A circuit design of intelligent cache DRAM with automaticwrite-back capability

An intelligent cache based on a distributed architecture that consists of a hierarchy of three memory sections-DRAM (dynamic RAM), SRAM (static RAM), and CAM (content addressable memory) as an on-chip tag-is reported. The test device of the memory core is fabricated in a 0.6 μm double-metal CMOS standard DRAM process, and the CAM matrix and control logic are embedded in the array. The array architecture can be applied to 16-Mb DRAM with less than 12% of the chip overhead. In addition to the tag, the array embedded CAM matrix supports a write-back function that provides a short read/write cycle time. The cache DRAM also has pin compatibility with address nonmultiplexed memories. By achieving a reasonable hit ratio (90%), this cache DRAM provides a high-performance intelligent main memory with a 12 ns(hit)/34 ns(average) cycle time and 55 mA (at 25 MHz) operating current     

A 1 MB Cache Subsystem Prototype With 1.8 ns Embedded DRAMs in 45 nm SOI CMOS

We describe a single voltage supply, 1 MB cache subsystem prototype that integrates 2 GHz embedded DRAM (eDRAM) macros with on-chip word-line voltage supply generation , a 4 Kb one-time-programmable read-only memory ( OTPROM ) for redundancy and repair control, on-chip OTPROM programming voltage generation, clock generation and distribution, array built-in self-test circuitry (ABIST), user logic and pervasive logic. The eDRAM employs a programmable pipeline, achieving 1.8 ns latency, and features concurrent refresh capability.      

A read disturbance free differential read SRAM cell for low power and reliable cache in embedded processor

Energy consumption and data stability are vital requirement of cache in embedded processor. SRAM is a natural choice for cache memory owing to their speed and energy efficiency. Noise insertion to the SRAM cell during read is a serious problem which reduces its stability. A read disturbance free differential SRAM cell consisting of seven transistors is proposed here which increases cell stability along with maintaining the most desirable differential read technique for faster read. The read SNM of the proposed cell is 154%, 31% and 58% large than that of the conventional 6T-SRAM cell and 2 other 7T-SRAM cells [5,6] compared here. Various factors such as short circuit current reduction, use of single write access transistor, partial bit line swing etc. reduces the overall energy consumption of the proposed cell by 41% compared to 6T-SRAM cell. The proposed cell is also compared with an eight transistor based read disturbance free SRAM cell. The cell delay of the proposed cell is around 55% lesser than that of the 8T-SRAM cell. Besides CMOS the performance achievement of the proposed 7T-SRAM cell is also validated at miniaturized dimension of 20 nm using FinFET based predictive technology model library.     

An experimental 1-Mbit cache DRAM with ECC

A cache DRAM which consists of a dynamic RAM (DRAM) as main memory and a static RAM (SRAM) as cache memory is proposed. An error checking and correcting (ECC) scheme utilizing the wide internal data bus is also proposed. It is constructed to be suitable for a four-way set associated cache scheme with more than a 90% hit rate estimated to be obtained. An experimental cache DRAM with 1-Mb DRAM and 8-kb SRAM has been fabricated using a 1.2-μm, triple-polysilicon, single-metal CMOS process. A SRAM access time of 12 ns and a DRAM access time of 80 ns, including an ECC time of 12 ns, have been obtained. Accordingly, an average access time of 20 ns is expected under the condition that the hit rate is 90%. The cache DRAM has a high-speed data mapping capability and high reliability suitable for low-end workstations and personal computers     

A 100-MHz 4-Mb cache DRAM with fast copy-back scheme

A 4-Mb cache dynamic random access memory (CDRAM), which integrates 16-kb SRAM as a cache memory and 4-Mb DRAM into a monolithic circuit, is described. This CDRAM has a 100-MHz operating cache, newly proposed fast copy-back (FCB) scheme that realizes a three times faster miss access time over with the conventional copy-back method, and maximized mapping flexibility. The process technology is a quad-polysilicon double-metal 0.7-μm CMOS process, which is the same as used in a conventional 4-Mb DRAM. The chip size of 82.9 mm² is only a 7% increase over the conventional 4-Mb DRAM. The simulated system performance indicated better performance than a conventional cache system with eight times the cache capacity     

