Null Convention Logic Gates Research Articles

Design and Characterization of a Novel FinFET based NCL Cell Library for High Performance Asynchronous Circuits

In recent times, synchronous circuits are facing design related issues like clock skew, glitch power, EMI, leakage power, etc. The clock-less design paradigm – Asynchronous design challenges most of these issues and accepted as a better alternative to clocked circuits. QDI based Null Convention Logic (NCL) is such a clock-less design concept. However, NCL designs couldn’t get wide spread acceptance due to unavailability of commercial CAD tools and design compatible NCL standard cell library. The proposed research work in this paper demonstrates design and characterization of FinFET based NCL cell library to facilitate QDI based asynchronous circuit design. The NCL cells are designed with ASAP 7nm PDK. A complete set of 27 NCL threshold gates are developed and characterized in cadence using ocean scripting. Various time and energy models are extracted for different process corners using EDA platform. The proposed work will help research scholars to implement NCL based asynchronous circuits. This paper also demonstrates comparative performance analysis of bulk-CMOS and multi-gate FinFET based NCL threshold gates in 16 nanometer technology. The analysis has concluded average 19% of improvement in power-delay produce for FinFET based cells compared to its CMOS counterparts. To showcase two-dimensional comparison, various static and semi-static NCL gate structures are also compared in term of their power and speed. Various arithmetic circuits are designed using these standard NCL cells to demonstrate its application. The results indicated substantial performance improvement in terms of power and speed.

Arquitecturas Pipeline Asincrónicas Register Less NULL Convention Logic (RL-NCL) Usando Puertas Básicas

Asynchronous circuits is an alternative to design digital systems that is becoming the interest of many researchers in the digital design area mainly due to it’s low-power consumption and robustness. One of the most compelling design paradigms of asynchronous circuits is the NULL Convention Logic (NCL). The pipeline is a very common technique used in digital circuits to achieve high throughput. Although one can implement a pipeline using NCL gates, recent works have shown that register-less pipelines are possible using modified NCL gates. In this paper we propose two new Register-Less NCL (RL-NCL) pipeline architectures and two new methods to design NCL gates, which can be implemented even in Field Programmable Gate Arrays (FPGAs) or using the standard cells method. The new design of the proposed architecture was able to achieve an average area reduction of 27,32%, an average latency reduction of 14,1% and an average throughput increase of 5,54% comparing with the conventional NCL pipeline architecture.

Clockless Spintronic Logic: A Robust and Ultra-Low Power Computing Paradigm

Asynchronous logic offers the advantages of no clock tree, robust circuit operation, avoidance of worst-case timing margins, and a reduced emission spectrum. Thus, computational paradigms are sought to attain advantages of clockless logic by leveraging the complementary characteristics of emerging devices and CMOS transistors within novel circuit designs. This paper introduces Spin Torque Enabled NULL Convention Logic (STENCL), which exploits the physical characteristics of non-volatile Domain-Wall (DW) and memristive devices to realize the Quasi-Delay-Insensitive (QDI) NULL Convention Logic (NCL) asynchronous design methodology. First, a formal algorithm is developed to transform NCL-based threshold m-of-n gate realizations to STENCL, in order to generate the corresponding input memristance and NULL module memristance required for nominal currents achieving DW device biasing. Second, hysteresis and set/reset conditions are realized by determining the corresponding current fluctuations required to move the DW within each threshold logic gate to realize all 27 foundational NCL gate structures, which are then simulated to assess energy and delay metrics. Third, a case study of a four-stage pipelined 32-bit IEEE single-precision floating point co-processor implemented as a dual-rail STENCL architecture is compared to a conventional CMOS-based NCL design implemented by an IBM SOI1250 45nm CMOS process. Fourth, a sensitivity analysis is performed to assess the impact of write accuracy and drift on memristor and DW device operation. Results indicate that STENCL-based designs achieve between 2-fold to 20-fold reduction in energy consumption with up to 8-fold reduction in area, over an equivalent CMOS-based NCL design for 32-bit full adders. Comparisons for various four-stage pipelined 32-bit IEEE single-precision floating-point co-processors and ISCAS benchmarks further substantiate those benefits for operation within acceptable tolerances at identical process technology nodes.

Static Differential NCL Gates: Toward Low Power

This brief proposes a new topology for implementing differential null convention logic gates. The new topology relies on the static implementation of conventional versions of such gates and uses a set of extra minimum-sized transistors to cut off connections to the power rails in specific nodes while the gate is switching. It shows that albeit the extra transistors adding cost in area, they enable solid savings in dynamic and static power and improve transition delays. Electrical simulation results for a Kogge-Stone adder case study led to savings of 67.3% in dynamic power, 61.9% in static power, 67.2% in energy per operation, and 8.9% in forward propagation delay, when compared with a state-of-the-art differential topology.

Gate Mapping Automation for Asynchronous NULL Convention Logic Circuits

Design automation techniques are a key challenge in the widespread application of timing-robust asynchronous circuit styles. In this paper, a new methodology for mapping multi-rail logic expressions to a NULL convention logic (NCL) gate library is proposed. The new methodology is then compared to another recently proposed mapping approach, demonstrating that the new methodology can further reduce the area and improve the delay of NCL circuits. Also, in contrast to the original approach, which only targets area reduction, the new methodology can target any arbitrary cost function or use any subset of the NCL gate library for mapping. In order to automate the new methodology and compare it with the original one, both methodologies were implemented in the Perl programming language and compared in terms of mapping performance and runtime. The results show that, depending on the test circuit, the new methodology can offer up to 10% improvement in area, and 39% improvement in delay.

Design of an FPGA Logic Element for Implementing Asynchronous NULL Convention Logic Circuits

Two versions of a reconfigurable logic element are developed for use in constructing afield-programmable gate array NULL convention logic (NCL) field-programmable gate array (FPGA): one with extra embedded registration capability, which requires additional area, and one without. Both versions can be configured as any of the 27 fundamental NCL gates, including resettable and inverting variations, and both can utilize embedded registration for gates with three or fewer inputs; however, only the version with the additional embedded registration capability can utilize embedded registration with four-input gates. These two approaches are compared with each other and with an existing approach, showing that both versions developed herein yield a more area efficient NCL circuit implementation, compared to the previous work. The two FPGA logic elements are simulated at the transistor level using the 1.8-V, 180-nm TSMC CMOS process.