KR20090110648A - How to write data to flash memory, how to read data recorded in flash memory, and flash memory system - Google Patents

Abstract

The present invention relates to a flash memory system using Trellis Coding Modulation (TCM) and a method of writing and reading data in a flash memory system. The data is written after TCM encoding the data into the flash memory. According to the present invention, errors occurring during the process of writing or reading data to and from the flash memory can be reduced.

Description

How to Write Data to Flash Memory, How to Read Data Written to Flash Memory, and Flash Memory System {Flash Memory System Using Tresllis Coding Modulation}

The present invention relates to a method of writing data to a flash memory, a method of reading data written to a flash memory, and a flash memory system. The present invention relates to a data writing / reading method and a flash memory system applicable when data is written to or read from an integrated multi-level cell (MLC) type flash memory.

Flash memory is widely used in embedded systems and mobile devices because it has a non-volatile, fast access speed and consumes less power like a hard disk.

In consideration of its hardware characteristics, the flash memory must first perform an operation of erasing the entire block containing the sector in order to perform a write operation on an already written memory sector. Partial programming is also possible, where data is written to only part of the pages that make up a flash memory block.

Devices using flash memory are increasing. For example, MP3 players, digital cameras, portable terminals, camcorders, solid state drives (SSD), and the like use flash memory as storage.

1 is a diagram illustrating the structure of a general flash memory system. The flash memory 10 includes a plurality of flash memories 10 capable of recording data to be written by the host 30, and a flash controller 20 that accesses the flash memory 10 to write or read data.

However, there is a problem that an error occurs in writing data as the flash memory 10 is integrated. In addition, when reading data written to the flash memory 10, an error occurs due to interference between adjacent transistors.

The flash controller 20 may also write ECC to the flash memory 10 to correct an error occurring in the data recorded in the flash memory 10. However, when recording the ECC, there is a problem that the amount of data to be written to the flash memory 10 increases.

The present invention reduces the probability of error occurring when writing data to the flash memory. In addition, the present invention reduces the probability of error in the process of reading data from the flash memory. In addition, the present invention does not need to use ECC to correct an error occurring in the data recorded in the flash memory.

The flash memory system according to the present invention for solving the above problems is a flash memory system comprising a flash memory and a flash controller for writing or reading data to and from the flash memory, wherein the data requested by a host is written by Trellis Coding Modulation And encoded in the flash memory.

According to an aspect of the present invention, a method of writing data into a flash memory includes at least one block having pages composed of a predetermined number of sectors, and writes data in units of sectors or pages, and blocks the data. A method of writing data to a flash memory for erasing data on a per-unit basis, the method comprising: performing trellis coding modulation (TCM) coding on data requested by a host in a write operation; And writing the encoded data to a main area of the flash memory page.

According to the present invention, a method of reading data written in a flash memory according to the present invention is a method of reading data from a flash memory in which data is written by the above method, and corresponds to a logical address requested for a read operation from a host. Mapping the resulting physical address; Reading data written to the physical address; And transmitting the read data to the host by TCM decoding.

According to the present invention, TCM encoding is performed before data is written to the flash memory. In the process of recording the TCM-coded data in the flash memory, ECC recording necessary for correcting the recording data error can be omitted. Also, data is read from the flash memory and then decoded by TCM. Therefore, as the flash memory becomes smaller, it is possible to prevent an error from occurring in the process of reading data.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

2 shows the structure of an actual flash memory. As shown, one flash memory consists of 8192 blocks. The block is composed of 32 pages, and one page may be divided into a main region of 512B and an auxiliary region of 16B. In the main area, user data is usually recorded and can be viewed as a set of sectors. In the auxiliary area, information on the validity of data recorded in the main area, ECC, Logical Block Address (LBA) or Logical Sector Number (LSN), erase count, and the like are recorded.

In the present invention, TCM encoding is performed before data is written to the flash memory. Therefore, the process of describing the ECC in the auxiliary region can be omitted.

FIG. 2 illustrates a small block flash memory in which a write / read unit of a flash memory and a write / read unit requested by an external host match. However, the present invention can also be applied to a large block flash memory in which the write / read unit of the flash memory is larger than the write / read unit requested by the external host. In the case of large block flash memory, the main area is composed of four sectors. In large block flash memory, data is recorded in sector units or page units.

Memory cells of a flash memory are classified into a single level cell (SLC) and a multi level cell (MLC) according to the number of data bits that can be stored. The single level cell SLC may store one bit data, and the multi level cell MLC may store multi bit data.

The multi-level cell MLC is programmed to have any one of four states 11, 10, 01, 00 according to the threshold voltage distribution. 2-bit data is written to the multi-level cell according to the threshold voltage distribution of the multi-level cell MLC.

FIG. 3 illustrates 2-bit data information stored in the multi-level cell MLC according to the threshold voltage distribution of the multi-level cell MLC.

