Scott C. Best

Challenges and solutions for next generation main memory systems

Todays high performance computing memory systems mainly consist of with DDR3 DRAMs offering 800Mb/s to 1600Mb/s data rates. Extending the performance of these main memory systems beyond the current data rate is quite challengeable as the signal integrity issues with physical channel remains relatively constant compared to the device performance which improves as process advances. This paper presents three key technologies which help the current memory architecture to reach the data rates of 1600~3200Mb/s without sacrificing memory capacity, increasing power consumption, or switching to more advanced differential signaling. These key features include FlexPhase™ timing adjustment to eliminate trace length matching, dynamic point-to-point signaling to increase memory capacity at high data rates, and near ground signaling to reduce IO signaling power. This paper demonstrates the benefits of these features from signal and power integrity point of view.

Co-design and optimization of a 256-GB/s 3D IC package with a controller and stacked DRAM

This paper presents a double-sided flip-chip package. The package consists of a memory controller on one side of an organic substrate, and 3D-stacked, disaggregated memory chips, integrated with TSVs, on the opposite side. Thermal isolation is one of the key motivations for this configuration. Co-design of all physical layers is required to optimize the integrated 3D package within electrical and manufacturing constraints. Double-sided flip-chip packaging also presents unique challenges in the design of the power delivery network (PDN). A pre-layout design strategy is described, which optimizes the PDN design across 11 power domains to meet stringent impedance targets.

System Co-Design and Co-Analysis Approach to Implementing the XDR Memory System of the Cell Broadband Engine Processor; Realizing 3.2 Gbps Data Rate per Memory Lane in Low Cost, High Volume Production

This paper describes the design and analysis of the 3.2 Gbps XDRtrade memory system of the Cell Broadband Enginetrade (Cell BE) processor developed by Sony Corporation, Sony Computer Entertainment, Toshiba and IBM. A system co-design and co-analysis approach was applied where different components of the system are designed and analyzed simultaneously to allow trade-offs to be made to optimize system electrical characteristics at low overall system cost. The XDR memory interface circuit implemented in the Cell BE processor, the power delivery system design and analysis, and the interface statistical signal integrity analysis will be described to illustrate this design and analysis approach.

Signal and power integrity analysis of a 256-GB/s double-sided IC package with a memory controller and 3D stacked DRAM

This paper presents signal and power integrity analysis of a double-sided flip-chip package. A memory controller is attached on one side of the organic substrate, and 3D-stacked, disaggregated memory chips, integrated with through silicon vias (TSVs), are connected on the opposite side. The signaling path of this 3D memory system consists of a short channel consisting of wafer-level redistribution layer (RDL) traces and small TSV vias. The signal integrity is not a source of concern for this extremely short channel; power integrity, however, poses significant challenges and consequently can limit the achievable data rate of this system. The double-sided flip-chip packaging p resents unique challenges in the design of l o w-impedance the power delivery network (PDN) and circuit design with low-sensitivity to power supply noises. All physical layers are code sign to optimize the integrated 3D package within electrical and manufacturing constraints in conjunction with robust circuit design that meets the power constraint. The detailed signal integrity analysis is presented to design robust link with low-swing signals and power integrity analysis to optimize the PDN designs to meet the PDN impedance targets.

Characterization of a low-power 6.4 Gbps DDR DIMM memory interface system

A memory system that meets the bandwidth, power efficiency, and capacity needs of future computing systems is presented in this paper. A 6.4 Gbps single-ended DDR memory interface for the controller and the DRAM was designed in a 28-nm CMOS process for a main memory system with dual-rank DIMMs. The architecture features a novel clocking scheme, per-pin timing adjustment, dynamic point-to-point signaling topology, and near ground signaling. The system V-T budget simulations and the characterization results of the fabricated memory interface are presented.

Power-efficient I/O design considerations for high-bandwidth applications

Power-efficiency results from several generations of I/O interfaces with specific goals are presented as well as the tradeoffs made within and across those designs. Foundational work in active-power reduction at a single rate for a symmetric system, the subsequent application of that work to a burst-mode asymmetric interface, and recent research on low-overhead bursting are discussed. Dynamic voltage frequency scaling and efficiency increases enabled by system level interconnect improvements are also considered as important techniques.