Design for Guaranteed EMC Compliance · 2013. 4. 30. · Calculator (MREMC) Development of...

Automotive EMC Workshop

Clemson Vehicular Electronics Laboratory

Reliable Automotive Electronics

Design for Guaranteed EMC Compliance

April 29, 2013

Todd Hubing Clemson University

EMC Requirements and Key Design Considerations

Radiated Emissions Radiated Susceptibility

Transient Immunity

Electrostatic Discharge

Bulk Current Injection

• 1 HF GND • Risetime Control • Filtered I/O • Adequate

Decoupling • Balance Control

• 1 HF GND • Filtered I/O • Adequate


• LF Current Path Control

• Chassis GND on board

• Filtered I/O • Adequate

Decoupling

• LF Current Path Control

• Chassis GND on board

• Filtered I/O • Adequate

Decoupling

• 1 HF GND • Chassis GND on

board • Filtered I/O • Adequate


2

In 2011, CVEL began to guarantee that the automotive products they reviewed/designed would meet all automotive EMC

requirements the first time they were tested.

Clemson Vehicular Electronics Laboratory - 2013

What we are NOT doing

3

NOT Relying on EMC Design Guidelines


What we are NOT doing

4

NOT Modeling Products with Numerical EM Modeling Codes

Numerical EM modeling codes give precise answers to precisely defined problems. EMC geometries are not well-defined.

We don’t want to know how much a given configuration will radiate. The answer to that question depends on a lot of factors that we have no control over. We want to know if our product will meet its requirements.


What we ARE doing

5

Identifying all possible sources, victims and coupling paths

SOURCE ANTENNA


History

6

1989 2013 1995 2006

Begin development of

numerical modeling

software for EMC analysis at

UMR

Formation of EMC Expert

System Consortium

First Maximum Radiated Emission Calculator (MREMC)

Development of Performance-Based Design

for EMC Process

Investigation of fundamental EMI source mechanisms driving common-mode radiation from printed circuit boards with attached cables, IEEE Trans. on EMC, Nov. 1996.

Calculating radiated emissions due to I/O line coupling on printed circuit boards using the imbalance difference method,” IEEE Trans. on EMC, Feb. 2012.

Estimating maximum radiated emissions from printed circuit boards with an attached cable, IEEE Trans. on EMC, Feb. 2008.

Development of algorithms for calculating radiated emissions and EM coupling for various PCB structures

~40 publications relating to ability of various PCB structures to radiate


Maximum Radiated Emissions Concept

7

315 MHz RF Transmitter (5 watts)

Connector for Antenna

What is the maximum 3-meter radiated field strength at 315 MHz?

a. impossible to predict without knowing what antenna is connected b. impossible to predict even if the antenna is known c. 15 V/m d. none of the above



8




2

02

14 2

radrec

EPP D

rπ η= = 022max

radPE D

rη

π=



9




02 2

377 5 6 4 14 62 2 3max

( )( W)( . ) . V/m

( m)radP

E Dr

ηπ π

Ω= = =



10


We can put an upper bound on the radiated emissions at any given frequency! The more we know about the product design, the lower this upper bound becomes.



11

Possible Antenna? Possible Source?

(Processor with 200-MHz clock)


Maximum Radiated Emissions Calculation

12

~

Cable Equivalent

voltage

VCM

heatsink

board

=CM DMCV VC

boardmax

heatsink board cable

0.2234= × ×DMC rV E

C F F

To Floor

To Floor

~ VDM Noise voltage

Heatsink

References [1] H. Shim and T. Hubing, “Model for Estimating Radiated Emissions from a Printed Circuit Board with Attached Cables Driven by Voltage-Driven Sources,” IEEE Transactions on Electromagnetic Compatibility, vol. 47, no. 4, Nov. 2005, pp. 899-907. [2] Shaowei Deng, Todd Hubing, and Daryl Beetner, "Estimating Maximum Radiated Emissions From Printed Circuit Boards With an Attached Cable,“ IEEE Trans. on Electromagnetic Compatibility, vol. 50, no. 1, Feb. 2008, pp. 215-218.


