Application Guide - Common Mode Filter. Common-mode filters with integrated ESD protection for portable devices

Transcription

1 Application Guide - Common Mode Filter Common-mode filters with integrated ESD protection for portable devices

2 Table of contents 1. Two challenges: ESD and EMI Common-mode filters and the future of mobile Filtering and protecting MIPI lines (PCMFxDFN1) Filtering and protecting USB 2.0 (IP3319CX6) A special situation: ESD protection for the SoC 19 2

3 Introduction Protecting portables Today s portable devices use very fast data lines to support displays, cameras, and other interfaces. Advanced processors, wireless features, and high-speed data lines help to maintain high levels of performance in these portable systems, but these features also present certain design challenges. They re susceptible to EMI, can be vulnerable to ESD strikes, and can emit EMI. For these reasons, they require a certain amount of filtering and protection. The block diagrams show how NXP s PCMF family of common-mode filters with integrated ESD protection can improve performance and reduce risk in cell phones and other portable devices. Generic smartphone / tablet computer Tactile keys Display Processor GSM/3G/LTE WiFi Diplexer/Antenna Applications with differential data lines Back Side Camera Front Side Camera ESD protection Common Mode Filter with ESD protection EMI interference Risk of ESD strikes - directly or through gaps in the cabinet

4 The NXP advantage Our common-mode filters with integrated ESD protection are just one small part of what we can do for portable systems. As a recognized leader in portable and mobile applications, we offer a comprehensive portfolio of best-in-class solutions. We have strong partnerships with major handset, computer, and tablet makers, and consistently introduce new technologies that set the standard for performance, efficiency, and size. We are known for reliability, and back all our products with a cost-efficient supply chain and a company-wide commitment to the highest standards in quality. Simply put, our customers gain the confidence that comes from working with a world-class partner. Generic set-top box Tactile keys Processor ESD protection for optional low-speed interfaces HDMI interface This guide This Application guide summarizes key concepts for working with portable systems equipped with differential data lines and introduces how to use our common-mode filters with integrated ESD protection. To learn more, please visit USB interface WiFi/Bluetooth antenna ESD protection Common Mode Filter with ESD protection EMI interference Risk of ESD strikes - directly or through gaps in the cabinet 4

5 1. Two challenges: ESD and EMI Electrostatic discharge (ESD) ESD is the sudden release of static electricity. It can be caused by two electrically charged objects coming into contact, or coming close enough to allow air-discharge. ESD can damage electronics and cause product returns ESD sensitivity can violate regulation Opportunities for ESD strikes are just about everywhere. Wool or silk clothing, in combination with friction, can generate up to 10 kv of static electricity. Similar ESD conditions can be caused by something as simple as walking across a carpeted room or brushing against an upholstered seat when getting out of a car. Dry air, caused by cold weather or air conditioning, enhances this effect. ESD Strike Portable devices are especially prone to ESD strikes because they go everywhere we go and are exposed to a very wide variety of environments. NXP s common-mode filters with integrated ESD protection provide advanced countermeasures that prevent ESD from damaging portable devices. Non-compliant product can be blocked from sale 5

6 1. Two challenges: ESD and EMI Electromagnetic interference (EMI) The interference generated by electromagnetic fields can disrupt the operation of electronic devices. In cell phones, for example, EMI can lead to dropped calls and other malfunctions. EMI can impair functionality EMI can violate regulations EMI can come from external sources, such as nearby electronics systems, which can produce EMI over a wide frequency range, but EMI can also come from within the system itself. High-speed data lines are a particular source of EMI. In a cell phone equipped with a high-speed MIPI line that supports a camera or display, the MIPI line can generate enough EMI to cause a dropped call. It s important to understand and meet the guidelines for electromagnetic compatibility (EMC), since portable devices that violate these regulations may be blocked from sale. NXP s common-mode filters with integrated ESD protection work as filters that minimize the impact of EMI emission and reception, making it easier to design portable systems that meet EMC requirements. Dropped phone calls can be caused by a MIPI line emitting EMI Affected products can be blocked from sale 6