Assuming that the threshold voltage distributions of the multi-level cell (MLC) are -2.7 V or less, 0.3 V to 0.7 V, 1.3 V to 1.7 V, and 2.3 V to 2.7 V, respectively, [11] is -2.7 V or less, [10] Is 0.3 to 0.7V, [01] corresponds to 1.3V to 1.7V, and [00] corresponds to 2.3V to 2.7V.

In a flash memory system having a multi-level cell (MLC), a constant amount of bit line current and a step waveform word line voltage are applied to a cell array to read data. The data of the far-level cell MLC is sensed by the current difference when the bit line current and the word line voltage flow through the selected cell. During a read operation for reading data, voltages of stepped waveforms are sequentially applied to word lines in order from high voltage to low voltage.

In order to read data in a multi-level cell (MLC) having a threshold voltage distribution as in the present embodiment, V _rd3 = 2V is applied, then V _rd2 = 1V, and finally V _rd1 = 0V.

4 is a flowchart illustrating a method of writing data into a flash memory. As shown, when a data write operation request is made by the host (S11), the data transmitted for writing to the flash memory by the host is TCM encoded (S12). That is, the data requested by the host is recorded (programmed) in the flash memory after the TCM encoding process (S13).

As in the present invention, when data is written to the flash memory after TCM encoding, it is not necessary to write additional bits (ECC, etc.) in the additional area in order to perform error correction in a subsequent data reading process.

That is, as shown in FIG. 5, user data to be recorded by the host is recorded in the main area M1 of the general flash memory page a, and user data is called in the auxiliary area S1. The logical address LNA and error correction code ECC are recorded.

In the case of recording the TCM encoded data in the flash memory according to the present invention, as shown in (b), an error correction code for correcting user data recorded in the main area M2 is recorded in the auxiliary area S2. no need. Of course, if necessary, the ECC may be recorded in the auxiliary area so that an error occurrence rate occurring during data writing or reading is reduced.

6 is a diagram illustrating a process of reading data written to a flash memory according to the present invention.

When the host requests a data read operation (S21), the physical address corresponding to the logical address called by the host is mapped and selected, and a data read command written to the physical address is transmitted to the flash memory (S22).

When data is read from the flash memory, TCM decryption is performed (S23), and the decrypted data is transmitted to the host (S24). According to the present invention, the reference voltages for configuring the TCM decoder are taken as an intermediate value of voltages at which each write data bit can be detected without error. That is, the intermediate value of the threshold voltage range applied to the flash memory to represent each data bit is the reference voltage for configuring the TCM decoder.

In addition, since the amount of electrons accumulated in the multi-level cell (MLC) can be easily discriminated, the middle value of the threshold voltage range is set as a reference voltage for configuring the TCM decoder so as to correspond to the variable amount of electrons. .

7 is a diagram showing a first embodiment of a flash memory system according to the present invention.

As shown, the flash memory system writes data to the flash memory 100 in response to a data write / read operation request of the host 300, or reads the data recorded in the flash memory 100. It consists of.

The flash controller 200 includes a TCM encoder 210 and a TCM decoder 220 capable of TCM encoding or decoding data transmitted from a host in a process of writing or reading data into a flash memory.

The flash controller 200 further includes a buffer 230 in which data input / output to the flash controller is stored so that data can be encoded or decoded.

The flash controller 200 controls the flash memory 100 to write data to the flash memory cell array 110 in response to a write operation request input from the host 300. Also, the flash controller 200 controls the flash memory 100 to read data written in the flash memory cell array 110 in response to a read operation request input from the host 300. The buffer 230 of the flash controller 200 temporarily stores data to be written to the flash memory 100 or data read from the flash memory 100.

The flash memory 100 includes a flash memory cell array 110, a page buffer 120, a bit line selector 130, a decoder 140, a data buffer 150, and a control unit 160.

The flash memory cell array 110 is composed of a plurality of memory cells. The memory cell is nonvolatile, and the data is not erased even when the power is turned off after storing the data. One memory cell is composed of a plurality of memory blocks. Each memory block is composed of a plurality of pages. In the case of a NAND flash memory, erase operations are performed in units of memory blocks, and write and read units are performed in units of pages.

The decoder 140 is connected to the flash memory cell array 110 through word lines WL0 to WLn and controlled by the control unit 160. The decoder 140 receives the address ADD through the flash controller 200 and selects a single word line or selects the selection signal Yi from the bit line selector 130 to select bit lines BL0 to BLm. ). The page buffer 120 is connected to the flash memory cell array 100 through bit lines BL0 to BLm.

The page buffer 120 stores data transmitted from the flash controller 200. One page of data is loaded into the page buffer 120, and the loaded data simultaneously writes data to a selected page during a program (data recording) operation. In addition, the page buffer 120 reads data from a page during a read operation and stores the read data.

The bit line selector 130 is a circuit for selecting a bit line in response to the selection signal Yi. The data buffer 150 is a data input / output buffer used for data transfer between the flash controller 200 and the flash memory 100. The control unit 160 receives a control signal from the flash controller 200 and controls the internal operation of the flash memory 100 in response thereto.

