Design of Integrated EMI Filtering and ESD Protection Scheme Based on Portable Equipment

Today's mobile phones and other portable devices are becoming smaller and thinner. At the same time, they are integrating more and more new functions or features, such as large-size display screen, high-resolution camera module, high-speed data interface, Internet access, TV reception, etc., making the data rate and clock frequency of portable devices higher and higher. In this way, portable devices are faced with many potential electromagnetic interference (EMI) / radio frequency interference (RFI) sources, such as switching load, power supply voltage fluctuation, short circuit, inductive switch, lightning, switching power supply, RF amplifier and power amplifier, interconnection between ribbon cable and video display screen, high-frequency noise of clock signal, etc. Therefore, designers need to select a suitable EMI / RFI filtering scheme for portable devices according to multiple locations such as audio jack / headset, USB port, speaker, keyboard, microphone, camera and display interconnection.

For EMI / RFI filters, from the perspective of architecture, the most common architecture is "Pi" filter. As the name suggests, this architecture is similar to the Greek letter "". There are two common type filters: c-r-c (capacitance resistance capacitance) filter and c-l-c (capacitance inductance capacitance) filter. Among them, c-r-c filter (see Figure 1a) is also known as RC - filter or RC filter, which is used for audio and low-speed data filtering applications; C-l-c filter (see Fig. 1b) is also called LC - filter or LC filter, which is used for audio, low-speed and high-speed data filtering applications.

filter also has an expansion type, that is, ladder shaped filter. The most common is LC (inductance capacitance) ladder filter (see Fig. 1c). This filter bears higher data rate, but when the filter elements (inductance or capacitance) increase, the size and cost will become a problem, resulting in higher material cost and larger packaging.

Figure 1: structural diagram of common EMI / RFI filter types: a) type RC; b) type LC; c) LC ladder.

Among these types of EMI / RFI filters, from the comparison of frequency amplitude response, type RC filter has the widest transition band and the lowest rolloff; - type LC filter has low turning rate but moderate transition band; Trapezoidal filter can achieve very high turning rate and narrow transition bandwidth.

In terms of EMI / RFI filtering, taking mobile phone applications as an example, a traditional reference frequency is 800 MHz, because 800 MHz is close to the starting frequency of the frequency band used by mobile phones. In most cases, mobile phone design engineers require filtering at frequencies above 800 MHz, which generally means a minimum signal attenuation of 30 dB. With the increase of functions in mobile phones and the classification of clock and data signals, the reference frequency is decreasing. Many portable electronics manufacturers require EMI / RFI filtering at 400 MHz and may require EMI / RFI filtering at lower frequencies in the future.

Integrated EMI filtering and ESD protection

In portable products, the filter is generally located adjacent to the connection port, microphone and speaker. These locations may also face electrostatic discharge (ESD) events. Taking the audio line as an example, if the discrete component scheme is adopted for EMI filtering and ESD protection respectively, the number of components required to perform these two functions will be faced. For EMI filter, if a discrete type LC filter is used, two surface mount capacitors and one surface mount inductor are required. In order to provide ESD protection, an additional type of surface mount transient voltage suppressor (TVS) diode needs to be added. In this way, EMI filtering and ESD protection of an audio line require four independent components. The precious space of portable devices occupied by these components has not been mentioned here. If there is more than one audio line, it is more impractical to adopt the discrete component scheme.

Therefore, the simplest solution is to integrate EMI filtering and ESD protection functions in the same element. Firstly, the integrated TVS diode in the integration scheme also provides the capacitance required for EMI filtering; Secondly, improving the process technology can also greatly improve the quality of integrated inductors. By integrating these integrated components into the silicon wafer, the original scheme that requires multiple independent components can adopt the integrated EMI filtering ESD protection scheme (see Figure 2).

Among them, in terms of ESD protection level, IEC61000-4-2 standard specifies the system level test conditions and protection levels in detail, which are divided into four types. Portable applications usually need level 4 protection, that is, under the IEC61000-4-2 test conditions of 8 kV contact discharge or 15 kV air discharge, portable equipment needs to be able to withstand the impact of ESD events.

In general, by cost-effective integration of EMI filtering and ESD protection, portable application designers can reduce costs, reduce the number of bill of materials (BOM) components, and reduce the space occupied by circuit boards.

