NFC power adaptive adjustment system and method for EMVCo certification

Abstract

The application discloses an NFC power self-adaptive adjustment system and method for EMVCo authentication. The system comprises a power supply, a DC-DC boost converter, a power control module, a low dropout linear regulator and a radio frequency transmitter module. A mapping table of field intensity, voltage, current and impedance under different distances is established through a pre-test stage; in the working stage, the power control module calculates the load impedance according to the current value and the current voltage measured by the low dropout linear regulator in real time, queries the mapping table to obtain the target voltage, and cooperatively adjusts the output voltage of the DC-DC boost converter and the low dropout linear regulator. The application realizes closed-loop control of the NFC transmission power, so that the field intensity can be stably kept within the EMVCo specification range under different distances, effectively adapts to power fluctuation and load change, and improves the system stability and authentication debugging efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to an NFC power adaptive adjustment system for EMVCo authentication, and also relates to an NFC power adaptive adjustment method. BACKGROUND

[0002] With the popularity of near field communication (NFC) technology in the field of financial payment, POS machines supporting NFC function have become the core terminal of offline transactions. In order to ensure the interconnection and transaction security between global NFC payment devices and POS machines, the industry generally takes EMVCo L1 authentication as a mandatory standard for the NFC radio frequency performance of POS machines. The authentication puts forward extremely strict and fine requirements on the field strength range that can be inducted by the analog payment card (PICC) at different coupling distances.

[0003] In order to meet the above field strength requirements, the prior art generally adopts a debugging scheme based on a fixed impedance matching circuit. Such a scheme attempts to make the field strength fall within the authentication range at a specific distance by repeatedly adjusting the matching network (such as capacitance and inductance) at the periphery of the antenna end. However, there is a natural contradiction between the inherent "near strong and far weak" distribution characteristics of the magnetic field and the requirement of the EMVCo authentication that the field strength needs to be stable at multiple distances. More troublesome is that the equivalent impedance of the antenna will dynamically change with the communication distance, card type and environmental factors in actual work, which makes the debugging process based on the fixed circuit extremely complex, time-consuming and highly dependent on the experience of engineers, seriously restricting the large-scale production and rapid listing of products.

[0004] Although there are some attempts to improve, for example, in the Chinese patent application with the publication number CN119129616A, the communication parameters (such as modulation depth) are adjusted by table lookup method, but these schemes are mostly limited to optimization of the internal registers or the later stage of the signal chain, which belong to "local correction". These schemes fail to fundamentally solve the problem of unstable radio frequency energy output caused by power supply fluctuation and load impedance change, and lack a power supply system that can actively and quickly compensate. Specifically, the existing schemes cannot effectively cope with the voltage drop of battery-powered devices during discharging, nor can they offset the change of antenna impedance caused by distance change in real time, resulting in a sharp fluctuation of field strength in the entire authentication space, and the authentication pass rate and product consistency are difficult to guarantee.

[0005] Therefore, there is an urgent need in the field for a new technical solution that can globally, closed-loop and adaptively adjust the NFC transmission power from the power supply end, to fundamentally solve the core pain points of uneven field strength at multiple distances, poor power adaptability and low debugging efficiency in the EMVCo authentication debugging. SUMMARY

[0006] The primary technical problem to be solved by the present application is to provide an NFC power adaptive adjustment system for EMVCo certification.

[0007] Another technical problem to be solved by the present application is to provide an NFC power adaptive adjustment method for EMVCo certification.

[0008] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0009] According to a first aspect of an embodiment of the present application, an NFC power adaptive adjustment system for EMVCo certification is provided, comprising a power supply, a DC-DC boost converter, a power control module, a low-dropout linear regulator, and a radio frequency transmitter module.

[0010] The input end of the DC-DC boost converter is connected to the power supply for providing an adjustable first voltage.

[0011] The input end of the low-dropout linear regulator is connected to the output end of the DC-DC boost converter, and the output end of the low-dropout linear regulator is connected to the power input end of the radio frequency transmitter module for providing an adjustable second voltage and powering the radio frequency transmitter module. The low-dropout linear regulator internally integrates a current measurement circuit for real-time measurement of the load current at the output end.

[0012] The power control module is in communication connection with the DC-DC boost converter, the low-dropout linear regulator, and the radio frequency transmitter module, respectively.

[0013] The power control module internally stores a mapping table established in a pre-test phase. The mapping table contains the corresponding relationship of the second voltage, the load current, and the calculated load impedance required to achieve the target field strength at different communication distances.

[0014] The power control module is configured to, in the working phase: receive the load current measured by the low-dropout linear regulator, calculate the real-time load impedance in combination with the current second voltage; query the mapping table to determine the target second voltage corresponding to the real-time load impedance; based on the target second voltage, generate a control instruction to cooperatively adjust the first voltage output by the DC-DC boost converter and the second voltage output by the low-dropout linear regulator, so that the field strength generated by the radio frequency transmitter module is stabilized within the EMVCo specification range.

[0015] Preferably, the power control module is connected to and controls the DC-DC boost converter through a first I 2 C bus and controls the low-dropout linear regulator through a second independent I 2The C bus connects and controls the output voltage of the low-dropout linear regulator, and the low-dropout linear regulator is connected through the SPI bus to read the measurement data of the load current.

