RFID IC WITH DISTURBANCE FILTER FOR DIGITALLY MODULATED SIGNALS

Abstract

There is described an RFID IC, comprising:

i) an RFID interface configured to receive a digitally modulated signal, wherein the digitally modulated signal comprises: a first slot with a first pulse, and a second slot with a second pulse; and
ii) a processing unit configured to
a) determine a first position of the first pulse in the first slot,
b) filter a region that follows the determined first position of the first pulse,
c) determine a second position of the second pulse in the second slot, and, if the second position of the second pulse cannot be determined in the second slot, assume that the second position of the second pulse in the second slot is at the filtered region.

Claims

1-15. (canceled)

16. An RFID IC, comprising: an RFID interface configured to receive a digitally modulated signal, wherein the digitally modulated signal comprises: a first slot with a first pulse; a second slot with a second pulse; and a processing unit configured to determine a first position of the first pulse in the first slot, filter a region that follows the determined first position of the first pulse, determine a second position of the second pulse in the second slot, and if the second position of the second pulse cannot be determined in the second slot, assume that the second position of the second pulse in the second slot is at the filtered region.

17. The RFID IC according to claim 16, wherein the processing unit is further configured to restore the second position of the second pulse in the second slot at the filtered region.

18. The RFID IC according to claim 16, wherein the processing unit is further configured to, if the second position of the second pulse in the second slot is at least one of determined and restored, demodulate the second slot.

19. The RFID IC according to claim 16, wherein the processing unit is further configured to assume that the position of the second pulse in the second slot is at the filtered region only, if the first position of the first pulse is at the last position in the first slot.

20. The RFID IC according to claim 16, wherein the digitally modulated signal comprises a disturbance following the first pulse.

21. The RFID IC according to claim 20, wherein the disturbance comprises an overshoot.

22. The RFID IC according to claim 20, wherein the start of the disturbance is following the start of the filtered region.

23. The RFID IC according to claim 16, wherein the RFID IC is configured according to the ISO15693 standard.

24. The RFID IC according to claim 16, wherein the RFID IC is configured according to the NFC T5T standard.

25. The RFID IC according to claim 16, wherein the digitally modulated signal is modulated by amplitude shift keying, ASK.

26. The RFID IC according to claim 25, wherein the digitally modulated signal comprises at least one of 10% ASK and 100% ASK modulation.

27. The RFID IC according to claim 25, wherein it is inherent to the processing unit to partially interpret 100% ASK as 10% ASK.

28. The RFID IC according to claim 25, wherein the disturbance in the filtered region comprises a 10% ASK pulse or is at least partially interpreted as a 10% ASK pulse by the processing unit.

29. The RFID IC according to claim 16, wherein the first position of the first pulse is at the last pulse position in the first slot, and wherein the second position of the second pulse is at the first pulse position in the second slot.

30. The RFID IC according to claim 16, wherein the digitally modulated signal comprises at least one of a “1 out of 4” mode and a “1 out of 256” mode.

31. The RFID IC according to claim 30, wherein the “1 out of 4” mode is applied, wherein the first pulse corresponds to term “11”, and wherein the second pulse corresponds to term “00”.

32. The RFID IC according to claim 30, wherein the “1 out of 256” mode is applied, wherein the first pulse corresponds to term “0xFF” or term “SOF”, and wherein the second pulse corresponds to term “0x00”.

33. An RFID arrangement, comprising: an RFID IC according to claim 16; and a further RFID IC configured to transmit the digitally modulated signal to the RFID IC, wherein the further RFID IC is configured to digitally modulate the signal either by 10% ASK or 100% ASK, wherein it is inherent to the RFID IC to partially interpret 100% ASK as 10% ASK.

34. The RFID arrangement according to claim 33, wherein it is inherent to the RFID IC to partially interpret 100% ASK as 10% ASK in case when a disturbance occurs.

