阅读说明：本技术 用于近场通信中的协议检测和解码的集成电路和方法 (Integrated circuit and method for protocol detection and decoding in near field communication ) 是由 M·什蒂格利奇 I·布拉图兹 A·佩维克 R·本科维克 于 2019-06-17 设计创作，主要内容包括：一种用于解码由调制信号承载的数据流的方法,包括接收调制信号。调制信号是根据属于包括至少三个协议的协议组的协议进行调制的。该方法还包括从所接收的调制信号中提取时钟信号,检测协议,以及使用所提取的时钟信号根据检测到的协议来解码数据流。(A method for decoding a data stream carried by a modulated signal includes receiving the modulated signal. The modulated signal is modulated according to a protocol belonging to a protocol group comprising at least three protocols. The method also includes extracting a clock signal from the received modulated signal, detecting a protocol, and decoding the data stream according to the detected protocol using the extracted clock signal.)

1. A method for decoding a data stream carried by a modulated signal, the method comprising:

receiving the modulated signal, the modulated signal being modulated according to a protocol belonging to a protocol group comprising at least three protocols;

extracting a clock signal from the received modulated signal;

detecting the protocol; and

decoding the data stream according to the detected protocol using the extracted clock signal.

2. The method of claim 1, wherein detecting the protocol comprises determining a duration of a non-modulated signal.

3. The method of claim 1, further comprising:

performing Amplitude Shift Keying (ASK) demodulation on the modulated signal to generate a first signal; and

performing on-off keying (OOK) demodulation on the modulated signal to generate a second signal, wherein

Detecting the protocol includes detecting the protocol using the first signal and the second signal.

4. The method of claim 3, wherein:

when the level of the modulation signal is greater than a first threshold, the second signal is in a first state;

when the level of the modulation signal is lower than a second threshold, the second signal is in a second state; and

detecting the protocol further comprises:

stopping the clock signal in response to detecting that the second signal is in the second state, an

The clock signal is maintained during reception of the non-modulated signal.

5. The method of claim 1, wherein the protocol suite includes a class a protocol of the ISO/IEC14443 standard, a class B protocol of the ISO/IEC14443 standard, and a class F protocol of the jis.x.6319 standard.

6. A method for decoding a data stream carried by a modulated signal, the method comprising:

receiving the modulated signal, the modulated signal being modulated according to a protocol belonging to a protocol group including a class A protocol of ISO/IEC14443 standard, a class B protocol of ISO/IEC14443 standard, and a class F protocol of JIS.X.6319 standard;

extracting a clock signal from the received modulated signal;

detecting the protocol; and

decoding the data stream according to the detected protocol using the extracted clock signal.

7. The method of claim 6, further comprising:

performing Amplitude Shift Keying (ASK) demodulation on the modulated signal to generate a first signal comprising transitions between a first state and a second state; and

performing on-off keying (OOK) demodulation on the modulated signal to generate a second signal comprising transitions between the first state and the second state,

wherein a transition between the first state and the second state of the second signal is a result of modulating the modulated signal according to the class A protocol or the class F protocol, an

Wherein detecting the protocol comprises detecting the protocol using both the first signal and the second signal.

8. The method of claim 7, wherein detecting the protocol further comprises:

analyzing the first signal to distinguish between the class B protocol and the class F protocol.

9. The method of claim 7, wherein:

the second signal has the first state when the level of the modulation signal is greater than a first threshold;

the second signal has the second state when the level of the modulated signal is below a second threshold; and

detecting the protocol further comprises:

stopping the clock signal in response to detecting that the second signal is in the second state, an

The clock signal is maintained during reception of the non-modulated signal.

10. The method of claim 9, wherein detecting the protocol comprises: determining a duration of the non-modulated signal to distinguish between the class A protocol and the class F protocol.

11. The method of claim 9, wherein detecting the protocol further comprises resuming forwarding of the clock signal in response to:

detecting that the second signal is in the second state, an

It is detected that the protocol is a class F protocol.

