Application Guide - Common Mode Filter - Nexperia · GSM/3G/LTE WiFi Diplexer/Antenna ... ESD is...

Common-mode filters with integrated ESD protectionfor portable devices

Application Guide - Common Mode Filter

2

Table of contents

1. Two challenges: ESD and EMI 6-9

3. Filtering and protecting MIPI lines (PCMFxDFN1) 11-15

2. Common-mode filters and the future of mobile 10

4. Filtering and protecting USB 2.0 (IP3319CX6) 16-18

5. A special situation: ESD protection for the SoC 19

Protecting portablesToday’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.

Display Applicationswith differential

data lines

Back SideCamera

Front SideCamera

ESD protection

Common Mode Filter with ESD protection

EMI interference

Risk of ESD strikes - directly or through gaps in the cabinet

Tactile keys

GSM/3G/LTEWiFi

Diplexer/Antenna

Processor

Generic smartphone / tablet computer

Introduction

4

The NXP advantageOur 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.

This guideThis 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 www.nxp.com.

ESD protection for optional low-speed interfaces

HDMI interface

ESD protection

Common Mode Filter with ESD protection

EMI interference

Risk of ESD strikes - directly or through gaps in the cabinet

Tactile keys

USB interface

WiFi/Bluetoothantenna

Processor

Generic set-top box

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.

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.

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.

ESD Strike

ESD can damage electronics and cause product returns

ESD sensitivity can violate regulation

Non-compliant product can be blocked from sale

6


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 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.

EMI can impair functionality

EMI can violate regulations

Dropped phone calls can be caused by a MIPI line

emitting EMI

Affected products can be blocked from sale

7


Common-mode noiseToday’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.

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 run-time differences, and it can be the result of the line pair not being symmetrical to the source of noise.

For this reason, portable systems benefit from common-mode filtering.

Conversion of differential mode to common mode

Line pair not symmetrical to source of noise

Imbalancedsignal symmetries

Run-timedifferences

8


How common-mode filters workCommon-mode filters have two magnetically-coupled coils.

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.

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 filtersIn the figure, the scattering parameter (S-parameter) describe the transmission coefficients, the ratio between the incoming and outgoing signal.

0.1 1 10 100 1000 10000 frequency (MHz)

0

Differential Mode Pass-Band

-3 dB loss

Atte

nuat

ion |S

21| (

dB)

Common-mode Pass-Band

Common-mode (noise) S-Parameter S21cc Differential Mode (signal)

S-Parameter S21dd

Differential mode signals will pass the filter

Unwanted Common-mode signals are attenuated

Common-mode filter

9


Frequency bands used in mobile devicesPortable 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 filtersThe 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.

In practice, ferrite-based common mode have more narrow-band CMRs, hence they suppress only a part of the critical frequency bands, while PCMFxDFN1 covers all critical frequencies with strong rejection.

1E91E81E7 8E9

-30

-25

-20

-15

-10

-5

-35

0

freq (Hz)

Scc21 (dB)

PCMFxDFN1

be�er

CMR offerrite-basedCMFs

Common-Mode relevant frequencies

1,00E+08 1,00E+09 1,00E+10

Frequency (Hz)

Bluetooth

WiFi

LTE

GSM/3G

GPS/GLONASS

GSM 900 – up 890-915 MHz GSM 900 – dwn 935-960 MHz GSM 1800 – up 1710-1785 MHz GSM 1800 – dwn 1805-1880 MHz

GSM 850 – up 824-849 MHz GSM 850 – dwn 869-894 MHz

GSM 1900 – up 1850-1910 MHz GSM 1900 – dwn 1930-1990 MHz WIFI 2.4 – 2.5 GHz WIFI 4.9 – 5.8 GHz

LTE 700/800 MHz, 1700/1900 MHz LTE 900 MHz, 1.8, 1.9, 2.5, 2.6 GHZ

Bluetooth, 2.4-2.5 GHz GPS 1.2, 1.5 GHz, GLONASS 1.6 GHz

Common-mode relevant frequencies

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 pass-band close to the 3rd harmonics of the data.

Frequency (Hz)

Good common-mode rejection

is needed in this frequency range

1,00E+08 1,00E+09 1,00E+10

USB 2.0

HDMI 1.4

USB 3.0

HDMI 2.0

700 MHz – 5.8 GHz

Fundamental3rd harmonics

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.