35. A method of demodulating a digitally modulated RF signal, the method comprising: receiving the digitally modulated signal, wherein the digitally modulated signal comprises a first slot with a first pulse, and a second slot with a second pulse; determining a first position of the first pulse in the first slot; filtering a region that follows the determined first position of the first pulse; determining a second position of the second pulse in the second slot, and if the second position of the second pulse cannot be determined in the second slot, assuming that the second position of the second pulse in the second slot is at the filtered region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 illustrates a method of demodulating a digitally modulated RF signal according to an exemplary embodiment of the present disclosure.

[0042] FIG. 2 illustrates a method of demodulating a digitally modulated RF signal according to another exemplary embodiment of the present disclosure.

[0043] FIG. 3 illustrates a data coding according to ISO15693 standard.

[0044] FIG. 4 illustrates a “1 out of 4” data encoding mode and a double pulse scenario.

[0045] FIG. 5 illustrates the occurrence of an overshoot and a corresponding erroneous demodulation.

[0046] FIGS. 6a to 6e illustrate the effects that can change the modulation index seen by the RFID IC.

[0047] The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs.

DETAILED DESCRIPTION OF THE DRAWINGS

[0048] Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the present disclosure have been developed.

[0049] According to an exemplary embodiment of the present disclosure, tag ICs compliant to ISO 15693 and NFC T5T need to decode ASK modulation pulses which can be very close (minimum spacing) in certain symbol sequences (e.g. “3” followed by “0”) (double pulses). ISO 15693 offers the choice of two ASK modulation indices: 10% or 100% ASK (i.e. 10 . . . 30% or 90 . . . 100%). Although there seems to be a lot of margin between 30% and 90% ASK, in reality 30% ASK can look like 90% modulation on chip level (see FIGS. 6a-e). This can occur depending on tuning of the transponder, modulation shape, ringing, field strength and on-chip limiter characteristics.

[0050] According to an exemplary embodiment, the modulation index, which the RFID IC “sees” (interprets), can change which the RFID IC sees (e.g. 30% ASK can look like 90% modulation on chip level). In an example, when a modulation pulse occurs, the antenna voltage (Vin) drops, the input capacitance (Cp) of the RFID IC changes, and therefore, the tuning of the transponder. Depending on the tuning of the transponder at continuous wave, the resulting tuning during the modulation may be improved or degraded in comparison to the tuning at continuous wave. As a consequence, the resulting modulation index may be higher or lower than originally transmitted by the reader. In this manner, for example, a 30% modulation may increase to a level which is interpreted as 100% modulation by the RFID IC (processing unit). These effects are illustrated in the FIGS. 6a to 6e.

[0051] FIG. 6a shows a relation between input capacitance (Cp) and antenna voltage (Vin): when the voltage increase, the capacitance increases as well (and the other way around).

[0052] FIG. 6b shows a relation between magnetic field strength H and (resonance) frequency f: H is lowest exactly at the resonance frequency 13.56 MHz.

[0053] FIG. 6c shows an example, wherein a transponder is tuned below resonance frequency with additional tuning capacity. The voltage drops during modulation, the capacity Cp of the RFID device goes down, while the tuning of the RFID device goes up. This effect moves the RFID device into the direction of resonance. In this case, the chip may be tuned better than during continuous wave and the resulting modulation depth may be lower.

[0054] FIG. 6d shows an example of a “perfectly” tuned case.

[0055] FIG. 6e shows an example, wherein a transponder is tuned above resonance with additional tuning capacity. The voltage drops during modulation, the capacity Cp of the RFID device goes down, while the tuning of the RFID device goes up. This effect moves the RFID device further away from resonance. In this case, the chip may be tuned worse than during continuous wave and the resulting modulation depth may be higher.

