Analysis of RFID card reader application examples based on GW Instek spectrum analyzer detection

1. About RFID

RFID is the abbreviation of Radio Frequency Identification, which is a contactless automatic recognition technology that automatically identifies target objects and obtains relevant data through radio frequency signals. The recognition work does not require human intervention. It can identify high-speed moving objects and can identify multiple tags at the same time.

The most basic RFID system consists of three parts: reader, electronic tag (Tag) or transponder and antenna. Its working principle is that the reader transmits a radio wave energy of a specific frequency to the transponder to drive the transponder circuit to send out the internal data. At this time, the reader receives and interprets the data in sequence and sends it to the application for corresponding processing. There are two types of coupling of radio frequency signals between the reader and the transponder.

(1) Inductive coupling. The transformer model realizes coupling through high-frequency alternating magnetic field in space, based on the law of electromagnetic induction. Inductive coupling is generally suitable for short-range radio frequency identification systems operating at medium and low frequencies. Typical operating frequencies are: 125kHz, 225kHz and 13.56MHz. The identification range is less than 1m, and the typical range is 10 to 20 cra.

(2) Electromagnetic backscatter coupling: Radar principle model, the electromagnetic wave emitted, reflected after hitting the target, and at the same time carrying back the target information, is based on the spatial propagation law of electromagnetic waves. Electromagnetic backscatter coupling is generally suitable for long-distance radio frequency identification systems working at high frequencies and microwaves. Typical operating frequencies are: 433MHz, 915MHz, 2.45GHz , 5.8GHz. The identification range is greater than 1m, and the typical range is 3-10m.

The reader can be a read or read/write device according to the structure and technology used. It is the information control and processing center of the RFID system. The reader is usually composed of a coupling module, a transceiver module, a control module and an interface unit. The reader and the tag generally use half-duplex communication to exchange information. At the same time, the reader provides energy and timing to the passive transponder through coupling. In practical applications, the management functions such as the collection, processing and remote transmission of object identification information can be further realized through Ethernet or WLAN.

2. Connection Example

The example uses the universal second-generation resident ID card verification device of Shandong Shensi Electronics, and needs to measure the working frequency and transmission power of the card reader. Since the card reader continuously transmits RF into space when working, the signal of the card reader can be directly measured by using a spectrum analyzer and a common RF antenna. In order to avoid the influence of spatial noise, a circular near-field antenna can be used. Connect the loop antenna to the RF input terminal of the spectrum analyzer (as shown in Figure 1), and then place the receiving end of the loop antenna close to the sensing area of ​​the card reader (as shown in Figure 2), thus forming a simple and easy RFID reader test system.

figure 1

figure 2

3. Signal capture and measurement

Set the GSP-830 center measurement frequency to 13.56MHz, Span 5MHz, reference level 20dBm, RBW automatic (30KHz), cursor 1 on, Trace B real-time update, and limit line off.

When the second-generation ID card is not placed on the card reader (the card reader does not read the card), the card reader continuously transmits a 13.56MHz, 15dBm RF signal into space, as shown by the red curve in Figure 3. The RF signal can also be observed with an oscilloscope, as shown in Figure 4.

image 3

Figure 4

When the second-generation ID card (Tag) is placed in the card reader's sensing area, the Tag senses the electromagnetic field of the card reader's RF transmission signal, and returns the information stored in the chip to the card reader with the energy obtained by the induced current. The return signal is a double-sideband modulation signal with a carrier of 13.56MHz. After the card reader reads and decodes the information, it is sent to the central information system for relevant data processing, and the reading speed is once per second.

The GSP-830 spectrum analyzer can also measure the return signal of the tag. The antenna coupling method is shown in Figure 1 and Figure 2. The spectrum analyzer center frequency is set to 13.56MHz, Span 5MHz, reference level 20dBm, RBW automatic (30KHz), Trace A peak hold. The captured tag return signal is shown in the green curve in Figure 3. The frequencies of the two sidebands are 12.7MHz and 14.4MHz respectively.

4. Conclusion

The above application example of using Goodwill spectrum analyzer to detect RFID card readers is also a universal detection solution, which can be widely used in many aspects such as debugging during the development of RFID card readers and active electronic tags, and inspection of production lines.

Since RFID itself has a very broad range of applications, such as logistics and supply management, manufacturing and assembly, airline baggage handling, mail/express package handling, commercial POS machines, document tracking/library management, animal identification, sports timing, access control/electronic tickets, automatic road toll collection, etc., the application prospects of this test solution are also very promising.