Abstract:
Methods, apparatuses, and systems for performing refresh operations on a memory cell array that does not have an Nth-power-of-2 number of memory mats are disclosed. An address counter configured to skip the refresh addresses not assigned to a memory mat is disclosed. An address counter configured to distribute the refresh addresses not assigned to a memory mat across a refresh period is disclosed. A mask determination circuit that suppresses refresh operations for refresh addresses not assigned to a memory mat is disclosed.

Description:
BACKGROUND 
       [0001]    Some semiconductor memories (e.g., dynamic random access memory (DRAM)) may require periodic refresh operations to maintain data stored therein. A memory device typically sequentially refreshes portions of a memory. A portion of memory may include a word line, a plurality of word lines, a memory array, a plurality of arrays, and/or another sub-set of the memory. The portions of the memory may be associated with refresh addresses. A refresh address counter included in the memory may be used to generate internal refresh addresses in turn to ensure all portions of the memory are refreshed, for example, during self-refresh. The refresh address counter may be a binary counter, and the number of refresh addresses generated by the refresh address counter may be an Nth power of 2. 
         [0002]    Some memories may have memory configurations such that the number of portions to be assigned a refresh address is not an Nth power of 2. In memory devices including these memories, the binary address counter may produce refresh addresses to which no portion of the memory is assigned. This may cause wasteful time gaps in the refresh operations in the memory device and/or poor distribution of current in the memory device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a block diagram of a semiconductor memory device according to an embodiment of the disclosure. 
           [0004]      FIG. 2  is a schematic illustration of a memory array. 
           [0005]      FIG. 3  is a schematic illustration of a counter cell. 
           [0006]      FIG. 4  is a schematic illustration of an address counter according to an embodiment of the disclosure. 
           [0007]      FIG. 5  is a timing diagram of the operation of a memory including an address counter according to an embodiment of the disclosure. 
           [0008]      FIG. 6A  is a timing diagram of refresh operation intervals for a memory. 
           [0009]      FIG. 6B  is a timing diagram of refresh operation intervals for a memory including the address counter of  FIG. 4  according to an embodiment of the disclosure. 
           [0010]      FIG. 7  is a schematic illustration of an example alternative address counter according to an embodiment of the disclosure. 
           [0011]      FIG. 8  is a schematic illustration of an alternative address counter according to an embodiment of the disclosure. 
           [0012]      FIG. 9  is a timing diagram of refresh operation intervals for a memory including the address counter of  FIG. 8  according to an embodiment of the disclosure. 
           [0013]      FIG. 10  is a schematic illustration of an alternative address counter according to an embodiment of the disclosure. 
           [0014]      FIG. 11  is a timing diagram of refresh operation intervals for a memory including the address counter of  FIG. 10  according to an embodiment of the disclosure. 
           [0015]      FIG. 12  is a schematic illustration of an example comparison circuit. 
           [0016]      FIG. 13  is a schematic illustration of a mask determination circuit including a comparison circuit according to an embodiment of the disclosure 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Certain details are set forth below to provide a sufficient understanding of embodiments of the invention. However, it will be clear to one skilled in the art that embodiments of the invention may be practiced without these particular details. Moreover, the particular embodiments of the present invention described herein are provided by way of example and should not be used to limit the scope of the invention to these particular embodiments. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention. 
         [0018]      FIG. 1  is a block diagram of a semiconductor memory device  10  according to an embodiment of the disclosure. The semiconductor memory device  10  may include a memory cell array  20  that may include a plurality of memory cells MC. The memory cell array  20  may include a plurality of word lines WL and a plurality of bit lines BL arranged intersecting with each other, and each of the memory cells MC may be located at the intersections of the word lines WL and bit lines BL. The memory cell array  20  may be divided into portions, herein referred to as banks, and each bank may be further divided into segments. 
         [0019]    Word lines WL included in the memory cell array  20  may be selected by a word line control circuit  21 . The selection may be based on a row selection signal Xadd or a refresh address RefADD. Selection of bit lines BL included in the memory cell array  20  may be performed by a column switch group  22 . The selection may be based on a column selection signal YSWY or a forced on signal YSWFON. The column switch group  22  may include a plurality of column switches YSW coupled to the corresponding bit lines BL. 
