De-embedding and Equalization Techniques In RealTime
Feb 4, 2009 - Go to the Math function menu and select the *CDeconvolve operator. Set Source 1 .... â¢http://cp.literature.agilent.com/litweb/pdf/5989-3777EN.pdf.
De-embedding and Equalization Techniques In RealTime Oscilloscopes
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PWRP_301 N6705A Hands-On S800 November 2008
Why de-embed is important Enable Next Generation Of Serial Measurements Measurement of electrical performance always requires some type of fixture or probing to get at the signal Losses in the fixtures and probing get in the way of validating that your design meets the requirements Requirement For Next Generation Of Compliance – Gen 2 And Beyond Critical for Customers at 5Gbit and above, especially for silicon validation/compliance testing Enables Customer to Compensate for Channel Loss, Probe Virtually, and Emulate Equalization/De-emphasis at Receiver Customers Are Asking Agilent to Solve This Problem Page 2
AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
TERMINOLOGY •Channel •Medium Signal
•Fixture
Signal
Source
•Cables
Consumer
•Adapters •Wires
Magnitude and phase behaviors over frequency are described by aremove channel set of S-parameters. de-embed de-convolve transform
add channel embed
A signal processor or measurement device
convolve filter
Measurement Plane
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PWRP_301 N6705A Hands-On S800 November 2008
Source of Measurement Inaccuracies •impedance mismatches •probing effects •smaller geometries •test cables and adapters •fixturing •device packaging, etc. •SCOPE NOISE FLOOR! There are multiple ways to offset these measurement impairments. •calibration methods •mathematical signal processing •de-embedding/embedding techniques
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Measurement system noise will be amplified by de-embedding techniques PWRP_301 N6705A Hands-On S800 November 2008
Fixture Error Correction Techniques Most Accurate
S-Parameter De-embedding
Agilent Actively Developing Customer Solutions Here
Skew Calibration Probe Attenuation/offset Channel Vertical Cal Channel Trigger Cal Calibrating Calibrating the the Scope Scope DSO91304A 13GHz Oscilloscope
De-embedding De-embedding the the CLB/CBB CLB/CBB N5230A PNA-L Network Analyzer Fixture effects Removed
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PWRP_301 N6705A Hands-On S800 November 2008
What are S-Parameters
S jk =
a b
bj ak
S21 a1 Port 1
b2 S11
DUT
b1
Port 2
S22 a2
S12
b 1 S 11 = b 2 S 21
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S 12 a 1 S 22 a 2
b j = S jk a k PWRP_301 N6705A Hands-On S800 November 2008
Ports
a b Ports define the interface to a DUT
Port on a DUT
A Port is a signal-return path connection Into each port are simultaneously, in going and out going sine waves, superimposed on the same conductors. They do not interact on the port ‘a’ voltage waves enter the DUT ‘b’ voltage waves leave the DUT Page 8
PWRP_301 N6705A Hands-On S800 November 2008
4-Port S-Parameters
Defining the ports
Differential ports
Single ended ports
Single ended ports
1 3
2 4
1
Input Ports
Differential ports 2
Output Ports
This Port mapping is needed for using UDF functions Page 9
PWRP_301 N6705A Hands-On S800 November 2008
Challenge: Obtaining the Fixture S-Parameters
Direct measurement Extracting equivalent model from a measurement Calculate S-Parameters from a scalable, analytical approximation Calculate S-Parameters from a 2D or 3D field solver model
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PWRP_301 N6705A Hands-On S800 November 2008
De-embedding – Loss Compensation or Gain Function De-embedded Eye
Measured Eye
V
•• Compensate Compensate for for Probing Probing and and Fixture Fixture Loss Loss –– Add Add Margin Margin to to Transmitter Transmitter Characterization Characterization •• Allows Allows more more accurate accurate measurement measurement of of de-emphasis de-emphasis levels levels at at transmitter transmitter •• Compliance Compliance Requirement Requirement for for Gen Gen 22
