Abstract: A resonant power feeding system that can provide high power transmission efficiency between a power feeding device and a power reception device without dynamically controlling the oscillation frequency in accordance with the distance between the power feeding device and the power reception device. High power transmission efficiency between the power feeding device and the power reception device is obtained by addition of a structure for adjusting the matching condition to both the power reception device and the power feeding device. Specifically, a transmission-reception circuit and a matching circuit are provided in both the power reception device and the power feeding device, and wireless signals for adjusting the matching circuit are transmitted and received through a resonant coil. Thus, the power feeding device can efficiently supply power to the power reception device without adjusting the oscillation frequency.

Abstract: An object is to provide a wireless power feeding system using the resonance method, which can increase power transmission efficiency. The wireless power feeding system includes a power transmission coil electrically connected to a high-frequency power supply, a power transmission resonance coil for transmitting power by electromagnetic induction with the power transmission coil, a power reception resonance coil for exciting high-frequency power by magnetic resonance, a load coil for exciting high-frequency power by electromagnetic induction with the power reception resonance coil, a load, and a variable element. The load includes a microprocessor for controlling the impedance of the load, a battery charger, and a battery. The battery charger is configured to charge the battery with the high-frequency power excited by the load coil.

Abstract: A wireless power feed system with high transfer efficiency of electric power is disclosed. The wireless power feed system includes a power feeding device and a power receiving device, wherein the power feeding device includes a first electromagnetic coupling coil that is connected to an AC power source via a directional coupler; a first resonant coil; a switch connected to the opposite ends of the first resonant coil; a control circuit which conducts switching on/off of the switch based on a parameter of an amplitude of a reflective wave detected by the directional coupler; and an analog-digital converter provided between the first electromagnetic coupling coil and the control circuit; and the power receiving device includes a second resonant coil; and a second electromagnetic coupling coil, and wherein the first electromagnetic coupling coil is provided between the first resonant coil and the second resonant coil.

Abstract: When a portable electronic appliance is provided with two systems, a wireless power-feeding system and a wireless communication system, each system requires two power-receiving devices, a coil and an antenna, leading to a problem of increased electronic appliance size and cost. Wireless power feeding employs the resonance method and uses a resonance coil using the resonance method and a power-receiving coil that receives power from the resonance coil. At least one of the resonance coil and the power-receiving coil can also be used as an antenna for wireless communication. Thus, a power-receiving device that can be used for two systems, wireless power feeding and wireless communication, can be provided.

Abstract: A power feeding device utilizing an electromagnetic resonance coupling method and a contactless power feeding system can be provided. A coupling coefficient of electromagnetic induction coupling in the power feeding device and/or the inside of a power receiving device is optimized to improve electric power transmission efficiency of a resonance frequency regardless of positions of the power feeding device and the power receiving device. Provided is a power feeding device or a contactless power feeding system in which an S11 parameter which is a reflection component of electric power output from a high-frequency power source of the power feeding device is monitored, and one or both of positions of a transmission coil and a first resonant coil in the power feeding device and positions of a reception coil and a second resonant coil in a power receiving device are changed to adjust a coupling coefficient of electromagnetic induction coupling.

Abstract: A semiconductor device with a reduced area and capable of higher integration and larger storage capacity is provided. A multi-valued memory cell including a reading transistor which includes a back gate electrode and a writing transistor is used. Data is written by turning on the writing transistor so that a potential according to the data is supplied to a node where one of a source electrode and a drain electrode of the writing transistor and a gate electrode of the reading transistor are electrically connected to each other, and then turning off the writing transistor and holding a predetermined potential in the node. Data is read by supplying a reading control potential to a control signal line connected to one of a source electrode and a drain electrode of the reading transistor, and then detecting potential change of a reading signal line.