[0016] Preferably, the power control module is further configured to calculate the target second voltage by linear interpolation when the real-time load impedance is between two pre-stored impedance values in the mapping table.

[0017] Preferably, when the power control module adjusts the first voltage output by the DC-DC boost converter, the first voltage is always higher than the second voltage output by the low-dropout linear regulator, and a preset fixed voltage difference is maintained.

[0018] Preferably, a self-restoring fuse is connected in series between the output end of the low-dropout linear regulator and the power input end of the radio frequency transmitter module.

[0019] According to a second aspect of the embodiment of the present application, a NFC power adaptive adjustment method for EMVCo certification is provided, comprising the following steps:

[0020] In the pre-test phase, first adjust the second voltage output by the low-dropout linear regulator to make the field strength coupled to the test card reach a predetermined target value within the EMVCo specification range under different communication distances, and record the second voltage and the load current measured by the internal current measurement circuit of the low-dropout linear regulator at the same time, calculate the load impedance, form a mapping table containing distance, second voltage, load current and load impedance, and store it;

[0021] In the working phase, the load current is monitored in real time by the internal current measurement circuit of the low-dropout linear regulator;

[0022] Based on the current second voltage output by the low-dropout linear regulator and the real-time monitored load current, the real-time load impedance is calculated;

[0023] The mapping table is queried to determine the target second voltage corresponding to the real-time load impedance;

[0024] Based on the target second voltage, the first voltage output by the DC-DC boost converter and the second voltage output by the low-dropout linear regulator are dynamically and cooperatively adjusted.

[0025] Preferably, the step of adjusting the first voltage output by the DC-DC boost converter is specifically:

[0026] The target second voltage is added to a preset fixed voltage difference value, and the obtained voltage value is used as the target value of the first voltage for adjustment.

[0027] Preferably, in the pre-test stage, the predetermined target field strength is set to a same constant value at all test distances, which is located in the middle region of the EMVCo specification field strength range.

[0028] Preferably, in the working stage, if the calculated real-time load impedance is between two pre-stored impedance values in the mapping table, the target second voltage is calculated by linear interpolation.

[0029] Preferably, the method further comprises a field strength verification step: after completing voltage adjustment, the field strength is verified by a field strength detection auxiliary circuit inside the radio frequency transmitter module, and if the field strength deviation exceeds the tolerance, the pre-test stage process is triggered for recalibration.

[0030] Compared with the prior art, the present application realizes precise control of NFC transmission power by constructing a dynamic closed-loop power supply system composed of a power control module, a DC-DC boost converter and a low dropout linear regulator, and combining a pre-test mapping table adjustment mechanism based on real-time impedance calculation. With the present application, the NFC field strength can be stabilized to meet the requirements of EMVCo specification in the distance range of 0cm to 4cm, effectively improving the field strength uniformity; at the same time, it has the adaptability to power voltage fluctuation and load impedance change, improving the stability of NFC equipment under different working conditions; in addition, by converting the traditional debugging process relying on manual trial and error into an automated data-driven process, the efficiency of authentication and debugging and the consistency of product performance are improved. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 For the first embodiment of the present application, a structural schematic diagram of an NFC power adaptive adjustment system for EMVCo authentication;

[0032] Figure 2 For the first embodiment of the present application, a circuit principle diagram of a DC-DC boost converter, a low dropout linear regulator and a power control module

[0033] Figure 3 For the first embodiment of the present application, a working principle flow chart of an NFC power adaptive adjustment system for EMVCo authentication. DETAILED DESCRIPTION

[0034] The technical content of the present application will be described in detail below in combination with the drawings and specific embodiments.

[0035] The technical concept of the embodiment of the present application is to provide a dynamic closed-loop control logic of "adjusting two-stage voltage based on real-time load impedance query mapping table". Specifically, by establishing the accurate mapping relationship between the communication distance, target field strength, output voltage, load current and calculated impedance in the pre-test stage, the complex field strength debugging problem is converted into the monitoring and response to the key electrical parameter of load impedance. In the working stage, by measuring the load current and voltage in real time, the current load impedance is dynamically calculated, and it is used as the index to query the pre-stored mapping table to quickly determine the optimal working voltage required to maintain the target field strength under the current communication environment. Subsequently, the power control module generates a cooperative control instruction based on the target voltage to synchronously adjust the output voltage of the front-stage DC-DC boost converter and the rear-stage low dropout linear regulator, thereby forming a complete closed loop from impedance perception to power execution. This unique design enables the NFC power adaptive adjustment system to actively and quickly compensate for the changes in antenna impedance and energy supply fluctuations caused by changes in communication distance, card type differences and power fluctuations, thereby ensuring the stability and consistency of the NFC field strength in the full distance range required by EMVCo certification from the source.

[0036] First embodiment

[0037] As shown in Figure 1 The first embodiment of the present application provides an NFC power adaptive adjustment system for EMVCo certification, which comprises a power supply, a DC-DC boost converter, a power control module, a low dropout linear regulator and a radio frequency transmitter module.

