Power Efficient Data-Aware SRAM Cell for SRAM-Based FPGA Architecture

The design of low-power SRAM cell becomes a necessity in today\u27s FPGAs, because SRAM is a critical component in FPGA design and consumes a large fraction of the total power. The present chapter provides an overview of various factors responsible for power consumption in FPGA and discusses the design techniques of low-power SRAM-based FPGA at system level, device level, and architecture levels. Finally, the chapter proposes a data-aware dynamic SRAM cell to control the power consumption in the cell. Stack effect has been adopted in the design to reduce the leakage current. The various peripheral circuits like address decoder circuit, write/read enable circuits, and sense amplifier have been modified to implement a power-efficient SRAM-based FPGA

Ultra low-power fault-tolerant SRAM design in 90nm CMOS technology

With the increment of mobile, biomedical and space applications, digital systems with low-power consumption are required. As a main part in digital systems, low-power memories are especially desired. Reducing the power supply voltages to sub-threshold region is one of the effective approaches for ultra low-power applications. However, the reduced Static Noise Margin (SNM) of Static Random Access Memory (SRAM) imposes great challenges to the subthreshold SRAM design. The conventional 6-transistor SRAM cell does not function properly at sub-threshold supply voltage range because it has no enough noise margin for reliable operation. In order to achieve ultra low-power at sub-threshold operation, previous research work has demonstrated that the read and write decoupled scheme is a good solution to the reduced SNM problem. A Dual Interlocked Storage Cell (DICE) based SRAM cell was proposed to eliminate the drawback of conventional DICE cell during read operation. This cell can mitigate the singleevent effects, improve the stability and also maintain the low-power characteristic of subthreshold SRAM, In order to make the proposed SRAM cell work under different power supply voltages from 0.3 V to 0.6 V, an improved replica sense scheme was applied to produce a reference control signal, with which the optimal read time could be achieved. In this thesis, a 2K ~8 bits SRAM test chip was designed, simulated and fabricated in 90nm CMOS technology provided by ST Microelectronics. Simulation results suggest that the operating frequency at VDD = 0.3 V is up to 4.7 MHz with power dissipation 6.0 ƒÊW, while it is 45.5 MHz at VDD = 0.6 V dissipating 140 ƒÊW. However, the area occupied by a single cell is larger than that by conventional SRAM due to additional transistors used. The main contribution of this thesis project is that we proposed a new design that could simultaneously solve the ultra low-power and radiation-tolerance problem in large capacity memory design

The impact of random doping effects on CMOS SRAM cell

The SRAM has a very constrained cell area and is consequently sensitive to the intrinsic parameter fluctuations ubiquitous in decananometer scale MOSFETs. Using a statistical circuit simulation methodology, which can fully collate intrinsic parameter fluctuation information into compact model sets, the impact of random device doping on 6-T SRAM static noise margins, and read and write characteristics are investigated in detail for well-scaled 35 nm physical gate length devices. We conclude that intrinsic parameter fluctuations will become a major limitation to further conventional MOSFET SRAM scaling

A fully integrated SRAM-based CMOS arbitrary waveform generator for analog signal processing

This dissertation focuses on design and implementation of a fully-integrated SRAM-based arbitrary waveform generator for analog signal processing applications in a CMOS technology. The dissertation consists of two parts: Firstly, a fully-integrated arbitrary waveform generator for a multi-resolution spectrum sensing of a cognitive radio applications, and an analog matched-filter for a radar application and secondly, low-power techniques for an arbitrary waveform generator. The fully-integrated low-power AWG is implemented and measured in a 0.18-¥ìm CMOS technology. Theoretical analysis is performed, and the perspective implementation issues are mentioned comparing the measurement results. Moreover, the low-power techniques of SRAM are addressed for the analog signal processing: Self-deactivated data-transition bit scheme, diode-connected low-swing signaling scheme with a short-current reduction buffer, and charge-recycling with a push-pull level converter for power reduction of asynchronous design. Especially, the robust latch-type sense amplifier using an adaptive-latch resistance and fully-gated ground 10T-SRAM bitcell in a 45-nm SOI technology would be used as a technique to overcome the challenges in the upcoming deep-submicron technologies.Ph.D.Committee Chair: Kim, Jongman; Committee Member: Kang, Sung Ha; Committee Member: Lee, Chang-Ho; Committee Member: Mukhopadhyay, Saibal; Committee Member: Tentzeris, Emmanouil

