Method and system for aligning the phase of a replica carrier signal used to demodulate a subcarrier signal

Abstract

The test and measurement system includes a proximity coupling device that transmits a modulated carrier signal and a proximity integrated circuit card that load modulates the transmitted modulated carrier signal to generate a modulated subcarrier signal on the wireless carrier signal. The test and measurement device includes a phase-aligned subcarrier demodulator that acquires the modulated carrier signal and demodulates the carrier signal, including the modulated subcarrier signal. The demodulator detects commands and responses in the modulated carrier signal, removes the commands, and identifies a correlation index for each response. Each correlation index indicates the phase of the modulated carrier signal of the corresponding response relative to the replica carrier signal. The demodulator adjusts the phase of the replica carrier signal based on the correlation index of each response and down-converts each response using the phase-aligned replica carrier signal. The modulated subcarrier signal is low-pass filtered to demodulate the responses.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to demodulation of modulated subcarrier signals on a carrier signal, and more particularly to aligning the phase of replica carrier signals used to demodulate modulated subcarrier signals. [Background technology]

[0002] Near Field Communication (NFC) is a set of wireless communication protocol standards that define communication between two electronic devices within a short distance of each other. NFC provides communication between two NFC-enabled electronic devices through modulated carrier signals and magnetic field coupling of two antennas on the two NFC-enabled electronic devices. Various types of electronic devices utilize NFC for various applications, such as mobile payments and radio frequency identification (RFID) tags for applications such as access authentication for residential and commercial building doors, as well as vehicle doors. NFC-enabled electronic devices can be passive, such as RFID tags, or active, such as smartphones or payment terminals, where an active device initiates a communication session with a nearby passive device. This communication is called "near-field" communication because the distance between the two devices is much shorter than the wavelength of the modulated carrier signal. For example, for a 13.56 MHz modulated carrier signal, the wavelength is approximately 22 meters, but a typical distance between a polling NFC-enabled device and a listening NFC-enabled device is less than 10 cm.

[0003] A typical NFC system includes a proximity coupling device (PCD) and a proximity integrated circuit card (PICC). The PCD is sometimes referred to herein as the "reader" or "polling device," and the PICC is sometimes referred to as the "tag" or "listening device." The PCD and PICC are magnetically coupled and communicate wirelessly using one of the NFC standard communication protocols. The PCD transmits commands to the PICC by modulating the amplitude of a carrier signal, and the PICC decodes these commands and responds with load modulation. Various types of load modulation are used in various NFC standards. NFC-A type devices communicate according to the ISO / IEC 14443A standard, where the PCD sends commands to the PICC using amplitude modulation, and the PICC, in turn, responds to these commands using load modulation on-off keying (OOK). OOK is a type of amplitude-shift keying (ASK). NFC-B type devices communicate according to the ISO / IEC 14443B standard, where the PCD uses amplitude modulation to send commands to the PICC, and the PICC uses load modulation to generate binary phase shift keying (BPSK) modulated signals to respond to these commands.

[0004] The number of applications utilizing NFC continues to grow, and with each new application, testing NFC-enabled devices is critical to ensuring proper operation. Manufacturers of test and measurement equipment, such as oscilloscopes, produce mixed-signal oscilloscopes (MSOs) with radio frequency (RF) channels suitable for testing wireless electronic devices, including NFC-enabled devices. As part of testing an NFC-enabled device, the oscilloscope demodulates the received wireless signal using an appropriate demodulation method. This demodulation typically involves generating a replica carrier signal in the oscilloscope for down-conversion of the received wireless signal. When using a replica carrier signal for demodulation, the replica carrier signal must be phase-synchronized with the modulated carrier signal transmitted by the PCD. Any phase difference can result in distortion of the demodulated signal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0336824 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0168002 [Patent Document 3] US Patent Application Publication No. 2015 / 0207574 [Patent Document 4] US Patent Application Publication No. 2011 / 0206142 [Patent Document 5] US Patent Application Publication No. 2016 / 0315656 [Non-patent literature]

[0006] [Non-Patent Document 1] "Mixed Signal Oscilloscope" introduction site, Tektronix, [online], [Retrieved October 18, 2025], Internet<https: / / www.tek.com / ja / oscilloscope-mixed-signal-oscilloscope> Summary of the Invention [Problem to be solved by the invention]

[0007] While techniques for phase synchronization of carrier signals are known, many of these known techniques are relatively computationally intensive and therefore tend to be difficult to implement in equipment with limited computing resources, such as test and measurement instruments. Thus, there is a need for improved techniques for demodulating wireless signals that can be implemented in test and measurement instruments, such as oscilloscopes and other devices, to enable the test and measurement instruments to perform, for example, testing of NFC-enabled devices. [Means for solving the problem]

[0008] Embodiments of the disclosed technology relate to a method for demodulating a modulated subcarrier signal and a system for performing this demodulation. Conventional demodulation of a modulated carrier signal, including a modulated subcarrier signal, requires a device receiving the modulated carrier signal to generate a replica carrier signal. The replica carrier signal is used to down-convert the modulated carrier signal as part of the demodulation of the modulated subcarrier signal.

[0009] In an embodiment of the disclosed technology, a test and measurement instrument captures a modulated carrier signal generated by an NFC-enabled device, and a phase-aligned subcarrier demodulator generates a phase-aligned replica carrier signal, which is used to demodulate a modulated subcarrier signal included in the captured modulated carrier signal. The NFC-enabled devices include a polling device and a listening device. If these are NFC-A type devices, the modulated subcarrier signal is an OOK-modulated subcarrier signal. If the NFC-enabled device is an NFC-B type device, the modulated subcarrier signal is a BPSK-modulated subcarrier signal.

[0010] The phase-aligned subcarrier demodulator operates to first detect commands and responses contained in the captured modulated carrier signal and mute or remove the detected commands to generate a response vector including only the responses contained in the captured modulated carrier signal. The phase-aligned subcarrier demodulator then determines a correlation index for each response in the response vector. Each correlation index indicates the phase of the modulated carrier signal of the corresponding response relative to the replica carrier signal. The demodulator adjusts the phase of the replica carrier signal based on the correlation index of each response in the response vector to align the phase of the replica carrier signal and the modulated carrier signal with respect to the response, and demodulates each response in the response vector using the replica carrier signal having the corresponding adjusted phase to generate a demodulated response vector including a plurality of demodulated responses.

