Patent ID: 8643470

Claim:
A semiconductor integrated circuit comprising: a first antenna coupling terminal; a second antenna coupling terminal; a power circuit; a demodulator circuit; and a determination circuit, wherein a Radio Frequency (RF) signal received by an antenna is supplied between the first antenna coupling terminal and the second antenna coupling terminal, wherein the RF signal is an Amplitude Shift Keying (ASK) modulated carrier, wherein the power circuit supplies the demodulator circuit and the determination circuit with operating voltage generated by rectifying and smoothing the RF signal, wherein the demodulator circuit includes a first demodulator circuit and a second demodulator circuit, wherein the RF signal supplied between the first antenna coupling terminal and the second antenna coupling terminal is supplied in parallel to an input of the first demodulator circuit and an input of the second demodulator circuit, wherein the first demodulator circuit demodulates a first reception signal having a first degree of modulation as the RF signal and generates a first demodulated output signal, wherein the second demodulator circuit demodulates a second reception signal having a second degree of modulation different from the first degree of modulation as the RF signal and having a first communication start signal in a first format and a third reception signal having the second degree of modulation and a second communication start signal in a second format, and generates a second demodulated output signal, wherein the first demodulated output signal of the first demodulator circuit and the second demodulated output signal of the second demodulator circuit are supplied to the determination circuit, wherein, when the determination circuit determines that the first demodulator circuit generates the first demodulated output signal, the determination circuit determines that the first reception signal having the first degree of modulation is received as the RF signal, wherein, when the determination circuit determines that the first demodulator circuit does not generate the first demodulated output signal, the determination circuit determines a difference in format between the first communication start signal and the second communication start signal, wherein, when the determination circuit determines that the second demodulator circuit generates the second demodulated output signal by demodulating the second reception signal having the first communication start signal in the first format, the determination circuit determines that the second reception signal is received as the RF signal, and wherein, when the determination circuit determines that the second demodulator circuit generates the second demodulated output signal by demodulating the third reception signal having the second communication start signal in the second format, the determination circuit determines that the third reception signal is received as the RF signal.