Abstract:
A method for controlling access operations of a flash memory includes: receiving first source data from a host; generating a plurality of first scrambled signals according to a plurality of pseudo random sequences and the first source data; obtaining a plurality of transmission powers of the first scrambled signals; and selecting a target scrambled signal from the first scrambled signals according to the transmission powers for storing to the flash memory. An associated flash memory device and an associated flash memory controller are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 12/692,618 filed on Jan. 24, 2010, the entirety of which is incorporated by reference herein. The U.S. patent application Ser. No. 12/692,618 claims the benefit of U.S. Provisional Application No. 61/222,465, filed on Jul. 1, 2009. 
     The U.S. patent application Ser. No. 12/692,618 claims priority of Taiwan Patent Application No. 98126689, filed on Aug. 10, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to memories, and more particularly to data access of memories. 
     2. Description of the Prior Art 
     Before data is written to a memory, a controller of the memory usually scrambles the data with a scrambler, thus making bits  0  and  1  to have a random distribution in the data. The scrambled data is then stored in the memory, thus preventing bits  0  and  1  from massing in a specific segment of the data. For example, a flash memory is classified into a single-level-cell (SLC) flash memory or a multi-level-cell (MLC) flash memory. When data is written to a MLC flash memory, if the data comprises segments comprising massed bits  0  or massed bits  1 , an error bit rate of the data is increased. A controller of the MLC flash memory therefore has to scramble the data before the data is written to the MLC flash memory. 
     The data scrambled by a scrambler, however, has deficiency. A controller usually transmits data to a flash memory via a data bus. When the controller sends a data bit  1  to the flash memory, a voltage level of the data bus is increased to a logic high level. When the controller sends a data bit  0  to the flash memory, the voltage level of the data bus is decreased to a logic low level. Because bits  0  and  1  in scrambled data have randomized distributions, when the controller sends the scrambled data to the memory for storage via the data bus, the voltage level on the data bus frequently oscillates between the logic high level and the logic low level. The data bus therefore requires high power due to the frequent oscillation of voltage levels thereon, thus increasing power consumption of a system. When the system comprising the controller and the memory is a portable device with a battery power supply, the time span in which the system operates under a normal voltage supply is shorten, thus degrading the performance of the system. Thus, a controller which can scramble data with low power consumption is desired. 
     SUMMARY OF THE INVENTION 
     According to at least one preferred embodiment of the present invention, a flash memory device is disclosed. The flash memory device comprises: a flash memory; and a controller, coupled to the flash memory, receiving first source data from a host, generating a plurality of first scrambled signals according to a plurality of pseudo random sequences and the first source data, obtaining a plurality of transmission powers of the first scrambled signals, and selecting a target scrambled signal from the first scrambled signals according to the transmission powers for storing to the flash memory. 
     According to at least one preferred embodiment of the present invention, a flash memory controller for controlling access operations of a flash memory is disclosed. The flash memory controller receives first source data from a host and comprises: a plurality of scramblers, for generating a plurality of first scrambled signals according to a plurality of pseudo random sequences and the first source data; a transmission power calculation module, for obtaining a plurality of transmission powers of the first scrambled signals; and a selector, for selecting a target scrambled signal from the first scrambled signals according to the transmission powers for storing to the flash memory. 
     According to at least one preferred embodiment of the present invention, a method for controlling access operations of a flash memory is disclosed. The method comprises: receiving first source data from a host; generating a plurality of first scrambled signals according to a plurality of pseudo random sequences and the first source data; obtaining a plurality of transmission powers of the first scrambled signals; and selecting a target scrambled signal from the first scrambled signals according to the transmission powers for storing to the flash memory. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a data storage device according to the invention; 
         FIG. 2  is a block diagram of a write-data processing circuit of a controller according to the invention; 
         FIG. 3  is a flowchart of a method for processing data to be written to a memory according to the invention; 
         FIG. 4  is a circuit diagram of a transmission power calculation module according to the invention; 
         FIG. 5  is a block diagram of a read-data processing circuit of a controller according to the invention; 
         FIG. 6  is a flowchart of a method for processing data read out from a memory according to the invention; and 
         FIG. 7  is a schematic diagram of an embodiment of a data access method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     Referring to  FIG. 1 , a data storage device  104  according to the invention is shown. The data storage device  100  is coupled to a host  102  and accesses data according to instructions from the host  102 . In one embodiment, the data storage device  104  comprises a controller  112  and a memory  114 . The memory  114  is for data storage. The controller  112  accesses data stored in the memory  114  according to instructions sent by the host  102 . In one embodiment, a data bus is coupled between the controller  112  and the memory  114  for data transmission. For example, when the host  102  wants to store data D 1  to the data storage device  104 , the controller  112  first receives data D 1  from the host  102 , then encodes the data D 1  to obtain an error correction code C 1 , and then sends the error correction code C 1  to the memory  114  for storage. When the host  102  wants to read data from the data storage device  104 , the controller  112  directs the memory  114  to read an error correction code C 2  stored therein, then decodes the error correction code C 2  to obtain data D 2 , and then sends the data D 2  to the host  102 . 
