IRDrop analysis in power delivery network design

This paper describes effect of designing resonant free power delivery network (PDN) on the performance of voltage regulator modules (VRM) commonly used in microprocessor systems. The performance parameters of the VRM as a result of decoupling capacitors (DECAPS) added at different stages of the PDN to realize the resonant free target impedance is described using the output impedance as a key parameter. Parametric curves and simulation results are presented to support the validity of the design oriented analysis with special emphasis on the performance of the VRM considering voltage sensing for feedback at different stages of the microprocessor PDN

Power delivery network (PDN) design is already a challenging problem for single die designs using advanced process technologies. For systems created using stacked dies with TSVs, several additional issues that affect power delivery and reliability have to be addressed. In stacked die configuration, the dies higher up in the stack-up experience additional drop and noise in their power supply as it propagates through the TSV networks of one or more dies placed lower in the stack-up. For the lower dies, the presence of the TSV farm and associated metals/vias affects the homogeneity of their own power delivery network. And if multiple dies share power and ground domains, then there could be an inter-die propagation of supply noise. So it becomes important that a PDN design and optimization flow for stacked die designs models and analyzes the presence of multiple dies and also the switching and the noise impact from the dies on each other. The analysis could be concurrent or model based, depending upon whether full databases for all the chips are available or their electrically equivalent models such as Chip Power Model (CPM) are available, respectively. For both of these approaches, a DC and time-domain analysis has to be done at the chip layout level to accurately predict the power/ground noise in the stacked die design. These analyses need to done starting early, in order to enable prototyping and design trade-off decisions. In this paper, a prototyping and verification solution for multi-die TSV based designs is outlined along with results from various design decisions undertaken.

Suboptimal design of power delivery networks (PDNs) may cause performance deterioration and severe functional failures on high-speed computer platforms. Voltage regulators (VRs) distribute controlled voltage in the PDN to the active devices, providing a steady power supply at a desired DC voltage level with an acceptable noise level or ripple. Unacceptable voltage drops can be caused by transient switching currents at the devices. Many decoupling capacitors are commonly used to lower the PDN impedance profile in order to reduce power supply noise and to supply fast transient current to switching devices. However, commercially available decoupling capacitors typically present large manufacturing variability. In this article, we first propose an optimization methodology that gradually finds the best compensation parameter values of a buck converter VR to meet suitable stability criteria. Simultaneously, the number of parallel decoupling capacitors in the PDN is minimized while meeting a frequency-domain impedance profile specification and a time-domain minimum voltage droop requirement under nominal parameter values. Finally, a statistical analysis, yield estimation, and yield optimization of the nominally optimized PDN subject to large decoupling capacitor tolerances is presented. We consider the impedance profile, transient voltage droop, and VR stability as the responses of interest for yield calculation.

With increasing core counts ushering in power-constrained 3-D multiprocessor system-on-chips (MPSoCs), optimizing communication power dissipated by the 3-D network-on-chip (NoC) fabric is critical. At the same time, with increased power densities in 3-D ICs, problems of IR drops in the power delivery network (PDN) as well as thermal hot spots on the 3-D die are becoming very severe. Even though the PDN and NoC design goals are nonoverlapping, both the optimizations are interdependent. Unfortunately, designers today seldom consider the design of the PDN, while designing NoCs. Moreover, for each new configuration of computation core and communication mapping on an MPSoC, the corresponding intercore communication patterns, 3-D on-chip thermal profile, as well as IR-drop distribution in the PDN can vary significantly. Based on this observation, we propose a novel design-time system-level application-specific cosynthesis framework that intelligently maps computation and communication resources on a die, for a given workload. The goal is to minimize the NoC power as well as chip-cooling power and optimize the 3-D PDN architecture; while meeting performance goals and satisfying thermal constraints, for a microfluidic cooling-based application-specific 3-D MPSoC. Our experimental results indicate that the proposed 3-D NoC-PDN cosynthesis framework is not only able to meet PDN design goals unlike prior 3-D NoC synthesis approaches, but also provides better overall optimality with the solution quality improvement of up to 35.4% over a probabilistic metaheuristic-based cooptimization approach proposed in prior work.

