Abstract: An object is to provide a semiconductor memory device capable of copying memory data without using an external circuit. The semiconductor memory device includes a bit line to which first terminals of a plurality of memory cells are connected in common; a pre-charge circuit which is connected to the bit line and pre-charges the bit line with a specific potential in data reading; a data holding circuit comprising a capacitor which temporarily holds data read out from the memory cell or data which is written to the memory cell; and an inverted data output circuit which outputs inverted data of data held in the data holding circuit to the bit line. The inverted data output circuit includes a means for controlling output of inverted data of data held in the data holding circuit.

Abstract: One object is to provide a method for measuring current by which minute current can be measured. A value of current flowing through an electrical element is not directly measured but is calculated from change in a potential observed in a predetermined period. The method for measuring current includes the steps of: applying a predetermined potential to a first terminal of an electrical element having the first terminal and a second terminal; measuring an amount of change in a potential of a node connected to the second terminal; and calculating, from the amount of change in the potential, a value of current flowing between the first terminal and the second terminal of the electrical element. Thus, the value of minute current can be measured.

Abstract: A semiconductor device which can operate normally even when the communication distance is extremely short, and which stores excess electric power which is not needed for circuit operation of the semiconductor device when a large amount of electric power is supplied thereto. The following are included: an antenna; a first AC/DC converter circuit which is connected to the antenna; a second AC/DC converter circuit which is connected to the antenna through a switching element; a detecting circuit which controls operation of the switching element in accordance with the value of a voltage output from the first AC/DC converter circuit; and a battery which stores electric power supplied from the antenna through the second AC/DC converter circuit. When the switching element is operated, electric power supplied from outside is at least partly supplied to the battery through the second AC/DC converter circuit.

Abstract: A semiconductor device which can operate normally even when the communication distance is extremely short, and which stores excess electric power which is not needed for circuit operation of the semiconductor device when a large amount of electric power is supplied thereto. The following are included: an antenna; a first AC/DC converter circuit which is connected to the antenna; a second AC/DC converter circuit which is connected to the antenna through a switching element; a detecting circuit which controls operation of the switching element in accordance with the value of a voltage output from the first AC/DC converter circuit; and a battery which stores electric power supplied from the antenna through the second AC/DC converter circuit. When the switching element is operated, electric power supplied from outside is at least partly supplied to the battery through the second AC/DC converter circuit.

Abstract: To provide a semiconductor device whose power can be turned off without the need for a peripheral circuit for data to escape temporarily and in which stored data is not lost even in an off state of the power of the device, and a memory device including the semiconductor device. In a holding circuit of the semiconductor device, a transistor that includes a semiconductor layer (at least a channel formation region) including an oxide semiconductor material with which small off-state current can be achieved is used. Further, the semiconductor device includes a switching element which enables a comparison circuit in which comparison between data stored in the holding circuit and reference data input from the outside does not need to be performed to become forcibly inactive.

Abstract: A semiconductor device which can operate normally even when the communication distance is extremely short, and which stores excess electric power which is not needed for circuit operation of the semiconductor device when a large amount of electric power is supplied thereto. The following are included: an antenna; a first AC/DC converter circuit which is connected to the antenna; a second AC/DC converter circuit which is connected to the antenna through a switching element; a detecting circuit which controls operation of the switching element in accordance with the value of a voltage output from the first AC/DC converter circuit; and a battery which stores electric power supplied from the antenna through the second AC/DC converter circuit. When the switching element is operated, electric power supplied from outside is at least partly supplied to the battery through the second AC/DC converter circuit.

Abstract: An object is to provide a semiconductor device which operates normally even when the communication distance is extremely short, while the maximum communication distance is maintained, and which can make amplitude of a response waveform large even when a large amount of electric power is supplied to the semiconductor device and a protection circuit operates. The object is achieved with a semiconductor device including a first modulation circuit and a second modulation circuit each of which performs load modulation by an input signal, a detection circuit which determines an output signal by electric power supplied externally, a protection circuit which is controlled by the output signal of the detection circuit, and a modulation selecting circuit which switches the first modulation circuit and the second modulation circuit depending on the output signal of the detection circuit.

