Power Integrity Measurements Choosing The Right Tools
Kenny Johnson
Keysight Technologies
R&D/Marketing Engineer
February 26, 2015
125MHz
clock
Page Webinar Goals or Outcome
Show you some things you can do today to:
– Debug and test PDN’s (power distribution networks) with
more precision, accuracy and confidence.
– More easily isolate root cause of PDN noise.
– Avoid false negative (or positive) test results.
– Become aware of specialized tools that can make your job
easier.
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Simple Advanced things you can do today (10 things)
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Power Integrity Measurements
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Believe it or not, this is what a
typical1.8V DC supply looks like if you
zoom-in on the top of it. The Need for Power Integrity
Measurements
• Increased functionality, higher power density
and higher frequency operation drives need for
lower supply voltages
• Power rail tolerances are much tighter (from +/-
5% down to +/- 1%)
• Ripple, noise and transients riding on these
lower DC supplies can adversely affect clocks
and digital data—Power Supply Induced Jitter
(PSIJ)
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The Case For Power Integrity
Confidentiality Label
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Moore’s Law: transistors on an integrated circuit will double every two years.
Past Present Past Present
10% 1-5%
Tolerances
Past Present
1-3%
Goal: improve power
consumption with each
generation
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The Case For Power Integrity
Confidentiality Label
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Power supply noise causes clock/data jitter.
Power Supply Tolerances
Switching Threshold Variation
Input
Output
Jitter
Jitter Jitter
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Power Integrity Measurements
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Switching loads can
cause high frequency
supply noise.
Clock/Data
Power Rail
Additional Challenge
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Power Integrity Measurements
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• Supply drift
• PARD (Periodic and Random
Disturbances)—noise, ripple and
switching transients on power
rails.
• Static and dynamic load
response.
• Programmable power rail
response.
• High frequency transients and
noise.
• Product electrical validation at
extended temperatures.
Common Power Integrity Measurements
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Power Integrity Measurements Fundamental Challenge
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Challenge: Measure small
ac signal on top of large dc
signal
Measurement System Noise
(Scope, Probe, Connection…) 1. Measurement system noise
2. Large signal offset
Issues to overcome:
Tolerance Band
DC
Probing “golden” rule:
3. Do no harm (probe loading)
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Power Integrity Measurements
– Null measurement: Baseline noise of the oscilloscope measurement
system to verify that the tools being used are appropriate for the
task at hand.
• Set-up you scope and probe as they will be used—V/div,
connection accessories…
• Short the input and measure the baseline noise.
First things first—Null Measurement (Sanity Check)
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Power Integrity Measurements Null Measurement Compare—Ends of The Spectrum
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Specialized General Purpose
N7020A Power Rail Probe 10:1 Passive Probe
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Power Integrity Measurements
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The Set-up
Infiniium S-Series High-Definition Oscilloscope
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Power Integrity Measurements Null Measurement Compare—Ends of The Spectrum
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Need Actual screen shot
1.1mVp-p Noise
23.3mVp-p Noise
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Power Integrity Measurements 3.3V Supply Measurement Compare
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31.8mVp-p Noise
62.3mVp-p Noise
(96% Larger)
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Power Integrity Measurements Things You Can Do.
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Begin with a Null
measurement.
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Power Integrity Measurements Both Ends of The Spectrum
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N7020A Power Rail Probe
Termination: 50Ω
Attenuation: 1:1
Bandwidth: 2GHz
Gnd connect: Coax “pigtail”
Passive Probe
Termination: 1MΩ
Attenuation: 10:1
Bandwidth: 500MHz
Gnd connect: “Alligator” clip
Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
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Power Integrity Measurements Both Ends of The Spectrum
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N7020A Power Rail Probe
Termination: 50Ω
Attenuation: 1:1
Bandwidth: 2GHz
Gnd connect: Coax “pigtail”
Passive Probe
Termination: 1MΩ
Attenuation: 10:1
Bandwidth: 500MHz
Gnd connect: “Alligator” clip
Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
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Power Integrity Measurements Scope Input Termination—Lowest Noise Path
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50Ω: 0.6mVp-p Noise
1MΩ: 2.4mVp-p Noise
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Power Integrity Measurements Things You Can Do.
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Choose the low noise path.
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Power Integrity Measurements Both Ends of The Spectrum
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N7020A Power Rail Probe
Termination: 50Ω
Attenuation: 1:1
Bandwidth: 2GHz
Gnd connect: Coax “pigtail”
Passive Probe
Termination: 1MΩ
Attenuation: 10:1
Bandwidth: 500MHz
Gnd connect: “Alligator” clip
Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
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Power Integrity Measurements Attenuation Ratio Effects Noise—Ex. 50mVpp Sine Wave
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1:1 Passive Probe—52mVpp
10:1 Passive Probe—65mVpp
Overstated ~4%
Overstated ~30%
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Power Integrity Measurements Things You Can Do.
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Reduce attenuation ratio.
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Power Integrity Measurements Both Ends of The Spectrum
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N7020A Power Rail Probe
Termination: 50Ω
Attenuation: 1:1
Bandwidth: 2GHz
Gnd connect: Coax “pigtail”
Passive Probe
Termination: 1MΩ
Attenuation: 10:1
Bandwidth: 500MHz
Gnd connect: “Alligator” clip
Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
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Power Integrity Measurements BW Effects Noise—Ex. N7020A Probe/S-Series Scope
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800µVp-p
460µVp-p
860µVp-p
20MHz BW Limit
1GHz BW Limit
500MHz
BW Limit
2GHz BW Limit
1,040µVp-p
1GHz BW Limit
860µVp-p
500MHz BW Limit
800µVp-p
20MHz BW Limit
460µVp-p
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Power Integrity Measurements Things You Can Do.
