Impacto da variabilidade PVT em somadores construídos com XORs

A operação de soma é a mais usada em Unidades Lógicas e Aritméticas (ULA). A ULA é a unidade mais importante no processamento de dados. Em sistemas digitais, é desejado um somador completo com baixo consumo de energia e um alto desempenho. O somador completo faz parte do caminho crítico em sistemas computacionais, ele pode ser implementado de diversas maneiras, a maioria delas tendo como seu principal sub-circuito a porta lógica OU-exclusivo (XOR). Consequentemente, o estudo de somadores completos compostos por combinações de portas lógicas XOR é de grande valia para pesquisas na literatura. Melhorias nos módulos aritméticos pode reduzir significativamente o consumo de potência dos sistemas, mas em tecnologias nanométricas é necessário considerar o impacto da variabilidade. Esse trabalho tem como objetivo analisar projetos de somadores completos que quando submetidos aos efeitos de variabilidade devem ser robustos, ter um bom desempenho e mostrar bons resultados em consumo de energia, quando estão operando em tensão nominal e em tensão de quase limiar. Além disso, foi utilizada uma técnica chamada de célula de desacoplamento (Dcell) visando uma alternativa para a redução da variabilidade de processo. Esse trabalho analisa e compara 4 somadores tradicionais e 9 somadores completos construídos através de 3 blocos lógicos, dos quais 2 deles são substituídos por portas lógicas XOR, em uma tecnologia FinFET de 7nm. Foi observado que circuitos somadores que foram construídos usando a XOR da família lógica CMOS, especialmente no segundo bloco, obtiveram piores resultados de desempenho e consumo energético. Somadores operando em tensão nominal são cerca de 80% mais robustos quanto ao impacto da variabilidade de processo no consumo máximo. A operação em quase limiar implica em uma alta sensibilidade no desempenho e consumo, alcançando mais de 300% nos piores casos. Em relação à variabilidade de processo, foi verificado um aumento de sensibilidade de cerca de 40% no desempenho quando foram utilizadas a XOR V5 e a XOR V8 no segundo bloco dos somadores quando operando em tensão nominal. Para a operação em tensão de quase limiar o uso da metodologia proposta nesse trabalho mostrou ser uma boa opção para alcançar uma maior robustez quanto ao consumo dos circuitos. Considerando o uso da Dcell, na operação em tensão nominal, foi verificado uma redução no desempenho juntamente com uma redução na variabilidade. O melhor caso foi o somador FAV5V8 que para um aumento de 20% no atraso, obteve uma redução de 20% na variabilidade. Em relação ao consumo, houve uma redução de 16% na potência dinâmica, juntamente com uma redução de quase 30% na variabilidade, como o que ocorreu com o somador FAV8V1. Foi possível observar casos de redução da variabilidade em mais de 40% com um pequeno aumento no consumo dinâmico. O uso dessa técnica teve um alto impacto nos resultados de circuitos que operavam em tensão de quase limiar, chegando em alguns casos a mais de 40% de redução do desempenho para uma pequena redução na variabilidade. Quanto ao consumo, nesse caso, os somadores tradicionais foram os menos afetados, e novamente o uso da XOR V8 no segundo bloco para construção dos somadores mostrou ser uma boa opção para aumento da robustez dos circuitos.The sum operation is the most used in the Arithmetic and Logic Units (ALU). In digital systems, a complete adder with low energy consumption and high performance is desired. The full adder is part of the critical path in computer systems. It can be implemented in several ways, most of them having the OR-exclusive logic gate (XOR) as its main sub-circuit. Consequently, the study of full adders composed of combinations of XOR logic gates has a great value in the literature. Improvements in arithmetic modules can significantly reduce the power consumption of systems, however, in nanometric technologies it is necessary to consider the impact of variability. This work aims to analyse designs of full adders considering variability effects, comparing performance and energy consumption when operating at nominal voltage and also at near threshold voltage. In addition, a technique called decoupling cell (Dcell) was used to provide an alternative for reducing process variability. This work analyses and compares four traditional adders and nine adders built using three logic blocks, where two of them are replaced by XOR logic gates, in a 7nm FinFET technology. It was observed that full adders that were built using the XOR of the CMOS logic family, especially in the second block, had worse results in performance and energy consumption. Full adders operating at nominal voltage regime are about 80% more robust in terms of the impact of process variability on maximum consumption. The near threshold operation implies a high sensitivity in performance and consumption, reaching more than 300% in the worst cases. Regarding the process variability, there was an increase in sensitivity of about 40% in performance when the XOR V5 and XOR V8 were used in the second block of the adder when operating at nominal voltage. For the voltage operation of near threshold, the use of the methodology proposed in this work demonstrate to be a good option to achieve greater robustness regarding the consumption of the circuits. Considering the use of Dcell, in the operation at nominal voltage, a reduction in performance was verified together with a reduction in variability. The best case was the adder FAV5V8 which for a 20% increase in delay, obtained a reduction of 20% in variability. In relation to dynamic consumption, there was a 16% reduction in power, together with a reduction of almost 30% in variability, as occurred with the FAV8V1 adder. It was possible to observe cases of reduced variability by more than 40% with a small increase in dynamic consumption. The use of this technique had a high impact on the results of circuits operating at near threshold voltage, in some cases reaching more than 40% reduction in performance for a small reduction in variability. For consumption, in this case, the traditional full adders were the least affected, and again the use of the XOR V8 in the second block for the construction of the adder proved to be a good option for increasing the robustness of the circuits

