Method and apparatus for checking a circuit

1. A method for checking a circuit devised for contactless data communication, which comprises an antenna and an electronic component coupled with the antenna, comprising the steps of:

generating an alternating magnetic field for the circuit;

exciting the circuit by means of an energy pulse,

capturing an oscillation of the circuit in response to the excitation by the energy pulse; and

evaluating the captured oscillation of the circuit;

wherein the generating of the alternating magnetic field is effected or temporarily interrupted during the exciting, and

wherein the evaluating of the captured oscillation is effected in dependence on the field strength of the alternating magnetic field in which the circuit is arranged.

2. The method according to claim 1 , wherein

arranging the circuit in the region of the alternating field.

3. The method according to claim 1 , wherein the exciting of the circuit is effected as inductive exciting by means of a pulsed magnetic field, with the magnetic field being generated by a single current pulse.

4. The method according to claim 3 , wherein the current pulse is generated as a direct-current pulse in the form of a Dirac impulse.

5. The method according to claim 1 , wherein the exciting of the circuit is carried out contactlessly by means of an external exciting coil, and/or that the capturing of the oscillation of the circuit is carried out contactlessly by means of an external measuring coil.

6. The method according to claim 1 , wherein the alternating field is generated by means of a transmitting antenna, and that the field strength of the alternating field is measured by means of a calibrating antenna in order to enable a generating of the alternating field according to a pre-specified field strength, with the calibrating antenna and the antenna of the circuit being arranged relative to the transmitting antenna such that an alternating magnetic field of the same field strength is respectively present in the region of the calibrating antenna and in the region of the antenna of the circuit.

7. The method according to claim 1 , wherein the exciting of the circuit by the energy pulse is effected with the alternating magnetic field constantly present.

8. The method according to claim 7 , wherein the capturing of the oscillation of the circuit comprises a capturing of a superimposition of a sinusoidal oscillation of the circuit brought about by the alternating field, with a free, damped oscillation of the circuit, with the free, damped oscillation resulting from the excitation by the energy pulse.

9. The method according to claim 8 , wherein the evaluating of the captured oscillation of the circuit comprises a subtraction of the constant sinusoidal oscillation from the captured oscillation in order to ascertain the free, damped oscillation.

10. The method according to claim 9 , wherein the subtraction of the constant sinusoidal oscillation from the captured oscillation is carried out by means of software or by means of hardware, in particular while employing an amplifier and/or by addition of a signal which corresponds to the signal captured by the calibrating antenna and inverted.

11. The method according to claim 1 , wherein the alternating magnetic field is temporarily switched off, and that the exciting of the circuit by the energy pulse and the capturing of the oscillation of the circuit are effected with the alternating magnetic field switched off.

12. The method according to claim 11 , wherein the alternating field is switched off only briefly, and the duration of the switch-off of the alternating magnetic field is so short that the circuit remains supplied with energy during the switch-off of the alternating field.

13. The method according to claim 11 , wherein the excitation by means of the energy pulse with the alternating magnetic field switched off is effected only when the sinusoidal oscillation of the circuit resulting from the alternating field has decayed.

14. The method according to claim 13 , wherein the capturing of the oscillation of the circuit corresponds to the capturing of the free, damped oscillation of the circuit.

15. The method according to claim 9 , wherein in the evaluating step there is ascertained from the captured or ascertained free, damped oscillation of the circuit the self-resonant frequency and/or the quality factor of the circuit for the field strength (H) of the alternating magnetic field.

16. The method according to claim 1 , wherein the method is repeated with a changed field strength of the alternating magnetic field.

17. The method according to claim 1 , wherein in the evaluating step a field strength-dependent property of the circuit is determined for the generated field strength.

18. The method according to claim 1 , wherein the evaluating of the captured oscillation is effected in dependence on an operating or switching state of one or more parts of the electronic component that is due to the presence of the alternating magnetic field.

19. An apparatus for checking a circuit devised for contactless data communication, which comprises an antenna and an electronic component coupled with the antenna, having:

a transmitting device having a transmitting antenna which is devised to generate an alternating magnetic field for a circuit to be checked which is arrangeable in the measuring apparatus,

a pulse means which is devised to additionally excite the circuit to be checked, and

an evaluation means which is devised to evaluate an oscillation of the circuit to be checked which is captured in response to the excitation by the pulse means,

wherein the apparatus is devised to either temporarily switch off or maintain the alternating magnetic field while the circuit is additionally excited, and

wherein the evaluation of the captured oscillation is effected in dependence on the field strength of the alternating magnetic field in which the circuit is arranged.