阅读说明：本技术 一种快速寻找nand闪存最佳重读电压的方法 (Method for quickly searching optimal rereading voltage of NAND flash memory ) 是由 原顺 于 2019-08-06 设计创作，主要内容包括：本发明提出一种快速寻找NAND闪存最佳重读电压的方法,包括以下步骤：A、分别确定在所有可能的读电压值下,NAND闪存中的至少一页中的所有数据出现位反转的数量；B、将出现最小位反转数量所对应的一个或多个读电压值设置为第一读电压数据集,并且将第一读电压数据集中的所有数据值的中值作为最佳重读电压；C、若所述最佳重读电压在所述NAND闪存中重读电压范围内,则将所述最佳重读电压应用到所述NAND闪存。(The invention provides a method for quickly searching the optimal rereading voltage of a NAND flash memory, which comprises the following steps: A. respectively determining the number of bit reversals of all data in at least one page in the NAND flash memory under all possible read voltage values; B. setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median value of all data values in the first reading voltage data set as the optimal rereading voltage; C. and if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory, applying the optimal rereading voltage to the NAND flash memory.)

1. A method for quickly searching the optimal rereading voltage of a NAND flash memory is characterized by comprising the following steps:

A. respectively determining the number of bit reversals of all data in at least one page in the NAND flash memory under all possible read voltage values;

B. setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median value of all data values in the first reading voltage data set as the optimal rereading voltage;

C. and if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory, applying the optimal rereading voltage to the NAND flash memory.

2. The method of claim 1, wherein the data in at least one page of the NAND flash memory is randomly distributed, and the data "0" and the data "1" are 50% in percentage.

3. The method of claim 1, wherein the amount of data that can be placed in each memory cell of the NAND flash memory is 1 bit.

4. A method for quickly searching the optimal rereading voltage of a NAND flash memory is characterized by comprising the following steps:

a', writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

b', respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results, and respectively calculating the number of read-out 1;

c ', reading out the absolute value of the difference between the numbers of the adjacent two times as ' 1 ', and determining one or more reading voltage values corresponding to the minimum absolute value as an optimal re-reading voltage data set.

5. The method of claim 4, wherein the number of all possible read voltages is 256.

6. The method of claim 4, wherein when the number of data in the optimal reread voltage data set is greater than 1, the method further comprises the following steps after the step C' is performed:

d ', the absolute value of the difference between the numbers of ' 1 ' is used as the ordinate, and a two-dimensional scatter distribution diagram is drawn.

7. The method according to claim 6, wherein the origin of coordinates of the scatter distribution chart in step D' corresponds to a factory default read voltage value of the NAND flash memory.

8. An apparatus for fast finding an optimal re-read voltage of a NAND flash memory is provided, which comprises the following modules:

the initialization module is used for respectively determining the number of bit reversals of all data in at least one page in the NAND flash under all possible read voltage values;

the judging module is used for setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median of all data values in the first reading voltage data set as the optimal rereading voltage;

and the target determining module is used for applying the optimal rereading voltage to the NAND flash memory if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory.

9. An apparatus for fast finding an optimal re-read voltage of a NAND flash memory is provided, which comprises the following modules:

the random writing module is used for writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

the reading test module is used for respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results and respectively calculating the number of read-out 1;

and the optimum searching module is used for searching the absolute value of the difference between the numbers which are read out as 1' twice in two adjacent times and determining one or more reading voltage values corresponding to the minimum absolute value as the optimum re-reading voltage data set.

10. A computer-readable storage medium, on which a computer program is stored, characterized in that the computer program realizes the steps of the method according to any one of claims 1-7 when executed by a processor.

Technical Field

The invention relates to the field of data processing, in particular to a method for quickly searching the optimal rereading voltage of a NAND flash memory.

Background

The NAND flash memory is a memory chip widely used nowadays, and has excellent characteristics such as high speed and non-volatility. The internal part of the NAND flash memory actually represents data in the form of stored charges, and in the actual use process, the amount of the stored charges changes due to changes of various internal and external conditions, and if the changes are accumulated to a certain degree, the NAND flash memory is accessed by default read operation, and correct data is probably not obtained. Generally, manufacturers of NAND flash memories allow a read voltage for determining a state of a cell to be adjusted, and correct data is recovered by adjusting the read voltage, which is generally called a readretry. The invention provides a method for drawing threshold voltage distribution of a page memory unit in a NAND flash memory, and provides a basis for selecting a proper readretry method and analyzing data errors.