Power Delivery Network (PDN) is a critical component in modern System-on-Chip (SoC) designs. With the rapid development in applications, the quality of PDN, especially Package (PKG) PDN, determines whether a sufficient amount of power can be delivered to critical computing blocks. In conventional PKG design, PDN design typically takes multiple weeks including many manual iterations for optimization. Also, there is a large discrepancy between (i) quick simulation tools used for quick PDN quality assessment during the design phase, and (ii) the golden extraction tool used for signoff. This discrepancy may introduce more iterations. In this work, we propose a learning-based methodology to perform PKG PDN quality assessment both before layout (when only bump/ball maps, but no package routing, are available) and after layout (when routing is completed but no signoff analysis has been launched). Our contributions include (i) identification of important parameters to estimate the achievable PKG PDN quality in terms of bump inductance; (ii) the avoidance of unnecessary manual trial and error overheads in PKG PDN design; and (iii) more accurate design-phase PKG PDN quality assessment. We validate accuracy of our predictive models on PKG designs from industry. Experimental results show that, across a testbed of 17 industry PKG designs, we can predict bump inductance with an average absolute percentage error of 21.2% or less, given only pinmap and technology information. We improve prediction accuracy to achieve an average absolute percentage error of 17.5% or less when layout information is considered.

Modern client processors typically use one of three commonly-used power delivery network (PDN) architectures: 1) motherboard voltage regulators (MBVR), 2) integrated voltage regulators (IVR), and 3) low dropout voltage regulators (LDO). We observe that the energy-efficiency of each of these PDNs varies with the processor power (e.g, thermal design power (TDP) and dynamic power-state) and workload characteristics (e.g., work-load type and computational intensity). This leads to energy-inefficiency and performance loss, as modern client processors operate across a wide spectrum of power consumption and execute a wide variety of workloads. To address this inefficiency, we propose FlexWatts, a hybrid adaptive PDN for modern client processors whose goal is to provide high energy-efficiency across the processor's wide range of power consumption and workloads. FlexWatts provides high energy-efficiency by intelligently and dynamically allocating PDNs to processor domains depending on the processor's power consumption and workload. FlexWatts is based on three key ideas. First, FlexWatts combines IVRs and LDOs in a novel way to share multiple on-chip and off-chip resources and thus reduce cost, as well as board and die area overheads. This hybrid PDN is allocated for processor domains with a wide power consumption range (e.g., CPU cores and graphics engines) and it dynamically switches between two modes: IVR-Mode and LDO-Mode, depending on the power consumption. Second, for all other processor domains (that have a low and narrow power range, e.g., the IO domain), FlexWatts statically allocates off-chip VRs, which have high energy-efficiency for low and narrow power ranges. Third, FlexWatts introduces a novel prediction algorithm that automatically switches the hybrid PDN to the mode (IVR-Mode or LDO-Mode) that is the most beneficial based on processor power consumption and workload characteristics. To evaluate the tradeoffs of PDNs, we develop and open-source PDNspot, the first validated architectural PDN model that enables quantitative analysis of PDN metrics. Using PDNspot, we evaluate FlexWatts on a wide variety of SPEC CPU2006, graphics (3DMark06), and battery life (e.g., video playback) workloads against IVR, the state-of-the-art PDN in modern client processors. For a 4 W thermal design power (TDP) processor, FlexWatts improves the average performance of the SPEC CPU2006 and 3DMark06 workloads by 22% and 25%, respectively. For battery life workloads, FlexWatts reduces the average power consumption of video playback by 11% across all tested TDPs (4W-50W). FlexWatts has comparable cost and area overhead to IVR. We conclude that FlexWatts provides high energy-efficiency across a modern client processor's wide range of power consumption and wide variety of workloads, with minimal overhead.

Power integrity design has been a challenging task especially with devices that high in power consumption but require high performance and with very tight voltage budgeting. Most of the time, the solution space is also limited by the product cost target. Designer will need to validate the power delivery network (PDN) performance with various design operation activities to identify the worst-case current profile. Step load current is one of the common profiles that is used to verify the PDN dynamic noise against the voltage specification. This paper introduces a formulation to estimate the PDN transient response to the step load current profile and the induced 1st droop voltage noise. It provides a quantitative model to analyze the PDN characteristic and its response with different step load bandwidth profile. PDN bandwidth metric is also introduced in the formulation to study the relationship with the step load bandwidth. The PDN step load response will be separated to resistive and reactive impedance response and as well the ripple from the LC oscillation. This serves as the dynamic voltage budgeting methodology with respect to 1st droop event to quantify the IR drop and ripple voltage noise budget across board, package and die to meet the product voltage specification.