Tx
Channel
Rx
Measured Waveform
PHY
PHY
De-Convolve Function
De-embedded Waveform
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AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
Example: De-embedding the DDR2 BGA Probe S-Parameters obtained using ADS Term Term4
S-PARAMETERS
Num=4 Z=50 Ohm
S_Param SP1
Deembed2
Start=50 MHz
SNP5
1
Stop=20 GHz
File="average_40a750_gssg.s2p"
Ref
Step=50 MHz 2
Ref
4
1
2
1
Ref
2
2
3
Term Term1
Deembed2
1
Ref
S4P
Deembed2
Term
SNP3
Term2 Num=2
SNP1
Deembed2 SNP6
2
Ref
1
De-embed circuit element
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Term Term3 Num=3 Z=50 Ohm
PWRP_301 N6705A Hands-On S800 November 2008
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PWRP_301 N6705A Hands-On S800 November 2008
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PWRP_301 N6705A Hands-On S800 November 2008
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PWRP_301 N6705A Hands-On S800 November 2008
Make Rise Time Measurement Apply rise time measurement to the bga interposer and via waveforms.
Waveform at Via
Waveform measured at BGA interposer
Rise Time (Via) = 183ps
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Rise Time (BGA) = 391ps PWRP_301 N6705A Hands-On S800 November 2008
Apply the De-embedding UDF Go to the Math function menu and select the *CDeconvolve operator. Set Source 1 to Memory 1. Set Filter File Name to ddr2bga_deembed_prelim.s2p from scope_setup_files\de-embed. The DDR2 BGA probe S2P file is still preliminary as we are still fine-tuning the loss. This S2P file is generated through ADS (Advanced Design System). Set Signal BW to 2GHz. This is sometimes required to limit the noise amplification at higher bandwidth.
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PWRP_301 N6705A Hands-On S800 November 2008
Rise Time Measurement on De-embedded Waveform Apply rise time measurement to the de-embedded waveforms.
De-embedded Waveform
Rise Time (De-embed) = 171ps Page 18
PWRP_301 N6705A Hands-On S800 November 2008
FFT of the BGA and De-embedded Waveforms In order to view the FFT spectrum of bga waveform and de-embedded waveform, you can set FFT Graph in the Math function menu to On.
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PWRP_301 N6705A Hands-On S800 November 2008
Signal Bandwidth Settings The signal bandwidth setting is sometimes important to not over compensate for the loss that will cause noise amplification at higher bandwidth. The de-embedded waveform then becomes very noisy. The signal bandwidth can be limited using the UDF or during the S-parameter (S2P) file generation. Signal BW = 2GHz Signal BW = 6GHz
Noise
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PWRP_301 N6705A Hands-On S800 November 2008
De-embedding – Loss Function Connector
Pin
Rx
TP1
TP2
TP3
Virtual Probe and Deemphasis/Equalization •• Simulate Simulate Channel Channel Loss Loss on on Signal Signal Measured Measured at at Tx Tx •• Simulate Simulate Equalization/De-emphasis Equalization/De-emphasis at at Rx Rx
Channel
PHY
Tx Signal
Virtual Probe
TP1
Rx PHY
Rx Equalization
TP3 TP2
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Tx
AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
Using UDF with de-embed functions: choosing your function Measure channel frequency response with VNA/PNA or TDR and import result to oscilloscope. •
VNA sparameter file is most accurate but TDR response is easiest to obtain
2. To de-embed channel, select “CDeconvolve” UDF function 3. To add channel effects select “CConvolve”
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PWRP_301 N6705A Hands-On S800 November 2008
Using UDF with de-embed functions: sparameter selection Select sparameter file from test fixture(s). More than one sparameter file can be loaded to concatenate several components that may have been measured separately.
