| 摘要 |
<p>A radio frequency (RF) transponder circuit comprises two input ports 15A, 15B, in which each port has an oscillating voltage signal EA, EB, applied to it and in which a rectifying circuit 19, with a constant output signal VR, is connected across one input port 15A and a voltage polarity biassed modem circuit 16, with an output signal VM which fluctuates with the applied oscillating voltage EB, is connected across the other input port 15B. The voltage polarity of the rectifying and modem circuits 19, 16 may be the same such that they can be added together to provide a data signal at a voltage level which is sufficient to operate digital circuits without the need for comparator circuitry. Impedance matching circuits 29, 30 may be used at the said input ports of the circuits. The circuits may comprise diodes and capacitors in appropriate rectifier arrangements. Also disclosed is a RF transponder having an antenna comprising at least two ports operable to receive signals such that, in use, the signals in combination establish at least two current nulls on the antenna, each of the ports being located substantially at a current null (see figure 9).</p> |