In the use process of the NAND flash memory product, due to the influence of internal and external conditions of a load, the number of electrons in a cell changes, so that correct data cannot be obtained by default reading voltage, and an original factory usually provides a plurality of sets of readretry methods to restore data by adjusting the reading voltage. In order to quickly find the most effective condition from these readretry methods, we need to know the threshold voltage distribution of the memory cells in the page where the failure data is located.

Since the original factory does not directly provide an external command to obtain the threshold voltage distribution of the cell, the conventional solution is to try re-reading one group by one group during the actual recovery process of the readretry until the data can be correctly read, however, the operation is time-consuming and inefficient.

Disclosure of Invention

In order to solve the problems that time and efficiency are wasted when rereading voltage is determined in the prior art, the invention provides a method for quickly searching the optimal rereading voltage of a NAND flash memory.

Firstly, the invention provides a method for quickly searching the optimal rereading voltage of a NAND flash memory, which comprises the following steps:

A. respectively determining the number of bit reversals of all data in at least one page in the NAND flash memory under all possible read voltage values;

B. setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median of all data values in the first reading voltage data set as the optimal rereading voltage;

C. and if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory, applying the optimal rereading voltage to the NAND flash memory.

Further, in the above method proposed by the present invention, data in at least one page in the NAND flash memory is randomly distributed, and a duty ratio of data "0" and a duty ratio of data "1" are both 50%.

Further, in the above method provided by the present invention, the data size that can be placed in each memory cell in the NAND flash memory is 1 bit.

Secondly, the invention further provides a method for rapidly searching the optimal rereading voltage of the NAND flash memory, which comprises the following steps:

a', writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

b', respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results, and respectively calculating the number of read-out 1;

c ', reading out the absolute value of the difference between the numbers of the adjacent two times as ' 1 ', and determining one or more reading voltage values corresponding to the minimum absolute value as an optimal re-reading voltage data set.

Further, in the above method proposed by the present invention, the number of all possible read voltages is 256.

Further, in the method provided by the present invention, when the number of data in the optimal reread voltage data set is greater than 1, the method further includes, after performing step C', the steps of:

d ', the absolute value of the difference between the numbers of ' 1 ' is used as the ordinate, and a two-dimensional scatter distribution diagram is drawn.

Further, in the method provided by the present invention, the origin of coordinates of the scatter distribution diagram in step D' corresponds to a factory default read voltage value of the NAND flash memory.

The invention provides a device for quickly searching the optimal rereading voltage of the NAND flash memory, which comprises the following modules:

the initialization module is used for respectively determining the number of bit inversion of all data in at least one page in the NAND flash under all possible read voltage values;

the judging module is used for setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median of all data values in the first reading voltage data set as the optimal rereading voltage;

and the target determining module is used for applying the optimal rereading voltage to the NAND flash memory if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory.

The invention provides a device for quickly searching the optimal rereading voltage of the NAND flash memory, which comprises the following modules:

the random writing module is used for writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

the reading test module is used for respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results and respectively calculating the number of read-out 1;

and finding an optimal module, which is used for reading out the absolute value of the difference between the numbers of the adjacent two times as '1' and determining one or more reading voltage values corresponding to the minimum absolute value as an optimal re-reading voltage data set.

Finally, the invention proposes a computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the above-mentioned method.

The beneficial results of the invention are: by executing the steps of the method provided by the invention, the optimal reread voltage of the NAND flash memory can be quickly and effectively found.

Drawings

FIG. 1 is a flowchart illustrating a method for quickly finding an optimal re-read voltage for a NAND flash memory according to a first embodiment of the present invention;

FIG. 2 is a flowchart illustrating a method for quickly finding an optimal re-read voltage for a NAND flash memory according to a second embodiment of the present invention;

FIG. 3 is a flowchart illustrating a method for quickly finding an optimal re-read voltage for a NAND flash according to a third embodiment of the present invention;

FIG. 4 is a scattering diagram of reread voltage distribution according to a fourth embodiment of the method for rapidly finding the optimal reread voltage of the NAND flash memory in accordance with the present invention;

FIG. 5 is a scattering diagram of reread voltage distribution according to a fifth embodiment of the method for rapidly finding the optimal reread voltage of the NAND flash memory in accordance with the present invention;

FIG. 6 is a first block diagram of an apparatus for fast finding the optimal rereading voltage of a NAND flash according to the present invention;

FIG. 7 is a second block diagram of an apparatus for fast finding the optimal re-read voltage for a NAND flash according to the present invention.

