Debugging method for improving non-contact card reading performance

Abstract

The invention belongs to the technical field of non-contact card reading performance, and discloses a debugging method for improving non-contact card reading performance, which comprises the following specific steps of: designing an antenna: according to the design of the shape of the antenna, the parameters of the antenna are related to the size of a coil, the number of turns, the width of the coil, the distance between the coils and the thickness of a PCB (Printed Circuit Board); inputting the size of the antenna, and adjusting the turn number N of the coil to obtain an inductance value; by optimizing antenna design, component parameter selection and matching circuit design, the application range of the system is widened, the stability and accuracy of card reading signals are improved, and the probability of misreading and misreading is reduced; by adjusting the external impedance, the EMC filter circuit and the like, the accurate control on the card reading field intensity is realized, and the consistency and reliability of card reading are improved; by adjusting the gain of the receiver and starting noise suppression measures such as AGC and Squelch functions, the noise level of the system is effectively reduced, and the card reading performance is further improved; a magnetic conductive protection measure is provided for the influence of a metal environment on the performance of the antenna.

Description

Technical Field

[0001] The invention belongs to the technical field of contactless card reading performance, and in particular relates to a debugging method for improving the contactless card reading performance. Background Art

[0002] In today's world, electronic technology is developing rapidly and has widely penetrated into all areas of social life, playing an increasingly important role in economic and social development. As a branch of the development of electronic technology, the emergence of contactless card reading technology has the characteristics of high reliability, convenient and fast operation, anti-collision, wide application range, good encryption performance, etc. Now my country has widely used contactless technology in public transportation, attendance systems, second-generation ID cards, campus cards, access cards, etc. in many cities.

[0003] In real life, there are many types of contactless card readers with varying performances. Often when users read cards for payment, some cards fail to be read due to incompatibility with various types of cards, or due to surrounding signal interference, card aging, and other issues, resulting in card reading failures due to low card reading distance or slow card reading. Especially during peak hours in the morning and evening, when passenger flow is large, sensitivity and accuracy are low, affecting user experience, and easily causing congestion and creating safety hazards. The superior and stable performance of contactless card reading is a core competitiveness in the market, and provides necessary guarantees for order and safety in public places. Therefore, it is very meaningful to invent a debugging method to improve the performance of contactless card reading. Summary of the invention

[0004] The object of the present invention is to provide a debugging method for improving the performance of contactless card reading, so as to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solution: a debugging method for improving the performance of contactless card reading, the specific steps are as follows:

[0006] Step 1: Antenna Design

[0007] According to the design of antenna shape, the parameters of antenna are related to coil size, number of turns, coil width, spacing between coils and PCB thickness. By inputting the size of antenna, the number of coil turns N can be adjusted to obtain the inductance value between 500nHˉ1000nH.

[0008] Step 2: Antenna parameter measurement

[0009] The antenna is composed of inductance, resistance and capacitance. These parameters and their natural frequency need to be measured to calculate the equivalent circuit, Q value and parameters of the subsequent matching circuit.

[0010] Measurement steps:

[0011] 2.1: Set the bandwidth of the network analyzer to 1MHz to 150MHz and calibrate the network analyzer;

[0012] 2.2: Disconnect the antenna from the matching circuit, and solder the signal and ground of the connector connected to the network analyzer to the two ends of the antenna respectively;

[0013] 2.3: Display using Smith circle chart format (R+jX);

[0014] 2.4: Measure S(1.1) at the mark point of 1MHz and record the inductance and DC resistance of the antenna;

[0015] 2.5: Move the mark point to intersect the real axis. At this time, the inductance and capacitance cancel each other out. Record the parallel resistance and self-oscillation frequency.

[0016] In the Smith graph, when "Mark1" is the 1Mhz frequency point, Lant = 774nH, Rsdc = 245mΩ; "Mark2" is the resonant frequency point of the antenna, when X = 0, Rp@fres = 5.7KΩ, fres = 83Mz;

[0017] Step 3: Selection of component parameters

[0018] 3.1: Method for selecting EMC low-pass filter parameters

[0019] The transmitter of the multi-protocol contactless card reader chip is composed of 13.56MHz and high-frequency components, and an EMC low-pass filter circuit is required to filter out the high-frequency components. The EMC low-pass filter circuit is generally composed of a series inductor and a parallel capacitor.

