An apparatus for improving the performance of contactless smart card communications

Abstract

The utility model discloses a device that improves non -contact intelligent card communication performance. The device includes antenna, rectification filter module, power management module, control module, waveform amplitude limitation module, demodulation module and load modulation module, wherein, antenna is connected with rectification filter module, waveform amplitude limitation module, demodulation module and load modulation module respectively, rectification filter module is connected with power management module, power management module is connected with control module, waveform amplitude limitation module, demodulation module and load modulation module respectively, demodulation module is connected with control module, control module is connected with waveform amplitude limitation module and load modulation module respectively. The utility model discloses through change the waveform amplitude limitation adjustment modulation depth under different state, has solved the problem that the traditional non -contact intelligent card modulation depth fixed results in to the card reader receiving sensitivity requirement high, communication distance is limited.

Description

Technical Field

[0001] This utility model relates to a device for improving the communication performance of contactless smart cards, and belongs to the field of smart card technology. Background Technology

[0002] A contactless smart card (hereinafter referred to as "the card") is a passive device based on radio frequency identification (RFID) technology. Its operating power comes from the alternating magnetic field generated by the reader, and it interacts with the reader via the same magnetic field. This communication process uses a half-duplex mode: when the reader sends a command, the card demodulates the signal by sensing voltage changes on its antenna; when the card replies, it changes the load on its own antenna (i.e., load modulation), thereby affecting the energy consumption of the reader's magnetic field. The reader detects this change to demodulate the data sent by the card.

[0003] The effectiveness of load modulation is determined by the key indicator of modulation depth, which directly affects the strength and signal-to-noise ratio of the received signal, and thus the reliability and effective range of communication. In traditional contactless smart card designs, such as products conforming to the ISO / IEC 14443-A standard, a fixed modulation depth scheme is commonly used. This design is mainly based on considerations of reception stability: during reception, a waveform amplitude limiting module is needed to stabilize the antenna induced voltage at a low level (e.g., 6V) to provide a stable operating environment for the demodulation circuit and prevent instruction parsing errors.

[0004] However, this fixed modulation depth design has revealed inherent and serious flaws in practice: 1. Limited communication distance: A fixed, low modulation depth means that the magnetic field changes caused by the card's load modulation are small when the card is in the transmission state. This makes it difficult for the card reader to effectively detect the weak signals emitted by the card at a distance, forcing users to bring the card very close to the reader to complete the operation, sacrificing convenience.

[0005] 2. Stringent requirements for reader sensitivity: Due to the insufficient signal strength returned by the card, the card reader must have extremely high receiving sensitivity to accurately identify the card. This not only increases the cost and design complexity of the card reader system, but also significantly increases the communication failure rate when there is strong electromagnetic interference in the environment.

[0006] While existing technologies strive to improve communication performance, none have fundamentally solved the aforementioned problems. For example, Chinese invention patent CN103606001A discloses an adaptive threshold adjustment method in a contactless smart card demodulation system. This method optimizes the accuracy of command demodulation by dynamically adjusting the threshold of the demodulation comparator in the receiving state. However, when the card is in the transmitting state, its modulation depth remains fixed. It only optimizes the card's "listening" ability but does not enhance the card's "speaking" strength. Therefore, this method cannot overcome the fundamental bottleneck of short communication distance and high sensitivity requirements of the card reader caused by the fixed modulation depth at the transmitting end.

[0007] In summary, a long-standing and urgent core technical problem in the field of contactless smart card technology is how to break through the limitation of fixed modulation depth and dynamically increase the modulation depth in the transmission state while ensuring the stability of the receiving state, thereby extending the communication distance, reducing the requirements for card reader sensitivity, and comprehensively improving communication performance. Utility Model Content

[0008] The technical problem to be solved by this utility model is to provide a device for improving the communication performance of contactless smart cards.

