RFID TRANSCEIVER WITH IMPLEMENTED PHASE CALIBRATION, AND PHASE CALIBRATION METHOD

Abstract

There is described an RFID device, comprising: a transmitter, a matching device, and a receiver.

The transmitter is hereby coupled via the matching device to the receiver. The transmitter is configured to transmit a transmitter signal through the matching device, thereby obtaining a calibration signal. The receiver is configured to receive the calibration signal and estimate a phase shift of the calibration signal. Further, the RFID device is configured to adjust at least one of a transmitter phase shift and a receiver phase shift in order to compensate for the estimated phase shift.

Further, a method of calibrating a phase shift in an RFID device is described.

Claims

1-15. (canceled)

16. A radio frequency identification (RFID) device, comprising: a transmitter; a matching device; and a receiver; wherein the transmitter is coupled via the matching device to the receiver; wherein the transmitter is configured to transmit a transmitter signal through the matching device, thereby obtaining a calibration signal; wherein the receiver is configured to receive the calibration signal and estimate a phase shift of the calibration signal; and wherein the RFID device is configured to adjust at least one of a transmitter phase shift and a receiver phase shift in order to compensate at least partially for the estimated phase shift.

17. The RFID device according to claim 16, wherein adjusting at least one of the transmitter phase shift and the receiver phase shift results in a calibrated phase at the receiver in a reader mode.

18. The RFID device according to claim 17, wherein the receiver is further configured to: determine the phase shift between the transmitter and the receiver; and adjust said phase shift in order to obtain the calibrated phase at the receiver in the reader mode.

19. The RFID device according to claim 16, wherein the RFID device further comprises: an antenna, coupled to the matching device; and wherein adjusting at least one of the transmitter phase shift and the receiver phase shift results in a calibrated phase at the antenna in the card emulation mode.

20. The RFID device according to claim 19, wherein the RFID device is further configured to: determine a phase shift at the matching device; and adjust said phase shift in order to obtain the calibrated phase at the antenna in the card emulation mode.

21. The RFID device according to claim 16, wherein the receiver is further configured to sample the amplitude of the calibration signal.

22. The RFID device according to claim 21, wherein the receiver comprises an estimation unit which is configured to provide an I-path signal and a Q-path signal based on the sampled amplitude, and estimate the phase shift based on the obtained I-path signal and the obtained Q-path signal.

23. The RFID device according to claim 22, wherein the estimation unit comprises a carrier cancelation loop,

24. The RFID device according to claim 16, further comprising: a transmitter phase shifter, coupled to the transmitter, and configured to adjust the transmitter phase shift in order to at least partially compensate for the estimated phase shift.

25. The RFID device according to claim 16, further comprising: a receiver phase shifter, coupled to the receiver, and configured to adjust the receiver phase shift in order to at least partially compensate for the estimated phase shift.

26. The RFID device according to claim 16, further comprising a clock generator coupled to the transmitter and the receiver, wherein the clock generator is configured to perform at least one of synchronize a transmitter clock and a receiver clock, or tune the transmitter clock or the receiver clock.

27. The RFID device according to claim 16, wherein the transmitter signal is an unmodulated signal.

28. The RFID device according to claim 16, wherein the receiver further comprises a signal amplitude regulation unit configured to provide a signal amplitude close to a predefined value.

29. The RFID device according to claim 16, wherein the RFID device is an NFC device.

30. A method of phase calibrating a radio frequency identification (RFID) device, the method comprising: transmitting an unmodulated transmitter signal through a matching device of the RFID device in order to obtain a calibration signal; receiving the calibration signal and estimating a phase shift from the calibration signal; and adjusting at least one of a transmitter phase shift and a receiver phase shift, within the RFID device, in order to compensate at least partially for the estimated phase shift.

31. The method according to claim 30, wherein the method is performed when the RFID device is coupled with a further RFID device.

32. The method according to claim 31, wherein the method is performed when there is no modulation of signals communicated between the RFID device and the further RFID device.

