This paper presents a comprehensive survey of existing techniques for interconnect optimization during the VLSI physical design process, with emphasis on recent studies on interconnect design and optimization for high-performance VLSI circuit design under the deep submicron fabrication technologies. First, we present a number of interconnect delay models and driver/gate delay models of various degrees of accuracy and efficiency which are most useful to guide the circuit design and interconnect optimization process. Then, we classify the existing work on optimization of VLSI interconnect into the following three categories and discuss the results in each category in detail: (i) topology optimization for highperformance interconnects, including the algorithms for total wire length minimization, critical path length minimization, and delay minimization; (ii) device and interconnect sizing, including techniques for efficient driver, gate, and transistor sizing, optimal wire sizing, and simultaneous topology construction, buffer insertion, buffer and wire sizing; (iii) highperfbrmance clock routing, including abstract clock net topology generation and embedding, planar clock routing, buffer and wire sizing for clock nets, non-tree clock routing, and clock schedule optimization. For each method, we discuss its effectiveness, its advantages and limitations, as well as its computational efficiency. We group the related techniques according to either their optimization techniques or optimization objectives so that the reader can easily compare the quality and efficiency of different solutions.

this paper. Given the MOS circuit topology, the delay can be controlled byvarying the sizes of transistors in the circuit. Here, the size of a transistor is measured in terms of its channel width, since the channel lengths in a digital circuit are generally uniform. Roughly speaking, the sizes of certain transistors can be increased to reduce the circuit delay at the expense of additional chip area

Gate sizing consists of choosing for each node of a mapped network a gate implementation in the library so that some cost function is optimized under some constraints. It has a significant impact on the delay, power dissipation, and area of the final circuit. This paper compares five gate sizing algorithms targeting discrete, non-linear, non-unimodal, constrained optimization. The goal is to overcome the non-linearity and nonunimodality of the delay and the power to achieve good quality results within a reasonable CPU time, e.g., handling a 10000 node network in 2 hours. We compare the five algorithms on constraint free delay optimization and delay constrained power optimization, and show that one method is superior to the others. 1 Introduction Early work on gate sizing targeting area/delay optimization can be found in [20, 12]. Using a RC delay model, TILOS [8] expresses the delay and area as posynomials. Geometric programming or heuristics based greedy approaches can be used to so...

We propose to use the dominant time constant of a resistor-capacitor (RC) circuit as a measure of the signal propagation delay through the circuit. We show that the dominant time constant is a quasiconvex function of the conductances and capacitances, and use this property to cast several interesting design problems as convex optimization problems, specifically, semidefinite programs (SDPs). For example, assuming that the conductances and capacitances are affine functions of the design parameters (which is a common model in transistor or interconnect wire sizing), one can minimize the power consumption or the area subject to an upper bound on the dominant time constant, or compute the optimal tradeoff surface between power, dominant time constant, and area. We will also note that, to a certain extent, convex optimization can be used to design the topology of the interconnect wires. This approach has two advantages over methods based on Elmore delay optimization. First, it handles a far wider class of circuits, e.g., those with non-grounded capacitors. Second, it always results in convex optimization problems for which very efficient interiorpoint methods have recently been developed. We illustrate the method, and extensions, with several examples involving optimal wire and transistor sizing.

The portable communications industry’s vision of integrating a complete multimedia complex on a single die, coupled with the desktop computing industry’s vision of inte-grating multimedia functionality into general-purpose microprocessors has trans-formed lowering the power dissipation of digital signal processing (DSP) datapath circuits into an increasingly important challenge in current and future fabrication pro-cesses. Fully-static CMOS logic accompanied with supply voltage scaling has enjoyed widespread usage in lowering datapath power dissipation over the last decade. How-ever, fundamental limitations preclude device threshold voltage scaling under the con-stant drain-source field scaling paradigm in future deep-submicron processes, imposing limitations on voltage scaling. This has motivated a strong necessity for exploring new methodologies to lower the power dissipation of next-generation high-speed datapath circuits. This thesis investigates Mixed Swing techniques for reducing the power dissipa-tion of static CMOS datapath operators while retaining their high performance, or

As very large scale integrated (VLSI) circuits move into the era of deepsubmicron (DSM) technology and gigahertz frequency, the system performance has increasingly become dominated by the interconnect delay. This dissertation presents five related research topics on interconnect layout optimization, and interconnect extraction and modeling: the multi-source wire sizing (MSWS) problem, the simultaneous transistor and interconnect sizing (STIS) problem, the global interconnect sizing and spacing (GISS) problem, the interconnect capacitance extraction problem, and the interconnect inductance extraction problems. Given a routing tree with multiple sources, the MSWS problem determines the optimal widths of the wire segments such that the delay is minimized. We reveal several interesting properties for the optimal MSWS solution, of which the most important is the bundled refinement property. Based on this property, we propose a polynomial time algorithm, which uses iterative bundled refinement operations to compute lower and upper bounds of an optimal solution. Since the algorithm often achieves identical lower and upper bounds in experiments, the optimal solution is obtained simply by the bound computation. Furthermore, this algorithm can be used for single-source wire sizing problem and runs 100x xxi faster than previous methods. It has replaced previous single-source wire sizing methods in practice.

In this paper a method for choosing appropriate transistor topology for use with transistor sizing is presented. In combinatorial blocks of static CMOS circuits transistor sizing can be applied for delay balancing in order to guarantee synchronously arriving signal slopes at the input of logic gates. Since the delay of a logic gate depends directly on transistor sizes, the variation of channel-widths and-lengths (W and L) allows to equalize different path delays without influencing the total propagation delay of the circuit. Thus, glitching can be avoided. To achieve optimal results, transistor lengths have to be increased, which results in both increased gate capacitances and area. Splitting the long transistors counteracts this negative influence and reduces the power dissipated. A program GliMATS for automated circuit optimization has been implemented. Experimental results show that significant power savings can be achieved with this method. 1.