12. The method of claim 6, further comprising activating a class A decoder prior to detecting the protocol, wherein

Decoding the data stream includes decoding the data stream using a selected decoder of a plurality of decoders including:

the class A decoder, wherein the class A decoder is configured to decode the data stream according to the class A protocol,

a class B decoder configured to decode the data stream according to the class B protocol, an

A class F decoder configured to decode the data stream according to the class F protocol.

13. The method of claim 12, further comprising:

stopping the clock signal during receipt of a modulated pulse of the modulated signal and in response to detecting that the protocol is the class A protocol;

storing a demodulated signal corresponding to the modulated pulse; and

decoding the data stream based on the stored demodulated signal using the selected decoder during reception of the non-modulated signal.

14. The method of claim 12, wherein decoding the data stream according to the detected protocol comprises: activating the selected decoder while disabling all remaining decoders of the plurality of decoders.

15. An integrated circuit for decoding a data stream carried by a modulated signal, comprising:

a wireless receiver configured to receive the modulated signal, the modulated signal being modulated according to a protocol belonging to a protocol group selected from the group consisting of a class A protocol of the ISO/IEC14443 standard, a class B protocol of the ISO/IEC14443 standard, and a class F protocol of the JIS.X.6319 standard;

a clock extractor coupled to the wireless receiver and configured to extract a clock signal from the received modulated signal;

a detector coupled to the wireless receiver and configured to detect the protocol; and

a decoder configured to decode the data stream according to the detected protocol using the extracted clock signal.

16. The integrated circuit of claim 15, wherein the detector comprises:

an amplitude shift keying, ASK, demodulator configured to perform ASK demodulation on the modulated signal to generate a first signal including transitions between a first state and a second state; and

an on-off keying (OOK) demodulator configured to perform OOK demodulation on the modulated signal to generate a second signal comprising transitions between the first state and the second state;

wherein a transition between the first state and the second state of the second signal is a result of modulating the modulated signal according to the class A protocol or the class F protocol; and

wherein the detector is further configured to detect the protocol using both the first signal and the second signal.

17. The integrated circuit of claim 16, wherein the detector is further configured to detect the protocol by analyzing the first signal to distinguish between the class B protocol and the class F protocol.

18. The integrated circuit of claim 16, further comprising:

a blocking circuit coupled to the clock extractor and configured to stop the clock signal in response to detecting that the second signal is in the second state and to hold the clock signal during reception of a non-modulated signal;

wherein the second signal has the first state when the level of the modulated signal is greater than a first threshold; and

wherein the second signal has the second state when the level of the modulated signal is below a second threshold.

19. The integrated circuit of claim 18, wherein the detector is further configured to: detecting the protocol by determining a duration of the non-modulated signal to distinguish between the class A protocol and the class F protocol.

20. The integrated circuit of claim 18, wherein the prevention circuit is further configured to resume forwarding of the clock signal in response to:

detecting that the second signal is in the second state, an

It is detected that the protocol is a class F protocol.

21. The integrated circuit of claim 15, further comprising:

a controller configured to activate a class A decoder prior to detection of the protocol,

wherein the decoder comprises a plurality of decoders and is further configured to decode the data stream according to the detected protocol using a selected decoder of the plurality of decoders; and

wherein the plurality of decoders comprise:

the class A decoder, wherein the class A decoder is configured to decode the data stream according to the class A protocol;

a class B decoder configured to decode the data stream according to the class B protocol; and

a class F decoder configured to decode the data stream according to the class F protocol.

22. The integrated circuit of claim 21, further comprising:

a blocking circuit configured to stop the clock signal during receipt of a modulated pulse of the modulated signal and in response to detecting that the protocol is the class A protocol;

wherein the class A protocol includes a memory configured to store a demodulated signal corresponding to the modulated pulse; and

wherein the detector is further configured to decode the data stream based on the stored demodulated signal using the selected decoder during reception of the non-modulated signal.

