# An Open Architecture for Improving VLSI Circuit Performance

### Fred W. Obermeier

###
EECS Department

University of California, Berkeley

Technical Report No. UCB/CSD-89-522

August 1989

### http://www.eecs.berkeley.edu/Pubs/TechRpts/1989/CSD-89-522.pdf

Electrical performance and area improvement are important parts of the overall integrated circuit design task. However, few design tools allow easy exploration of the design space (area, delay, and power) or offer designers different performance alternatives. Given designer specified constraints on area, delay, and power, EPOXY will size a circuit's transistors and will attempt small circuit changes to help meet the constraints. The system provides an open flexible framework for developing and evaluating the effects of different area and electrical models, optimization algorithms, and circuit modifications.

EPOXY takes a physical and electrical description of the circuit and produces a series of symbolic equations that model its performance. This results in circuit performance 5 times faster than Crystal and 56 times faster when these equations are subsequently compiled. EPOXY employs a virtual-grid area model since the sum of transistor area is a better measure of dynamic power than cell area. Optimization of a CMOS eight-stage inverter chain illustrates this difference; a typical minimum power implementation is 32% larger than the one for minimum area.

Next EPOXY attempts to find a parameter assignment for the input variables of these equations, transistor widths, to meet the constraints while minimizing the user defined objective function. Previous transistor sizing systems are limited to fixed electrical models and only consider time and power tradeoffs. After evaluating two non-linear optimization techniques, the TILOS-style heuristic and augmented Lagrangian algorithm, a combination of the two was found to produce quality results rapidly.

If the performance constraints cannot be met by transistor sizing, EPOXY considers inserting buffers stages, rearranging transistors within a pull-down or pull-up tree, and splitting large transistors so that cell height and width can be traded off. This level handles the discrete decisions of proposing circuit alternatives while the two lower levels determine the best possible implementation for this alternative. From an implementation viewpoint, EPOXY's underlying equation abstraction of circuit performance automatically provides critical path information and allows rapid modification of the curcuit structure. A typical speed improvement of 23% for several CMOS circuits was achieved over transistor sizing alone while satisfying difficult height (pitch) constraints.

**Advisor:** Randy H. Katz

BibTeX citation:

@phdthesis{Obermeier:CSD-89-522, Author = {Obermeier, Fred W.}, Title = {An Open Architecture for Improving VLSI Circuit Performance}, School = {EECS Department, University of California, Berkeley}, Year = {1989}, Month = {Aug}, URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/1989/5914.html}, Number = {UCB/CSD-89-522}, Abstract = {Electrical performance and area improvement are important parts of the overall integrated circuit design task. However, few design tools allow easy exploration of the design space (area, delay, and power) or offer designers different performance alternatives. Given designer specified constraints on area, delay, and power, EPOXY will size a circuit's transistors and will attempt small circuit changes to help meet the constraints. The system provides an open flexible framework for developing and evaluating the effects of different area and electrical models, optimization algorithms, and circuit modifications. <p>EPOXY takes a physical and electrical description of the circuit and produces a series of symbolic equations that model its performance. This results in circuit performance 5 times faster than Crystal and 56 times faster when these equations are subsequently compiled. EPOXY employs a virtual-grid area model since the sum of transistor area is a better measure of dynamic power than cell area. Optimization of a CMOS eight-stage inverter chain illustrates this difference; a typical minimum power implementation is 32% larger than the one for minimum area. <p>Next EPOXY attempts to find a parameter assignment for the input variables of these equations, transistor widths, to meet the constraints while minimizing the user defined objective function. Previous transistor sizing systems are limited to fixed electrical models and only consider time and power tradeoffs. After evaluating two non-linear optimization techniques, the TILOS-style heuristic and augmented Lagrangian algorithm, a combination of the two was found to produce quality results rapidly. <p>If the performance constraints cannot be met by transistor sizing, EPOXY considers inserting buffers stages, rearranging transistors within a pull-down or pull-up tree, and splitting large transistors so that cell height and width can be traded off. This level handles the discrete decisions of proposing circuit alternatives while the two lower levels determine the best possible implementation for this alternative. From an implementation viewpoint, EPOXY's underlying equation abstraction of circuit performance automatically provides critical path information and allows rapid modification of the curcuit structure. A typical speed improvement of 23% for several CMOS circuits was achieved over transistor sizing alone while satisfying difficult height (pitch) constraints.} }

EndNote citation:

%0 Thesis %A Obermeier, Fred W. %T An Open Architecture for Improving VLSI Circuit Performance %I EECS Department, University of California, Berkeley %D 1989 %@ UCB/CSD-89-522 %U http://www.eecs.berkeley.edu/Pubs/TechRpts/1989/5914.html %F Obermeier:CSD-89-522