Reducing leakage in a high-performance deep-submicron instructioncache

Deep-submicron CMOS designs maintain high transistor switching speeds by scaling down the supply voltage and proportionately reducing the transistor threshold voltage. Lowering the threshold voltage increases leakage energy dissipation due to subthreshold leakage current even when the transistor is not switching. Estimates suggest a five-fold increase in leakage energy in every future generation. In modern microarchitectures, much of the leakage energy is dissipated in large on-chip cache memory structures with high transistor densities. While cache utilization varies both within and across applications, modern cache designs are fixed in size resulting in transistor leakage inefficiencies. This paper explores an integrated architectural and circuit-level approach to reducing leakage energy in instruction caches (i-caches). At the architecture level, we propose the Dynamically ResIzable i-cache (DRI i cache), a novel i-cache design that dynamically resizes and adapts to an application's required size. At the circuit-level, we use gated-V_dd, a novel mechanism that effectively turns off the supply voltage to, and eliminates leakage in, the SRAM cells in a DRI i-cache's unused sections. Architectural and circuit-level simulation results indicate that a DRI i-cache successfully and robustly exploits the cache size variability both within and across applications. Compared to a conventional i-cache using an aggressively-scaled threshold voltage a 64 K DRI i-cache reduces on average both the leakage energy-delay product and cache size by 62%, with less than 4% impact on execution time. Our results also indicate that a wide NMOS dual-V_t gated-V_dd transistor with a charge pump offers the best gating implementation and virtually eliminates leakage energy with minimal increase in an SRAM cell read time area as compared to an i-cache with an aggressively-scaled threshold voltage     

On-chip test circuitry for a 2-ns cycle, 512-kb CMOS ECL SRAM

On-chip test circuitry that provides 8-b-deep emitter-coupled logic (ECL) level patterns to 12 input pads of a 512-kb CMOS ECL static RAM (SRAM) at cycle times as fast as 1.4 ns has been built in a 0.8- mu m CMOS technology with L/sub eff/=0.5 mu m. A unique approach for synchronizing the input signals to the chip-select signal in order to provide an optimum setup time and data-valid windows as the operating frequency changes is described. Measured results and extensive simulation demonstrate the stability of the on-chip test circuitry for cycle times of 1.4-50 ns. The on-chip test circuitry makes it possible to test the SRAM chip at its pipelined cycle time. In addition, the speed of the on-chip test circuitry will track future technology improvements, making it possible to generate test patterns as SRAM performance continues to improve.<>     

A third-generation SPARC V9 64-b microprocessor

This quad-issue processor achieves 1-GHz operation through improved dynamic circuit techniques in critical paths and a more extensive on-chip memory system which scales in both bandwidth and latency. Critical logic paths use domino, delayed clocked domino, and logic embedded in dynamic flip-flops for minimum delay. A 64-KB sum-addressed memory data cache combines the address offset add with the cache decode, allowing the average memory latency to scale by more than the clock ratio. Memory bandwidth is improved by using wave pipelined SRAM designs for on-chip caches and a write cache for store traffic. Memory power is controlled without increased latency by use of delayed-reset logic decoders. The chip operates at 1000 MHz and dissipates less than 80 W from a 1.6-V supply. It contains 23 million transistors (12 million in RAM cells) on a 244 mm² die     

静态随机存储器低泄漏设计技术

随着CMOS工艺发展,高性能SoC的泄漏功耗占整体能耗的比例越来越大,内嵌存储器的泄漏是整体泄漏的主要来源,有两方面原因:(1)芯片内嵌的静态随机存储器SRAM容量越来越大;(2)每次访存操作时SRAM仅小部分阵列工作,大部分存储阵列处于非工作状态.总结SRAM低泄漏的电路设计技术,并总结工艺发展对于低泄漏设计技术的挑...     

A 90-MHz 16-Mb system integrated memory with direct interface toCPU

This paper describes a system integrated memory with direct interface to CPU which integrates an SRAM, a DRAM, and control circuitry, including a tag memory (TAG). This memory realizes a computer system without glue chips, and thus enables a computer system which is low cost, low power, and compact size, but still with sufficient performance. Also fast clock cycle time and access time is realized using a newly proposed clock driver and internal signal generator. This memory is fabricated with a quad-polysilicon double-metal 0.55-μm CMOS process which is the same as used in a conventional 16-Mb DRAM. The chip size of 145.3 mm² is only a 12% increase over the conventional 16-Mb DRAM. The maximum operating frequency is 90-MHz and the operating current at cache-bit is 156-mA. This memory is suitable for various types of computer systems such as personal digital assistants (PDA's), personal computer systems, and embedded controller applications     

Code and Data Placement for Embedded Processors with Scratchpad and Cache Memories

This paper proposes a code placement problem, its ILP formulation, and a heuristic algorithm for reducing the total energy consumption of embedded processor systems including a CPU core, on-chip and off-chip memories. Our approach exploits a non-cacheable memory region for an effective use of a cache memory and as a result, reduces the number of off-chip accesses. Our algorithm simultaneously finds a code layout for a cacheable region, a scratchpad region, and the other non-cacheable region of the address space so as to minimize the total energy consumption of the processor system. Experiments using a commercial embedded processor and an off-chip SDRAM demonstrate that our algorithm reduces the energy consumption of the processor system by 23% without any performance degradation compared to the best result achieved by the conventional approach.     

