| 摘要 |
The present invention relates to a receiver and transmitter arrangement for a price information system which includes a plurality of price information units in a shop or store, for instance. Each price information unit includes a loop (20) for receiving a signal (f1) from the control unit. When there is no communication with the price information unit, a voltage-controlled oscillator (50) is controlled by an incorporated crystal (46) via a phase locked loop. When communication is effected with the price information units, the voltage-controlled oscillator (50) is controlled in a manner such that the frequency and phase position of the oscillators in the control unit and the price information unit will coincide. This is achieved by activating a phase comparator (58) (with switch 60) which then receives the following input signals: a real value signal (f6) from the voltage-controlled oscillator (50), and two control value signals [(f3a), (f4a)] obtained by passing the signal (f) through two filter and demodulator circuits (30) and (32) and two comparators (34) and (36). The output signal obtained from the voltage-controlled oscillator (50) is passed directly to the filter and demodulator circuit (32) and indirectly to the filter and demodulator circuit (30), via a phase shift circuit (42). |