23. The integrated circuit of claim 21, wherein the controller is further configured to: activating the selected decoder while disabling all remaining decoders of the plurality of decoders.

Technical Field

The present invention relates generally to protocol detection and decoding in the field of wireless communications, and, in particular embodiments, to integrated circuits and methods for protocol detection and decoding in Near Field Communications (NFC).

Background

Embodiments of the present invention relate to the field of wireless communications, particularly Near Field Communications (NFC), and more particularly to detecting and decoding at a multi-protocol transponder or tag a protocol used by a reader in communication with the transponder or tag.

Near Field Communication (NFC) is a set of standards for wireless devices, particularly smart phones and similar devices, for establishing radio communication between two devices by bringing them into contact or bringing them close together, typically at a distance of 10cm or less.

NFC uses electromagnetic induction between two loop antennas located within each other's near field to effectively form an air core transformer. For example, it operates at 13.56 MHz. NFC involves an initiator and a target. The initiator or reader actively generates an RF field that can power passive targets, powerless chips called transponders or "tags". This enables NFC targets to take simple form factors such as sticker labels, key fob or cards that do not use batteries.

Communication from the reader to the tags is accomplished by the reader amplitude modulating a carrier signal according to some standard.

The tag may be passive or active. In the first case, the tag does not generate an electromagnetic field, while in the second case it also generates an electromagnetic field, and the communication between the reader and the tag uses Active Load Modulation (ALM).

NFC technology is standardized in ISO/IEC 18092, ISO/IEC 21481, and NFC FORUM documents, but encompasses various pre-existing standards, including the class A and B protocols standardized in ISO/IEC 14443.

The class a protocols (also known as ISO 14443A and NFC-a techniques) are based on-off keying (OOK) modulation using improved miller pulse positions. The start of a frame (called the SOF symbol) consists of only one pulse. The end of frame (EOF) is marked by a non-modulation period.

The class B protocols (also known as ISO 14443B and NFC forum NFC-B technologies) are based on Amplitude Shift Keying (ASK) modulation and employ direct bit coding. The SOF symbol comprises 10 to 11 low bits followed by 2 to 3 high bits. EOF is represented by some low bits.

FeliC protocol a (also known as NFC-F technology) is standardized in jis.x.6319 and based on ASK modulation, and is completely different. The data is Manchester encoded on a subcarrier clock at 212kHz or 424 kHz. The SOF has 48 or more unmodulated subcarrier clocks. The start of the data is marked by a first phase change of the subcarrier. The EOF is signaled by the data.

Due to the different amplitude modulation indices, two differently structured demodulators are generally employed in the known solutions: OOK demodulators and ASK demodulators.

If a class B or F protocol is detected, the usual method for decoding the data sent to the tag by a class B or F decoder is a clock signal with a frequency proportional to the reader carrier signal frequency. The clock signal is generated by a clock extractor coupled to the tag antenna coil.

However, in the case of a class a protocol detected, the clock signal frequency will not be proportional to the reader carrier signal frequency. Therefore, the clock signal cannot be used as a clock for the class a decoder. Alternatively, an oscillator is used which generates a clock signal.

A disadvantage of using this concept is that the oscillator results in increased implementation costs. It also requires testing, which increases testing time.

Disclosure of Invention

Embodiments of the present invention propose an architecture that uses only the clock signal extracted from the reader field to decode the data received by the tag, whether protocol A, B or F is detected. Embodiments propose a solution that can reduce the implementation cost of multi-protocol detection within a tag.

In a first aspect, a method for decoding a data stream carried by a modulated signal is presented. The signal is modulated according to a protocol belonging to the group comprising protocols a and B of the ISO/IEC14443 standard and protocol F of the jis.x.6319 standard. The method includes receiving a modulated signal, detecting a protocol and decoding a data stream according to the protocol using a clock signal.

According to this aspect, the clock signal is a clock signal extracted from the received modulated signal regardless of the detected protocol. For example, regardless of the detected protocol, only the extracted clock signal is used to decode the data stream.