[0038] The power supply provides initial power for the whole NFC power adaptive adjustment system. The battery can be a lithium battery, a nickel-hydrogen battery, or a DC adapter connected to the mains, which is not specifically limited in the application. The first input end of the DC-DC boost converter is connected with the power supply, which functions to increase the voltage output by the power supply to meet the demand of the system for high voltage. The first input end of the low-dropout linear regulator is connected with the output end of the DC-DC boost converter, which can on the one hand reduce the high voltage output by the DC-DC boost converter to an appropriate level, and on the other hand can measure the current output by the low-dropout linear regulator in real time and transmit the measured current information to the power control module. The voltage output by the low-dropout linear regulator is finally sent to the radio frequency transmitter module through the second output end as the power source for driving the radio frequency transmitter module to work. The power control module is connected with the second input end of the DC-DC boost converter, the second input end of the low-dropout linear regulator and the first output end of the low-dropout linear regulator, respectively, for receiving the current measurement data transmitted by the low-dropout linear regulator, and adjusting the output voltage of the DC-DC boost converter and the output voltage of the low-dropout linear regulator based on the data, so as to form a closed-loop control system and realize real-time dynamic adjustment of the NFC transmission power.

[0039] In an embodiment of the application, the positive pole of the power supply is connected to the input end of the DC-DC boost converter through a low-impedance wire, which needs to ensure no significant voltage drop and avoid input voltage fluctuation caused by excessive wire resistance. The negative pole of the power supply is directly connected with the system common ground to form a complete current loop, and a 10 μF ceramic capacitor is usually connected in parallel between the negative pole and the ground to absorb high-frequency interference signals and suppress ground noise.

[0040] In addition, a self-resetting fuse is connected in series between the power supply and the DC-DC boost converter, which will automatically disconnect when overcurrent occurs in the circuit to protect the power supply and subsequent modules from damage. After the fault is eliminated, the fuse can automatically restore conduction without manual replacement. The power supply has no other control signal connection and only realizes power transmission through wires, and its output state is completely determined by the working state of the DC-DC boost converter. When the DC-DC boost converter starts, the power supply starts to supply power. When the DC-DC boost converter is turned off, the power supply stops outputting current and is in standby state. This connection mode ensures efficient use of power supply energy and avoids unnecessary power loss.

[0041] As shown in FIG. 1, the power supply is connected with the DC-DC boost converter through a low-impedance wire, and the output end of the DC-DC boost converter is connected with the low-dropout linear regulator through another low-impedance wire. The power control module is connected with the second input end of the DC-DC boost converter, the second input end of the low-dropout linear regulator and the first output end of the low-dropout linear regulator, respectively. The radio frequency transmitter module is connected with the first output end of the low-dropout linear regulator. Figure 2As shown, in one embodiment of the present application, the DC-DC boost converter specifically adopts the Boost boost circuit topology, which dynamically adjusts the internal reference voltage REF according to the first digital reference control signal REF1_CTRL<7:0> output by the power control module, so as to accurately set the output voltage VUP. In view of the characteristic that the load current of the NFC system is basically stable when working, the embodiment preferably adopts the pulse width modulation (PWM) control mode, which has higher stability and more concise control logic in the stable state, and is beneficial to improving the system reliability.

[0042] It should be noted that the DC-DC boost converter is the "first hurdle" of voltage regulation, and its connection relationship involves three dimensions of power input, voltage output and control signal interaction. At the power input level, the input end of the DC-DC boost converter is directly connected to the positive output end of the power supply to receive the original voltage of 3.0V-4.2V; its ground end is connected to the system common ground to form a loop with the negative pole of the power supply. In order to stabilize the input voltage, a 100μF electrolytic capacitor and a 1μF ceramic capacitor are usually connected in parallel between the VIN pin and the GND of the DC-DC boost converter, the former is used to filter out low-frequency ripple, and the latter is used to absorb high-frequency noise, to ensure the stability of the input voltage.

[0043] The output end of the DC-DC boost converter is connected to the input end of the low-dropout linear regulator through a shielded wire, and the shield layer is grounded to reduce electromagnetic interference. The core function of this connection is to transmit the boosted voltage to the low-dropout linear regulator to provide a basis for subsequent voltage regulation. The capacitor combination is also connected in parallel between the output end and the ground to further filter out the ripple generated in the boosting process, to ensure the purity of the output voltage.

[0044] The control interface of the DC-DC boost converter is composed of I 2 C bus and enable end. Among them, the I 2 C bus is directly connected to the corresponding I 2 C interface of the power control module, which is used to receive the voltage regulation instruction sent by the power control module. For example, when the power control module needs to adjust the output voltage to 5.7V, it will send a data packet containing the target voltage value through the I 2 C bus, and the DC-DC boost converter receives and analyzes the instruction, and adjusts the output voltage through the internal PWM controller. The SCL pin is the clock line, which is responsible for synchronizing data transmission; the SDA pin is the data line, which realizes bidirectional data communication. The enable end is connected to a GPIO pin of the power control module, when the power control module outputs high level, the DC-DC boost converter starts to work; when the output is low, the DC-DC boost converter enters the sleep state and stops outputting voltage, to reduce standby power consumption.

[0045] In addition, the over-temperature detection pin of the DC-DC boost converter is connected to the GPIO pin of the power control module through a 10kΩ pull-up resistor. When the internal temperature of the module exceeds the set threshold, the OT pin outputs a low level. After the power control module detects the signal, it immediately sends a command to reduce the output voltage until the temperature returns to normal, forming an over-temperature protection mechanism.