[0011] The demodulated response vector is low-pass filtered as part of generating the demodulated response vector. For NFC-A type devices, the phase-aligned subcarrier demodulator also operates to suppress voltage peaks or spikes that arise from phase changes caused by the deletion of commands in the response vector and subsequent low-pass filtering after down-conversion of the response vector. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 illustrates a test and measurement system having a test and measurement instrument including a phase-aligned subcarrier demodulator for use in testing NFC-enabled devices, according to some embodiments of the present disclosure. [Figure 2] FIG. 2 is a more detailed block diagram of a portion of the phase-matched subcarrier demodulator of FIG. 1 in accordance with some embodiments of the present disclosure. [Figure 3] FIG. 3 is a flowchart of an example demodulation process performed by the phase-aligned subcarrier demodulator of FIG. 1 according to some embodiments of the present disclosure. [Figure 4] FIG. 4 is a signal diagram illustrating signals utilized and generated by the phase-aligned subcarrier demodulator of FIG. 1 during operation to decode an OOK modulated subcarrier signal at an NFC-A type device, according to some embodiments of the present disclosure. [Figure 5] FIG. 5 is a signal timing diagram illustrating suppression or removal of spikes contained in the demodulated subcarrier signal provided to the low-pass filter of the phase-aligned subcarrier demodulator of FIG. 1 in accordance with some embodiments of the present disclosure. [Figure 6A] FIG. 6A is a flowchart illustrating in more detail the demodulation process performed by the phase-matched subcarrier demodulator of FIG. [Figure 6B] FIG. 6B is a flowchart illustrating in more detail the demodulation process performed by the phase-matched subcarrier demodulator of FIG. [Figure 7] FIG. 7 is a signal timing diagram illustrating signals utilized and generated by the phase-aligned subcarrier demodulator of FIG. 1 during operation to decode a BPSK-modulated subcarrier signal at an NFC-B type device, according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 1 is a block diagram of a test and measurement system 100 including a test and measurement instrument 102 including a phase-aligned subcarrier demodulator 104 for demodulating a subcarrier signal SUBC-MOD modulated during some tests in accordance with an embodiment of the disclosed technique. The test and measurement instrument 102 includes one or more main processors 150 configured to execute instructions from a main memory 152 and may perform any method or associated steps indicated by such instructions. A user interface 154 is coupled to the one or more processors 150 and may include, for example, a keyboard, mouse, touchscreen, output display, file storage, or any other operating device that allows a user to interactively operate the test and measurement instrument 102. In some embodiments, the user interface 154 may be connected to or controlled by a remote interface (not shown), allowing a user to control operation of the test and measurement instrument 102 from a location physically separate from the test and measurement instrument. The display of the user interface 154 may be a digital screen such as an LCD or any other monitor for displaying waveforms, measurements, and other data to a user. In some embodiments, the main output display of the user interface 154 may be located remotely from the test and measurement instrument 102.

[0014] One or more measurement units 156 perform the primary function of measuring parameters and other characteristics of signals from NFC-enabled device 106 that are measured by test and measurement instrument 102. Typical measurements include measuring the voltage, current, and power of the input signal in the time domain, as well as measuring the characteristics of the signal in the frequency domain. Measurement unit 156 represents any measurement typically performed on a test and measurement instrument, and phase-aligned subcarrier demodulator 104 may be integrated into or coupled to such measurement unit 156.

[0015] 1 also shows NFC-enabled devices 106, including a polling device or proximity coupling device (PCD) 108 and a listening device or proximity integrated circuit card (PICC) 110, which may be either NFC-A or NFC-B type devices in embodiments of the test and measurement system 100. These NFC-enabled devices 106 communicate via NFC in the form of a modulated carrier signal (MCS) generated in accordance with the ISO / IEC 14443A or ISO / IEC 14443B standards. A radio frequency (RF) probe 112 is coupled to the input of the test and measurement instrument 102 and is appropriately positioned or coupled to the listening device 110 to detect the modulated carrier signal MCS. In operation, the polling device 108 transmits the radio modulated carrier signal MCS to both provide power and transmit commands to the listening device 110. The listening device 110 load modulates the modulated carrier signal MCS to generate a modulated subcarrier signal SUBC-MOD on the modulated carrier signal and transmits a response to the polling device 108 .

[0016] The type of load modulation implemented by the listening device 110 depends on whether the polling device 108 and the listening device 110 are NFC-A or NFC-B type devices. For NFC-A type devices, the listening device 110 utilizes on-off keying (OOK) load modulation to generate an OOK-modulated subcarrier signal SUBC-MOD on a modulated carrier signal MCS. For NFC-B type devices, the listening device 110 utilizes binary phase shift keying (BPSK) load modulation to generate a BPSK-modulated subcarrier signal SUBC-MOD on a modulated carrier signal MCS. The polling device 108 transmits commands to the polling device 110 for both NFC-A and NFC-B type devices using amplitude shift keying (ASK) on the modulated carrier signal MCS, although the characteristics of the ASK modulation implemented by the polling device vary depending on the device type, as defined in the ISO / IEC 14443A and 14443B standards.

[0017] During testing of these NFC-enabled devices 106, the test and measurement instrument 102 captures the modulated carrier signal MCS detected by the RF probe 112, and the phase-aligned subcarrier demodulator 104 generates a phase-aligned replica carrier signal RCS that is used to demodulate the modulated subcarrier signal SUBC-MOD included in the captured modulated carrier signal, as described in more detail below. If the polling device 108 and the listening device 110 are NFC-A type devices, the modulated subcarrier signal SUBC-MOD is an OOK modulated subcarrier signal, as described above, and in this embodiment, the phase-aligned subcarrier demodulator 104 is further operative to first detect commands CMD and responses RSP included in the captured modulated carrier signal MCS and mute or remove these detected commands to generate a response vector RSPVEC that includes only the responses included in the captured modulated carrier signal. In this embodiment, the phase-aligned subcarrier demodulator 104 further operates to suppress voltage peaks or spikes that appear in the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD that are generated in the process of low-pass filtering the OOK modulated subcarrier signal SUBC-MOD. The operation of the phase-aligned subcarrier demodulator 104 in removing detected commands and suppressing such voltage spikes is described in more detail below.

