Whitepaper

ESD Protection for Automotive
High-Speed Video Links
The challenges in protecting high-speed Video Links
without compromising signal integrity
Dr.-Ing. Andreas Hardock, Application Marketing Manager for ESD and EMC, Nexperia
Lukas Droemer, Product Manager for ESD and EMC, Nexperia

Autonomous driving is one of the big trends predicted to change the future of theautomotive industry. Its successful adoption is dependent on overcoming barriers such as
the need for more safety and information for the driver and the passengers. This in turn isdriving the development of Advanced Driver Assist Systems (ADAS) and safety infotainment
applications for use in future autonomous vehicles.

Due to this trend, the number of cameras and displays
in a car’s interior is multiplying rapidly. While Video
Links provide adequate data rates (up to 16Gbits) tosatisfy the need for quality content, vehicles still a roughenvironment for those sensitive interfaces. The physicallayer (PHY) technology for such highly sophisticated links
requires external electrostatic discharge (ESD) protectionthat is compliant with the automotive electromagnetic
compatibility (EMC) requirements. For the ESD protection
itself, this introduces some new challenges. On the one
handthe ESD device should protectthe circuit against highvoltage ESD events. On the other hand ESD device should
be mostly invisible during normal operation, havindg nosignificant impact on the signal integrity (SI). Besides
package and routing , the main intrinsic parameter for SI
compliance is the capacitance of the ESD device. As data
rates rise, the demand for lower capacitance grows.
This paper discusses the impact of the ESD protection
device on SI in comparison to other link components suchas cable, connector and the PCB in a differential Video Link.
Therefore the entire link from Rx to Tx is built up in ADSandscattering parameters simulation is performed.

Video Links
Video Links, or serializer/deserializer (SerDes), areumbrella terms for devices using serial interfaces totransmit data that is available from a parallel data stream.
These interfaces are high bandwidth, point-to-point by
design, and latency is usually not critical. The interfaces
mainly operate unidirectionally or bidirectionally wherethe bandwidth in one direction is significantly higher thanin the other.

The physical implementation of the serial data stream canbe differential, using low voltage differential signaling(LVDS), or single-ended, using a coaxial cable. (Optical links
are also possible, but they are not standard and therefore
will not be discussed here.) Furthermore, Video Link
interfaces with a single-ended physical layer are sometimes
used to transmit power to the ECU in addition to the datastream. For coaxial single-ended links, this technique iscalled Power-over-Coax (PoC) in the same vein as Powerover-Data-line (PoDl) or Power-over-Ethernet (PoE).
Video Link interfaces are mainly used to transmit video
data. The most common applications are in infotainment
to connect displays, body and convenience applications likeparking cameras, and cameras used for ADAS applications.
Especially for cameras, the PoC functionality is very
attractive. In the modern zonal architecture, Video Link
interfaces are the exceptional point-to-point connections
that are required to make high-resolution sensor data
available. There is an initiative ongoing to standardize Video
Link interfaces for automotive applications, but currently
no common standard is available. Proprietary solutions are
therefore common in the automotive domain, such as thefollowing examples.

APIX – Automotive Pixel Link

FPD-Link – Flat Panel Display Link

Automotive Pixel Link (APIX) was designed by Inova
Semiconductors and licensed in 2008 by Fujitsu. It can beused to transmit digital video signals over a distance of up
to 15 m. Third generation APIX3 has been available since2016, suppling data rates up to 6Gbit/s.

FPD-Link was originally designed for displays but is also
commonly used to connect cameras to ADAS computingunits. Today, FPD-Link is owned by TI and very popular for
automotive ADAS applications. FPD-Link III allows for datarates of up to 13.3 Gbit/s and bi-directional communication
on a single link. Additionally, FPD-Link III allows the usage of
coaxial cables and PoC in a single-ended variant.