EMI filtering ESD protection scheme for specific application of portable equipment

In the portable device market, mobile phones occupy an important position. Naturally, many locations in the mobile phone will be applied to filters with integrated ESD protection. For mobile phone applications, in addition to LC and RC filters, there are common mode choke EMI filters, which help reduce parasitic inductance and provide better common mode filtering. The type bandwidth spectrum of these mobile phone filters is shown in Figure 3.

Figure 3: bandwidth spectrum of mobile phone filter type.

Different mobile phone applications need different filters. Generally speaking, the higher the data rate of the application, the smaller the total capacitance of the filter line. For mobile phone applications with relatively low data rate such as audio lines, the standard capacitance of EMI filter in the range of hundreds of PF is enough to provide excellent filtering performance and minimum signal interference.

Among them, in audio applications such as speakers, microphones, audio jacks / headphones, LC or RC filters can be selected, such as nuf2441fct1g, nuf2450mut1g, nuf2114mnt1g, nuf2116mnt1g and nuf420mnt1g of ansenmey semiconductor. These filters are integrated with ESD protection function to protect 2 to 4 audio lines, and the diode capacitance is between tens of PF and 240 PF. Taking nuf2441fc as an example, this LC filter provides EMI filtering and IEC61000-4-2 level 4 ESD protection functions for two audio lines. It is encapsulated by flip chip, and a single IC replaces two inductors, four capacitors and four TVs diodes to help save cost and reduce the occupied space of the circuit board.

Nuf2450mut1g is also a two-wire LC type EMI filter and ESD protection device, providing attenuation greater than - 30 dB in the frequency range of 800 MHz to 5.0 GHz; This device uses space saving udfn 1.2 one point eight The 0.5mm ultra small package provides a 20 MHz cut-off frequency and minimal line impedance, which is ideal for audio applications requiring low bandpass attenuation. Nuf2114mnt1g is a two-wire RC type EMI filter and ESD protection device. It is packaged in dfn8 and provides attenuation greater than - 30 dB at the frequency of 900 MHz to 3.0 GHz. It also replaces up to 10 discrete components with a single IC to help reduce cost and save space.

In mobile phone applications, the bandwidth of data lines such as display screen and camera is higher than that of audio, and RC filter can be used. For example, ansenmey semiconductor adopts a series of devices such as nuf40xx, nuf60xx and nuf80xx encapsulated by udfn. In addition, ansenmey semiconductor also launched X3 series RC filters in very small wdfn / udfn packages for data line filtering applications, including nuf4310mn and nuf4110mn. This new series of 4-channel RC filters has a line capacitance of only 17 pf at 2.5 V and integrates 40 discrete components to provide a very small footprint (1.0 one point four 0.75 mm/1.0 one point six 0.75 mm), extremely low impedance (100 ) and industry-leading ESD protection (IEC61000-4-2 level 4), supporting up to 120 Mbps bandwidth, suitable for high-resolution camera module and display screen of portable products such as mobile phone, mobile interconnection device (MID), portable media player (PMP), digital camera, laptop or netbook.

In the above data applications such as high-resolution display screen of mobile phone and camera interface, high-speed LC filter can also be used, such as nuf2900mn of ansenmey semiconductor. Compared with the traditional RC filter, the high-speed LC filter has higher cut-off frequency, greater broadband attenuation and lower insertion loss. For example, the typical cut-off frequency of nuf2900mn is 350 MHz, which provides attenuation greater than - 30 dB at frequencies from 800 MHz to 6.0 GHz, and the insertion loss performance is also more advantageous. See Figure 4.

Figure 4: comparison of response performance between typical RC EMI filter and high-speed LC EMI filter (nuf2900).

It is worth mentioning that there are more and more high bandwidth applications in mobile phones, with larger display size, higher resolution and limited space, which promote the conversion of parallel data to serial data. The solution is to use low-voltage differential signaling (LVDS) to serial MDDI, MPPI, USB 2.0 and userdes data, and adopt common mode choke (CMC) EMI / RFI filter accordingly, Through the high bandwidth differential signal, the unwanted common mode EMI / RFI signal is filtered at the same time. In this regard, the nuc2401mn high-speed serial data filter of ansenmey semiconductor can be used. This is the industry's first CMC filter integrating ultra-low capacitance (0.8 PF) ESD protection and common mode filtering technology, using a small 2.0 In 2.2 mm DFN package, a single element is suitable for a variety of high-speed designs such as USB2.0 (480 Mbps), IEEE1394 (400 Mbps), MDDI (up to 550 Mbps), Mipi (up to 1.0 Gbps) and HDMI 1.2 (up to 1.32 Gbps per channel), eliminating common mode noise and providing pure data stream for these applications.

