Field-programmable gate arrays (FPGAs), which are pre-fabricated, programmable digital integrated circuits (ICs), provide easy access to state-of-the-art integrated circuit process technology, and in doing so, democratize this technology of our time. This book is about comparing the qualities of FPGA – their speed performance, area and power consumption, against custom-fabricated ICs, and exploring ways of mitigating their de ciencies. This work began as a question that many have asked, and few had the resources to answer – how much worse is an FPGA compared to a custom-designed chip? As we dealt with that question, we found that it was far more dif cult to answer than we anticipated, but that the results were rich basic insights on fundamental understandings of FPGA architecture. It also encouraged us to nd ways to leverage those insights to seek ways to make FPGA technology better, which is what the second half of the book is about. While the question “How much worse is an FPGA than an ASIC?” has been a constant sub-theme of all research on FPGAs, it was posed most directly, some time around May 2004, by Professor Abbas El Gamal from Stanford University to us – he was working on a 3D FPGA, and was wondering if any real measurements had been made in this kind of comparison. Shortly thereafter we took it up and tried to answer in a serious way.
Field-Programmable Gate Arrays (FPGAs) have become the dominant digital implementation medium as measured by design starts. They are preferred because designers can avoid the pitfalls of nanoelectronic design and because the designer can change the design up until the last minute. However, it has always been understood that FPGAs use more area, are slower, and consume far more power than the alternative: Application-Specific ICs built from standard cells. But how much? Quantifying and Exploring the Gap Between FPGAs and ASICs is the first book to explore exactly what that difference is, to enable system designers to make better in-formed choices between these two media and to give insight to FPGA makers on the deficiencies to attack and thereby improve FPGAs. The gap is a very nuanced thing, though: it strongly depends on the nature of the circuit being implemented, in sometimes counterintuitive ways. The book presents a careful exploration of these issues in its first half. The second half of the book looks at ways that creators and users of FPGAs can close the gap between FPGAs and ASICs. It presents the most sweeping exploration of FPGA architecture and circuit design ever performed. The authors show that, with careful use of transistor-level design, combined with good choices of the soft-logic architecture, that a wide spectrum of FPGA devices can be used to narrow specific selected gaps in area, speed and power.
