Designing a 3D tree-based FPGA: Optimization of butterfly programmable interconnect topology using 3D technology

The CMOS technology scaling has greatly improved the overall performance and density of the Mesh-based Field Programmable Gate Arrays (FPGAs), nonetheless the gap between FPGAs and ASICs in terms of logic density, speed and power consumption remains very wide mainly due the programming overhead. The logic density and area overhead is improved by using Tree-based FPGA architecture using Butterfly-Fat-Tree (BFT) based network topology. However the wire-length increases exponentially as the tree grows to higher levels. We have introduced a horizontally partitioned 3-dimensional (3D) design methodology to optimize the BFT based programmable interconnect delay of the Tree-based FPGA. In this paper we describe a 2 tier horizontally partitioned 3D stacked Tree-based FPGA demonstrator, designed and implemented using Tezzaron´s 130nm, 3D technology. We finally evaluate the speed and area overhead of the proposed 3D Tree-based FPGA using the newly developed experimental design and evaluation methodology and show that the horizontally partitioned BFT programmable interconnect topology based 3D Tree-based FPGA improves speed by 2.06 times and reduce interconnect area by 2.8 times compared to 3D Mesh-based FPGA with identical logic resources.