| 摘要 |
<p>The tag reader (Fib. 1) of a radio frequency identification system transmits a reference signal (REF) that is modulated and returned to the reader as a data signal (DATA). The reader develops a sampling signal (DLYOUT) for sampling the data signal, the sampling signal being displaced in phase from the reference signal by 2x, where x is the difference in phase between the reference and data signals. This improves detection of the data signal even though the amplitude modulation of the signal may be partly converted to phase modulation because of tolerances or variations in circuit component values. A dual edge phase detector detects (32) the difference in phase between the reference and data signals and produces an offset signal (UPA or DOWNA) having a duration proportional to 2x. The offset signal is used to inject a delay of 2x into a delay locked loop (30) having a phase detector (34) for comparing the phase of the reference signal relative to the sampling signal and a controllable delay circuit (40) for producing the sampling signal from the reference signal. The sampling signal is thus locked to the reference signal with a phase displacement of 2x.</p> |
