Abstract:
A memory device comprises first memory block having first boundary cell and second memory block having second boundary cell. Data of the first and the second boundary cells are outputted simultaneously corresponding to a plurality of column selection signals.

Description:
[0001]    This application is a continuation application of co-pending application Ser. No. 12/391,351, filed on Feb. 24, 2009, which claims priority to provisional application Ser. No. 61/048,247, filed Apr. 28, 2008. These related applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates in general to a memory control circuit, and more particularly to a memory control circuit performing erase verification operation on a memory array of a memory. 
         [0004]    2. Description of the Related Art 
         [0005]    Referring to  FIG. 1 , a schematic illustration of a conventional memory is shown. In an example, a memory array MA includes memory banks BNK 0  to BNKN, each of which includes M memory blocks, wherein N is a natural number greater than 1 and M is a natural number greater than 1. For example, the memory bank BNK 0  includes memory blocks BLO 1  to BLOM. Since an erase process and an erase verification process performed on each of the memory blocks BLO 1  to BLOM are similar, only the process performed on the memory block BLO 1  is cited as an example described in the following paragraphs. 
         [0006]    The memory block BLO 1  includes memory cells Ce 1  to Ce 7 , and boundary memory cell CB, each of which is for storing 2 bit data. For example, the boundary memory cell CB stores bit data BT 1  and BT 2 . Generally, in an erase verification process performed on the memory block BLO 1 , data stored in the memory cells Ce 1  to Ce 7  and the boundary memory cell CB are sensed for determining whether the memory block BLO 1  is verified to be erased. If not, the erase process will be executed for erasing the memory block BLO 1 . 
         [0007]    Bit data stored in the memory cells Ce 1  to Ce 7  and the bit data BT 1  stored in the boundary memory cell CB are sensed and erased by a sense amplifier SE 1  and a bias circuit BS 1 , which are both corresponding to the memory block BLO 1 . However, due to the circuitry structure of the memory block BLO 1 , bit data BT 2  stored in the boundary memory cell CB is sensed by the sense amplifier SE 1  corresponding to the memory block BLO 1 , but is erased by a bias voltage VB provided by a bias circuit BS 2  corresponding to the memory block BLO 2 . 
         [0008]    For example, when the bit data BT 2  is erased, the bias voltage VB provided by the bias circuit BS 2  is provided to the end of the boundary memory cell CB storing the bit data BT 2  via the Y-multiplexer YM 2 , the bit line BL 1 ′, the bank selection switch Sell corresponding to the memory block BLO 2 . Thus, the sensed result corresponding to the bit data BT 2  should be considered in the control of the bias circuit BS 2  via which the erase voltage erasing the bit data BT 2  stored in the boundary memory cell CB is provided. 
         [0009]    Referring to  FIG. 2 , a schematic illustration of the Y-multiplexers in  FIG. 1  is shown. In  FIG. 2 , only the Y-multiplexers YM 1  to YM 3  are shown as example. The Y-multiplexer YM 1 , YM 2 , and YM 3  respectively includes data channels Ysa 0  to Ysa 3 , Ysb 0  to Ysb 7 , and Ysc 0  to Ysc 4 . As shown in  FIG. 2 , each data channels Ysa 0  to Ysa 3 , Ysb 0  to Ysb 7 , and Ysc 0  to Ysc 4  are arranged in accordance with the sequence of the mark numbers and the data channels with the greatest mark numbers (i.e. 3, 7, and 4) correspond with the boundary memory cells of the corresponding memory blocks. 
         [0010]    In an example, the mark numbers indicate the corresponding address value of an address Adr. For example, the data channels with mark number of 1, (i.e. Ysa 1 , Ysb 1 , and Ysc 1 ) are enabled in response to the first value of the address Adr. The value of the address Adr is sequentially altered from its initial value to its terminal value. 
         [0011]    When the address Adr indicates the value of 3, the bit data BT 2  of the boundary memory cell CB of the memory block MLO 1  is sensed by the sense amplifier SE 1 . According to the previous paragraphs, it can be obtained that the sensed bit data BT 2  should be considered in the control of the bias circuit BS 2 . However, a bit data of a memory cell of the memory block MLO 2 , which is provided by the Y-multiplexer YM 2  in response to the third value of the address Adr, is also sensed and outputted by the sense amplifier SE 2 . Thus, additional logic circuits and control signals are needed to control the operation of the bias circuit BS 2  based on the two sensed result is a challenging task. 
