Microprocessor Power Delivery Research Articles

Combined feedback–feedforward control of Ćuk CCM converter for achieving fast transient response

The Ćuk converters operating in continuous conduction mode (CCM) can be preferred in applications such as microprocessor power delivery and pulsed load because these circuits have advantages of being able to step up/down, a small number of power components, and low input/output current ripples. However, they show poor transient performance due to right-half-plane-zeros (RHPZs) in the closed-loop transfer function of the Ćuk CCM converter. To enhance the transient response, a combined feedback–feedforward control for the Ćuk CCM converter is proposed. The proposed control scheme comprises a feedback control signal based on a Lyapunov function and a duty-ratio feedforward control signal. A Lyapunov-function-based controller (LBC) achieves fast dynamic response even under large-signal variations from the operating point. The duty ratio feedforward controller (DFFC) is developed to predict the effect of the disturbances and compensate it, while alleviating the burden of LBC. The proposed control logic makes the closed-loop system of the Ćuk CCM converter globally exponentially stable and thus provides a fast transient response even under large-signal variations. To construct the proposed controller, the authors make use of the large-signal averaged model of the Ćuk CCM converter, and consider the parasitic elements. To verify the proposed control scheme, numerical simulations and experimental tests are conducted.

Power Delivery for High-Performance Microprocessors—Challenges, Solutions, and Future Trends

The power delivery requirements for the early microprocessors were fairly rudimentary due to the relatively low power levels. However, several decades of exponential scaling powered by Moore's law have greatly increased the power requirements and the complexity of the power delivery scheme. The breakdown in Dennard scaling in the mid-2000s has ushered in the multicore era which has increased the number of cores and the power consumption in microprocessors. The steady growth in the power levels and the number of power rails in high-performance microprocessors have increased the power delivery challenges. Integrated voltage regulators (IVRs) have emerged as a key power delivery technology to address these challenges. There are a number of IVR schemes implemented on-die ranging from the simple power gate to fully integrated switching regulators. After covering the fundamentals of power delivery, this article discusses the pros and cons of different types of IVR as well as the technology ingredients required to meet future IVR requirements. This article concludes with a section on advanced packaging technologies that are being developed and needed to enable heterogeneous integration and their impact on power delivery.

A 10 W On-Chip Switched Capacitor Voltage Regulator With Feedforward Regulation Capability for Granular Microprocessor Power Delivery

Granular power delivery with per-core regulation for microprocessor power delivery has the potential to significantly improve the energy efficiency of future data centers. On-chip switched capacitor converters can enable such granular power delivery with per-core regulation given a high efficiency, high power density, fast response time, and high output power converter design. This paper details the implementation of an on-chip switched capacitor voltage regulator in a $32\,\mathrm{n}\mathrm{m}$ SOI CMOS technology with deep trench capacitors. A novel feedforward control for reconfigurable switched capacitor converters is presented. The feedforward control reduces the output voltage droop following a transient load step. This leads to a reduced minimum microprocessor supply voltage, thereby reducing the overall power consumption of the microprocessor. The implemented on-chip switched capacitor voltage regulator provides a $0.7-1.1$ V output voltage from $1.8$ V input. It achieves a $85.1\%$ maximum efficiency at $3.2\,\mathrm{W}\mathrm{/}\mathrm{m}\mathrm{m}^2$ power density, a subnanosecond response time with improved minimum supply voltage capability, and a maximum output power of $10\,\mathrm{W}$ . For an output voltage of $850\,\mathrm{m}\mathrm{V}$ , the feedforward control reduces the required voltage overhead by $60\,\mathrm{m}\mathrm{V}$ for a transient load step from $10\%$ to $100\%$ of the nominal load. This can reduce the overall power consumption of the microprocessor by $7\%$ .