[0020] The cutoff frequency of the EMC low-pass filter is set to 14-15MHz according to the following calculation formula, and the parallel capacitor needs to be recalculated and adjusted;

[0021] Cut-off frequency formula:

[0022]

[0023] 3.2: Method for selecting matching circuit parameters

[0024] The purpose of the matching circuit is to match the chip transmitter with the antenna after passing through the EMC low-pass filter. The matching circuit consists of a DC-blocking capacitor and a ground capacitor. Assume that C1 represents the DC-blocking capacitor, C2 represents the ground capacitor, and Cpa represents the parallel capacitor at the antenna end.

[0025] The calculation formula is as follows:

[0026]

[0027] Step 4: Selection and adjustment of quality factor

[0028] The quality factor Q is an important parameter in antenna design, which directly affects the edge of the modulation waveform and the performance of card reading;

[0029] According to the Q value calculation table, the transmission rate of ISO 14443 is theoretically calculated to be 106 kbit / s, which requires the Q value to be less than 41;

[0030] Method for selecting antenna circuit parameters:

[0031] The antenna end parallel capacitor, using a network analyzer, when the frequency is around 13.56MHz, to determine the parameters of the antenna end parallel capacitor, the antenna end parallel resistor, using a simulation board or oscilloscope, the field strength value is below the EMV standard 8.75V, to determine the parameters of the antenna end parallel resistor;

[0032] Step 5: Selection of receiving circuit parameters

[0033] After the parameters of the transmitter are determined, adjust the receiving voltage of the multi-protocol contactless card reader chip. Since the receiving end is limited to 3V, it is necessary to measure the VPP (peak) voltage connected to RFN and RFP. If the voltage exceeds 3V, it is necessary to adjust the parameter value of the receiving circuit RC. It is recommended to adjust it to 2.5V.

[0034] Step 6: Smith Chart Debugging

[0035] 6.1: Set the bandwidth of the network analyzer to 10MHz to 20MHz and recalibrate;

[0036] 6.2: Turn off the power of the device, and solder the signal and ground of the network analyzer to the TX1 and TX2 positions of the multi-protocol contactless reader / writer core respectively;

[0037] 6.3: Use Smith Chart (R+jX) format and mark the 13.56MHz frequency point;

[0038] Step 7: Output waveform debugging

[0039] If the rise or fall time of Type A and Type B protocol waveforms exceeds the specified time limit, the antenna parallel resistance needs to be increased to reduce the quality factor Q value.

[0040] Step 8: Field test

[0041] ISO 14443 has the following requirements for field strength: the minimum unmodulated working field is Hmin, which is 1.5A / m (rms), and the maximum unmodulated working field is Hmax, which is 7.5A / m (rms);

[0042] The PICC should work continuously between Hmin and Hmax as expected, and the PCD should generate a field strength of at least Hmin but not exceeding Hmax at the position (working space) specified by the manufacturer. The magnitude of the field strength can be characterized by voltage measurement. EMVco uses the following test method to measure the field strength of the PICC in the PCD working field;

[0043] The field strength can be adjusted in the following ways:

[0044] Increasing the external impedance will reduce the output field strength, and vice versa;

[0045] Connecting a 1-2Ω resistor in series before the EMC filter circuit will reduce the field strength;

[0046] Change the EMC filter inductor. The increase in inductance value will increase the internal resistance and thus reduce the field strength, but at the same time, the response filter capacitor value needs to be adjusted;

[0047] Adjust the value of the field strength output impedance configuration register to adjust the output impedance;

[0048] Adjust the input voltage of VSP_RF. The higher the voltage, the higher the field strength, but the maximum should not exceed 5.5V.