         [0012]    Furthermore, similar boundary situation will occur whenever two adjacent memory blocks corresponding to different numbers of data channels. Thus, it is challenging and time-consuming to design corresponding logic for all those logic control. Besides, once the order of the memory blocks is changed, all the logic circuits must be redesigned since the time of referencing the sensing result of the sense amplifier corresponding to the adjacent memory block is totally different. Therefore, it is desirable to design a circuit to simplify and unify the erase operation on the boundary of different memory blocks. 
       SUMMARY OF THE INVENTION 
       [0013]    The invention is directed to a memory control circuit for performing erase verification on a memory circuit including lots of memory blocks. The memory control circuit can effectively simplify and unify the erase operation on the boundary of different memory blocks. 
         [0014]    According to a first aspect of the present invention, a memory device is provided. The memory device includes a first memory block and a second memory block. The first memory block has a first boundary cell, and the second memory block has a second boundary cell. Data of the first and the second boundary cells are outputted simultaneously corresponding to a plurality of column selection signals. 
         [0015]    According to a second aspect of the present invention, a memory device is provided. The memory device includes a first boundary channel and a second boundary channel. The first boundary channel corresponds to a first boundary bit, and the second boundary channel corresponds to a second boundary bit. The first and the second boundary channels output the first and the second boundary bits simultaneously corresponding to column selection signals. 
         [0016]    The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  (Prior Art) is a schematic illustration of a conventional memory. 
           [0018]      FIG. 2  (Prior Art) is a schematic illustration of the Y-multiplexer YM 1  to YMM illustrated in the  FIG. 1 . 
           [0019]      FIG. 3  is a block diagram of a memory control circuit  10  according to the embodiment of the invention. 
           [0020]      FIG. 4  is a schematic illustration of the memory control circuit according to the prevent embodiment of the invention. 
           [0021]      FIG. 5  is a flow chart of a method for memory accessing according to the present embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    According to an embodiment of invention, a memory control circuit is provided to read the boundary data of the boundary cells of the corresponding memory blocks in response to one column selection signal. Thus, the operations of the logic circuits in each control units, which correspond with the respective memory blocks, can be simplified and unified. 
         [0023]    Generally, in an erase verification operation performed on a particular memory block, data stored in the memory cells of the memory block are read and used to determine whether the corresponding memory cells are erased. For example, when the data has a value of 1, it is suggested that the corresponding memory cell is erased. When the data a value of 0, it is suggested that the corresponding memory cell is not erased. In the following passages, an example for an erase operation and an erase verification operation performed on a memory will be provided for detailed explanation. 
         [0024]    Referring to  FIG. 3 , a block diagram of a memory control circuit  10  according to the embodiment of the invention is shown. The memory control circuit  10  is applied in a memory system  100  to perform an erase operation and an erase verification operation on a memory array  20 . For example, the memory array  20  includes memory banks BK 0  to BKN, each of which includes M memory blocks. M and N are natural numbers greater than 1. For example, the memory bank BK 0  includes memory blocks BL( 1 ) to BL(M). In  FIG. 3 , only the memory blocks BL(i) and BL(i+1) are shown, wherein i is a natural number smaller than M. In the following paragraphs, the erase operation and the erase verification operation performed on the memory block BL(i) and BL(i+1) are cited as examples for further explanation. 
         [0025]    The memory block BL(i+1) includes memory cells C 1  to C 7  and a boundary memory cell CBD, each of which stores 2 bit data. Bank selection switches SI 1  to SI 8  are used for connecting the source/drain ends of the memory cells C 1  to C 7  and the boundary memory cell CBD to corresponding bit lines BTL 1  to BTL 4 . Thus, data stored in the memory cells C 1  to C 7  and the boundary memory cell CBD can be outputted via the bit lines BTL 1  to BTL 4  and bias voltages can be applied to the corresponding source/drain end of the memory cells C 1  to C 7  and the boundary memory cell CBD. 
