Memory-fast DRAMs for sharper TV

It is argued that HDTV will require even greater memory throughput than computers do, for future television features such as high-definition display and picture enhancement. Current TV memories are described, and the features of HDTV that require faster memories are examined. The constraints composed by DRAM characteristics on TV designers are considered     

Memory-fast computer memories

The search for new dynamic RAM (DRAM) technologies to reduce memory access time and so unleash computer performance is discussed. The typical memory hierarchy of internal registers, cache, main memory, and mass storage is described. DRAM technologies that aim at simplifying this hierarchy by speeding up main memory to the point where the need for a separate, external cache is moot are examined     

Voltage limiters for DRAMs with substrate-plate-electrode memorycells

To prevent substrate-plate-electrode (SPE) cell weakness due to substrate-bias voltage bounce, voltage limiters were applied to both the substrate and the sense-circuit supply source. A supply voltage V _CC bump test was introduced to evaluate their effectiveness. The voltage limiters have been implemented on an experimental 4-Mb DRAM. It was found that a wider operational margin, as compared to conventional DRAMs (without voltage limiters) having SPE cells, was achievable through the use of voltage limiters. These voltage limiters may be considered suitable for wide operational margin DRAMs with SPE cells. The substrate-bias voltage limiter, in particular, is more effective than the sense-circuit supply voltage limiter and offers a means of improving the operational margin of V_CC bump     

Twisted bit-line technique for multi-gigabit DRAMs

A new twisted bit-line (TBL) technique is presented to reduce bit-line coupling noise for multi-gigabit DRAMs. Sufficient noise reduction effects have been monitored through soft-error rate measurement on test chips using the proposed TBL technique. Also, the problem of excessive chip area penalty in the conventional TBL techniques can be solved in the proposed TBL technique     

BiCMOS circuit technology for high-speed DRAMs

A BiCMOS circuit technology featured by a novel bit-line sense amplifier has been developed. The bit-line sense amplifier is composed of a BiCMOS differential amplifier, the impedance-converting means featured by the CMOS current mirror circuit or the clocked CMOS inverter between the bit line and the base node of the BiCMOS differential amplifier, and a conventional CMOS flip-flop. This technology can reduce the access time to half that of a conventional CMOS DRAM access time. Applied to a 1-kb DRAM test chip, a new BiCMOS circuit technology was successfully verified. Furthermore, the sensitivity and area penalty of the new BiCMOS bit-line sense amplifier and future applications to megabit DRAMs are discussed     

High-speed sensing scheme for CMOS DRAMs

A significant improvement in sensing speed over the half-V_DD bit-line precharge sensing scheme is obtained by precharging the bit line to approximately 2/3 V_DD. The 2/3-V_DD sensing scheme also results in higher-bit-line capacitance, asymmetrical bit-line swing, and higher power consumption. However, the speed advantage of 2/3-V_DD sensing may outweigh the disadvantages and can significantly improve DRAM performance. For the unboosted word-line case, symmetrical bit-line swing can be retained by limiting the bit-line downward voltage swing through a clamping circuit added to the sense amplifier, resulting in almost no loss of stored charge in a cell. The authors show that the 2/3-V_DD sensing with a limited bit-line swing has several distinct advantages over the half-V_DD sensing scheme and is particularly suitable for high-performance high density CMOS DRAMs     

Decoded-source sense amplifier for high-density DRAMs

The decoded-source sense amplifier (DSSA) for high-speed, high-density DRAMs is discussed. To prevent clamping of the common-source node of the sense amplifier caused by bit-line discharge current, the DSSA has an additional latching transistor with a gate controlled by a column decoder. The DSSA has been successfully installed in a 4-Mb DRAM and provided a RAS access time of 60 ns under a V_cc of 4 V at 85°C     

Twisted bit-line architectures for multi-megabit DRAMs

As the memory cell array of DRAM has been scaled down, inter-bit-line coupling noise has emerged as a serious problem. The signal loss due to this noise is estimated at about 40% of the signal amplitude in a polycide-bit-line 16-Mb DRAM with a technologically attainable scaling scheme. Twisted bit-line architectures to reduce or eliminate the noise are proposed and demonstrated by the soft-error rate improvement of a 1-Mb DRAM. The effective critical charge is improved by 35%, which is attributed not only to the improvement of the signal amplitude but also to the elimination of large coupling noise during the sensing operation. The impact of these twisted bit-line architectures from a scaling viewpoint is also examined, and they are shown to be promising candidates for overcoming the scaling problems of DRAMs     

New nibbled-page architecture for high-density DRAMs

A nibbled-page architecture which can be used to access all column addresses on the selected row address randomly in units of 8 bits at the 100 Mbit/s data rate is discussed. To realize such high-speed architecture, three key circuit techniques have been developed. An on-chip interleaved circuit has been used for the high-speed serial READ and WRITE operations. Column address prefetch and WE signal prefetch techniques have been introduced to eliminate idle time between 8 bit units. The nibbled-page architecture has been successfully implemented in an experimental 16 Mb DRAM, and 100 Mb/s operation has been achieved. The DRAM with nibbled-page mode is very effective in simplifying the design of high-speed data transfer systems     

Low-voltage, high-speed circuit designs for gigabit DRAMs

This paper describes several new circuit design techniques for low V_CC regions: 1) a charge-amplifying boosted sensing (CABS) scheme which amplifies the sensing voltage difference (ΔV_BL ) as well as the V_GS margin by boosting the sensing node voltage with a voltage dependent boosting capacitor and 2) an I/O current sense amplifier with a high gain using a cross-coupled current mirror control scheme and reduced temperature sensitivity using a simple temperature-compensation scheme. An experimental 16 Mb DRAM chip with the 0.18-μm twin-well, triple-metal CMOS process has been fabricated, and an access time from the row address strobe (t_RAC) of 28 ns at V_cc=1.5 V and T=25°C has been obtained     