Detailed Description

The conception, the specific structure and the technical effects of the present invention will be clearly and completely described in conjunction with the embodiments and the accompanying drawings to fully understand the objects, the schemes and the effects of the present invention. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The same reference numbers will be used throughout the drawings to refer to the same or like parts.

It should be noted that, unless otherwise specified, when a feature is referred to as being "fixed" or "connected" to another feature, it may be directly fixed or connected to the other feature or indirectly fixed or connected to the other feature. Furthermore, the descriptions of upper, lower, left, right, etc. used in this application are only relative to the mutual positional relationships of the various elements of the application in the drawings. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The exemplary embodiments described herein and depicted in the drawings should not be considered limiting. Various mechanical, compositional, structural, electrical, and operational changes, including equivalents, may be made without departing from the scope of this disclosure and the claims. In certain instances, well-known structures and techniques have not been shown or described in detail to avoid obscuring the disclosure. The same reference numbers in two or more drawings identify the same or similar elements. Moreover, elements and their associated features, which are described in detail with reference to one embodiment, may be included in other embodiments, where they are not specifically shown or described, where practicable. For example, if an element is described in detail with reference to one embodiment and not described with reference to the second embodiment, it may also be claimed to be included in the second embodiment.

Furthermore, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any combination of one or more of the associated listed items.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element of the same type from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present application. The word "if" as used herein may be interpreted as "at … …" or "at … …" depending on the context.

In an embodiment of the invention, the method steps may be performed in another order. The invention is not limited to the order in which the steps of the method are performed.

Since the original factory does not directly provide an external command to obtain the threshold voltage distribution of the cell, the read voltage distribution is usually unknown, and the conventional solution is that a set of separate attempts is usually made during the actual use of readretry to recover data until a set of readretry methods capable of correctly reading data can be found. The existing method for selecting readretry is a polling strategy, when data has errors, from a first group of trial to a last group of a plurality of groups of readretys given by an original factory, polling is stopped if one group of readretys can correct the data correctly. The method has great blindness, and particularly when the number of ready sets provided by the original factory is large, the scheme can cause the time for correctly recovering the data to be greatly prolonged.

Therefore, the invention provides a method for quickly and effectively finding the optimal readtry.

Specifically, referring to the flowchart of the first embodiment of the method for fast finding the optimal re-reading voltage of the NAND flash memory proposed by the present invention in fig. 1, in one embodiment of the present invention, the proposed method comprises the following steps:

A. respectively determining the number of bit reversals of all data in at least one page in the NAND flash memory under all possible read voltage values;

B. setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median value of all data values in the first reading voltage data set as the optimal rereading voltage;

C. and if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory, applying the optimal rereading voltage to the NAND flash memory. Specifically, the case where bit inversion occurs means that data "0" is read out as "1" or vice versa and data "1" is read out as "0". Specifically, in one embodiment of the present invention, the above-mentioned "median value" may be in the meaning of an average value.

Further, in one embodiment of the present invention, data in at least one page in the NAND flash memory is randomly distributed, and a duty ratio of data "0" and a duty ratio of data "1" are both 50%. The randomly distributed data can avoid the influence of the stored data on finding the optimal rereading voltage, and can reflect the data storage condition of the universal flash memory, namely, the probability of the occurrence of the data "0" and the data "1" is basically the same and is 50% in the general condition without considering the particularity of the stored data.

Further, in an embodiment of the present invention, the data size that each memory cell in the NAND flash memory can hold is 1bit, that is, the NAND flash memory is an SLC NAND flash memory.

