the harvested energy and for supplying power to the communication device 200. The energy storage component maybe, or comprise, at least one capacitor or at least one battery. The communication device 200 further comprises at least one voltage detector 230. The at least one voltage detector 230 is configured to determine a charge level of the communication device 200 by being arranged to measure a voltage over the energy storage component. The charging level may represent either a current energy level stored in the energy storage 220 or an indication of whether the energy storage 220 has reached at least one predefined charge threshold. The communication device 200 further comprises a backscatter module 240. The backscatter module 240 is configured to generate an information sequence representative of the voltage, and to use backscatter modulation of a wirelessly received second input signal 160 for backscattering the information sequence. The information sequence conveys information about the charge level. In this respect, the first input and the second input signal maybe one and the same signal or maybe different input signals. For example, in case the first input signal is an RF signal received from the network node 150, then this first input signal may also represent the second input signal. That is, the second input signal used for backscattering may be the same RF signal as used for energy harvesting.

[0040] The communication device 200 may further comprise an application module 250. Depending on the type of communication device 200, the application module 250 maybe configured to perform different operations. In order to do so, the application module 250 may comprise one or more sensors, processing circuitry, a communication interface, and a storage medium. The storage medium may hold instructions that are executed by the processing circuitry, in combination with the communication interface and the one or more sensors, for fulfilling the intended functionality of the communication device 200. In some aspects, the applicationmodule 250 implements a power management functionality. For example, the energy storage component may supply power to the communication device 200 via the application module 250.

[0041] Further aspects of the voltage detector and the backscatter module will be disclosed next with reference to the block diagram of Fig. 3. In Fig. 3 is illustrated part of the communication device in Fig. 2, focusing on the backscatter module 310 and the voltage detector. The voltage detector, described in detail below, will detect if the energy storage is above or below a certain level. The communication device may comprise a plurality of voltage detectors, as in Fig. 3 represented by N>1 voltage detectors 360-1, 360-N.

[0042] Further aspects of the backscatter module 310 will be disclosed next.

[0043] In the example of Fig. 3, the backscatter module 310 comprises a low-frequency oscillator 320 and implements a digital state machine 330. The low-frequency oscillator 320 maybe configured to either operate continuously or until a charge level of the energy storage 220 reaches a predefined low charge threshold. In some examples, the low-frequency oscillator 320 is a low-frequency relaxation oscillator. The low-frequency relaxation oscillator can be realized in the picowatt range. The digital state machine 330 is configured to generate the information sequence to be communicated based on input from the one or more voltage detectors 360-1, 360-N The digital state machine 330 is arranged to be clocked by the low-frequency oscillator 320 for generating the information sequence to be backscattered. The frequency can be from the Hz range to the kHz range.

[0044] The communication device 200 further comprises an antenna 350. In the block diagram of Fig. 3, the antenna 350 is part of the backscatter module 310. The antenna 350 is arranged to wirelessly receive the second input signal 160 and to backscatter the information sequence. In general terms, the antenna 350 may be composed of one single antenna element or comprise two or more antenna elements. In some examples, the antenna 350 is shared with the energy harvester 210, depending on the type of energy harvester 210. For example, in case the energy harvester 210 is based on receiving RF signals, then the antenna 350 maybe shared between the backscatter module 310 and the energy harvester 210. Further, the antenna 350 maybe coupled to the digital state machine 330 via a transistor 340. The transistor 340 is arranged toreceive the information sequence at its gate terminal and to provide a corresponding impedance sequence to the antenna 350.

[0045] Thus, an antenna 250 could be coupled to a transistor 340 switching between two impedances. When the digital signal is low, the transistor 340 is off, with a gate voltage near zero, the impedance is high. When the digital signal instead is high, the gate voltage is close to the supply voltage, and the impedance presented by the transistor to the antenna 350 is lower. The reflected, back-scattered, signal is then lower in magnitude than for the transistor off-state, and may even change polarity if the transistor 340 is turned on with enough voltage.

