DESIGN AND PERFORMANCE COMPARISON OF AVERAGE 8T SRAM WITH EXISTING 8T SRAM CELLS

This paper presents 8T SRAM cell by using various techniques. The conflicting design requirement of read versus write operation in a conventional 8T SRAM bit cell is eliminated using separate read/write access transistors The read stability and the write-ability can be optimized independently by optimizing the respective access transistor size. A new average-8T write/read decoupled SRAM architecture for low-power sub/near-threshold SRAM used in power-constraint applications such as biomedical implants and autonomous sensor nodes. The proposed architecture consists of several novel concepts in dealing with issues in sub/near-threshold SRAM including the differential and data-independent-leakage read port that facilitates robust and faster read operation Simulation result of 8T SRAM design using TANNER tool shows the reduction in total average power and delay. DOI: 10.17762/ijritcc2321-8169.15029

Reconfigurable negative bit line collapsed supply write-assist for 9T-ST static random access memory cell

This paper presents a reconfigurable negative bit line collapsed supply (RNBLCS) write driver circuit for the 9T Schmitt trigger-based static random-access memory (SRAM) cell (9T-ST), significantly improving write performance for real-time memory applications. In deep sub-micron technology, increasing device parameter deviations significantly reduce SRAM cells' write-ability. The proposed RNBLCS write-assist driver for 9T-ST SRAM cell has 0.84×, 0.48×, 0.27× optimized write access delay and 1.05×, 1.08×, 1.19× improvement in write static noise margin (WSNM), 1.05×, 1.13×, and 1.39× improvement in write margin (WM), 0.96×, 0.89× and 0.72× minimum write trip-point (WTP) from transient-negative bit line (Tran-NBL), capacitive charge sharing (CCS), and conventional write circuits respectively. The proposed RNBLCS is functionally verified using a synopsys custom compiler with a 16 nm BSIM4 model card for bulk complementary metal-oxide semiconductor (CMOS)

Power Efficient SRAM Design with Integrated Bit Line Charge Pump

Bit line toggling of SRAM systems in write operations leads to the largest portion of power dissipation. To reduce this amount of power loss and achieve power efficient memory, we propose a new SRAM design that integrates charge pump circuits to harvest and reuse bit line charge. In this work, a power-efficient charge recycling SRAM is designed and implemented in 180nm CMOS technology. Post-layout simulation demonstrates an 11% of power saving and 3.8% of area overhead, if the bit width of SRAM is chosen as 8. Alternatively, 22% of power reduction is obtained if the bit width of SRAM is extended to 64. Compared with existing charge recycling SRAM schemes, this proposed SRAM is robust to process variation, demonstrates good read/write stability, and illustrates better trade-off between design complexity and power reduction

Design and statistical analysis (MONTE-CARLO) of low-power and high stable proposed SRAM cell structure

The reduction of the channel length due to scaling increases the leakage current resulting in a major contribution to the static power dissipation and for stability of the SRAM cell good noise margin is required so noise margin is the most important parameter for memory design. The higher noise margin of the cell confirms the high-speed of SRAM cell. In this work, a novel SRAM cell with eight transistors is being proposed to reduce the static hence total power dissipation. When compared to the conventional 6T SRAM and NC-SRAM cell, the proposed SRAM shows a significant reduction in the gate leakage current, static and total power dissipation while produce higher stability. In the technique employed for the proposed SRAM cell, the operating voltage is reduced in idle mode. The technique led a reduction of 31.2% in the total power dissipation, a reduction of 40.4% on static power dissipation, and The SVNM SINM WTV and WTI of proposed SRAM cell was also improved by 11.17%, 52.30%, 2.15%, 59.1% respectively as compare to 6T SRAM cell and as compare to NC-SRAM cell is 27.26%, 47.44%, 4.31%, 64.44% respectively. It can be found that the proposed cell is taking 28.6% extra area from the conventional SRAM cell whereas it is almost same with NC-SRAM cell. Cadence Virtuoso tools are used for simulation with 90- nm CMOS process technology