7 1. Two challenges: ESD and EMI Common-mode noise Today s portable systems replace single-ended signals with differential data lines that support high-speed interfaces. Differential data lines are typically more robust than single-ended signals, since they are less sensitive to common-mode noise, a type of EMI that runs along signal lines with the same amplitude and polarity. Conversion of differential mode to common mode Imbalanced Run-time signal symmetries differences When a signal from the transmitter is passed on to the receiver, the receiver detects the difference between the signals on the positive and negative lines. When the same amount of common-mode noise is added to both lines, the receiver does not detect it in an ideal system. The system isn t influenced by common-mode noise and will not generate EMI. The reality, however, is that common-mode noise is rarely in perfect balance on both lines. This is because common-mode noise can come from many sources, including the system chip. It can also come from the conversion of differential mode to common mode, which can be created by imbalances in signal symmetries and runtime differences, and it can be the result of the line pair not being symmetrical to the source of noise. Line pair not symmetrical to source of noise For this reason, portable systems benefit from common-mode filtering. 7

8 1. Two challenges: ESD and EMI How common-mode filters work Common-mode filters have two magnetically-coupled coils. Differential mode signals will pass the filter When a differential signal passes through the filter, it generates a magnetic field in each coil. The magnetic fields compensate each other, resulting in an inductance close to zero. The high bandwidth of the filter lets the differential signals pass without attenuation. Common-mode filter When common-mode noise signals pass through the filter, the magnetic fields have the same direction. These fields add up and the resultant inductance is therefore as designed. This establishes a low pass, which reduces the common-mode part of the signal. Frequency behavior in common-mode filters In the figure, the scattering parameter (S-parameter) describe the transmission coefficients, the ratio between the incoming and outgoing signal. Attenuation S 21 (db) 0 Unwanted Common-mode signals are attenuated Common-mode (noise) S-Parameter S 21 cc Common-mode Pass-Band Differential Mode Pass-Band Differential Mode (signal) S-Parameter S 21 dd -3 db loss frequency (MHz) 8

9 1. Two challenges: ESD and EMI Frequency bands used in mobile devices Portable devices operate within a wide spectrum of wireless frequency bands. A good common-mode filter has strong common-mode rejection for all these bands. In all these bands, interference with other signals can cause EMI issues. NXP PCMFxDFN1 filters The NXP family of PCMFxDFN1 common-mode filters with integrated ESD protection delivers exceptional common-mode rejection (CMR) throughout the mobile frequency range. CMR performance in the critical GSM, 3G, LTE, and WiFi bands is particularly good. LTE GSM/3G WiFi Bluetooth GPS/GLONASS Common-mode relevant frequencies 1,00E+08 1,00E+09 1,00E+10 Frequency (Hz) GSM 850 up MHz GSM 850 dwn MHz GSM 900 up MHz GSM 900 dwn MHz GSM 1800 up MHz GSM 1800 dwn MHz GSM 1900 up MHz GSM 1900 dwn MHz WIFI GHz WIFI GHz Bluetooth, GHz GPS 1.2, 1.5 GHz, GLONASS 1.6 GHz LTE 700/800 MHz, 1700/1900 MHz LTE 900 MHz, 1.8, 1.9, 2.5, 2.6 GHZ In practice, ferrite-based common mode have more narrowband CMRs, hence they suppress only a part of the critical frequency bands, while PCMFxDFN1 covers all critical frequencies with strong rejection. Scc21 (db) Common-Mode relevant frequencies CMR of ferrite-based CMFs E7 1E8 PCMFxDFN1 freq (Hz) 1E9 be er 8E9 9

10 2. Common-mode filters and the future of mobile As faster data transfers become standard for mobile devices, common-mode filters need to maintain strong common-mode rejection in the range between 700 MHz and 5.8 GHz and, at the same time, offer differential passband close to the 3rd harmonics of the data. Good common-mode rejection is needed in this frequency range 700 MHz 5.8 GHz USB 2.0 HDMI 1.4 Fundamental 3 rd harmonics USB 3.0 HDMI 2.0 1,00E+08 1,00E+09 1,00E+10 Frequency (Hz) 10