[0046] Further aspects of the voltage detectors 360-1, 360-N will be disclosed next. Further aspects of the voltage detectors will also be disclosed further below with reference to Fig. 5-

[0047] In general terms, the higher the number of voltage detectors is, the higher the resolution of the SOC measurement and the higher the power consumption and complexity will be. Depending on the application and on the power budget available, more or fewer voltage detectors may be implemented, provided, or engaged, to either minimize complexity and power consumption or to improve SOC measurement resolution.

[0048] In general terms, the voltage detectors 360-1, 360-N sense a voltage level across the energy storage component (not shown in Fig. 3) and therefrom provide digital signals to the digital state machine 330 indicating whether the sensed voltage is above or below a certain level. Hence, the at least one voltage detector 360-1, 360-N is configured to generate a digital signal indicating whether the voltage measured over the energy storage 220 is above or below a predefined voltage level. In this respect, different voltage detectors 230, 360-1, 360-N may use transistors with different threshold voltages to detect different supply voltage levels. Thus, each of the plurality of voltage detectors 230, 360-1, 360-N may comprise transistors having different threshold voltages. Then each given voltage detector 360-1, 360-N maybe configured to detect whether the voltage over the energy storage 220 is above or below the threshold voltage level for this given voltage detector 230, 360-1, 360-N. The threshold voltage level may be a predefined voltage level, which is dependent on the threshold voltage levels and dimensions of the transistors. In some examples,assuming there are N>1 voltage detectors, some of the voltage detectors maybe dynamically enabled and disabled via switches, to select the desired resolution and energy consumption of the SOC measurement. In addition, to save power, when one voltage detector shows a low result, voltage detectors for higher voltages can be disabled as their results are then known to be low as well. The number of active voltage detectors may be selected by the network or by the communication device itself, for example if the harvested energy from the environment decreases or increases.

[0049] The low frequency oscillator may also clock the voltage detectors 230, 360-1, 360-N. In particular, the low-frequency oscillator 320 may further be arranged to provide clock signals for duty-cycling operation of the plurality of voltage detectors 360-1, 360-N to reduce the static power consumption.

[0050] Operations of the digital state machine 400 will be disclosed next with reference to Fig. 4- As disclosed above, the digital state machine 400 may receive digital input signals from the voltage detectors 230, 360-1, 360-N as the voltage detectors 230, 360-1, 360-N are sensing the supply voltage, so that the generated information sequence will be different depending on the measured voltage over the energy storage component. That is, the digital state machine 330 is configured to receive the digital signal as input, for the information sequence as generated by the digital state machine 330, 400 to depend on the voltage measured over the energy storage 220. As disclosed above, the digital state machine 400 is arranged to be clocked by the low-frequency oscillator 320. The digital state machine 400 maybe implemented in hardware using flip-flops and CMOS logic (where CMOS is short for complementary metal-oxide-semi conductor).

[0051] In the example in Fig. 4 there are signals Deti and Det2 from two voltage level detectors serving as inputs to the state machine. The state machine comprises four D-type flip-flops 4ioa:4iod storing the state, being clocked by a clock signal derived from the low frequency oscillator. The state machine has the architecture of a linear feedback shift register, where feedback is created by an XOR gate 420. The XOR gate 420 takes one input at the output of the first flip-flop 410a in the shift register, and effectively it takes the other input as a combined output of the second, third, or fourthflip-flop 4iob:4iod. That other input is also inverted for proper functionality. The selection of feedback signal point between the three flip-flop outputs is realized by a multiplexer that is formed by three AND gates 43oa:43od followed by a 3-input NOR gate 440, and where the signal inversion thus is realized by the use of the NOR gate 440 rather than an OR gate. The selection of feedback point will determine the sequence created at the output, and if no detector signal is high, a NOR gate 450 controls the AND gate 430a corresponding to the second D-flip-flop output to select that signal. The state machine will then go through a cycle of 3 states creating an output signal that is high 33% of the time. If the first detector signal is high, but not the second, the feedback will, by means of the AND gate 480 having an inverter at one of its inputs, be taken at the output of the third flip-flop, and the state machine will go through a cycle of 7 states, creating a different pattern of the output (..., 0,0, 0,1, 0,1,1, ...). Finally, if the second detector signal is high, the output of the fourth flip-flop is selected for feedback, and the circuit will go through a series of 15 states, creating yet another sequence. In all cases, if the state of the flip-flops would be all high, the state machine gets stuck in that state. For that reason, a NAND gate 460 is provided to detect that state, and ensure that in such a case a zero is inserted into the first flip-flop 410 (via AND gate 470), after which the circuit will enter the desired cycle.

