Portable product EMI filtering solution

Mobile phones are one of the most popular portable electronic products in recent years. In each mobile phone, there must be at least one SIM (Subscriber Identity Module) card for user identification and storage of data. In the new smart phones, most mobile phone brands have MMC (Multimedia Card)/SD (Secure Digital Storage) cards for storage of photos, phone books, e-mails or short messages. use.

In the normal use state, when the mobile phone SIM card or MMC/SD card is in the process of data transmission, the frequency-multiplied harmonic radiation signal of the basic frequency of the transmission signal (referred to as the fundamental frequency) appears in the communication frequency band of the mobile phone, Causes some degree of interference to the mobile phone RF communication signal.

On the contrary, the radiation generated by the mobile phone RF communication signal is also coupled to the data transmission signal of the SIM card or the MMC/SD card, causing distortion of the signal waveform. If it is serious, it will lead to errors in data transmission.

For SIM card and MMC/SD card applications, Jingyu Technology provides the corresponding electromagnetic interference filters AZM-SIM01-03F and AZM-MMC01-06F, which can solve the above electromagnetic interference problem. Table 1 shows the basic characteristic parameters of the AZM-SIM01-03F and AZM-MMC01-06F EMI filters. Both types of EMI filters are suitable for rated voltage circuits below 5V or 5V. The line capacitance values ​​are 22pF and 24.5pF respectively. When the operating frequency is 1GHz, the insertion loss can reach -20dB and -21.5dB respectively. The electromagnetic interference signal strength is significantly reduced to less than one tenth to maintain the normal operation of the protected circuit.

Table 1: Basic characteristics of the electromagnetic interference filter applied by SIMC Technology to SIM cards and MMC/SD cards.

In terms of electrostatic discharge protection, the transient voltage suppressors in this series have extremely low clamping voltages. AZM-MMC01-06F anti-static protection can be up to 10kV (IEC 61000-4-2, contact mode ±10kV), AZM-SIM01-03F anti-static protection can be as high as 15kV or more (IEC61000-4-2, contact mode ±15kV).

When an electrostatic discharge event (ESD) occurs, the lower the clamp voltage of the transient voltage suppressor, the more instantaneous the electrostatic discharge current can be turned on, so that the protected circuit is permanently protected from electrostatic discharge. Loss of effectiveness. Figure 1 shows the clamp voltage diagrams for the AZM-SIM01-03F and AZM-MMC01-06F products measured using the Transmission Line Pulse Generation System (TLP). It can be clearly seen from the figure that the two kinds of electromagnetic interference filters have a clamp voltage of less than 8.5V under the high electrostatic discharge current of the output line of the transmission line generating system, which can effectively provide a fast protection circuit. An effective electrostatic discharge bypass path.

Figure 1: AZM-SIM01-03F and AZM-MMC01-06F electromagnetic interference filters introduced by Jingsheng Technology: The clamp voltage corresponding to 17A is less than 8.5V.

In addition, according to the specifications established by the IEC 61000-4-2 standard, the fourth-level protection needs to provide at least 8kV of contact discharge mode and 15kV of air discharge mode. This series of products provides electrostatic discharge protection capability of contact discharge mode of 10kV or more, which obviously exceeds the required value specified in the fourth level of IEC 61000-4-2 standard.

Since the portable device needs to rely on the battery to supply the required power, the larger the leakage current when the component is in normal use, the larger the power consumption of the battery and the shorter the power supply time. Figure 2 shows the current-voltage (IV) characteristics of the new AZM-SIM01-03F and AZM-MMC01-06F EMI filters from Jingsheng Technology. As can be seen from the graph, the leakage current of the new EMI filter product is much less than 1uA when the applicable system operating voltage (here, 5V or less), thus prolonging the battery life of portable devices.

Figure 2: AZM-SIM01-03F and AZM-MMC01-06F electromagnetic interference filter products from Jingsheng Technology: The DC leakage current measured by the I/O terminal to ground (GND or VSS) is much less than 1uA.

In terms of packaging, this series of products from Crystal Technology uses a rectangular planar leadless package (DFN) with a 0.4mm pitch. Therefore, in the system design, the board area occupied by the electromagnetic interference filter component can be effectively reduced, the design of other circuit components can be facilitated, and the rework can be easily performed, and the surface mount of the component can be performed. When it is not easy to cause component damage.

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