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Patent Issued for Method and Memory System Using a Priori Probability Information to Read Stored Data

January 29, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- Samsung Electronics Co., Ltd. (Suwon-si, Gyeonggi-do, KR) has been issued patent number 8631306, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Lee, Ki jun (Seoul, KR); Son, Hong Rak (Anyang-si, KR); Kong, Jun jin (Yongin-si, KR).

This patent was filed on January 6, 2011 and was published online on January 14, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Embodiments of the inventive concept relate generally to semiconductor devices. More particularly, embodiments of the inventive concept relate to memory systems using a priori probability information to read stored data and methods of operating the memory systems.

"Semiconductor memory devices play a significant role in a wide variety of consumer and industrial technologies, ranging from home computers to satellite equipment. Consequently, improvements in semiconductor memory technology can have a significant impact on the performance of numerous technical applications.

"Semiconductor memory devices can be roughly divided into two categories based on whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Examples of volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM), and examples of nonvolatile memory devices include read only memory (ROM), ferroelectric random access memory (FeRAM), phase-change random access memory (PRAM), and flash memory.

"Flash memory has become an especially popular form of nonvolatile memory due to its relatively low cost, low power consumption, high integration density, and ability to withstand physical shock. However, as the demand for flash memory continues to increase, researchers continue to seek ways to increase its storage capacity and performance.

"One technique that has been developed to increase the storage capacity of flash memory is to store multiple bits of data in flash memory cells. A multi-bit flash memory cell stores multiple bits of data using multiple threshold voltage distributions that correspond to different values of multi-bit data. For instance, a 2-bit flash memory cell can store data using four different threshold voltage distributions each corresponding to one of logical states '11', '10', '00', and '01'.

"The performance and reliability of multi-bit flash memory cells tends to decrease as the number of threshold voltages increases. For instance, in a multi-bit flash memory cell that stores data using a large number of threshold voltage distributions, the threshold voltage distributions can become overlapped, which can change stored data. Accordingly, researchers continue to seek ways to improve the reliability of multi-bit flash memory cells."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Embodiments of the inventive concept provide memory systems that use a priori probability information to read stored data and methods of operating the memory systems.

"According to one embodiment of the inventive concept, a memory system comprises a non-volatile memory device that stores user data and state information regarding the user data, and a memory controller that accesses the state information and the user data in a read operation of the non-volatile memory device, calculates a priori probabilities of the user data based on the state information, calculates a posteriori probabilities of the user data based on the a priori probabilities, and performs a soft-decision operation to detect logical states of the user data based on the a posteriori probabilities.

"In certain embodiments, the state information is stored as meta-data of the user data.

"In certain embodiments, the state information indicates a number of bits of the user data that have been programmed to each of various logical states.

"In certain embodiments, the a priori probabilities comprise a first a priori probability indicating a proportion of bits of the user data that have been programmed to a first logical state, and a second a priori probability indicating a proportion of bits of the user data that have been programmed to a second logical state.

"In certain embodiments, the a posteriori probabilities comprise a first a posteriori probability that is calculated by multiplying the first a priori probability with a first conditional probability and a second a posteriori probability that is calculated by multiplying the second a priori probability with a second conditional probability.

"In certain embodiments, the soft-decision operation compares the first a posteriori probability with the second a posteriori probability and identifies a value of one or more bits of the user data according to which of the first and second a posteriori probabilities is larger.

"In certain embodiments, the first conditional probability is a probability that a bit is read with the first logical state, given that the bit was programmed with the first logical state.

"In certain embodiments, the memory controller comprises an a priori probability computation unit that calculates the a priori probabilities based on the state information, an a posteriori probability computation unit that calculates the a posteriori probabilities based on the a priori probabilities, and a soft-decision decoder that determines logical states of bits of the user data by performing the soft-decision operation based on the a posteriori probabilities.

"In certain embodiments, the non-volatile memory device is a multi-level cell flash memory device.

"In certain embodiments, the controller reads a page of data comprising the user data and the state information and computes an a posteriori probability for a codeword of user data in the page.

"According to one embodiment of the inventive concept, a method of processing data in a non-volatile memory device comprises receiving data and state information regarding the data from the non-volatile memory device, calculating a priori probabilities for the data according to the state information, calculating a posteriori probabilities of a bit or codeword of the data according to the a priori probabilities, and determining a value of the bit or the codeword based on the a posteriori probabilities.

"In certain embodiments, the data and the state information are stored in a same page of the non-volatile memory device.

"In certain embodiments, the state information is stored in a meta-data area of the page.

"In certain embodiments, the state information indicates a number of bits of the data that have been programmed to each of various logical states.

"In certain embodiments, the method further comprises programming the data and the state information in the non-volatile memory device.

"In certain embodiments, the a priori probabilities are multiplied by conditional probabilities to calculate the a posteriori probabilities.

"In certain embodiments, a first one of the conditional probabilities is a probability that a bit is read with a first logical state, given that the bit was programmed with the first logical state, and a second one of the conditional probabilities is a probability that the bit is read with the first logical state, given that the bit was programmed with the second logical state.

"In certain embodiments, the first and second logical states are one bit logical states.

"In certain embodiments, receiving the data and state information from the non-volatile memory device comprises operating a memory interface of a memory controller to communicate with the non-volatile memory.

"In certain embodiments, the non-volatile memory device is a NAND flash memory device."

For the URL and additional information on this patent, see: Lee, Ki jun; Son, Hong Rak; Kong, Jun jin. Method and Memory System Using a Priori Probability Information to Read Stored Data. U.S. Patent Number 8631306, filed January 6, 2011, and published online on January 14, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=13&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=626&f=G&l=50&co1=AND&d=PTXT&s1=20140114.PD.&OS=ISD/20140114&RS=ISD/20140114

Keywords for this news article include: Semiconductor, Random Access Memory, Samsung Electronics Co. Ltd..

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Source: Electronics Newsweekly


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