33. A method of phase calibrating a radio frequency identification (RFID) device using a loop from a transmitter via a matching network to a receiver in order to phase calibrate the RFID device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIGS. 1 to 3 illustrate respectively an RFID device according to an exemplary embodiment of the present disclosure.

[0041] FIG. 4 illustrates a method of phase calibrating an RFID device according to an exemplary embodiment of the present disclosure.

[0042] FIG. 5 illustrates a method of phase calibrating an RFID device in real-time according to an exemplary embodiment of the present disclosure.

[0043] FIG. 6 illustrates a matching device according to an exemplary embodiment of the present disclosure.

[0044] FIG. 7 illustrates a receiver with an estimation unit according to an exemplary embodiment of the present disclosure.

[0045] FIGS. 8 and 9 illustrate respectively sampling amplitudes of the calibration signal.

[0046] The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0047] Before, referring to the drawings, embodiments will be described in further detail, some basic considerations will be summarized based on which embodiments of the disclosure have been developed.

[0048] According to an exemplary embodiment, the present disclosure makes it possible to achieve a small phase error in card emulation mode (CEM) and reader mode (RM) despite matching network RLC (resistor, loop, capacitor) components spread. This may be achieved by the following calibration steps:

i) an NFC device transmitter is configured to transmit a (RF) transmitter signal (square or continuous wave) through a matching network,
ii) this RF signal is looped-back toward the NFC device receiver inputs through the matching network,
iii) the NFC receiver contains a carrier cancelation loop (or DCO (DC offset) loop) which cancels the sampled carrier signal amplitude on an I-path and a Q-path,
iv) the carrier cancelation loop I- and Q-control signals are used to estimate the phase shift through the matching network, and
v) the phase shift is adjusted in the transmitter (and/or receiver) in order to compensate for the estimated phase shift, resulting in a constant-over-production phase at the antenna (CEM mode) and/or at the receiver mixer (reader mode).

[0049] According to a further exemplary embodiment, CEM and RM phase calibrations are addressed with a single measurement point using fully integrated measurement instruments. It relies on a carrier-cancelation loop of a receiver, synchronous receiver and transmitter, tuneable receiver and transmitter clocks, which are used to estimate and correct the delay between the transmitted transmitter signal and the received receiver (calibration) signal. This technique allows calibrating the transmitter/receiver clock phases during operation, which opens up new capabilities such as compensation of matching device detuning during operation.

[0050] FIG. 1 illustrates an RFID device 100 according to an exemplary embodiment of the present disclosure. The RFID device in this example is an NFC transceiver (e.g. implemented in an NFC phone) and comprises a transmitter 110, coupled to a transmitter phase shifter 115, and a receiver 120, coupled to a receiver phase shifter 126. Both, the transmitter 110 and the receiver 120, are further coupled to a clock generator 160 that is configured to synchronize the transmitter clock and the receiver clock and/or tune them independently. The clock generator 160 is further connected to a PLL (phase-locked loop) unit. Further, both of the transmitter 110 and the receiver 120, are coupled to a matching device 130 that comprises RLC components (see FIG. 6). The matching device 130 is further connected to an NFC antenna 140. In this manner, the receiver 120 is coupled (connected) via the matching device 130 to the transmitter 110 as a loop. In the example shown, the transmitter 110 and the receiver 120 are implemented in a common integrated circuit (IC) which is further connected to the matching device 130 and the antenna 140.

[0051] A phase shift, that occurs between the transmitter 110 and the matching device 130, is indicated as φ.sub.MN. This phase shift has to be calibrated in particular for the CEM mode. Phase shifts between the transmitter 110, and the receiver 120 are indicated as φ.sub.TX and φ.sub.RX, respectively. These phase shifts have to be calibrated (using the phase shifters 115, 126 and/or the clock generator 160) in particular for the reader mode.

