Howard H. Smith

On-chip wiring design challenges for gigahertz operation

This paper reviews the status of present day on-chip wiring design methodologies and understanding. A brief explanation is given of the fundamental transmission-line properties that should be considered for accurate prediction of crosstalk, common-mode noise and clock skew. The deficiencies of RC-circuit representation are highlighted and design guidelines are given for using modeling and simulation techniques that have been previously used for package interconnections. Such techniques are believed to teach designers how to make better use of available technologies and help them architect systems that operate with many-GHz clock rates.

When are transmission-line effects important for on-chip interconnections

Short, medium and long on-chip interconnections having line widths of 0.45-52 /spl mu/m are analyzed in a five-metal-layer structure. We study capacitive coupling for short lines, inductive coupling for medium-length lines, inductance and resistance of the current return path in the power buses and line resistive losses for the global wiring. Design guidelines and technology changes are proposed to achieve minimum delay and contain crosstalk for local and global wiring. Conditional expressions are given to determine when transmission-line effects are important for accurate delay and crosstalk prediction.

Modeling, simulation, and measurement of mid-frequency simultaneous switching noise in computer systems

Complementary metal-oxide-semiconductor (CMOS) microprocessors operating in the hundreds of megahertz create significant current deltas due to the variation in switching activity front clock cycle to clock cycle. In addition to the high-frequency voltage variations more commonly discussed, a lower frequency noise component is also produced that lasts from 50-200 ns which we refer to as mid-frequency noise. In this paper, we discuss the design of IBMs CMOS S/390 computer for control of mid-frequency noise. This machine has a 10-way multiprocessor on a 127 mm by 127 mm multichip module (MCM) on a FR4 board. The chips on the MCM cause a current step of tens of Amps in a few cycles that can be sustained for many cycles. The power distribution and decoupling capacitors must supply that current without disturbing the voltage level at the circuits. The design of the system power distribution and modeling and verification of mid-frequency noise in this system is presented.

The importance of inductance and inductive coupling for on-chip wiring

The importance of inductance and inductive coupling for accurate delay and crosstalk prediction in on-chip interconnections is investigated experimentally for the top three layers in a five-layer wiring structure and guidelines are formulated. In-plane and between-plane crosstalk and delay dependence on driver and receiver circuit device sizes and line lengths and width are analyzed with representative CMOS circuits. Simplified constant-parameter, distributed coupled-line RLC-circuit representation that approximates the waveforms predicted with frequency-dependent line parameters is shown to be feasible.

IBM POWER6 microprocessor physical design and design methodology

The IBM POWER6™ microprocessor is a 790 million-transistor chip that runs at a clock frequency of greater than 4 GHz. The complexity and size of the POWER6 microprocessor, together with its high operating frequency, present a number of significant challenges. This paper describes the physical design and design methodology of the POWER6 processor. Emphasis is placed on aspects of the design methodology, technology, clock distribution, integration, chip analysis, power and performance, random logic macro (RLM), and design data management processes that enabled the design to be completed and the project goals to be met.

A 5.2GHz microprocessor chip for the IBM zEnterprise™ system

The microprocessor chip for the IBM zEnterprise 196 (z 196) system is a high-frequency, high-performance design that adds support for out-of-order instruction execution and increases operating frequency by almost 20% compared to the previous 65nm design, while still fitting within the same power envelope. Despite the many difficult engineering hurdles to be overcome, the design team was able to achieve a product frequency of 5.2GHz, providing a significant performance boost for the new system.

MCM technology and design for the S/390 G5 system

The multichip module (MCM) that contains the central electronic complex (CEC) of the S/390 G5 system is described in this paper. The glass-ceramic module, topped with six layers of polyimide full-field thin-film wiring for chipto-chip interconnection, represents IBM’s most advanced packaging technology. This MCM provides a large wiring capacity, with 595 meters of routed interconnection; it supports the highest synchronous interconnection performance in the industry at 300 MHz; and it allows for cooling flexibility at the system level—either a heat sink for air-cooled systems or a cooling “hat” for systems using refrigeration cooling. The physical and electrical characteristics of this packaging technology, necessary to support the aggressive system performance goals (1040 MIPS) of the IBM G5 Enterprise Servers, are presented here. In addition, the approach used to produce a robust electrical and physical design is described.

A comprehensive 2-D inductance modeling approach for VLSI interconnects: frequency-dependent extraction and compact circuit model synthesis

Although three-dimensional (3-D) partial inductance modeling costs have decreased with stable, sparse approximations of the inductance matrix and its inverse, 3-D models are still intractable when applied to full chip timing or crosstalk analysis. The 3-D partial inductance matrix (or its inverse) is too large to be extracted or simulated when power-grid cross-sections are made wide to capture proximity effect and wires are discretized finely to capture skin effect. Fortunately, 3-D inductance models are unnecessary in VLSI interconnect analysis. Because return currents follow interconnect wires, long interconnect wires can be accurately modeled as two-dimensional (2-D) transmission lines and frequency-dependent loop impedances extracted using 2-D methods . Furthermore, this frequency dependence can be approximated with compact circuit models for both uncoupled and coupled lines. Three-dimensional inductance models are only necessary to handle worst case effects such as simultaneous switching in the end regions. This paper begins by explaining and defending the 2-D modeling approach. It then extends the extraction algorithm to efficiently include distant return paths. Finally, a novel synthesis technique is described that approximates the frequency-dependent series impedance of VLSI interconnects with compact circuit models suitable for timing and noise analysis.

Circuit and Physical Design Implementation of the Microprocessor Chip for the zEnterprise System

This paper describes the circuit and physical design features of the z196 processor chip, implemented in a 45 nm SOI technology. The chip contains 4 super-scalar, out-of-order processor cores, running at 5.2 GHz, on a die with an area of 512 mm2 containing an estimated 1.4 billion transistors. The core and chip design methodology and specific design features are presented, focusing on techniques used to enable high-frequency operation. In addition, chip power, IR drop, and supply noise are discussed, being key design focus areas. The chips ground-breaking RAS features are also described, engineered for maximum reliability and system stability.

Mid-frequency simultaneous switching noise in computer systems

CMOS microprocessors operating in the hundreds of megahertz create significant current deltas due to the variation in switching activity from clock cycle to clock cycle. In addition to the high-frequency voltage variations more commonly discussed, a lower frequency noise component is also produced that lasts from 50 to 200 ns which we refer to as mid-frequency noise. In this paper, we discuss the design of IBMs CMOS S/390 computer for control of mid-frequency noise. This machine has a 10-way multiprocessor on a 127 mm by 127 mm MCM on a FR4 board. The chips on the MCM cause a current step of tens of Amps in a few cycles that can be sustained for many cycles. The power distribution and decoupling capacitors must supply that current without disturbing the voltage level at the circuits. The design of the system power distribution and modeling and verification of mid-frequency noise in this system is presented.