[0046] In an embodiment of the present application, the low-dropout linear regulator (labeled as TX_LDO in the figure) has dual functions in the system: one is to provide a high-stability voltage source for the rear-stage radio frequency transmitter module; the other is to detect the load current of the radio frequency transmitting circuit in real time. The low-dropout linear regulator also receives the second digital reference control signal REF2_CTRL<7:0> from the power control module and accurately sets its output voltage VOUT_TXLDO by adjusting the internal reference voltage. By making the value of REF2_CTRL<7:0> always smaller than REF1_CTRL<7:0> by a fixed difference (Delta), it can be ensured that the output voltage VUP of the DC-DC boost converter is always higher than the output voltage VOUT_TXLDO of the low-dropout linear regulator by a pre-set fixed voltage difference. This design enables the entire NFC power adaptive adjustment system to achieve stable output while optimizing energy conversion efficiency. In terms of current detection, the low-dropout linear regulator generates a detection voltage signal TXI_DET strictly linearly related to the load current through its internally integrated mirror circuit, providing a key technical means for real-time and lossless current measurement.

[0047] As a composite unit for voltage regulation and current measurement, the connection relationship of the low-dropout linear regulator needs to meet the dual demands of power transmission and data acquisition. In terms of power input, the input end of the low-dropout linear regulator is directly connected to the output end of the DC-DC boost converter to receive the boosted voltage signal. To adapt to the dynamic changes of the output voltage of the DC-DC boost converter, a tantalum capacitor is connected in parallel between the input pin of the low-dropout linear regulator and the ground, which utilizes the low ESR (equivalent series resistance) characteristic of the tantalum capacitor to stabilize the input voltage and avoid voltage spikes caused by load mutations.

[0048] In an embodiment of the present application, the output end of the low-dropout linear regulator is connected to the power input end of the radio frequency transmitter module through a twisted pair, with an output voltage range of 1.8V-5.0V, directly serving as the operating power supply for the radio frequency transmitter module. A 10μF ceramic capacitor and a 100nF ceramic capacitor are connected in parallel between the output end and the ground, with the former used to filter low-frequency ripples and the latter used to suppress high-frequency noise, ensuring that the radio frequency transmitter module operates in a stable voltage environment.

[0049] The low-dropout linear regulator transmits the amplified voltage signal to the power control module through the SPI bus, and the AD converter inside the power control module converts the amplified voltage signal into a digital current value. The connection of the SPI bus includes: the SCK (clock) pin of the low-dropout linear regulator is connected to the SPI clock output pin of the power control module, the MISO (master input slave output) pin is connected to the SPI data input pin of the power control module, the MOSI (master output slave input) pin is connected to the SPI data output pin of the power control module, and the CS (chip select) pin is connected to the GPIO pin of the power control module. When the power control module needs to read the current data, the CS pin is pulled low, and then the clock signal is sent through the SCK pin. The low-dropout linear regulator transmits the current data to the power control module through the MISO pin under the driving of the clock, and the time consumption of single data transmission does not exceed 10μs, ensuring real-time performance.

[0050] It should be noted that the quantization object of the above-mentioned AD converter includes but is not limited to the output voltage VOUT_TXLDO of the low-dropout linear regulator and the TXI_DET voltage representing the load current. After the AD converter converts the collected analog voltage and current information into digital signals, it is transmitted to the power control module. Based on these real-time data, the power control module calculates the optimal reference voltage control words REF1_CTRL<7:0> and REF2_CTRL<7:0> through the internal adaptive algorithm, and then completes the coordinated adjustment of the two-stage power supply. When the adjustment is completed, the system reaches a stable state, and the desired operating voltage VOUT_TXLDO is obtained, so as to output the radio frequency power meeting the EMVCo field strength specification.

[0051] The voltage regulation interface of the low-dropout linear regulator also uses the I 2 C bus, which is connected with the I 2 C interface of the power control module (multiplexing the I 2 C bus of the DC-DC boost converter, and is distinguished by different device addresses). The power control module controls the reference voltage source inside the low-dropout linear regulator by sending instructions to realize precise regulation of the output voltage. The enable end of the low-dropout linear regulator is connected with the GPIO pin of the power control module, and the control logic is consistent with that of the DC-DC boost converter, that is, high level starts and low level sleeps.

[0052] It should be noted that a self-resetting fuse is connected in series between the output terminal of the low dropout linear regulator and the radio frequency transmitter module. The resistance of the fuse is less than 50 mΩ at room temperature, and when the load current exceeds the set threshold, the resistance value increases sharply to the order of kilo-ohms within milliseconds, effectively cutting off the power supply circuit; after the fault is eliminated and the temperature returns to normal, the resistance of the fuse automatically returns to the normal value. This protection design not only prevents equipment damage under overcurrent conditions, but also realizes automatic recovery of system faults, significantly improving system reliability and service life, and particularly exhibits obvious advantages in frequent debugging and certification test scenarios. At the same time, a current detection point is also set on the series path, which can monitor the waveform of the output current in real time through an oscilloscope, for fault troubleshooting during debugging.