[0009] To achieve the above technical objectives, the present invention adopts the following technical solution: A device for improving the communication performance of contactless smart cards includes: an antenna, a rectification and filtering module, a power management module, a control module, a waveform amplitude limiting module, a demodulation module, and a load modulation module; The antenna's output is connected to the input of the rectifier-filter module, the first input of the waveform amplitude limiting module, the first input of the demodulation module, and the first input of the load modulation module, respectively. The output of the rectifier-filter module is connected to the input of the power management module. The output of the power management module is connected to the first input of the control module, the second input of the waveform amplitude limiting module, the second input of the demodulation module, and the second input of the load modulation module, respectively. The output of the demodulation module is connected to the second input of the control module. The output of the control module is connected to the third input of the waveform amplitude limiting module and the third input of the load modulation module, respectively.

[0010] Preferably, the waveform amplitude limiting module includes a first diode, a second diode, a third diode, a fourth diode, a first MOSFET, a second MOSFET, a third MOSFET, a first resistor, and a second resistor; The antenna's first output terminal is connected to the anodes of the second and fourth diodes, respectively; the antenna's second output terminal is connected to the anodes of the first and third diodes, respectively; the cathodes of the first and second diodes are both connected to a preset node, and the other end of the preset node is connected to the source of the first and second MOS transistors, respectively; the gate of the first MOS transistor is connected to the gate of the second MOS transistor; the drain of the second MOS transistor is connected to a second resistor; the cathodes of the third and fourth diodes are both connected to the drain of the third MOS transistor; the gate of the third MOS transistor is connected to the drain of the second MOS transistor; and the first resistor, the second resistor, and the source of the third MOS transistor are all grounded.

[0011] Preferably, both the first MOS transistor and the second MOS transistor are PMOS transistors, and the gate and drain of the first MOS transistor are shorted together and grounded through a first resistor.

[0012] Preferably, the third MOS transistor is an NMOS transistor, forming a complementary structure with the first and second MOS transistors.

[0013] Preferably, the load modulation module consists of a switched capacitor and a control circuit. Under the control of the control module, the equivalent load of the antenna is changed by changing the connection state of the switched capacitor, thereby achieving modulation of the waveform on the antenna.

[0014] Compared with existing technologies, this invention constructs a dynamic switching mechanism based on hardware circuitry. In receiving mode, the waveform amplitude limiting module clamps the antenna waveform amplitude to a first preset threshold, ensuring stable operation of the demodulation circuit. In transmitting mode, the control module switches the signal to a second preset threshold, significantly improving the modulation depth generated by the load modulation module. This invention effectively overcomes the limitations of traditional fixed modulation depth schemes, significantly improving the strength and signal-to-noise ratio of the card's transmitted signal while maintaining receiving sensitivity, thereby extending the communication distance and reducing the sensitivity requirements of the card reader. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a device for improving the communication performance of contactless smart cards in an embodiment of this utility model; Figure 2 This is a circuit diagram of the waveform amplitude limiting module in an embodiment of the present invention; Figure 3 This is a logic flowchart of a device for improving the communication performance of contactless smart cards in an embodiment of this utility model; Figure 4 This is a schematic diagram of the waveform after the transmitted waveform is expanded in an embodiment of this utility model. Detailed Implementation

[0016] The technical content of this utility model will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1 As shown in the figure, an embodiment of the present invention provides a device for improving the communication performance of contactless smart cards, comprising: an antenna, a rectification and filtering module, a power management module, a control module, a waveform amplitude limiting module, a demodulation module, and a load modulation module.

[0018] The antenna's output is connected to the input of the rectifier-filter module, the first input of the waveform amplitude limiting module, the first input of the demodulation module, and the first input of the load modulation module, respectively. The output of the rectifier-filter module is connected to the input of the power management module. The output of the power management module is connected to the first input of the control module, the second input of the waveform amplitude limiting module, the second input of the demodulation module, and the second input of the load modulation module, respectively. The output of the demodulation module is connected to the second input of the control module. The output of the control module is connected to the third input of the waveform amplitude limiting module and the third input of the load modulation module, respectively.

[0019] In one embodiment of this utility model, the antenna is made of multi-turn copper wire and is used to couple the magnetic field emitted by the card reader to achieve energy acquisition and signal transmission.

[0020] In one embodiment of this utility model, the rectifier and filter module converts the alternating voltage sensed by the antenna into a DC voltage and performs filtering processing to provide a stable DC power supply for subsequent modules.

[0021] In one embodiment of this utility model, the power management module is responsible for adjusting and distributing the rectified and filtered voltage, providing suitable operating voltages for various modules such as the control module and the waveform amplitude limiting module.

