Portable RFID RFID reader in the design and implementation (1)

Radio frequency identification (RFlD) is a non-contact automatic identification technology, its basic principle is to use RF signal and spatial coupling and transmission characteristics of static or automatic recognition of moving objects.

A radio frequency identification systems typically include RFID tag, the reader and the host of several parts. Currently applied to the UHF RFID reader less, and the whole machine is expensive, bulky, need external antennas or antenna arrays, not easy to carry and more cannot stand-alone work. The aim of this design to hardware costs as low as possible for an approach based on ISO/IEC18000-6B standard portable RFID reader and software upgrades to support other standards or standards.

1, theoretical analysis

RFID systems work, the first reader launches a specific step in the process.

Ask the signal, when the radio frequency labels after induction into this signal, it will give the phase 2 reader hardware design should answer signal; the reader receives this response signals processed and returned to the external host or carry out the operation.

This article implements the reader contains RF transceiver modules and digital baseband processing modules, including RF transceiver modules also include RF transmitters and RF Receiver in two parts, the overall structure as shown in Figure 1.

System in the work of first generation digital baseband processing module needs to be sent to the RFID tag, and then asking signal by radio-frequency transmitter will this signal is converted into a radio frequency signal transmission.

Radio frequency labels receive this signal, will give out the corresponding answer signal, ECHO.

The echo signal is received by the RF Receiver and processed, converted into a digital signal to digital baseband module for further processing.

2. reader hardware design

As mentioned earlier, this reader hardware including RF transceiver modules, returned to the external host or to the appropriate operation.

Block and digital baseband processing modules, including RF transceiver module including RF transmitters and RF Receiver, and the overall structure as shown in Figure 1. The choice of the system architecture, this reader to reduce costs as the main target, RF transmitters and RF receiver uses a zero-if architecture, to a large extent reduces the required devices; digital baseband processing module using a microcontroller-based structure, without using high-speed DSP, it saves certain costs.

2.1 RF transmitter

Transmitter circuits include crystal oscillator, frequency synthesizer, power splitter, ASK modulator, power amplifier (PA), as well as the transmitting antenna, etc.

This design, frequency synthesizer with integrated chip S14133, this is a programmable PLL digital programming, you can control its output frequency.

It is through this performance, the system in a 960MHz 860MHz frequency range of frequency hopping, avoiding in-band interference from other signals. By S14133 output RF carrier through a power splitter, all the way to the receiver as a local oscillator signal LO, another way is to ASK modulator. Here ASK modulator using a structure very simple chip HMCl95, it can be simplified into a high-speed switch, by the need to send digital signals to control the on/off, modulating the carrier to complete. By modulation of the carrier by the power amplifier, finally sent to the antenna transmitting out.

In view of the actual work required, there is no use of high-performance power amplifiers, instead of using a cheap buffer amplifier chip AG503, its output power up to 17dBm, i.e. O.05W.

The antenna also adopts very simple PCB printed dipole antenna, no need to add. At this point the reader working distance of up to 80cm. Due to the carrier in the near distance attenuation of free space and communication distance proportional to the square approximation to, so you can calculate the equivalent when the transmitter power (EIRP) reached 36dBm, 4W, reader working distance you can reach 7m.

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