Simulating Complex Power- Ground Plane Shapes with Variable-Size - - PowerPoint PPT Presentation

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Simulating Complex Power- Ground Plane Shapes with Variable-Size Cell SPICE Grids

Istvan Novak, Jason R. Miller, Eric Blomberg SUN Microsystems, Inc. One Network Drive, Burlington, MA 01803

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Outline

• Uniform, rectangular plane models
• Need for adaptive, non-uniform grids
• Impedance profiles with various cutouts
• Hardware correlation with adaptive grid
• Conclusions

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Upper conductor Dielectric material Lower conductor x y

Conductive plane pair with dielectric separation:

X cells Y cells Subckt: L_line_g Subckt: L_line_e

Grid subcircuit model:

Simulation Model for Plane Pairs

(Rectangular and Uniform)

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Irregular Plane Shape with Cutouts

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Symmetrical Cutout in Middle (1)

• 1/16” FR4 double-sided 4”x6” rectangular

plane pair

• Transfer impedance along shorter side
• Removed copper

– None – 0.5”x0.75” rectangular cutout – 1”x1.5” rectangular cutout – 2”x3” rectangular cutout – 3”x5” rectangular cutout

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Symmetrical Cutout in Middle (2)

Impedance magnitude [ohm]

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+08 1.E+09 Frequency [Hz] full 0.5x0.75 1.0x1.5 2.0x3.0 3.0x4.5

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Symmetrical Cutout in Middle (3)

Frequency

• f first

modal resonance peak

Percentage frequency change over percentage copper removed

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 10 20 30 40 50 60 70 Relative copper area removed [%]

1.0”x1.5” 3.0”x5.0” 2.0”x3.0” 0.5”x0.75”

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Symmetrical Slot in Middle (1)

• 1/16” FR4 double-sided 4”x6” rectangular

plane pair

• Transfer impedance along shorter side
• Slot in middle, 0.125” wide

– None – 0.75” rectangular cutout – 1.5” rectangular cutout – 3” rectangular cutout – 4.5” rectangular cutout

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Symmetrical Slot in Middle (2)

Impedance magnitude [ohm]

0.01 0.1 1 10 100 1.00E+08 1.00E+09 Frequency [Hz] full 0.75 1.5 3 4.5

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Symmetrical Slot in Middle (3)

Frequency

• f first

modal resonance peak

Percentage frequency change over percentage copper removed

• 0.4
• 0.2

0.2 0.4 0.6 0.8 1 0.5 1 1.5 2 2.5

Relative copper area removed [%]

0.75” 1.5” 3.0” 4.5”

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Cut from Side (1)

• 1/16” FR4 double-sided 3”x6” rectangular

plane pair

• Transfer impedance along 1” on side
• Cut from side, 0.03” wide

– None – 0.5” cut – 1” cut – 2” cut – 3” cut – 4” cut – 5” cut

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Cut from Side (2)

Impedance magnitude [ohm]

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+08 1.E+09 Frequency [Hz] full 0.5" cut 1" cut 2" cut 3" cut 4" cut 5" cut

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Cut from Side (3)

Frequency

• f first

modal resonance peak

Percentage frequency change over percentage copper removed

• 10

10 20 30 40 50 60 0.2 0.4 0.6 0.8 1

Relative copper area removed [%]

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Limitations of Rectangular Uniform Grids

• Many cells may fall
• utside of shape
• SPICE run-time grows

sharply with node numbers

• Unnecessary nodes

increase run time

• Cant switch to fine

mesh in sensitive areas

• Modal resonances may

not be captured correctly

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Cell and Diamond Definitions

Fupper Flower Fpair

Diamond1 Diamond2 Diamond3 Diamond4

Cell Diamond Segment Node

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EPEP2002 Full cell Partially empty cell Empty cell Cell Diamond

Definitions of Example Shape

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Grid with Adaptive Sub Gridding

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Correlation on Modal Resonances (1)

Example shape from Slide 4:

• Irregular outline
• Cutouts

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Impedance measured, simulated: adaptive grid and simulated: fixed grid [ohm]

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+07 1.E+08 1.E+09 Frequency [Hz]

Correlation on Modal Resonances (2)

Self-impedance at white arrow Uniform grid:

• Overestimates

static capacitance

• Overestimates

resonance frequencies Adaptive grid:

• Good

correlation

Fixed uniform grid Adaptive grid Measured

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Acknowledgement

Pre-processor SKILL script was written by Roger Cleghorn, Cadence SPICE equivalent circuits were created by perl code, written by Ken Laird, North Eastern University Further contributions and support:

• Hemant Shah (Cadence)
• Nick Laplaca (SUN)
• Deborah Foltz (SUN)
• Paul Baker (SUN)
• Paul Sorkin (SUN)

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Conclusions

• Odd shapes, cutouts and perforations change

– Static capacitance – Modal resonances

• Modal resonances do not scale with static

capacitance

• Adaptive, non-uniform plane models can

– Allow for finer mesh in critical areas – Capture modal resonances of odd shapes – Capture signatures of perforated planes

• Adaptive grid showed good hardware correlation

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TDR and TDT response [V]

• 3.00E-01
• 2.50E-01
• 2.00E-01
• 1.50E-01
• 1.00E-01
• 5.00E-02

0.00E+00 5.00E-02 4.50E-08 4.55E-08 4.60E-08 4.65E-08 4.70E-08 4.75E-08

Time [sec]

• 2.48E-01
• 2.46E-01
• 2.44E-01
• 2.42E-01
• 2.40E-01
• 2.38E-01
• 2.36E-01
• 2.34E-01

Correlation on Perforated Plane (1)

1.8”x1.6”x0.002” Measured in the middle, front/back Via pair: 20mil drill, 50-mil center-to- center TDR source:

• 150psec
• 50 ohm

TDT input:

• 50 ohm

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Simulated and measured response [V]

• 2.48E-01
• 2.47E-01
• 2.46E-01
• 2.45E-01
• 2.44E-01
• 2.43E-01
• 2.42E-01

4.55E-08 4.56E-08 4.57E-08 4.58E-08 4.59E-08 4.60E-08 4.61E-08

Time [sec]

Correlation on Perforated Plane (2)

Adaptive grid captures accurately:

• Plane

perforations

• Edge

reflections