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Agilent EEsof EDA
Group/Presentation TitleAgilent Restricted
Month ##, 200XPage 1
Eye Diagram Measurements in
Advanced Design System
Page 2
Eye Diagram Measurements in ADS
Page 2
Agenda
• Why an Eye Diagram ?
• Eye Diagram Measurements in ADS.
• Frequency Domain Analysis of an Interconnect.
• Optimization of an Equalizer Performance.
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Eye Diagram Measurements in ADS
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Why create an Eye Diagram?
Difficult to Characterize a Waveform
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Eye Diagram Measurements in ADS
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Eye Diagram Functions In ADSTwo eye diagram functions in ADS• eye(node_name, data_rate, number_of_cycles, delay)• FrontPanel_eye( node_name, data_rate, number_of_cycles, delay)
Difference between two eye functions
Unit Interval
…
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Eye Diagram Measurements in ADS
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Characterizing an Eye DiagramEye diagram parameters• Eye level 1 & level 0
• Eye rise/ fall time
• Eye opening
• Eye width
• Eye height
• Eye amplitude
• Eye signal to noise ratio
• Peak to peak & RMS jitter
• …
50 psec delay
FrontPanel_eye( node_name, data_rate, number_of_cycles, delay)
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Eye Diagram Measurements in ADS
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Eye Binning Function
451 Columns32
1 R
ows
Eqn = eye_binning( eye_plot,num_x_bins,num_y_bins)
Outer IndependentInner Independent
Number of Traces
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Eye Diagram Measurements in ADS
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Histogram PlotsMajority of Eye calculations are based on histogram plotsTwo types of histograms
• Horizontal histogram - For every time point, sum up the number of traces across vertical binsFrontPanel_eye_horizontal_histogram()
• Vertical histogram – For every amplitude point, sum up the number of points across time axisFrontPanel_eye_vertical_histogram_index()
Statistical calculation• Mean value, Standard Deviation ( 1 σ ), and
Three Standard Deviation ( 3 σ )Frontpanel_get_histogram_mean_stddev ()
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Eye Diagram Measurements in ADS
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Calculate Eye DelayEqn=FrontPanel_eye_delay(Waveform_Data,Default_DataRate,Data_Type)Function calculates the time delay required to position eye crossing at the center of the UI (Only applicable to NRZ type data)
Creates Eye DiagramConvert Eye data to bin dataDetermine Max and Min amplitudeCreate horizontal histogram in a narrow stripFind Mean value of horizontal histogramCompare Mean position as compared with UI/2
Calculated Delay
Delay calculation is required for automated eye parameter measurements.Binning the eye diagram makes this calculation easy.
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Eye Diagram Measurements in ADS
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Eye Crossing Measurements
Create horizontal histogram across a narrow central strip
The mean value provides eye crossing
time
Create vertical histogram @ mean crossing time points
The mean value will provide eye crossing
amplitude Mean Value of Horizontal Histogram Give Eye Crossing Time Value
Mean Value (Eye Crossing Amplitude Point)
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Eye Diagram Measurements in ADS
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Measurements of Eye Level One/Zero
Level zero
Upper half
Lower half
0% 40% 60%Measurement boundaries
Level one
100%
Determine Eye Crossing points ( t1, t2)
Determine (40-60% ) Eye
Boundaries
Calculate vertical histograms in upper half
region
Calculate Level One Mean & Standard
Deviation
Calculate vertical histograms in lower half
region
Calculate Level Zero Mean & Standard
Deviation
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Eye Diagram Measurements in ADS
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40-60% Region
Zero level histogram mean
Upper half
Lower half
One level histogram mean
Eye Amplitude = Level One – Level Zero
Measurements of Eye Amplitude, Height, and S/NEy
e Am
plitu
de
3 σ
3 σ
Eye Height = (Eye level one- 3σ)- (Eye level zero+3σ)
Eye
Heigh
t
1 σ
1 σ
Eye S/N= (Eye level one-Eye level zero)1σ level one+1σ level zero
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Eye Diagram Measurements in ADS