[0018] As described above, the polling device 108 and the listening device 110 communicate via NFC communication, which is represented in FIG. 1 by the modulated carrier signal MCS. The characteristics of the modulated carrier signal MCS and the NFC communication between the polling device 108 and the listening device 110 will now be briefly described in more detail to better understand the operation of the phase-matched subcarrier demodulator 104 according to an embodiment of the disclosed technology. The polling device 108 and the listening device 110 each have an antenna 108A and 110A, respectively, which are coupled to electronic components (not shown) of the corresponding polling device 108 or listening device 110. The antennas 108A and 110A are positioned in close physical proximity to one another such that the antennas are inductively coupled by the modulated carrier signal MCS in the same manner as the coils of a transformer. In this manner, the antennas 108A and 110A can be considered as coils of an air-core transformer, and the modulated carrier signal MCS can be considered to represent the alternating magnetic field generated by the polling device 108 due to an alternating signal applied to the antenna 108A. This alternating signal is a 13.56 MHz carrier signal specified in the ISO / IEC 14443A and 14443B standards when the polling device 108 and the listening device 110 are NFC-A and NFC-B type devices. Those skilled in the art will understand the characteristics of magnetic coupling between the antennas 108A and 110A and NFC in comparison to conventional far-field propagation of electromagnetic signals between antennas. Therefore, the characteristics of NFC will be briefly described herein but will not be described in detail, as such details are not necessary for understanding embodiments of the disclosed technology.

[0019] During operation of an NFC communication session, the polling device 108 and the listening device 110 exchange information by communicating a command CMD and a response RSP via a modulated carrier signal MCS. The NFC communication session is represented in FIG. 1 by a PICC activation command ACT-PICC (activate PICC command), a PICC send command SND-PICC (send PICC command), and a response RSP from the PICC listening device 110. The polling device 108 occasionally transmits the modulated carrier signal MCS to determine whether any listening devices 110 are located in its vicinity. When the polling device 110 approaches the polling device 108, the modulated carrier signal MCS is received by the antenna 110A of the listening device 110. At this time, the listening device is a passive device, and this signal is rectified and used to power electrical components within the listening device. The reception of this modulated carrier signal MCS and the generation of power derived therefrom correspond to the PICC activation command ACT-PICC in Figure 1. After the PICC activation command ACT-PICC, the polling device 108 transmits a PICC send command SND-PICC to the listening device 110 by modulating the modulated carrier signal MCS. The type of modulation used by the polling device 108 to transmit the PICC send command SND-PICC is ASK according to either the ISO / IEC 14443A or 14443B standard, as described above, when the polling device 108 and the listening device 110 are NFC-A and NFC-B type devices, respectively.

[0020] The listening device 110 receives the ASK modulated carrier signal MCS and demodulates it to decode the SND-PICC command sent by the polling device 108. The listening device 110 then processes the decoded SND-PICC command and transmits an appropriate response RSP corresponding to the decoded command. To transmit this response, the polling device 108 load-modulates the modulated carrier signal MCS. The load modulation changes the impedance of the antenna 110A of the listening device 110, and due to the magnetic coupling between the antennas 108 and 110A, this variation in the impedance of the antenna 110A causes a change in the signal at the antenna 108A of the polling device 108. In this way, the listening device 110 modulates the modulated carrier signal MCS to transmit the response RSP to the polling device 108. If the polling device 108 and the listening device 110 are NFC-A or NFC-B type devices that communicate according to the ISO / IEC 14443A or 14443B standard, the listening device 110 uses an 848 kHz subcarrier signal modulated by OOK or BPSK. The frequency of the subcarrier signal is determined by a modulation coefficient N, where N is the frequency of the modulated carrier signal F. C The frequency F obtained by dividing by the modulation coefficient N SC (F SC =(F C / N)). If F C = 13.56MHz and N = 16, F SC= (13.56 MHz / 16) = 848 kHz. Thus, the listening device 110 load modulates the modulated carrier signal MCS to include either an OOK modulated subcarrier signal (NFC-A) or a BPSK modulated subcarrier signal (NFC-B) that contains the response RSP to the command SND-PICC sent by the polling device 108. During testing of the polling device 108 and the listening device 110, the phase-aligned subcarrier demodulator 104 of the test and measurement instrument 102 demodulates this OOK modulated subcarrier signal or BPSK modulated subcarrier signal that forms the response RSP from the listening device 110, as will be described in more detail with reference to Figures 1-3.

[0021] 2 is a more detailed block diagram of a phase-aligned subcarrier demodulator 200 according to some embodiments of the present disclosure. The phase-aligned subcarrier demodulator 200 corresponds to one embodiment of a portion of the phase-aligned subcarrier demodulator 104 of FIG. 1. The phase-aligned subcarrier demodulator 200 may be implemented, for example, by suitable instructions stored in memory 152 and executed by one or more processors 150 within the test and measurement instrument 102 of FIG. 1. In the demodulator 200, a multiplier or mixer 202 receives a modulated carrier signal MCS at a first input and a phase-aligned replica carrier signal PA-RCS generated by a phase-aligned replica carrier generator 204 at a second input. The mixer 202 multiplies the MCS and PA-RCS signals to generate a baseband signal in the form of a modulated subcarrier signal SUBC-MOD at an output of the mixer. The modulated subcarrier signal SUBC-MOD is an OOK modulated subcarrier signal or a BPSK modulated subcarrier signal when the modulated carrier signal MCS is an NFC-A or NFC-B type signal (i.e., when the polling device 108 and the listening device 110 are NFC-A or NFC-B type devices). The low-pass filter 206 receives the modulated subcarrier signal SUBC-MOD output by the mixer 202 and generates a low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD that is used to complete demodulation of the modulated subcarrier signal SUBC-MOD, which will be described in further detail below.

[0022] FIG. 3 is a flowchart of a response demodulation process 300 performed by the phase-aligned subcarrier demodulator 104 of FIG. 1 in accordance with some embodiments of the present disclosure. The response demodulation process 300 may be implemented by suitable instructions stored in memory 152 and executed by one or more processors 150 within the test and measurement instrument 102 of FIG. 1. The response demodulation process 300 is described with reference to FIGS. 1, 3, and 4A-4F, which are signal diagrams illustrating signals utilized and generated by the phase-aligned demodulator 104 during operation with an NFC-A type NFC-enabled device 106 in decoding an OOK modulated subcarrier signal SUBC-MOD in accordance with some embodiments of the present disclosure. Each of the signal diagrams 4B-4F shows voltage along the vertical axis and time along the horizontal axis, while FIG. 4A shows frequency along the horizontal axis and amplitude along the vertical axis.