[0053] In an embodiment of the present application, the power control module establishes control connection with the DC-DC boost converter and the low dropout linear regulator through two independent I 2 C buses respectively, and realizes data communication with the low dropout linear regulator through an SPI bus. Specifically, the power control module connects the control interface of the DC-DC boost converter through the first I 2 C bus (SCL1, SDA1 pins), adopts standard I 2 C communication protocol, and sends a digital instruction packet containing the target voltage value by specifying the device address. The data frame format includes a start bit, a device address, a register address, 8-bit voltage data, and a check sequence, ensuring the integrity and reliability of the instruction transmission. The DC-DC boost converter adjusts the output voltage immediately after receiving the instruction, and can return the current actual output voltage value through a read operation for the power control module to check. At the same time, the power control module connects the control interface of the low dropout linear regulator through the second physically isolated I 2 C bus (SCL2, SDA2 pins), adopts the same communication protocol as the DC-DC boost converter but allocates a different device address, effectively avoiding bus conflicts and realizing accurate setting of the output voltage of the low dropout linear regulator.

[0054] To acquire the load state information in real time, the power control module reads the current measurement data integrated by the low-dropout linear regulator through the SPI bus (SCK, MISO, MOSI, CS pins) at a sampling rate of 1 MHz. The SPI communication protocol is configured as mode 0, including clock synchronization, 16-bit data frame and CRC check mechanism, to ensure that a single current sampling is completed within 10 μs, providing a high-precision data basis for real-time impedance calculation. The power control module checks immediately after receiving the current data, and if the data is valid, it is used for impedance calculation, and if it is invalid, the data is discarded and the next frame transmission is waited, avoiding abnormal adjustment caused by error data. This multi-bus independent cooperative communication architecture not only realizes accurate control of each power module, but also ensures real-time acquisition of load state information.

[0055] The power control module realizes continuous mapping of impedance-voltage by using linear interpolation method. When the real-time calculated load impedance is between two pre-stored impedance values in the mapping table, the interpolation calculation is automatically started, and the accurate target second voltage is obtained through mathematical operation of the microprocessor according to the proportional relationship between impedance difference and voltage difference. For example, when the impedance of 17.0 Ω is detected, based on the pre-stored data of 16.4 Ω corresponding to 2.6 V and 17.4 Ω corresponding to 3.1 V, the target second voltage is calculated according to the formula (17.0-16.4) / (17.4-16.4) x (3.1-2.6)+2.6=2.9 V. The above linear interpolation method is realized in real time by hardware, and the processing delay is less than 5 μs, effectively avoiding the step fluctuation of field strength caused by the discreteness of the mapping table, and significantly improving the continuity and control accuracy of power regulation.

[0056] It should be noted that the power control module ensures the system efficiency by fixed voltage difference maintenance mechanism. Specifically, when regulating the first voltage output by the DC-DC boost converter, the control logic always sets the first voltage as the sum of the target second voltage and the pre-set fixed voltage difference, which is usually set to 0.2 V, and dynamically adjusts according to the minimum voltage difference requirement of the low-dropout linear regulator. In the specific implementation process, the voltage difference compensation unit in the power control module will calculate the target value of the first voltage in real time, and send it to the DC-DC boost converter through the I 2 C bus in synchronization, ensuring that the input voltage of the low-dropout linear regulator is always higher than the output voltage and maintaining the optimal working voltage difference. This cooperative regulation strategy not only ensures the stable work of the power supply system, but also optimizes the overall power conversion efficiency.

[0057] In an embodiment of the present application, the field strength verification process is automatically started after each voltage adjustment is completed. The power control module collects an analog voltage signal proportional to the field strength through the field strength detection auxiliary circuit integrated inside the radio frequency transmitter module, and digitizes the signal at a rate of 100kSPS using a 12-bit ADC. When the deviation of the detected field strength value from the target value exceeds the tolerance range, the pre-test process is automatically triggered to recalibrate and update the voltage-impedance correspondence in the mapping table. This closed-loop verification mechanism effectively compensates for performance changes caused by device aging, temperature drift, and other environmental factors, ensuring the stability of the system over a long period of time, and fundamentally solving the technical problem of field strength drift in traditional open-loop solutions.

[0058] In addition, in terms of pre-test parameter setting, an optimization strategy of unified field strength reference is adopted. Under all test distances, the target field strength is set to the middle value of the EMVCo specification field strength range. This setting method avoids the critical risk brought by boundary value debugging and simplifies the mapping table data structure. By establishing a voltage-impedance mapping relationship with a constant field strength as the target, the system can achieve field strength stability at the minimum adjustment cost under different communication distances, significantly improving the pass rate and debugging efficiency of EMVCo certification.

[0059] In terms of connection with the radio frequency transmitter module, the GPIO1 pin of the power control module is connected to the enable end of the radio frequency transmitter module. When GPIO1 outputs a high level, the radio frequency transmitter module starts working and begins to emit a 13.56MHz radio frequency signal. When it outputs a low level, the radio frequency transmitter module is turned off and stops signal emission. The GPIO2 pin of the power control module is connected to the mode control end (MODE) of the radio frequency transmitter module, which is used to switch the working mode of the radio frequency transmitter module, i.e., high level for active mode (the radio frequency transmitter module actively sends carrier signals), and low level for passive mode (only responds when receiving external signals). This switching function can adapt to different NFC communication scenarios. In addition, the state feedback pin (READY) of the radio frequency transmitter module is connected to the GPIO3 pin of the power control module through a pull-up resistor. When the radio frequency transmitter module completes initialization and is ready, the state feedback pin outputs a high level. The power control module detects this signal and then starts the subsequent power adjustment process, ensuring that the radio frequency transmitter module is in a normal working state.

