Application Guide - Common Mode Filter
Common-mode filters with integrated ESD protection
for portable devices
Table of contents
1.
Two challenges: ESD and EMI
2.
Common-mode filters and the future of mobile
3.
Filtering and protecting MIPI lines (PCMFxDFN1) 11-15
4.
Filtering and protecting USB 2.0 (IP3319CX6)
5.
A special situation: ESD protection for the SoC
6-9
10
16-18
19
2
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.
Generic smartphone / tablet computer
Tactile keys
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
Processor
Applications
with differential
data lines
Back Side
Camera
Front Side
Camera
GSM/3G/LTE
WiFi
Diplexer/Antenna
ESD protection
EMI interference
Common Mode Filter with ESD protection
Risk of ESD strikes - directly or through gaps
in the cabinet
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.
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 www.nxp.com.
Generic set-top box
Tactile keys
ESD protection for
optional low-speed
interfaces
HDMI interface
Processor
USB interface
WiFi/Bluetooth
antenna
ESD protection
EMI interference
Common Mode Filter with ESD protection
Risk of ESD strikes - directly or through
gaps in the cabinet
4
1.
Two challenges: ESD and EMI
 ESD can damage electronics and cause product returns
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 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
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
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
signal symmetries
Run-time
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
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.
Unwanted Common-mode signals are attenuated
Common-mode (noise)
S-Parameter S21cc
Differential Mode (signal)
S-Parameter S21dd
0
Attenuation |S21| (dB)
1.
0.1
-3 dB
loss
Common-mode
Pass-Band
Differential Mode
Pass-Band
1
10
100
1000
10000
frequency (MHz)
8
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.
Common-mode
relevant frequencies
GSM 850 – up 824-849 MHz
GSM 850 – dwn 869-894 MHz
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.
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.
LTE
GSM 900 – up 890-915 MHz
GSM/3G
GSM 1800 – up 1710-1785 MHz
WiFi
GSM 1900 – up 1850-1910 MHz
Bluetooth
WIFI 2.4 – 2.5 GHz
GPS/GLONASS
Bluetooth, 2.4-2.5 GHz
1,00E+08
GSM 900 – dwn 935-960 MHz
GSM 1800 – dwn 1805-1880 MHz
GSM 1900 – dwn 1930-1990 MHz
WIFI 4.9 – 5.8 GHz
1,00E+09
1,00E+10
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
Frequency (Hz)
0
Common-Mode relevant frequencies
Scc21 (dB)
-5
-10
CMR of
ferrite-based
CMFs
-15
-20
-25
PCMFxDFN1
-30
-35
1E7
beer
1E8
freq (Hz)
1E9
8E9
9
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
USB 3.0
Fundamental
3rd harmonics
1,00E+08
HDMI 2.0
1,00E+09
1,00E+10
Frequency (Hz)
10
Filtering and protecting MIPI lines (PCMFxDFN1)
CLK_P
FLEX FOIL CONNECTOR
CLK_N
D0_P
D0_N
D1_P
D1_N
SYSTEM-ON-CHIP
(SoC)
FLEX FOIL
CAMERA
MODULE
SUPPLY AND
CONTROL
aaa-007392
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
typical configuration for MIPI CSI, and the bottom figures shows
one for MIPI DSI.
PCMF3DFN1
CLK_P
CLK_N
D0_P
FLEX FOIL
D0_N
D1_P
FLEX FOIL CONNECTOR
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.
PCMF2DFN1
(PCMF3DFN1)
MIPI LANE MODULE
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.
MIPI LANE MODULE
3.
D1_N
D2_P
D2_N
D3_P
D3_N
LIQUID CRYSTAL
DISPLAY
(LCD)
PCMF2DFN1
SYSTEM-ON-CHIP
(SoC)
SUPPLY,
CONTROL
AND BACKLIGHT
aaa-007393
11
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.
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 EMI
Creating 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 foil
for SoC
connection
Design with good RF integrity
Layout aspects
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
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 IEC61000-4-2 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
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
0
Scc21 (dB)
0
Scc21 (dB)
-5
-5
-10
-10
-15
-15
-20
-20
-25
-25
PCMFxDFN1
-30
1E8
freq (Hz)
1E9
PCMFxDFN1
-30
beer
-35
1E7
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.
CM suppression with PCMFxDFN1 versus silicon-based
solutions from other suppliers
8E9
PCMFxDFN1 differential-mode pass-band (S21 dd)
-35
1E7
1E8
freq (Hz)
1E9
8E9
MIPI eye diagram at 1.5 Gb/s (max D-PHY data rate)
aaa-007663
0.0
S21dd
(dB)
-2.5
-5.0
-7.5
-10.0
106
107
108
109
f (Hz)
1010
14
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
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).
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.
Common-mode rejection
S21dd
Mag (dB)
4.
0
Other supplier
-5
-10
IP3319CX6
-15
-20
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.
-25
1,E+06
1,E+07
1,E+08
1,E+09
1,E+10
f (MHz)
16
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) common mode 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
αil
(dB)
aaa-006138
0
-6
(1)
(1)
Differential
mode
-12
(2)
(2)
-18
Common-mode
-24
-30
105
106
107
108
109
f (Hz)
1010
Typical IP3319CX6 application using Micro USB connector Type B
17
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
IP3319CX6 at TP4 with limits of 300 mV.
0.4
differential signal, V
4.
0.2
0.0
mask
-0.2
-0.4
0.0
0.5
1.0
1.5
2.0
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
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 ITLP (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
System
Connector
Signal
lines
Clamped ESD
pulse
ESDprotection
System on Chip (SoC)
Internal ESD protection
to allow safe assembly
Path of ESD-pulse
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
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© 2014 NXP Semiconductors N.V.
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Date of release: May 2014
information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and
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