Dynamic stability and noise margins of SRAM arrays in nanoscaled technologies

SRAM stability is one of the primary bottlenecks of current VLSI system design, and the unequivocal supply voltage scaling limiter. Static noise margin metrics have long been the de-facto standard for measuring this stability and estimating the yield of SRAM arrays. However, in modern process technologies, under scaled supply voltages and increased process variations, these traditional metrics are no longer sufficient. Recent research has analyzed the dynamic behavior and stability of SRAM circuits, leading to dynamic stability metrics and dynamic noise margin definition. This paper provides a brief overview of the limitations of static noise margin metrics and the resulting dynamic stability and noise margin concepts that have been proposed to overcome them

Cache Power Optimization Using Multiple Voltage Supplies to Exploit Read/Write Asymmetry

Power consumption becomes more and more critical in computer systems nowadays. Most of the previous work has been focusing on general-purpose computational core, but optimization techniques for conventional CPU core has reached a limit. Our experimental results show that read operations in SRAM can be performed at a lower supply with much reduced power consumption compared to write operations. Based on this observation and the fact that cache, consisting mostly of SRAM, often occupies significant on-chip area of the CPU and consumes a huge portion of the CPU power, we propose a new method to reduce the power consumption of cache. By dynamically switching the cache voltage supply between a lower voltage for read and a higher voltage for write, our method can effectively reduce cache power without affecting the performance of the multi-level cache hierarchy in a computer system. We can realize further power savings by lowering the supply below read voltage for hold-only operations when the cache is idle. Both the power switching controller implementation and the power consumption statistics from various SPEC benchmarks will be presented to demonstrate the efficiency of our proposed methods

Multi-port Memory Design for Advanced Computer Architectures

In this thesis, we describe and evaluate novel memory designs for multi-port on-chip and off-chip use in advanced computer architectures. We focus on combining multi-porting and evaluating the performance over a range of design parameters. Multi-porting is essential for caches and shared-data systems, especially multi-core System-on-chips (SOC). It can significantly increase the memory access throughput. We evaluate FinFET voltage-mode multi-port SRAM cells using different metrics including leakage current, static noise margin and read/write performance. Simulation results show that single-ended multi-port FinFET SRAMs with isolated read ports offer improved read stability and flexibility over classical double-ended structures at the expense of write performance. By increasing the size of the access transistors, we show that the single-ended multi-port structures can achieve equivalent write performance to the classical double-ended multi-port structure for 9% area overhead. Moreover, compared with CMOS SRAM, FinFET SRAM has better stability and standby power. We also describe new methods for the design of FinFET current-mode multi-port SRAM cells. Current-mode SRAMs avoid the full-swing of the bitline, reducing dynamic power and access time. However, that comes at the cost of voltage drop, which compromises stability. The design proposed in this thesis utilizes the feature of Independent Gate (IG) mode FinFET, which can leverage threshold voltage by controlling the back gate voltage, to merge two transistors into one through high-Vt and low-Vt transistors. This design not only reduces the voltage drop, but it also reduces the area in multi-port current-mode SRAM design. For off-chip memory, we propose a novel two-port 1-read, 1-write (1R1W) phasechange memory (PCM) cell, which significantly reduces the probability of blocking at the bank levels. Different from the traditional PCM cell, the access transistors are at the top and connected to the bitline. We use Verilog-A to model the behavior of Ge2Sb2Te5 (GST: the storage component). We evaluate the performance of the two-port cell by transistor sizing and voltage pumping. Simulation results show that pMOS transistor is more practical than nMOS transistor as the access device when both area and power are considered. The estimated area overhead is 1.7�, compared to single-port PCM cell. In brief, the contribution we make in this thesis is that we propose and evaluate three different kinds of multi-port memories that are favorable for advanced computer architectures