[0060] The power control module also has a storage unit integrated inside, and its data interface is connected to the host controller through an internal bus, used to store the "distance-voltage-current-impedance" parameter table in the pre-test stage. During data writing, the host controller sends addresses and data to the storage unit through the SPI interface to complete table storage. During dynamic adjustment, the host controller quickly reads the corresponding data through address addressing, and the table lookup time does not exceed 10μs, ensuring rapid adjustment response.

[0061] In order to realize the debugging and configuration with external equipment, the power control module is also provided with a UART interface (TX, RX pins) connected to the USB interface of the host computer through a level conversion chip. The engineer can send instructions through the host computer, and the power control module receives and executes the corresponding operation, and returns the result. This interface plays an important role in the equipment research and production debugging stage, and can be used for parameter calibration, fault diagnosis, etc.

[0062] In an embodiment of the present application, the radio frequency transmitter module serves as the transmission source of the NFC signal, and its connection relationship directly affects the signal quality and power control accuracy. In terms of power supply connection, the power input end of the radio frequency transmitter module is directly connected to the output end of the low-dropout linear regulator, receiving a working voltage of 1.8V-5.0V. A 2.2μF ceramic capacitor is connected in parallel between the power pin and the ground, which is used to filter high-frequency noise on the power line and ensure the stable operation of the internal oscillation circuit of the radio frequency transmitter module. The ground end of the radio frequency transmitter module is connected to the system common ground, and is connected to the ground end of the low-dropout linear regulator and the DC-DC boost converter through a large area of copper to realize common ground, reduce the potential difference caused by the ground impedance, and avoid noise coupling.

[0063] In terms of radio frequency signal transmission, the antenna interface of the radio frequency transmitter module is connected to the NFC antenna through a matching circuit. The matching circuit is composed of two adjustable capacitors and one adjustable inductor, which matches the output impedance of the radio frequency transmitter module with the actual impedance of the antenna, maximally reduces signal reflection, and improves power transmission efficiency. The antenna adopts a PCB planar coil structure, and its two lead-out ends are connected to the output ends of the matching circuit. When the radio frequency transmitter module outputs alternating current, the antenna will generate an alternating magnetic field, and the magnetic field strength is proportional to the current size, which further determines the field strength coupled to the PICC.

[0064] In terms of control signal connection, the enable end of the radio frequency transmitter module is connected to the GPIO1 pin of the power control module. As described above, the start and stop of the radio frequency transmitter module are controlled by high and low levels. The modulation signal input end of the radio frequency transmitter module is connected to the PWM output pin of the power control module. The power control module modulates the 13.56MHz carrier output by the radio frequency transmitter module through the PWM signal with different duty cycles to realize data transmission. The modulation depth can be adjusted by the PWM duty cycle to meet the requirements of the NFC communication standard for the modulation signal.

[0065] The RF transmitter module also integrates a field strength detection auxiliary circuit, whose output is connected to the ADC input pin of the power control module. This circuit is used to assist in calibrating the field strength during the pre-test phase. When the PICC is at different distances, the voltage signal output by the FS pin is proportional to the field strength. The power control module acquires this signal through the ADC and can quickly determine whether the field strength has reached the target value, thus assisting in recording the pre-test parameters.

[0066] The working principle of this invention will be explained in detail below:

[0067] like Figure 3 As shown, firstly, a pre-test is conducted. Based on the median value of EMVCoL1 certification (to avoid approaching the upper or lower limit), the target field strength from 0cm to 4cm is set to 5V (this value is within the specification range for all distances: 4.3 to 7.35V for 0cm and 3.84 to 7.35V for 4cm).

[0068] Next, tests were conducted at various distances:

[0069] 0cm distance test:

[0070] Fix the PICC at 0cm from the antenna (closely).

[0071] The power control module initializes the DC-DC boost converter output to 3.0V and the low dropout linear regulator output to 2.0V. At this time, the RF transmitter module starts working, and the PICC measures a field strength of 3.2V (lower than the 5V target).

[0072] The power control module gradually increases the output voltage of the low dropout linear regulator (by 0.1V each time) through instructions from the host computer, while recording the output current of the low dropout linear regulator and the field strength value of the PICC.

[0073] When the PICC field strength reaches 5V, stop adjusting and record the parameters at this time: Low dropout linear regulator output voltage 2.2V, current 145mA, calculate impedance:

[0074] Z = 2.2V / 0.145A ≈ 15.2Ω

[0075] The parameters "distance 0cm, target field strength 5V, voltage 2.2V, current 145mA, impedance 15.2Ω" are stored in the storage unit of the power control module.

[0076] 1cm distance test:

[0077] When the PICC is moved to a distance of 1cm, the electric field strength at the original voltage of 2.2V drops to 3.8V (below the target) due to the increased distance.

