Analysis of Parameter Tuning on Energy Efficiency in Asynchronous Circuits

Power and energy consumption are the primary concern of the digital integrated circuit (IC) industry. Asynchronous logic, in the past several years, has increased in popularity due to its low power nature. This thesis analyzes a collection of array multipliers with different parameters to compare two asynchronous design paradigms, NULL Convention Logic (NCL) and Multi-Threshold NULL Convention Logic (MTNCL). Several commercially available pieces of software and custom scripts are used to analyze the asynchronous circuits and their components to provide the energy consumption estimation on various parts of each circuit. The analysis of the software results revealed that MTNCL circuits are more energy efficient for any size provided the number of pipeline stages does not become too great. Otherwise NCL would consume less energy. A combinational logic gate count to register gate count ratio of 3 was given to help determine when an MTNCL circuit would have too many pipeline stages for circuits designed with IBM\u27s 130nm 8RF-DM design kit

A low-power quadrature digital modulator in 0.18um CMOS

Quadrature digital modulation techniques are widely used in modern communication systems because of their high performance and flexibility. However, these advantages come at the cost of high power consumption. As a result, power consumption has to be taken into account as a main design factor of the modulator.In this thesis, a low-power quadrature digital modulator in 0.18um CMOS is presented with the target system clock speed of 150 MHz. The quadrature digital modulator consists of several key blocks: quadrature direct digital synthesizer (QDDS), pulse shaping filter, interpolation filter and inverse sinc filter. The design strategy is to investigate different implementations for each block and compare the power consumption of these implementations. Based on the comparison results, the implementation that consumes the lowest power will be chosen for each block. First of all, a novel low-power QDDS is proposed in the thesis. Power consumption estimation shows that it can save up to 60% of the power consumption at 150 MHz system clock frequency compared with one conventional design. Power consumption estimation results also show that using two pulse shaping blocks to process I/Q data, cascaded integrator comb (CIC) interpolation structure, and inverse sinc filter with modified canonic signed digit (MCSD) multiplication consume less power than alternative design choices. These low-power blocks are integrated together to achieve a low-power modulator. The power consumption estimation after layout shows that it only consumes about 95 mW at 150 MHz system clock rate, which is much lower than similar commercial products. The designed modulator can provide a low-power solution for various quadrature modulators. It also has an output bandwidth from 0 to 75 MHz, configurable pulse shaping filters and interpolation filters, and an internal sin(x)/x correction filter

Design and Analysis of an Adaptive Asynchronous System Architecture for Energy Efficiency

Power has become a critical design parameter for digital CMOS integrated circuits. With performance still garnering much concern, a central idea has emerged: minimizing power consumption while maintaining performance. The use of dynamic voltage scaling (DVS) with parallelism has shown to be an effective way of saving power while maintaining performance. However, the potency of DVS and parallelism in traditional, clocked synchronous systems is limited because of the strict timing requirements such systems must comply with. Delay-insensitive (DI) asynchronous systems have the potential to benefit more from these techniques due to their flexible timing requirements and high modularity. This dissertation presents the design and analysis of a real-time adaptive DVS architecture for paralleled Multi-Threshold NULL Convention Logic (MTNCL) systems. Results show that energy-efficient systems with low area overhead can be created using this approach

Doctor of Philosophy

dissertationThe design of integrated circuit (IC) requires an exhaustive verification and a thorough test mechanism to ensure the functionality and robustness of the circuit. This dissertation employs the theory of relative timing that has the advantage of enabling designers to create designs that have significant power and performance over traditional clocked designs. Research has been carried out to enable the relative timing approach to be supported by commercial electronic design automation (EDA) tools. This allows asynchronous and sequential designs to be designed using commercial cad tools. However, two very significant holes in the flow exist: the lack of support for timing verification and manufacturing test. Relative timing (RT) utilizes circuit delay to enforce and measure event sequencing on circuit design. Asynchronous circuits can optimize power-performance product by adjusting the circuit timing. A thorough analysis on the timing characteristic of each and every timing path is required to ensure the robustness and correctness of RT designs. All timing paths have to conform to the circuit timing constraints. This dissertation addresses back-end design robustness by validating full cyclical path timing verification with static timing analysis and implementing design for testability (DFT). Circuit reliability and correctness are necessary aspects for the technology to become commercially ready. In this study, scan-chain, a commercial DFT implementation, is applied to burst-mode RT designs. In addition, a novel testing approach is developed along with scan-chain to over achieve 90% fault coverage on two fault models: stuck-at fault model and delay fault model. This work evaluates the cost of DFT and its coverage trade-off then determines the best implementation. Designs such as a 64-point fast Fourier transform (FFT) design, an I2C design, and a mixed-signal design are built to demonstrate power, area, performance advantages of the relative timing methodology and are used as a platform for developing the backend robustness. Results are verified by performing post-silicon timing validation and test. This work strengthens overall relative timed circuit flow, reliability, and testability