Specifically, referring to the flowchart of the second embodiment of the method for fast finding the optimal re-reading voltage of the NAND flash memory proposed by the present invention in fig. 2, in one embodiment of the present invention, the proposed method comprises the following steps:

a', writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

b', respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results, and respectively calculating the number of read-out 1;

c ', reading out the absolute value of the difference between the numbers of the adjacent two times as ' 1 ', and determining one or more reading voltage values corresponding to the minimum absolute value as an optimal re-reading voltage data set.

Preferably, referring to the flowchart of fig. 3 of a third embodiment of a method for quickly finding an optimal rereading voltage of a NAND flash memory, in an embodiment of the present invention, when the number of data in the optimal rereading voltage data set is greater than 1, after the step C 'is performed, a step D' is further included, where an absolute value of a difference between the numbers of "1" and a reading voltage value is taken as an abscissa, and a two-dimensional scatter plot is drawn.

Specifically, in one embodiment of the present invention, the number of all possible read voltages is 256.

Preferably, in a preferred embodiment of the present invention, an SLC page is taken as an example to describe a method for specifically drawing a cell threshold voltage distribution near an default read voltage in the page. The SLC type page cell has only two states of "0" and "1", and the read voltage is used to distinguish the state of each cell as "0" or "1", and due to the influence of the NAND flash write mechanism, the threshold voltage of a cell in a page should be approximately normally distributed. The detailed steps of the preferred embodiment are as follows:

1. and writing a whole page of random data into the slc page to be tested. In general, in the actual use process, the original factory will require that the written data of all pages are random, and the random data at least meets the condition that the proportion of data "0" and data "1" is 50%;

2. the read voltage is shifted from left to right by using a set offset command provided by the original factory, and the original data of the page is read out once every shift, and the number of '1' is calculated. Assuming that the set offset command provided by the factory can shift the read voltage 256 times, the obtained data can be filled into the table shown in table 1 below;

3. taking the absolute value of the difference of the number of the adjacent two times of '1'; the difference in the number of "1" s may indirectly reflect the number of bit reversals;

4. drawing a scatter diagram by taking the first column of the table as an abscissa and the third column as an ordinate, wherein the diagram can reflect the variation trend of the threshold voltage in the page, as shown in FIG. 4;

5. the appropriate location of the read voltage is found from the profile and compared to the readretry value provided by the foundry to obtain a set of readretries closest to this value.

TABLE 1

Specifically, referring to fig. 4, a rereading voltage distribution scatter diagram of a fourth embodiment of a method for quickly finding an optimal rereading voltage of a NAND flash memory is shown, in the diagram, a threshold voltage distribution of an SLC page is plotted within a range of 127 resolutions (one resolution represents a vendor-defined voltage scale) around a default reading voltage, an abscissa is a relative position to the default reading voltage, and a 0 scale is a position of the default reading voltage. It can be seen that the distribution boundary is far from scale 0, meaning that "0" and "1" in the cell can be well distinguished by the default read voltage, and data can be correctly read with the default voltage. There is no need to enter a readretry flow.

However, in practical use, the distribution of data in the NAND flash memory is shifted due to read-write interference, high and low temperatures, etc., and the drawn distribution may be as shown in fig. 5, where the default read voltage is within the distribution of data "0", so that the data read by the default read voltage will have bit reversal, and the read voltage should be shifted to the left to better distinguish the distribution of "0" and "1". The reading voltage should be shifted left by about 25 units to correctly read the data, and the readretry method of shifting left by approximate scales can be selected to recover the data by referring to the readretry method provided by a manufacturer.

In particular, in both fig. 4 and fig. 5, only one of the distributions, namely the right data "0" distribution, can be seen, because the SLC page "0" distribution and "1" distribution are far away, and the read voltage offset range provided by the original factory is limited, the left data "1" distribution is not within the read voltage setting range, and it is not necessary to set the read voltage within the data "1" distribution range in the preferred embodiment.

It should be understood that the NAND flash memory used according to the proposed method of the present invention is preferably SLC NAND flash memory, but other types of flash memory can be used without departing from the spirit of the present invention, and is not limited to SLC NAND flash memory, such as MLC NAND flash memory, TLC NAND flash memory, etc.

