Yasuhiro Takai

A 1-Gb/s/pin 512-Mb DDRII SDRAM using a digital DLL and a slew-rate-controlled output buffer

We developed a 1-Gb/s/pin 512-Mb DDRII SDRAM composed of a digital delay-locked loop (DLL) and a slew-rate controlled output buffer. The digital DLL has a frequency divider for the DLL input, which performs at a operating frequency of up to 500 MHz at 1.6 V, and it provides internal clocking with 50% duty-cycle correction. The DLL has a current-mirror-type interpolator, which enables a resolution as high as 14 ps, is standby-current-free, and can operate at voltages as low as 0.8 V. The slew-rate impedance-controlled output buffer circuit reduces the output skew from 107 to 10 ps. This SDRAM was tested using a 0.13-/spl mu/m 126.5 mm/sup 2/ 512 Mb device.

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

A 3.3-V 512-k/spl times/18-b/spl times/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-mm/sup 2/, which is the same die size as the conventional DRAM, has been achieved with 0.50-/spl mu/m CMOS process technology. >

1.8-V 800-Mb/s/pin DDR2 and 2.5-V 400-Mb/s/pin DDR1 compatibly designed 1Gb SDRAM with dual-clock input-latch scheme and hybrid multi-oxide output buffer

Two circuit techniques of DDR1/DDR2 compatible chip architecture designed for both high-speed and high-density DRAMs are presented. The dual clock input latch scheme, which reduces the excessive timing margin for random input commands by using a pair of latch circuits controlled by dual-phase 1-shot clock signals, achieves a 0.9-ns reduction in cycle time from 3.05 ns to 2.15 ns. By using these techniques in combination with a hybrid multi-oxide output buffer, we developed a 175.3 mm/sup 2/ 1Gb SDRAM which operates as a 800-Mb/s/pin DDR2 or 400Mb/s/pin DDR1.

1.8-V 800-Mb/s/pin DDR2 and 2.5-V 400-Mb/s/pin DDR1 compatibly designed 1Gb SDRAM with dual clock input latch scheme and hybrid multi-oxide output buffer

This paper describes three circuit techniques for a DDR1/DDR2-compatible chip architecture designed for both high-speed and high-density DRAMs: 1) a dual-clock input-latch scheme, which reduces the excessive timing margin for random input commands by using a pair of latch circuits controlled by dual-phase one-shot clock signals, achieves a 0.9-ns reduction in cycle time from 3.05 to 2.15 ns; 2) a hybrid multi-oxide output buffer reduces the area penalty of the output buffer caused by compatible chip design from 1.35% to 0.3%; and 3) a quasi-shielded distributed data transfer scheme enables a 2.6-ns reduction in access time to 10.25 ns in both 2-b and 4-b prefetch operations. By using these techniques, we developed a 175.3-mm/sup 2/ 1-Gb SDRAM that operates as an 800-Mb/s/pin DDR2 or 400-Mb/s/pin DDR1.