[0056] According to an exemplary embodiment, it is beneficial if a chip can decode a mixture of 10% and 100% ASK throughout a command when operating in an ISO 15693 environment. NFC T5T is a sub-set of ISO 15693 supporting only 100% ASK, however, allowing higher overshoots in the modulation waveshapes than ISO 15693. These overshoots cannot trigger a 100% ASK signal, but a 10% ASK signal. Such a 100% ASK signal followed by a 10% ASK signal caused by an overshoot can look like a regular double pulse scenario for the chip. The present disclosure proposes a scheme how to resolve this conflict between ISO 15693 and NFC T5T requirements. It also helps to overcome potential difficulties of the demodulator to detect a 10% ASK shortly after another one.

[0057] According to an exemplary embodiment of the present disclosure, the following steps can be performed: i) ISO 15693 uses 1oo4 coding (among others), the value is encoded in the position of an ASK pulse, ii) pulses potentially caused by an overshoot are filtered, iii) a double pulse (pulse with minimum spacing) can occur depending on the sequence of symbols, and iv) in case of such a situation, a real double pulse is assumed in case of a code violation. In this embodiment also a missing double pulse is restored irrespective of the used modulation index. This can be beneficial, since detecting a pulse short after another one is a limiting factor in analog demodulator design, because the first pulse changes the operating point of the demodulator for the second one.

[0058] FIG. 1 illustrates a method of demodulating a digitally modulated RF signal 105 according to an exemplary embodiment of the present disclosure. In the example shown, the signals 105 have been modulated by an RFID reader using amplitude shift keying (ASK) and have been transmitted to an RFID IC (tag). The RFID IC comprises an RFID interface to receive the signals 105 and a processing unit for processing (in particular demodulating) the signals 105.

[0059] There are shown five digitally modulated RF signals 105 that correspond to those shown in FIG. 4 (see above). Each signal 105 comprises a first slot 110 and a second slot 120. Further, each first slot 110 comprises a first pulse 115 at a first position and each second slot 120 comprises a second pulse 125 at a second position. The difference to the example of FIG. 4 is, that a region 130 that follows the determined first pulse 115 is filtered. Thereby, e.g. pulses caused by an overshoot, may be filtered. The filter can be implemented with different measure, for example by a gate such as an AND-gate. Preferably, the start of a pulse or disturbance (that may follow the first pulse) is following (timely after) the start of the filtered region 130. In this manner, each pulse or disturbance that follows (directly) after the first pulse can be efficiently cancelled. For the first four signals 105, this scheme functions properly. The corresponding second pulse 125 at the second position can be determined and then both, the first slot 110 and the second slot 120, can be demodulated. In other words, the encoded bits of the respective signal 105 are then decoded.

[0060] In the last signal 105, however, there is a minimum spacing between the first pulse 115 at the last position of the first slot 110, and the second pulse 125 at the first position of the second slot 120 (double pulse). In this case, the second pulse 125 is in the filtered region 130 and will be cancelled. This circumstance may result in a failure during demodulation.

[0061] FIG. 2 illustrates a method of demodulating a digitally modulated RF signal 105 according to another exemplary embodiment of the present disclosure. The example of FIG. 2 is based on the last signal 105 of FIG. 1, wherein the second pulse 125 has been cancelled by the filter step 130. In this manner, the second pulse 125 cannot be determined in the second slot 120. Since there is no pulse and no ASK modulation left, a code violation occurs. Nevertheless, based on the fact that no second pulse is present at all, it is assumed that the position of the second pulse 125 is at the filter region 130. Following this assumption, the second pulse 125 can be restored at the position of the filter region 130. In the example shown (1oo4 mode), the term “00” is assumed. Hence, after the restoring, both, the first slot 110 and the second slot 120, can be efficiently decoded.

[0062] In this specification, embodiments have been presented in terms of a selected set of details. However, a person of ordinary skill in the art would understand that many other embodiments may be practiced which include a different selected set of these details. It is intended that the following claims cover all possible embodiments.

REFERENCE NUMERALS

[0063] 105 Digitally modulated signal [0064] 110 First slot [0065] 115 First pulse [0066] 116 Disturbance, overshoot [0067] 120 Second slot [0068] 125 Second pulse [0069] 130 Filtered region