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Measurement of Eye Width
Eye width = (Eye crossing@t2- 3σ)- (Eye crossing@t1+3σ)
Eye Width3 σ
t1 t2
3 σ
Calculate Eye Crossing points
Calculate Horizontal Histograms around Eye
Crossing Amplitude
Calculate Mean value and Standard Deviation
Calculate Eye Width
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Eye Diagram Measurements in ADS
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Calculating Rise Time
Horizontal histogram plot for 20% threshold
Horizontal histogram plot for 50% threshold
Horizontal histogram plot for 80% threshold
Plot single Eye Diagram with delay
Determine Level One and Level Zero
Get the Rising Edgeswhich qualifies forall three thresholds
Calculate Horizontal Histogram for Qualified
Edge @ all three threshold values
Calculate Mean value for all three histograms
Rise time is the difference between the
Mean value of Histograms @ low and
high threshold
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Eye Diagram Measurements in ADS
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Jitter Histogram
Jitter Histogram - Horizontal histogram across Eye Crossing point.Standard Deviations - Represents RMS Jitter ( If only Random Jitter is present)Peak to Peak Jitter is the histogram width
Jitter (p-p)
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Eye Diagram Measurements in ADS
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Eye Diagram FrontPanel • Automated measurements using Eye Diagram FrontPanel
In addition to eye diagram measurements, it performs many waveform parameter measurements
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Eye Diagram Measurements in ADS
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Compare Eye FP to DCA on same waveform
DCA Measurement
1G Data Rate through 20” trace
Eye Diagram FrontPanel on the DCA output file.
[NOTE: FrontPanel data is from a single trace. DCA measurements are averaged with 16 measurements.]
FrontPanel DCA typ DCA min/max
Level 1 212mV 211.3mV 211.3/213.5
Level 0 -177.4mV -177.5mV -177.5/-178.5
Rise Time 219pS 222pS 219/226
Fall Time 212pS 215pS 211/219
Eye Amp 389.4mV 389mV 386.3/389.4
Eye Height 274.7mV 274.7mV 273.9/274.9
Eye S/N 10.18 10.07 10.01/10.23
Jitter p-p 22.2pS 22.2pS 22.2/22.2
Jitter rms 5.8pS 5.7pS 5.7/5.8
ADS Eye Diagram FrontPanel
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Eye Diagram Measurements in ADS
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Case Study
Design an equalizer to improve eye diagram performance
– Frequency domain simulator to predict channel performance– Simulation of a channel with equalizer– Optimization of an equalizer for eye performance
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Eye Diagram Measurements in ADS
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Time Domain Simulation (Convolution)S-Parameter representationof the channel
For this example, channel is just a passive interconnect.
Can one use frequency domain simulators?
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Eye Diagram Measurements in ADS
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Why use Frequency Domain Simulators?• No exclusive time domain components (IBIS model)
• Fast simulation
• Accurately accounts for all the frequency domain effects
• Availability of frequency domain bit sequence source
• No convergence issue
• Voltage at any node can be converted to time domain
• Eye diagram measurements can be accomplished
• Extremely fast and accurate simulation
Requirement: S-parameter/models should have sufficient bandwidth to satisfy the time sampling requirement
Limitation: Cannot be used with IBIS models (Rise and fall tables are defined as the timing waveforms )
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Eye Diagram Measurements in ADS
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AC Simulation of Channel Model
AC simulation setup
Frequency domain simulation Time domain characterizationWhat we are trying to accomplish?
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Eye Diagram Measurements in ADS
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Comparison shows good correlation.
Comparing Time and Frequency Domain Simulation Results
Time Domain SimulationFrequency Domain Simulation
Calculate eye parameters?
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Eye Diagram Measurements in ADS
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Characterizing Eye Diagram using ADS FrontPanel
Eye diagram measurements
Can one measure eye parameters during simulation?What are the advantages?
