Automated Performance Optimization of Custom Integrated Circuits

Citation

Trimberger, Stephen Mathias (1983) Automated Performance Optimization of Custom Integrated Circuits. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8YDZ-G637. https://resolver.caltech.edu/CaltechETD:etd-11072005-081513

Abstract

The complexity of integrated circuits requires a hierarchical design methodology that allows the user to divide the problem into pieces, design each piece independently, and assemble the pieces into the complete system. The design hierarchy brings out composition problems, problems that are a property of the assembly as a whole, not of one single instance in the hierarchy.

Recent research has produced tools that automate part of the composition task - the logical connection of the pieces. However, these tools do not ensure that signals driven over these connections will be driven sufficiently to give reasonable cycle speed of the resulting chips. It is easily possible to specify an assembly in which a small-sized gate is required to drive an enormous load. Parasitic capacitance of the wiring made automatically by the logical connection tool can be the dominant source of delay, so assembly tools can actually worsen the performance of the circuit and hide this fact from the designer.

When required to make large circuits, automated layout tools such as PLA generators can blindly make layouts that give abysmally poor performance. Here again, the delay is in a part of circuit that the designer did not specify, so it is hidden. Finding and correcting these problems is a difficult and time-consuming task in integrated circuit design, and one that consumes vastly more people's time and computer time than the simple assembly of the chip.

The task of guaranteeing that circuits meet performance specifications has been left mainly to the designer. Computer aided design has provided analysis tools, tools that tell the designer the performance statistics of the current design. It is then the designer's burden to interpret the performance statistics and use them as guides to make changes in the circuit.

This thesis views performance optimization as an electrical composition task. Poor performance as a result of mismatched loads on devices is a problem of composition and should be corrected by the composition tool. Such a tool is presented in this thesis -- a program that automatically sizes transistors in a symbolic description of a chip to match the load the transistors are driving. The results are encouraging: they show that delays can be cut by a factor of two in many current designs.

Thesis Files