Design and Implementation of Antenna and Card Power Supply in RF Card
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Non-contact IC card, also known as RF card, is a new technology developed in the world in recent years. It successfully combines RFID technology and IC card technology to solve passive (no power in card) and free Touch this puzzle. The function modules and principles inside the MIFARE 1 RF card are shown in Figure 1 below. 
Since the card itself has no power supply, it needs to pass through the power generation circuit therein to rectify, filter, and stabilize the core. The function of each block in the digital part of the chip circuit is: reset response circuit - automatically transmits the relevant information of the card to the reader when the reader performs power-on reset on the IC card, so that the reader correctly recognizes the Ic card. Type and act accordingly. Anti-collision circuit When there are multiple cards in the working range of the reader, the reader first selects one of the many cards as the object to be processed in the next step, and puts the unselected card into the suspended state to wait for the next time. be chosen. Application Selection circuit - MIFARE l can be "one card multi-purpose", which is responsible for selecting the desired application from the storage area. The authentication and access control circuitry verifies the password and access rights to control access to the EEPROM. The control and arithmetic unit pair card system performs configuration, control, and addition and subtraction of data in the card. The encryption unit encrypts and decrypts a pair of communication data. The EEPROM interface circuit performs decoding, reading and writing, and the like on a pair of EEP-ROMs. EEPROM - Stores data.
1.1 RF card design principle
The MIFARE 1 (M1) type RF card has a capacity of 8K bits, and the data retention period is 10 years. It can be rewritten 100,000 times and read unlimited times. The M1 card has no power supply and has its own antenna. It contains encryption control logic circuit and communication logic circuit. The communication between the card and the reader adopts the international DES and RES secret cross algorithm, which has extremely high security performance.
Working principle: The card is composed of only one antenna and ASIC in the electrical part, there is no other external device; Antenna: The antenna of the card is only a few sets of winding coils, which is suitable for packaging into ISO cards; ASIC: ASIC of card A high-speed (106KB baud rate) interface consists of a control unit and an 8K-bit EEPROM.
The working principle of the M1 RF card is: the reader sends a set of electromagnetic waves of fixed frequency to the Ml card, and the card has an LC series resonant circuit whose frequency is the same as the frequency of the reader, and the LC resonance is excited by the electromagnetic wave. The circuit generates resonance, so that there is a charge in the capacitor. At the other end of the capacitor, a single-pass electronic pump is connected, and the charge in the capacitor is sent to another capacitor for storage. When the accumulated charge reaches 2V. When used, this capacitor can be used as a power supply to supply operating voltages to other circuits, to transmit data from the card or to access data from the reader.
1.2 Design and application of RF card power generation circuit
The function of the RF card consists of two parts, a radio frequency interface circuit and a digital circuit. Solving the source of the card's energy and the wireless transmission of the signal is a prominent advantage of the RF card, and this is also the key technology of the RF interface circuit. The RF signal transmitted from the card reader can be DC-operated by the three processes of coupling, rectification, filtering and voltage regulation in the card.
1.2.1 Coupling. L1 and L2 are the primary and secondary coils of the antenna, respectively. L2 couples high-frequency electromagnetic waves of a certain energy from L1 (carrier frequency is 13.56 MHz), and the voltage at both ends is the received high-frequency signal.
For the in-card receiving antenna L2, at the frequency of f=13.56 MHz, there is an equivalent inductance, capacitance and loss resistance value, which constitutes a series resonant circuit.
For the card reader itself, the electromagnetic wave energy emitted by it is constant, and the induced voltage on the card is determined by the energy of the emitted electromagnetic wave and the distance between the card and the card reader. Then, after obtaining the equivalent inductance, capacitance and loss resistance value of the inductor L2, it is possible to calculate the L2 by changing the distance between the card and the card reader and testing the corresponding voltage value on the resistor by changing the resistance of the inductor L2 and the variable resistor. The value of the equivalent voltage source sensed on it.
1.2.2 Rectifier filtering. The coupling voltage obtained on the antenna is sent to the FWR full-wave rectification circuit through C, thereby obtaining a single-sided AC signal. The high-frequency signal is filtered by the filter capacitor CP, and the voltage outputted at both ends is the DC power supply voltage required in the card; the capacitor is also used as an energy storage device to compete for load. Here, the signal can be obtained as a DC voltage after the filter capacitor, but at this time the voltage is not stable enough, and voltage regulation measures should be taken.
1.2.3 voltage regulator circuit. The VDD outputted at both ends of the filter capacitor CP is unstable. When the distance between the card and the card reader changes, it changes with the voltage coupled to the coil E in the card.
The voltage circuit can stabilize it at around 3.5V. Here, the voltage drop of 3.5V is provided by several series connected saturated MOS transistors. The Rload in Figure 1 represents the sum of the internal resistances of all the circuits in the card. Thus, for the electromagnetic field energy under normal working conditions, the power generation circuit can obtain about 3.5V after Rload=910Ω through the above process. DC operating voltage. The specific voltage regulator circuit is shown in Figure 2. 
1.3 Conclusion
1.3.1 When the on-chip resistance is 910Ω and the capacitance is 500PF, when the distance between the card and the reader is 5CM, 6CM, 10CM, the output voltage can reach 3.5V, there is fluctuation of about 02V, and it has good stability. .
1.3.2 When the distance is 5CM, change the on-chip capacitance, take 200PF, 500PF, IO00PF respectively, and the stability of the output voltage increases with the increase of the capacitance.
1.3.3 Fixed on-chip capacitance is 500PF, change the input power Vip value, that is, the change of analog output voltage VDD with the change of distance d. When Vip is lower than 4.5V, VDD is 2.8V lower, which can not maintain the normal operation of the circuit, so Vip should be higher than 4.5V; with Vip rising, VDD is slightly raised, basically stable at about 3.5V. However, the stability of the power supply is deteriorated.
In summary, within the normal working distance of the card reader within 5-10CM, the power generating circuit can provide the 3.5V DC voltage required for the normal operation of the card internal circuit, and solve the continuous stable voltage source circuit in the card. Design needs, have practical significance.
2 conclusion
RF card technology is a combination of RF technology, low-power technology, packaging technology, information security technology and modern microcomputer technology. It is a new-generation high-tech product with invaluable application value and application prospects. We should strengthen the development and application of RF cards. Under the guidance of China's gold card project, gradually implement unified standards and unified management, which will enable RF cards to develop healthier and more rapidly.
About the Author:
Xinzhongxin Electronics Co., Ltd., Heilongjiang Harbin Bajinguo Jiangmin Harbin Second Construction Engineering Company, Heilongjiang Harbin Penghai