     Before the controller  112  stores the data D 1  to the memory  114 , the controller  112  scrambles the bits  0  and  1  of the data D 1 , thus making the bits  0  and  1  of the scrambled data have randomized distributions, and making the scrambled data have a characteristic that is consuming lower power during being transmitted. The scrambled data is then encoded to obtain the error correction code C 1 . Thus, when the data bus transmits the error correction code C 1  from the controller  112  to the memory  114 , the transmission power required by the data bus is reduced. Similarly, because the error correction code C 2  is stored in a format with a low transmission power in the memory  114 , when the data bus transmits the error correction code C 2  from the memory  114  to the controller  112 , the data bus requires less power to transmit the error correction code C 2 . The data storage device  104  therefore consumes a less power than that of a conventional data storage device. The data storage device  104  therefore has improved performance in comparison with a conventional data storage device. 
     Referring to  FIG. 2 , a block diagram of a write-data processing circuit of a controller  200  according to the invention is shown. The other circuit components irrelevant to processing of write data are omitted in  FIG. 2 . In one embodiment, the controller  200  comprises a plurality of scramblers  201 ˜ 20 N, a transmission power calculation module  212 , a selector  214 , an index appending module  216 , and an error correction code (ECC) encoder  218 . Referring to  FIG. 3 , a flowchart of a method  300  for processing data to be written to a memory  114  according to the invention is shown. The controller  200  processes data received from the host  102  according to the method  300  shown in  FIG. 3 . First, the controller  200  receives source data D 1  to be written to the memory  114  from the host  102  (step  302 ). The scramblers  201 ,  202 , . . . ,  20 N then respectively scramble the data D 1  according to a plurality of pseudo random sequences M 1 , M 2 , . . . , M N  to obtain a plurality of scrambled signals S 1 , S 2 , . . . , S N  (step  304 ). In one embodiment, the scramblers  201 ˜ 20 N respectively performs XOR operations on the data D 1  and the plurality of pseudo random sequences M 1 , M 2 , . . . , M N  to obtain the scrambled signals S 1 , S 2 , . . . , S N . Because the bits  0  and  1  in the scrambled signals S 1 , S 2 , . . . , S N  have random distributions, the scrambled signals S 1 , S 2 , . . . , S N  have low error bit rates when the scrambled signals S 1 , S 2 , . . . , S N  are stored in the memory  114 . 
     The transmission power calculation module  212  then calculates a plurality of transmission powers of the scrambled signals S 1 , S 2 , . . . , S N  to be transmitted on the data bus (step  306 ). The transmission power calculation module  212  then selects a target scrambled signal with the lowest transmission power from the scrambled signals S 1 , S 2 , . . . , S N  (step  308 ), and then outputs an index I 1  of a target pseudo random sequence corresponding to (for generating) the target scrambled signal. In one embodiment, the number of the pseudo random sequences M 1 , M 2 , . . . , M N  is N, and the bit number of the index I 1  of the target pseudo random sequence is less than Log 2 N. The selector  214  then selects the target scrambled signal J 1  with the lowest transmission power from the scrambled signals S 1 , S 2 , . . . , S N  according to the index I 1 . The index appending module  216  then appends the index I 1  to the end of the target scrambled signal J 1  to obtain an output data K 1  (step  310 ). The error correction code encoder  218  then encodes the output data K 1  to obtain an error correction code C 1  to be stored in the memory  114  (step  312 ). Because the error correction code C 1  has the same bit content with that of the target scrambled signal except for a parity and the index I 1 , the data bus transmits the error correction code C 1  to the memory  114  with a low transmission power. 
     Referring to  FIG. 4 , a circuit diagram of a transmission power calculation module  400  according to the invention is shown. The transmission power calculation module  400  comprises a delay unit  402 , an XOR gate  404 , and a counter  406 . Assume that the transmission power calculation module  400  receives a scrambled signal S k  from a scrambler, wherein the index k may be selected from the numbers 1˜N. The delay unit  402  delays the scrambled signal S k  by a clock period to obtain a delayed signal S k ′. The XOR gate  404  then performs an XOR operation on the delayed signal S k ′ and the scrambled signal S k  to obtain a transition signal T. When the bit of the scrambled signal S k  changes from the value 0 to the value 1 or from the value 1 to the value 0, the transition signal has a corresponding value of 1. The counter  406  then accumulates the transition signal to count the number CN of times of value changes of the scrambled signal S k . Thus, when the number CN of times of value changes of the scrambled signal S k  is high, the data bus requires a high power to transmit the scrambled signal S k . 