11 3. Filtering and protecting MIPI lines (PCMFxDFN1) What are MIPI lines? To provide a flexible, high-speed serial interface for today s high-resolution cameras and displays, the MIPI Alliance established the D-PHY interface. The camera interface is referred to as CSI, and the display interface is DSI. The D-PHY interface is a low-voltage, differential-signal standard that supports high resolution cameras and displays. It limits the number of data lines and minimizes the energy required for data transport. The D-PHY interface also supports operation in the same frequency range required for GSM/3G/LTE/Wi-Fi transmission. MIPI LANE MODULE CLK_P CLK_N D0_P D0_N D1_P D1_N SYSTEM-ON-CHIP (SoC) PCMF2DFN1 (PCMF3DFN1) SUPPLY AND CONTROL FLEX FOIL CONNECTOR FLEX FOIL CAMERA MODULE aaa PCMFxDFN1 filters NXP s PCMFxDFN1 filters are designed to protect and filter designs that use MIPI D-PHY CSI or DSI. The top figure shows a CLK_P PCMF3DFN1 typical configuration for MIPI CSI, and the bottom figures shows one for MIPI DSI. MIPI LANE MODULE CLK_N D0_P D0_N D1_P D1_N D2_P D2_N D3_P D3_N FLEX FOIL CONNECTOR FLEX FOIL LIQUID CRYSTAL DISPLAY (LCD) PCMF2DFN1 SYSTEM-ON-CHIP (SoC) SUPPLY, CONTROL AND BACKLIGHT aaa

12 3. Filtering and protecting MIPI lines (PCMFxDFN1) Why do MIPI lines need ESD protection? ESD can find its way to the MIPI data lines via air discharge, through gaps in the body of the mobile devices that accommodate the camera fittings, for example or even thin layers of plastic. The main source of ESD is human contact, and the average device can be handled by a person several, if not dozens of times each day. Lens system Lens fitting Sensor NXP s PCMFxDFN1 filters have integrated ESD protection, so they can protect the data lines while also reducing the impact of common-mode noise. Flex foil for SoC connection Avoiding EMI Creating a design that has good RF integrity helps to reduce EMI. This involves two aspects of development, the layout and the signal. Layout aspects Design with good RF integrity Signal aspects Use boards with multiple (ground) layers Use of differential signals Separate RF, analog, digital, and power blocks Choose the right filters Use straight, parallel routing to avoid discontinuities 12

13 3. Filtering and protecting MIPI lines (PCMFxDFN1) A closer look at the PCMFxDFN1 series The PCMFxDFN1 series protects and filters MIPI CSI and DSI configurations in smartphones, tablets, and other portable devices. It can also be used with HDMI interfaces. PCMF2DFN1 for two differential line pairs By delivering the widest bandwidth of common-mode suppression, the PCMFxDFN1 series offers the best insurance against EMI issues. The PCMF2DFN1 protects and filters two differential pairs, the PCMF3DFN1 protects and filters three. Key features Industry-leading common-mode suppression (> 14 db in the range between 500 MHz and above 8 GHZ) Very wide differential pass-band (> 2 GHz), ensuring signal integrity for all MIPI frequencies Best-in-class system-level ESD protection due to deep snapback and > 15 kv contact ruggedness against IEC pulses Industry-standard footprint Very thin package: 0.5 mm (max) PCMF3DFN1 for three differential line pairs Key benefits Minimized EMI emission and -susceptibility of the system Optimized ESD protection for the SoC makes the system robust Minimized impact on signal for easy system integration 13

14 3. Filtering and protecting MIPI lines (PCMFxDFN1) Industry-leading common-mode suppression Compared to ferrite- and other silicon-based common-mode filters, the PCMFxDFN1 family offers much wider and deeper common-mode suppression across the full range of possible EMI-critical frequencies and their higher harmonics. CM suppression with PCMFxDFN1 versus ferrite-based common-mode filters Scc21 (db) E7 1E8 PCMFxDFN1 freq (Hz) 1E9 be er 8E9 CM suppression with PCMFxDFN1 versus silicon-based solutions from other suppliers Scc21 (db) E7 1E8 PCMFxDFN1 freq (Hz) 1E9 8E9 RF performance The PCMFxDFN1 has a differential pass-band bandwidth of more than 2 GHz, which exceeds the requirements of the MIPI D-PHY standard. PCMFxDFN1 differential-mode pass-band (S21 dd) 0.0 S21dd (db) -2.5 aaa MIPI eye diagram at 1.5 Gb/s (max D-PHY data rate) f (Hz) 14

15 3. Filtering and protecting MIPI lines (PCMFxDFN1) PCMFxDFN1 layout recommendations The figure gives a sample layout for a fivechannel MIPI interface. The PCMF2DFN1 and the PCMF3DFN1 are connected to a flex-foil connector. 5 differential MIPI line pairs, impedance controlled 2 mm Flex foil connector Separation of differential line pairs by GND to support RF performance and ESD protection 15