[0052] In general terms, the voltage detectors should have low power consumption and still be able to provide comparisons with accurate levels. Examples of how such voltage detectors can be provided will be disclosed next with reference to Fig. 5. In Fig. 5 is illustrated a circuit diagram of one such voltage detector according to an example. In this example, the voltage detector comprises a transistor M3 arranged to receive one of the aforementioned clock signals for clocking the voltage detector. Further, as disclosed above, the different voltage detectors may use transistors with different threshold voltages to detect different supply voltage levels. The clocking reduces the power consumption by duty-cycling the voltage detector. It is especially efficient if the clock has a low duty-cycle, which can be the case if a relaxation oscillator with nonequal charging and discharging current of the oscillator capacitor is used. For instance, the relaxation oscillator may rapidly charge the capacitor and slowly discharge it. Then the control signal activating the charging switch will have a low duty cycle.The clocking of the voltage detector is performed by transistor M3 turning on the voltage comparison branch composed of transistors Ml, M2 and M3. When that voltage comparison branch is on, the output is sampled on capacitor C using the clocked transmission gate M4, M5 which is active at the same time as transistor M3. A non-clocked version of the supply voltage detector would only consist of transistors Mi, M2, M6 and M7. Depending on the digital state-machine, also the buffering provided by transistors M6, M7 may be optional for both clocked and non-clocked voltage detectors.

[0053] It is possible to merge transistors M2 and M3 into a single transistor if a larger clock load is acceptable, or if the circuit is not to be clocked at all. For this purpose, an NMOS transistor (where NMOS is short for N-type metal-oxide-semiconductor) with a larger W / L aspect ratio than the combined transistor M2 and M3 can be used, where the NMOS transistor has a higher absolute threshold voltage than the PMOS transistor M2 (where PMOS is short for p-channel metal-oxide-semiconductor). When the inverted clock (elk) signal is low, thus activating the branch, there is a competition between the NMOS transistor and the PMOS transistor, and depending on which transistor can conduct more drain current determines if the output goes high or low. It is also possible to reverse the roles of NMOS transistor and the PMOS transistor, with a larger PMOS transistor with higher absolute threshold voltage, and the output signal will then have opposite digital values for low and high supply voltage, compared to what is described below.

[0054] When the supply voltage is low, both NMOS and PMOS transistors are in the subthreshold region and have an exponential gate voltage to drain current characteristic. The transistors are sized so that the PMOS transistor with its lower threshold voltage provides more saturated drain current, even if the NMOS transistor is larger and has higher mobility. The output of the transistor branch Ml, M2, M3 is then high. The high value is sampled on the capacitor, and inverted by the transistor branch M6, M7 to a low output value. When the supply voltage is higher, well exceeding the threshold voltage of the PMOS transistor, the PMOS characteristic is no longer exponential. The NMOS transistor will then catch up and eventually get a higher saturated current, pulling the output low. The low value is sampled on the capacitor, and inverted by the transistor branch M6, M7 to a high output value.Since the output is different for low and high supply voltages, the voltage detector performs its task. The transition point is to a large extent related to the threshold voltages of the NMOS transistor and the PMOS transistor and their aspect ratios. Since those quantities are accurately known, also the detection level becomes accurate. If multiple detection levels are needed, different transistor aspect ratios can be used in different voltage detectors, but it may be even better if transistors with different threshold voltage options are available in the semiconductor process used. Depending on process used, there may also be different options for body-biasing to alter the threshold voltages. For instance, in Silicon On Insulator (SOI) processes rather high body biases can often be applied.

[0055] One non-limiting example of approximating the power consumption per voltage detector will be disclosed next.

[0056] Assume first a non-clocked voltage detector consisting of transistors Ml and M2 implemented in 6snm CMOS technology according to specifications available here https: / / www.eit.lth.se / f1leadmin / eit / courses / etin3o / 65nm_CMOS_Process_Data_S heet.pdf as available per 14 March 2025. Assume, for example, that transistor M2 has a threshold voltage of -0.6V, whereas transistor Mi has a threshold voltage of 0.3V. Assume, for example, that transistor Mi has W / L ratio equal to 0.01, and that transistor M2 has a W / L ratio equal to 4.

