An electronic tag to read the study and design of the Terminal (1)

Electronic tags and reading terminal is an RFID system.

This article on low-frequency RFID tag and Reader roles between terminal base, conducted a study on analysis, accordingly to the base station chip EM4095 to RF interface for reading terminal hardware design, and decoding program design specific key issues.

1 Introduction

Radio frequency identification (RF ID) is the use of wireless mode on electronic data carriers (RFID) for identification of an emerging technology.

And contactless Ic card and barcode recognition, System comparison, it has a huge advantage. Use of radio frequency identification technology, can enable large quantities, the regional distribution of information and intelligence to achieve the purpose of high efficiency and fast operation, especially in logistics, transportation, shipping, automatic charges, service areas, and so has a broad application prospects.

For a working frequency for 100kHz 150kHz electronic tag EM4100. presented its reading terminal design.

2 passive RF chip EM4100 work base Li

EM4100 series for micro-and low-power electronic tag chips, operating frequency range 100kHz ~ 150kHz, main clock and the power is taken from the reader launch signal.

As receiving antenna coil and micro-chip connection and packaged together. Internal simulation circuit module and most digital module 2. Simulation module including: a full-wave rectifier circuit, clock reference circuit, modulation circuit; digital modules include: sequence generator, read-only memory. data encoder.

Passive RFID tag and Reader roles between distance meet relations r << λ (wavelength), depending on antenna theory, belongs to the near-field antenna (i.e. the induction field).

Therefore, RFID tag antennas and reading terminal antenna is based on the principle of electromagnetic induction, equivalent circuit shown in Figure 1. Of these, Ll-reader antenna inductance, L2 as electronic tag coil inductance, R2 is the internal resistance of the coil electronic label, R L e-label of the equivalent load resonant circuit.

Mutual inductance M in L2 on the voltage as L2 circuit of signal source, by the equivalent circuit can be loop output voltage expression:

Other things being equal, if reading terminal emission of the signal frequency and the resonant frequency resonant circuit () equal, then the maximum output voltage; deviation from the resonant frequency, voltage will quickly reduce.

Harmonic signals through rectifier filtering as a piece of work, when the voltage value reached EM4100, chip startup work. The resonant circuit output voltage value depends on the Q value, alternating magnetic field strength and frequency. Obviously, the RFID tag and the distance between the reading terminal directly impacts the value of the voltage.

In the clock recovery circuit from coil induction signal extraction of the main clock, sequence generator produces memory addressing, data serial output control, data coding control signal.

Chip storage has unique 64bit code: 9bit start bit, 40bit information bits, lbit 14bit parity, stop bits. Code via encoded control modulator of current switch. realization of f0 = 125kHz carrier for am. Each bit data width and carrier cycle ratio have 3 choices: 64, 32, 16. Data signal control portable antenna load connected and disconnected from the reader antenna. voltage will follow changes, is actually a transponder (RFID) data on the reader antenna voltage amplitude modulation, transponder data transmission to the reader. This is the so-called load modulation. Effective role in reading terminal, electronic tags within the loop send realizing 64bit code data, data transmission to the reading terminal.

3 reading terminal hardware system design

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