         [0020]    The row selection signal Xadd and the column selection signal YSWY may be generated based upon command address signals CA 0 -CA 9  which may be supplied from a memory controller (not shown). The command address signals CA 0 -CA 9  may be latched by an address latch circuit  23 , and portions corresponding to row addresses may be decoded by an X decoder  24  and outputted as the row selection signal Xadd, while portions corresponding to column addresses may be decoded by a Y decoder  25  and outputted as the column selection signal YSWY. 
         [0021]    The command address signals CA 0 -CA 9  may also be provided to a register circuit  26 . The register circuit  36 , which may include a command register  27  and a mode register  28 , may receive the command address signals CA 0 -CA 9  and a command signal CMD, and may generate one or more output signals based upon the provided signals. The command signal CMD may include a clock signal CK, a clock enable signal CKE, and a chip select signal CS. 
         [0022]    The command register  27  may output a self-refresh internal command SR in response to the issue of a self-refresh command. The command register  27  may output an auto-refresh internal command AR in response to an auto-refresh command. The self-refresh internal command SR may be supplied to a self-refresh oscillator  31 . When the self-refresh internal command SR is activated, the self-refresh oscillator  31  may automatically generate an internal refresh signal OSC in a periodic manner. The period of generating the internal refresh signal OSC may be set to a period with which information stored in all the memory cells MC included in the memory cell array  20  may be maintained. 
         [0023]    The internal refresh signal OSC and the auto-refresh internal command AR may be supplied to an address counter  33  via an OR gate  32 . The address counter  33  may be a counter that generates a refresh address RefADD. A counter value of the address counter  33  may be updated in response to the internal refresh signal OSC and/or the auto-refresh internal command AR. The refresh address RefADD may be supplied to a mask determination circuit  34  and a refresh operation control circuit  35 . 
         [0024]    The mask determination circuit  34  may be activated by the self-refresh internal command SR and may activate a match signal HIT to a high logic level in response to detection of a match between the refresh address RefADD and mask information MASK. The refresh operation control circuit  35  may be activated by the self-refresh internal command SR and/or the auto-refresh internal command AR, and when the match signal HIT is not activated, it may generate a refresh operation signal RefOPGEN. The refresh operation signal RefOPGEN may be supplied to the word line control circuit  21 , by which a refresh operation for the specified refresh address RefADD may be performed. When the match signal HIT is activated, the refresh operation control circuit  35  may not generate the refresh operation signal RefOPGEN, and the refresh operation may be disabled. 
         [0025]    The mask information MASK may include information that indicates a bank and/or a segment for which the self-refresh operation is not performed among the banks and/or the segments included in the memory cell array  20 . The information may be supplied from a mask information storage circuit  36 . The mask information storage circuit  36  may include a bank mask information storage circuit  37  and a segment mask information storage circuit  38 . The bank mask information storage circuit  37  may store information indicating one or more banks for which the self-refresh operation is not performed and the segment mask information storage circuit  38  may store information indicating one or more segments for which the self-refresh operation is not performed. With this configuration, it may be possible to specify whether to perform the self-refresh operation for each of the banks and each of the segments of the memory cell array  20 . Settings of the mask information MASK in the bank mask information storage circuit  37  and the segment mask information storage circuit  38  may be performed by setting signals MR 16  and MR 17 , respectively. The setting signals MR 16  and MR 17  may be provided by the mode register  28 . 
         [0026]    As shown in  FIG. 1 , the semiconductor memory device  10  may further include an input/output buffer circuit  52 , a data latch circuit  53 , and write amplifier  54 . The input/output buffer circuit  52  may buffer data that is input and output via a data input/output terminal  51 . The data latch circuit  53  may latch data that is input and output via the input/output buffer circuit  52 . The write amplifier  54  may amplify write data that is latched in the data latch circuit  53 . With this configuration, at the time of a read operation, any one of the column switches YSW specified by the column selection signal YSWY may be switched on, by which read data that is read out from the bit line BL selected by the column selection signal YSWY may be output to the data input/output terminal  51  via the data latch circuit  53  and the input/output buffer circuit  52 . At the time of a normal write operation, write data input to the data input/output terminal  51  may pass through the input/output buffer circuit  52 , the data latch circuit  53 , and the write amplifier  54 , and may be supplied to the selected bit line BL via any one of the column switches YSW specified by the column selection signal YSWY. 