PCMFxDFN1 filtersNXP’s PCMFxDFN1 filters are designed to protect and filter designs that use MIPI D-PHY CSI or DSI. The top figure shows a typical configuration for MIPI CSI, and the bottom figures shows one for MIPI DSI.

aaa-007393

FLEX

FO

IL C

ON

NEC

TOR

PCMF3DFN1

SUPPLY,CONTROL

AND BACKLIGHT

FLEX FOIL

LIQUID CRYSTALDISPLAY

(LCD)

CLK_P

CLK_N

D0_P

D0_N

D1_P

D1_N

SYSTEM-ON-CHIP (SoC)

PCMF2DFN1

D2_P

D2_N

D3_P

D3_N

MIP

I LA

NE

MO

DU

LE

FLEX

FO

IL C

ON

NEC

TOR

PCMF2DFN1(PCMF3DFN1)

SUPPLY ANDCONTROL

FLEX FOIL

CAMERAMODULE

CLK_P

CLK_N

D0_P

D0_N

D1_P

D1_N

SYSTEM-ON-CHIP(SoC)

MIP

I LA

NE

MO

DU

LE

aaa-007392

12


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.

NXP’s PCMFxDFN1 filters have integrated ESD protection, so they can protect the data lines while also reducing the impact of common-mode noise.

Avoiding EMICreating a design that has good RF integrity helps to reduce EMI. This involves two aspects of development, the layout and the signal.

Lens system

Lens fitting

Sensor

Flex foilfor SoC connection

Layout aspects

Separate RF, analog, digital,and power blocks

Use straight, parallel routingto avoid discontinuities

Use boards with multiple (ground)layers

Use ofdifferential signals

Choose the right filters

Signal aspects

Design with good RF integrity

13

A closer look at the PCMFxDFN1 seriesThe 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.

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 IEC61000-4-2 pulses Industry-standard footprint Very thin package: 0.5 mm (max)

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

PCMF2DFN1 for two differential line pairs

PCMF3DFN1 for three differential line pairs


14

Industry-leading common-mode suppressionCompared 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.

RF performanceThe PCMFxDFN1 has a differential pass-band bandwidth of more than 2 GHz, which exceeds the requirements of the MIPI D-PHY standard.

1E91E81E7 8E9

-30

-25

-20

-15

-10

-5

-35

0

freq (Hz)

Scc21 (dB)

PCMFxDFN1

be�er

aaa-007663

106 107 108 109 1010f (Hz)

S21ddS21dd(dB)(dB)

-10.0

-7.5

-5.0

-2.5

0.0

1E91E81E7 8E9

-30

-25

-20

-15

-10

-5

-35

0

freq (Hz)

Scc21 (dB)

PCMFxDFN1

CM suppression with PCMFxDFN1 versus ferrite-basedcommon-mode filters

PCMFxDFN1 differential-mode pass-band (S21 dd)

CM suppression with PCMFxDFN1 versus silicon-basedsolutions from other suppliers

MIPI eye diagram at 1.5 Gb/s (max D-PHY data rate)


15

PCMFxDFN1 layout recommendationsThe figure gives a sample layout for a five-channel MIPI interface. The PCMF2DFN1 and the PCMF3DFN1 are connected to a flex-foil connector.

2 mm

Flex foilconnector

Separation of differentialline pairs by GND to supportRF performance and ESD protection

5 differentialMIPI line pairs,impedancecontrolled


16

IP3319CX6 filterNXP’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 chip-scale package (WLCSP6).

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.

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.

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.

-25

-20

-15

-10

-5

0

1,E+06 1,E+07 1,E+08 1,E+09 1,E+10

S 21d

d M

ag (d

B)

f (MHz)

Common-mode rejection

4. Filtering and protecting USB 2.0 (IP3319CX6)

Other supplier

IP3319CX6

17


IP3319CX6 Key features Very wide differential pass band > 1 GHz Very broadband common-mode attenuation Two-line (one differential channel) common-

mode filterESD 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

Typical IP3319CX6 application using Micro USB connector Type B

aaa-006138

105 106 107 108 109 1010-30

-24

-18

-12

-6

0

f (Hz)

αilαil(dB)(dB)

(1)(1)

(2)(2)

(1) Differential mode

(2) Common-mode

18


IP3319CX6 USB 2.0 eye diagramThe eye diagram shows measurements using test template 5 on a test board with the IP3319CX6 at TP4 with limits of 300 mV.

IP3319CX6 layout recommendationsA 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).

time, ns

0.0

-0.4

-0.2

0.0

0.2

0.4

0.5 1.0 1.5 2.0

di�e

rent

ial s

igna

l, V

mask

Signal clearly in specification

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 measurementsTransmission-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 ITLP (VTLP) 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.

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.

System

System on Chip (SoC) Connector ESD- protection

Signal lines

Clamped ESD pulse

Path of ESD-pulse

pulse

Internal ESD protection to allow safe assembly

IEC ESD

Measurement 1 Measurement 2

© 2014 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: 9397 750 17547

Printed in the Netherlands

www.nxp.com

Application Guide - Common Mode Filter - Nexperia · GSM/3G/LTE WiFi Diplexer/Antenna ... ESD is...

Documents

Transcript of Application Guide - Common Mode Filter - Nexperia · GSM/3G/LTE WiFi Diplexer/Antenna ... ESD is...