[0022] In one embodiment of this invention, the control module can be implemented using a microcontroller (such as STM32, Arduino, etc.). As the control core of the entire device, it is responsible for coordinating the work of various modules, including receiving and decoding card reader commands, controlling state switching, and sending reply commands.

[0023] like Figure 2 As shown, in one embodiment of this utility model, the waveform amplitude limiting module includes a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a first MOSFET M1, a second MOSFET M2, a third MOSFET M3, a first resistor R1, and a second resistor R2.

[0024] The antenna's first output terminal ANT1 is connected to the anodes of the second diode D2 and the fourth diode D4, respectively; the antenna's second output terminal ANT2 is connected to the anodes of the first diode D1 and the third diode D3, respectively; the cathodes of the first diode D1 and the second diode D2 are both connected to a preset node, the other end of which is connected to the source of the first MOSFET M1 and the second MOSFET M2, respectively; the gate of the first MOSFET M1 is connected to the gate of the second MOSFET M2; the drain of the second MOSFET M2 is connected to the second resistor R2; the cathodes of the third diode D3 and the fourth diode D4 are both connected to the drain of the third MOSFET M3; the gate of the third MOSFET M3 is connected to the drain of the second MOSFET M2; the first resistor R1, the second resistor R2, and the source of the third MOSFET M3 are all grounded.

[0025] It should be noted that both the first MOSFET M1 and the second MOSFET are PMOS transistors. The gate and drain of the first MOSFET M1 are shorted and grounded through the first resistor R1. This diode connection makes M1 a voltage reference element. When the voltage in the circuit exceeds a set threshold, M1 conducts, shunting the current to achieve voltage clamping. In the enhancement-limiting state (receive state), the clamping voltage is set to approximately 6V to ensure stable operation of the demodulation circuit; in the reduction-limiting state (transmit state), the clamping voltage is increased to 8V or higher to increase the modulation depth.

[0026] In the waveform amplitude limiting module, the first MOS transistor (PMOS transistor), the second MOS transistor (PMOS transistor), and the third MOS transistor (NMOS transistor) form a complementary structure. The PMOS transistor handles the positive half-cycle signal or high-voltage side clamping, while the NMOS transistor handles the negative half-cycle signal or low-voltage side clamping. This combination ensures bidirectional amplitude limiting of the antenna's AC signal, improving the circuit's symmetry and reliability.

[0027] The waveform amplitude limiting module sets the limiting voltage through the conduction threshold of the MOSFET. When the waveform amplitude exceeds the threshold voltage set by the MOSFET and resistor network, the corresponding MOSFET turns on, clamping the waveform amplitude. In the enhanced limiting state, the reference voltage is set to 6V (first preset threshold). When the waveform amplitude exceeds 6V, the switching transistor turns on, shunting part of the current and reducing the amplitude to 6V. In the weakened limiting state, the reference voltage is set to 8V (second preset threshold) or higher. The switching transistor only turns on when the waveform amplitude exceeds the set high voltage, thus allowing the waveform amplitude to increase.

[0028] In one embodiment of this utility model, the demodulation module is used to demodulate the modulated signal received by the antenna carrying the card reader instruction, extract the digital instruction signal, and transmit it to the control module for processing.

[0029] In one embodiment of this utility model, the load modulation module consists of a switched capacitor and a control circuit. Under the control of the control module, the equivalent load of the antenna is changed by changing the connection state of the switched capacitor, thereby achieving modulation of the waveform on the antenna and sending the reply command to the card reader.

[0030] The working principle of this device will be explained in detail below: like Figure 3 As shown, the contactless smart card first enters the receiving state. In this state, the waveform amplitude limiting module inside the card is in an enhanced limiting state, strictly limiting the waveform amplitude on the antenna to approximately 6V. This ensures the card can stably wait for and receive commands from the reader. At this time, the card's modulation depth is determined by this fixed amplitude and remains at a low level. This is to ensure stability during command reception and avoid excessive amplitude fluctuations affecting the accurate reception and decoding of reader commands.