A 7.1-GB/s low-power rendering engine in 2-D array-embedded memorylogic CMOS for portable multimedia system

A single-chip rendering engine that consists of a DRAM frame buffer, a SRAM serial access memory, pixel/edge processor array and 32-b RISC core is proposed for low-power three-dimensional (3-D) graphics in portable systems. The main features are two-dimensional (2-D) hierarchical octet tree (HOT) array structure with bandwidth amplification, three dedicated network schemes, virtual page mapping, memory-coupled logic pipeline, low-power operation, 7.1-GB/s memory bandwidth, and 11.1-Mpolygon/s drawing speed. The 56-mm² prototype die integrating one edge processor, eight pixel processors, eight frame buffers, and a RISC core are fabricated using 0.35-μm CMOS embedded memory logic (EML) technology with four poly layers and three metal layers. The fabricated test chip, 590 mW at 100 MHz 3.3 V operation, is demonstrated with a host PC through a PCI bridge     

High-speed/high-bandwidth design methodologies for on-chip DRAMcore multimedia system LSI's

Recently, as multimedia large scale integrated devices (LSIs) have developed, there has been strongly increased demand for high-speed/high-bandwidth LSIs which integrate the DRAM core and logic elements (CPU etc.). However, the high-speed/high-bandwidth operation induces the large switching noise. This noise degrades the DRAM's operating margin, and especially its data retention characteristics. In this paper, we analyze the noise transmission model and propose DRAM and logic compatible design methodologies to maintain the reliability of high-speed/high-bandwidth system LSIs. We also show that good experimental results are obtained on the test device. Furthermore, we propose the most suitable V_DD/GND line scheme for on-chip DRAM system LSI     

Hybrid crossbar architecture for a memristor based cache

This paper describes a new memristor crossbar architecture that is proposed for use in a high density cache design. This design has less than 10% of the write energy consumption than a simple memristor crossbar. Also, it has up to 3 times the bit density of an STT-MRAM system and up to 11 times the bit density of an SRAM architecture. The proposed architecture is analyzed using a detailed SPICE analysis that accounts for the resistance of the wires in the memristor structure. Additionally, the memristor model used in this work has been matched to specific device characterization data to provide accurate results in terms of energy, area, and timing. The proposed memory system was analyzed by modeling two different devices that vary in resistance range and switching time. This system does not require that the memristor devices have inherent diode effects which limit alternate current paths. Therefore this system is capable of utilizing a much broader class of devices.An architectural analysis has also been completed that shows how the memory system may perform as a cache memory. A hybrid cache structure was used to alleviate the long write latencies of memristor devices. This approach consisted of the tag array being made of SRAM cells while the data array was made of the memristor circuit proposed. This hybrid scheme allows multiple reads and writes to concurrently access different sub-arrays within a cache. The performance of these novel memristor based caches was compared to SRAM and STT-MRAM based caches through detailed simulations. The results show that the memristor caches are denser and allow better performance along with lower system power when compared to the STT-MRAM and SRAM caches.     

A reprogrammable EDGE baseband and multimedia handset SoC with 6-mbit embedded DRAM

A CMOS EDGE baseband and multimedia handset SoC features a dual core (microcontroller and DSP) architecture together with all the necessary interface logic and hardware accelerators interconnected by a multi-layer bus. The DSP memory hierarchy features an instruction cache coupled to a 6-Mbit embedded DRAM instruction memory allowing in the field software flexibility (for example dynamic upgrade of DSP software), while minimizing power and area (closely matching a ROM based solution). The chip is implemented in a 130-nm 6-metal layer CMOS process and is packaged in a 12 /spl times/ 12 ball-grid array. Full chip standby mode current is 690 /spl mu/A (with data retention), resulting in a 500 hour complete GSM/EDGE terminal autonomy.     