GMSL – Gigabit Multimedia Serial Link
GMSL is a proprietary SerDes interface by Maxim Integrated
mainly used for camera applications. The third generation ofincreases the data rate beyond 10Gbit/s range supporting
also PoC as an option.

e.g. Head Unit

Connector

Shieldedtransmission~ several meters(STP)

e.g. display, HUDConnector

CMC

CMC
TxRx
ESD2

ESD1

Capacitive coupling of theshield to avoid high reverse
currents (optional)

ESD1

ESD1/2 and CMC are(optional), depending onrequirements and therobustness of the PHY

ESD2

Capacitive coupling of theshield to avoid high reverse
currents (optional)

Two possible positions
for ESD protection:
ESD1 or ESD2

aaa-033481

Figure 1: Schematic of a differential video link including the transceiver and receiver

ESD Requirements for Video Links
The requirements for external protection are similar for
all three Video Link interfaces introduced in the previoussection. As mentioned previously, there are two main
parameters topics to be focused on when choosing the right
ESD protection device, ESD and SI. Both will be addressed inthe following.
To achieve ESD protection up to 10kV or more and tohave a very robust system in the field, state-of-the-art
protection technology is required – such as a siliconcontrolled rectifier (SCR) or open base transistor. As
illustrated in Figure 1, there are two possible positions for
an ESD protection device: ESD1 and ESD2. For optimal ESDprotection performance, the position to choose is the ESD1,
which allows the ESD pulse to be clamped down directlyat the connector, far away from the sensitive PHY and thecircuitry.

2ESD Protection for Automotive High-Speed Video Links

Typically, in automotive testing a ‘short to battery’ is also
performed for Video Links. In this case the ESD1 position
can be populated, which requires the reverse standoff
voltage (VRWM) of the ESD protection device to be above
13.5V. If short to battery is not tested, then a VRWM of5V or lower can be chosen. Position ESD2 is not impacted
by the short to battery test since the DC capacitors areblocking the DC current. Here, lower standoff voltages of of
5V or below can be used. In some cases, capacitive couplingof the shield of the cable is required and can be considered
as a possible ground reference for the ESD protection
device.
Today’s infotainment in automotive requires a highresolution and high-quality video stream. Hence, the data
rate of Video Links is increasing rapidly. With the newgenerations of video links, a data rate of up to 13Gbps isstate-of-the-art and will increase to 16Gbps in future. Insuch scenarios, signal integrity plays a key role for designengineers.

When choosing an ESD protection device with SI focus there
are several parameters to consider. During normal operation
the voltage across the ESD protection device is very smallusually below 1V. In this case, the ESD protection device
behaves as a capacitance parallel in the signal transmission
path.

This device capacitance Cd is one of the most importantparameters for the SI. Due to the high data rates upt to16Gbit/s, very low values Cd < 1 pF are key here. The generaleffect of such a capacitance on S-parameter is shown in
Figure 2 up to 6GHz.

aaa-033482

0S21(dB)-2-4

PESD30VF1BL

Nexperia-6

Bidirectional ESD protection diode9. Characteristics

Cd = 0.3 pF

Table 6. Characteristics-8Parameter

Conditions

VRWM

Reverse standoﬀ voltage

Tamb = 25ºC

VBR

Breakdown voltage

IR = 10 mA: Tamb = 25ºC

IRM

Reverse leakage current

VR = 30 V: Tamb = 25ºC

Cd4
Diode capacitance

5f = 1 MHz; VR: Tamb = 25ºC

-1001

2

Cd = 0.5 pF

Symbol3VCL

Clamping voltage

Cd = 1.0 pF
Cd = 1.5 pF

Capacitance values below 1pF clearly stay above the 3dBlimit, even above 1dB for 0.5pF. So, in general, values below
1pF or even below 0.5pF allow very good signal transmission
up to 6GHz.
In addition, the package and its impact on routing of signallines may have a significant impact on the signal integrity.
As a general rule, the best choices are compact andleadless packages such as DFN (dual-flat no leads), which
are generally less parasitic compared to leaded ones. Inaddition, they usually have a very compact footprint withNexperia
PESD30VF1BL
only a minor impact on the routing of the signal Bidirectionallines, ESD
hence,
protection diode9. Characteristics
on theirthe impedance. So, the capacitance of the ESD
Table 6. Characteristics
protection
can be seen as a dominant value.