[0023] Process 300 begins at step 302, where it identifies commands CMD from the polling device 108 and responses RSP from the listening device 110 contained in the modulated carrier signal MCS. In an embodiment of the disclosed technology, step 302 detects the presence of a command in the modulated carrier signal MCS using edge detection along with known parameters of the command CMD transmitted by the polling device 108 in accordance with the ISO / IEC 14443A standard. The width of the signal pulses forming the command CMD, and thus the duration of these pulses and the duration of the command, are known due to the use of the ASK of the modulated carrier signal MCS as described above. In this manner, step 302 can detect the first and last edges or voltage transitions of each command CMD, thereby identifying or detecting each command in the modulated carrier signal MCS. Similarly, step 302 also detects each response RSP in the modulated carrier signal MCS. According to the ISO / IEC 14443A standard, a response RSP is received a specific response time after the end (i.e., the last edge) of the previous command CMD and has a known duration. These parameters of the response RSP on the modulated carrier signal MCS allow the process 300 to detect the response to the detected command CMD in step 302. The start of the response RSP relative to the end or final edge of the command is known, along with the duration of the response, which allows the detection of the portion of the modulated carrier signal MCS that contains the response.

[0024] 4A-4F, a modulated carrier signal MCS and the command CMD and response RSP included therein are shown captured by the test and measurement instrument 102 (FIG. 1). Before process 300 is performed, the test and measurement instrument 102 first acquires or acquires (acquires waveform data) the modulated carrier signal MCS. In acquiring the modulated carrier signal MCS, the test and measurement instrument 102 digitizes the modulated carrier signal for subsequent processing. Thus, each signal being processed by process 300 is a digital signal, as described in more detail below with reference to FIGS. 5A and 5B. In the example shown in FIGS. 4A-4F, the test and measurement instrument 102 acquires the modulated carrier signal MCS and performs a frequency domain analysis of the acquired signal to generate a frequency or spectral representation 400 of the acquired signal, as shown in FIG. 4A. The spectral representation 400 shows a peak component 402, which is located at a frequency of approximately 13.56 MHz and corresponds to the carrier signal specified in the ISO / IEC 14443A standard.

[0025] From the frequency domain analysis shown in spectral display 400, the test and measurement instrument 102 generates in-phase and quadrature (IQ) data corresponding to a time domain display of the acquired modulated carrier signal MCS. This time domain display 404 includes commands CMD and responses RSP, which are not visible in FIG. 4B due to the time scale. FIG. 4C shows the acquired modulated carrier signal MCS on an expanded time scale, where the modulated carrier signal MCS in FIG. 4C corresponds to portion 404 of the modulated carrier signal MCS in FIG. 4B. In FIG. 4C, two commands CMD are labeled on the acquired modulated carrier signal MCS. FIG. 4D shows the final result of step 402, where all commands CMD and responses RSP in the acquired modulated carrier signal MCS have been identified. In the example of FIG. 4D, the identified commands include three commands CMD1-CMD3, and the identified responses include three responses RSP1-RSP3.

[0026] Process 400 proceeds from step 402 to step 404, where the command CMD specified in the acquired modulated carrier signal MCS is muted or removed to generate a response vector RV. FIG. 4E illustrates the response vector RV. The vertical voltage scale in FIG. 4E has been expanded to better illustrate the voltage levels of the responses RSP1-RSP3, which are necessarily smaller than the voltage levels of the commands CMD1-CMD3 seen in FIG. 4D. Removing the commands CMD1-CMD3 means that the voltage levels of samples in the signal where each command CMD is present are set to zero. The commands CMD1-CMD3 are removed because the voltage levels of the OOK-modulated responses RSP1-RSP3 must be detected when demodulating the responses. This removal of the much larger voltage commands CMD1-CMD3 is necessary to reliably detect the voltage levels of the responses RSP1-RSP3, which is necessary for demodulating these OOK-modulated responses.

[0027] The response vector RV in Figure 4E includes three identified responses RSP1-RSP3, with the corresponding commands CMD1-CMD3 deleted. This deletion is indicated by 406 for command CMD1, 408 for command CMD2, and 410 for command CMD3. Once the response vector RV is generated, it is used by the phase-aligned subcarrier demodulator 104 to demodulate the responses RSP1-RSP3. Figure 4F shows the command data CDATA corresponding to the command CMD, which was encoded on the modulated carrier signal MCS and decoded by the polling device 108, and the response data RDATA corresponding to the responses RSP encoded in the OOK modulated subcarrier signal SUBC-MOD, decoded by the test and measurement equipment 102 (Figure 1) in accordance with the ISO / IEC 14443A standard in this embodiment. The 14443A standard specifies the format of the SND-PICC commands sent by the polling device 108 and the RSP responses from the listening device 110, and includes definitions of the fields included in these commands and responses. The test and measurement instrument 102 is configured to utilize the 14443A format information in decoding the demodulated commands CMD and RSP responses.

[0028] Returning to the response demodulation process 300 of FIG. 3, once the response vector RV is generated in step 304, the process proceeds to step 306, where a correlation index CI is generated for each of the response RSPs in the response vector RV. The correlation index CI corresponds to the index of the sample with the largest voltage in the response RSP, which occurs when the phase of the modulated carrier signal MCS is aligned with the phase of the replica carrier signal RCS. Each response RSP does not start at exactly zero phase of the replica carrier signal RCS. The correlation index CI effectively indicates the phasor angle of the response RSPs relative to the replica carrier signal RCS and is used to adjust or align the phase of the replica carrier signal during demodulation of each response. In step 306, the correlation index CI for each response RSP is calculated. After the correlation index CI for each response RSP is determined in step 306, process 300 proceeds to step 308, where the correlation index CI for each response RSP is used to adjust the phase of a replica carrier signal RCS, which is used to down-convert the responses to generate a corresponding OOK modulated subcarrier signal SUBC-MOD for each response.

[0029] Once step 308 has generated an OOK-modulated subcarrier signal SUBC-MOD for each response, process 300 then proceeds to step 310, where the OOK-modulated subcarrier signal SUBC-MOD for each response RSP is low-pass filtered to generate a low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD. The low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD contains voltage peaks or spikes SPK caused by phase changes resulting from adjusting the phase of the replica carrier signal using the correlation index CI for each response RSP. These voltage spikes SPK and their suppression or removal are described in more detail with reference to Figures 5A-5D, which are signal timing diagrams illustrating the suppression or removal of these voltage spikes. Figure 5A shows the down-converted OOK-modulated subcarrier signal SUBC-MOD output from mixer 202 (Figure 2), and Figure 5B shows the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD. The low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD contains responses RSP and also voltage spikes SPK, which immediately precede each response in the low-pass filtered demodulated subcarrier signal. These spikes SPK in the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD result from muting or deleting the commands CMD in the OOK modulated subcarrier signal SUBC-MOD, as described above with reference to Figure 4E. Setting the voltage level of the samples in the CMD portion of the modulated subcarrier signal SUBC-MOD to zero can result in phase discontinuities at the beginning and end of the deleted commands CMD (see 406, 408, and 410 in Figure 4E). These phase discontinuities cause spikes SPK in the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD, as seen in Figure 5B.