In this paper, a new concept of distributed port is proposed, and a systematic method for the modeling, analysis, and design of the high-speed power delivery network (PDN) is developed. The distributed port uses multiple lumped ports dispersed uniformly in the power-delivery networks to capture the distributed characteristics of the large and irregular power-delivery structures. This concept provides a feasible scheme for the accurate analysis of the whole or any part of a power-delivery network. The modeling methods and modeled results are discussed in depth. The applications of the distributed port in the PDN design, systematic PDN modeling, and package/connector performance evaluation and optimization are discussed in detail. The validity of the distributed port is demonstrated by numerical examples and verified by simulations and extractions.

Extended adaptive voltage positioning (EAVP) is a new robust methodology for the design and analysis of a low impedance resonant free power delivery network, which utilizes and extends the theory of adaptive voltage positioning (AVP) that is commonly used in voltage regulator module (VRM) design and operation. Using EAVP, uncertainties in design guardband noise budget can be removed, resulting in significant performance bin-split improvement and cost reduction. Design optimization of decoupling capacitors with EAVP will be illustrated by using both time and frequency domain analysis.

In modern DRAM design, IR-drop has emerged as a critical factor leading to operation failures, primarily due to reduced metal resources and increased supply current demands. Consequently, estimating and addressing IR-drop throughout the DRAM design process has become a crucial sign-off consideration. The proposed comprehensive methodology for the power delivery network (PDN) includes accurate and efficient estimation at two key stages: early in the design process (Early PDN) and during post-physical design sign-off validation (Iterative PDN). The Early PDN approach employs simplified modeling to achieve reasonable accuracy, serving as a guideline for the initial PDN design. Subsequently, the Iterative PDN method provides a fast yet detailed analysis of the entire DRAM, including the PDN, ensuring it is suitable for final sign-off. By applying this methodology, PDN behavior can be effectively predicted and optimized, ensuring robustness. This enhances the reliability and performance of DRAM designs.

The reliable Power Delivery Network (PDN) design is a challenging aspect in Three-Dimensional-Integrated-Circuits (3D-ICs). In order to ensure the robustness of the 3D PDN, the number and the locations of the Power/Ground (P/G) Through-Silicon-Vias (TSVs) should be carefully planned. Non-regular P/G TSV placement has superior performance compared to the regular one in terms of TSV count. However, the corresponding deadspace optimization is necessary, which complicates the traditional 3D floorplanning. In this work, we propose an efficient deadspace-aware P/G TSV planning combined with the 3D floorplanning to simultaneously place the 2D blocks and P/G TSVs to minimize the total wirelength and the number of inserted TSVs under IR-drop and fixed-outline constraints.

Power supply induced clock jitter accumulation is a function of several variables including the power supply rejection characteristics of circuits in the signal path, signal path electrical length, signaling frequency, and voltage supply noise magnitude and frequency. Brute force, closed-loop, transistor-level modeling and simulation of clock timing in the presence of an extracted power delivery network are resource intensive. In addition, circuit and power delivery network designs are often not complete enough to run such analyses at an early stage in the design cycle, and the longer a design waits to identify circuit and supply sensitivities, the more costly the corrections become. Understanding the relationships between the signal path electrical length, signaling frequency and supply noise frequency enables early jitter estimation and can be used to drive both circuit and power delivery network design optimization. This paper summarizes the general inter-dependencies between these variables and then demonstrates how these principles might be used to make design optimizations in the context of the Low Power Double Data Rate Four (LPDDR4) interface.

With each technology generation, delivering a timevarying current with reduced nominal supply voltage variation is becoming more difficult due to increasing current and power requirements. The power delivery network design becomes much more complex and requires accurate analysis and optimizations at all levels of abstraction in order to meet the specifications. In this paper, we describe techniques for estimation of the supply voltage variations that can be used in the design of the power delivery network. We also describe the decoupling capacitor hierarchy that provides a low impedance to the increasing high-frequency current demand and limits the supply voltage variations. Techniques for high-level power estimation that can be used for performance vs. power trade-offs to reduce the current and power requirements of the circuit are also presented.

Signal and power integrity are crucial for ensuring high performance in high speed digital systems. As the operating frequency of digital systems increases, the power and ground bounce created by simultaneous switching noise (SSN) has become a limiting factor for the performance of these devices. SSN is caused by parasitic inductance that exists in the power delivery network (PDN), and voltage fluctuations on the power and ground rails can lead to reduced noise margins and can limit the maximum frequency of a digital device. A new PDN design has been suggested that achieves significantly reduced SSN [1] by replacing the power plane structure with a power transmission line (PTL). In this paper, a new power delivery scheme is shown to significantly reduce switching noise at lower power. This concept has been demonstrated through theory, simulation, and measurements.

