In recent years, there have been more and more smartphone models equipped with NFC functions. Therefore, this time we will introduce NFC.
NFC (Near Field Communication) is a short-range wireless communication function that enables communication in a short distance of a few centimeters close to a device that also has an NFC function. Compared with other wireless communication such as Bluetooth and WiFi, NFC has a slower data transmission speed for small data transmission. In fact, NFC is also used for smartphones, payment services on wearable device terminals, WiFi settings, Bluetooth pairing settings.
In a circuit that functions as an NFC, an inductor is indispensable. The necessary characteristics and products of the inductor used in the NFC circuit are described below.
1 Necessary characteristics of NFC inductors
The ANFC circuit is composed of an NFC IC, an LC filter, a matching circuit, and an antenna.
Figure 1. Composition of the NFC circuit
The LC filter has a low-pass filter that removes high-frequency components that are not required for communication from the signals emitted by the IC. However, since the matching circuit in the latter stage is close to the circuit, the constant of the LC filter has an influence on the matching. Therefore, the inductance value of the inductor used on the LC filter is required to have a narrow tolerance. Similarly, it is also desirable that the inductance value of the inductor used for the LC filter does not depend on the current value.
In addition, since components in the circuit generate losses, the inductor is required to have low loss in order not to cause unnecessary power loss. Specifically, since the 13.56 MHz AC current flows in the NFC circuit, it is important that the ACR*1 of the frequency is low.
*1 ACR (AC resistance)
2 Introduction to NFC inductors: LQW, LQM series
The inductors that can be used in NFC circuits are described below: LQW18CN series, LQW15CN series, LQM18JN series.
As the current value of the inductor changes, the inductance value also changes. As shown in Figure 2, the LQW18CN series has very little dependence on the inductance of the AC current. Therefore, even if the AC current flowing through the NFC circuit becomes large, the characteristics do not greatly change. In addition, as shown in Figure 3, low ACR can be maintained even with high currents.
Figure 2. Inductance - AC current (Irms) characteristics
Figure 3. AC Impedance - AC Current Characteristics
The LQW15CN series is a compact product of the LQW18CN series. A new magnetically shielded LQM18JN series is also available.
For details of LQW18CN, please click here to confirm. For details of LQW15CN, please click here to confirm. For details of LQM18JN, please click here to confirm.
3 unbalanced circuit NFC
When it comes to NFC circuits, it is generally the balance circuit of Figure 1, as well as the case of connecting unbalanced circuits as shown in Figure 4. At this point, a balun is required between the matching circuit and the antenna for balanced-unbalanced conversion. The balun that can be used here has the DXW21BN series. The DXW21BN series can be used for floating type and transformer type, but in fact, the transformer type is often used in the NFC circuit.
DXW21BN Please click here to confirm.
Figure 4. Circuit composition when connecting an unbalanced circuit
Tianma Microelectronics Co.,Ltd., founded in 1983, is a high-tech enterprise specializing in the production and operation of liquid crystal display (LCD) and liquid crystal display module (LCM). After more than 30 years of development, has developed into a set of LCD research and development, design, production, sales and service as one of the large public listed companies. Tianma of Shenzhen, Tianma of Shanghai, Tianma of Chengdu, Tianma of Wuhan, Tianma of Xiamen, Tianma of Europe, Tianma of the United States, Tianma of South Korea, etc. STN-LCD, CSTN-LCD, TFT-LCD and CF production lines and module factories. The company's marketing network throughout the world, products are widely used in mobile phones, MP3/MP4, on-board display, instrumentation, household appliances and other fields. In terms of technical level, product quality, product grade and market share, it ranks among the top in the same industry in China and has become a leading enterprise in the field of small and medium-sized display.
The company is mainly engaged in the design, manufacture and sales of LCD and related materials, equipment and products, providing related technology development, technical consultation, technical services and technology transfer, and engaged in the import and export of goods and technology. Specializing in LCD screen and module design, research and development, manufacturing, sales and after-sales service. Production used for LCD, laptop, LCD TV, digital video and audio, car GPS, industrial medical products and other models of display screen and module. Products are widely used in mobile terminals, car display, aviation display, industrial control medical, entertainment display and other small and medium-sized display fields.
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