A 7-ns 140-mW 1-Mb CMOS SRAM with current sense amplifier

A 7-ns 140-mW 1-Mb CMOS SRAM was developed to provide fast access and low power dissipation by using high-speed circuits for a 3-V power supply: a current-sense amplifier and pre-output buffer. The current-sense amplifier shows three times the gain of a conventional voltage-sense amplifier and saves 60% of power dissipation while maintaining a very short sensing delay. The pre-output buffer reduces output delays by 0.5 ns to 0.75 ns. The 6.6-μm² high-density memory cell uses a parallel transistor layout and phase-shifting photolithography. The critical charge that brings about soft error in a memory cell can be drastically increased by adjusting the resistances of poly-PMOS gate electrodes. This can be done without increasing process complexity or memory cell area. The 1-Mb SRAM was fabricated using 0.3-μm CMOS quadrupole-poly and double-metal technology. The chip measures 3.96 mm×7.4 mm (29 mm²)     

An 18-ns 1-Mbit CMOS SRAM

A 1-Mb (256 K×4 b) CMOS static random-access memory with a high-resistivity load cell was developed with 0.7-μm CMOS process technology. This SRAM achieved a high-speed access of 18 ns. The SRAM uses a three-phase back-bias generator, a bus level-equalizing circuit and a four-stage sense amplifier. A small 4.8×8.5-μm² cell was realized by the use of a triple-polysilicon structure. The grounded second-polysilicon layer increases cell capacitance and suppresses α-particle-induced soft errors. The chip size measures 7.5×12 mm²     

A 46-ns 1-Mbit CMOS SRAM

A 1-Mb (128 K×8-bit) CMOS static RAM (SRAM) with high-resistivity load cell has been developed with 0.8-μm CMOS process technology. Standby power is 25 μW, active power 80 mW at 1-MHz WRITE operation, and access time 46 ns. The SRAM uses a PMOS bit-line DC load to reduce power dissipation in the WRITE cycle, and has a four-block access mode to reduce the testing time. A small 4.8×8.5-μm² cell has been realized by triple-polysilicon layers. The grounded second polysilicon layer increases cell capacitance and suppresses α-particle-induced soft errors. The chip size is 7.6×12.4 mm²     

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     

An 833-MHz 1.5-W 18-Mb CMOS SRAM with 1.67 Gb/s/pin

This paper describes an 833-MHz 18-Mb CMOS SRAM with a 1.67-Gb/s/pin data rate. Issues that had to be overcome from previous-generation SRAMs to meet the performance goals are addressed. The SRAM has been successfully fabricated using a 0.18-μm CMOS process with copper interconnects. It operates in two user-selectable double-data-rate modes (DDR and DDR2) and consumes 1.5 W of power at 833 MHz. In addition to the performance benefits resulting from this 0.18-μm copper technology, architecture improvements, a data-to-echo-clock tracking system, and data symmetric output drivers made possible the high frequency of operation     

A 23-ns 4-Mb CMOS SRAM with 0.2-μA standby current

A 4-Mb CMOS SRAM having 0.2-μA standby current at a supply voltage of 3 V has been developed. Current-mirror/PMOS cross-coupled cascade sense-amplifier circuits have achieved the fast address access time of 23 ns. A new noise-immune data-latch circuit has attained power-reduction characteristics at a low operating cycle time without access delay. A 0.5-μm CMOS, four-level poly, two-level metal technology with a polysilicon PMOS load memory cell, yielded a small cell area of 17 μm² and the very small standby current. A quadruple-array, word-decoder architecture allowed a small chip area of 122 mm²     

A 12.5-ns 16-Mb CMOS SRAM with common-centroid-geometry-layoutsense amplifiers

A 16-Mb CMOS SRAM using 0.4-μm CMOS technology has been developed. This SRAM features common-centroid-geometry (CCG) layout sense amplifiers which shorten the access time by 2.4 ns. A flexible redundancy technique achieves high efficiency without any access penalty. A memory cell with stacked capacitors is fabricated for high soft-error immunity. A 16-Mb SRAM with a chip size of 215 mm² is fabricated and an address access time of 12.5 ns has been achieved     

A 7.5-ns 32 K×8 CMOS SRAM

A 256 K (32 K×8) CMOS static RAM (SRAM) which achieves an access time of 7.5 ns and 50-mA active current at 50-MHz operation is described. A 32-block architecture is used to achieve high-speed access and low power dissipation. To achieve faster access time, a double-activated-pulse circuit which generates the word-line-enable pulse and the sense-amplifier-enable pulse has been developed. The data-output reset circuit reduces the transition time and the noise generated by the output buffer. A self-aligned contact technology reduces the diffused region capacitance. This RAM has been fabricated in a twin-tub CMOS 0.8-μm technology with double-level polysilicon (the first level is polycide) and double-level metal. The memory cell size is 6.0×11.0 μm² and the chip size is 4.38×9.47 mm ²     