Figure 5: integrated CMC filter nuf2401mn with ultra-low Capacitance ESD protection for high-speed applications such as USB2.0.

It is worth mentioning that nuc2401mn provides better ESD clamping performance compared with silicon competitive devices with a capacitance of less than 1 PF. It is very suitable for EMI filtering and ESD protection applications of high-speed data lines.

summary

With the improvement of data rate and clock frequency, portable devices such as mobile phones increasingly need high-performance EMI filtering and ESD protection schemes. Ansenmey Semiconductor provides a new integrated EMI filter. While providing excellent EMI / RFI filtering performance, it also provides ESD protection function in accordance with IEC61000-4-2 level 4 standard. A single IC replaces 10 or even dozens of discrete components. It is very suitable for audio and data line applications in portable applications such as mobile phones.

Source; Mobile China

Design of Integrated EMI Filtering and ESD Protection Scheme Based on Portable Equipment 1

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What Is the Forming Process of the Flexible Touch Screen
Every day, new products, new experiences, professional membrane switch proofing factory, 12 hour expedited shipmentFrom the hot sale of Samsung Galaxy edge flagship series to the advent of various curved screen bracelets and TVs, it is no doubt that curved screen technology has been widely valued and sought after by consumers and the industry in recent years. In the future, with the continuous development and improvement of fixed curvature curved screen technology, the flexible touch screen that can realize arbitrary bending will become an important development direction. On the 25th, at the 13th International touch screen and display technology development forum, Huang Hanfeng, deputy general manager of touch R & D from Shenzhen oufeiguang technology, made a detailed introduction to the flexible touch screen from the perspective of the industrial chain around the four key elements of flexible display, flexible touch, flexible cover plate and flexible bonding.Flexible displayFor LCD display, the LCD is usually responsible for controlling the display gray, and the three primary color filters control the display color, which requires them to correspond one by one in order to display normally. If the LCD panel is used as a curved screen, the inner circumference and outer circumference will be unequal, and the original one-to-one corresponding liquid crystal and filter will have position deviation, resulting in color distortion. In addition, it will also cause a series of problems such as light leakage, dark screen ghosting and snowflakes. Therefore, for the curved screen, the OLED display technology represented by AMOLED has almost become the best choice.Huang Hanfeng said that at present, Samsung is the undisputed AMOLED overlord in terms of patents, production capacity, yield and technology accumulation. The sixth generation AMOLED panel that began mass production at the end of 2014 can now produce 50000 pieces per month, and the yield can reach 60%. The second is LG, but LG has been focusing on large screen curved TV. At present, with the increasingly obvious trend of small screen AMOLED, LG is also accelerating the layout of small and medium-sized flexible screens. Although its output is not as good as Samsung, its yield can also reach more than 60%. The latest release of Xiaomi note 2 is the flexible AMOLED screen of LG. In addition, Japan's JDI and sharp (already acquired by Hon Hai), Taiwan's Youda, domestic BOE, Rouyu and other screen manufacturers are also accelerating the layout of their own AMOLED technology. It is the general trend for AMOLED to replace LCD.Flexible touchIn terms of touch control, ITO (indium tin oxide) transparent conductive film has become the most important touch layer material for display screens such as non curved LCD and OLED due to its good light transmittance, low thickness, excellent hardness and conductivity, mature manufacturing technology and many other reasons. However, as ITO itself is a brittle material, it is not suitable for making flexible touch layer with large curvature or even free bending, and the cost and cost are high. At present, it accounts for about 30% - 40% of the cost of the upstream material part of the whole touch screen industry, and uses "indium", a rare metal with limited reserves. Therefore, with the advent of the era of curved surface and flexibility, it is likely to be replaced.Huang Hanfeng said that at present, the main substitutes for ITO materials are graphene, carbon nanotubes, nano silver and metal mesh. Graphene and carbon nanotubes are very good substitutes for ITO from the characteristics of the material itself. However, graphene is still in the R & D stage and is still far from mass production. The industrial mass production technology of carbon nanotubes is not perfect, and the conductivity of the thin film products made of carbon nanotubes is not as good as that of ITO. Therefore, from the perspective of technology and marketization, metal grid and nano silver technology will be the protagonists of development in recent years. Metal grid technology has been applied in some PC display markets.The metal mesh