     Referring to  FIG. 5 , a block diagram of a read-data processing circuit of a controller  500  according to the invention is shown. In one embodiment, the controller  500  comprises an error correction code (ECC) decoder  502 , an index separation module  504 , a selector  506 , and a descrambler  508 . Referring to  FIG. 6 , a flowchart of a method  600  for processing data read out from the memory  114  according to the invention is shown. The controller  500  processes data read out from the memory  114  according to the method  600  and then delivers the processed data to the host  102 . First, when the controller  500  receives a read command from the host  102 , the controller  500  directs the memory  114  to read an error correction code C 2 . After the controller  500  receives the error correction code C 2  from the memory  114 , the ECC decoder  502  then decodes the error correction code C 2  to obtain output data K 2  (step  602 ). 
     Because the output data K 2  comprises a scrambled signal and an index of a target pseudo random sequence, the index separation module  504  retrieves the scrambled signal J 2  and the index I 2  of the target pseudo random sequence from the output data K 2  (step  604 ). The selector  506  then selects the target pseudo random sequence M* from a plurality of pseudo random sequences M 1 , M 2 , . . . , M N  according to the index I 2  (step  606 ). The descrambler  508  then descrambles the scrambled signal J 2  according to the target pseudo random sequence M* to obtain source data D 2  (step  608 ). In one embodiment, the descrambler  508  performs an XOR operation on the bits of the scrambled signal J 2  and the target pseudo random sequence M* to obtain the source data D 2 . Finally, the controller  500  sends the source data D 2  to the host  102  to complete the read operation. 
     Referring to  FIG. 7 , a schematic diagram of an embodiment of a data access method according to the invention is shown. Assume that the controller  112  receives source data D 1  to be written to the memory  114  from the host  102 , as shown in (a) of  FIG. 7 . The controller  112  then converts the source data D 1  to scrambled signal J 1  shown in (b) of  FIG. 7 , wherein the scrambled signal J 1  has the lowest transmission power. The controller  112  then appends an index K 1N  of a pseudo random sequence and a parity to the end of the scrambled signal J 1  to obtain an error correction code C 1 , as shown in (b) of  FIG. 7 . The plurality of pseudo random sequences M 1 , M 2 , . . . , M N  shown in  FIG. 2  have the same data length as the source data D 1 , and the controller  112  must comprise buffers to store the pseudo random sequences M 1 , M 2 , . . . , M N . To shorten the buffer length of the controller  112 , the data lengths of the source data D 1  and the pseudo random sequences M 1 , M 2 , . . . , M N  are reduced, thus reducing hardware costs of the controller  112 . 
     In another embodiment, the controller  112  divides the source data D 1  (e.g. data length of the source data D 1  is a page) into a plurality of segments D 11 , D 12 , . . . , D 1N , as shown in (c) of  FIG. 7 . Each segment D 11 , D 12 , . . . , D 1N  has a data length equal to 1/N of that of the source data D 1 . The controller  112  then sequentially scrambles the segments D 11 , D 12 , . . . , D 1N  to obtain scrambled signals J 11 , J 12 , . . . , J 1N , as shown in (d) of  FIG. 7 . The controller  112  then combines the indexes K 11 , K 12 , . . . , K 1N  of the pseudo random sequences with the scrambled signals J 11 , J 12 , . . . , and J 1N , to obtain the error correction code C 1 ′, as shown in (e) of  FIG. 7 . Because each of the segments D 11 , D 12 , . . . , D 1N  has a data length equal to 1/N of the source data D 1 , the data lengths of the buffers of the controller  112  are also equal to 1/N of the source data D 1  to hold the pseudo random sequences M 1 , M 2 , . . . , M N , thus reducing hardware costs of the controller  112 . 
     In another embodiment, encoding of an error correction code and scrambling of data are simultaneously performed. After the index appending module  216  appends the index K 11  to the end of the scrambled signal J 11 , the error correction code encoder  218  simultaneously encodes the scrambled signal J 11  and the index K 11  to obtain an error correction code C 11  comprising a parity P 11 . When the error correction code encoder  218  generates the error correction code C 11 , the scrambler  201 ˜ 20 N scrambles the segment D 12 , and the transmission power calculation module  212  and the selector  214  selects a scrambled signal J 12  with the lowest transmission power. Similarly, when the error correction code encoder  218  generates the error correction code C 12 , the scrambler  201 ˜ 20 N scramble the segment D 13 , and the transmission power calculation module  212  and the selector  214  selects a scrambled signal J 13  with the lowest transmission power. Thus, encoding of an error correction code and scrambling of data are simultaneously performed to improve performance of the controller  200 . 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.