Publications on Signal Integrity, Power Integrity, Simulation & Measurement
DesignCon 2024 - Design, Simulation and Validation of a 2000-Amp Core Power Rail
Abstract: This paper will demonstrate how to measure, model, and validate a scalable, 2k-Amp core power rail. The technological growth in Data Centers, AI, Graphics, and Super-Computing has pushed the core power rail current to 2k-Amps and is climbing. Designing such a power rail is a complex task, involving architectural design choices as well as simulation and validation challenges. Lower core voltages reduce power but also reduce operating noise margins. Combined, these require greater expertise in design choices, much greater simulation accuracy, and more rigorous validation of the power rail. This paper will address this 2k-Amp project from the beginning with a variety of architectural design choices and resulting modeling and simulation challenges, including cascaded VRMs, current sharing, and thermal simulation. The assessment of PDN impedance has become a well-published mantra, and yet core power rail validation generally requires time domain testing as well as impedance testing, which presents yet greater challenges. Therefore, the final validation of this design is done using time domain testing at full ASIC power with dynamic modulation at package speeds of up to 100MHz to address the large signal response phenomenon. Simulation to measurement correlation will be shown for electrical and thermal behavior.
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Link to SLIDES
Link to PAPER
DesignCon 2024 - Unmasking Voltage Regulator Instability: What Vendor Reference Designs Aren't Telling You
Abstract: Voltage regulator vendor reference designs serve as indispensable instruments for designers aiming to integrate a vendor’s voltage regulator into their specific design projects. While these evaluation boards offer valuable insights into regulator performance, it is essential for designers to recognize that these boards are engineered to cater to a diverse range of applications, rather than being tailored to a specific systems' requirements. This demonstration will shed light on the inherent instability often observed in these vendor reference designs through the utilization of the non-invasive stability measurement (NISM) technique.
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Link to SLIDES
Who Put that Inductor in My Capacitor
Abstract:
Accurate measurement and characterization of capacitors are essential for designing optimal power distribution networks (PDNs) in a modern printed circuit board assembly (PCBA) and application specific integrated circuits (ASICs). Vendor provided capacitor models often include additional inductance from the capacitor mount used for measurement, impacting the PDN simulation and performance. This paper highlights the importance of having accurate capacitor models by demonstrating their impact on PDNs. The inclusion of additional inductance in vendor provided capacitor models leads to inaccurate representation of the capacitor’s impedance over frequency. De-embedding the PCB mount from a measurement-based model removes the added inductance, removing model error and enabling higher fidelity PDN simulation.
Accurate capacitor modeling ensures the design meets the power integrity requirements needed for design signoff by removing simulation errors that can occur in the PDN. This paper uses a system-level PDN, comprised of a state-space average voltage regulator module (VRM) model, PCB, package, and die to provide a comparative simulation analysis in frequency domain as well as time domain between vendor models and measurement-based capacitor models. Where the overall objective is to demonstrate how important it is to have accurate capacitor models as part of a PDN design for sign-off.
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COMING SOON
The Challenge of Measuring a 40 uOhm (2000 Amp) PDN with a 2-Port Probe
In this two-part Extreme Measurements article, Steve Sandler and I discuss the CMRR requirements to make sub-40 uOhm impedance measurements on a PDN with a 2-port probe.
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BLOG PART 1: How Much CMRR is Needed?
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BLOG PART 2: The Measurement Result!
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EDICON 2023 What is Enough? VDDQ Package Power Integrity Analysis with a DDR4 PHY
Abstract: As voltage margins for power rails continue to decrease, end-to-end power integrity modeling is already difficult without having to be concerned if all the models that are part of your simulation are correct. As system designers, we typically expect and, in most cases, assume that all the models from vendors are correct.
So, what does an engineer do if one of the models needed for a power integrity simulation is not correct? What if this is a die model? How does an engineer verify if the die model is accurate or has enough on-die capacitance to manage high-frequency currents?
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This presentation will demonstrate how to build and model an end-to-end power Integrity model for a DDR4 PHY and package. As part of this discussion, analysis will be shown to determine if the DDR PHY integrated into a custom ASIC has sufficient on-die capacitance for the respective DDR4 power domain.
At the end of this presentation, engineers will understand how to model and develop an end-to-end power Integrity model for their ASIC while determining if their ASIC has sufficient on-die capacitance for their application.
