| 摘要 |
A near-field RF communicator 100, e.g. an RFID device, has an antenna circuit 120 to receive a modulated radio frequency signal by inductive coupling and demodulation circuitry 130 to extract the modulation from a received modulated RF signal. Demodulation circuitry 130 comprises demodulator 114 and differential amplifier 115 which has respective inputs coupled to junctions J1, J2 of antenna circuit 120. Thus, demodulation circuitry 130 receives two modulated RF signals from antenna circuit 120 and extracts modulation using both signals. Amplifier 115 amplifies the modulated RF signal to remove common mode components. Amplifier 115 may have low impedance input circuits 123,124 which may be virtual earth, i.e. current mirror, circuits (fig. 6). Alternatively, the demodulation circuitry may have a differential mixer (400, fig. 3), such as a Gilbert mixer, or be a synchronous IQ demodulator having an I differential mixer (400, fig. 5) and a Q differential mixer (400a). The invention provides near-field RF communicators which are less noise sensitive and which minimise overloading. |