Abstract: A resonant power feeding system that can provide high power transmission efficiency between a power feeding device and a power reception device without dynamically controlling the oscillation frequency in accordance with the distance between the power feeding device and the power reception device. High power transmission efficiency between the power feeding device and the power reception device is obtained by addition of a structure for adjusting the matching condition to both the power reception device and the power feeding device. Specifically, a transmission-reception circuit and a matching circuit are provided in both the power reception device and the power feeding device, and wireless signals for adjusting the matching circuit are transmitted and received through a resonant coil. Thus, the power feeding device can efficiently supply power to the power reception device without adjusting the oscillation frequency.

Abstract: To prevent damage on an element even when a voltage high enough to break the element is input. A semiconductor device of the invention operates with a first voltage and includes a protection circuit which changes the value of the first voltage when the absolute value of the first voltage is higher than a reference value. The protection circuit includes: a control signal generation circuit generating a second voltage based on the first voltage and outputting the generated second voltage; and a voltage control circuit. The voltage control circuit includes a transistor which has a source, a drain, and a gate, and which is turned on or off depending on the second voltage input to the gate and thus controls whether the value of the first voltage is changed based on the amount of current flowing between the source and the drain. The transistor also includes an oxide semiconductor layer.

Abstract: A highly reliable light-emitting device is provided. A lighting device or a display device with a high level of safety and without an exposed electrode is provided. A lighting device or a display device with high layout flexibility is provided. A light-emitting system or a display system to which the light-emitting device or the display device can be applied is provided. An electrode for receiving power and a rectifier circuit are provided in a light-emitting device including an organic EL element and arranged so as to face an electrode for transmitting power, whereby alternating-current power is supplied to the light-emitting device. The alternating-current power is rectified by the rectifier circuit to direct-current power so that the organic EL element in the light-emitting device is driven.

Abstract: A modulation circuit includes a load and a transistor serving as a switch. The transistor has an oxide semiconductor layer in which hydrogen concentration is 5×1019/cm3 or less. The off-state current of the transistor is 1×10?13 A or less. A modulation circuit includes a load, a transistor serving as a switch, and a diode. The load, the transistor, and the diode are connected in series between the terminals of an antenna. The transistor has an oxide semiconductor layer in which hydrogen concentration is 5×1019/cm3 or less. An off-state current of the transistor is 1×10?13 A or less. On/off of the transistor is controlled in accordance with a signal inputted to a gate of the transistor. The load is a resistor, a capacitor, or a combination of a resistor and a capacitor.

Abstract: A power receiving device and a power feeding system which are capable of performing communication and power feeding at the same time are provided. Further, a power receiving device and a power feeding system which are capable of stably performing communication during power feeding are provided. One embodiment of the present invention relates to a power receiving device which includes an antenna for communication and power feeding that receives AC power, a rectifier circuit that rectifies the received AC power including the modulation signal into DC power, a smoothing circuit that smoothes the resulting DC power, a power storage device that stores the smoothed DC power, a communication control unit that analyzes the modulation signal included in the AC power, and a transformer that is positioned between the antenna and the rectifier circuit and changes a reference potential of the AC power, and a power feeding device.

Abstract: A semiconductor device with a reduced area and capable of higher integration and larger storage capacity is provided. A multi-valued memory cell including a reading transistor which includes a back gate electrode and a writing transistor is used. Data is written by turning on the writing transistor so that a potential according to the data is supplied to a node where one of a source electrode and a drain electrode of the writing transistor and a gate electrode of the reading transistor are electrically connected to each other, and then turning off the writing transistor and holding a predetermined potential in the node. Data is read by supplying a reading control potential to a control signal line connected to one of a source electrode and a drain electrode of the reading transistor, and then detecting potential change of a reading signal line.

Abstract: Disclosed is a semiconductor device having a memory cell which comprises a transistor having a control gate and a storage gate. The storage gate comprises an oxide semiconductor and is able to be a conductor and an insulator depending on the potential of the storage gate and the potential of the control gate. Data is written by setting the potential of the control gate to allow the storage gate to be a conductor, supplying a potential of data to be stored to the storage gate, and setting the potential of the control gate to allow the storage gate to be an insulator. Data is read by supplying a potential for reading to a read signal line connected to one of a source and a drain of the transistor and detecting the change in potential of a bit line connected to the other of the source and the drain.