According to one embodiment, the detection protocol includes: amplitude shift keying, ASK, demodulation is performed on the modulated signal to provide a first signal, and on-off keying, OOK, demodulation is performed on the modulated signal to provide a second signal.

If the modulated signal is modulated according to the protocol A, B or F, the first signal has transitions between a first state (e.g., "1") and a second state (e.g., "0").

The second signal has a transition between the first state and the second state if the modulated signal is modulated according to protocol a or finally according to protocol F.

The protocol is detected from the first signal and the second signal.

Thus, ASK demodulation is performed by the ASK demodulator. The ASK demodulator comprises for example a comparator with a first reference voltage that is so high (for example 95% of the non-modulation level) that it can detect modulation according to the three protocols A, B and F.

OOK demodulation, on the other hand, is performed by an OOK demodulator. The OOK demodulator includes, for example, a comparator having a reference voltage set low to detect only class a protocols. However, sometimes the OOK demodulator may also detect the F-class protocol when the modulation according to the F-class protocol is deep.

More precisely, the maximum modulation index of class F according to the standard specification is 30%. At such a modulation index, the modulation level is 54% of the non-modulation level. However, some installed readers have even lower modulation levels, such as 50% of the non-modulation level. 50% is also a typical threshold for the OOK demodulator in the protocol detection mode, which means that the OOK demodulator can also detect F-class protocols.

In one embodiment, the second signal has a first state if the level of the modulated signal is greater than a first threshold and a second state if the level of the modulated signal is less than a second threshold, and the detection protocol comprises: the clock signal is stopped if the second signal has a second state, i.e., when the OOK demodulator detects a modulation, which may be a class a or F protocol, and the clock signal is not stopped during reception of the non-modulated signal.

For example, the first threshold is about 50% of the non-modulation level, and the second threshold is varied to remain above the level of the modulation signal even if the level becomes zero. The second threshold facilitates rapid detection of the rising edge of the modulated signal.

The first and second thresholds are typically implemented in an OOK demodulator.

If the OOK demodulator detects a class a or class F protocol, the clock signal may be forced to a constant value, e.g., zero. Once the protocol is identified, the clock remains stopped if the protocol is a class a protocol, but the clock signal is no longer stopped if the protocol is a class F protocol.

The clock signal is never stopped during reception of the unmodulated signal, e.g. during two consecutive modulated pulses.

Detecting the protocol among protocols a and F includes advantageously determining the duration of the non-modulated signal, because the clock signal is stopped when OOK modulation is detected.

In other words, when the clock signal stops, protocols a and F can be distinguished by determining the duration of the non-modulated signal that differs for the two protocols. For example, when the first data bit is "0", the duration of the non-modulated signal of the class A protocol at a rate of 106kbps is about 96/fc (carrier frequency f)_C) And the duration of the non-modulated signal of the class F protocol at a rate of 212kbps is approximately 32/F_C。

If the OOK demodulator detects OOK modulation and the clock signal stops, the duration of time to distinguish between the a and F protocols can be determined once the tag receives the non-modulated signal, which requires the use of the clock signal.

Detecting protocol B or F may also include analyzing the first signal.

The ASK demodulator can detect A, B and the F protocol. The B and F protocols can be distinguished by analyzing the first signal as the output signal of the ASK demodulator. This can be done by detecting class F preambles and class B SOFs.

As described above, if the second signal has the second state and the F protocol has been detected, the clock signal may no longer be stopped.

In other words, if the OOK demodulator configured to detect the class a protocol detects the class F protocol, the clock signal is no longer stopped because the clock signal frequency is proportional to the frequency of the signal induced on the antenna coil tag.

In one embodiment, decoding the data stream comprises using one of three decoders intended to decode the data stream modulated according to the protocols A, B and F, respectively, and the decoder intended to decode the data stream modulated according to the protocol a has been activated before detecting the protocol.

In one embodiment, if protocol a is detected, the clock signal is stopped during reception of the modulated pulses of the modulated signal, the second signal corresponding to the modulated pulses is stored, and the corresponding decoder will decode the data stream based on the stored second signal only during reception of the non-modulated signal.