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BW—use what is needed.
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Power Integrity Measurements Tradeoff with BW limiting—Use What is Needed
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BW: 2.5 GHz
Captures high-freq transients
BW: 20 MHz
Attenuates high-freq transients
Switching
currents cause
transients that
can easily exceed
1GHz.
Supply noise is a
leading cause of
clock/data jitter.
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N7020A 2 GHz, 1:1
N2870A 35 MHz, 1:1
Power Integrity Measurements Having Enough BW is Critical
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Specialized
General Purpose
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Power Integrity Measurements Things You Can Do.
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BW—have enough.
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Power Integrity Measurements Both Ends of The Spectrum
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N7020A Power Rail Probe
Termination: 50Ω
Attenuation: 1:1
Bandwidth: 2GHz
Gnd connect: Coax “pigtail”
Passive Probe
Termination: 1MΩ
Attenuation: 10:1
Bandwidth: 500MHz
Gnd connect: “Alligator” clip
Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
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Power Integrity Measurements Gnd Connection Length Effects Noise: Ex. Passive Probe
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44.8 mVp-p
51.5 mVp-p (15% Larger)
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Power Integrity Measurements Gnd Connection Length Effects Noise
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27.7 mVp-p
44.8 mVp-p (62% Larger)
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Power Integrity Measurements Things You Can Do.
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Minimize ground loop area.
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Power Integrity Measurements Large DC Signal Offset
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Remove DC Signal Offset
• Probe Offset
• DC Block
At larger V/div
• Sensitivity is decreased
• Scope noise relative to small ac
signal is increased. 131mVp-p
With Full Offset: 83mVp-p
(58% Larger)
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Power Integrity Measurements Removing Large DC Signal—Probe Offset or DC Block
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DC Block
Using a DC Block
Using Probe Offset
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Power Integrity Measurements Removing Large DC Signal—Probe Offset of DC Block
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0V
1.5V
DC Block
Using a DC Block
Using Probe Offset
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Power Integrity Measurements Things You Can Do.
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Use probe offset.
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Power Integrity Measurements A Word of Caution: Direct 50Ω Connection
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The scope you are using may have enough frame offset for some signals.
Beware of 50Ω load at dc.
Specialized
General Purpose
N7020A—50kΩ @ DC
DC Vrms= 3.31V
50Ω cable to oscilloscope 50Ω input
(50Ω @ DC)
50Ω @ DC pulled this
supply down ~60mV
(changed the target this
much)
DC Vrms= 3.25V
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Power Integrity Measurements Things You Can Do.
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Minimize loading.
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Power Integrity Measurements Gaining Insight—Using The Frequency Domain
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Example:
In time domain view
switching currents of
high speed digital
signals may not be
obvious
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Power Integrity Measurements Gaining Insight—Using The Frequency Domain
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Example:
Using FFT’s can
enable identification
of possible noise
sources.
In this case, digital
circuits operating off
5V are causing noise
on 3.3V supply
3.3V supply
2.8MHz switcher 10MHz clock
125MHz clock
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Power Integrity Measurements Things You Can Do.
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Use The Frequency Domain
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Power Integrity Measurements Track Down Noise Sources with Trigger and Averaging.
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Example:
Using FFT’s we see
that the digital
circuits are causing
noise on the 3.3V
supply.
Is it worth making
changes (how much
are they effecting the
supply)?
3.3V supply
10MHz clock
2.8MHz switcher 10MHz clock
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Power Integrity Measurements Track Down Noise Sources with Trigger and Averaging.
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Example:
Triggering on
possible noise
source and enabling
averaging shows the
noise on the supply
that is coherent to
the noise source.
3.3V supply
Trigger on the clock
Turn on averaging
Signal content not related to trigger source is averaged out.
10MHz clock
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Power Integrity Measurements Things You Can Do.
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Use triggering and averaging.
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Power Integrity Measurements Summary
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Good for qualitative measurements Good for quantitative measurements
Specialized General Purpose
1. Begin with a Null measurement.
2. Choose the low noise path.
3. Reduce attenuation ratio.
4. BW—use what is needed.
5. BW—have enough.
6. Minimize ground loop area.
7. Use probe offset.
8. Minimize loading.
9. Use The Frequency Domain.
10.Use triggering and averaging.
Bonus Tip: Use a specialized tool
Keysight N7020A Power Rail Probe:
www.keysight.com/find/N7020A
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Power Integrity Measurements Used Today: Infiniium S-Series High-Definition Oscilloscope
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– Low noise front end at small vertical
settings
– Full 10-bit ADC support with full BW
down to 16 mV full screen
– Analog and DSP-based bandwidth
limit filters
– Measurement capability including
FFTs, axis annotation, dynamic delta
markers
Keysight N7020A Power Rail Probe:
www.keysight.com/find/N7020A
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Power Integrity Measurements N7020A Power Rail Probe
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InfiniiVision 3000 X-Series Oscilloscopes
InfiniiVision 4000 X-Series Oscilloscopes
InfiniiVision 6000 X-Series Oscilloscopes
Also Compatible With:
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Upcoming WebEx on Power Integrity
Customizable in
Footer
Live demonstrations and Q&A with Kenny (1 hour)
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Power Integrity Challenges, Measurements and Labs
Tuesday, February 23 at 1:00 pm PT
Go to: www.keysight.com/find/events
and scroll down to Feb 23 to register
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Power Integrity Measurements Things You Can Do.
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Thank you for your time.