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PWRP_301 N6705A Hands-On S800 November 2008
Using UDF with de-embed functions: BW setting Select BW limit desired. Remember the signal component frequencies are what you use to determine this setting. Most accurately measure via Spectrum Analyzer. Selecting a BW setting higher than necessary will increase vertical noise due to amplifying noise associated with measurement system.
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PWRP_301 N6705A Hands-On S800 November 2008
Using UDF with de-embed functions: Select FFT display on/off Use this plot to determine the correct BW setting needed for your signal
•FFT On will automatically display the plot shown •Red is FFT of input signal (measured)
SNR limit desired determines right BW
•Green is Filter derived from sparameter file •Blue is signal output after filter is applied Page 25
PWRP_301 N6705A Hands-On S800 November 2008
Results from UDF de-embed of 5Gbps signal
Measured 5Gpbs PCIe signal
Deconvolved 5Gpbs PCIe signal Page 26
PWRP_301 N6705A Hands-On S800 November 2008
Results from UDF Convolved (loss function) of 5Gbps signal Measured 5Gpbs PCIe signal
Convolved 5Gpbs PCIe signal
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PWRP_301 N6705A Hands-On S800 November 2008
Key Messages Automated De-embedding Solution for Gen 2 and other Standards above 5GHz Ease of Use in Compliance Application Leverage Key Competitive Advantage of Low Noise Floor General Purpose Solution for Non Standard Applications Agilent is Industry Expert We have de-embedding capabilities now We are actively developing advanced features for deembedding and equalization Now. Page 28
AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
Agilent Equalization Solutions
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AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
Why Equalization? Higher data rates coupled with longer backplanes and interconnect distances result in greater signal attenuation at the receiver. When the data rate is higher than the BW of the channel the eye will essentially be closed at the receiver.
40in Channel
Critical for Customers at 5Gbit and above, especially for Receiver silicon equalizer validation testing and verification.
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AgilentPWRP_301 Restricted N6705A Hands-On 4, 2008 2009 S800February November
Using Equalization Select Equalization function from menu
2. Wizard walks you through setups for FFE or DFE
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PWRP_301 N6705A Hands-On S800 November 2008
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PWRP_301 N6705A Hands-On S800 November 2008
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PWRP_301 N6705A Hands-On S800 November 2008
Equalization SW Connector
Pin
Rx
TP1
TP2
TP3
Tx
r to c e n n o C
Channel
r to c e n n o C
PHY
N5461A
Rx PHY
Typical Scope BW: DSA91204A – 12GHz
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AgilentPWRP_301 Restricted N6705A Hands-On S800February November 4, 2008 2009
Wrap-up Key learnings from today • What is de-embedding? • What is equalization? • What do we have now? • What’s coming next year!
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PWRP_301 N6705A Hands-On S800 November 2008
FAQ •Can De-embed be put into a dedicated menu? Current UDF access via math functions is a kludge. Will feedback to R&D •How do we help customers get their fixtures characterized or get them sparameters models? ADS/VNA/TDR opportunities for AEs and Agilent to educate and offer this as service. • Does Lecroy handle uncorrelated components with de-embed or equalization? SS thinks they ignore these effects. Need to research this. •Will the de-embedding of the BGA probe be incorporated into our probe selection option window? This is being discussed •What is our relationship with CTD? Are we working on messaging relating to our VNA expertise and years of experience? Engaged with CTD but need to strengthen this relationship. •How do you go from De-embed to creating an eye pattern? This is not straight forward and should have some type of Wizard to help the user do this. Will feed back to R&D •Will you be providing detailed demo guides and customer presentations for deembedding and equalization? Yes •Transmitter equalization: FIR function/UDF can do this today. •Demo strategy: demo board and known lossy channels are needed to create a standard demo method
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PWRP_301 N6705A Hands-On S800 November 2008
Additional information Equalization application note: •http://cp.literature.agilent.com/litweb/pdf/5989-3777EN.pdf
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