Logic Tiles Research Articles

COFFE 2

FPGAs are becoming more heteregeneous to better adapt to different markets, motivating rapid exploration of different blocks/tiles for FPGAs. To evaluate a new FPGA architectural idea, one should be able to accurately obtain the area, delay, and energy consumption of the block of interest. However, current FPGA circuit design tools can only model simple, homogeneous FPGA architectures with basic logic blocks and also lack DSP and other heterogeneous block support. Modern FPGAs are instead composed of many different tiles, some of which are designed in a full custom style and some of which mix standard cell and full custom styles. To fill this modelling gap, we introduce COFFE 2, an open-source FPGA design toolset for automatic FPGA circuit design. COFFE 2 uses a mix of full custom and standard cell flows and supports not only complex logic blocks with fracturable lookup tables and hard arithmetic but also arbitrary heterogeneous blocks. To validate COFFE 2 and demonstrate its features, we design and evaluate a multi-mode Stratix III-like DSP block and several logic tiles with fracturable LUTs and hard arithmetic. We also demonstrate how COFFE 2’s interface to VTR allows full evaluation of block-routing interfaces and various fracturable 6-LUT architectures.

Experimental study on heavy ion single-event effects in flash-based FPGAs

With extensive use of flash-based field-programmable gate arrays (FPGAs) in military and aerospace applications, single-event effects (SEEs) of FPGAs induced by radiations have been a major concern. In this paper, we present SEE experimental study of a flash-based FPGA from Microsemi ProASIC3 product family. The relation between the cross section and different linear energy transfer (LET) values for the logic tiles and embedded RAM blocks is obtained. The results show that the sequential logic cross section depends not too much on operating frequency of the device. And the relationship between 0 → 1 upsets (zeros) and 1 → 0 upsets (ones) is different for different kinds of D-flip-flops. The devices are not sensitive to SEL up to a LET of 99.0 MeV cm2/mg. Post-beam tests show that the programming module is damaged due to the high-LET ions.

Layout Technique for Double-Gate Silicon Nanowire FETs With an Efficient Sea-of-Tiles Architecture

As we advance into the era of nanotechnology, semiconductor devices are scaled down to their physical limits, thereby opening up venues for new transistor channel materials based on nanowires and nanotubes. Transistors based on nanowires and nanotubes inherently exhibit ambipolar behavior. While technologists aim to suppress ambipolar behavior of these transistors, new design methodologies are proposed by exploiting the phenomenon of controllable polarity. In this paper, we propose regular layout fabrics, with an emphasis on silicon nanowires (SiNWs) as the candidate technology. A double-gate ambipolar SiNW field-effect transistor operates as p-type or n-type by electrically controlling the polarity of the second gate. We propose layout techniques to address gate-level routing congestion, as every transistor has two gates to route. Novel symbolic layouts, which are technology independent, are proposed for ambipolar circuits. In the second part of this paper, we present an approach for designing an efficient regular layout called sea-of-tiles (SoTs). A logic tile is essentially an array of prefabricated transistor-pairs grouped together. We design four logic tiles, which form the basic building block of the SoT fabric. We run extensive comparisons of mapping standard benchmarks onto the SoT fabric to find the optimum tile. This paper shows that SoT with $\mathrm{Tile}_{\mathit {G2}}$ and $\mathrm{Tile}_{\mathit {G1h2}}$ , on an average, outperforms the one with $\mathrm{Tile}_{\mathit {G1}}$ by 16% and 14% in area utilization, respectively.

Programmable nanowire circuits for nanoprocessors

A nanoprocessor constructed from intrinsically nanometre-scale building blocks is an essential component for controlling memory, nanosensors and other functions proposed for nanosystems assembled from the bottom up. Important steps towards this goal over the past fifteen years include the realization of simple logic gates with individually assembled semiconductor nanowires and carbon nanotubes, but with only 16 devices or fewer and a single function for each circuit. Recently, logic circuits also have been demonstrated that use two or three elements of a one-dimensional memristor array, although such passive devices without gain are difficult to cascade. These circuits fall short of the requirements for a scalable, multifunctional nanoprocessor owing to challenges in materials, assembly and architecture on the nanoscale. Here we describe the design, fabrication and use of programmable and scalable logic tiles for nanoprocessors that surmount these hurdles. The tiles were built from programmable, non-volatile nanowire transistor arrays. Ge/Si core/shell nanowires coupled to designed dielectric shells yielded single-nanowire, non-volatile field-effect transistors (FETs) with uniform, programmable threshold voltages and the capability to drive cascaded elements. We developed an architecture to integrate the programmable nanowire FETs and define a logic tile consisting of two interconnected arrays with 496 functional configurable FET nodes in an area of ∼960 μm(2). The logic tile was programmed and operated first as a full adder with a maximal voltage gain of ten and input-output voltage matching. Then we showed that the same logic tile can be reprogrammed and used to demonstrate full-subtractor, multiplexer, demultiplexer and clocked D-latch functions. These results represent a significant advance in the complexity and functionality of nanoelectronic circuits built from the bottom up with a tiled architecture that could be cascaded to realize fully integrated nanoprocessors with computing, memory and addressing capabilities.

Circuit design of a novel FPGA chip FDP2008

A novel FPGA chip FDP2008 (Fudan Programmable Logic) has been designed and implemented with the SMIC 0.18 μm CMOS logic 1P6M process. The new design method means that the configurable logic block can be configured as distributed RAM and a shift register. A universal programmable routing circuit is also presented; by adopting offset lines, complementary hanged end-lines and MUX + Buffer routing switches, the whole FPGA chip is highly repeatable, and the signal delay is uniform and predictable over the total chip. A standard configuration interface SPI is added in the configuration circuit, and a group of highly sensitive amplifiers is used to magnify the read back data. FDP2008 contains 20 × 30 logic TILEs, 200 programmable IOBs and 10 × 4 kbit dual port block RAMs. The hardware software cooperation test shows that FDP2008 works correctly and efficiently.

The design of a SRAM-based field-programmable gate array-Part II: Circuit design and layout

For Pt.I see ibid., vol.7, pp.191-7 (1999). Field-programmable gate arrays (FPGA's) are now widely used for the implementation of digital systems, and many commercial architectures are available. Although the literature and data books contain detailed descriptions of these architectures, there is very little information on how the high-level architecture was chosen and no information on the circuit-level or physical design of the devices. In Part I of this paper, we described the high-level architectural design of a static random-access memory programmable FPGA. This paper will address the circuit-design issues through to the physical layout. We address area-speed tradeoffs in the design of the logic block circuits and in the connections between the logic and the routing structure. All commercial FPGA designs are done using full-custom hand layout to obtain absolute minimum die sizes. This is both labor and time intensive. We propose a design style with a minitile that contains a portion of all the components in the logic tile, resulting in less full-custom effort. The minitile is replicated in a 4/spl times/4 array to create a macro tile. The minitile is optimized for layout density and speed, and is customized in the array by adding appropriate vias. This technique also permits easy changing of the hard-wired connections in the logic block architecture and the segmentation length distribution in the routing architecture.