The second signal is stored, for example, by a flip-flop or latch, until the clock signal again appears during reception of the non-modulated signal.

According to another embodiment, decoding a data stream modulated according to a detected protocol includes activating the corresponding decoder and deactivating the other decoders.

If a class A protocol is detected, the class A decoder remains enabled and the other decoders may remain disabled. If a class B protocol is detected, class B decoding is enabled and other decoders may be disabled, and if a class F protocol is detected, a class F decoder is enabled and other decoders may be disabled.

In another aspect, an integrated circuit is proposed for decoding a data stream carried by a modulated signal modulated according to a protocol belonging to the group comprising protocols a and B of the ISO/IEC14443 standard and protocol F of the jis.x.6319 standard. The integrated circuit includes: a receiver configured to receive the modulated signal; a detector configured to detect a protocol; and a decoder configured to decode the data stream according to the protocol using the clock signal. Regardless of the detected protocol, the clock signal is a clock signal extracted from the received modulated signal.

According to one embodiment, the detector comprises: an amplitude shift keying, ASK, demodulator configured to perform ASK demodulation on the modulated signal and provide a first signal; and an on-off keying (OOK) demodulator configured to perform OOK demodulation on the modulated signal and provide a second signal. The first signal has transitions between the first state and the second state if the modulated signal is modulated according to protocol A, B or F, and the second signal has transitions between the first state and the second state if the modulated signal is modulated according to protocol a or finally according to protocol F. The detector is configured to detect a protocol from the first signal and the second signal.

In one embodiment, the second signal has a first state if the level of the modulated signal is greater than a first threshold and a second state if the level of the modulated signal is below a second threshold, and wherein the integrated circuit further comprises a blocking module coupled to an output of the OOK demodulator and configured to: the clock signal is stopped if the second signal has a second state and is no longer stopped during reception of the non-modulated signal.

The blocking module is configured to force the clock signal to a constant value, e.g. zero.

According to another embodiment, the detector is configured to detect the protocol among protocols a and F by determining a duration of the non-modulated signal.

In one embodiment, the detector is configured to detect protocols B and F by analyzing the first signal.

In one embodiment, if the second signal has the second state and the detector detects the F protocol, the blocking module is configured to no longer stop the clock signal.

According to another embodiment, the decoder comprises three decoders intended to decode the data streams modulated according to the protocols A, B and F, respectively, and the integrated circuit further comprises control means configured to activate the decoder intended to decode the data stream modulated according to the protocol a before the detector detects the protocol.

In one embodiment, if the detector detects protocol a, the blocking module is configured to stop the clock signal during reception of the modulated pulses of the modulated signal. The integrated circuit includes a memory configured to store a second signal corresponding to the modulated pulse, and a corresponding decoder is to decode the data stream based on the stored second signal only during reception of the non-modulated signal.

In one embodiment, the controller is configured to activate a decoder intended to decode the data stream according to the detected protocol and to disable the other decoders.

In another aspect, a tag comprising an integrated circuit is presented.

Drawings

Other features and advantages of the present invention will be apparent from the following description, given by way of example only and in view of the following drawings, in which:

fig. 1 to 5 schematically show different embodiments of the proposed invention.

Detailed Description

Embodiments of the present invention relate to the field of wireless communications, particularly Near Field Communications (NFC), and more particularly to detecting and decoding at a multi-protocol transponder or tag a protocol used by a reader in communication with the transponder or tag.

Fig. 1 shows an integrated circuit IC of a tag TG comprising a tag input 100 coupled to a coil antenna ANT of the tag TG. The coil antenna ANT may be configured to receive the modulation signal SIG when the tag communicates with the reader RD in a non-contact manner.

The modulation signal SIG is sent to a detector MD, which is configured to detect the protocol from among the protocol suite. For example, the set of protocols may include a class A, a class B, and a class F protocol. The modulated signal SIG is then sent to a decoder circuit DEC configured to decode the data stream carried by the modulated signal SIG.