LDD MOSFETs using disposable sidewall spacer technology

A technology for fabricating lightly doped drain (LDD) MOSFET devices based on disposable sidewall spacers is presented. Using a thin polysilicon buffer layer between the low-temperature oxide (LTO) sidewall spacers and the oxidized polysilicon gate, a single masking step can be used to form the n^- and n⁺ or p^- and p⁺ source/drain implants for the NMOS and PMOS devices, respectively. In addition, the LTO sidewall spacers may be removed by a wet HF strip, thus minimizing additional damage to the gate oxide that may be caused by reactive ion etch removal. The disposable sidewall spacer technology is easily adaptable to a CMOS process as demonstrated by the fabrication of a 4 K×4 SRAM circuit using a conventional 1.5-μ CMOS technology     

An ultrahigh-density high-speed loadless four-transistor SRAM macrowith twisted bitline architecture and triple-well shield

We have developed two schemes for improving access speed and reliability of a loadless four-transistor (LL4T) SRAM cell: a dual-layered twisted bitline scheme, which reduces coupling capacitance between adjacent bitlines in order to achieve highspeed READ/WRITE operations, and a triple-well shield, which protects the memory cell from substrate noise and alpha particles. We incorporated these schemes in a high-performance 0.18-μm-generation CMOS technology and fabricated a 16-Mb SRAM macro with a 2.18-μm² memory cell. The macro size of the LL4T-SRAM is 56 mm², which is 30% to 40% smaller than a conventional six-transistor SRAM when compared with the same access speed. The developed macro functions at 500 MHz and has an access time of 2.0 ns. The standby current has been reduced to 25 μA/Mb with a low-leakage nMOSFET in the memory cell     

250 Mbyte/s synchronous DRAM using a 3-stage-pipelined architecture

A 3.3-V 512-k×18-b×2-bank synchronous DRAM (SDRAM) has been developed using a novel 3-stage-pipelined architecture. The address-access path which is usually designed by analog means is digitized, separated into three stages by latch circuits at the column switch and data-out buffer. Since this architecture requires no additional read/write bus and data amp, it minimizes an increase in die size. Using the standardized GTL interface, a 250-Mbyte/s synchronous DRAM with die size of 113.7-mm², which is the same die size as the conventional DRAM, has been achieved with 0.50-μm CMOS process technology     

A 1-Gb/s bidirectional I/O buffer using the current-mode scheme

A current-mode bidirectional I/O buffer was designed, and the maximum effective bandwidth of 1.0 Gb/s per wire was obtained from measurements. To enhance the operating speed, the voltage swing on the transmission line was reduced to 0.5 V and the internal nodes of the buffer were designed to be low impedance nodes using the current-mode scheme. An automatic impedance-matching scheme was used to generate bias voltages, which adjust output resistance of the buffer to be equal to the characteristic impedance of the transmission line in spite of process variations. The chip was fabricated by using a 0.8-μm CMOS technology. The chip size was 500×330 μm², and the power consumption was 50 mW at a supply voltage of 3 V     

A 1.5-ns access time, 78-μm2 memory-cell size, 64-kbECL-CMOS SRAM

A 1.5-ns access time, 78-μm² memory-cell size, 64-kb ECL-CMOS SRAM has been developed. This high-performance device is achieved by using a novel ECL-CMOS SRAM circuit technique: a combination of CMOS cell arrays and ECL word drivers and write circuits. These ECL word drivers and write circuits drive the CMOS cell arrays directly without any intermediate MOS level converter. In addition to the ultrahigh-speed access time and relatively small memory-cell size, a very short write-pulse width of 0.8 ns and sufficient soft-error immunity are obtained. This ECL-CMOS SRAM circuit technique is especially useful for realizing ultrahigh-speed high-density SRAMs, which have been used as cache and control storages of mainframe computers     

A 6-ns 4-Mb CMOS SRAM with offset-voltage-insensitive current senseamplifiers

A 4-Mb CMOS SRAM with 3.84 μm² TFT load cells is fabricated using 0.25-μm CMOS technology and achieves an address access time of 6 ns at a supply voltage of 2.7 V. The use of a current sense amplifier that is insensitive to its offset voltage enables the fast access time. A boosted cell array architecture allows low voltage operation of fast SRAM's using TFT load cells     