Digital and analog TFET circuits: Design and benchmark

In this work, we investigate by means of simulations the performance of basic digital, analog, and mixed-signal circuits employing tunnel-FETs (TFETs). The analysis reviews and complements our previous papers on these topics. By considering the same devices for all the analysis, we are able to draw consistent conclusions for a wide variety of circuits. A virtual complementary TFET technology consisting of III-V heterojunction nanowires is considered. Technology Computer Aided Design (TCAD) models are calibrated against the results of advanced full-quantum simulation tools and then used to generate look-up-tables suited for circuit simulations. The virtual complementary TFET technology is benchmarked against predictive technology models (PTM) of complementary silicon FinFETs for the 10 nm node over a wide range of supply voltages (VDD) in the sub-threshold voltage domain considering the same footprint between the vertical TFETs and the lateral FinFETs and the same static power. In spite of the asymmetry between p- and n-type transistors, the results show clear advantages of TFET technology over FinFET for VDDlower than 0.4 V. Moreover, we highlight how differences in the I-V characteristics of FinFETs and TFETs suggest to adapt the circuit topologies used to implement basic digital and analog blocks with respect to the most common CMOS solutions

Digital and analog TFET circuits: Design and benchmark

In this work, we investigate by means of simulations the performance of basic digital, analog, and mixed-signal circuits employing tunnel-FETs (TFETs). The analysis reviews and complements our previous papers on these topics. By considering the same devices for all the analysis, we are able to draw consistent conclusions for a wide variety of circuits. A virtual complementary TFET technology consisting of III-V heterojunction nanowires is considered. Technology Computer Aided Design (TCAD) models are calibrated against the results of advanced full-quantum simulation tools and then used to generate look-up-tables suited for circuit simulations. The virtual complementary TFET technology is benchmarked against predictive technology models (PTM) of complementary silicon FinFETs for the 10 nm node over a wide range of supply voltages (VDD) in the sub-threshold voltage domain considering the same footprint between the vertical TFETs and the lateral FinFETs and the same static power. In spite of the asymmetry between p- and n-type transistors, the results show clear advantages of TFET technology over FinFET for VDDlower than 0.4 V. Moreover, we highlight how differences in the I-V characteristics of FinFETs and TFETs suggest to adapt the circuit topologies used to implement basic digital and analog blocks with respect to the most common CMOS solutions

Ultra Low Power Digital Circuit Design for Wireless Sensor Network Applications

Ny forskning innenfor feltet trådløse sensornettverk åpner for nye og innovative produkter og løsninger. Biomedisinske anvendelser er blant områdene med størst potensial og det investeres i dag betydelige beløp for å bruke denne teknologien for å gjøre medisinsk diagnostikk mer effektiv samtidig som man åpner for fjerndiagnostikk basert på trådløse sensornoder integrert i et ”helsenett”. Målet er å forbedre tjenestekvalitet og redusere kostnader samtidig som brukerne skal oppleve forbedret livskvalitet som følge av økt trygghet og mulighet for å tilbringe mest mulig tid i eget hjem og unngå unødvendige sykehusbesøk og innleggelser. For å gjøre dette til en realitet er man avhengige av sensorelektronikk som bruker minst mulig energi slik at man oppnår tilstrekkelig batterilevetid selv med veldig små batterier. I sin avhandling ” Ultra Low power Digital Circuit Design for Wireless Sensor Network Applications” har PhD-kandidat Farshad Moradi fokusert på nye løsninger innenfor konstruksjon av energigjerrig digital kretselektronikk. Avhandlingen presenterer nye løsninger både innenfor aritmetiske og kombinatoriske kretser, samtidig som den studerer nye statiske minneelementer (SRAM) og alternative minnearkitekturer. Den ser også på utfordringene som oppstår når silisiumteknologien nedskaleres i takt med mikroprosessorutviklingen og foreslår løsninger som bidrar til å gjøre kretsløsninger mer robuste og skalerbare i forhold til denne utviklingen. De viktigste konklusjonene av arbeidet er at man ved å introdusere nye konstruksjonsteknikker både er i stand til å redusere energiforbruket samtidig som robusthet og teknologiskalerbarhet øker. Forskningen har vært utført i samarbeid med Purdue University og vært finansiert av Norges Forskningsråd gjennom FRINATprosjektet ”Micropower Sensor Interface in Nanometer CMOS Technology”