[0052] The transmitter 110 is configured to transmit an unmodulated transmitter signal 111 (e.g. a square signal) via the matching device 130 to the receiver 120. In the present context, the transmitter signal 111, after it passed through the matching network 130, is termed calibration signal 121. The phase shift will be estimated based on this calibration signal 121 that carries a matching network phase shift information (delay, spread, etc.). The matching device 130 can process the transmitter signal, for example using a low pass filter. Therefore, in FIG. 1, the calibration signal 121 is shown as a sinusoidal signal in comparison to the square transmitter signal 111. Furthermore, an antenna signal 141 at the antenna 140 is shown, however, the antenna signal 141 does not interfere with the calibration signal 121.

[0053] The receiver 120 is configured to estimate a phase shift of the calibration signal 121 through the matching network 130 using a carrier cancellation loop in an estimation unit (see details in FIG. 7). The NFC device 100 (in particular the transmitter phase shifter 115) is configured to adjust (compensate) the phase shift in order to compensate for the estimated phase shift.

[0054] FIG. 2 illustrates an RFID device 100 according to an exemplary embodiment of the present disclosure that is in the CEM mode. It is indicated that there may be a need for a calibrated (constant) phase at the antenna 140 despite RLC components spread in the matching device 130.

[0055] FIG. 3 illustrates an RFID device 100 according to an exemplary embodiment of the present disclosure that is in the RM mode. It is indicated that there may be a need for a calibrated (constant) phase at the receiver 120 input despite RLC components spread in the matching device 130.

[0056] FIG. 4 illustrates a method of phase calibrating an RFID device according to an exemplary embodiment of the present disclosure. The calibration algorithm can be implemented (for example in the NFC transceiver described for FIG. 1) as described in the following exemplary example:

1) after start-up, booting, and configuration, the transmitter (TX) 110 is transmitting an unmodulated signal (see step 3).
2) the transmitter 110 is connected to the matching device 130. A spread (offset) of the phase shift through the matching device 130 is mainly caused by the SMD components and the antenna (for example production spread on the inductors Le, La (see FIG. 6), and their associated parasitic components) and is reflected in the calibration signal 121. The present disclosure may also work for any other topology of matching device.
3) the matching device 130 has a feedback path (loop) towards the receiver (RX) 120 for the calibration signal 121.
4) the receiver 120 processes this calibration signal 121.
5) the receiver 120 can include an “HF-att” regulation loop (signal amplitude adjustment loop). This loop is run (see step 5) in order to get a signal amplitude at receiver P and/or receiver N close to a regulation loop target (predefined value). The loop can use a dichotomy approach or a more complex algorithm.
6) the receiver 120 includes a carrier cancellation (DC offset) loop in an estimation unit 125, which subtracts the estimated carrier amplitude from the sampled input calibration signal 121, independently on the I-path and the Q-path (see step 6). This loop ensures that the signals at an ADC output are both at their minimum (see FIG. 7 for details).
Hereby, the I-path signal “dco_i” and the Q-path signal “dco_q” settle to the instantaneous carrier amplitudes which are carried out by the input signal at the receiver I-path and Q-path sampling instants. During a reader mode reception, this process allows adding gain between the mixer and the ADC to improve receiver sensitivity (receiver noise reduction), while not saturating the signal path (the carrier amplitude removal reduces the signal amplitude, which allows adding gain w/o causing saturation in the signal path). The loop algorithm can for instance use a dichotomy approach or a more complex algorithm.
7) For reader mode (RM): once the DC offset loop has settled, the transmitter-to-receiver phase shift can be calculated as (step 8): φ.sub.meas=atan 2 (dco_q, dco_i). The Cordic algorithm might be used for example to calculate the phase shift from the I-path and the Q-path. φ.sub.meas is here the reference phase shift for the reader mode. The transmitter phase shifter 115 and/or the receiver phase shifter 126 settings are then modified by φ.sub.meas in order to configure the transceiver 100 at peak sampling or other sampling instants such as π/4-sampling. For example: if a peak sampling strategy is targeted and the measured phase shift is φ.sub.meas=22°, the transmitter phase shifter 115 setting shall be reduced by 22°. Alternatively, the receiver phase shifter 126 could be increased by 22°. Any phase shift partitioning between the transmitter phase shifter and the receiver phase shifter may also be valid.
8) For card emulation mode (CEM): the (IC internal) phase shifts are de-embedded from the measured phase shift (step 9): φ.sub.MN=φ.sub.meas−φ.sub.IC or φ.sub.meas−φ.sub.RX+φ.sub.TX. φ.sub.MN is the phase shift through the matching device 130, and as such is the relevant phase shift for CEM. The optimum transmitter phase shift can be modified in order to compensate for this phase shift: φ.sub.TX=−φ.sub.MN, and guarantee a constant-over-production antenna signal phase.