Optimized sensing scheme of DRAMs

The half-V_cc sensing scheme of CMOS dynamic RAMs (DRAMs) has been analyzed. It has been found that fluctuations of the cell-plate bias must be taken into account since they can degrade the sense signal. An improvement is possible by connecting the bit lines to the cell plate and its half-V_cc generator during precharge. Optimum performance of the sense amplifier is achieved if the PMOS and NMOS latches are activated simultaneously. The advantages are: (1) the sensitivity is improved due to the elimination of the offset contribution caused by unmatched capacitive loads; (2) the sensing speed is enhanced due to faster sense signal amplification; and (3) the peak current is reduced since the NMOS latch does not lower the voltage level of both bit line and reference bit line     

Two-phase back-bias generator for low-voltage gigabit DRAMs

A two-phase back-bias (V_BB) generator is proposed for use in gigabit DRAMs using triple-well CMOS technology. The lower limit of V_CC for the proposed V_BB generator is a single V_T (threshold voltage), whereas that for the conventional generator is 2-V_p     

A flexible redundancy technique for high-density DRAMs

The limitations of conventional redundancy techniques are pointed out and a novel redundancy technique is proposed for high-density DRAMs using multidivided data-line structures. The proposed technique features a flexible relationship between spare lines and spare decoders, as well as lower probability of unsuccessful repair. With this technique the yield improvement factor of 64-Mb DRAMs and beyond is estimated to be more than twice that with the conventional technique in the early stages of production     

Two-phase boosted voltage generator for low-voltage DRAMs

A two-phase boosted voltage (V/sub PP/) generator circuit was proposed for use in gigabit DRAMs. It reduced the maximum gate-oxide voltage of pass transistor and the lower limit of supply voltage to V/sub PP/ and V/sub TN/, respectively, while those for the conventional charge-pump circuit are V/sub PP/+V/sub DD/ and 1.5 V/sub TN/ respectively. Also, the pumping current was increased in the new circuit. The newly proposed two-phase V/sub PP/ charge-pump circuit worked successfully at V/sub DD/ down to 0.8 V by eliminating the threshold voltage loss of the control pulse generator and was tested successfully in a 0.16-/spl mu/m test chip using triple-well CMOS technology.     

Fully Programmable Memory BIST for Commodity DRAMs

To accomplish a high‐speed test on low‐speed automatic test equipment (ATE), a new instruction‐based fully programmable memory built‐in self‐test (BIST) is proposed. The proposed memory BIST generates a high‐speed internal clock signal by multiplying an external low‐speed clock signal from an ATE by a clock multiplier embedded in a DRAM. For maximum programmability and small area overhead, the proposed memory BIST stores the unique sets of instructions and corresponding test sequences that are implicit within the test algorithms that it receives from an external ATE. The proposed memory BIST is managed by an external ATE on‐the‐fly to perform complicated and hard‐to‐implement functions, such as loop operations and refresh‐interrupts. Therefore, the proposed memory BIST has a simple hardware structure compared to conventional memory BIST schemes. The proposed memory BIST is a practical test solution for reducing the overall test cost for the mass production of commodity DDRx SDRAMs.     

Multiple twisted dataline techniques for multigigabit DRAMs

To provide reliable scaled DRAMs, new multiple twisted dataline techniques are proposed and analyzed. Their effectiveness in reducing both the bitline (BL) and wordline (WL) coupling noises in scaled DRAM's was evaluated by means of soft-error-rate measurements on 256-Mbit and 1-Gbit DRAM test chips. At the 1-Gbit level of integration, in our proposed scheme-compared to the conventional twisted bitline (TBL) scheme-the chip area penalty due to twisting is reduced by 66% and the BL coupling noise is reduced by 45%. At the 256-Mbit level, when the proposed technique is applied to both the BL and WL structures, we achieved a 64% coupling noise reduction compared to the conventional TBL and WL schemes. Faster data access time can also be expected when the proposed technique is applied to BL and/or WL structures     

A built-in Hamming code ECC circuit for DRAMs

An error checking and correcting (ECC) technique that checks multiple cell data simultaneously and allows fast column access is described. The ECC circuit is optimized with respect to the increase in the chip area and the access-time penalty, and can be applied to a 16-Mbit DRAM with 20% chip area increase and less access-time penalty. The soft error rate has been estimated to be about 100 times smaller than that of the basic horizontal-vertical parity-code ECC technique     

Multiple twisted data line technique for scaled DRAMs

A new multiple twisted data line technique to reduce both bit-line and word-line coupling noises is proposed and demonstrated. An improved noise/signal ratio resulting from the application of the proposed technique is confirmed by soft-error rate tests. A faster data access time can also be expected when the proposed technique is incorporated into dynamic random access memories     

DDR DRAM削减膝上计算机功耗

看第一眼,你觉得PC100／133与DDRDRAM在省电方面似乎没有什么两样,但仔细分析以后,你会发现DDR是更好的选择。为了探索更高的性能和更低的功耗,膝上计算机的设计正开始从SDRAM（PC10O／133）转向双速率（Doub卜DataRate,DDR）的DDRDRAM。在采用新的DDR做设计时,有几个因素是系统工程师必须考虑的,其中主要的因素是功耗问题。影响设计和布局布线的新结构特点也必须加以考虑。同样重要的是对成本与性能特性的理解。DDR功率分析比较两种不同的存储器系统的功耗是很有意义的,其中一个采用PC133SDRAM,另～个采用266M…