[0078] The output voltage of the low dropout linear regulator is gradually increased to 2.6V, at which point the current rises to 159mA and the PICC field strength reaches 5V, and the impedance is calculated:

[0079] Z = 2.6V / 0.159A ≈ 16.4Ω

[0080] The parameters are stored: "distance 1cm, voltage 2.6V, current 159mA, impedance 16.4Ω".

[0081] 2cm, 3cm, 4cm distance test:

[0082] Repeat the above steps and record:

[0083] 2cm: voltage 3.1V, current 178mA, impedance 17.4Ω;

[0084] 3cm: voltage 4.4V, current 234mA, impedance 18.8Ω;

[0085] 4cm: voltage 5.7V, current 288mA, impedance 19.8Ω.

[0086] Data verification: after completing all distance tests, place the PICC in each position again, call the stored voltage parameters, and verify whether the field strength is stable within the range of 5V ± 0.1V. If the deviation exceeds 0.1V, retest and calibrate.

[0087] The pre-test data is stored in the storage unit of the power control module in table form, with the following format (in array form):

[0088] Table 1 Pre-test data table

[0089]

[0090] The above table supports interpolation calculation. When the actual impedance is between two recorded values (such as 17.0Ω between 16.4Ω and 17.4Ω), the power control module will calculate the corresponding target voltage through linear interpolation, for example:

[0091]

[0092] It should be noted that the "distance-voltage-current-impedance" mapping table established in the pre-test phase is the core of adaptive adjustment. To further improve the precision of power control, the sampling gear of pre-test can be increased. For example, in the current 0cm to 4cm range, the distance step is encrypted from 1cm to 0.5cm or 0.25cm; in addition, multi-point testing can be introduced in the horizontal direction at a fixed height to construct a more comprehensive spatial impedance mapping model.

[0093] To ensure the NFC power adaptive adjustment system provided by the present application can be stably and reliably operated, a crucial design criterion is that, within the effective working range of the entire system, the load impedance of the radio frequency transmitter module must exhibit strict monotonicity with the change of the output voltage of the low-dropout linear regulator. This means that, for a given load impedance value, there is only one corresponding target output voltage value in the mapping table. This monotonicity constraint is the key to ensuring the determinacy and uniqueness of the control logic. If the impedance and voltage exhibit non-monotonicity or multi-value correspondence, ambiguity will occur when querying the target voltage according to the load impedance, resulting in adjustment oscillation or field strength out of control. Therefore, in the pre-test stage, not only the data needs to be recorded, but also the establishment of this monotonicity needs to be verified and ensured.

[0094] Next, the authentication test is performed. In the EMVCo L1 authentication test, the test equipment gradually moves the simulated payment card (PICC) from 4 cm to 0 cm, and the present system needs to adjust the transmission power in real time to ensure that the field strength of the PICC at all positions meets the specifications. The following explains the process of dynamic adjustment in combination with specific scenarios:

[0095] Initial state (PICC is located at 4 cm):

[0096] When the test starts, the PICC is fixed at 4 cm, and the power control module calls the parameters corresponding to 4 cm in the pre-test table: voltage 5.7 V, current 288 mA, impedance 19.8 Ω;

[0097] The power control module sends an instruction to the DC-DC boost converter: "adjust the output voltage to 5.7 V + low-dropout linear regulator voltage difference (0.2 V) = 5.9 V" (the voltage difference of the low-dropout linear regulator is the difference between the input and output, ensuring that the input voltage is 0.2 V higher than the output voltage);

[0098] The DC-DC boost converter responds to the instruction and adjusts the output voltage to 5.9 V, and the low-dropout linear regulator module stabilizes the output voltage at 5.7 V after receiving it. At this time, the power voltage of the radio frequency transmitter module is 5.7 V;

[0099] The low-dropout linear regulator module measures the current as 288 mA and transmits it to the power control module in real time, calculating the impedance Z = 5.7 V / 0.288 A ≈ 19.8 Ω, which is consistent with the pre-stored value, and the field strength is stabilized at 5 V (complying with the specification of 3.84-7.35 V at 4 cm).

[0100] Adjustment process when the PICC moves to 2 cm:

[0101] When the test equipment moves the PICC from 4 cm to 2 cm, the magnetic field coupling is enhanced due to the shortened distance, and if the voltage remains 5.7 V, the PICC field strength will rise to 6.8 V (exceeding the target of 5 V), and the load impedance of the radio frequency transmitter module will decrease from 19.8 Ω to 17.4 Ω (the equivalent impedance of the antenna decreases due to the shortened distance);

[0102] The impedance change causes the output current of the low-dropout linear regulator to increase from 288 mA to 327 mA;

[0103] The low-dropout linear regulator module transmits the current data of 327 mA to the power control module in real time, and calculates the current impedance Z = 5.7 V / 0.327 A ≈ 17.4 Ω;

[0104] The power control module queries the pre-test table and finds that the target voltage corresponding to 17.4 Ω at 2 cm is 3.1 V;

[0105] Immediately send the command "output voltage adjustment to 3.1 V + 0.2 V = 3.3 V" to the DC-DC boost converter, and send the command "output voltage adjustment to 3.1 V" to the low-dropout linear regulator module;

[0106] The DC-DC boost converter reduces the output voltage from 5.9 V to 3.3 V within 100 μs, and the low-dropout linear regulator module synchronously reduces the output voltage to 3.1 V;

[0107] After adjustment, the low-dropout linear regulator measures the current to be 178 mA, the impedance returns to 17.4 Ω, and the field strength stabilizes at 5 V (consistent with the specification of 4.2-7.35 V at 2 cm).