In the embodiment of FIG. 7, the TCM encoder 210 and the TCM decoder 220 are located in the flash controller 200.

However, if necessary, as in the second embodiment of FIG. 8, the TCM encoder 161 and the TCM decoder 162 may be included in the control unit 160 of the flash memory 100.

The TCM encoder 161 performs TCM encoding on the data stored in the data buffer 150 before being written to the flash memory cell array 110. In the data read operation, the TCM decoder 162 performs TCM decoding before transmitting the data stored in the data buffer 150 to the flash controller 200.

9 and 10 show the third and fourth embodiments of the flash memory system according to the present invention.

As shown, the TCM encoder 240 is positioned inside the flash controller 200. Therefore, when the data write operation request is received from the host 300, the data is encoded through the TCM encoder 240 and transmitted to the flash memory 100.

The control unit 160 writes the data stored in the data buffer 150 to the flash memory cell array 110.

When the host 300 requests a data read operation, the flash controller 200 transmits a read command to the control unit 160 of the flash memory 100. The control unit 160 selects a page to read data through the decoder 140 and the bit line selector 130 and reads out the data.

In the third embodiment, the TCM decoder performs TCM decoding before the read data is stored in the page buffer 120. Therefore, it is possible to prevent an error from occurring in the process of reading data.

The TCM decoded data is stored in the page buffer 120 and then transmitted to the flash controller 200 through the data buffer 150. The flash controller 200 transmits the transmitted data to the host 300.

FIG. 10 is a diagram illustrating the location of the TCM encoder 164 and the TCM decoder 165 in the flash memory 100.

As shown, the TCM encoder 164 inside the control unit 160 performs TCM encoding on data written in the data buffer 150 and writes the data in the flash memory cell array 110.

When a data read operation of a flash memory in which TCM encoded data is stored is requested, when data is read from the flash memory cell array 110, the data is decoded by the TCM decoder 165 before being stored in the page buffer 120.

The TCM decoded data is stored in the page buffer 120 and then transmitted to the flash controller 200 through the data buffer 150. The flash controller 200 transmits the transmitted data to the host 300.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. You will understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a block diagram showing the structure of a flash memory system to which the present invention is applied;

2 is a diagram showing the structure of a flash memory to which the present invention is applied;

3 is a diagram illustrating a state of a flash memory according to the present invention;

4 illustrates a method of writing data into a flash memory according to the present invention;

5 is a diagram illustrating data written in a flash memory page according to the present invention;

6 illustrates a method of reading data written to a flash memory according to the present invention;

7 to 10 are diagrams showing the structure of a flash memory system according to the present invention.

Claims (11)

A flash memory system comprising a flash memory and a flash controller that writes or reads data to and from the flash memory. Flash memory system, characterized in that the write operation request data from the host is Trellis Coding Modulation (TCM) coded to be written to the flash memory. The method of claim 1, The flash controller includes: a TCM encoder for TCM encoding data requested for write operation in the host; And And a TCM decoder configured to TCM decode data read from the flash memory when a read operation is requested by the host. The method of claim 2, The flash controller may further include a buffer configured to store data that is requested to be written by the host or data that is read from the flash memory. The method of claim 1, The flash memory includes a flash memory cell array; A data buffer storing data to be written to the flash memory cell array or data read from the memory cell array; And a control unit for performing TCM encoding on the data stored in the data buffer before writing data to the cell array, and decoding the TCM before transmitting the data to the flash controller. The method of claim 1, The flash controller system comprises a TCM encoder for TCM encoding the data requested write operation from the host. The method of claim 5, wherein The flash memory may include a flash memory cell array in which TCM encoded data is written by the flash controller; A TCM decoder for TCM decoding the data read from the flash memory cell array; A data buffer in which the TCM decoded data is stored; And And a control unit which transmits the data stored in the data buffer to the flash controller. The method of claim 1, The flash memory includes a flash memory cell array; A data buffer in which data to be written to the flash memory cell array is stored; And a control unit for TCM encoding data stored in the data buffer and writing the data to the flash memory cell array. The method of claim 7, wherein The flash memory further includes a TCM decoder for TCM decoding data read from the flash memory cell array, And the control unit transmits the TCM decoded data stored in the data buffer to the flash controller. 10. A method of writing data in a flash memory having at least one block having pages composed of a predetermined number of sectors, writing data in units of sectors or pages, and erasing data in units of blocks. Performing Trellis Coding Modulation (TCM) encoding on the data requested by the host for write operation; And And writing the coded data to a main area of the flash memory page. The method of claim 9, And the data writing step omits ECC recording necessary for error correction occurring when writing the encoded data in an additional area of the flash memory page. A method of reading data from a flash memory in which data is written by claim 9, Mapping a physical address corresponding to a logical address requested for a read operation in a host; Reading data written to the physical address; And TCM decoding the read data and transmitting the read data to the host.

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