         [0026]    The boundary memory cell CBD stores bit data BD 1  and BD 2 . The bit data BD 2  is a boundary bit data, which are sensed by the sense amplifier corresponding to the memory block BL(i) but are erased by the bias circuit BC(i+1) corresponding to the memory block BL(i+1), outputted via the bit line BTL 4 . 
         [0027]    The memory block BL(j+1), which has a circuit structure substantially the same as that of the memory block BL(j), includes memory cells C 1 ′ to C 7 ′ and a boundary memory cell CBD′, which stores bit data BD 1 ′ and BD 2 ′. Bank selection switches SI 1 ′ to SI 8 ′ are used for connecting the source/drain of the memory cells C 1 ′ to C 7 ′ and the boundary memory cell CBD′. The bit data BD 2 ′ is a boundary bit data, which are sensed by the sense amplifier SA(i+1) corresponding to the memory block BL(i+1) but are erased by the bias circuit BC 3  corresponding to the memory block BL(i+2), outputted via the bit line BTL 4 ′. 
         [0028]    The memory control circuit  10  includes a control logic circuit LCA and M control units CU( 1 ) to CU(M) for controlling the M respective memory blocks BL( 1 ) to BL(M). The control logic circuit LCA receives a column selection signal Addr to accordingly provide control signals for controlling the M control units CU( 1 ) to CU(M). 
         [0029]    The column selection signal Addr is capable of being a boundary value. When the column selection signal Addr indicates a boundary value, the control logic circuit LCA provides an enabled boundary control signal Sbd to the M control units CU( 1 ) to CU(M). When the column selection signal Addr indicates value other than the boundary value, the control logic circuit LCA provides a disabled boundary control signal Sbd to the M control units CU( 1 ) to CU(M). 
         [0030]    The M control units CU( 1 ) to CU(M) have substantially the same circuit structure and operation. In  FIG. 3 , only the control units CU(i) and CU(i+1), which correspond to the memory blocks BL(i) and BL(i+1) respectively, are shown. The control unit CU(i+1) includes a Y-multiplexer YX(i+1), a bias circuit BC(i+1), a sense amplifier SA(i+1) and a logic circuit LC(i+1). The control unit CU(i) includes a Y-multiplexer YX(i), a bias circuit BC(i), a sense amplifier SA(i), and a logic circuit LC(i), which perform substantially the same operation as the corresponding circuits in the control unit CU(i+1). 
         [0031]    The Y-multiplexer YX(i+1) includes 4 data channels corresponding to the respective bit lines BTL 1 ′ to BTL 4 ′. The Y-multiplexer YX(i+1) enables a data channel within it in response to a column selection signal Addr for outputting output data Da(i+1), which are stored in a selected memory cell in the memory block BL(i+1) and outputted via a corresponding bit line among the bit lines BTL 1 ′ to BTL 4 ′, to the sense amplifier SA(i+1). Besides, the Y-multiplexer YX(i+1) also enables a data channel connecting the bit lines BTL 1 ′ to BTL 4 ′ to the bias circuit BC(i+1). Similarly, the Y-multiplexer YX(i) has substantially the same circuit structure as the Y-multiplexer YX(i) and performs substantially the same operation as the Y-multiplexer YX(i+1). 
         [0032]    The bias circuit BC(i+1) provides a bias voltage VB to the memory block BL(i+1) via the Y-multiplexer YX(i+1) so as to perform the erase operation on the memory block BL(i+1). The sense amplifier SA(i+1) senses data provided by the Y-multiplexer YX(i+1) for accordingly providing a sensing signal Ssen(i+1). Similarly, the bias circuit BC(i) performs an erase operation on the memory block BL(i) and the sense amplifier SA(i) accordingly provides a sensing signal Ssen(i). 
         [0033]    The logic circuit LC(i+1) is for providing a verification signal Sver(i+1) indicating whether to control the bias circuit BC(i+1) to provide the bias voltage VB for performing the erase operation on the memory block BL(i+1). The logic circuit LC 3 (i+1) is, for example, implemented with a multiplexer, which provides the sensing signal Ssen(i) as a verification signal Sver(i+1) according to the enabled boundary control signal Sbd and provides the sensing signal Ssen(i+1) as the verification signal Sver(i+1) according to the disabled boundary control signal Sbd. 