An 8-ns 256K ECL SRAM with CMOS memory array and battery backupcapability

The authors describe the first high-performance, high-density ECL SRAM (emitter-coupled-logic static random-access memory) compatible with battery backup techniques. The 256K device has a measured access time of 8 ns. Fabricated in a 0.8-μm BiCMOS process, the chip uses 117-μm ², full-CMOS, six-transistor memory cells and measures 6.5×8.15 mm². The design methodology described here illustrates the extent to which bipolar devices can be integrated into the periphery of a CMOS memory array. This integration was achieved through the use of a novel sensing scheme which provided three stages of bipolar differential sensing, with the first stage of sensing taking place directly on the bit lines     

A 10-b 20-Msample/s analog-to-digital converter

A 10-b 20-Msample/s analog-to-digital converter fabricated in a 0.9-μm CMOS technology is described. The converter uses a pipelined nine-stage architecture with fully differential analog circuits and achieves a signal-to-noise-and-distortion ratio (SNDR) of 60 dB with a full-scale sinusoidal input at 5 MHz. It occupies a 8.7 mm² and dissipates 240 mW     

A 16-Mb CMOS SRAM with a 2.3-μm2 single-bit-linememory cell

A novel architecture that enables fast write/read in poly-PMOS load or high-resistance polyload single-bit-line cells is developed. The architecture for write uses alternate twin word activation (ATWA) with bit-line pulsing. A dummy cell is used to obtain a reference voltage for reading. An excellent balance between a normal cell signal line and a dummy cell signal line is attained using balanced common data-line architecture. A newly developed self-bias-control (SBC) sense amplifier provides excellent stability and fast sensing performance for input voltages close to V_CC at a low power supply of 2.5 V. The single-bit-line architecture is incorporated in a 16-Mb SRAM, which was fabricated using 0.25-μm CMOS technology. The proposed single-bit-line architecture reduces the cell area to 2.3-μm² , which is two-thirds of a conventional two-bit-line cell with the same processes. The 16-Mb SRAM, a test chip for a 64-Mb SRAM, shows a 15-ns address access time and a 20-ns cycle time     

An experimental 1-Mbit CMOS SRAM with configurable organization andoperation

A 1-Mb SRAM (static random-access memory) configurable as a 128-kb×8, 256-kb×4, or 1-Mb×1 memory featuring asynchronous operation with static-column and chip-enable-access speedup modes or synchronous operation with a fast-page (toggle) or static-column mode is described. It has been fabricated in a double-metal, double-polysilicon CMOS process with 0.7-μm geometry and special SRAM structures. The measured synchronous access of 29 ns with a fast-page mode access of 22 ns. Measured asynchronous access is 34 ns with a static-column access of 33 ns and a chip-select speedup access of 29 ns. The SRAMs six-transistor CMOS memory cell is 58.24 μm²     

A 3.8-ns 16 K BiCMOS SRAM

A 2 K×8-b, ECL 100 K compatible BiCMOS SRAM with 3.8-ns (-4.5 V, 60°) address access time is described. The precisely controlled bit-line voltage swing (60 mV), a current sensing method, and optimized ECL decoding circuits permit a reliable and fast readout operation. The SRAM features an on-chip write pulse generator, latches for input and output bits, and a full six-transistor CMOS cell array. Power dissipation is approximately 2 W, and the chip size is 3.9×5.9 mm². The SRAM was based on 1.2-μm BiCMOS, using double-metal, triple-polysilicon, and self-aligned bipolar transistors     

A 14-b, 100-MS/s CMOS DAC designed for spectral performance

A 14-bit, 100-MS/s CMOS digital-to-analog converter (DAC) designed for spectral performance corresponding more closely to the 14-bit specification than current implementations is presented. This DAC utilizes a nonlinearity-reducing output stage to achieve low output harmonic distortion. The output stage implements a return-to-zero (RZ) action, which tracks the DAC once it has settled and then returns to zero. This RZ circuit is designed so that the resulting RZ waveform exhibits high dynamic linearity. It also avoids the use of a hold capacitor and output buffer as in conventional track/hold circuits. At 60 MS/s, DAC spurious-free dynamic range is 80 dB for 5.1-MHz input signals and is down only to 75 dB for 25.5-MHz input signals. The chip is implemented in a 0.8-μm CMOS process, occupies 3.69×3.91 mm ² of die area, and consumes 750 mW at 5-V power supply and 100-MS/s clock speed