Nexperia

SymbolParameter

Conditions

MinTypMax

Unit

VRWM

Reverse standoﬀ voltage

Tamb = 25ºC--30

VVBR

Breakdown voltage

IR = 10 mA: Tamb = 25ºC

313439VIRM

Reverse leakage current

VR = 30 V: Tamb = 25ºC-0.1

50nACdDiode capacitancef = 1 MHz; VR: Tamb = 25ºC-0.27

0.4

pF

VCL

Clamping voltage

9. Characteristics
Rdyn

Dynamic resistancePESD30VF1BL
6.5
V

IPPM = 1 A: Tamb = 25ºC

[1]

IPP = 16 A: Tamb = 25ºC

Bidirectional
ESD protection diode23V[2]-

IR = 7.5 A: Tamb = 25ºC

[2]--

0.7-

ΩTypMax

Unit--30

V

31

3439

V

50nA

0.4

pF-V-

Table 6. Characteristics
ParameterConditions

VRWM

Reverse standoﬀ voltage

Tamb = 25ºC

VBR

Breakdown voltageSymbol

Min

VCL

C
IR = 10 mA: Tamb = 25ºC
C9TermG
Reverse leakage current
V = 30 V: Tamb = 25ºC
C - 0.27 pF
TermG11 R
Diode capacitance:T=25ºC
f=1MHz;V
Num = 11R
amb
Z = 50 Ω I = 1 A: T = 25ºC
PPM
amb
Clamping voltage
Measured S-Par

Rdyn

Dynamic resistanceIRM
Cd

IPP = 16 A: Tamb = 25ºC
IR = 7.5 A: Tamb = 25ºC

1 2RefTermG
TermG9
Num = 9Z = 50 ΩS2P
SNP8CC9C - 0.27 pF

TermG
TermG11[1]TermG0.1TermG120.27
Num= 12Z = 50 Ω6.5-

[2]-

23-

V[2]-0.7-ΩTermG
TermG10Num = 10Z = 50 ΩTypMaxUnit--30V313439V-

0.150nA-60.27

0.4pF

IPPM = 1 A: Tamb = 25ºC

Freq (GHz)[1]-

6.5-

V

IPP = 16 A: Tamb = 25ºC

[2]-23-

VR

[2]-

0.7-

ΩFigure 2: Insertion loss versus frequency for typical device capacitance values. Values below 1.1pF
no impact onI thesignaltransmission.
R have nearly
Dynamic resistance= 7.5 A:T = 25ºCdynMin

amb

CC9C - 0.27 pF

TermG
TermG11
Num = 11
Z = 50 Ω

TermG
TermG12
Num = 12Z = 50 ΩMeasured S-Par
1 2RefTermG
TermG9Num = 9
Z = 50 ΩIL(dB)

TermG
TermG10
Num = 10
Z = 50 ΩS2P
SNP80-0.5-1.0-1.5-2.0
Cd = 0.27 pH simulation
PESD30VF1BL measurement

0IL -2.5(dB)-3.0-0.50
RL -1.0(dB)-1.5-10-2.0
Cd = 0.27 pH simulation
PESD30VF1BL measurement-20-2.5-3.0-30

Cd = 0.27 pH simulation
PESD30VF1BL measurement

0RL -400(dB)-10123456Frequency (GHz)

TermG
TermG12aaa-033483

Figure 3: S-Parameterof a device capacitance of CdNum= 0.27pF= 12 and a comparison with measured S-Parameter from a real device. Good agreement
Num simulation= 11-20
Z = 50 Ω
can be obtained up
to506GHz.
Z=ΩMeasured S-Par

312ESD Protection for Automotive
High-Speed Video Links
Ref
TermG
TermG9Num = 9Z = 50 ΩS2P
SNP8TermG
TermG10Num = 10Z = 50 Ω-30-40

Cd = 0.27 pH simulation
PESD30VF1BL measurement0123456

Figure 3 shows the comparison of capacitance in a simulated
device with a measurement of a real ESD protection device
PESD30VF1BL. Here, the typical value of Cd = 0.27pF fromthe datasheet was used for the simulation. This product is atiny leadless Surface-Mounted Device (SMD) plastic package
designed to protect one signal line from the damage
caused by ESD and other transients. Both, insertion loss (IL)and return loss (RL) show a good comparison up to 6GHz,demonstrating that device capacitance gives a very goodindication for signal integrity purposes.
To investigate the impact on the signal integrity of the entire
link, including serializer (Tx) and deserializer (Rx), the entire
PCB board and cable transmission was simulated in ADS,
see Figure 4. The PCB was simulated using lossy microstrip
lines of 100Ω. As a substrate a typical FR4 with ε-r=4.6,tanδ = 0.02 was used. Ideal 100nF capacitors were chosen
as DC block. The cable is represented by the measured
S-parameter of a typical shielded parallel pair cable (SPP)
with a length of 10m.