[0031] In receiving mode, the card's internal circuitry continuously operates, constantly coupling the magnetic field emitted by the card reader through the antenna. The magnetic field energy is converted into electrical energy, powering the various modules within the card. Simultaneously, the demodulation circuit analyzes the instruction information carried in the magnetic field in real time. Because the waveform amplitude is limited to approximately 6V, the demodulation circuit can operate under a stable voltage environment, improving the accuracy of instruction parsing. Even if a slight change in the distance between the card reader and the card causes fluctuations in the magnetic field strength, the waveform amplitude limiting module can quickly respond, stabilizing the amplitude at approximately 6V, ensuring stable and reliable reception.

[0032] Secondly, once the card successfully receives the instruction sent by the card reader through its internal demodulation circuit, it automatically switches from receiving mode to transmitting mode. This switching process is controlled by the card's internal control module. After confirming that a valid instruction has been received, the control module sends a state switching signal to the relevant modules, initiating various preparations for transmitting.

[0033] During the state transition, the card's internal circuitry undergoes a series of adjustments. The demodulation circuitry, active in the receive state, gradually ceases operation, while the load modulation module and other components required for the transmit state begin operation. Simultaneously, the waveform amplitude limiting module receives control signals from the control module, preparing to adjust its operating state. This transition process is rapid and efficient, ensuring the card can respond promptly to the reader's commands and reducing communication latency.

[0034] Next, after the card enters the transmission state, the control module immediately sends a command to the waveform amplitude limiting module to reduce the limiting effect. Upon receiving this command, the waveform amplitude limiting module changes its internal circuitry, weakening its limiting effect on the waveform amplitude on the antenna. This causes the waveform amplitude on the antenna to no longer be limited by 6V, but instead increase to 8V or higher (see reference). Figure 4 ).

[0035] The formula for calculating the modulation depth is as follows: Modulation depth = (V1 - V2) / (V1 + V2) Where V1 is the amplitude of the unmodulated carrier wave; V2 is the amplitude of the modulated wave signal.

[0036] The increased waveform amplitude directly leads to a greater modulation depth in the card's response command. Increased modulation depth means that the waveform amplitude changes more significantly on the antenna during load modulation. When the card changes the equivalent load of the antenna through the load modulation module, the larger waveform amplitude base results in a greater amplitude change, allowing the card reader to more clearly perceive the card's response signal. For example, with a traditional fixed 6V amplitude, load modulation might result in a 1V amplitude change, while with an 8V amplitude, the same load modulation operation might result in a 1.5V or even greater amplitude change, greatly improving signal recognition.

[0037] In transmit mode, the increase in waveform amplitude is strictly controlled by the card's internal circuitry. The waveform amplitude limiting module does not completely remove the limit; instead, it raises the limiting threshold from 6V to 8V or higher. This design aims to fully utilize the modulation depth while preventing damage to internal card components due to unrestricted amplitude increases. The card's internal voltage monitoring circuit monitors the waveform amplitude on the antenna in real time, ensuring that its increase does not exceed the set safety threshold. If, due to certain abnormal conditions, such as a sudden increase in the reader's magnetic field, the waveform amplitude tends to exceed the safety threshold, the waveform amplitude limiting module will temporarily activate a protection mechanism, appropriately increasing the limit to control the amplitude within a safe range. Once the abnormal condition is resolved, it will revert to a reduced limiting state.

[0038] During transmission, the card loads the reply command onto the waveform on the antenna via the load modulation module and continuously sends it to the card reader. The control module monitors the transmission progress of the reply command in real time. This monitoring is achieved by tracking the encoded digital signal frames. When signals indicating the end of command transmission, such as the frame end flag and check bit, are detected, the control module determines that the card's reply command transmission has ended. The load modulation module precisely controls the change in the equivalent load of the antenna according to the content of the reply command, so that the waveform amplitude on the antenna is modulated according to the encoding rules of the command. Because the waveform amplitude is larger and the modulation depth is higher at this time, the reply command can be transmitted with stronger signal strength, ensuring signal integrity and accuracy even at a distance from the card reader. Simultaneously, the timing module inside the card monitors the transmission time to ensure that the command is transmitted within the specified time, avoiding communication timeouts.