Over the course of 60 years, since the invention of the integrated circuit (IC), exponential improvements in cost, performance and power consumption were observed. Such advances have been strongly linked with the continuous reduction of the dimensions in manufactured ICs, but this trend has shown decreasing benefits as fundamental limits are reached. Notice that such tiny devices have increased variability, which generates unpredictable variations in the behavior of the manufactured devices. These uncertainties are typically addressed by defining margins on the clock period, estimated during the design phase. However, the overly conservative margins produce significant degradations in performance. Additionally, the evolution that enabled circuits with increasingly higher density of components, also resulted in an extremely complex IC design. At every step, electronic design automation (EDA) tools are challenged to handle this increasing complexity, requiring more powerful techniques to comply with the specification constraints within an affordable runtime. This thesis investigates alternatives in order to improve power, performance, area, and cost, using established IC manufacturing technologies. Advances in EDA are proposed in three distinct topics: area minimization using Boolean methods, area and delay reduction for designs based on fieldprogrammable gate array (FPGA), and an alternative clocking scheme to reduce timing margins. The first contribution consists of a technology-independent method for area minimization of combinational logic. Local optimization is applied on and-inverter graphs (AIGs), performing multi-output Boolean decomposition using two-literal divisors, targeting node count reduction. The second contribution regards two methods targeting technology mapping of FPGAs. On one hand, a functional decomposition approach, which uses the support size as cost function, exploring the inherent characteristics of FPGAs. On the other hand, an approach for recursive remapping, which reduces the structural bias of the subject graph, uses the mapping results as cost function, and obtains significant reductions in area and delay. The third contribution evaluates the dynamic variability mitigation and simplification of power delivery networks (PDNs) using an adaptive clocking scheme based on ring oscillator clocks (ROCs). The impact of the PDN parameters and ROC location is investigated, showing potential improvements in performance, leakage power and cost. A lo largo de los 60 años desde la invención del circuito integrado (CI), se han producido mejoras exponenciales en su coste, rendimiento y consumo de energía. Ese progreso esta fuertemente vinculado a la reducción continua de las dimensiones de fabricación de los circuitos integrados, pero esta tendencia ha ido mostrando menos beneficios a medida que se alcanzan límites fundamentales. Estos dispositivos minúsculos tienen una mayor variabilidad, lo que genera variaciones impredecibles en el comportamiento de los dispositivos fabricados. Estas incertidumbres generalmente se abordan mediante la definición de márgenes en el período de reloj, estimado durante la fase de diseño. Sin embargo, márgenes excesivamente conservadores producen degradaciones significativas en el rendimiento. Además, la evolución que permitió crear circuitos con una densidad de componentes cada vez mayor, también incrementado la complejidad de los CI. En cada paso del proceso de diseño, las herramientas de automatización de diseño electrónico (EDA) se enfrentan al desafío de manejar esta complejidad creciente, lo que requiere técnicas más potentes para cumplir con las restricciones impuestas por las especificaciónes dentro de un tiempo de ejecución asequible. Esta tesis investiga alternativas para mejorar el consumo de energía, el rendimiento, el área y el coste, utilizando las tecnologías de fabricación de CI ya establecidas. Los avances en EDA se proponen en tres temas distintos: minimización de área usando métodos booleanos, reducción de retardo y área para diseños basados en matrices de puertas programables (FPGA), y un esquema de reloj alternativo para reducir los márgenes de tiempo excesivamente conservadores. La primera contribución consiste en un método independiente de tecnología para minimizar el área de la lógica combinacional. Se aplica optimización local en grafos de AND-inversor, utilizando una descomposición Booleana de múltiples salidas con divisores de dos literales, con el objetivo de reducir la cantidad de nodos. La segunda contribución propone dos métodos para el mapeo tecnológico de los FPGA. Por un lado, un método de descomposición funcional, que utiliza el tamaño del soporte como función de coste, explorando las características inherentes de los FPGA. Por otro lado, un método de mapeo recursivo, que reduce la distorsión estructural del grafo sujeto, utiliza los resultados del mapeo como función de coste y obtiene reducciones significativas en área y retardo. La tercera contribución evalúa la mitigación de la variabilidad dinámica y la simplificación de la red de suministro de energía (PDN) utilizando un esquema de reloj adaptativo basado en un oscilador en anillo (ROC). Se investiga el impacto de los parámetros de la PDN y la ubicación del ROC, mostrando mejoras potenciales en el rendimiento, consumo estático y coste.