HIGH PERFORMANCE RFID TRANSPONDER WITH FAST DOWNLINK

1 . A RFID transponder comprising:

a high quality factor antenna (LR);

a resonance capacitor (CR) coupled to the high quality factor antenna (LR) for providing a resonant circuit (LR, CR), wherein the RFID transponder is adapted to vary the quality factor of the resonant circuit (LR, CR) such that the quality factor is low during downlink data transmission when the RFID transponder receives data through the antenna (LR), and the quality factor is high during uplink data transmission, when the RFID transponder transmits data.

2 . The RFID transponder according to claim 1 , wherein the RFID transponder is adapted to have the high quality factor during a charging phase, when the RFID transponder is charged by an electromagnetic wave received through the antenna (LR).

3 . The RFID transponder according to claim 1 , further comprising a demodulation stage (EOB) adapted to detect an end of burst of a RF signal received using the high quality factor and adapted to detect an end of burst received using the low quality factor.

4 . The RFID transponder according to claim 1 , further comprising a first demodulation stage adapted to detect an end of burst of a RF signal received using the high quality factor and a second demodulation stage adapted to detect an end of burst of a RF signal received using the low quality factor.

5 . The RFID transponder according to claim 3 , wherein the demodulation stage (EOB) is adapted to self-adjust a reference level used for detecting ends of bursts of a received RF signal in response to a change of the quality factor.

6 . The RFID transponder according to claim 5 , wherein the demodulation stage (EOB) is adapted to detect OFF periods of a received RF signal when the RFID transponder is set to the low quality factor.

7 . The RFID transponder according to claim 1 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

8 . The RFID transponder according to claim 1 , further comprising a start-stop stage which is adapted to start an oscillation maintenance stage to maintain the resonant circuit oscillation only when the quality factor is high and when the end of burst stage has detected an end of burst of a received RF signal, and to start the oscillation maintenance stage during uplink data transmission.

9 . A RFID system having a R/W-unit and a RFID transponder, the transponder comprising:

a high quality factor antenna (LR);

a resonance capacitor (CR) coupled to the high quality factor antenna (LR) for providing a resonant circuit (LR, CR), wherein the RFID transponder is adapted to vary the quality factor of the resonant circuit (LR, CR) such that the quality factor is low during downlink data transmission when the RFID transponder receives data through the antenna (LR), and the quality factor is high during uplink data transmission, when the RFID transponder transmits data, and wherein the R/W-unit is adapted to transmit data during downlink data transmission with reduced OFF periods, when the RFID transponder has a low quality factor of the resonant circuit.

10 . A R/W-unit to be used with a RFID transponder comprising:

means to change the quality factor of its resonant circuit between uplink data transmission and downlink data transmission, wherein the R/W-unit comprises means to transmit data during downlink data transmission with reduced OFF periods, when the RFID transponder has switched to a low quality factor of the resonant circuit.

11 . A method for operating a RFID transponder, the method comprising:

switching a resonant circuit of the RFID transponder for receiving and transmitting an RF signal to a low quality factor during downlink data transmission; and

Switching to a high quality factor during uplink data transmission.

12 . The method according to claim 11 , further comprising switching to the high quality factor during a charging phase, in which the RFID transponder is charged by use of an RF signal.

13 . The RFID transponder according to claim 2 , further comprising a demodulation stage (EOB) adapted to detect an end of burst of a RF signal received using the high quality factor and adapted to detect an end of burst received using the low quality factor.

14 . The RFID transponder according to claim 2 , further comprising a first demodulation stage adapted to detect an end of burst of a RF signal received using the high quality factor and a second demodulation stage adapted to detect an end of burst of a RF signal received using the low quality factor.

15 . The RFID transponder according to claim 2 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

16 . The RFID transponder according to claim 3 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

17 . The RFID transponder according to claim 4 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

18 . The RFID transponder according to claim 5 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

19 . The RFID transponder according to claim 6 , further comprising a damping capacitor (Cd), a damping resistor (Rd) and a switch (S 1 ) all coupled in series for switching the series of the damping capacitor (Cd) and the damping resistor (Rd) in parallel to the resonant circuit (LR, CR) in order to selectively reduce or maintain the quality factor of the resonant circuit (LR, CR).

20 . The RFID transponder according to claim 2 , further comprising a start-stop stage which is adapted to start an oscillation maintenance stage to maintain the resonant circuit oscillation only when the quality factor is high and when the end of burst stage has detected an end of burst of a received RF signal, and to start the oscillation maintenance stage during uplink data transmission.