[0049] Step 9: System Noise Debugging

[0050] 9.1: Register 02h bit4 rx_man is selected as 1 "Manual channel selection" to improve the accuracy of card reading;

[0051] 9.2: Reduce the first stage receiver gain register 0Ch bit7-5;

[0052] 9.3: Enable the second and third level AGC and Squelch functions;

[0053] Step 10: Modulation depth debugging

[0054] For the Type B protocol required by ISO 14443, the modulation depth is allowed to range from 8% to 14%. Two modulation depth adjustment methods are supported: one is automatic adjustment, which is achieved by sending a direct command, Cal ibrate Modulation Depth; the other is to adjust the value of the modulation depth register to set the modulation depth fixedly. However, this method has certain limitations, that is, when a contactless card is close to a card reader, it will affect the antenna performance of the card reader, thus causing a change in the modulation depth;

[0055] Step 11: Magnetic protection.

[0056] Preferably, the recommended antenna inductance range in step one is 500nHˉ1000nH, the self-resonant frequency is preferably higher than 80MHz, the recommended number of coil turns is 1-3 turns, and after adding a parallel resistor or a series resistor to the antenna to reduce the Q value, the antenna Q value is recommended to be adjusted to 30.

[0057] Preferably, the inductor in step 3 is selected to be 56nH-1000nH, and a winding inductor must be selected, and its rated current must be at least 250mA.

[0058] Preferably, the recommended antenna Q value in step 4 is 20, and the EMV demo recommended antenna Q value is 30.

[0059] Preferably, the marking point of the Smith graph in step six is ​​13.56 MHz. The position and size of the graph can be changed by adjusting the parallel capacitor at the antenna end and the EMC low-pass filter circuit. If the position of the marking point falls on the real axis and the impedance is 10-20Ω, it is considered that the impedance matching has been completed.

[0060] Preferably, if the waveform overshoots in step seven, the overshoot can be solved by adjusting the EMC filter inductance and capacitance values, adjusting the external impedance to make the resonance reach 13.56MHz, and adjusting the Q value to less than 30.

[0061] Preferably, when the receiving register in step nine is set to 0, the gain is fully open at 15dB, when it is set to 1-6, the gain is reduced by 2.5dB per step, and when it is set to 7, the gain is 15+5.5dB.

[0062] Preferably, the adjustment of the modulation depth in step 10 needs to ensure that the value setting of the output impedance configuration register remains unchanged, and the change of the output impedance configuration register requires re-adjustment of the modulation depth.

[0063] Preferably, in step eleven, the magnetic conductive protection uses non-metallic magnetic materials to protect the antenna in a metal environment.

[0064] Preferably, the non-metallic magnetic material is ferrite.

[0065] The beneficial effects of the present invention are as follows:

[0066] By optimizing antenna design, component parameter selection and matching circuit design, the system's application range and the stability and accuracy of the card reading signal are improved, and the probability of misreading and missed reading is reduced; by adjusting external impedance, EMC filtering circuit and other methods, precise control of the card reading field strength is achieved, and the consistency and reliability of card reading are improved; by adjusting the receiver gain, turning on AGC and Squelch functions and other noise suppression measures, the system noise level is effectively reduced, and the card reading performance is further improved; in response to the impact of metal environment on antenna performance, magnetic protection measures are proposed to effectively eliminate the adverse effects of metal on antenna performance, ensure the stability and reliability of the card reading system in complex environments, and through a series of sophisticated debugging steps and parameter optimization measures, significantly improve the overall performance of the contactless card reading system, providing users with a more efficient, stable and reliable card reading experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 is an equivalent circuit diagram of the antenna coil in the present invention;

[0068] Figure 2 is an equivalent circuit diagram of an antenna coil with adjustable resonant frequency in the present invention;

[0069] Figure 3 A reference diagram for the shape design of the antenna in the present invention;

[0070] Figure 4 This is a relationship diagram between antenna size, coil turns and inductance in the present invention;

[0071] Figure 5 It is the Smith figure in the present invention;

[0072] Figure 6 It is the spectrum distribution diagram of the present invention;

[0073] Figure 7 It is the EMC low-pass filter circuit diagram of the present invention;

[0074] Figure 8 It is the Type A modulation waveform and standard diagram in the present invention;

[0075] Fig. 9 is a relationship table between current carrying time and Q value in the present invention;

[0076] Fig.10 It is the Q value calculation table of the present invention;

