Transponder unit

1. A method for transferring data from a transponder unit of a portable data carrier to a reading device which receives data from transponders by load modulation of a field of the reading device, comprising the steps:

the transponder unit, in a first operating mode, generating a modulated transponder field and emitting the modulated transponder field containing the data to be transferred as a first signal which emulates load modulation of the reading device field by a transponder, wherein a ring modulator of the transponder unit suppresses a carrier frequency signal generated by an oscillator of the transponder unit in favor of a subcarrier signal modulated with the data to be transferred by supplying the carrier frequency into a first input end of the ring modulator and by supplying the subcarrier signal modulated with the data to be transferred into a second input end of the ring modulator,

wherein the transponder unit in a second operating mode performs load modulation for transferring the data to the reading device, wherein in the second operating mode the field of the reading device is loaded by the transponder unit and a second signal containing the data to be transferred from the transponder unit is received through coupled modulation of the field of the reading device,

and wherein the portable data carrier is a chip card.

2. The method according to claim 1 , wherein the transponder unit uses the second operating mode within a passive communication range of the reading device, and uses the first operating mode outside the passive communication range.

3. The method according to claim 1 , including the steps of: receiving an input signal from the reading device, demodulating the input signal to extract received data from the input signal, and supplying the extracted data to a controller, whereupon the data to be transferred to the reading device is generated in the controller.

4. The method according to claim 1 , including the step of generating the frequency of the subcarrier signal by binary division of the frequency of the oscillator signal.

5. The method according to claim 1 , wherein the data to be transferred to the reading devices is supplied to a load modulator of the transponder unit or the ring modulator of the transponder unit.

6. The method according to claim 1 , including the step of limiting, by means of a voltage limiter, a voltage induced on an antenna of the transponder unit by the reading device.

7. The method according to claim 1 , including the step of coupling the oscillator signal with a signal received from the reading device via a phase locked loop circuit.

8. The method according to claim 1 , including the step of amplifying the first signal before it is transmitted to the reading device.

9. A transponder unit of a portable data carrier configured to transfer data to a reading device which receives data from transponders by load modulation of a field of the reading device, comprising:

a ring modulator, in a first operating mode, configured to generate and emit a modulated transponder field containing the data to be transferred as a first signal which emulates load modulation of the reading device field by a transponder, wherein the ring modulator of the transponder unit is configured to supress a carrier frequency signal generated by an oscillator in the transponder unit in favor of a subcarrier signal modulated with the data to be transferred by supplying the carrier frequency into a first input end of the ring modulator and by supplying the subcarrier signal modulated with the data to be transferred into a second input end of the ring modulator,

wherein the transponder unit in a second operating mode performs load modulation for transferring the data to the reading device, wherein in the second operating mode the field of the reading device is loaded by the transponder unit and a second signal containing the data to be transferred from the transponder unit is received through coupled modulation of the field of the reading device,

and wherein the portable data carrier is a chip card.

10. The transponder unit according to claim 9 , wherein the transponder unit is configured to use the second operating mode within a passive communication range of the reading device and to use the first operating mode outside the passive communication range.

11. The transponder unit according to claim 9 , including at least one antenna; a receiver configured to demodulate and extract data from a signal received by the at least one antenna transmitted from the reading device; and an electronic circuit which is set up to process the extracted data and to generate data to be transferred to the reading device.

12. The transponder unit according to claim 9 , including an energy supply associated with the transponder unit.

13. The transponder unit according to claim 9 , including a load modulator and a switch-over device which is set up to switch, depending on a level of a voltage induced on an antenna, between the load modulator and the ring modulator.

14. The transponder unit according to claim 13 , wherein the switch-over device switches automatically from the ring modulator to the load modulator when the induced voltage exceeds a given value.

15. The transponder unit according to claim 9 , including a voltage limiter for limiting a voltage induced on an antenna.

16. The transponder unit according to claim 9 , wherein the oscillator is coupled via a phase locked loop circuit to a signal received from the reading device which serves as a reference signal for the oscillator.

17. The transponder unit according to claim 9 , comprising a device arranged to temporarily deactivate the transponder unit.

18. A value document, comprising a transponder unit of a portable data carrier configured to transfer data to a reading device which receives data from transponders by load modulation of a field of the reading device, comprising:

a ring modulator, in a first operating mode, configured to generate and emit a modulated transponder field containing the data to be transferred as a first signal which emulates load modulation of the reading device field by the transponder, wherein the ring modulator of the transponder unit is configured to supress a carrier frequency signal generated by an oscillator in the transponder unit in favor of a subcarrier signal modulated with the data to be transferred by supplying the carrier frequency into a first input end of the ring modulator and by supplying the subcarrier signal modulated with the data to be transferred into a second input end of the ring modulator, and

wherein the transponder unit in a second operating mode performs load modulation for transferring the data to the reading device, wherein in the second operating mode the field of the reading device is loaded by the transponder unit and a second signal containing the data to be transferred from the transponder unit is received through coupled modulation of the field of the reading device.