[0057] At low supply voltages both transistors Ml and M2 will be in the subthreshold region. At Vdd=o.3V the saturated drain current of the communication device is given by:

[0058]

[0059] This becomes o.8onAfor the PMOS transistor and lynAfor the NMOS transistor. The NMOS transistor will pull the drain node to a low potential, and the direct current (DC) level will be determined by the PMOS transistor. The power consumption of the branch becomes o.8onA • 0.3V = 24opW, when active.

[0060] At higher Vdd, the NMOS transistor will enter strong inversion, and will have less saturation current than the PMOS transistor. At Vdd=o.5V, the NMOS transistor will have a saturation current of:

[0061]

[0062] The PMOS transistor will then have a saturation current of 140 nA. The PMOS transistor is now stronger and will pull the drain node to a high voltage level. The DC current is then set by the NMOS, and the power consumption becomes 88nA • 0.5V = 44nW.

[0063] While these power levels are low, in an energy harvesting node there may be a need for even lower power. If the voltage detector is duty-cycled, clocked with a 1% dutycycle clock from the relaxation oscillator, the power consumption of the voltage detector will be reduced to 2.4pW at 3V and o.44nW at 0.5V. The clocking at a few Hz will not cause significant power consumption in the voltage detector circuit.

[0064] The expected total power consumption of a voltage detector may therefore be in the range from a pW to a nW, depending on the supply voltage, making the implementation feasibility for a low power energy harvesting device. The power consumption is very low at low supply voltages when little energy is available.

[0065] Fig. 6 is a flowchart illustrating embodiments of methods for conveying charge level information. The methods are performed by the communication device no, 200. The methods are advantageously provided as computer programs. The methods may be implemented in accordance with what has been disclosed with reference to Fig. 2, Fig. 3, fig. 4, and Fig. 5.

[0066] S102: The communication device no, 200 harvests energy by receiving a first input signal 130 from an energy source 120. The energy source 120 maybe external to the communication device no, 200 or it maybe a part of the communication device 110, 200.

[0067] S104: The communication device no, 200 stores, in an energy storage 220 comprising an energy storage component, the harvested energy and supplies power to the communication device no, 200.

[0068] S106: The communication device no, 200 determines, by at least one voltage detector 230, 360-1, 360-N arranged to measure a voltage over the energy storage component, a charge level of the communication device 110, 200. The at least onevoltage detector 230, 360-1, 360-N thus senses the supply voltage level and generates digital signals indicating whether the supply voltage is above or below a certain level. As disclosed above, each voltage detector may comprise transistors with a certain threshold voltage to detect a given supply voltage level. The transistor threshold voltage maybe dynamically set (e.g., by tuning transistor body bias voltage) to detect different supply voltage levels.

[0069] S108: The communication device no, 200 generates an information sequence representative of the voltage level. The information sequence may by the communication device no, 200 be generated using a digital state machine, having the voltage detector signals as input. Multiple voltage detectors can be used to detect various supply voltage levels and the digital state machine can thus generate the corresponding backscatter sequences. A low frequency oscillator may clock the digital state machine. The low frequency oscillator may also clock the voltage detectors. The low frequency oscillator maybe a relaxation oscillator.

[0070] S112: The communication device no, 200 backscatters the information sequence using backscatter modulation of a wirelessly received second input signal 160. The information sequence conveys information about the charge level. Hence, different backscattered information sequences represent different charging states. The charging state can be a voltage level detected from the energy storage component which supplies power to the communication device no, 200.

[0071] Embodiments relating to further details of conveying charge level information as performed by the communication device no, 200 will now be disclosed with continued reference to Fig. 6.

[0072] As disclosed above, the second input signal 160 maybe received via an antenna in the communication device no, 200. Hence, in some embodiments, the communication device 110, 200 is configured to perform (optional) step S110.

[0073] S110: The communication device no, 200 wirelessly receives the second input signal 160.