[0030] Process 300 proceeds from step 310 to step 312, where spike SPKs are removed from the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD, as shown in FIG. 5C. In some embodiments, the location of the spike SPKs is determined using the frame delay time (FDT) parameter defined in the ISO / IEC 14443A standard, where FDT=(1172 / F C ) and F C is 13.56 MHz in this standard. Each command CMD is contained in one frame as defined in the ISO / IEC 14443A standard. The samples of the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD are set to zero in the time interval that includes the end of the frame containing the command CMD and the beginning of the next response RSP. The time interval (from -FDT / 2 to +FDT / 2) is used to set to zero the part of the low-pass filtered demodulated subcarrier signal LPF-SUBC-DEMOD that contains the spike SPK, thereby erasing or removing the spike.

[0031] Process 300 proceeds from step 312 to step 312, where the low-pass filtered subcarrier signal LPF-SUBC-DEMOD of each response RSP is compared to a voltage threshold to complete demodulation of each response RSP. FIG. 5D shows command data CDATA corresponding to the command CMD encoded on the modulated carrier signal MCS decoded by polling device 108, and response data RDATA corresponding to the decoded response RSP, which is generated in step 314.

[0032] 6A and 6B are flowcharts illustrating in more detail a demodulation process 600 performed by the phase-matched demodulator 104 of FIG. 1. Process 600 begins at step 602, where the test and measurement instrument 102 acquires a modulated carrier signal MCS containing modulated commands CMD and responses RSPs. At step 604, a response vector RV is generated as described above with reference to steps 302 and 304 of process 300 of FIG. 3. From step 604, process 600 proceeds to step 606, where a first variable q is set to 0. Note that the variable q is used to process all of the response RSPs contained in the response vector RV. Process 600 then proceeds from step 606 to step 608, where it is determined whether the variable q is less than a response count value RC of the response vector RV. The response count value RC indicates the total number of response RSPs contained in the response vector RV. If the determination at step 608 is negative, all responses RSP in the response vector RV have been processed and the process 600 proceeds to step 610 and ends.

[0033] If the determination at step 608 is positive, the process 600 proceeds to step 612 to determine the samples-per-cycle (SPC) parameter, where SPC=(F S / F SC ), F SC is the frequency of the OOK modulated subcarrier signal SUBC-MOD (which is F C / N, i.e., 848 kHz), and F S is the sampling frequency of the test and measurement instrument 102 (FIG. 1). S defines the rate at which the modulated carrier signal MCS is acquired or sampled. The parameter SPC indicates the number of samples of the acquired modulated carrier signal MCS per cycle of the subcarrier signal SUBC-MOD. If the time between samples is defined as a time SCALE, then the sampling frequency F S=(1 / SCALE). After calculating the parameter SPC in step 612, process 600 proceeds to step 614 where the second variable k is set to zero. Process 600 proceeds from step 614 to step 616 to determine whether the variable k is less than or equal to the parameter SPC. The variable k tracks the processing of all samples of the modulation carrier signal SUBC-MOD for a given response RSP processed by process 600.

[0034] Process 600 proceeds from step 616 to step 618 where two variables i and j are initialized (i = 0 and j = k). Next, process 600 proceeds from step 618 to step 620 to determine whether the variable i is less than the response size RS of the response RSP being processed minus the variable k (i.e., i < (RS - k)). At this time, the response size is the size of the response from the perspective of the number of samples forming the response. Each signal processed by process 600 is a digital signal as described above in relation to the processing of 300 in FIG. 3. The response size RS is the size of each response RSP from the perspective of the number of samples forming the response. Step 620 further determines whether the variable j is less than the response size RS (j < RS). If the determination in step 620 (i < (RS - k) and (j < RS)) is affirmative, process 600 proceeds to step 622 where the variable INDEX is calculated for the current sample of the current response RSP being processed. The variable INDEX is equal to r(t)cos(2π*F C / N*SCALE). Here, r(t) is the current sample of the current response RSP being processed.

[0035] The value of the variable INDEX is calculated in step 622 and stored in the demodulation vector DEMODV in step 624. From step 624, process 600 proceeds to step 626, where variables i and j are incremented, and then the process returns to step 620 to determine whether processing of the portion of the current response RSP being processed is complete. Process 600 continues executing steps 620-626 to process samples of the current response and determine a correlation index CI for that response. This processing continues until the determination at step 620 is negative, at which point process 600 proceeds to step 628 and stores the variable MAXINDEX for the current response RSP. The variable MAXINDEX is now the maximum value stored in the demodulation vector DEMODV generated for that response. The variable MAXINDEX corresponds to the correlation index CI for the current response RSP being processed. After step 628, process 600 proceeds to step 630, increments variable k, and then returns to step 616 to continue processing the current response RSP through execution of steps 616 through 630.

[0036] If the determination at step 616 is negative, the variable MAXINDEX, which corresponds to the correlation index CI for the current response RSP, has been determined, and process 600 proceeds from step 616 to step 632 of FIG. 6B to demodulate the current response using the correlation index. In step 632, process 600 retrieves the correlation index CI (MAXINDEX) of the current response RSP and then proceeds to step 634 to set variables i=0 and j=MAXINDEX. Next, process 600 proceeds from step 634 to step 636 to determine whether variable i is less than variable SIZE-SUBC-MOD, which corresponds to the size (number of samples) of signal SUBC-MOD output by mixer 202 of FIG. 2. Step 636 also determines whether variable j is less than the size (number of samples) of the response RSP to be demodulated. If the determination at step 636 is positive, the process 600 proceeds to step 638 to calculate the value of the final response output signal FINALRSPOUT corresponding to the signal SUBC-MOD, as shown in FIG. 2. From step 638, the process 600 proceeds to step 640 to increment variables i and j, and then returns to step 636. As long as the determination at step 636 is true, that is, as long as more values ​​of the signal FINALRSPOUT need to be calculated, the process continues executing steps 636-640, thereby generating all values ​​of the signal FINALRSPOUT. If the determination at step 636 is negative, all values ​​of the signal FINALRSPOUT for the current response RSP to be demodulated have been calculated. In this situation, the process 600 proceeds from step 636 to step 642 to increment variable q, which indicates the current response to be demodulated in the captured modulated carrier signal MCS. From step 642, process 600 returns to step 608 to determine whether the next response RSP is currently being modulated, or whether all responses have been demodulated, ending process 600 at step 610.

