Patent ID: 9607194
Date: 2017-03-28
CPC Classifications: G06K

Claim:
1. A half-duplex passive transponder comprising: a resonant circuit including an antenna and an input capacitor and configured to allow an electrical signal to oscillate in the resonant circuit when the transponder periodically receives across the antenna an activation signal from a reader; a rectifier positioned downstream of the resonant circuit; an energy storage capacitor positioned downstream of the rectifier; at least one switch positioned between the input capacitor and the storage capacitor so that the input capacitor and storage capacitor are placed in parallel when the switch is turned on; a peak voltage detector configured to measure amplitude of the electrical signal oscillating in the resonant circuit; wherein the transponder is configured to send at least one communication signal to the reader in a transmission period when the activation signal is interrupted, and to deliver plucking pulses during the transmission period in the resonant circuit to sustain the electrical signal oscillation while maintaining at least a certain amplitude of the oscillating electrical signal; wherein the transponder further comprises a variable voltage threshold determination circuit defining, for each plucking pulse, a specific voltage threshold which is used to trigger the plucking pulses and is lower in absolute value than a last peak voltage measured by the peak voltage detector relative to a medium voltage of the oscillating electrical signal such that the specific voltage threshold is redefined after the last measured peak voltage; and wherein the transponder is configured to trigger each plucking pulse when the voltage of the oscillating electrical signal substantially attains the specific voltage threshold in a respective period before an extremum of the oscillating electrical signal and in a half-cycle of the extremum.