Youngjoo Lee

6.4Gb/s multi-threaded BCH encoder and decoder for multi-channel SSD controllers

Solid-state drives (SSDs), built with many flash memory channels, is usually connected to the host through an advanced high-speed serial interface such as SATA III associated with a transfer rate of 6Gb/s [1-2]. However, the performance of SSD is in general determined by the throughput of the ECC blocks necessary to overcome the high error-rate [3]. The binary BCH code is widely used for the SSD due to its powerful error-correction capability. As it is hard to achieve high-throughput strong BCH decoders [4-5], multiple BCH decoders are typically on a high-performance SSD controller, leading to a significant increase of hardware complexity. This paper presents an efficient BCH encoder/decoder architecture achieving a decoding throughput of 6Gb/s. The overall architecture shown in Fig. 25.3.1 includes a single BCH decoder and a multi-threaded BCH encoder. The single BCH encoder is responsible for all the channels and services a channel at a time in a round-robin manner.

Melting Behaviors of Icosahedral Metal Clusters Studied by Monte Carlo Simulations

We present an atom‐resolved analysis method that traces physical quantities such as the root‐mean‐square bond length fluctuation and coordination number for individual atoms as functions of temperature or time. This method is applied to explain the temperature‐dependent behaviors of three types of NiN (N=12,13,14) clusters. The detailed studies for the three types of clusters reveal characteristics as follows: (a) as the temperature increases, all three types of clusters undergo two‐stage melting, irrespective of the existence of vacancy or adatom on the icosahedral surfaces, (b) the melting of icosahedral clusters with vacancy starts with vacancy hopping, which has not been observed for any type of small clusters (N<34), (c) the melting of the icosahedral clusters with adatom (N=14) is initiated by adatom hopping, followed by the site exchange between the adatom and surface atoms.

Compositional and structural identification of natural gas hydrates collected at Site 1249 on Ocean Drilling Program Leg 204

In contrast to the structural studies of laboratory-grown gas hydrate, this study has been performed on naturally grown clathrate hydrates from the sea floor. The PXRD pattern of natural gas hydrate shows that the sample had a structure I hydrate. The13C NMR spectrum was obtained for the natural gas hydrate sample in order to identify the cage occupancy of guest molecules and determine the hydration number. The NMR spectrum reveal that the natural gas hydrates used in this study contain only methane with no noticeable amount of other hydrocarbons. The existence of two peaks at different chemical shifts indicates that methane molecules are encapsulated in both large and small cages. In addition, Raman spectroscopic analysis is also carried out to identify natural hydrates and compared with the NMR results. Investigating the composition and structure of natural gas hydrates is essential for applying natural gas hydrates as a novel energy source.

Low-Complexity Parallel Chien Search Structure Using Two-Dimensional Optimization

To achieve a high-throughput decoder, massive-parallel computations are normally applied to the Chien search, but the parallel realization increases the hardware complexity significantly. To reduce the hardware complexity of the parallel Chien search, this brief proposes a 2-D optimization method. In contrast to the previous 1-D optimizations, the proposed method maximizes the sharing of common subexpressions in both the row and column directions. All the partial products needed in the parallel structure are represented in a single matrix, and the finite-field adders are completely eliminated in effect. Simulation results show that the proposed 2-D optimization leads to a significant reduction of the hardware complexity. For the (8191, 7684, 39) BCH code, the count of xor gates in the parallel Chien search is reduced by 92% and 22%, compared to the straightforward and strength-reduced structures, respectively.

A 2.74-pJ/bit, 17.7-Gb/s Iterative Concatenated-BCH Decoder in 65-nm CMOS for NAND Flash Memory

To improve the reliability of MLC NAND flash memory, this paper presents an energy-efficient high-throughput architecture for decoding concatenated-BCH (CBCH) codes. As the data read from the flash memory is hard-decided in practical applications, the proposed CBCH decoding method is a promising solution to achieve both high error-correction capability and energy efficiency. In the proposed CBCH decoding, the number of on-chip memory accesses consuming much energy is minimized by computing and updating syndromes two-dimensionally. To achieve an area-efficient hardware realization, row and column decoders are unified into one decoder and some syndromes are computed when they are needed. In addition, the decoding throughput is enhanced remarkably by skipping redundant decoding processes. Based on the proposed CBCH decoding architecture, a prototype chip is implemented in a 65-nm CMOS process to decode the (70528, 65536) CBCH code. The proposed decoder provides a decoding throughput of 17.7 Gb/s and an energy efficiency of 2.74 pJ/bit, being vastly superior to the state-of-the-art architectures.

Low-Complexity Tree Architecture for Finding the First Two Minima

This brief presents an area-efficient tree architecture for finding the first two minima as well as the index of the first minimum, which is essential in the design of a low-density parity-check decoder based on the min-sum algorithm. The proposed architecture reduces the number of comparators by reusing the intermediate comparison results computed for the first minimum in order to collect the candidates of the second minimum. As a result, the proposed tree architecture improves the area-time complexity remarkably.

7.3 Gb/s universal BCH encoder and decoder for SSD controllers

This paper presents a universal BCH encoder and decoder that can support multiple error-correction capabilities. A novel encoding architecture and on-demand syndrome calculation technique is proposed to reduce both hardware complexity and power consumption. Based on the proposed methods, 32-parallel universal encoder and decoder are designed for BCH (8192+14t, 8192, t) codes, where the error-correction capability t is configurable to 8, 11, 16, 24, 32, and 64. The prototype chip achieves a throughput of 7.3 Gb/s and occupies 2.24 mm2 in 0.13μm CMOS technology.

Low-latency area-efficient decoding architecture for shortened reed-solomon codes

The shortened RS code is traditionally decoded based on the standard decoding process by padding zero symbols. As additional cycles are redundantly taken to deal with the zero symbols, the processing latency of the shortened code is almost the same as that of the mother RS code from which the shortened code is derived. A new architecture is proposed in this paper to decrease the processing latency to the codeword length of the shortened RS code, which can be implemented at the cost of small additional hardware resources. The additional hardware complexity is minimized by reutilizing the hardware resources resident in the adjacent block. Experimental results show that the proposed method leads to a significant reduction of the overall latency. For the RS (32, 24) code, the overall processing latency is reduced by 85.2% and 33.6% compared to the conventional and the previous work, respectively. Moreover, the additional hardware complexity of the proposed method is smaller than those of the previous architectures.

High-Throughput and Low-Complexity BCH Decoding Architecture for Solid-State Drives

This paper presents a high-throughput and low-complexity BCH decoder for NAND flash memory applications, which is developed to achieve a high data rate demanded in the recent serial interface standards. To reduce the decoding latency, a data sequence read from a flash memory channel is re-encoded by using the encoder that is idle at that time. In addition, several optimizing methods are proposed to relax the hardware complexity of a massive-parallel BCH decoder and increase the operating frequency. In a 130-nm CMOS process, a (8640, 8192, 32) BCH decoder designed as a prototype provides a decoding throughput of 6.4 Gb/s while occupying an area of 0.85 mm2.

Small-area parallel syndrome calculation for strong BCH decoding

This paper presents a new optimization method to reduce the hardware complexity of syndrome calculation in strong BCH decoding. All the operations required in the parallel syndrome calculation are reformulated as a single matrix computation to enlarge the search area for common sub-expressions. The computational complexity of syndrome calculation is significantly reduced by finding and sharing common terms in the single matrix computation. Implementation results show that the proposed architecture saves 55% of area overheads compared to the conventional structure.