[0057] It should be noted that additional steps could be taken in the phase calibration. For instance, calibration against internal ICs errors could be added depending on the transceiver characteristics.

[0058] FIG. 5 illustrates a method of phase calibrating an RFID device 100 in real-time according to an exemplary embodiment of the present disclosure, when calibration is launched before and during a transaction (i.e. calibration algorithm for real-time implementation). In other words, the calibration method is performed when the RFID device 100 is coupled (in communication) with a further RFID device 200. In particular, when no modulation of signals communicated between the RFID device 100 and the further RFID device occurs, the phase calibration method is applied. In the example shown, the RFID device 100 is a (card) reader (PCD, proximity-coupling device) device) with the transmitter 110 and the receiver 120, while the further RFID device 200 is a (smart) card (PICC, proximity integrated circuit card) with a transmitter.

[0059] The coupling/communication starts with an unmodulated signal (continuous wave, CW) of the RFID device 110. Then, a modulated signal (PCD-to-PICC frame) is communicated from RFID device 100 to the further RFID device 200 which, after a short duration, transmits a further modulated signal (PICC-to-PCD frame) to the RFID device 100. In the example shown, the above described phase calibration (indicated as “ON”) is applied at the receiver 120 of the RFID device 100, when no modulated signal is transferred between RFID device 100 and the further RFID device 200. In such a way, it is possible to maintain the PCD receiver sampling instants independent from the proximity card coupled device (PICC) position, even under strong detuning conditions.

[0060] FIG. 6 illustrates a matching device 130 connected to a transmitter 110 and a receiver 120 according to an exemplary embodiment of the present disclosure. In this example, a balanced matching network with RLC components is shown.

[0061] FIG. 7 illustrates a receiver 120 with an estimation unit 125 according to an exemplary embodiment of the present disclosure. The receiver architecture includes a carrier cancellation calibration loop (or DC offset (DCO) loop). The receiver 120 is configured to sample the amplitude of the calibration signal 121. The receiver 120 is further configured to subtract the sampled amplitude of the calibration signal 121 in an I-path and a Q-path. The phase shift is estimated based on the obtained I-path signal “dco_i” and the Q-path signal “dco_q”. The estimation unit 125 may run a plurality of loops, for example around ten. Additionally, the estimation unit 125 is partially implemented as a signal amplitude regulation unit (HF-att) configured to provide a signal amplitude close to a predefined value (see signal “g-hfatt”). Even though FIG. 7 shows a single-ended signal path, the signal path could also be differential.

[0062] FIG. 8 illustrates a sampling of the calibration signal 121 with a DC offset calibration steady state in peak sampling configuration, while FIG. 9 illustrates a sampling of the calibration signal 121 with a DC offset calibration steady state in π/4 sampling configuration. It shall be noticed that the receiver is illustrated to have a sampling rate equal to the carrier frequency but could include some oversampling factor as well. Typically, this oversampling could be in the range of 2 to 8.

[0063] 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

[0064] 100 RFID device, NFC transceiver [0065] 110 Transmitter [0066] 111 Transmitter signal [0067] 115 Transmitter phase shifter [0068] 120 Receiver [0069] 121 Calibration signal [0070] 125 Estimation unit [0071] 126 Receiver phase shifter [0072] 130 Matching device [0073] 140 Antenna [0074] 141 Antenna signal [0075] 160 Clock generator [0076] 200 Further RFID device