The detector MD comprises a first demodulator DEM1 configured to receive the modulated signal SIG on a first detector input 101. The first demodulator DEM1 is further configured to perform ASK demodulation of the modulated signal SIG and deliver a first signal SIG1 at a first demodulator output 103.

In the illustrated example, the detector MD is configured to distinguish between the class B protocol and the class F protocol and deliver a signal on a first controller input 118 belonging to the controller MC through the detector output 108.

More precisely, the detector MD comprises a first protocol detection circuit RB configured to detect the class B protocol SOF and a second protocol detection circuit RF configured to detect the class F protocol SOF.

In this example, the first and second protocol detection circuits RB and RF are globally referenced by the detection circuit DET and their connections will be detailed in fig. 4. According to a possible variant, the first protocol detection circuit RB and the second protocol detection circuit RF can be incorporated in the controller MC.

The detector MD further comprises a second demodulator DEM2 configured to receive the modulated signal SIG at a second detector input 102. The demodulator DEM2 is also configured to perform OOK demodulation and output a second signal SIG2 at a second demodulator output 104.

The decoder DEC includes a class B decoder DB configured to receive the first signal SIG1 on a first DB decoder input 122 and decode the first signal SIG 1. The decoder DEC further includes a class F decoder DF configured to receive the first signal SIG1 on a first DF input 123 and decode the first signal SIG 1. The decoder DEC also includes a class a decoder DA. The class a decoder DA may initially run. That is, the class a decoder DA may operate before receiving the first signal SIG 1. For example, the initial run may indicate that the decoder DA is already running before any protocol detection process starts.

In this example, the class a decoder DA is configured to receive the second signal SIG2 on the first DA input 119, the second signal SIG2 being stored by a memory MMA within the decoder DA. The class a decoder DA is further configured to detect the class a protocol by attempting to decode the stored second signal SIG 2. More specifically, if the class a decoder DA successfully decodes the second signal SIG2, it indicates that the second signal SIG2 has been modulated according to the class a protocol.

On the other hand, if the class a decoder DA is not able to decode the second signal SIG2, this indicates that the second signal SIG2 has been modulated according to the class F protocol. Thus, the class a decoder DA is configured to inform the controller MC on the second controller input 121 whether the decoding has succeeded or failed from the first DA output 120. In case of a failure, if the circuit RF detects a class F protocol, the class a decoder DA will be disabled and the class F decoder DF will be activated to decode the first signal SIG 1.

According to a possible variant, the detector MD may comprise a third protocol detection circuit coupled to the second demodulator DEM2 and to the class a decoder DA. The third protocol detection circuit may be configured to receive the second signal SIG2 and detect the start of a frame of the class a protocol. The third detection circuit may be further configured to determine a duration of the non-modulated signal to distinguish between the class a protocol and the class F protocol.

For example, when the first data bit is "0", the duration of the non-modulated signal of the class A protocol at a rate of 106kbps is approximately 96 divided by the carrier frequency (96/f)_C) And the duration of the non-modulated signal of the class F protocol at a rate of 212kbps is approximately 32 divided by the carrier frequency (32/F)_C)。

If the third detection block detects a class A protocol, the third detection block sends the second signal SIG2 to the class A decoder DA to decode the second signal SIG 2. The class a decoder DA may initially operate as previously described. That is, the class a decoder DA may be initially enabled to decode the second signal SIG 2.

The controller MC is configured to send a signal from the first controller output 124 to the second DB input 115 of the class B decoder DB, from the second controller output 125 to the second DF input 116 of the class F decoder DF, and from the third controller output 126 to the second DA input 117 of the class a decoder DA.

The modulated signal SIG is also sent to a clock input 105 belonging to a clock extractor CLKEX, which is configured to extract timing information from the modulated signal SIG. The clock extractor CLKEX is also configured to deliver the clock signal CLK at the clock output 106.

