Patent ID: 7764046

Claim:
A semiconductor device comprising: an antenna; a battery; a power supply portion; a charging determination portion; and a signal processing portion, wherein the power supply portion includes a rectifier circuit that is connected to the antenna, a charging control circuit that is connected to the rectifier circuit, and a power supply circuit that is connected to the battery, wherein the charging determination portion includes a demodulation circuit that demodulates a signal inputted to the antenna, a determination circuit that determines whether the battery is in a charging state or a non-charging state in accordance with the signal and outputs a signal that switches the charging state and the non-charging state, a counter circuit that counts charging time of the battery and outputs a signal to the determination circuit, and a modulation circuit that modulates a signal outputted from the antenna, and wherein the modulation circuit modulates the signal outputted from the antenna so that the signal becomes a first signal, when the battery is determined to be in the charging state by the determination circuit, or modulates the signal outputted from the antenna so that the signal becomes a second signal, when the battery is determined to be in the non-charging state by the determination circuit.