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Eye Diagram Measurements in ADS
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Eye Diagram Measurements during Simulation
Eye diagram measurement equations defined on the schematic page.
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Eye Diagram Measurements in ADS
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What we are achieving?
• Running AC simulation
• Plotting time domain waveform
• Plotting eye diagram measurements
Advantage• Fast and accurate channel simulation
• No convergence issues
• Measure eye diagram performance
Download example project from ADS knowledge website.
Provides simulation setup and measurement equations.
Frequency domain simulation Time Domain Characterization
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Eye Diagram Measurements in ADS
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Eye Diagram Measurements
Is Eye Performance Acceptable?How to improve eye diagram performance?
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Eye Diagram Measurements in ADS
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Why Equalization?As data rate increases, the frequency response and attenuation
characteristics of PCB traces degrade signalsEnables channel to operate at higher data rates
faster, better, cheaper
How to negate channel effects?
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Eye Diagram Measurements in ADS
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Consider Passive Equalizer Design A high pass filter
How to determine equalizer parameters?
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Eye Diagram Measurements in ADS
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Comparing Simulation Results
Without Equalizer With Equalizer
Eye height and Jitterp-p is improved.Can equalizer design be further improved?
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Eye Diagram Measurements in ADS
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Optimize Equalizer Design for Eye Opening
The goal is to optimize equalizer design to maximize Eye Opening
Goal: Improve Eye Opening Factor from 0.59 to 0.9
Parameter to be optimized
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Eye Diagram Measurements in ADS
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Eye Parameter Measurements and Optimization
Optimizing Eye Opening Factor
Eye Measurements
Frequency Domain Simulation
Change in the reactive element value will change the flight time. Will the optimization goals works with varying flight time?
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Eye Diagram Measurements in ADS
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Advantages
• Works well even if the flight time delay is changed due to changein the reactive element value.
• Automatically calculates delay required for eye positioning
• Automatically detects eye crossing point and 40-60% region
• Optimize eye diagram performance
Any eye diagram parameter such as eye opening factor, eye height, peak to peak jitter, rise time … can be used as an optimization goal.
• Unique and extremely powerful• Essential for state of the art serial link design
Frequency domain simulation Time domain characterizationTime domain optimization
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Eye Diagram Measurements in ADS
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Optimizing Eye Diagram ParametersLimitation: One cannot send Eye Diagram Measurements to data display during optimization
Deactivate output Node Voltage and Measurement Equations while performing optimization ( Defined in Simulator Controller)
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Eye Diagram Measurements in ADS
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Comparing Simulation Result
Eye Diagram without equalizer Eye Diagram with optimized equalizer
Improvement in Jitter
ADS Eye Diagram plots
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Eye Diagram Measurements in ADS
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ADS Waveform in DCA – without Equalization
ADS simulated waveform was sent to DCA for post processing
DCA Eye Diagram display showing ADS simulated waveform
ADS Eye Diagram
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Eye Diagram Measurements in ADS
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Eye Jitterp-p 15.7 psEye Signal to Noise 4.75
Eye Rise Time 33 psec
ADS Waveform in DCA with EqualizationDCA Eye Diagram display showing ADS simulated waveform
ADS Eye Diagram
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Eye Diagram Measurements in ADS
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Comparing Simulation Results
Channel+ Equalizer before Optimization Channel+ Equalizer after Optimization
Optimizer type – Random optimizerNumber of iterations – 40Optimization time – 15 Minutes
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Eye Diagram Measurements in ADS
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Conclusion• ADS has been used for SI design for over 20 years
• ADS has a multitude of accurate built in models
• ADS allows you to build accurate physical models
• ADS brings IP, simulation and measurement together
• Reviewed Eye Diagram measurement algorithms in ADS• ADS allows you to predict time domain performance using frequency domain simulators
• Allows you to characterize and optimize Eye Diagram Performance
You can optimize eye diagram performance not only using the AC simulator, but ADS also allows you to optimize interconnects for eye diagram performance using numeric, time and other frequency domain simulators.
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