Reducing EMI Noise by Suppressing Power-Distribution ...electrical-integrity.com/Paper_download_files/...Noise by Suppressing Power-Distribution Resonances Istvan Novak Distinguished

1

Reducing EMI Noise by

Suppressing Power-Distribution

Resonances

Istvan NovakDistinguished Engineer,

Signal and Power IntegritySun Microsystems

2Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems

• Introduction: revisiting the definition of EMI

• Possible resonances in PDN

• Suppressing resonances

• Conclusions

Outline


In traditional view, the three disciplines are applied independently

• SI: 1D wave propagation effects

• Reflections, termination, crosstalk

• PI: 2D and 2.5D wave propagation effects

• Plane resonances, SSN due to via inductance

• EMI: 3D wave propagation effects

• EM interaction through distance (out-of system source)

IntroductionSI, PI, EMI


More and more the interactions cant be ignored

• SI>EMI: Resonances on no-care signals may create EMI problems

• PI>EMI: Resonances on power distribution increase radiation

• PI>SI: Resonances on power distribution increase jitter and BER

• EMI>SI: conducted and radiated noise from in-system modules reduce BER

In-system EMI is becoming an increasing problem

IntroductionSI, PI, EMI revisited


Trends in Power Distribution Design

• Clock frequencies rise>> BW goes up• Supply voltages drop>>more domains>>tighter tolerances>>higher currents>>lower PDN impedance

0

10

20

5 10 15 200

IOL drive

(mA)

t pd (nsec)

30

40

50

60

HC/HCTLV

AH/AHCT

ALB, ALVCLVC

AC

AHC

ALVT

ALVCAVC

5V3V2.5V1.8V

0

10

20

5 10 15 200

IOL drive

(mA)IOL driveIOL drive

(mA)

t pd (nsec)t pdt pd (nsec)

30

40

50

60

HC/HCT

ABT BCT, 74F

AC/ACT

LVAH/AHCT

LVT, ALVT

ALB, ALVC

AC

AHC

ALVCAVC

AVC ALVC LVC

Supply voltage:

1.2V1.5V

0.8V

AUPAUC

Source: Texas Instruments Logic Selection Guide, 2006; SDYU001Yhttp://www.ti.com


Trends in PDN RequirementsTarget impedance predicted in early 1998

0.1

1

10

100

1000

1992 1994 1996 1998 2000

Ztarget

Frequency

VddCurrent

Power Larry Smith, “Power Distribution for High Performance Systems,”Conference Class 4, EPEP98, West Point, NY, October 26-28, 1998


• Increasing number of independent supply rails (less room for planes and PDN components)

• Increasing system density (noise sources and sensitive circuits are closer). Note: scaling.

• Higher efficiency (lower losses create more high-frequency noise)

• Size and cost constraints (resonances may not be sufficiently suppressed)

PDN Trends


PDN Design Process Worst-case PDN noise calculation

Step response [V]

Worst-case positive response [V]

Stimulus edgeLog time [sec]

Δt1

Δt2 V0

V1

V2 Time [sec]

Δt1

Δt2

Vp =V0 - V1 +V2

VDC

t=0Worst-case peak-to-peak transient:Vpp = 2*Vp - VDC

Drabkin, et al, “Aperiodic Resonant Excitation of Microprocessor power Distribution Systems and the Reverse Pulse Technique,” Proc. of EPEP 2002, p. 175


PDN Design (1)Ideal response Impedance magnitude [ohm]

1.0E-3

1.0E-2

1.0E-1

1.E+2 1.E+4 1.E+6 1.E+8Frequency [Hz]

Step response [V]

-2.50E-030.00E+002.50E-035.00E-037.50E-031.00E-021.25E-02

1.E-9 1.E-8 1.E-7 1.E-6 1.E-5 1.E-4Time [sec]

-0.01-RL [nH]ESR [ohm]C [uF]

Worst-case peak-to-peak transient:10mVpp/A


PDN Design (2)The practical best: R-L

Worst-case peak-to-peak transient:10mVpp/A

Step response [V]

-2.50E-03

0.00E+00

2.50E-03

5.00E-03

7.50E-03

1.00E-02

1.25E-02

1.E-09 1.E-08 1.E-07 1.E-06 1.E-05

Time [sec]

0.150.01-R-LL [nH]ESR [ohm]C [uF]

R-L

Impedance magnitude [ohm]

1.E-3

1.E-2

1.E-1

1.E+2 1.E+4 1.E+6 1.E+8

Frequency [Hz]


PDN Design (3)PDN comparison with voltage positioning

Worst-case peak-to-peak transient:R-L: 10 mVpp/A, blue traceMultipole: 15.7 mVpp/A, red trace“Big-V”: 21.4 mVpp/A, green trace


1.E-03

1.E-02

1.E-01

1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8

Frequency [Hz] Step response [V]

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.E-9 1.E-8 1.E-7 1.E-6 1.E-5 1.E-4Time [sec]