Maximum Radiated Emissions Calculation

13

heatsink

board

0.43 pF5.14 pF

==

CC

20cm 20cm

100 cm

5cm 5cm

1cm

Spacing between heatsink and board is 1 cm


Maximum Radiated Emissions Calculator

14


Performance-Based EMC Design Procedure

15

1. Determine worst-case signal characteristics

2. Calculate maximum possible emissions from signal driving matched antenna

3. If > limit at any frequency, control risetime with series resistor

4. Recalculate maximum possible emissions from signal driving matched antenna

5. Proceed to Step II.

Step I: For each net on each board:


MS Excel Spreadsheet Calculation

16


Design Review Procedure

17

1. Determine worst-case emissions due to each of the 5 MREMC algorithms that apply to your design

2. For any net that does not meet the specification at every frequency as determined by a given algorithm, adjust the design until the net is compliant.

Step II: For each net at each frequency over the limit:


Example 1: Microcontroller Output Driver

18

Vsource = 3.3 V

Imax = 20 mA

Cin = 5 pF

Rseries = 0 Ω

CLK Freq = 100 kHz

Available Information

Rsource = 165 Ω

T = 10 µs

tr = 1.82 ns

Calculated Parameters

Suppose we connected an output of this microcontroller directly up to an impedance-matched antenna…

Automotive microcontroller in typical application:

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

10 100 1000

3-M

ETER

E-F

IELD

IN D

B(u

V/M

)

FREQUENCY IN MHZ

Maximum Radiated Field

FCC Limit

Absolute maximum possible emissions!



19

Vsource = 3.3 V

Imax = 20 mA

Cin = 5 pF

Rseries = 20 kΩ

CLK Freq = 100 kHz


Rsource = 8165 Ω

T = 10 µs

tr = 220.0 ns



Same output with 20-kΩ series resistor:

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

10 100 1000

3-M

ETER

E-F

IELD

IN D

B(u

V/M

)

FREQUENCY IN MHZ

Maximum RadiatedFieldFCC Limit


Series Resistors

20

Optimal control

Minimal cost / Minimal footprint

Predictable behavior

Easy to adjust without affecting layout

Reduces power bus noise

Why use series resistors to control transition times?



21

Vsource = 3.3 V

Imax = 20 mA

Cin = 5 pF

Rseries = 0 kΩ

CLK Freq = 1 MHz


Rsource = 165 Ω

T = 1 µs

tr = 1.82 ns



Same output with 1 MHz output:

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

10 100 1000

3-M

ETER

E-F

IELD

IN D

B(u

V/M

)

FREQUENCY IN MHZ


FCC Limit



22

Vsource = 3.3 V

Imax = 20 mA

Cin = 5 pF

Rseries = 8 kΩ

CLK Freq = 1 MHz


Rsource = 8165 Ω

T = 1 µs

tr = 90 ns



Same output with 1 MHz output and 8-kΩ series resistor:

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

10 100 1000

3-M

ETER

E-F

IELD

IN D

B(u

V/M

)

FREQUENCY IN MHZ


FCC Limit


Example 3: Xilinx Vertex-6 FPGA SelectIOTM

23

Vsource = 2.5 V

Imax = 240 mA*

Cin = 5 pF

Rseries = 0 kΩ

CLK Freq = 1 MHz


Rsource = 50 Ω

T = 1 µs

tr = 0.55 ns


Suppose we connected an output of this FPGA directly up to an impedance-matched antenna…

With 1 MHz output :



24

Vsource = 2.5 V

Imax = 240 mA*

Cin = 5 pF

Rseries = 20 kΩ

CLK Freq = 1 MHz


Rsource = 50 Ω

T = 1 µs

tr = 221 ns


With 1 MHz output and 20-kΩ series resistor: Suppose we connected an output of this FPGA directly up to an impedance-matched antenna…



25

Vsource = 2.5 V

Imax = 240 mA*

Cin = 5 pF

Rseries = 0 kΩ

CLK Freq = 32 MHz


Rsource = 50 Ω

T = 31 ns

tr = 0.55 ns


With 32 MHz output and 0-Ω series resistor: Suppose we connected an output of this FPGA directly up to an impedance-matched antenna…