         [0034]    Similarly, the logic circuit LC(i) provides a verification signal Sver(i) indicating whether to control the bias circuit BC(i) to provide the bias voltage VB for performing the erase operation on the memory block BL(i). The logic circuit LC(i) provides a sensing signal Ssen(i−1) corresponding to a previous memory block of the memory block BL(i) (i.e. the memory block BL(i−1)) based on the enabled boundary control signal Sbd and provides the sensing signal Ssen(i) as the verification signal Sver(i) based on the disabled boundary control signal Sbd. For example, the sensing signal Ssen(i−1) corresponds to the boundary bit data of the memory block BL(i−1). 
         [0035]    In an operation example, when the column selection signal Addr indicates the boundary value, the Y-multiplexer YX(i+1) and YX(i) respectively enable the data channel corresponding to the boundary bit data BD 2 ′ (i.e. the data channel corresponding to the boundary bit line BTL 4 ′) and the data channel corresponding to the boundary bit data BD 2  (i.e. the data channel corresponding to the boundary bit line BTL 4 ). Thus, the sensing signal Ssen(i+1) corresponding to the boundary bit data BD 2 ′ and the sensing signal Ssen(i) corresponding to the boundary bit data BD 2  can be obtained. Similarly, the sensing signal Ssen(i−1) corresponding to the boundary bit data of the memory block BL(i−1) can also be obtained. 
         [0036]    In the meantime, the control logic circuit LCA provides the enabled boundary control signal Sbd. Thus, the logic circuits LC(i) and LC(i+1) select the sensing signals corresponding to the boundary bit data of their previous memory block (i.e. the sensing signal Ssen(i−1) and Ssen(i)) as the corresponding verification signals Sver(i) and Sver(i+1) when the column selection signal Addr indicates the boundary value. 
         [0037]    In analogy, when the column selection signal Addr indicates the boundary value, the M logic circuits in the M control units CU( 1 ) to CU(M) perform substantially the same operation to apply the sensing signals corresponding to the boundary bit data of their previous memory block as the corresponding verification signals. Thus, the boundary issue can be effectively solved and with simple and unified logic circuits and a control logic circuit. 
         [0038]    The control logic circuit LCA further provides empty control signals Se( 1 ) to Se(M) to respectively control the logic circuits within the control units CU( 1 ) to CU(M). In the following paragraphs, an operation example of the memory control circuit  10  is described for further explanation of the operation controlled by those empty control signals. 
         [0039]    Referring to  FIG. 4 , a schematic illustration of the memory control circuit according to the prevent embodiment of the invention is shown. The memory control circuit  10 ′ includes M control units CU′( 1 ) to CU′(M), but in  FIG. 4 , only the control units CU′(j) to CU′(j+3) are shown. The column selection signal Addr′ is capable of having 7 values {1, 2, 3, 4, 5, 6, 7}. In an example, the value of the column selection signal Addr′ is increased progressively form 1 to 7. After the column selection signal Addr′ reaches the value of 7/, the value of the column selection signal Addr′ goes back to the value of 1. 
         [0040]    In an example, the value of 7 of the column selection signal Addr′ is designated as the boundary value. Thus, for all of the Y-multiplexers of the memory control circuit  10 ′, the data channels corresponding to each of the boundary bit data are enabled in response to the column selection signal Addr′ having the value of 7. For example, the Y-multiplexer YX′(j) to YX′(j+3) respectively have data channels Ya 7 , Yb 7 , Yc 7 , and Yd 7 , which respectively correspond with the boundary bit data of the memory block BL(j) to BL(j+3) and are enabled in response to the column selection signal Addr′ having the value of 7. The mark numbers of 7 shown in the data channels Ya 7 , Yb 7 , Yc 7 , and Yd 7  indicate the corresponding values (i.e. the value of 7) of the column selection signal Addr′ for enabling them. 