[0108] It should be noted that the above multiple embodiments are only illustrative. The technical solutions of each embodiment can be combined, and all are within the protection scope of the present application.

[0109] The NFC power self-adaptive adjustment system and method for EMVCo certification provided by the present application are described in detail above. Any obvious modification made by a person skilled in the art without departing from the essential content of the present application will constitute an infringement of the patent right of the present application and will bear the corresponding legal responsibility.

Claims

1. An NFC power adaptive adjustment system for EMVCo certification, characterized in that The power supply, a DC-DC boost converter, a power control module, a low dropout linear regulator and a radio frequency transmitter module are included. An input end of the DC-DC boost converter is connected to the power supply for providing an adjustable first voltage. An input end of the low dropout linear regulator is connected to an output end of the DC-DC boost converter, and an output end of the low dropout linear regulator is connected to a power input end of the radio frequency transmitter module for providing an adjustable second voltage and powering the radio frequency transmitter module. The power control module is in communication connection with the DC-DC boost converter, the low dropout linear regulator and the radio frequency transmitter module respectively. The power control module has a mapping table established in a pre-test phase stored therein, and the mapping table contains a corresponding relationship among the second voltage, the load current and the load impedance calculated for reaching a target field strength at different communication distances. In the working phase, the power control module is configured to receive the load current measured by the low dropout linear regulator, calculate a real-time load impedance in combination with the current second voltage, query the mapping table to determine a target second voltage corresponding to the real-time load impedance, and generate a control instruction based on the target second voltage to cooperatively adjust the first voltage output by the DC-DC boost converter and the second voltage output by the low dropout linear regulator, so that the field strength generated by the radio frequency transmitter module is stabilized within the EMVCo specification range.

2. The NFC power adaptive adjustment system of claim 1, wherein:

3. The NFC power adaptive adjustment system of claim 1 or 2, wherein: The power control module is connected with the first path I 2 The C bus connects and controls the DC-DC boost converter, and the second path independent I 2 The C bus connects and controls the output voltage of the low dropout linear regulator, and the low dropout linear regulator is connected through the SPI bus to read the measurement data of the load current. The power control module is further configured to calculate the target second voltage by using a linear interpolation method when the real-time load impedance is between two pre-stored impedance values in the mapping table.

4. The NFC power adaptive adjustment system of claim 3, wherein: When the power control module adjusts the first voltage output by the DC-DC boost converter, the first voltage is always higher than the second voltage output by the low dropout linear regulator, and a preset fixed voltage difference is maintained.

5. The NFC power adaptive adjustment system of claim 1, wherein: A self-resetting fuse is connected in series between the output end of the low dropout linear regulator and the power input end of the radio frequency transmitter module. The method comprises the following steps:

6. An NFC power adaptive adjustment method for EMVCo certification, based on the NFC power adaptive adjustment system of any one of claims 1-5, characterized in that In the pre-test phase, first, the second voltage output by the low dropout linear regulator is adjusted so that the field strength to which the test card is coupled reaches a predetermined target value within the EMVCo specification range at different communication distances, the second voltage and the load current measured by the current measurement circuit inside the low dropout linear regulator are recorded synchronously, the load impedance is calculated, and a mapping table containing the distance, the second voltage, the load current and the load impedance is formed and stored. In the working phase, the load current is monitored in real time by the current measurement circuit inside the low dropout linear regulator. ​ calculating a real-time load impedance based on a second voltage outputted by the low-dropout linear regulator and a real-time monitored load current; inquiring the mapping table to determine a target second voltage corresponding to the real-time load impedance; dynamically and cooperatively adjusting a first voltage outputted by the DC-DC boost converter and the second voltage outputted by the low-dropout linear regulator based on the target second voltage.

7. The method of claim 6, wherein the NFC power adaptation is performed by the NFC controller. The step of adjusting the first voltage outputted by the DC-DC boost converter is specifically: adding the target second voltage and a preset fixed voltage difference value, and taking the obtained voltage value as a target value of the first voltage for adjustment.

8. The NFC power adaptive adjustment method of claim 6, wherein: in the pre-test phase, the predetermined target field strength is set to a same constant value at all test distances, and the constant value is located in a middle region of the EMVCo specification field strength range.

9. The NFC power adaptive adjustment method of claim 6, wherein: in the working phase, if the calculated real-time load impedance is between two pre-stored impedance values in the mapping table, the target second voltage is calculated by a linear interpolation method.

10. The method of claim 6, wherein the NFC power adaptation is performed in response to a change in a power level of the NFC device. Further comprising a field strength verification step: after the voltage adjustment is completed, field strength verification is performed by a field strength detection auxiliary circuit inside the radio frequency transmitter module, and if the field strength deviation exceeds a tolerance, the pre-test phase process is triggered to perform recalibration.

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