Reducing EMI Noise by Suppressing Power-Distribution...
Transcript of Reducing EMI Noise by Suppressing Power-Distribution...
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
3Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
4Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
5Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
6Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
7Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
• 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
8Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
9Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
10Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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]
11Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
Impedance magnitude [ohm]
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]
12Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
PDN Design (4)PDN comparison without voltage positioning
Impedance magnitude [ohm]
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
13Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
PDN in the Frequency Domain• DC sources: low frequency• Bypass capacitors: mid frequency• PDN planes, board and chassis features: high frequency
Impedance magnitude [ohm]
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
14Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
15Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
Impedance magnitude [ohm]
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]
16Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
17Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Peaking Between DC Source and Bulk
• Low-frequency peaking• PI concern, no EMI risk
Impedance magnitude [ohm]
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+07Frequency [Hz]
Powered
Unpowered
18Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Peaking Between Capacitor Banks
• Low-frequency peaking• PI concern, no EMI risk
Impedance magnitude [ohm]
1.E-03
1.E-02
1.E-01
1.E+00
1.E+07 1.E+08Frequency [Hz]
19Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Peaking Between Capacitors and Plane
• High-frequency peaking• PI and EMI risk
Impedance magnitude [ohm]
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10Frequency [Hz]
20Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Peaking Between Capacitors and Plane: How to Solve
• Matched termination• Area capacitors• Hardest peaking to
suppress
21Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Structural Plane Resonances
• High-frequency peaking• PI and EMI risk
Impedance magnitude [ohm]
1.E-03
1.E-02
1.E-01
1.E+07 1.E+08 1.E+09 1.E+10Frequency [Hz]
22Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Structural Plane Resonances: How to Solve
Options:
• Thin laminates
• Resistive termination
• Area capacitors
23Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
24Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
25Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
Structural Plane Resonances: Resistive Termination
Implementation options:• Discrete R-C• Embedded R• Controlled-ESR capacitors
Impedance magnitude [ohm]
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
26Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
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
27Ansoft EMI Control and PCB Power Analysis, 22 August 2007, Boston, MAIstvan Novak, SUN Microsystems
EMI from AC-DC Source
With PSU #1 With PSU #2
Only the AC/DC power supply was changed
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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