The clock signal CLK is sent to a blocking input 109 of a blocking circuit ST configured to deliver the same clock signal CLK or stop the clock signal at a forwarded clock signal output 110. The clock signal CLK clocks the decoding processes of the class B decoder DB, the class F decoder DF and the class a decoder DA using the first clock decoder input 114, the second clock decoder input 113 and the third clock decoder input 112, respectively, and clocks the controller MC using the clock controller input 111.

Fig. 2 shows a detailed architecture of an implementation of a demodulator according to an embodiment of the invention. The demodulator of fig. 2 may be a specific implementation of other embodiments of demodulators described herein, such as, for example, the first demodulator DEM1 of fig. 1. The first demodulator DEM1 as shown in fig. 2 is an ASK modulation detector. The first demodulator DEM1 circuit includes a first detector input 101 for receiving a modulated signal SIG.

The first demodulator DEM1 further comprises a first set of components including a first resistor R_ENVA first diode D1 and a first capacitor C_ENVThe first set of components is configured to provide an envelope signal ENV. The signal ENV is then sent on the positive input 300 of the comparator COMP 1.

The first demodulator DEM1 further comprises a second set of components comprising a second resistor R forming a resistive divider RDIV₀₁And a third resistor R₀₂A second capacitor C_REFAnd a first switch SW1, a firstSwitch SW1 is connected between midpoint 302 of resistor divider RDIV and second capacitor C_REFBetween the terminals 303.

The second set of components is configured to provide a first reference voltage REF95 having a reference level that is approximately 95% of the non-modulated level of signal ENV. The first reference voltage REF95 is set to a suitably high level so that the first demodulator DEM1 can detect modulation according to three protocols of class a, class B and class F.

A second capacitor C_REFBuffering the first reference voltage REF95, the first reference voltage REF95 will be used with the first switch SW1 open. A first reference voltage REF95 is sent on the negative input 301 of comparator COMP 1.

Referring now to the right-hand portion of fig. 2, if the amplitude of the modulated signal SIG drops below the first reference voltage REF95, comparator COMP1 changes state and delivers the first signal SIG1 at a low level, which turns off the first switch SW 1. Thus, due to the second capacitor C_REFSo comparator COMP1 continues to compare signal ENV with reference voltage REF 95. A low level of the first signal SIG1 may indicate that the modulation is ASK modulation.

Once the amplitude of the modulation signal SIG becomes greater than the amplitude of the first reference voltage REF95, the comparator COMP1 changes state again and delivers the first signal SIG1 at a high level, which causes the switch SW1 to close.

Fig. 3 shows a detailed architecture of an implementation of a demodulator according to an embodiment of the invention. The demodulator of fig. 3 may be a specific implementation of other embodiments of demodulators described herein, such as, for example, the second demodulator DEM2 of fig. 1. The second demodulator DEM2 as shown in fig. 3 is for example an OOK modulation detector as known in the art.

The second demodulator DEM2 includes the components described above and some additional components. Accordingly, the same reference numerals are maintained for ease of understanding.

It includes a fourth resistor R in addition to the inverter INV₀₃With a voltage source V configured to generate a DC voltage_OFFAre connected in series. For example, the DC voltage may be several tens of millivolts.

A second reference voltage REF50, here representing a first threshold value of the second demodulator DEM2, is sent to the negative input 301 of the comparator COMP 1. The second demodulator DEM2 also includes a second switch SW2 controlled by the inverter output 407 of the inverter INV.

Referring now to the bottom portion of fig. 3, if the amplitude of the modulated signal SIG drops below the second reference voltage REF50, the comparator COMP1 changes state and delivers the second signal SIG2 at a low level, which opens the first switch SW1 and closes the second switch SW 2. A low level of the second signal SIG2 may indicate that the modulation is OOK modulation.

When the second switch SW2 is turned on, the second reference voltage REF50 varies according to the magnitude of the signal ENV. In this case, the second reference voltage REF50 represents a second threshold value that varies according to the magnitude of the signal ENV.