A Process Variation Tolerant Self-Compensation Sense Amplifier Design

As we move under the aegis of the Moore\u27s law, we have to deal with its darker side with problems like leakage and short channel effects. Once we go beyond 45nm regime process variations also have emerged as a significant design concern.Embedded memories uses sense amplifier for fast sensing and typically, sense amplifiers uses pair of matched transistors in a positive feedback environment. A small difference in voltage level of applied input signals to these matched transistors is amplified and the resulting logic signals are latched. Intra die variation causes mismatch between the sense transistors that should ideally be identical structures. Yield loss due to device and process variations has never been so critical to cause failure in circuits. Due to growth in size of embedded SRAMs as well as usage of sense amplifier based signaling techniques, process variations in sense amplifiers leads to significant loss of yield for that we need to come up with process variation tolerant circuit styles and new devices. In this work impact of transistor mismatch due to process variations on sense amplifier is evaluated and this problem is stated. For the solution of the problem a novel self compensation scheme on sense amplifiers is presented on different technology nodes up to 32nm on conventional bulk MOSFET technology. Our results show that the self compensation technique in the conventional bulk MOSFET latch type sense amplifier not just gives improvement in the yield but also leads to improvement in performance for latch type sense amplifiers. Lithography related CD variations, fluctuations in dopant density, oxide thickness and parametric variations of devices are identified as a major challenge to the classical bulk type MOSFET. With the emerging nanoscale devices, SIA roadmap identifies FinFETs as a candidate for post-planar end-of-roadmap CMOS device. With current technology scaling issues and with conventional bulk type MOSFET on 32nm node our technique can easily be applied to Double Gate devices. In this work, we also develop the model of Double Gate MOSFET through 3D Device Simulator Damocles and TCAD simulator. We propose a FinFET based process variation tolerant sense amplifier design that exploits the back gate of FinFET devices for dynamic compensation against process variations. Results from statistical simulation show that the proposed dynamic compensation is highly effective in restoring yield at a level comparable to that of sense amplifiers without process variations. We created the 32nm double gate models generated from Damocles 3-D device simulations [25] and Taurus Device Simulator available commercially from Synopsys [47] and use them in the nominal latch type sense amplifier design and on the Independent Gate Self Compensation Sense Amplifier Design (IGSSA) to compare the yield and performance benefits of sense amplifier design on FinFET technology over the conventional bulk type CMOS based sense amplifier on 32nm technology node effective in restoring yield at a level comparable to that of sense amplifiers without process variations. We created the 32nm double gate models generated from Damocles 3-D device simulations [25] and Taurus Device Simulator available commercially from Synopsys [47] and use them in the nominal latch type sense amplifier design and on the Independent Gate Self Compensation Sense Amplifier Design (IGSSA) to compare the yield and performance benefits of sense amplifier design on FinFET technology over the conventional bulk type CMOS based sense amplifier on 32nm technology node