Asynchronous 3D (Async3D): Design Methodology and Analysis of 3D Asynchronous Circuits

This dissertation focuses on the application of 3D integrated circuit (IC) technology on asynchronous logic paradigms, mainly NULL Convention Logic (NCL) and Multi-Threshold NCL (MTNCL). It presents the Async3D tool flow and library for NCL and MTNCL 3D ICs. It also analyzes NCL and MTNCL circuits in 3D IC. Several FIR filter designs were implement in NCL, MTNCL, and synchronous architecture to compare synchronous and asynchronous circuits in 2D and 3D ICs. The designs were normalized based on performance and several metrics were measured for comparison. Area, interconnect length, power consumption, and power density were compared among NCL, MTNCL, and synchronous designs. The NCL and MTNCL designs showed improvements in all metrics when moving from 2D to 3D. The 3D NCL and MTNCL designs also showed a balanced power distribution in post-layout analysis. This could alleviate the hotspot problem prevalently found in most 3D ICs. NCL and MTNCL have the potential to synergize well with 3D IC technology

Asynchronous Data Processing Platforms for Energy Efficiency, Performance, and Scalability

The global technology revolution is changing the integrated circuit industry from the one driven by performance to the one driven by energy, scalability and more-balanced design goals. Without clock-related issues, asynchronous circuits enable further design tradeoffs and in operation adaptive adjustments for energy efficiency. This dissertation work presents the design methodology of the asynchronous circuit using NULL Convention Logic (NCL) and multi-threshold CMOS techniques for energy efficiency and throughput optimization in digital signal processing circuits. Parallel homogeneous and heterogeneous platforms implementing adaptive dynamic voltage scaling (DVS) based on the observation of system fullness and workload prediction are developed for balanced control of the performance and energy efficiency. Datapath control logic with NULL Cycle Reduction (NCR) and arbitration network are incorporated in the heterogeneous platform for large scale cascading. The platforms have been integrated with the data processing units using the IBM 130 nm 8RF process and fabricated using the MITLL 90 nm FDSOI process. Simulation and physical testing results show the energy efficiency advantage of asynchronous designs and the effective of the adaptive DVS mechanism in balancing the energy and performance in both platforms

Energy Aware Design and Analysis for Synchronous and Asynchronous Circuits

Power dissipation has become a major concern for IC designers. Various low power design techniques have been developed for synchronous circuits. Asynchronous circuits, however. have gained more interests recently due to their benefits in lower noise, easy timing control, etc. But few publications on energy reduction techniques for asynchronous logic are available. Power awareness indicates the ability of the system power to scale with changing conditions and quality requirements. Scalability is an important figure-of-merit since it allows the end user to implement operational policy. just like the user of mobile multimedia equipment needs to select between better quality and longer battery operation time. This dissertation discusses power/energy optimization and performs analysis on both synchronous and asynchronous logic. The major contributions of this dissertation include: 1 ) A 2-Dimensional Pipeline Gating technique for synchronous pipelined circuits to improve their power awareness has been proposed. This technique gates the corresponding clock lines connected to registers in both vertical direction (the data flow direction) and horizontal direction (registers within each pipeline stage) based on current input precision. 2) Two energy reduction techniques, Signal Bypassing & Insertion and Zero Insertion. have been developed for NCL circuits. Both techniques use Nulls to replace redundant Data 0\u27s based on current input precision in order to reduce the switching activity while Signal Bypassing & Insertion is for non-pipelined NCI, circuits and Zero Insertion is for pipelined counterparts. A dynamic active-bit detection scheme is also developed as an expansion. 3) Two energy estimation techniques, Equivalent Inverter Modeling based on Input Mapping in transistor-level and Switching Activity Modeling in gate-level, have been proposed. The former one is for CMOS gates with feedbacks and the latter one is for NCL circuits