Fourth resistor R₀₃And a second capacitor C_REFTogether providing a time constant. Even if the input signal SIG becomes zero, the source voltage V_OFFThe second reference voltage REF50 is also allowed to remain above the amplitude value of the signal ENV.

The second reference voltage REF50 is set lower than the reference voltage REF95 at a suitable level that ensures that no modulation according to the class B protocol is detected and that modulation according to the class a protocol is detected. In some cases, modulation according to the class F protocol may also be detected at a second reference voltage REF 50.

Once the amplitude of the modulation signal SIG begins to rise, a rising edge is detected. The comparator COMP1 changes state and delivers the second signal SIG2 at a high level.

Fig. 4 shows a schematic diagram of a first protocol sensing circuit RB and a second protocol sensing circuit RF connected to a controller MC according to an embodiment of the invention.

The first protocol detection circuit RB is configured to receive at the first protocol detection input 130 the first signal SIG1 transmitted by the first demodulator DEM 1. The first protocol detection circuit RB is further configured to deliver the first detection signal SB from the first detection signal output 131 to the first detection signal input 141 of the controller MC.

The second protocol detection circuit RF is configured to receive at the second protocol detection input 132 the signal SIG1 transmitted by the first demodulator DEM 1. The second protocol detection circuit RF is further configured to deliver the second detection signal SF from the second detection signal output 137 to the second detection signal input 140 of the controller MC. The clock signal CLK clocks the detection process of the first and second protocol detection circuits RB, RF using the first and second clock signal inputs 133, 134 and clocks the controller MC using the clock controller input 111.

Fig. 5 shows a flow diagram of a method of decoding a data stream carried by a modulated signal according to an embodiment of the invention.

Step 1 comprises receiving, by the antenna coil tag, a modulated signal SIG which is modulated according to one of the protocols of the group. For example, the set of protocols may include a class A, a class B, and a class F protocol.

After step 1, steps 21 and 22 are performed. For example, step 21 and step 22 may be performed in parallel (i.e., simultaneously). In step 21, the modulated signal SIG is sent to the first demodulator DEM1 to detect the presence or absence of ASK modulation. If the demodulator DEM1 detects ASK modulation, the first signal SIG1 is sent to the first protocol detection circuit RB to detect in step 31 whether the modulated signal is modulated according to the class B protocol. In step 41, in case a type B protocol is detected, the type B decoder DB is activated and the type a decoder DA is disabled. The decoder circuit decodes the data stream in step 71.

In parallel, the first signal SIG1 is stored in a flip-flop or latch and will be sent to the second protocol detection circuit RF to detect in step 32 whether the modulated signal is modulated according to the class F protocol. If the second protocol detection circuit RF detects the F protocol, the controller MC checks in step 5 whether the clock signal CLK is stopped. If the clock signal CLK is stopped, the controller MC disables the blocking circuit ST in step 6 to allow the clock signal CLK to run again. The F-type decoder DF is then activated and the class a decoder DA is disabled in step 42. Thus, the decoder circuit will decode the data stream in step 72. If the clock signal CLK is not stopped, the class F decoder DF is activated in step 42 to decode the data stream in step 72.

In step 22, the modulated signal SIG is sent to the second demodulator DEM2 to detect the presence of OOK modulation. If OOK modulation is detected, a second signal SIG2 is sent to the decoder DA in step 33 to decode the second signal stored by the memory MMA, which may be a flip-flop or a latch. In parallel, the prevention circuit ST stops the clock signal in step 34 until a non-modulated signal is received. The blocking circuit ST will not stop the clock signal once a non-modulated signal is received and the stored second signal SIG2 will be decoded.

If the decoder is not able to decode the data stream, this indicates that the modulation signal SIG has been modulated according to the class F protocol. The system will wait in step 73 for the second protocol detection circuit RF to detect the class F protocol in step 32. Then, if the class F protocol has been successfully detected, the clock signal is no longer stopped during the modulated pulse, as set forth in step 6.