LUT Cascades and Emulators for Realization of Logic Functions

Two types of programmable logic devices using LUTs (Look-Up Tables) are presented. An LUT cascade directly implements logic functions by a series connection of LUTs, while an emulator emulates an LUT cascade by sequentially accessing LUTs. The LUT cascade is faster, but has a limited logic capability, while the emulator is slower, but has a higher logic capability. LUT cascades and emulators can be directly generated from the BDDs of target functions. Their performances are easy to estimate. The C-measure that show the complexity of LUT cascades are also presented. Functions with small C-measures have efficient LUT cascade and emulator realizations. Classes of functions that are suitable for LUT cascade and emulator realizations are also presented.