[0077] Fig.11 It is the Smith figure in the present invention;

[0078] Fig.12 The waveform diagram of Type A and Type B protocols in the present invention;

[0079] Fig.13 It is the work flow chart of the present invention. DETAILED DESCRIPTION

[0080] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0081] like Figures 1 to 13 As shown, the embodiment of the present invention provides a debugging method for improving the performance of contactless card reading, and the specific steps are as follows:

[0082] Step 1: Antenna Design

[0083] According to the design of antenna shape, the parameters of antenna are related to coil size, number of turns, coil width, spacing between coils and PCB thickness. By inputting the size of antenna, the number of coil turns N can be adjusted to obtain the inductance value between 500nHˉ1000nH.

[0084] Step 2: Antenna parameter measurement

[0085] The antenna is composed of inductance, resistance and capacitance. These parameters and their natural frequency need to be measured to calculate the equivalent circuit, Q value and parameters of the subsequent matching circuit.

[0086] Measurement steps:

[0087] 2.1: Set the bandwidth of the network analyzer to 1MHz to 150MHz and calibrate the network analyzer;

[0088] 2.2: Disconnect the antenna from the matching circuit, and solder the signal and ground of the connector connected to the network analyzer to the two ends of the antenna respectively;

[0089] 2.3: Display using Smith circle chart format (R+jX);

[0090] 2.4: Measure S(1.1) at the mark point of 1MHz and record the inductance and DC resistance of the antenna;

[0091] 2.5: Move the mark point to intersect the real axis. At this time, the inductance and capacitance cancel each other out. Record the parallel resistance and self-oscillation frequency.

[0092] In the Smith graph, when "Mark1" is the 1Mhz frequency point, Lant = 774nH, Rsdc = 245mΩ; "Mark2" is the resonant frequency point of the antenna, when X = 0, Rp@fres = 5.7KΩ, fres = 83Mz;

[0093] Step 3: Selection of component parameters

[0094] 3.1: Method for selecting EMC low-pass filter parameters

[0095] The transmitter of the multi-protocol contactless card reader chip is composed of 13.56MHz and high-frequency components, and an EMC low-pass filter circuit is required to filter out the high-frequency components. The EMC low-pass filter circuit is generally composed of a series inductor and a parallel capacitor.

[0096] The cutoff frequency of the EMC low-pass filter is set to 14-15MHz according to the following calculation formula, and the parallel capacitor needs to be recalculated and adjusted;

[0097] Cut-off frequency formula:

[0098]

[0099] 3.2: Method for selecting matching circuit parameters

[0100] The purpose of the matching circuit is to match the chip transmitter with the antenna after passing through the EMC low-pass filter. The matching circuit consists of a DC-blocking capacitor and a ground capacitor. Assume that C1 represents the DC-blocking capacitor, C2 represents the ground capacitor, and Cpa represents the parallel capacitor at the antenna end.

[0101] The calculation formula is as follows:

[0102]

[0103] Step 4: Selection and adjustment of quality factor

[0104] The quality factor Q is an important parameter in antenna design, which directly affects the edge of the modulation waveform and the performance of card reading;

[0105] According to the Q value calculation table, the transmission rate of ISO 14443 is theoretically calculated to be 106 kbit / s, which requires the Q value to be less than 41;

[0106] Method for selecting antenna circuit parameters:

[0107] The antenna end parallel capacitor, using a network analyzer, when the frequency is around 13.56MHz, to determine the parameters of the antenna end parallel capacitor, the antenna end parallel resistor, using a simulation board or oscilloscope, the field strength value is below the EMV standard 8.75V, to determine the parameters of the antenna end parallel resistor;

[0108] Step 5: Selection of receiving circuit parameters

[0109] After the parameters of the transmitter are determined, adjust the receiving voltage of the multi-protocol contactless card reader chip. Since the receiving end is limited to 3V, it is necessary to measure the VPP (peak) voltage connected to RFN and RFP. If the voltage exceeds 3V, it is necessary to adjust the parameter value of the receiving circuit RC. It is recommended to adjust it to 2.5V.

