| 摘要 |
<p>To receive a response signal from a radio card (4B), a card reader (4A) transmits a carrier (not modulated) to the radio card (4B). In the radio card (4B), a phase modulator (51) phase-modulates the a sub-carrier with a response signal, thereby generating a PSK signal, and a phase modulator (50) phase-modulates the carrier with the PSK signal, producing a PSK-PSK signal. The PSK-PSK signal is supplied to an antenna (47) via a signal-extracting device (48). The antenna (47) sends the PSK-PSK signal toward the card reader (4A). In the card reader (4A), a distributor (53) distributes the PSK-PSK signal to a synchronous detector (54a) and an orthogonal detector (54b). The detectors (54a, 54b) performs synchronous detection by using carriers which differ in phase by 90 DEG . Low-pass filters (55a, 55b) extract sub-carrier components from the outputs of the detectors (54a, 54b). The sub-carrier components are delayed and detected by delay detectors (56a, 56b) and added together by an adder (57). The level of the output of the adder (57) is determined by a data discriminator (58), whereby the card reader (4A) obtains the response signal transmitted from the radio card (4B). <IMAGE></p> |