Low power predictable memory and processing architectures

Great demand in power optimized devices shows promising economic potential and draws lots of attention in industry and research area. Due to the continuously shrinking CMOS process, not only dynamic power but also static power has emerged as a big concern in power reduction. Other than power optimization, average-case power estimation is quite significant for power budget allocation but also challenging in terms of time and effort. In this thesis, we will introduce a methodology to support modular quantitative analysis in order to estimate average power of circuits, on the basis of two concepts named Random Bag Preserving and Linear Compositionality. It can shorten simulation time and sustain high accuracy, resulting in increasing the feasibility of power estimation of big systems. For power saving, firstly, we take advantages of the low power characteristic of adiabatic logic and asynchronous logic to achieve ultra-low dynamic and static power. We will propose two memory cells, which could run in adiabatic and non-adiabatic mode. About 90% dynamic power can be saved in adiabatic mode when compared to other up-to-date designs. About 90% leakage power is saved. Secondly, a novel logic, named Asynchronous Charge Sharing Logic (ACSL), will be introduced. The realization of completion detection is simplified considerably. Not just the power reduction improvement, ACSL brings another promising feature in average power estimation called data-independency where this characteristic would make power estimation effortless and be meaningful for modular quantitative average case analysis. Finally, a new asynchronous Arithmetic Logic Unit (ALU) with a ripple carry adder implemented using the logically reversible/bidirectional characteristic exhibiting ultra-low power dissipation with sub-threshold region operating point will be presented. The proposed adder is able to operate multi-functionally

Low Power Memory/Memristor Devices and Systems

This reprint focusses on achieving low-power computation using memristive devices. The topic was designed as a convenient reference point: it contains a mix of techniques starting from the fundamental manufacturing of memristive devices all the way to applications such as physically unclonable functions, and also covers perspectives on, e.g., in-memory computing, which is inextricably linked with emerging memory devices such as memristors. Finally, the reprint contains a few articles representing how other communities (from typical CMOS design to photonics) are fighting on their own fronts in the quest towards low-power computation, as a comparison with the memristor literature. We hope that readers will enjoy discovering the articles within

Adiabatic Circuits for Power-Constrained Cryptographic Computations

This thesis tackles the need for ultra-low power operation in power-constrained cryptographic computations. An example of such an application could be smartcards. One of the techniques which has proven to have the potential of rendering ultra-low power operation is ‘Adiabatic Logic Technique’. However, the adiabatic circuits has associated challenges due to high energy dissipation of the Power-Clock Generator (PCG) and complexity of the multi-phase power-clocking scheme. Energy efficiency of the adiabatic system is often degraded due to the high energy dissipation of the PCG. In this thesis, nstep charging strategy using tank capacitors is considered for the power-clock generation and several design rules and trade-offs between the circuit complexity and energy efficiency of the PCG using n-step charging circuits have been proposed. Since pipelining is inherent in adiabatic logic design, careful selection of architecture is essential, as otherwise overhead in terms of area and energy due to synchronization buffers is induced specifically, in the case of adiabatic designs using 4-phase power-clocking scheme. Several architectures for the Montgomery multiplier using adiabatic logic technique are implemented and compared. An architecture which constitutes an appropriate trade-off between energy efficiency and throughput is proposed along with its methodology. Also, a strategy to reduce the overhead due to synchronization buffers is proposed. A modification in the Montgomery multiplication algorithm is proposed. Furthermore, a problem due to the application of power-clock gating in cascade stages of adiabatic logic is identified. The problem degrades the energy savings that would otherwise be obtained by the application of power-clock gating. A solution to this problem is proposed. Cryptographic implementations also present an obvious target for Power Analysis Attacks (PAA). There are several existing secure adiabatic logic designs which are proposed as a countermeasure against PAA. Shortcomings of the existing logic designs are identified, and two novel secure adiabatic logic designs are proposed as the countermeasures against PAA and improvement over the existing logic designs