The connector was simulated by a mismatched microstrip
line of 120Ω. In reality, the impedance of the connector isvery strong dependent on the PCB stack-up and the layout,
and it can range from 60 to 150Ω or more which can be very
critical for the entire signal transmission.
In order to investigate the impact of the ESD protection
device, the measured S-parameter of the Nexperia
PESD30VF1BL was used. This device comes with a typicalcapacitance of 0.27pF and a very compact and leadlesspackage (SOD882BD). It should be mentioned that in thisset-up the PCB routing aspects are not considered here,
due a very compact package and its minor impact on theSI. Figure 4 shows the comparison of S-parameters (IL andRL) of the entire link from Tx to Rx with and without theESD protection device. It can be observed that the cable,
the connector and the PCB are the most dominant here.
The contribution of the ESD protection device is of lessimportance.

ESD Protection
measured S-param

1 cm(400 mil)

1 cm(400 mil)Tx

Lossy microstriplines (≈100 Ω diﬀerential)Ɛr = 4.6, tan δ = 0.02

SPP120 Ω

3 cm(1200 mil)

1 cm(400 mil)Connector

3 cm(1200 mil)Connector

1 cm(400 mil)

ESD Protection

Rx

Lossy microstriplines (≈100 Ω differential)
Ɛr = 4, tan � = 0.02

0|S-param|
(dB)
-5

-10

-15
-20

-25
-30

-35
-40

01

2

34

56
Freq (dB)aaa-033484

Figure 4: a ) Set-up for the link simulation in ADS to investigate the impact of an ESD protection device on the differential S-parameter.
b) The impact of the ESD device is minor compared to other components in the link, e.g. cable or connector.

4ESD Protection for Automotive High-Speed Video Links

Conclusions
The exploding demand of infotainment and safety inmodern car systems requires very sophisticated high-speed
solutions which pass the EMC compliant test and are robustin the field. ESD can cause a malfunction or even irreversible
destruction of the system which is a reason for costly recall
campaigns. ESD protection devices are necessary to avoid
those failures and leverage the system to a highly reliable
and very robust level.
Besides the existing Video Link protocols, the are somealternatives under discussion within the automotiveindustry. An open committee, Automotive Serdes Alliance,
has been formed to create a common standard for highspeed Video Links, which will give further assurance of theirreliability and performance.
In the meantime, tests demonstrate that Nexperia’s
automotive qualified devices for infotainment designs
offer the ideal combination of low capacitance, lowclamping voltage and high ESD robustness. They use
the same active silicon-controlled rectification technology
to overcome the traditional protection trade-off challenge.
As a result, capacitance is kept down to 0.5 pF, clamping
voltage is just 3 V and devices can withstand surge and ESD
pulses up to 10 A 8/20 µs. In addition, these ESD protection
devices comply with all automotive qualifications in a very
compact and suitable high-speed package.

About Nexperia
Nexperia is a leading expert in the high-volume
production of essential semiconductors that arerequired by every electronic design in the world.
The company’s portfolio includes diodes, bipolartransistors, ESD protection devices, MOSFETs,
GaN FETs and analog & logic ICs. Headquartered in
Nijmegen, the Netherlands, Nexperia annually ships
more than 90 billion products, meeting automotivestandards. These products are recognized as
benchmarks in efficiency – in process, size, power
and performance — with industry-leading small
packages that save valuable energy and space.
Nexperia has over 12,000 employees across Asia,
Europe and the US.
Find your regional sales office here

For more information about Nexperia ESD products for the automotive industry, visit:https://www.nexperia.com/applications/automotive/multimedia-bus-protection.html© 2021 Nexperia B.V.
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Date of release:
July 2021