A 1.8-ns access, 550-MHz, 4.5-Mb CMOS SRAM

An ultrahigh-speed 4.5-Mb CMOS SRAM with 1.8-ns clock-access time, 1.8-ns cycle time, and 9.84-μm² memory cells has been developed using 0.25-μm CMOS technology. Three key circuit techniques for achieving this high speed are a decoder using source-coupled-logic (SCL) circuits combined with reset circuits, a sense amplifier with nMOS source followers, and a sense-amplifier activation-pulse generator that uses a duplicate memory-cell array. The proposed decoder can reduce the delay time between the address input and the word-line signal of the 4.5-Mb SRAM to 68% of that of an SRAM with conventional circuits. The sense amplifier with nMOS source followers can reduce not only the delay time of the sense amplifier but also the power dissipation. In the SRAM, the sense-amplifier activation pulse must be input into the sense amplifier after the signal from the memory cell is input into the sense amplifier. A large timing margin required between these signals results in a large access time in the conventional SRAM. The sense-amplifier activation pulse generator that uses a duplicate memory-cell array can reduce the required timing margin to less than half of the conventional margin. These three techniques are especially useful for realizing ultrahigh-speed SRAM's, which will be used as on-chip or off-chip cache memories in processor systems     

A soft-error-immune 0.9-ns 1.15-Mb ECL-CMOS SRAM with 30-ps 120 klogic gates and on-chip test circuitry

A soft-error-immune, 0.9-ns address access time, 2.0-ns read/write cycle time, 1.15-Mb emitter coupled logic (ECL)-CMOS SRAM with 30-ps 120 k ECL and CMOS logic gates has been developed using 0.3-μm BiCMOS technology. Four key developments ensuring good testability, reliability, and stability are on-chip test circuitry for precise measurement of access time and for multibit parallel testing, a memory-cell test technique for an ECL-CMOS SRAM, a highly stable current source with a simple design using a current mirror, and a soft-error-immune memory cell using a silicon-on-insulator (SOI) wafer. These techniques will be especially useful for making the ultrahigh-speed, high-density SRAM's used as cache and control storages in mainframe computers     

A 600-MHz single-chip multiprocessor with 4.8-GB/s internal shared pipelined bus and 512-kB internal memory

A 600-MHz single-chip multiprocessor, which includes two M32R 32-bit CPU cores , a 512-kB shared SRAM and an internal shared pipelined bus, was fabricated using a 0.15-/spl mu/m CMOS process for embedded systems. This multiprocessor is based on symmetric multiprocessing (SMP), and supports modified-exclusive-shared-invalid (MESI) cache coherency protocol. The multiprocessor inherits the advantages of previously reported single-chip multiprocessors, while its multiprocessor architecture is optimized for use as an embedded processor. The internal shared pipelined bus has a low latency and large bandwidth (4.8 GB/s). These features enhance the performance of the multiprocessor. In addition, the multiprocessor employs various low-power techniques. The multiprocessor dissipates 800 mW in a 1.5-V 600-MHz multiprocessor mode. Standby power dissipation is less than 1.5 mW at 1.5 V. Hence, the multiprocessor achieves higher performance and lower power consumption. This paper presents a single-chip multiprocessor architecture optimized for use as an embedded processor and its various low-power techniques.     

一种交错并行隐式刷新增益单元eDRAM设计

设计了一种与逻辑工艺兼容的64 kb高速高密度嵌入式增益单元动态随机存储器(eDRAM)。该存储器单元通过结构和版图的优化,典型尺寸为同代SRAM的40%。高低阈值管的引入分别改善了单元的读取速度和数据保持时间。同时交错并行隐式刷新机制利用增益存储单元读、写端口独立的结构和操作特性,配以合适的时序和仲裁机制,使得在无额外通信信号和握手接口下,实现刷新与访问互不影响,数据访问率达到100%。相比其他隐式刷新技术,该技术不需要过大的外围开销即可完成访问带宽加倍。芯片用SMIC 0.13μm CMOS工艺实现,大小为1.35 mm×1.35 mm。     

Characterization of a Novel Nine-Transistor SRAM Cell

Data stability of SRAM cells has become an important issue with the scaling of CMOS technology. Memory banks are also important sources of leakage since the majority of transistors are utilized for on-chip caches in today's high performance microprocessors. A new nine-transistor (9T) SRAM cell is proposed in this paper for simultaneously reducing leakage power and enhancing data stability. The proposed 9T SRAM cell completely isolates the data from the bit lines during a read operation. The read static-noise-margin of the proposed circuit is thereby enhanced by 2 X as compared to a conventional six-transistor (6T) SRAM cell. The idle 9T SRAM cells are placed into a super cutoff sleep mode, thereby reducing the leakage power consumption by 22.9% as compared to the standard 6T SRAM cells in a 65-nm CMOS technology. The leakage power reduction and read stability enhancement provided with the new circuit technique are also verified under process parameter variations.