         [0041]    Except for the data channel Ya 7  corresponding to the boundary bit data of the memory block BL(j), the Y-multiplexers YX′(j) further has data channels Ya 1 , Ya 3 , and Ya 5 , wherein the mark number 1, 3, and 5 indicates the corresponding values of the column selection signal Addr′ for enabling the corresponding data channels Ya 1 , Ya 3 , and Ya 5 . In other words, when the column selection signal Addr′ has the values of 1, 3, and 5, the corresponding data channels Ya 1 , Ya 3 , and Ya 5  are respectively enabled for providing the corresponding bit data to the sense amplifier SA′(j) so as to provide a sensing signal Ssen(j) corresponding to those bit data. 
         [0042]    However, when the selection signal Addr′ has any one of the values of 2, 4, and 6, no data channels within the Y-multiplexer YX 1 ′(j) are accordingly enabled and no bid data is sensed. Thus, the sensing signal Ssen(j) and the verification signal Sver(j) cannot be obtained and the erase verification process would come to a halt. 
         [0043]    In the present example, when the column selection signal Addr′ has any of those values of 2, 4, and 6, the control logic circuit LCA′ provides an enabled empty control signal Sea) for controlling the logic circuit LC′(j) to provide a default signal as the verification signal Sver(j) for outputting. In an example, the default signal has a value the same as the value that indicating a corresponding memory cell is erased successfully. Thus, the erase verification process can keep moving on to check whether the memory cell corresponding to the next data channel is verified to be erased or not. 
         [0044]    Except for the data channel Yb 7  corresponding to the boundary bit data of the memory block BL(j+1), the Y-multiplexer YX′(j+1) further has data channels Yb 4 , Yb 5 , and Yb 6 . Similarly, The control logic circuit LCA′ provides a corresponding empty control signal Se(j+1) for controlling the corresponding logic circuit LC(j+1) to provide the default signal as the corresponding verification signal Sver(j+1) when the column selection signal Addr′ has any of the values of 1, 2, and 3, which are not correspond to any of its data channels Yb 4  to Yb 7 . 
         [0045]    In analogy, the control logic circuit LCA′ also provides other empty control signals Se for controlling the corresponding logic circuits to provide the default signal as the corresponding verification signal when the column selection signal Addr′ has the value does not correspond to any of its data channel. 
         [0046]    Referring to  FIG. 5 , a flow chart of a method for memory accessing according to the present embodiment of the invention is shown. Each and every steps of the method for memory accessing have been well disclosed in the previous paragraphs and the redundant description thereof is omitted. 
         [0047]    Although only the situation that the Y-multiplexers YX′(j) to YX′(j+3) have the data channel structures shown in  FIG. 4  is described as an example in the above paragraphs, the data channel structures of the Y-multiplexers YX′(j) to YX′(j+3) are not limited thereto. Except for the data channel corresponding to the boundary bit data should be designated with the same boundary value of the column selection signal Addr′, the rest of data channels within the Y-multiplexers can be freely designated with the rest values of the column selection signal Addr′. For example, the Y-multiplexer YX′(j+1) can also have its 3 data channels respectively correspond to the column selection signal Addr′ indicating the values of 1, 2, and 3, or that indicating the value 1, 2, and 5. 
         [0048]    Although only the situation that the biggest value (i.e. the value of 7) of the column selection signal Addr′ is designated as the boundary value of the column selection signal Addr′ is cited as an example for illustration in the present embodiment of the invention, the boundary value is not limited thereto. In other example, any values of the column selection signal Addr′ can be designated as the boundary value. 
         [0049]    In the present embodiment, the memory control circuit includes Y-multiplexers for reading boundary cells of present memory blocks in response to one boundary value of a column selection signal, accordingly obtaining sensing signals. The memory control circuit further includes selecting circuit for selecting the sensing signals thereof to determine whether to re-perform the erase operation on the next memory blocks and the boundary cells. Therefore, no matter how the variety of size the memory blocks may have, simple selecting circuits can be used to realize the logic circuits for determining whether to re-perform the erase operation on every memory blocks of the memory array. Consequently, the memory control circuit of the present embodiment can effectively simplify and unify the erase operation on the boundary of different memory blocks. 
         [0050]    While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.