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Signal Integrity Journal Article
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Link to Podcast discussing presentation HERE
EEworld ONLINE Article Discussing APEC Seminar
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APEC Power Integrity Seminar SLIDES
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TPS7H4003 State-Space Average Model Workspace Document
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APEC 2023 Professional Seminar - How Power Integrity Is Changing the World of Power Electronics
Abstract: In the world of power electronics, the focus is on the power supply, and the load is modeled as a simple resistor. In the world of power integrity, the focus is on the decoupling capacitors required for the digital load, and the power supply is modeled as a simple resistor in series with an inductor. In the real world, neither assumption solves the problem of simulating the power delivery ecosystem with switching power supply control loops, gigabit switching digital loads, and a PCB network of filtering and decoupling components. The challenge is how to simulate the Power Integrity ecosystem and include the feedback loop and switching noise of a switch mode power supply (SMPS) without waiting days for the simulation results.
The solution presented here uses control loop theory state space equations to create a behavioral model of an SMPS that allows for fast simulation. This Sandler State Space Average Model previously published [1] has the fidelity to include the dynamic control loop behavior for stability assessment, large signal and small signal noise ripple, and power supply rejection ratio. The model also works with the Non-Invasive Stability Measurement method to assess the control loop phase margin from simple output impedance data.
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DesignCon 2023 - VRM MODELING AND STABILITY ANALYSIS FOR THE POWER INTEGRITY ENGINEER
Abstract: You have probably heard of calibration, de-embedding, and fixture removal for network analyzer measurements, but do you know how to do it for a 2-port shunt low-impedance measurement? Impedance measurements are a must-have skill for Power Integrity engineers. The measurements provide models for Capacitors, Resistors, and Inductors that work in both time and frequency domain simulations. Impedance measurements are also critical for verifying the performance stability of a power delivery network (PDN).
In this session, you’ll learn the difference between these terms. You’ll learn, with demonstrations, how to remove the impact of fixturing using calibration and de-embedding steps. The process works for both connectorized devices or with PCB browser probes to provide accurate measurements that are compatible with your PCB EM simulator.
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DesignCon 2023 ChipHead - Hands-On PDN Impedance and Calibration Basics
Abstract: The voltage regulator module (VRM) is the foundation of power integrity. Due to their wide bandwidth and low cost, most newer VRM controllers employ transconductance feedback amplifiers, with the VRM manufacturers recommending a shunt compensation for the error amplifier design. However, most VRM designers and power integrity engineers may not be aware that they have another choice to improve the sensitivity and performance of their VRM design. The better performance of a current mode VRM with series compensation for the error amplifier is clearly demonstrated with simulations using the Sandler state-space average VRM model.
Additional analysis and discussion will be provided to show how the VRM’s performance has improved stability, reduced gain sensitivity, and overall improved performance with a series compensation network. A VRM case study will be presented in this technical session to show these performance improvements using the Sandler State Space Average model in Keysight PathWave ADS.
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ULTRA-ULTRA-LOW IMPEDANCE (4 MICRO-OHM) MEASUREMENTS
In this Extreme Measurements article, I discuss the lowered impedance targets that are a result of the increasing amount of current necessary for modern processor solutions. Read on to learn how to achieve impedance targets below 10 uOhms.
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Link to blog HERE
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DesignCon 2022 IMPROVED METHODOLOGY TO ACCURATELY PERFORM SYSTEM LEVEL POWER INTEGRITY ANALYSIS INCLUDING AN ASIC DIE
Abstract: The ASIC-based systems of today and tomorrow can no longer be designed by rules of thumb when it comes to power integrity. The current methods of evaluating power integrity for an ASIC die on a substrate are generally lacking sufficient accuracy. The key element for system-level PDN analysis is a chip die model, which requires specialized EDA tools to create. These EDA solutions typically create chip models using either vector-based or vector-less dynamic current profiles. Vector-based chip model solutions are challenging to create and typically do not cover the complete ASIC die use case. In addition, the benefits of models created for the die, substrate, and PCB have multiple possible configurations such as lumped, distributed, looped and partial. This paper provides a novel workflow on the benefits of using lumped-looped models to improve efficiency, while achieving accuracy, and reducing the overall risk to a given system PDN. Lastly, this paper provides an improved methodology on how to know if the voltage ripple at the die bumps on a substrate is violating the defined specification of the ASIC and shows the methods on how to evaluate the PDN target impedance across a system.