Abstract: A semiconductor device which can operate normally even when the communication distance is extremely short, and which stores excess electric power which is not needed for circuit operation of the semiconductor device when a large amount of electric power is supplied thereto. The following are included: an antenna; a first AC/DC converter circuit which is connected to the antenna; a second AC/DC converter circuit which is connected to the antenna through a switching element; a detecting circuit which controls operation of the switching element in accordance with the value of a voltage output from the first AC/DC converter circuit; and a battery which stores electric power supplied from the antenna through the second AC/DC converter circuit. When the switching element is operated, electric power supplied from outside is at least partly supplied to the battery through the second AC/DC converter circuit.

Abstract: An object is to provide a semiconductor memory device capable of copying memory data without using an external circuit. The semiconductor memory device includes a bit line to which first terminals of a plurality of memory cells are connected in common; a pre-charge circuit which is connected to the bit line and pre-charges the bit line with a specific potential in data reading; a data holding circuit comprising a capacitor which temporarily holds data read out from the memory cell or data which is written to the memory cell; and an inverted data output circuit which outputs inverted data of data held in the data holding circuit to the bit line. The inverted data output circuit includes a means for controlling output of inverted data of data held in the data holding circuit.

Abstract: A semiconductor device including a first transistor and a second transistor and a capacitor which are over the first transistor is provided. A semiconductor layer of the second transistor includes an offset region. In the second transistor provided with an offset region, the off-state current of the second transistor can be reduced. Thus, a semiconductor device which can hold data for a long time can be provided.

Abstract: One object is to provide a method for measuring current by which minute current can be measured. A value of current flowing through an electrical element is not directly measured but is calculated from change in a potential observed in a predetermined period. The method for measuring current includes the steps of: applying a predetermined potential to a first terminal of an electrical element having the first terminal and a second terminal; measuring an amount of change in a potential of a node connected to the second terminal; and calculating, from the amount of change in the potential, a value of current flowing between the first terminal and the second terminal of the electrical element. Thus, the value of minute current can be measured.

Abstract: A semiconductor device has a non-volatile memory cell including a write transistor which includes an oxide semiconductor and has small leakage current in an off state between a source and a drain, a read transistor including a semiconductor material different from that of the write transistor, and a capacitor. Data is written or rewritten to the memory cell by turning on the write transistor and applying a potential to a node where one of a source electrode and drain electrode of the write transistor, one electrode of the capacitor, and a gate electrode of the read transistor are electrically connected to one another, and then turning off the write transistor so that the predetermined amount of charge is held in the node.

Abstract: An object is to provide a semiconductor device which operates normally even when the communication distance is extremely short, while the maximum communication distance is maintained, and which can make amplitude of a response waveform large even when a large amount of electric power is supplied to the semiconductor device and a protection circuit operates. The object is achieved with a semiconductor device including a first modulation circuit and a second modulation circuit each of which performs load modulation by an input signal, a detection circuit which determines an output signal by electric power supplied externally, a protection circuit which is controlled by the output signal of the detection circuit, and a modulation selecting circuit which switches the first modulation circuit and the second modulation circuit depending on the output signal of the detection circuit.

Abstract: A semiconductor device which can operate normally even when the communication distance is extremely short, and which stores excess electric power which is not needed for circuit operation of the semiconductor device when a large amount of electric power is supplied thereto. The following are included: an antenna; a first AC/DC converter circuit which is connected to the antenna; a second AC/DC converter circuit which is connected to the antenna through a switching element; a detecting circuit which controls operation of the switching element in accordance with the value of a voltage output from the first AC/DC converter circuit; and a battery which stores electric power supplied from the antenna through the second AC/DC converter circuit. When the switching element is operated, electric power supplied from outside is at least partly supplied to the battery through the second AC/DC converter circuit.