Mechanical Reliability of Embedded Array Capacitors in Ultrahigh-Performance Microprocessors

Increasing power delivery and performance requirements for next-generation Intel microprocessors has led to the need for a high-capacitance low-inductance decoupling option very close to the die. An embedded array capacitor (EAC) is a large array capacitor embedded in the high-density interconnect (HDI) substrate core and provides a low-inductance path to the die. This paper describes technology development challenges encountered while enabling EACs on Intel's advanced microprocessors. Various package interfaces resulting from the EAC embedding showed very high stress and propensity to delaminate. These defects were addressed by tailoring suitable materials and process modifications during the manufacturing process. Expansion of the embedding material in the HDI substrate resulted in high C4 area warpage. This led to issues such as solder bump bridging, underfill voids, and reliability fails. The technology development challenges and the solution paths described in this paper are very useful to industry in understanding the integration of advanced decoupling options in ultrahigh-performance microprocessor packages.

Small-Resistance and High-Quality-Factor Magnetic Integrated Inductors on PCB

We have designed and fabricated both single-coil and parallel-coil magnetic integrated inductors with extremely small resistances and high quality factors on an 8-in-round printed circuit board (PCB) substrate for microprocessor power delivery applications. The dc resistances of these inductors are less than 12 mOmega. Soft magnetic material CoFeHfO was successfully integrated into the inductor fabrication to increase the inductance. The quality factors are more than 80 in a frequency range of 1.5-2 GHz for air-core inductors and more than 23 in a range of 200-300 MHz for magnetic inductors. The net inductance improvement of the magnetic inductor over air-core inductor is about 12%, which could be further enhanced with a thicker magnetic core, according to our theoretic calculation and HFSS simulation. We also characterized the permeability spectra of CoFeHfO material on the PCB substrate, simulated the high-frequency performance of the magnetic integrated inductor by HFSS, and, for the first time, reached a good agreement with the experimental data. The experimental and simulation results of the magnetic inductors as compared to those of the air-core inductors point out the future direction to further optimize magnetic integrated inductors.

Estimation of Microprocessor Instantaneous Load Current

The inability to accurately determine the die level current draw of microprocessors is a significant gap in the analysis and design of microprocessor power delivery networks (PDNs). Although low frequency methods of direct measurement are available, the large number of power and ground connections on a package makes high frequency measurements extremely difficult. This paper successfully demonstrates that the instantaneous load current can be accurately estimated to over 500 MHz with only a wide bandwidth measurement of the voltage at the die. The current estimate is obtained by using the measured output impedance to create a band-limited inverse filter to solve the linear deconvolution problem. The accuracy of the algorithm is verified by correctly estimating known loads drawn by a functioning microprocessor. Two separate methods are then used to estimate the instantaneous load current of a microprocessor executing instructions, and wide bandwidth io (t) results are presented and discussed.

Fully Monolithic Cellular Buck Converter Design for 3-D Power Delivery

A fully monolithic interleaved buck dc-dc point-of-load (PoL) converter has been designed and fabricated in a 0.18-mm SiGe BiCMOS process. Target application of the design is 3-D power delivery for future microprocessors, in which the PoL converter will be vertically integrated with the processor using wafer-level 3-D interconnect technologies. Advantages of 3-D power delivery over conventional discrete voltage regulator modules (VRMs) are discussed. The prototype design, using two interleaved buck converter cells each operating at 200 MHz switching frequency and delivering 500 mA output current, is discussed with a focus on the converter power stage and control loop to highlight the tradeoffs unique to such high-frequency, monolithic designs. Measured steady-state and dynamic responses of the fabricated prototype are presented to demonstrate the ability of such monolithic converters to meet the power delivery requirements of future processors.

