The application of radio frequency identification (RFID) has become more and more extensive, and the electromagnetic interference (EMI) problem of RFID has also attracted people's attention. This paper only introduces and analyzes the EMI problem of inductively coupled non-contact IC card in combination with relevant international standards.
introductionRadio frequency identification (RFID) technology has developed rapidly in recent years and has been widely used. However, as a kind of radio frequency technology, its electromagnetic compatibility (EMC) performance has also received more and more attention. RFID covers a wide range of frequencies, including multiple frequency bands below 135 kHz, 13.56 MHz, 433 MHz, 860-960 MHz, 2.45 GHz, and 5.8 GHz. This paper only introduces and analyzes the electromagnetic interference (EMI) problem of inductively coupled non-contact RFID cards in the two frequency bands below 135 kHz and 13.56 MHz in combination with relevant international standards.
1 Electromagnetic compatibility of electronic products
Q1-1, what is electromagnetic compatibility?
Electromagnetic compatibility of electronic products EMC includes two aspects: one is electromagnetic interference EMI, and the other is anti-electromagnetic interference capability EMS. EMI refers to any electromagnetic effect produced by an electronic product that may degrade the performance of other devices, equipment, systems, or may have adverse effects on organisms and substances. EMS refers to the ability of electronic products to resist deterioration in an electromagnetic environment.
Q1-2. Is there a limit to EMI for electronic products?
Electronic products EMI are strictly limited and are reflected in many international standards and related national standards. Representative institutions and organizations that develop these standards are: International Radio Interference Special Committee CISPR, International Organization for Standardization ISO, International Electrotechnical Commission IEC, Federal Communications Commission FCC, European Telecommunications Standards Institute EISI, etc. An electronic product must comply with the relevant EMI standards or it cannot be sold and used in the region or country.
2 Operating frequency range and standard
What is the operating frequency range and standard of the Q2-1 inductively coupled contactless IC card?
In general, inductively coupled non-contact IC cards operate at frequencies below 135 kHz and 13.56 MHz.
(1) The frequency of 135 kHz is mainly suitable for lower cost response tag chips. The system's readers can provide higher power. This band has a high penetration depth for non-metallic materials and water, so it has a wide range of applications in biometrics, water meters and other fields. Due to its low carrier frequency, although the power consumption of the transponder is low, the data transmission rate is not high. Currently, ISO/IEC 18000-2 gives the air interface standard for such systems.
(2) The non-contact IC card at 13.56 MHz can be further divided into a near-coupled IC card (PICC) and a loosely coupled card (VICC). Its readers are also known as PCD and VCD.
13.56MHz is the worldwide industrial, scientific and medical frequency band (ISM). RFID operating in this frequency band can use a microprocessor in the transponder because of the high carrier frequency, so that the smart contactless IC card function can be realized. In addition, at this carrier frequency, the antenna loop of the transponder can realize the resonant circuit of the on-chip capacitor and the printed inductor, which is very convenient for its application.
The main standards for 13.56MHz radio frequency identification are: 1ISO/IEC 14443, which is the standard for near-coupling IC card system. It is divided into TYPE A and TYPE B; 2ISO/IEC 15693, which is the standard for the loosely coupled IC card system; 3ISO /IEC18000-3 standard, it has two modes, namely MODE 1 and MODE 2, MODE 1 and ISO/IEC 15693 standards are compatible, and MODE 2 gives new methods such as phase jitter modulation (PJM).
3 EMI standards for non-contact IC cards
What is the EMI standard for Q3-1 and non-contact IC cards below 135 kHz?
In the non-contact IC card below 135 kHz, more chips are used at 125 kHz. The power amplifier of the reader circuit is a class B or class D circuit, and an antenna transmitter with an inductive loop is adopted, which belongs to low power and micro power transmission. For RFID systems in this frequency range, the following specifications apply:
Allow maximum field strength:
(1) FCC standard
Section 15 of Section F of the FCC Standard (FCC part 15.209) specifies the allowable field strength of its carrier, given by the maximum electric field strength E, ie E is not greater than (2400/f)? V/m@300m. Among them: f is 9~490kHz, @300m means the distance is 300m. Therefore, for a frequency of 125 kHz, its E should be no greater than 19.2 μV/m @ 300 m. If it is converted to dBμV, E = 19.2 mV/m is E = 20 log (19.2 / 1) = 25.66 dBμV / m.
(2) Other standards
In other standards, the maximum field strength allowed is given in the H field. For example EN300330 and the German standard 17TR2100. The values ​​of the E field and the H field can be estimated by the following equation: H[dBμA/m]=E[dBμV/m]-51.5dB. In the 17TR2100, the specified limit is H = 13.5dBμA/m@30m. Convert this value to the above equation to get E=65 dBμV/m@30m.
If we convert the 300m distance of the FCC standard to 30m and increase by 40dB/ten times (the attenuation value of the free field), 25.66dBμV/m@300m can be expressed as 65.66dBμV/m@30m. From the above calculations, the limits of the two standards are similar. If this is expressed as a field value at 10 m, then about 40 log (30/10) + 13.5 = 32.5 dBμA/m can be obtained.
Q3-2. What is the modulation bandwidth and spurious emissions?
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