[0039] Finally, once the confirmation reply command has been sent, the control module immediately sends a command to the waveform amplitude limiting module to restore the limiting state. Upon receiving this command, the waveform amplitude limiting module quickly returns to the enhanced limiting state, restoring the waveform amplitude on the antenna to approximately 6V. The card then switches from transmitting to receiving mode, awaiting the next command from the card reader.

[0040] Restoring the waveform amplitude to around 6V is to balance the card's power consumption and the stability of subsequent reception. In transmission mode, a larger waveform amplitude increases the card's power consumption, and maintaining transmission for extended periods may lead to rapid energy depletion, affecting its operating time in weak magnetic fields. Restoring the amplitude to around 6V reduces power consumption, allowing for longer communication. Simultaneously, returning to 6V prepares the card for the next reader command reception, ensuring stable and reliable reception in the next round.

[0041] During waveform amplitude recovery, the waveform amplitude limiting module smoothly adjusts the limiting strength to avoid drastic amplitude fluctuations. Drastic amplitude fluctuations can interfere with the normal operation of the card reader and may also cause over-voltage stress damage to the internal circuitry of the card. Through smooth adjustment, the waveform amplitude is steadily reduced from 8V or higher to around 6V, ensuring the continuity and stability of the communication process.

[0042] By repeating the above steps, the contactless smart card can dynamically adjust the modulation depth according to its own communication status, thereby effectively improving communication performance.

[0043] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] The above provides a detailed description of the device for improving the communication performance of contactless smart cards provided by this utility model. Any obvious modifications made by those skilled in the art without departing from the essential content of this utility model will constitute an infringement of the patent rights of this utility model and will incur corresponding legal liability.

Claims

1. A device for improving the communication performance of contactless smart cards, characterized in that... include: Antenna, rectifier and filter module, power management module, control module, waveform amplitude limiting module, demodulation module and load modulation module; The antenna's output is connected to the input of the rectifier-filter module, the first input of the waveform amplitude limiting module, the first input of the demodulation module, and the first input of the load modulation module, respectively. The output of the rectifier-filter module is connected to the input of the power management module. The output of the power management module is connected to the first input of the control module, the second input of the waveform amplitude limiting module, the second input of the demodulation module, and the second input of the load modulation module, respectively. The output of the demodulation module is connected to the second input of the control module. The output of the control module is connected to the third input of the waveform amplitude limiting module and the third input of the load modulation module, respectively.

2. The apparatus as described in claim 1, characterized in that... The waveform amplitude limiting module includes a first diode, a second diode, a third diode, a fourth diode, a first MOSFET, a second MOSFET, a third MOSFET, a first resistor, and a second resistor; The antenna's first output terminal is connected to the anodes of the second and fourth diodes, respectively; the antenna's second output terminal is connected to the anodes of the first and third diodes, respectively; the cathodes of the first and second diodes are both connected to a preset node, and the other end of the preset node is connected to the source of the first and second MOS transistors, respectively; the gate of the first MOS transistor is connected to the gate of the second MOS transistor; the drain of the second MOS transistor is connected to a second resistor; the cathodes of the third and fourth diodes are both connected to the drain of the third MOS transistor; the gate of the third MOS transistor is connected to the drain of the second MOS transistor; and the first resistor, the second resistor, and the source of the third MOS transistor are all grounded.

3. The apparatus as described in claim 2, characterized in that... Both the first MOS transistor and the second MOS transistor are PMOS transistors. The gate and drain of the first MOS transistor are shorted together and grounded through the first resistor.

4. The apparatus as described in claim 3, characterized in that... The third MOSFET is an NMOS transistor, forming a complementary structure with the first and second MOSFETs.

5. The apparatus as described in claim 4, characterized in that... When the waveform amplitude exceeds the preset threshold, the switch is turned on, shunting part of the current and reducing the amplitude to the same as the preset threshold; in the weakened limiting state, when the waveform amplitude exceeds the set voltage, the switch is turned on, thereby increasing the waveform amplitude.

6. The apparatus as claimed in claim 1, characterized in that... The load modulation module consists of a switched capacitor and a control circuit. Under the control of the control module, the equivalent load of the antenna is changed by changing the connection state of the switched capacitor, thereby achieving modulation of the waveform on the antenna.

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