[0110] Step 6: Smith Chart Debugging

[0111] 6.1: Set the bandwidth of the network analyzer to 10MHz to 20MHz and recalibrate;

[0112] 6.2: Turn off the power of the device, and solder the signal and ground of the network analyzer to the TX1 and TX2 positions of the multi-protocol contactless reader / writer core respectively;

[0113] 6.3: Use Smith Chart (R+jX) format and mark the 13.56MHz frequency point;

[0114] Step 7: Output waveform debugging

[0115] If the rise or fall time of Type A and Type B protocol waveforms exceeds the specified time limit, the antenna parallel resistance needs to be increased to reduce the quality factor Q value.

[0116] Step 8: Field test

[0117] ISO 14443 has the following requirements for field strength: the minimum unmodulated working field is Hmin, which is 1.5A / m (rms), and the maximum unmodulated working field is Hmax, which is 7.5A / m (rms);

[0118] The PICC should work continuously between Hmin and Hmax as expected, and the PCD should generate a field strength of at least Hmin but not exceeding Hmax at the position (working space) specified by the manufacturer. The magnitude of the field strength can be characterized by voltage measurement. EMVco uses the following test method to measure the field strength of the PICC in the PCD working field;

[0119] The field strength can be adjusted in the following ways:

[0120] Increasing the external impedance will reduce the output field strength, and vice versa;

[0121] Connecting a 1-2Ω resistor in series before the EMC filter circuit will reduce the field strength;

[0122] Change the EMC filter inductor. The increase in inductance value will increase the internal resistance and thus reduce the field strength, but at the same time, the response filter capacitor value needs to be adjusted;

[0123] Adjust the value of the field strength output impedance configuration register to adjust the output impedance;

[0124] Adjust the input voltage of VSP_RF. The higher the voltage, the higher the field strength, but the maximum should not exceed 5.5V.

[0125] Step 9: System Noise Debugging

[0126] 9.1: Register 02h bit4 rx_man is selected as 1 "Manual channel selection" to improve the accuracy of card reading;

[0127] 9.2: Reduce the first stage receiver gain register 0Ch bit7-5;

[0128] 9.3: Enable the second and third level AGC and Squelch functions;

[0129] Step 10: Modulation depth debugging

[0130] For the Type B protocol required by ISO 14443, the modulation depth is allowed to range from 8% to 14%. Two modulation depth adjustment methods are supported: one is automatic adjustment, which is achieved by sending a direct command, Cal ibrate Modulation Depth; the other is to adjust the value of the modulation depth register to set the modulation depth fixedly. However, this method has certain limitations, that is, when a contactless card is close to a card reader, it will affect the antenna performance of the card reader, thus causing a change in the modulation depth;

[0131] Step 11: Magnetic protection.

[0132] First, the antenna is designed and the LC resonant circuit is realized by adjusting the capacitor to match the operating frequency. Secondly, the antenna parameters are measured, including the use of a network analyzer to measure the inductance, resistance and self-resonance frequency. In the selection of component parameters, the design of the EMC low-pass filter and matching circuit, as well as the influence of the adjustment of the quality factor Q value on the card reading performance, are considered. In addition, the performance of the card reading system is optimized through the selection of receiving circuit parameters, Smith Chart debugging, output waveform debugging and field stress testing. Finally, the system noise debugging, modulation depth debugging and magnetic protection debugging techniques are used to improve the stability and reliability of the card reading system.

[0133] The recommended antenna inductance range in step 1 is 500nHˉ1000nH, the self-resonant frequency is preferably higher than 80MHz, and the recommended number of coil turns is 1-3. After adding a parallel resistor or a series resistor to the antenna to reduce the Q value, the antenna Q value is recommended to be adjusted to 30.