Robust low-power digital circuit design in nano-CMOS technologies

Device scaling has resulted in large scale integrated, high performance, low-power, and low cost systems. However the move towards sub-100 nm technology nodes has increased variability in device characteristics due to large process variations. Variability has severe implications on digital circuit design by causing timing uncertainties in combinational circuits, degrading yield and reliability of memory elements, and increasing power density due to slow scaling of supply voltage. Conventional design methods add large pessimistic safety margins to mitigate increased variability, however, they incur large power and performance loss as the combination of worst cases occurs very rarely. In-situ monitoring of timing failures provides an opportunity to dynamically tune safety margins in proportion to on-chip variability that can significantly minimize power and performance losses. We demonstrated by simulations two delay sensor designs to detect timing failures in advance that can be coupled with different compensation techniques such as voltage scaling, body biasing, or frequency scaling to avoid actual timing failures. Our simulation results using 45 nm and 32 nm technology BSIM4 models indicate significant reduction in total power consumption under temperature and statistical variations. Future work involves using dual sensing to avoid useless voltage scaling that incurs a speed loss. SRAM cache is the first victim of increased process variations that requires handcrafted design to meet area, power, and performance requirements. We have proposed novel 6 transistors (6T), 7 transistors (7T), and 8 transistors (8T)-SRAM cells that enable variability tolerant and low-power SRAM cache designs. Increased sense-amplifier offset voltage due to device mismatch arising from high variability increases delay and power consumption of SRAM design. We have proposed two novel design techniques to reduce offset voltage dependent delays providing a high speed low-power SRAM design. Increasing leakage currents in nano-CMOS technologies pose a major challenge to a low-power reliable design. We have investigated novel segmented supply voltage architecture to reduce leakage power of the SRAM caches since they occupy bulk of the total chip area and power. Future work involves developing leakage reduction methods for the combination logic designs including SRAM peripherals

Temperature Variation Operation of Mixed-VT 3T GC-eDRAM for Low Power Applications in 2Kbit Memory Array

Embedded memories were once utilized to transfer information between the CPU and the main memory. The cache storage in most traditional computers was static-random-access-memory (SRAM). Other memory technologies, such as embedded dynamic random-access memory (eDRAM) and spin-transfer-torque random-access memory (STT-RAM), have also been used to store cache data. The SRAM, on the other hand, has a low density and severe leakage issues, and the STT-RAM has high latency and energy consumption when writing. The gain-cell eDRAM (GC-eDRAM), which has a higher density, lower leakage, logic compatibility, and is appropriate for two-port operations, is an attractive option. To speed up data retrieval from the main memory, future processors will require larger and faster-embedded memories. Area overhead, power overhead, and speed performance are all issues with the existing architecture. A unique mixed-V_T 3T GC-eDRAM architecture is suggested in this paper to improve data retention times (DRT) and performance for better energy efficiency in embedded memories. The GC-eDRAM is simulated using a standard complementary-metal-oxide-semiconductor (CMOS) with a 130nm technology node transistor. The performance of a 2kbit mixed-V_T 3T GC-eDRAM array were evaluated through corner process simulations. Each memory block is designed and simulated using Mentor Graphics Software. The array, which is based on the suggested bit-cell, has been successfully operated at 400Mhz under a 1V supply and takes up almost 60-75% less space than 6T SRAM using the same technology. When compared to the existing 6T and 4T ULP SRAMs (others' work), the retention power of the proposed GC-eDRAM is around 80-90% lower

Design of Low-Voltage Digital Building Blocks and ADCs for Energy-Efficient Systems

Increasing number of energy-limited applications continue to drive the demand for designing systems with high energy efficiency. This tutorial covers the main building blocks of a system implementation including digital logic, embedded memories, and analog-to-digital converters and describes the challenges and solutions to designing these blocks for low-voltage operation

Memristor MOS Content Addressable Memory (MCAM): Hybrid Architecture for Future High Performance Search Engines

Large-capacity Content Addressable Memory (CAM) is a key element in a wide variety of applications. The inevitable complexities of scaling MOS transistors introduce a major challenge in the realization of such systems. Convergence of disparate technologies, which are compatible with CMOS processing, may allow extension of Moore's Law for a few more years. This paper provides a new approach towards the design and modeling of Memristor (Memory resistor) based Content Addressable Memory (MCAM) using a combination of memristor MOS devices to form the core of a memory/compare logic cell that forms the building block of the CAM architecture. The non-volatile characteristic and the nanoscale geometry together with compatibility of the memristor with CMOS processing technology increases the packing density, provides for new approaches towards power management through disabling CAM blocks without loss of stored data, reduces power dissipation, and has scope for speed improvement as the technology matures.Comment: 10 pages, 11 figure