Novel Non Precharging Single Bitline 8T Static Random Access Memory

Title from PDF of title page viewed August 25, 2017Thesis advisor: Masud H ChowdhuryVitaIncludes bibliographical references (pages 39-41)Thesis (M.S.)--School of Computing and Engineering. University of Missouri-Kansas City, 2016Novel 8T SRAM design, employs individual bit-line (BL) and word-line (WL) for each operation. The read operation uses read word-line (RWL) and read bit-line (RBL) respectively. On other hand the write operation employs write word-line (WWL) and write bit line (WBL). Due to single BL and WL the power consumption of the proposed 8T SRAM cell is significantly less.The proposed design avoids the stability and reliability issues of the conventional 6T and other existing SRAM cells. The read stability and the write ability of the proposed design are better compared to the standard 6T and other 7T, 8T and 9T SRAM designs. The proposed 8T SRAM is as good as the 10T design without the overheads. The power consumption of the proposed 8T SRAM cell is significantly lower than other SRAM cells. The proposed design is ratio-less, which makes the construction and operation of the proposed SRAM much simpler and the response time much faster. The proposed cell design and its reliability and stability have been analyzed for 45nm technology. We have also analyzed the static noise margin (SNM) and the stability of the proposed design. In this analysis, we have used three methods. First, the traditional SNM method with the butterfly curve is introduced. Second, the N-curve method is used. And finally, we used the bit-line voltage method. We have also analyzed the impact of some process and parametric variations. The write ability of the proposed design is also compared to that of the conventional 6T SRAM.Introduction -- Existing SRAM designs -- Proposed 8T SRAM -- Analysis of power and area overheads of the proposed 8T SRAM -- Stability analysis of the proposed 8T SRAM -- Analysis of process and parametric variation in the proposed 8T SRAM -- Monte Carlo analysis -- Conclusio

Static random-access memory designs based on different FinFET at lower technology node (7nm)