PDN Design (4)PDN comparison without voltage positioning


1.E-03

1.E-02

1.E-01

1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 1.E+8Frequency [Hz] Step response [V]

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.E-9 1.E-8 1.E-7 1.E-6 1.E-5 1.E-4

Time [sec]

Worst-case peak-to-peak transient:R-L: 19 mVpp/A, blue traceMultipole: 25 mVpp/A, red trace“Big-V”: 27.5 mVpp/A, green trace


PDN in the Frequency Domain• DC sources: low frequency• Bypass capacitors: mid frequency• PDN planes, board and chassis features: high frequency


1.E-03

1.E-02

1.E-01

1.E+00

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10

Frequency [Hz]

DC source PCBCapacitors


Potential PDN Resonances

• DC sources• Peaking due to improper loop design• High-frequency ringing due to switch parasitics

• Peaking between DC source and bulk capacitors• Peaking between capacitor banks• Peaking between capacitors and planes• Structural resonances of PDN planes• Structural resonances of boxes, enclosures


DC-source Resonance due to Loop• Typical switching frequency is in the 0.1-1MHz range• Typical loop peaking is in the tens of kHz range• No EMI concern, primarily a PI issue


1.E-03

1.E-02

1.E-01

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07Frequency [Hz]


Converter Ringing

• Typical ringing frequency is in the 50 – 500 MHz range

• High-current converters may switch 100+ A

• Sensitive clock signals run on a few mA

• 80+ dB ratio• EMI and SI risk


Peaking Between DC Source and Bulk

• Low-frequency peaking• PI concern, no EMI risk


1.E-03

1.E-02

1.E-01

1.E+00


Powered

Unpowered


Peaking Between Capacitor Banks

• Low-frequency peaking• PI concern, no EMI risk


1.E-03

1.E-02

1.E-01

1.E+00

1.E+07 1.E+08Frequency [Hz]


Peaking Between Capacitors and Plane

• High-frequency peaking• PI and EMI risk


1.E-03

1.E-02

1.E-01

1.E+00

1.E+01



Peaking Between Capacitors and Plane: How to Solve

• Matched termination• Area capacitors• Hardest peaking to

suppress


Structural Plane Resonances

• High-frequency peaking• PI and EMI risk


1.E-03

1.E-02

1.E-01

1.E+07 1.E+08 1.E+09 1.E+10Frequency [Hz]


Structural Plane Resonances: How to Solve

Options:

• Thin laminates

• Resistive termination

• Area capacitors


Structural Plane Resonances: Thin Laminates (Self-Z)

Thin laminates: • Dampen

structural resonances

• Make it harder to suppress plane-capacitor resonances

Magnitude of self impedance at center [ohm]

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

10”x10” planesBare boardSimulated, t =• 10-mil• 5-mil• 2-mil• 1-mil• 0.5-mil• 0.2-mil• 0.1-mil• 0.05-mil• 0.02-mil• 0.01-mil


Structural Plane Resonances: Thin Laminates (Transfer-Z)

Magnitude of transfer impedance corner-to-center [ohm]

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

10”x10” planesBare boardSimulated, t=• 10-mil• 5-mil• 2-mil• 1-mil• 0.5-mil• 0.2-mil• 0.1-mil• 0.05-mil (1.2um)• 0.02-mil• 0.01-mil


Structural Plane Resonances: Resistive Termination

Implementation options:• Discrete R-C• Embedded R• Controlled-ESR capacitors


1.E-03

1.E-02

1.E-01

1.E+00

1.E+02 1.E+04 1.E+06 1.E+08

Frequency [Hz]

Impedance with and without DET [ohm]

0.0E+00

2.0E-02

4.0E-02

6.0E-02

8.0E-02

1.0E-01

1.2E-01

1.4E-01

1.E+08 1.E+09Frequency [Hz]

2.2x

1.9x

T2000 CPU moduleHigh-current rail


Structural Plane Resonances: High-ESR and/or Area Capacitors

• Thin laminates require more capacitors

• Number of parts is proportional to plane area

PDN impedance [ohm]

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09Frequency [Hz]

Low-ESR capacitors, medium number

High-ESR capacitors, large number


EMI from AC-DC Source

With PSU #1 With PSU #2

Only the AC/DC power supply was changed


Conclusions• High-frequency PDN resonances adversely affect EMI• High-frequency PDN resonances may occur

• Inside AC-DC and DC-DC converters• Between capacitors and planes• In PCB structures• In board and chassis features

• Best defence• Not to excite resonances (Fsource < Fresonances)• Minimise loop sizes and coupling areas• Suppress resonances by impedance matching• Suppress resonances with area capacitors

29

THANK YOU

Istvan NovakSun [email protected]

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Reducing EMI Noise by Suppressing Power-Distribution ...electrical-integrity.com/Paper_download_files/...Noise by Suppressing Power-Distribution Resonances Istvan Novak Distinguished