[0134] In order to achieve a longer communication distance, the design of the antenna is the most important. A suitable antenna will greatly facilitate the debugging and matching of the entire system. In the equivalent circuit diagram of the antenna coil, the inductance of the coil is Lant, Rs-ant is the resistance loss of the coil, and Cant is the capacitance loss between the coils and the connector. If the antenna works at 13.56MHz, then a capacitor can be connected in parallel or in series outside the antenna to form an LC resonant circuit with the capacitor and the antenna coil. The capacitor size is adjusted so that the resonant frequency is the operating frequency of 13.56MHz. As much as possible, increase the antenna turns. The number of turns and coil area can increase the magnetic flux, thereby achieving a longer working distance. However, the larger the size of the antenna, the larger the inductance Lant of the coil, and the corresponding tuning capacitor C needs to be reduced. When the resonant frequency is 13.56MHz, if the inductance of the antenna exceeds 5uH, the capacitance value is very small, which makes it difficult to match the tuning capacitor. It should be noted that the more turns of the coil or the smaller the spacing between the coils, the lower the self-resonance frequency of the antenna will be. When reading the card, the external impedance of the chip will be easily affected by the card, thereby increasing the current and affecting the output power when reading the card.

[0135] In step 3, the inductor should be between 56nH and 1000nH. A winding inductor must be selected with a rated current of at least 250mA.

[0136] The most common function of inductors in circuits is to form LC filtering circuits together with capacitors. Capacitors have the characteristics of "blocking DC and passing AC", while inductors have the functions of "passing DC, blocking AC, passing low frequencies and blocking high frequencies". If DC accompanied by many interference signals passes through the LC filtering circuit, most of the AC interference signals will be blocked by the inductor and absorbed into magnetic induction and heat energy, and most of the rest will be bypassed to the ground by the capacitor, which can suppress the effect of the interference signal and obtain a relatively pure DC current at the output end. The rated current is guaranteed to be at least 250mA, thereby ensuring the current output capacity. If the inductor does not have enough current resistance, the field strength will decrease after long-term operation.

[0137] Among them, the recommended antenna Q value in step 4 is 20, and the EMV demo recommends an antenna Q value of 30.

[0138] A higher Q value will increase the current intensity in the antenna coil, thereby obtaining a higher field strength and card reading distance. On the contrary, the transmission bandwidth of the antenna changes inversely with the quality factor value. A too high Q value will reduce the bandwidth and significantly weaken the modulation edge received by the contactless card. According to the relationship between the current carrying time and the Q value, it can be seen that the increase in the Q value will slow down the rise and fall of the waveform, that is, the bandwidth is reduced. The reduction in the Q value can be achieved by changing the inductance and capacitance or by connecting a series or parallel resistor to the antenna. Since the values ​​of L and C must match the resonance and the series resistance adjustment degree is too small, the Q value is mainly changed by connecting a parallel resistor. Therefore, at the beginning of the design, it is necessary to leave a margin for the quality factor Q value as much as possible for later debugging. If the Q value is designed to be too small, it will be inconvenient to increase it later.

[0139] Among them, the mark point of the Smith graph in step six is ​​13.56MHz. By adjusting the parallel capacitor at the antenna end and the EMC low-pass filter circuit, the position and size of the graph can be changed. If the position of the mark point falls on the real axis and the impedance is 10-20Ω, it is considered that the impedance matching has been completed.

[0140] In actual debugging, it was found that for small-volume card reader devices, the antenna performance will be affected by the contactless card when reading the card. The maximum card reading distance cannot be achieved by placing the antenna resonance point on the real axis. Based on experience, the antenna is adjusted to be inductive, that is, the resonance point is located above the real axis, which can significantly increase the card reading distance.

[0141] If the waveform overshoots in step seven, the overshoot can be solved by adjusting the EMC filter inductance and capacitance, adjusting the external impedance to make the resonance reach 13.56MHz, and adjusting the Q value to less than 30.

[0142] By adjusting the EMC filter inductance and capacitance values, external impedance and Q value, the phenomenon of waveform overshoot can be avoided.

[0143] Among them, when the receiving register in step nine is set to 0, the gain is fully open at 15dB, when it is set to 1-6, the gain is reduced by 2.5dB per step, and when it is set to 7, the gain is 15+5.5dB.

[0144] The receive register gain settings are shown in the following table:

[0145]

[0146] The adjustment of the modulation depth in step 10 needs to ensure that the value of the output impedance configuration register remains unchanged, and the change of the output impedance configuration register requires the modulation depth to be readjusted.