Specifically, referring to fig. 6, a first frame diagram of an apparatus for fast finding an optimal re-reading voltage of a NAND flash memory is provided, and in an embodiment of the present invention, the apparatus includes the following modules:

the initialization module is used for respectively determining the number of bit reversals of all data in at least one page in the NAND flash under all possible read voltage values;

the judging module is used for setting one or more reading voltage values corresponding to the minimum bit reversal number as a first reading voltage data set, and taking the median of all data values in the first reading voltage data set as the optimal rereading voltage;

and the target determining module is used for applying the optimal rereading voltage to the NAND flash memory if the optimal rereading voltage is within the rereading voltage range in the NAND flash memory.

Preferably, in an embodiment of the present invention, the data in at least one page of the NAND flash memory in the above apparatus is randomly distributed, and the duty ratio of data "0" and the duty ratio of data "1" are both 50%.

Preferably, in an embodiment of the present invention, the amount of data that can be placed in each memory cell in the NAND flash memory in the above apparatus is 1bit, that is, the NAND flash memory is an SLC NAND flash memory.

Specifically, referring to fig. 7, a second frame diagram of an apparatus for fast finding the optimal re-reading voltage of the NAND flash memory is provided, and in an embodiment of the present invention, the apparatus includes the following modules:

the random writing module is used for writing random data of a whole page into at least one SLC page in the NAND flash memory to be tested;

the reading test module is used for respectively reading all data in at least one page in the NAND flash memory by using all possible reading voltages, respectively recording reading results and respectively calculating the number of read-out 1;

and the optimum searching module is used for searching the absolute value of the difference between the numbers which are read out as 1' twice in two adjacent times and determining one or more reading voltage values corresponding to the minimum absolute value as the optimum re-reading voltage data set.

Preferably, in one embodiment of the present invention, the number of all possible read voltages is 256.

Preferably, in an embodiment of the present invention, when the number of data in the optimal reread voltage data set is greater than 1, the finding module further includes a drawing module, configured to draw a two-dimensional scatter plot by taking the read voltage value as an abscissa and taking an absolute value of a difference between the numbers of "1" as an ordinate. Thus, the distribution situation can be known more intuitively.

Finally, the invention proposes a computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the above-mentioned method.

In summary, the following effects can be achieved by executing the steps of the method provided by the present invention:

1. the threshold voltage distribution of a cell in a page can be visually drawn and is used for analyzing the data state in the page;

2. the optimal readretry method can be visually selected according to the threshold voltage distribution of one page, blind try on readretry is not needed, and data recovery time is greatly shortened.

It should be recognized that embodiments of the present invention can be realized and implemented by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer readable memory. The methods may be implemented in a computer program using standard programming techniques, including a non-transitory computer-readable storage medium configured with the computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner, according to the methods and figures described in the detailed description. Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the program(s) can be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language. Furthermore, the program can be run on a programmed application specific integrated circuit for this purpose.

Further, the method may be implemented in any type of computing platform operatively connected to a suitable interface, including but not limited to a personal computer, mini computer, mainframe, workstation, networked or distributed computing environment, separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, and the like. Aspects of the invention may be implemented in machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optically read and/or write storage medium, RAM, ROM, etc., so that it can be read by a programmable computer, which when read by the computer can be used to configure and operate the computer to perform the procedures described herein. Further, the machine-readable code, or portions thereof, may be transmitted over a wired or wireless network. The invention described herein includes these and other different types of non-transitory computer-readable storage media when such media include instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor. The invention also includes the computer itself when programmed according to the methods and techniques described herein.

Embodiments of this disclosure are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those described embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments of the disclosure to be practiced otherwise than as specifically described herein. Accordingly, the scope of the present disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, the scope of the present disclosure encompasses any combination of the above-described elements in all possible variations thereof unless otherwise indicated herein or otherwise clearly contradicted by context.

While the present invention has been described in considerable detail and with particular reference to a few illustrative embodiments thereof, it is not intended to be limited to any such details or embodiments or any particular embodiments, but it is to be construed as effectively covering the intended scope of the invention by providing a broad, potential interpretation of such claims in view of the prior art with reference to the appended claims. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalent modifications thereto.

The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. However, it will be apparent that: various modifications and changes may be made thereto without departing from the broader spirit and scope of the application as set forth in the claims.

Other variations are within the spirit of the present application. Accordingly, while the disclosed technology is susceptible to various modifications and alternative constructions, certain embodiments thereof have been shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the application to the specific form or forms disclosed; on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the application, as defined in the appended claims.