Power Integrity Measurements Kenny Johnson Keysight...

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


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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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Switching loads can

cause high frequency

supply noise.

Clock/Data

Power Rail

Additional Challenge

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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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– 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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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


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Termination: 50Ω

Attenuation: 1:1

Bandwidth: 2GHz


Passive Probe

Termination: 1MΩ

Attenuation: 10:1

Bandwidth: 500MHz




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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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Choose the low noise path.

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Termination: 50Ω

Attenuation: 1:1

Bandwidth: 2GHz


Passive Probe

Termination: 1MΩ

Attenuation: 10:1

Bandwidth: 500MHz




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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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Reduce attenuation ratio.

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Termination: 50Ω

Attenuation: 1:1

Bandwidth: 2GHz


Passive Probe

Termination: 1MΩ

Attenuation: 10:1

Bandwidth: 500MHz




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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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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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BW—have enough.

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Termination: 50Ω

Attenuation: 1:1

Bandwidth: 2GHz


Passive Probe

Termination: 1MΩ

Attenuation: 10:1

Bandwidth: 500MHz




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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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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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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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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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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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Use triggering and averaging.

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Power Integrity Measurements Summary

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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

http://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

http://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



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

http://www.keysight.com/find/events

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Thank you for your time.

Power Integrity Measurements Kenny Johnson Keysight...

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