simulation of emissions and immunity for pcbs and other ... · • the car model includes a cable...

Simulation of Emissions and Immunity for PCBs and Other

Devices Inside Vehicles

Dr. Eddy JEHAMY: [email protected] Dr. Markus SCHICK: [email protected]

Dr. Martin VOGEL: [email protected]

09.09.2016

mailto:[email protected]



© 2016 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.

• Introduction

• Case 1: PCB emission on high level system

• Case 2: Cable radiation analysis from high rate digital PCB system (up

to 100Mb/s)

• Conclusion and perspectives

General overview


Introduction

DUT

EMC Antenna


Introduction: study context

• PCB 3D simulation analysis are high cost from computational resources aspects

• Measured nearfield data around PCB can be one alternative to have an equivalent radiation model

• Simplifying PCB models and focusing on excited modes on cables can be another alternative

• Two cases are considered in this workshop to perform PCB analysis inside vehicle environment


Case 1: PCB Emission on High Level System


Complete EMC studies: general study workflow

Export near fields

Considered PCB

Simulated near fields of the PCB generated

using a PCB analysis tool

Import them into 3D field solver


Complete EMC studies: coupling between cables, antennas

and devices on-board

Analysis of radiated emissions from PCB being coupled into:

• windscreen antenna

• cable harness

and considering different positions for the PCB in the car to take into account resonance aspects with the complete

environment

back left light back right light front left light

steering control tracking navigation


Digital Audio Broadcast (DAB) antenna

• The spectrum of the radiated emissions of the PCB has a peak at 200 MHz.

• This is relevant because it is at the center of the DAB band 174 -240 MHz

• A monopole design is chosen for the DAB antenna, which is integrated into the rear windscreen of the car

model.

• A matching circuit is included at the feed of the DAB antenna.

Surface currents and 3D gain pattern of the windscreen DAB antenna at 200 MHz

DAB

Antenna Port


• The car model includes a cable harness, considering:

• The cable is made of unshielded twisted pairs terminated at 3 locations in the car, and voltage probes are added to

record the coupled voltages at the terminations.

• The cables are included in the simulation using the MTL method (irradiation).

Cable paths and termination

Voltage probes at cable terminals

Cable

Harness


Complete EMC studies: coupling between cables, antennas

and devices on-board

• Complete analysis of induced voltages at the cable connectors and at the antenna port due to the

radiated emissions of the PCB considering the different positions of investigation:


Near fields due to radiated emissions from PCB

• Analysis of the resonance between PCB and the complete vehicle structure

• When the PCB is placed close to the side of the vehicle there is a stronger coupling with the vehicle

back left light back right light front left light steering control tracking navigation


Case 2: Cable Radiation Analysis from High Rate Digital PCB System (up to 100Mb/s)


• Chip (IC) produces clean differential signal: + and – in equal amounts

• At the edge of the PCB, + and – not in equal amounts anymore

• Signal is launched onto twisted wire pair

• Unbalanced fraction of signal causes the EMC problems.

• At data rates of interest in the automotive industry (up to 100 Mb/s),

dedicated PCB analysis tools are not necessary

• Simulation of the 3D environment to consider resonance phenomenon

Overview


Considerations

• Due to electrical length, radiation from cables exceeds radiation from PCB (at 100 MHz, PCB << wavelength; PCB

cannot act as antenna).

• On TWPs, radiation from differential mode signal is negligible. Radiation is generated by an unintentional common-

mode signal on the TWP.

• If you can estimate the common-mode signal, you can perform a good automotive EMC analysis.

• Small differences in line length à

Some differential mode converted to common mode à

Significant radiation possible• •

• •• •

• •

Connector

• •

• •• •

• •

• •

• •• •

• •

Layer change through vias

Different routing on the same layer

Details of reaching connector pins

• IC specifications may quantify this; otherwise hard to estimate.

CAN_H transitions earlier than CAN_L, and has a larger voltage.

CAN_H

CAN_L

CAN_H

CAN_L

Sum signal

Offset

Pulses due to

time difference


Example simplified PCB

• Preserved: PWR/GND planes, capacitors, selected differential signal lines and their neighbours, including vias and bond

wires.

• Not preserved: other signal lines, unnecessary apertures.


Routing of cable and 3D model

• Includes car, ground, aggressor cable, victim cable, windscreen antenna

• List of points define cable path

• Imported list (KBL format supported, Nastran, Custom data file)


Differential and common-mode circuits

• Broad-band frequency-domain responses first.

• In post processor, conversion to time domain and launching time-domain results from

previous stage.


Time-domain recipe: general workflow

Frequency domain

Post treatment

Post treatment


Voltage at terminal of victim cable

• Top: caused by

differential

signal

• Bottom:

caused by

common-mode

signal

In victim

order of magnitude

larger!!


Voltage at passive terminal of windscreen antenna

• Top: caused by

differential

signal

• Bottom:

caused by

common-mode

signal

Again

an order of magnitude

larger!!


Snapshot time-domain radiated field near maximum

• Top: caused by

differential signal.

• Bottom: caused by

common-mode

signal.

• Maxima don’t occur at the same

time, since signals are different.

Again

an order of magnitude

larger!!


Frequency-Domain recipe

• Emission =

[fraction of IC signal that is converted to common mode in the PCB] ×

[cable emission from 1 V common-mode signal] ×

[spectrum of the digital signal × receiver band width].

• Emission can be compared with regulations.


How will the results compare with CISPR 25 standard?


100 Mb/s, rise time 100 ps

• Short rise and fall times limitations are exceeded.

• fknee = 3.5 GHz


100 Mb/s, rise time 1 ns

• Reasonable rise time (1/10 of bit duration) just within limitations.

• fknee = 350 MHz


100 Mb/s, rise time 3 ns

• Long rise time regulations easily satisfied

• fknee = 117 MHz


Conclusion and Perspectives


Conclusion and perspectives

- Equivalent radiation model help to reduce PCB 3D complex simulation

- Other simplification method is considered for high rate PCB system simulation

- Asymmetries and common-mode analysis on PCB boards

- 3D environment consideration with surrounding devices (antenna, cable, connector,…)

simulation for complete EMC aspects studies

- New methods for equivalent radiation sources are under progress to reduce simulation

runtime

simulation of emissions and immunity for pcbs and other ... · • the car model includes a cable...

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