16 4. Filtering and protecting USB 2.0 (IP3319CX6) USB 2.0, which is by far the most common interface for charging and data exchange in portable systems, can be found in most smartphones and tablets. The regular version of USB 2.0 uses one differential line pair and one supply line of 5 V, while the mobile version, dubbed On-The-Go or OTG, adds an extra line so the system can act as a USB host for devices like keyboards, printers, and other peripherals. Although the nominal data rate for USB 2.0 is 480 Mbits/s, and the major part of the spectral power is below 480 MHz, significant power is still present around 960 MHz, which can interfere with systems operating near that part of the spectrum, including GSM-900 system. A common-mode filter can improve the situation by suppressing EMI from the GSM transmitter to the USB 2.0 data lines, and by reducing the impact of USB 2.0 emissions on the GSM receiver. IP3319CX6 filter NXP s IP3319CX6 filter is designed for use with USB 2.0 and USB OTG. It is a single-channel common-mode filter with integrated ESD protection (up to 15 kv contact discharge), and is housed in a 0.4 mm pitch wafer-level chipscale package (WLCSP6). Common-mode rejection S 21dd Mag (db) 0-5 Other supplier The filter also integrates two ultra-low capacitance rail-to-rail diodes for the differential data lines, plus a separate protection diode, for the ID-pin IP3319CX6 The IP3319CX6 delivers significantly higher common-mode rejection than a direct competitor. It also provides very strong common-mode rejection in the GSM900 spectrum, with signal integrity that is good enough to fully support USB 2.0 speeds ,E+06 1,E+07 1,E+08 1,E+09 1,E+10 f (MHz) 16

17 4. Filtering and protecting USB 2.0 (IP3319CX6) IP3319CX6 Key features Very wide differential pass band > 1 GHz Very broadband common-mode attenuation Two-line (one differential channel) commonmode filter ESD protection for the USB ID line Extremely low clamping ESD protection, excellent SoC protection ESD protection up to ±15 kv on external contact pins Ultra-low ESD diode capacitance Also supports interfaces for LVDS and DVI Very small WLCSP6 package (1.6 x 1.15 x 0.65 mm) with 0.4 mm pitch IP3319CX6 insertion losses for differential and common-modes α il (db) aaa f (Hz) (1) (2) (1) Differential mode (2) Common-mode Typical IP3319CX6 application using Micro USB connector Type B 17

18 4. Filtering and protecting USB 2.0 (IP3319CX6) IP3319CX6 USB 2.0 eye diagram The eye diagram shows measurements using test template 5 on a test board with the 0.4 IP3319CX6 at TP4 with limits of 300 mv. differential signal, V mask time, ns Signal clearly in specification IP3319CX6 layout recommendations A good GND connection between pin C1 (GND) and the USB connector ensures optimized ESD protection. Shorter connections minimize resistive and inductive impedance. Two sample layouts are shown. The lower layout uses a lower or bottom layer to connect the ID pin with the SoC. This makes a solid, low-ohmic, and low-impedance connection to pin C1 (GND). 18

19 5. A special situation: ESD protection for the SoC ESD pulses need to be kept away from the System on Chip (SoC) while maintaining signal integrity for all the frequencies used by the application. TLP measurements Transmission-line pulse (TLP) measurements are the industry standard for gauging the effectiveness of ESD protection for an SoC. The TLP characteristic is measured using a series of increasing I TLP (V TLP ) pulses. Each pulse is a point in the diagram. These pulses are generated by discharging a transmission line with a defined impedance of 50 Ω. The quality of protection for the SoC is shown by having a low TLP Voltage for a given TLP current. IEC ESD pulse Signal lines System Connector ESDprotection Path of ESD-pulse Clamped ESD pulse System on Chip (SoC) Internal ESD protection to allow safe assembly The diagrams show that the NXP CMF common-mode filters provide a higher degree of ESD protection for the SoC. This is, in part, due to the deep snap-back characteristics of PCMF devices. Measurement 1 shows, that the NXP PCMF Common Mode Filter provides SoC protection, which is more than one magnitude stronger compared to Ferrite based solutions with integrated ESD protection. Measurement 1 Measurement 2 19

20 NXP Semiconductors N.V. All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property rights. Date of release: May 2014 Document order number: Printed in the Netherlands