| 摘要 |
<p>A transaction system (10) comprises a terminal (12) and a contactless token (14). The terminal (12) and the token (14) communicate over an inductive coupling. Power and data are transmitted by the terminal (12) to the token (14) by a carrier signal. Data are transmitted by the token (14) to the terminal (12) by the token (14) modulating the level of the carrier signal at the terminal (12) by drawing more power from the carrier signal. Data from the token (14) are received in the terminal (12) by data receiving means (44). The data receiving means (44) receives a first and second carrier signal, the first carrier signal being a version of the carrier signal phase shifted by +X° and the second carrier signal being a version of the carrier signal phase shifted by (X+180)°. As a result, the first carrier signal is transmitted by the terminal (12) whilst the first and second carrier signals at the data receiving means (44) cancel each other out.</p> |