26

Vsource = 2.5 V

Imax = 240 mA*

Cin = 5 pF

Rseries = 500 Ω

CLK Freq = 32 MHz


Rsource = 50 Ω

T = 31 ns

tr = 6.0 ns


With 32 MHz output and 500-Ω series resistor : Suppose we connected an output of this FPGA directly up to an impedance-matched antenna…


3 Elements of a Radiated Emissions Problem

27

SOURCE ANTENNA


MREMC Algorithms (Nets)

28

Direct Radiation from Trace

Trace Drives an Attached Cable and/or Heatsink

Trace Couples to another Trace that Drives an Attached Cable

Trace Drives the Power Bus

Need to know: net dimensions

Need to know: net dimensions, net placement, connector placement, and board dimensions

Need to know: net dimensions, net placement, connector placement, and board dimensions

Need to know: board dimensions



29

Direct Radiation from 10-cm trace, 1-mm above plane



30




31




32



MREMC Algorithms (Components)

33

Direct Radiation from Component

Component Drives an Attached Cable and/or Heatsink

Component Couples to another Trace that Drives an Attached Cable

Component Drives the Power Bus

Negligible

Measure or model the equivalent dipole source for the component and use the trace algorithm

Measure or model the equivalent dipole source for the component and use the trace algorithm

Need to know: board dimensions, CPD and load Cs, component datasheet information


MREMC Algorithms (Shielded Products)

34

Board analysis should be done as if there were no shield

E-field coupling problems can be mitigated with E-field shielding

Common-mode currents on cables can be mitigated enclosure to cable filtering

Wiring Harness

Digital Return PlaneChassis Ground Plane

Capacitors connectingchassis ground to thedigital return plane

Chassis connectionto chassis ground

Chassis connectionto chassis ground


h = 0.5 - no plane h = small - w/ plane

MREMC Algorithms (Differential Signals)

35

Use Imbalance Difference Model to convert all differential signals to equivalent common-mode sources

Then apply the same algorithms used for single-ended signals


Susceptibility Calculations

36

PORT 1 PORT 2

Calculate Maximum Possible S21 Maximum Radiated Emissions Calculator (MREMC)


Application to Infotainment System

37

5 Circuit Boards, mixed-signal RF, audio, video

Internal ribbon cable connections

Unshielded external connections

AM/FM Radio

3 Camera Interfaces

GPS

DVD Player

USB

Fold-out Display


EMC Testing

38


Identify Antennas

39


Design Guidelines

40

e.g. No ground traces. No shared ground vias.

Many design “rules” were violated in the final design. Attempting to comply with a complete list of design rules would have made the product unnecessarily expensive.

Nevertheless, some rules make too much sense to ignore. (Even if they are not explicitly required.)


Design Flexibility

41

e.g. grounding option

It’s a good idea to leave options open to deal with unexpected issues.


Design Standards

42

e.g. GPS antenna interface

Many circuit geometries were based on known success with prior products.


For This Product Design (Nets)

43

Direct Radiation from Trace



Trace Drives the Power Bus

No calculations made. Provided HF current return for all nets not eliminated after Step 1 (critical nets).

Optimized each critical net, but relied on filtering to chassis to guarantee compliance.

No calculations made. Visually highlighted all I/O and kept several trace heights away from critical nets.

No calculations made. Focused on providing excellent HF decoupling.


For This Product Design (Components)

44

Direct Radiation from Component

Component Drives an Attached Cable and/or Heatsink

Component Couples to another Trace that Drives an Attached Cable

Component Drives the Power Bus

No calculations made. Negligible.

No calculations made. Judged to be a non-issue.

No calculations made. Visually highlighted all I/O and kept critical components away.

No calculations made. Focused on providing excellent HF decoupling.


Current Project Status

45

Documenting MREMC algorithms

Increasing awareness

Looking for software partner

Formulating radiated susceptibility algorithms


Performance-Based EMC Design of Electronic Systems

46

In Compliance Magazine, May 2013.

Automotive Testing Technology International, Nov. 2012.


Expected Outcomes

47

Software tools will make this technique easier to implement and accessible to non-expert design engineers

Will increase consumer demand for EMC-specific component information

Will not replace EMC engineers, but will allow more sophisticated designs

Will help engineers to use numerical EM modeling tools more effectively

Design for Guaranteed EMC Compliance · 2013. 4. 30. · Calculator (MREMC) Development of...

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