Patent ID: 6775323
Filing Date: 2004-08-10
Classification: G01S,H03M

Abstract:
A passive transponder system comprising a central unit and a radio frequency transponder,the radio frequency transponder comprising: an RF-to-DC power converter unit arranged, in response to a radio frequency interrogation signal from the central unit, to obtain DC power from the RF interrogation signal; and a modulating unit arranged, in response to the RF interrogation signal from the central unit, to code data to be transmitted to the central unit and represented by a number of symbols, using a coding system, the coding system comprising representing each symbol with a unique digital waveform obtained by switching between a high state and a low state, the RF-to-DC power converter unit generating higher DC power when the modulating unit is in the high state than the low state, and all the unique digital waveforms having a duty cycle greater than 50%.