[0074] In this respect, as disclosed above, the first input and the second input signal may be one and the same signal. For example, this could be the case where the first inputsignal is an RF signal received from the network node 150. Therefore, step S110 may only be performed in case the second input signal is different from the first input signal.

[0075] Fig. 7 schematically illustrates, in terms of a number of structural units, the components of a communication device 700 according to an embodiment. As per above, the communication device 700 maybe any of a low-power Internet of Things device, an extended reality device, a smart sensor, a wearable device, a medical implant, a smart home device, a monitoring device. Processing circuitry 710 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 810 (as in Fig. 8), e.g. in the form of a storage medium 730. The processing circuitry 710 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0076] Particularly, the processing circuitry 710 is configured to cause the communication device 700 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 730 may store the set of operations, and the processing circuitry 710 maybe configured to retrieve the set of operations from the storage medium 730 to cause the communication device 700 to perform the set of operations. The set of operations maybe provided as a set of executable instructions.

[0077] Thus the processing circuitry 710 is thereby arranged to execute methods as herein disclosed. The storage medium 730 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The communication device 700 may further comprise a communications (comm.) interface 720 at least configured for communications with other entities, functions, nodes, and devices, as in Fig. 1. As such the communications interface 720 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 710 controls the general operation of the communication device 700 e.g. by sending data and control signals to the communications interface 720 and the storage medium 730, by receiving data and reports from the communications interface 720, and by retrieving data and instructions from the storage medium 730.Other components, as well as the related functionality, of the communication device 700 are omitted in order not to obscure the concepts presented herein.

[0078] Further, as has been disclosed above with reference to Fig. 2, the communication device 700 may comprises an energy harvester, an energy storage, a voltage detector, a backscatter module, and an antenna.

[0079] Fig. 8 shows one example of a computer program product 810 comprising computer readable storage medium 830. On this computer readable storage medium 830, a computer program 820 can be stored, which computer program 820 can cause the processing circuitry 710 and thereto operatively coupled entities and devices, such as the communications interface 720 and the storage medium 730, to execute methods according to embodiments described herein. The computer program 820 and / or computer program product 810 may thus provide means for performing any steps as herein disclosed.

[0080] In the example of Fig. 8, the computer program product 810 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 810 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 820 is here schematically shown as a track on the depicted optical disk, the computer program 820 can be stored in any way which is suitable for the computer program product 810.

[0081] The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. A communication device (110, 200, 700) for conveying charge level information, wherein the communication device (no, 200, 700) comprises:an energy harvester (210) arranged to harvest energy by receiving a first input signal (130) from an energy source (120);an energy storage (220) comprising an energy storage component for storing the harvested energy and for supplying power to the communication device (no, 200, 700);at least one voltage detector (230, 360-1, 360-N, 500) configured to determine a charge level of the communication device (110, 200, 700) by being arranged to measure a voltage over the energy storage component; anda backscatter module (240, 310) configured to generate an information sequence representative of the voltage, and to use backscatter modulation of a wirelessly received second input signal (160) for backscattering the information sequence, wherein the information sequence conveys information about the charge level.

2. The communication device (110, 200, 700) according to claim 1, wherein the backscatter module (240, 310) comprises a low-frequency oscillator (320) and implements a digital state machine (330, 400).

3. The communication device (110, 200, 700) according to claim 2, wherein the low-frequency oscillator (320) is configured to operate continuously or until a charge level of the energy storage (220) reaches a predefined low charge threshold.

4. The communication device (110, 200, 700) according to claim 2 or 3, wherein the low-frequency oscillator (320) is a low-frequency relaxation oscillator.

5. The communication device (no, 200, 700) according to any of claims 2 to 4, wherein the digital state machine (330, 400) is arranged to be clocked by the low-frequency oscillator (320) for generating the information sequence to bebackscattered.

6. The communication device (110, 200, 700) according to any preceding claim, wherein the at least one voltage detector (230, 360-1, 360-N, 500) is configured to generate a digital signal indicating whether the voltage measured over the energy storage (220) is above or below a predefined voltage level.

7. The communication device (no, 200, 700) according to a combination of any of claims 2 to 5 with claim 6, wherein the digital state machine (330, 400) is configured to receive the digital signal as input, for the information sequence as generated by the digital state machine (330, 400) to depend on the voltage measured over the energy storage (220).

