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For the flexibility of implementing any given Boolean function(s), the FPGA uses re-configurable building blocks called LUTs. The price for this reconfigurability is a large number of registers and multiplexers required to construct the FPGA. While researchers have been working on complex LUT structures to reduce the area and power for several years, most of these implementations come at the cost of performance penalty. This paper demonstrates simultaneous improvement in area, power, and performance in an FPGA by using special logic cells called Threshold Logic Cells (TLCs) (also known as binary perceptrons). The TLCs are capable of implementing a complex threshold function, which if implemented using conventional gates would require several levels of logic gates. The TLCs only require 7 SRAM cells and are significantly faster than the conventional LUTs. The implementation of the proposed FPGA architecture has been done using 28nm FDSOI standard cells and has been evaluated using ISCAS-85, ISCAS-89, and a few large industrial designs. Experiments demonstrate that the proposed architecture can be used to get an average reduction of 18.1% in configuration registers, 18.1% reduction in multiplexer count, 12.3% in Basic Logic Element (BLE) area, 16.3% in BLE power, 5.9% improvement in operating frequency, with a slight reduction in track count, routing area and routing power. The improvements are also demonstrated on the physically designed version of the architecture. 

This paper describes a novel design of a threshold logic gate (a binary perceptron) and its implementation as a standard cell. This new cell structure, referred to as flash threshold logic (FTL), uses floating gate (flash) transistors to realize the weights associated with a threshold function. The threshold voltages of the flash transistors serve as a proxy for the weights. An FTL cell can be equivalently viewed as a multi-input, edge-triggered flipflop which computes a threshold function on a clock edge. Consequently, it can be used in the automatic synthesis of ASICs. The use of flash transistors in the FTL cell allows programming of the weights after fabrication, thereby preventing discovery of its function by a foundry or by reverse engineering. This paper focuses on the design and characteristics of the FTL cell. We present a novel method for programming the weights of an FTL cell for a specified threshold function using a modified perceptron learning algorithm. The algorithm is further extended to select weights to maximize the robustness of the design in the presence of process variations. The FTL circuit was designed in 40nm technology and simulations with layout-extracted parasitics included, demonstrate significant im- provements in the area (79.7%), power (61.1%), and performance (42.5%) when compared to the equivalent implementations of the same function in conventional static CMOS design. Weight selection targeting robustness is demonstrated using Monte Carlo simulations. The paper also shows how FTL cells can be used for fixing timing errors after fabrication. 

This paper proposes an alternative FPGA tile struc- ture that consists of three traditional LUTs combined with a new reconfigurable threshold logic cell (TLC). The TLC requires only 7 SRAM cells and can be configured to implement one of several threshold functions. The proposed architecture is implemented in a 28nm FDSOI process, and is evaluated on standard benchmark circuits and several large complex function blocks. The results demonstrate an average reduction of 8.9% in register count, 15.4% in multiplexer count, 7% average reduction in Basic Logic Element (BLE) area, and 8.2% average reduction in BLE power, with a maximum decrease in register count up to 64%, BLE multiplexer count up to 68%, BLE Area up to 51.6% and BLE power up to 61.6% without loss in performance. We also show a reduction of 21% in the area of a tile.