| 摘要 |
The terminal comprises a series resonant LC or RLC (14) circuit, with an inductive element (34) and capacitive element (20). There is a generator (12) for supplying an AC signal with a frequency near the resonant frequency, to radiate a magnetic field in the direction of a portable object. A receiver is coupled to the resonant circuit to capture a perturbation phase modulation of the field, induced by the portable object.. The receiver has a phase demodulation detector (40-50), which can evaluate the phase difference between a reference signal (Vref) from the resonant circuit, representing the generator phase, and a measurement signal (Vmes). This also comes from the resonant circuit, and represents the phase of the receiver signal. The measurement signal is taken off a fraction of capacitive or inductive elements, the former constituting a set of sub-elements (36,38) connected in the form of divider. The measurement signal is preferably taken off the capacitive element (20), and the resonant circuit is tuned below the frequency of the signal produced by the generator. The measurement signal may also be taken off the inductive element (34), and the resonant circuit is tuned above the frequency of the signal produced by the generator. The phase demodulation detector (40-50) comprises means in the form of circuits (40,42) for the application of a constant phase difference to the reference signal and/or to the measure signal, before the evaluation of the phase difference between the measure signal and the reference signal. The phase demodulation detector (40-50) comprises circuits (44,46) for the detection of zero passage and form of the reference and the measure signals, respectively, and a phase comparator (48) receives signals delivered by the two circuits. The circuits (44,46) for the detection of zero passage and form of signals comprise inverters (60,70) with inputs coupled to outputs by resistive elements (68,78). The phase comparator (48) contains an exclusive-OR gate (84) with two inputs receiving the signals from the circuits for the detection of zero passage and form of signals.
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