8. The communication device (no, 200, 700) according to any preceding claim, wherein the communication device (no, 200, 700) comprises a plurality of voltage detectors (230, 360-1, 360-N, 500).

9. The communication device (no, 200, 700) according to claim 8, wherein each of the plurality of voltage detectors (230, 360-1, 360-N, 500) comprises transistors having different threshold voltages, and wherein each given voltage detector (230, 360-1, 360-N, 500) is configured to detect whether the voltage over the energy storage (220) is above or below the threshold voltage level for said given voltage detector (230, 360-1, 360-N, 500).

10. The communication device (no, 200, 700) according to a combination of claim 2 with claim 9, wherein the low-frequency oscillator (320) is further arranged to provide clock signals for duty-cycling operation of the plurality of voltage detectors (230, 360-1, 360-N, 500).

11. The communication device (no, 200, 700) according to claim 9 or 10, wherein the plurality of voltage detectors (230, 360-1, 360-N, 500) each comprises a transistor (M3) arranged to receive a respective one of the clock signals.

12. The communication device (no, 200, 700) according to any preceding claim, wherein the charging level represents either a current energy level stored in the energy storage (220) or an indication of whether the energy storage (220) has reached at least one predefined charge threshold.13- The communication device (110, 200, 700) according to any preceding claim, wherein the communication device (no, 200, 700) further comprises:an antenna (350) arranged to wirelessly receive the second input signal (160) and to backscatter the information sequence.

14. The communication device (no, 200, 700) according to a combination of claim 2 with claim 13, wherein the antenna (350) is coupled to the digital state machine (330, 400) via a transistor (340), and wherein the transistor (340) is arranged to receive the information sequence at its gate terminal and to provide a corresponding impedance sequence to the antenna (350).

15. The communication device (no, 200, 700) according to any preceding claim, wherein the first input signal (130) is any of: a radio frequency signal, an acoustic signal, a light signal, a thermal signal, a mechanical signal, a magnetic signal, an electrostatic signal.

16. The communication device (no, 200, 700) according to any preceding claim, wherein the energy storage component is, or comprises, at least one capacitor or at least one battery.

17. The communication device (no, 200, 700) according to any preceding claim, wherein the communication device (no, 200, 700) is any of: a low-power Internet of Things device, an extended reality device, a smart sensor, a wearable device, a medical implant, a smart home device, a monitoring device.

18. A method for conveying charge level information of a communication device (no, 200, 700), the method being performed by the communication device (110, 200, 700), the method comprising:harvesting (S102) energy by receiving a first input signal (130) from an energy source (120);storing (S104), in an energy storage (220) comprising an energy storage component, the harvested energy and supplying power to the communication device (110, 200, 700);determining (S106), by at least one voltage detector (230, 360-1, 360-N, 500) arranged to measure a voltage over the energy storage component, a charge level of the communication device (no, 200, 700);generating (S108) an information sequence representative of the voltage; andbackscattering (S110) the information sequence using backscatter modulation of a wirelessly received second input signal (160), wherein the information sequence conveys information about the charge level.

19. The method according to claim 18, wherein the method further comprises:wirelessly receiving the second input signal (160).

20. A computer program (820) for conveying charge level information of a communication device (no, 200, 700), the computer program comprising computer code which, when run on processing circuitry (710) of the communication device (no, 200, 700), causes the communication device (110, 200, 700) to:harvest (S102) energy by receiving a first input signal (130) from an energy source (120);store (S104), in an energy storage (220) comprising an energy storage component, the harvested energy and supplying power to the communication device (110, 200, 700);determine (S106), by at least one voltage detector (230, 360-1, 360-N, 500) arranged to measure a voltage over the energy storage component, a charge level of the communication device (no, 200, 700);generate (S108) an information sequence representative of the voltage; andbackscatter (S110) the information sequence using backscatter modulation of a wirelessly received second input signal (160), wherein the information sequence conveys information about the charge level.

21. A computer program product (810) comprising a computer program (820) according to claim 20, and a computer readable storage medium (830) on which the computer program is stored.

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