technology mentioned here is a conductive metal mesh formed by pressing metal conductive materials such as silver and copper or oxides on thin film substrates such as pet. Its main advantages are low raw material cost and good folding ability. However, due to the problem of Murray interference ripple caused by yield, output and high-speed pixels, it is more suitable for desktop all-in-one computers, laptops, televisions and other products with low resolution and relatively long-distance use.Nano silver technology means that nano silver ink material is coated on pet or glass substrate, and then laser lithography is used to depict the conductive network of nano silver wire. Its main advantages are high yield, small linewidth, good conductivity and folding resistance, while its disadvantage is high cost. Moreover, compared with metal mesh, nano silver material has smaller radius of curvature and small resistance change rate during bending. In addition, due to the linewidth, it is more suitable for high-resolution close-up scenes such as mobile phones, smart watches and bracelets."By comprehensive comparison, I think nano silver has more advantages than metal grid," Huang Hanfeng said.Flexible cover plateIn order to bend at will, in addition to solving the flexible display and flexible touch, the last and most critical part is the flexible cover plate and fitting. However, due to its hard and fragile characteristics, glass cover plate is not the best choice in the field of flexibility.Huang Hanfeng said that compared with glass, pet and PI (polyimide) materials with high surface hardness and high light transmittance are better choices, but at present, pet and PI also have many problems to be solved. On the one hand, they are not resistant to high temperature and have poor light transmittance: pet and PI will have problems of partial melting and property change at low ambient temperature, and they do not have good light transmittance compared with glass.Secondly, it is difficult to achieve a balance between hardness and folding. Huang Hanfeng said that if you want to meet certain hardness requirements, you need to apply the hardened layer, but after coating the hardened layer, after repeated folding, the hardened layer will crack and reduce the hardness. Therefore, how to achieve a balance between the two is the biggest bottleneck at present.Compared with the flexible cover plate that needs further development, the 3D glass cover plate necessary for curved screen mobile phones has a very good development prospect.Some data show that 2018 may become the outbreak year of 3D glass cover plate. It is expected that the mobile phone penetration rate of 3D glass cover plate will exceed 50% around 2020. With the maturity of 3D glass cover plate processing technology and the decline of unit price, the penetration rate will further improve. It is expected that the market scale will reach more than 19 billion yuan in the future.Huang Hanfeng said that the common manufacturing processes of 1R (single radian bending) and 2R cover plates have been basically mature. They basically achieve a bending effect through hot bending technology. The difference is mainly in the coating of hardened layer. However, the yield is a problem to be solved, which is basically only 30%, and there is no room for improvement in the short term. If 4R is to be done in the future, the yield will be lower. Therefore, the yield is one of the urgent problems to be solved in the manufacture of cover plate.Flexible fitAfter the cover plate is selected, it is fitted, that is, the cover plate is integrated with the touch and display layer below to form a complete module. At present, there are two common methods: roller type and vacuum bonding: the roller has high efficiency and needs to roll the pasted object. The efficiency of vacuum type is relatively low, but it does not need to roll the pasted object, so it is not easy to cause damage to the pasted object.Huang Hanfeng said that if the curvature is large, you can only choose vacuum bonding. However, for the possible 4R bonding in the future, due to its special four side bending characteristics, it is difficult to avoid wrinkles and bubbles in places with large radians even if vacuum is adopted. At present, the industry has adopted customized extrusion airbags or plastic parts to alleviate this problem, but it has not been completely solved. Therefore, the industry still has room for progress in multi surface and high curvature fitting technology.Huang Hanfeng frankly said: "from the perspective of the supply chain, it will take several years for the flexible screen to really realize mass production. At the same time, it also needs the upstream and downstream supply chain to jointly overcome the relevant technical problems."For future development, Huang Hanfeng believes that the integration of various modules will be the general trend. He said: "in the incell technology of LCD, ITO touch film and liquid crystal layer are integrated together, which is a good integration. Now the fingerprint module is independent, and it can also be integrated with touch in the future. I think there will be a process of mutual integration and progress between functional modules in the future."
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