Minimization Of Power Dissipation In Digital Circuits Using Pipelining And A Study Of Clock Gating Technique

Power dissipation is one of the major design issues of digital circuits. The power dissipated by a circuit affects its speed and performance. Multiplier is one of the most commonly used circuits in the digital devices. There are various types of multipliers available depending upon the application in which they are used. In the present thesis report, the importance of power dissipation in today\u27s digital technology is discussed and the various types and sources of power dissipation have been elaborated. Different types of multipliers have been designed which vary in their structure and amount of power dissipation. The concept of pipelining is explained and the reduction in the power dissipation of the multipliers after pipelining is experimentally determined. Clock gating is a very important technique used in the design of digital circuits to reduce power dissipation. Various types of clock gating techniques have been presented as a case study. The technology used in the simulation of these circuits is 0.35µm CMOS and the simulator used is SPECTRE S

Technology Mapping, Design for Testability, and Circuit Optimizations for NULL Convention Logic Based Architectures

Delay-insensitive asynchronous circuits have been the target of a renewed research effort because of the advantages they offer over traditional synchronous circuits. Minimal timing analysis, inherent robustness against power-supply, temperature, and process variations, reduced energy consumption, less noise and EMI emission, and easy design reuse are some of the benefits of these circuits. NULL Convention Logic (NCL) is one of the mainstream asynchronous logic design paradigms that has been shown to be a promising method for designing delay-insensitive asynchronous circuits. This dissertation investigates new areas in NCL design and test and is made of three sections. The first section discusses different CMOS implementations of NCL gates and proposes new circuit techniques to enhance their operation. The second section focuses on mapping multi-rail logic expressions to a standard NCL gate library, which is a form of technology mapping for a category of NCL design automation flows. Finally, the last section proposes design for testability techniques for a recently developed low-power variant of NCL called Sleep Convention Logic (SCL)

Ultra-Low Leakage, Energy-Efficient Digital Integrated Circuit and System Design

The advances of the complementary metal-oxide-semiconductor (CMOS) technology manufacturing and design over the years have enabled a diverse range of applications across the power consumption, performance, and area (PPA) spectra. Many of the recent and prospective applications rely on the availability of energy-autonomous, miniaturized systems, i.e., ultra-low power (ULP) VLSI systems, which are generally characterized by extreme resource limitations. Some examples of applications are wireless sensing platforms, body-area sensor networks (BASN), biomedical and implantable devices, wearables, hearables, and monitors. Within the context of such applications, the key requirements are long lifetime and miniaturized size (sub-/millimeter-scale). In order to enable both requirements, energy-efficiency is the key metric. It allows for extended battery lifetime and operation with the energy that can be harvested from the environment, and it limits the size (volume) of the energy sources utilized to power these systems. Ultra-low voltage (ULV) operation is a key technique in which the VDD of circuits is reduced from nominal to near or below the threshold voltage of the transistor. It is a powerful knob that has been largely exploited by designers in order to achieve ultra-low power consumption and high energy-efficiency in CMOS. Existing ULP VLSI systems typically operate at a lower supply voltage thereby reducing their energy consumption by one to two orders of magnitude in order to enable the aforementioned applications. While supply voltage scaling is a promising measure for achieving low power and reducing energy consumption, it brings up several challenges. One critical issue is the leakage energy dissipated by the devices, which is magnified in portion to the total energy consumption at ULV. The reason is that, as VDD scales from nominal to near-threshold and sub-threshold, transistors become increasingly slower and they accumulate more leakage (i.e., static) power over longer cycle times. This energy waste accounts for a significant portion of the system's total energy consumption, offsets the gains provided by voltage scaling, defines the minimum energy per operation, and poses a practical limit for the system's energy-efficiency. This thesis presents selected research works on ultra-low leakage, energy-efficient digital integrated circuit design. More specifically, it describes novel and key techniques for minimizing the energy waste of idle/underutilized and always-on hardware. The main goal of such techniques is to push the envelope of energy-efficiency in energy-autonomous, miniaturized VLSI systems. Such techniques are applied to key building blocks of emerging mobile and embedded computing devices resulting in state-of-the-art energy-efficiencies