Abstract: There is provided a power transmission device which includes an antenna receiving a reflected power from a power receiving device, a power detection unit detecting a value of the reflected power received by the antenna, a control circuit determining a power adjustment value in accordance with the value of the reflected power, a power adjustment unit to which the reflected power whose value is detected is input and which adjusts impedance in accordance with the power adjustment value determined by the control circuit, and a demodulation circuit to which the reflected power having the power adjustment value determined by the control circuit is input via the power adjustment unit having the adjusted impedance, and relates to a power feeding system including the power transmission device.

Abstract: In a rectifier circuit, by using a transistor whose off-state current is small as a so-called diode-connected MOS transistor included in the rectifier circuit, breakdown which is caused when a reverse bias is applied is prevented. Thus, an object is to provide a rectifier circuit whose reliability is increased and rectification efficiency is improved. A gate and a drain of a transistor are both connected to a terminal of the rectifier circuit to which an AC signal is input. In the transistor, an oxide semiconductor is used for a channel formation region and the off-state current at room temperature is less than or equal to 10?20 A/?m, which is equal to 10 zA/?m (z: zepto), when the source-drain voltage is 3.1 V.

Abstract: A power receiving device and a power feeding system which are capable of performing communication and power feeding at the same time are provided. Further, a power receiving device and a power feeding system which are capable of stably performing communication during power feeding are provided. One embodiment of the present invention relates to a power receiving device which includes an antenna for communication and power feeding that receives AC power, a rectifier circuit that rectifies the received AC power including the modulation signal into DC power, a smoothing circuit that smoothes the resulting DC power, a power storage device that stores the smoothed DC power, a communication control unit that analyzes the modulation signal included in the AC power, and a transformer that is positioned between the antenna and the rectifier circuit and changes a reference potential of the AC power, and a power feeding device.

Abstract: Disclosed is a semiconductor device having a memory cell which comprises a transistor having a control gate and a storage gate. The storage gate comprises an oxide semiconductor and is able to be a conductor and an insulator depending on the potential of the storage gate and the potential of the control gate. Data is written by setting the potential of the control gate to allow the storage gate to be a conductor, supplying a potential of data to be stored to the storage gate, and setting the potential of the control gate to allow the storage gate to be an insulator. Data is read by supplying a potential for reading to a read signal line connected to one of a source and a drain of the transistor and detecting the change in potential of a bit line connected to the other of the source and the drain.

Abstract: Not a structure in which a resonance frequency of a power transmission device is set after a resonance frequency of a power receiving device is directly measured but a structure in which the resonance frequencies of the power receiving device and the power transmission device are estimated after reflection of an electromagnetic field for transmitting electric power to the power receiving device is monitored by the power transmission device is employed. After a capacitance value of a variable capacitor in a resonance coil of the power receiving device is once set to 0, an S11 parameter is detected while a frequency of an electromagnetic wave is changed, and the resonance frequency of the power transmission device is estimated on the basis of the S11 parameter.

Abstract: A novel power receiving device and a novel power transmission device are provided. Power feeding and communication are performed using a magnetic resonance method. Specifically, in one embodiment of the present invention, power feeding is performed by generating a second high-frequency voltage based on a first high-frequency voltage induced in a resonant coil and communication is performed by modulating amplitude of the first high-frequency voltage induced in the resonant coil. Thus, it is possible to perform communication and power feeding based on data obtained by the communication in pseudo-parallel.

Abstract: Disclosed is a semiconductor device having a memory cell which comprises a transistor having a control gate and a storage gate. The storage gate comprises an oxide semiconductor and is able to be a conductor and an insulator depending on the potential of the storage gate and the potential of the control gate. Data is written by setting the potential of the control gate to allow the storage gate to be a conductor, supplying a potential of data to be stored to the storage gate, and setting the potential of the control gate to allow the storage gate to be an insulator. Data is read by supplying a potential for reading to a read signal line connected to one of a source and a drain of the transistor and detecting the change in potential of a bit line connected to the other of the source and the drain.