Circuit Design and Routing For Field Programmable Analog Arrays

Abstract

Accurate, low-cost, rapid-prototyping techniques for analog circuits have been a long awaited dream for analog designers. However, due to the inherent nature of analog system, design automation in analog domain is very difficult to realize, and field programmable analog arrays (FPAA) have not achieved the same success as FPGAs in the digital domain. This results from several factors, including the lack of supporting CAD tools, small circuit density, low speed and significant parasitic effect from the fixed routing wires. These factors are all related to each other, making the design of a high performance FPAA a multi-dimension problem. Among others, a critical reason behind these difficulties is the non-ideal programming technology, which contributes a large portion of parasitics into the sensitive analog system, thus degrades the system performance.

This work is trying to attack these difficulties with development of a laser field programmable analog array (LFPAA). There are two parts of work involved, routing for FPAA and analog IC building block design. To facilitate the router development and provide a platform for FPAA application development, a generic arrayed based FPAA architecture and a flexible CAB topology were proposed. The routing algorithm was based on a modified and improved pathfinder negotiated routing algorithm, and was implemented in C for a prototype FPAA. The parasitic constraints for performance analog routing were also investigated and solutions were proposed. In the area of analog circuit design, a novel differential difference op amp was invented as the core building block. Two bandgap circuits including a low voltage version were developed to generate a stable reference voltage for the FPAA. Based on the proposed FPAA architecture, several application examples were demonstrated. The results show the flexible functionality of the FPAA. Moreover, various laser Makelink test structures were studied on different CMOS processes and BiCMOS copper process. Laser Makelink proves to be a powerful programming technology for analog IC design. A novel laser Makelink trimming method was invented to reduce the op amp offset. The application of using laser Makelink to reconfigure the analog circuit blocks was presented.