[0037] Demodulating the response RSPs via process 300 of FIG. 3 or process 600 of FIGS. 6A and 6B reduces amplitude variations in the detected responses. As discussed above, the peak-to-peak amplitude of the response RSPs contained in the modulated subcarrier signal SUBC-MOD on the modulated carrier signal MCS is very small, typically less than 1 mV, resulting in signal distortion. Adjusting the threshold used to reliably demodulate such response RSPs can be difficult. Processes 300 and 600, as implemented by the phase-matched subcarrier demodulator 104 of FIG. 1, alleviate such issues in demodulating the OOK-modulated subcarrier signal of the response RSPs used in NFC-A type devices. Embodiments of the disclosed technology reduce amplitude variations in the demodulated response RSPs resulting from a phase shift with the replica carrier signal RCS.

[0038] 7A-7F are signal timing diagrams illustrating signals utilized and generated by the phase-matching demodulator 104 of FIG. 1 during operation to decode a BPSK-modulated subcarrier signal SUBC-MOD using an NFC-B type device, according to some embodiments of the present disclosure. Each of signal diagrams 7B-7F illustrates voltage along the vertical axis and time along the horizontal axis, with FIG. 7A illustrating frequency along the horizontal axis and amplitude along the vertical axis. As noted above, the phase-matching demodulator 104 according to embodiments of the present disclosure may be utilized to demodulate responses RSP from NFC-B type devices in addition to NFC-A type NFC-enabled devices such as those described above in connection with FIGS. 1-6. When the NFC-enabled device 106 of FIG. 1 is an NFC-B type device, the modulated subcarrier signal SUBC-MOD can be considered a BPSK-modulated carrier signal, as opposed to the OOK-modulated subcarrier signal described above for an NFC-A type device. Thus, the processing performed to demodulate the BPSK modulated subcarrier signal SUBC-MOD is substantially identical to processes 300 and 600 described above, except that rather than generating the modulated subcarrier signal SUBC-MOD (the output of mixer 202 in FIG. 2 ), the subcarrier signal must be BPSK modulated and then low-pass filtered to demodulate the subcarrier signal.

[0039] FIG. 7A shows a frequency domain analysis of the modulated carrier signal MCS captured by the test and measurement instrument 102 in the form of a frequency or spectral display 700 of the acquired signal. Similar to the spectral display 400 of FIG. 4A of the ISO / IEC 14443A standard, the spectral display 700 also shows a peak component 702, which is located at a frequency of approximately 13.56 MHz and corresponds to the carrier signal specified in the ISO / IEC 14443B standard. FIG. 7B shows frequency domain IQ data generated by the test and measurement instrument 102, and FIG. 7C shows the acquired modulated carrier signal MCS on an expanded time scale, corresponding to portion 404 of the modulated carrier signal MCS in FIG. 7B. FIG. 7D shows the command CMD and response RSP on the modulated carrier signal MCS. FIG. 7E shows the demodulated response RSP of FIG. 7D demodulated by the phase-aligned subcarrier demodulator 104 according to an embodiment of the disclosed technique. FIG. 7F shows command data CDATA corresponding to command CMD encoded on modulated carrier signal MCS decoded by polling device 108 and response data RDATA corresponding to response RSP encoded on BPSK modulated subcarrier signal SUBC-MOD, as decoded by test and measurement equipment 102 (FIG. 1) in accordance with the ISO / IEC 14443B standard in this embodiment.

[0040] Aspects of the disclosed technology may operate on specially created hardware, firmware, digital signal processors, or specially programmed general-purpose computers, including processors that operate according to programmed instructions. The terms "controller" or "processor" herein contemplate microprocessors, microcomputers, ASICs, and dedicated hardware controllers, among others. Aspects of the disclosed technology may be implemented with computer-usable data and computer-executable instructions, such as one or more program modules, executed by one or more computers (including a monitoring module) or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., which, when executed by a processor in a computer or other device, perform particular tasks or implement particular abstract data types. Computer-executable instructions may be stored in computer-readable storage media, such as hard disks, optical disks, removable storage media, solid-state memory, RAM, etc. Those skilled in the art will appreciate that the functionality of the program modules may be combined or distributed as desired in various embodiments. Furthermore, such functionality may be embodied in whole or in part in firmware or hardware equivalents, such as integrated circuits, field programmable gate arrays (FPGAs), etc. Certain data structures may be used to more effectively implement one or more aspects of the disclosed technology, and such data structures are considered within the scope of the computer-executable instructions and computer-usable data described herein.

[0041] The disclosed aspects may, in some cases, be implemented in hardware, firmware, software, or any combination thereof. The disclosed aspects may also be implemented as instructions carried by or stored on one or more computer-readable media, which may be read and executed by one or more processors. Such instructions may be referred to as a computer program product. As used herein, computer-readable media refers to any medium that can be accessed by a computing device. By way of example, and not limitation, computer-readable media may include computer storage media and communication media.

[0042] "Computer storage media" means any medium that can be used to store computer-readable information. By way of example and not limitation, computer storage media may include random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other memory technologies, compact disc read-only memory (CD-ROM), digital video disc (DVD) and other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage and other magnetic storage devices, and any other volatile or nonvolatile, removable or non-removable medium implemented in any technology. "Computer storage media" excludes signals themselves and transitory forms of signal transmission. Example

[0043] The following examples are provided to aid in understanding the technology disclosed in this application. Embodiments of the technology may include one or more of the examples described below, and any combination thereof.

[0044] Example 1 is a method comprising: detecting commands and responses contained in a modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; identifying a correlation index of a response in the response vector indicating a phase of a modulated carrier signal of a corresponding response relative to a replica carrier signal; adjusting the phase of the replica carrier signal based on the correlation index of each of the responses in the response vector to match (phase align) the phase of the replica carrier signal with the modulated carrier signal relative to the response; demodulating each of the responses in the response vector using a replica carrier signal having a corresponding adjusted phase to generate a demodulated response vector including a plurality of demodulated responses; and low-pass filtering the demodulated response vector to generate a demodulated response vector.

[0045] In a second embodiment, the method according to the first embodiment is characterized in that the step of detecting the commands included in the modulated carrier signal includes detecting voltage transitions or edges of the modulated carrier signal to identify the start and end of each command.

[0046] Example 3 is the method according to example 2, in which the detecting the command further comprises detecting an edge of the modulated carrier signal based on a duration of a signal pulse forming the command.

[0047] Example 4 is the method according to Example 2, wherein the process of detecting the responses included in the modulated carrier signal includes a process of detecting the responses based on a final edge of each detected command and a known duration of each of the responses.