[0147] The modulation depth is dynamically adjusted using the table lookup method, as shown in the following table:

[0148]

[0149] Create an X, Y table and execute the "Measure Ampl i tude" command. The chip will perform AD conversion on the input voltage of the RF port and store it in the A / D Converter Output Register; read the value in the A / D Converter Output Register as the X value; use the value measured by the "Measure Ampl i tude" command to represent the distance between the card and the reader; read the value in the AM Modulation Depth Display Register as the Y value; the Y value is the value corresponding to the configuration of 11% modulation. In this way, in each card search process, first call the "Measure Ampl i tude" command to obtain the distance information between the card and the reader, and then look up the table to read the modulation depth setting value under the corresponding distance, so as to ensure the output of 11% modulation.

[0150] Among them, in step eleven, the magnetic conductive protection uses non-metallic magnetic materials to protect the antenna in the metal environment, and the non-metallic magnetic materials use ferrite.

[0151] Magnetic protection is to eliminate the influence of metal on the antenna. The metal surface can be the card reader frame, a metal-containing battery or the ground plane of the card reader PCB. If the metal and the antenna are placed very close, the alternating magnetic field will cause eddy currents in the metal. These eddy currents will absorb energy and cause the antenna to be detuned due to the reduction of self-inductance coefficient and quality factor. Therefore, for antennas in metal environments, non-metallic magnetic materials are used to protect them. Ferrite sheet itself is a high-temperature sintered non-metallic magnetic material, which is used in handheld devices such as NFC payment phones. By increasing the magnetic field strength, it can effectively increase the sensing distance.

[0152] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0153] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A debugging method for improving the performance of contactless card reading, characterized in that: The specific steps are as follows: Step 1: Antenna Design According to the design of antenna shape, the parameters of antenna are related to coil size, number of turns, coil width, spacing between coils and PCB thickness. By inputting the size of antenna, the number of coil turns N can be adjusted to obtain the inductance value between 500nHˉ1000nH. Step 2: Antenna parameter measurement The antenna is composed of inductance, resistance and capacitance. These parameters and their natural frequency need to be measured to calculate the equivalent circuit, Q value and parameters of the subsequent matching circuit. Measurement steps: 2.1: Set the bandwidth of the network analyzer to 1MHz to 150MHz and calibrate the network analyzer; 2.2: Disconnect the antenna from the matching circuit, and solder the signal and ground of the connector connected to the network analyzer to the two ends of the antenna respectively; 2.3: Display using Smith chart format (R+jX); 2.4: Measure S(1.1) at the mark point of 1MHz and record the inductance and DC resistance of the antenna; 2.5: Move the mark point to intersect the real axis. At this time, the inductance and capacitance cancel each other out. Record the parallel resistance and self-oscillation frequency. When "Mark1" in the Smith graph is 1Mhz frequency, Lant=774nH, Rsdc=245mΩ; "Mark2" is the resonant frequency point of the antenna, when X=0, Rp@fres=5.7KΩ, fres=83Mz; Step 3: Selection of component parameters 3.1: Method for selecting EMC low-pass filter parameters The transmitter of the multi-protocol contactless card reader chip is composed of 13.56MHz and high-frequency components, and an EMC low-pass filter circuit is required to filter out the high-frequency components. The EMC low-pass filter circuit is generally composed of a series inductor and a parallel capacitor. The cutoff frequency of the EMC low-pass filter is set to 14-15MHz according to the following calculation formula, and the parallel capacitor needs to be recalculated and adjusted; Cut-off frequency formula: 3.2: Method for selecting matching circuit parameters The purpose of the matching circuit is to match the chip transmitter with the antenna after passing through the EMC low-pass filter. The matching circuit consists of a DC-blocking capacitor and a ground capacitor. Assume that C1 represents the DC-blocking capacitor, C2 represents the ground capacitor, and Cpa represents the parallel capacitor at the antenna end. The calculation formula is as follows: Step 4: Selection and adjustment of quality factor The quality factor Q is an important parameter in antenna design, which directly affects the edge of the modulation waveform and the performance of card reading; According to the Q value calculation table, the transmission rate of ISO 14443 is theoretically calculated to be 106 kbit / s, which requires the Q value to be less than 41; Method for selecting antenna circuit parameters: The antenna end parallel capacitor, using a network analyzer, when the frequency is around 13.56MHz, to determine the parameters of the antenna end parallel capacitor, the antenna end parallel resistor, using a simulation board or oscilloscope, the field strength value is below the EMV standard 8.75V, to determine the parameters of the antenna end parallel resistor; Step 5: Selection of receiving circuit parameters After the parameters of the transmitter are determined, adjust the receiving voltage of the multi-protocol contactless card reader chip. Since the receiving end is limited to 3V, it is necessary to measure the VPP (peak) voltage connected to RFN and RFP. If the voltage exceeds 3V, it is necessary to adjust the parameter value of the receiving circuit RC. It is recommended to adjust it to 2.5V. Step 6: Smith Chart Debugging 6.1: Set the bandwidth of the network analyzer to 10MHz to 20MHz and recalibrate; 6.2: Power off the device, and solder the signal and ground of the network analyzer to the TX1 and TX2 positions of the multi-protocol contactless reader / writer core respectively; 6.3: Use Smith Chart (R+jX) format and mark the 13.56MHz frequency point; Step 7: Output waveform debugging If the rise or fall time of Type A and Type B protocol waveforms exceeds the specified time limit, the antenna parallel resistance needs to be increased to reduce the quality factor Q value. Step 8: Field test ISO 14443 has the following requirements for field strength: the minimum unmodulated working field is Hmin, which is 1.5A / m (rms), and the maximum unmodulated working field is Hmax, which is 7.5A / m (rms); The PICC should work continuously between Hmin and Hmax as expected, and the PCD should generate a field strength of at least Hmin but not exceeding Hmax at the position (working space) specified by the manufacturer. The magnitude of the field strength can be characterized by voltage measurement. EMVco uses the following test method to measure the field strength of the PICC in the PCD working field; Step 9: System Noise Debugging 9.1: Register 02h bit4 rx_man is selected as 1 "Manual channel selection" to improve the accuracy of card reading; 9.2: Reduce the first stage receiver gain register 0Ch bit7-5; 9.3: Enable the second and third level AGC and Squelch functions; Step 10: Modulation depth debugging Step 11: Magnetic protection.

2. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The recommended antenna inductance range described in step 1 is 500nHˉ1000nH, the self-resonant frequency is preferably higher than 80MHz, and the recommended number of coil turns is 1-3. After adding a parallel resistor or a series resistor to the antenna to reduce the Q value, the antenna Q value is recommended to be adjusted to 30.

3. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The inductor mentioned in step 3 should be 56nH-1000nH. You must choose a winding inductor with a rated current of at least 250mA.

4. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The recommended antenna Q value in step 4 is 20, and the EMV demo recommends an antenna Q value of 30.

5. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The mark point of the Smith graph in step six is ​​13.56 MHz. By adjusting the parallel capacitor at the antenna end and the EMC low-pass filter circuit, the position and size of the graph can be changed. If the position of the mark point falls on the real axis and the impedance is 10-20Ω, it is considered that the impedance matching has been completed.

6. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: As described in step 7, if the waveform has overshoot, the overshoot phenomenon can be solved by adjusting the EMC filter inductance and capacitance values, adjusting the external impedance to make the resonance reach 13.56MHz, and adjusting the Q value to less than 30.

7. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: When the receiving register in step nine is set to 0, the gain is fully open at 15dB. When it is set to 1-6, the gain is reduced by 2.5dB per step. When it is set to 7, the gain is 15+5.5dB.

8. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The adjustment of the modulation depth in step 10 needs to ensure that the value of the output impedance configuration register remains unchanged. Changes to the output impedance configuration register require re-adjustment of the modulation depth.

9. The debugging method for improving the performance of contactless card reading according to claim 1, characterized in that: The magnetic conductive protection described in step eleven uses non-metallic magnetic materials to protect the antenna in a metal environment.

10. A debugging method for improving the performance of contactless card reading according to claim 9, characterized in that: The non-metallic magnetic material uses ferrite.

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