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DesignCon 2022 DDR4-3200 FPGA-BASED SYSTEM WITH INTERPOSER POWER-AWARE SI SIMULATION TO MEASUREMENT CORRELATION
Abstract: DDR4-3200 SSO channel modeling is further challenged to ensure DQ compliance specification for eye-opening at an ultra-low 1E-16 BER. As DDR4-3200 edge rates approach < 100 ps, power-aware SI simulation is necessary to achieve higher fidelity modeling. The intent of this paper is to present methods for creating accurate power-aware signal integrity simulation which will demonstrate measurement correlation on the first DDR4-3200 FPGA memory controller, the Xilinx Versal, interfaced to a UDIMM with an interposer present during measurement.
This effort will combine simulation and measurement with the goal to show how to improve design margins during DDR4-3200 development cycles. Additionally, considerations and recommendations will be provided for higher-speed DDR5 designs with more complex power distribution, channel topologies, and receiver architectures.
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MEASURING THE BULK DIELETRIC CONSTANT (Dk) ON A MICROSTRIP WITH A TDR
Most modern circuit designs depend on accurate logic signals at the logic receiver. This assurance is based on the careful design of the signal path impedance, including printed circuit board (PCB) transmission lines, interconnects, vias, and cables.
If you have designed a controlled impedance transmission line based on a PCB stack-up, how do you know if the PCB fabrication house or another vendor built your stack-up to meet your controlled impedance specification? In fact, we have found, even after discussion with various laminate manufacturers, that the majority of dielectric constants specified in the vendor datasheet have uncertainty, with a lot of variability. This creates a call to action to measure these materials to get it right.
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Link to article HERE
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COMMON CENTS IMPEDANCE MEASUREMENTS
A technical article exploring different calibration techniques, with a 2-port probe, to archive to sub-100μΩ impedance measurements with U.S. pennies.
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Link to article HERE
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EDICON 2021 PARTIAL INDUCTANCE - THE SECRET TO CORRELATING SIMULATION TO MEASUREMENT
There's confusion about the measurement of capacitors, and particularly the series inductance or ESL. Different manufacturers calibrate or de-embed their measurement differently, making it difficult to compare one vendor to another. The differences between these measurements represent different locations of the measurement reference plane.
When correlating EM simulation and measurement results, where should the reference plane be for the capacitor measurement? Why does the target impedance measurement show much higher inductance than the simulator? Why do some experts recommend measuring impedance from both sides of the PCB and not just one side? In this session, Steve Sandler, Heidi Barnes, and I will provide analysis that answers all of these questions and more!
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CALIBRATING THE 2-PORT PROBE FOR LOW IMPEDANCE PDN MEASUREMENTS
Benjamin Dannan and Steve Sandler teamed up to explore the tradeoffs for various calibration methods and offer some recommendations and considerations to make accurate sub-milliohm impedance measurements.
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Link to article HERE
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PROJECT X DDR4-2400 SIGNAL INTEGRITY ANALYSIS
Northrop Grumman Case Study: Rigorous Design Analysis of a DDR4 DIMM-Based System
Analysis shows multi-board simulation model with custom ASIC, MCM package, PCBA, UDIMM, and RDIMM models.
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Project X DDR4-2400 Signal Integrity Analysis SLIDES
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EDICON 2020 DDR4-3200 CHANNEL MODELING AND SIGNAL INTEGRITY ANALYSIS USING AN FPGA
A presentation with the Xilinx VCK190 using the Versal on how to develop a DDR4-3200 simulation model. This looks at signal integrity in the channel, such as insertion loss, crosstalk, and tuning the DDR4 eye using ODT.
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EDICon 2020 DDR4-3200 Channel Modeling and Signal Integrity Analysis using an FPGA Slides
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As DDR data transmission rates continue to increase, the signal integrity of the DDR channel has become one of the most critical concerns. This article takes an extensive look at the impact of via stubs on the impedance of the signal lines on DDR4 memory, including test cases and ways to optimize design.
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This Best Paper Award was also republished on the Signal Integrity Journal in June 2020
Link to Article: Signal Integrity Characterization of Via Stubs on High Speed DDR4 Channels
HOW GROUND BOUNCE CAN RUIN YOUR DAY
Low-speed printed circuit board (PCB) designs now have to deal with high-speed switching problems. This article examines the ground bounce generated from an LCD assembly while evaluating the impact of the ground bounce on the system level EMI. Three solution strategies to mitigate the ground bounce are analyzed, the pros and cons of each strategy are provided along with the test results.
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Link to article HERE
ADDRESSING EMC CHALLENGES WITH IN-HOUSE EMC PRE-COMPLIANCE TESTING
This article discusses how to build an in-house EMC pre-compliance testing setup to improve the success rate in EMC compliance testing.
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Link to article HERE