[0048] Example 5 is the method according to example 1, wherein the modulated carrier signal is a digital signal including a plurality of samples, and removing the detected command includes setting samples of the response vector to zero for samples corresponding to portions of the modulated carrier signal including the detected command.

[0049] Example 6 is the method according to Example 1, wherein low-pass filtering each of the demodulation responses includes low-pass filtering each of the demodulation responses to generate low-pass filtered demodulated subcarrier signals.

[0050] Example 7 is the method according to example 6, wherein the low-pass filtered demodulated carrier signal includes voltage spikes at positions in the signal where the detected commands are deleted, and the method further comprises suppressing these voltage spikes.

[0051] Example 8 is the method according to example 7, further comprising: determining a location of a voltage spike associated with an end location of the deleted detected command; and determining a location of a voltage spike associated with a start location of the deleted detected command.

[0052] Example 9 is the method according to Example 1, further comprising: transmitting a modulated carrier signal from a nearby coupled device (proximity coupled device); and load-modulating the modulated carrier signal transmitted from the proximity coupled device by a nearby integrated circuit card (proximity integrated circuit card) to generate a modulated subcarrier signal on the transmitted modulated carrier signal.

[0053] Example 10 is the method according to Example 9, wherein, when the proximity coupling device and the proximity integrated circuit card are NFC-A type devices operating in accordance with the ISO / IEC 14443A standard, the modulated carrier signal comprises an OOK modulated subcarrier signal, and when the proximity coupling device and the proximity integrated circuit card are NFC-B type devices operating in accordance with the ISO / IEC 14443B standard, the modulated carrier signal comprises a BPSK modulated subcarrier signal.

[0054] Example 11 is a test and measurement system comprising: a proximity coupling device configured to transmit a modulated carrier signal; a proximity integrated circuit card configured to load modulate the transmitted modulated carrier signal to generate a modulated subcarrier signal on a transmitted wireless carrier signal; and a test and measurement instrument having one or more processors and a phase-matched subcarrier demodulator configured to acquire (acquire waveform data from) the modulated carrier signal; The phase-matched subcarrier demodulator demodulates the modulated subcarrier signal by detecting commands and responses contained in the modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; determining a correlation index for each of the responses in the response vector, the correlation index indicating the phase of the modulated carrier signal of the corresponding response relative to a replica carrier signal; adjusting the phase of the replica carrier signal based on a correlation index of each of the responses in the response vector to align the phase of the replica carrier signal with the phase of the modulated carrier signal with respect to the responses; demodulating each of the responses in the response vector using the replica carrier signal with a corresponding adjusted phase to generate a demodulated response vector having a plurality of demodulated responses; The demodulated response vector is low-pass filtered to generate a decoded response vector. The device is configured to:

[0055] A twelfth embodiment is the test and measurement system of claim 11, wherein the test and measurement device is an oscilloscope.

[0056] Example 13 is the test and measurement system according to example 11, further comprising an RF probe disposed proximate to the proximity coupling device and the proximity integrated circuit card and configured to detect the modulated carrier signal.

[0057] Example 14 is the test and measurement system according to Example 11, wherein the phase-aligned subcarrier demodulator is configured to, as part of the process of detecting commands, detect voltage transitions or edges in the modulated carrier signal to identify the beginning and end of each command.

[0058] Example 15 is the test and measurement system according to Example 14, wherein the phase-matched subcarrier demodulator is further configured to perform processing to detect edges of the modulated carrier signal based on the duration of a signal pulse forming a command.

[0059] Example 16 is the test and measurement system according to Example 11, wherein the phase-matched subcarrier demodulator is further configured to perform processing to detect the responses included in the modulated carrier signal based on the detected final edge of each command and the known duration of each of the responses.

[0060] Example 17 is the test and measurement system according to Example 11, wherein the modulated carrier signal is a digital signal including a plurality of samples, and the phase-matched subcarrier demodulator is configured to process samples in the response vector corresponding to portions of the modulated carrier signal including detected commands to delete the detected commands by setting the samples to zero.

[0061] Example 18 is a test and measurement system according to Example 11, wherein the process of low-pass filtering each of the demodulation responses includes a process of low-pass filtering each of the demodulation responses to generate a low-pass filtered demodulated subcarrier signal including voltage spikes at positions in the signal where the detected commands have been deleted, and the phase-matched subcarrier demodulator is further configured to perform a process of suppressing these voltage spikes.

[0062] Example 19 is a test and measurement system comprising: a proximity coupling device configured to transmit a modulated carrier signal; a proximity integrated circuit card configured to load modulate the transmitted modulated carrier signal to generate one of an OOK and BPSK modulated subcarrier signal on the transmitted wireless carrier signal; and a test and measurement instrument configured to acquire (acquire waveform data) the modulated carrier signal; the test and measurement instrument having a phase-matched subcarrier demodulator configured to demodulate the modulated subcarrier signal; The phase-matched subcarrier demodulator comprises: detecting commands and responses contained in the modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; determining a correlation index for each of the responses in the response vector, the correlation index indicating the phase of the modulated carrier signal of the corresponding response relative to a replica carrier signal; adjusting the phase of the replica carrier signal based on a correlation index of each of the responses in the response vector to phase align the replica carrier signal with the modulated carrier signal with respect to the responses; down-converting each of the responses in the response vector using the replica carrier signal with a corresponding adjusted phase to generate a modulated subcarrier signal for each of the responses in the response vector; low-pass filtering the modulated subcarrier signal to generate a demodulated response vector; The device is configured to:

[0063] Example 20 is a test and measurement instrument according to Example 19, wherein the test and measurement instrument is a mixed signal oscilloscope.

[0064] The above description is provided only to illustrate examples of embodiments of the disclosed technology and is not intended to be limiting. A person skilled in the art can incorporate the gist of the present invention and think of modifications of the disclosed embodiments, so the present invention should be interpreted as including all modifications within the scope of the present invention.

[0065] Although the above-described versions of the presently disclosed subject matter have many advantages that have been described or that will be apparent to those skilled in the art, not all of these advantages or features are required in every version of the disclosed devices, systems, or methods.

[0066] Additionally, the description in this application refers to specific features. All features disclosed in this specification, including the claims, abstract, and drawings, and all steps in all disclosed methods or processes, may be combined in any combination, unless they are at least partially mutually exclusive. Each feature disclosed in this specification, including the claims, abstract, and drawings, may be replaced with an alternative feature serving the same, equivalent, or similar purpose, unless otherwise specified.

[0067] Furthermore, when this application refers to a method having two or more defined steps or processes, these defined steps or processes may be performed in any order or simultaneously, unless the circumstances do not preclude this possibility.