Title from PDF of title page viewed January 15, 2020Thesis advisor: Masud H ChowdhuryVitaIncludes bibliographical references (page 50-57)Thesis (M.S.)--School of Computing and Engineering. University of Missouri--Kansas City, 2019The Static Random-Access Memory (SRAM) has a significant performance impact on current nanoelectronics systems. To improve SRAM efficiency, it is important to utilize emerging technologies to overcome short-channel effects (SCE) of conventional CMOS. FinFET devices are promising emerging devices that can be utilized to improve the performance of SRAM designs at lower technology nodes. In this thesis, I present detail analysis of SRAM cells using different types of FinFET devices at 7nm technology. From the analysis, it can be concluded that the performance of both 6T and 8T SRAM designs are improved. 6T SRAM achieves a 44.97% improvement in the read energy compared to 8T SRAM. However, 6T SRAM write energy degraded by 3.16% compared to 8T SRAM. Read stability and write ability of SRAM cells are determined using Static Noise Margin and N- curve methods. Moreover, Monte Carlo simulations are performed on the SRAM cells to evaluate process variations. Simulations were done in HSPICE using 7nm Asymmetrical Underlap FinFET technology. The quasiplanar FinFET structure gained considerable attention because of the ease of the fabrication process [1] – [4]. Scaling of technology have degraded the performance of CMOS designs because of the short channel effects (SCEs) [5], [6]. Therefore, there has been upsurge in demand for FinFET devices for emerging market segments including artificial intelligence and cloud computing (AI) [8], [9], Internet of Things (IoT) [10] – [13] and biomedical [17] –[18] which have their own exclusive style of design. In recent years, many Underlapped FinFET devices were proposed to have better control of the SCEs in the sub-nanometer technologies [3], [4], [19] – [33]. Underlap on either side of the gate increases effective channel length as seen by the charge carriers. Consequently, the source-to-drain tunneling probability is improved. Moreover, edge direct tunneling leakage components can be reduced by controlling the electric field at the gate-drain junction . There is a limitation on the extent of underlap on drain or source sides because the ION is lower for larger underlap. Additionally, FinFET based designs have major width quantization issue. The width of a FinFET device increases only in quanta of silicon fin height (HFIN) [4]. The width quantization issue becomes critical for ratioed designs like SRAMs, where proper sizing of the transistors is essential for fault-free operation. FinFETs based on Design/Technology Co-Optimization (DTCO_F) approach can overcome these issues [38]. DTCO_F follows special design rules, which provides the specifications for the standard SRAM cells with special spacing rules and low leakages. The performances of 6T SRAM designs implemented by different FinFET devices are compared for different pull-up, pull down and pass gate transistor (PU: PD:PG) ratios to identify the best FinFET device for high speed and low power SRAM applications. Underlapped FinFETs (UF) and Design/Technology Co-Optimized FinFETs (DTCO_F) are used for the design and analysis. It is observed that with the PU: PD:PG ratios of 1:1:1 and 1:5:2 for the UF-SRAMs the read energy has degraded by 3.31% and 48.72% compared to the DTCO_F-SRAMs, respectively. However, the read energy with 2:5:2 ratio has improved by 32.71% in the UF-SRAM compared to the DTCO_F-SRAMs. The write energy with 1:1:1 configuration has improved by 642.27% in the UF-SRAM compared to the DTCO_F-SRAM. On the other hand, the write energy with 1:5:2 and 2:5:2 configurations have degraded by 86.26% and 96% in the UF-SRAMs compared to the DTCO_F-SRAMs. The stability and reliability of different SRAMs are also evaluated for 500mV supply. From the analysis, it can be concluded that Asymmetrical Underlapped FinFET is better for high-speed applications and DTCO FinFET for low power applications.Introduction -- Next generation high performance device: FinFET -- FinFET based SRAM bitcell designs -- Benchmarking of UF-SRAMs and DTCO-F-SRAMS -- Collaborative project -- Internship experience at INTEL and Marvell Semiconductor -- Conclusion and future wor

Design and Analysis of Robust Low Voltage Static Random Access Memories.

Static Random Access Memory (SRAM) is an indispensable part of most modern VLSI designs and dominates silicon area in many applications. In scaled technologies, maintaining high SRAM yield becomes more challenging since they are particularly vulnerable to process variations due to 1) the minimum sized devices used in SRAM bitcells and 2) the large array sizes. At the same time, low power design is a key focus throughout the semiconductor industry. Since low voltage operation is one of the most effective ways to reduce power consumption due to its quadratic relationship to energy savings, lowering the minimum operating voltage (Vmin) of SRAM has gained significant interest. This thesis presents four different approaches to design and analyze robust low voltage SRAM: SRAM analysis method improvement, SRAM bitcell development, SRAM peripheral optimization, and advance device selection. We first describe a novel yield estimation method for bit-interleaved voltage-scaled 8-T SRAMs. Instead of the traditional trade-off between write and read, the trade-off between write and half select disturb is analyzed. In addition, this analysis proposes a method to find an appropriate Write Word-Line (WWL) pulse width to maximize yield. Second, low leakage 10-T SRAM with speed compensation scheme is proposed. During sleep mode of a sensor application, SRAM retaining data cannot be shut down so it is important to minimize leakage in SRAM. This work adopts several leakage reduction techniques while compensating performance. Third, adaptive write architecture for low voltage 8-T SRAMs is proposed. By adaptively modulating WWL width and voltage level, it is possible to achieve low power consumption while maintaining high yield without excessive performance degradation. Finally, low power circuit design based on heterojunction tunneling transistors (HETTs) is discussed. HETTs have a steep subthreshold swing beneficial for low voltage operation. Device modeling and design of logic and SRAM are proposed.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91569/1/daeyeonk_1.pd