Efficient Full-Wave Characterization of Discrete High-Density Multiterminal Decoupling Capacitors for High-Speed Digital Systems

This paper presents an efficient surface-based finite-element method for the full-wave characterization of high-density and multiterminal decoupling capacitors (2, 8, 14, and any arbitrary number of terminals). In contrast to traditional finite-element methods that involve 3-D volumetric unknowns, this method reduces the unknowns one needs to solve to those on 2-D surfaces only. In addition, the reduction from the 3-D volume-based matrix to a 2-D surface-based one is achieved efficiently by exploiting the geometrical specialty of the decap structure. The entire numerical procedure is numerically rigorous without making any approximation. Its efficiency and accuracy have been demonstrated by both measurements and numerical experiments. Based on its fast and accurate solution, different design configurations of capacitors were studied to identify the optimal configuration that can maximize the performance of a decoupling capacitor. Furthermore, the full-wave model obtained from the proposed method was employed to assess the accuracy of conventional series lumped RLC capacitor models. In addition, the full-wave model was incorporated into a high-performance microprocessor's power delivery network to investigate system performance.

Low Profile Integratable Inductor Fabricated Based on LTCC Technology for Microprocessor Power Delivery Applications

A novel low profile power inductor suitable for planar integration is designed and fabricated based on low temperature co-fired ceramics technology for microprocessor power delivery applications. The inductor was designed to operate at a switching frequency of 4 to 5MHz, carrying a nominal dc current of 20A with a ripple current of 8 to 10A in a 5-V to 1-V dc-dc converter. The design and fabrication procedure is discussed in this paper, followed by small signal measurement and magnetic characterization results. The inductor was implemented in a prototype converter and the large signal measurement results are presented and its performance evaluated

Power Delivery for High-Performance Microprocessors

Power Delivery for High-Performance Microprocessors

Measured electrical performance of V-groove inductors for microprocessor power delivery

Thin-film V-groove inductors for microprocessor power delivery are discussed. A 10-MHz, 3.3-V to 1.1-V, 7-A dc-dc converter with V-groove inductors has been predicted to have an efficiency of 88% and power density of 60 W of output power per cm/sup 2/ of substrate area. The first prototype inductors with composite granular Co-ZrO/sub 2/ thin-films were fabricated with dimensions smaller than those required for a 7-A converter in order to fabricate them on standard 25-mm silicon wafers. For these prototype devices, we predicted that a 10-MHz, 3.3-V to 1.1-V, 2.1-A dc-dc converter would have 60% efficiency. Measurements on the prototypes indicate that a 2.1-A converter would have 55% efficiency with a power density of 28 W/cm/sup 2/. Measured losses were 23% higher than predicted. We have demonstrated that V-groove inductors can be fabricated with performance close to predicted results.

AC resistance of planar power inductors and the quasidistributed gap technique

Low-AC-resistance planar or foil-wound inductors constructed using a quasidistributed gap comprising multiple small gaps that approximate a distributed gap are analyzed. Finite-element simulations are used systematically to develop a model broadly applicable to the design of such quasidistributed gap inductors. It is shown that a good approximation of a distributed gap is realized if the ratio of gap pitch to spacing between gap and conductor is less than four, or if the gap pitch is comparable to a skin depth or smaller. Large gaps can reduce AC resistance, but for most practical designs gap length has little effect. A closed-form expression, which closely approximates the AC resistance factor for a wide range of designs, is developed. The methods are illustrated with an inductor for a high-ripple-current fast-response voltage regulator module (VRM) for microprocessor power delivery.

Evaporatively deposited Co-MgF/sub 2/ granular materials for thin-film inductors

Co-MgF/sub 2/ granular thin films prepared by thermal evaporation are reported. The fabricated materials show promise as high-frequency, low-loss cores for microfabricated magnetic devices in microprocessor power delivery applications. Transmission electron microscopy (TEM) reveals Co grains of about 3.2 nm embedded in a MgF/sub 2/ matrix 1 to 2 nm wide. Films were prepared with 20% to 89% volume cobalt at substrate temperatures between -21/spl deg/C and 311/spl deg/C. Good soft magnetic properties in a range of 40% to 55% volume cobalt with high DC resistivity of 500 /spl mu//spl Omega/-cm to 100 /spl Omega/-cm are measured for films deposited at room temperature. Low intrinsic coercivity, H/sub ci/ of 0.76 Oe and susceptibility, /spl chi/ of 26 in the easy axis direction with quality factor, Q over 100 and saturation flux density, B/sub s/ of 0.7 T are obtained.