[0068] Although specific embodiments of the invention have been illustrated and described for purposes of illustration, it will be appreciated that various modifications can be made therein without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.

Claims

1. detecting commands and responses contained in a modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; determining a correlation index of said responses in the response vector, the correlation index indicating the phase of the modulated carrier signal of the corresponding response relative to the replica carrier signal; adjusting the phase of the replica carrier signal based on a correlation index of each of the responses in the response vector to align the replica carrier signal and the modulated carrier signal in phase with respect to the responses; demodulating each of the responses in the response vector using a replica carrier signal having a corresponding adjusted phase to generate a demodulated response vector including a plurality of demodulated responses; low-pass filtering the demodulated response vector to generate a decoded response vector; A method comprising:

2. 2. The method of claim 1, wherein detecting commands contained in the modulated carrier signal comprises detecting voltage transitions or edges in the modulated carrier signal to identify the beginning and end of each command.

3. 3. The method of claim 2, wherein detecting the command further comprises detecting edges of the modulated carrier signal based on the duration of signal pulses forming the command.

4. 3. The method of claim 2, wherein detecting responses contained in the modulated carrier signal comprises detecting the responses based on a final edge of each detected command and a known duration of each response.

5. 2. The method of claim 1, wherein the modulated carrier signal is a digital signal comprising a plurality of samples, and wherein removing the detected command comprises setting samples of the response vector to zero for samples corresponding to portions of the modulated carrier signal that include the detected command.

6. 2. The method of claim 1, wherein lowpass filtering each of the demodulation responses comprises lowpass filtering each of the demodulation responses to generate a lowpass filtered demodulated subcarrier signal.

7. 7. The method of claim 6, wherein the low-pass filtered demodulated carrier signal contains voltage spikes at locations in the signal where detected commands have been deleted, the method further comprising suppressing these voltage spikes.

8. 8. The method of claim 7, further comprising: locating a voltage spike relative to an end position of the deleted detected command; and locating a voltage spike relative to a start position of the deleted detected command.

9. transmitting the modulated carrier signal from a proximity coupled device; load modulating, by a proximity integrated circuit card, the modulated carrier signal transmitted from the proximity coupling device to generate a modulated subcarrier signal on the transmitted modulated carrier signal; The method of claim 1 further comprising:

10. 10. The method of claim 9, wherein the modulated carrier signal comprises an OOK modulated subcarrier signal when the proximity coupling device and the proximity integrated circuit card are NFC-A type devices operating in accordance with the ISO / IEC 14443A standard, and wherein the modulated carrier signal comprises a BPSK modulated subcarrier signal when the proximity coupling device and the proximity integrated circuit card are NFC-B type devices operating in accordance with the ISO / IEC 14443B standard.

11. a proximity coupling device configured to transmit a modulated carrier signal; a proximity integrated circuit card configured to load modulate the transmitted modulated carrier signal to generate a modulated subcarrier signal on the transmitted modulated carrier signal; a test and measurement instrument having one or more processors and a phase-aligned subcarrier demodulator configured to acquire the modulated carrier signal; Equipped with The phase-matched subcarrier demodulator demodulates the modulated subcarrier signal by detecting commands and responses contained in the modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; determining a correlation index for each of the responses in the response vector, the correlation index indicating the phase of the modulated carrier signal of the corresponding response relative to a replica carrier signal; adjusting the phase of the replica carrier signal based on a correlation index of each of the responses in the response vector to align the phase of the replica carrier signal with the phase of the modulated carrier signal with respect to the responses; demodulating each of the responses in the response vector using the replica carrier signal with a corresponding adjusted phase to generate a demodulated response vector having a plurality of demodulated responses; low-pass filtering the demodulated response vector to generate a decoded response vector; A test and measurement system configured to:

12. 12. The test and measurement system of claim 11, wherein the test and measurement instrument is an oscilloscope.

13. 12. The test and measurement system of claim 11, further comprising an RF probe positioned proximate to the proximity coupling device and the proximity integrated circuit card and configured to detect the modulated carrier signal.

14. 12. The test and measurement system of claim 11, wherein the phase-aligned subcarrier demodulator is configured to, as part of detecting commands, detect voltage transitions or edges in the modulated carrier signal to identify the beginning and end of each of the commands.

15. 15. The test and measurement system of claim 14, wherein the phase-matched subcarrier demodulator is further configured to process the modulated carrier signal to detect edges based on the duration of signal pulses forming the command.

16. 12. The test and measurement system of claim 11, wherein the phase-matched subcarrier demodulator is further configured to perform processing to detect the responses contained in the modulated carrier signal based on the detected final edge of each of the commands and the known duration of each of the responses.

17. 12. The test and measurement system of claim 11, wherein the modulated carrier signal is a digital signal including a plurality of samples, and the phase-aligned subcarrier demodulator is configured to process samples in the response vector corresponding to portions of the modulated carrier signal that include the detected command by setting those samples to zero.

18. 12. The test and measurement system of claim 11, wherein low-pass filtering each of the demodulation responses includes low-pass filtering each of the demodulation responses to produce a low-pass filtered demodulated subcarrier signal that includes voltage spikes at locations in the signal where the detected commands were deleted, and wherein the phase-aligned subcarrier demodulator is further configured to suppress these voltage spikes.

19. a proximity coupling device configured to transmit a modulated carrier signal; a proximity integrated circuit card configured to load modulate the transmitted modulated carrier signal to generate one of an OOK and a BPSK modulated subcarrier signal on the transmitted modulated carrier signal; a test and measurement instrument configured to acquire the modulated carrier signal; Equipped with the test and measurement instrument having a phase-matched subcarrier demodulator configured to demodulate the modulated subcarrier signal; The phase-matched subcarrier demodulator comprises: detecting commands and responses contained in the modulated carrier signal; removing the detected commands to generate a response vector including the removed commands and the detected responses; determining a correlation index for each of the responses in the response vector, the correlation index indicating the phase of the modulated carrier signal of the corresponding response relative to a replica carrier signal; adjusting the phase of the replica carrier signal based on a correlation index of each of the responses in the response vector to align the phase of the replica carrier signal with the phase of the modulated carrier signal with respect to the responses; down-converting each of the responses in the response vector using the replica carrier signal with a corresponding adjusted phase to generate a modulated subcarrier signal for each of the responses in the response vector; low-pass filtering the modulated subcarrier signal to generate a decoded response vector; A test and measurement system configured to:

20. 20. The test and measurement instrument of claim 19, wherein the test and measurement instrument is a mixed signal oscilloscope.

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