         [0027]    The semiconductor memory device  10  may further include a refresh write circuit  42 . The refresh write circuit may include a data inverting circuit  43  and a column switch control circuit  44 , by which an operation of inverting the write data and a forced on operation of the column switch YSW may be performed. 
         [0028]      FIG. 2  is a schematic illustration of a memory array  200 . In some embodiments, the memory array  200  may be used to implement the memory cell array  20  of  FIG. 1 . In some embodiments, the memory array  200  may be divided into eight portions referred to herein as banks. The address configuration of bank  0  is described; however, the same address configuration may be implemented for banks  1 - 7 . 
         [0029]    In bank  0 , column decoders YDEC 1  and YDEC 2  may be positioned on two opposing sides of bank  0 , and memory mats (e.g., memory blocks) extending from MAT 0  on the right-hand end (from the perspective of the reader) to MAT 24  in a center portion of bank  0  to MAT 48  on the left-hand end. Memory mats MAT( 0 - 48 ) labels are shown above bank  0  in  FIG. 2 . The memory mats may be accessible to column decoders YDEC 1  and YDEC 2 . Row decoder XDEC may be positioned adjacent to bank  0  in the row direction. Memory mats are described in detail in Japanese publication JP-A No. 2014-010845, published on Jan. 20, 2014, and U.S. publication No. 2014/0003113, published on Jan. 3, 2014, which are incorporated herein by reference for any purpose. The number of memory mats in the X-address direction of bank  0  corresponds to 48 memory mats. Six bits (X 9 - 14 ) of mat addresses may be used as the X-address, which means 64 (6 th  power of 2) memory mats may be selected even though only 48 memory mats are included in bank  0 . As a result, when both mat address bits X 13  and X 14  correspond to 1, no memory mat included in bank  0  is selected. That is, when both mat address bits X 13  and X 14  correspond to 1, the X-address corresponds to memory mats  49 - 63 , which are not included in bank  0 . In the Y-address direction, 32 (5 th  power of 2) memory mats may be included. 
         [0030]      FIG. 4  is a schematic illustration of an address counter  500  according to an embodiment of the disclosure. The address counter  500  may be used to implement address counter  33  in some embodiments. The address counter  500  includes counter cells CNT[ 0 ]-CNT[ 14 ]. The counter cells may count through count values from a minimum count value to a maximum count value (e.g., 000, 001 . . . 111). The counter cells CNT[ 0 ]-CNT[ 14 ] may be coupled in series with one another from a first counter cell CNT[ 0 ] to a last counter cell CNT[ 14 ] downstream of the first counter cell, and their outputs Rcnt[ 0 ]-Rcnt[ 14 ] may correspond to the address bit numbers X[ 0 - 14 ] of row addresses in a memory bank, such as bank  0  illustrated in  FIG. 2 . The outputs Rcnt[ 0 ]-Rcnt[ 14 ] may be provided to a refresh operation control circuit such as refresh operation control circuit  35  shown in  FIG. 1 , which may provide the corresponding address to a word line control circuit, such as word line control circuit  21  shown in  FIG. 1 . A clock signal OSC may be generated by a self-refresh oscillator, such as self-refresh oscillator  31  illustrated in  FIG. 1 . The clock signal OSC may be provided as the input to CNT[ 0 ] rather than an input of Rcnt[i−1]. 
         [0031]      FIG. 3  is a schematic illustration of a counter cell  300  according to an embodiment of the invention, which may be used to implement a counter cell CNT of the address counter  500  in some embodiments. The counter cell  300  may include a flip-flop  305  of a master-slave type. The flip-flop  305  may receive a signal Rcnt[i−1] at an input via an inverter  310 . The flip-flop  305  may receive the output of the inverter  310  through a second inverter  315  at a second input. The flip-flop  305  may also receive a reset signal at a third input. The flip-flop  305  may provide an output to a third inverter  320 . The third inverter  320  may provide the output to a fourth input of the flip-flop  305  and a fourth inverter  325 . The fourth inverter  325  may provide an output signal Rcnt[i]. 
         [0032]    The address counter  500  may be configured such that when the counter cells count to a count value corresponding to both refresh address bits X 13  and X 14  set to 1, the counter cells corresponding to the respective address bits are reset before reaching the maximum count value so as to skip the range of address having address bits X 13  and X 14  as 1. As a result, the address counter  500  may skip one or more count values so that the address counter  500  may not provide addresses that correspond to refresh addresses where both X 13  and X 14  are set to 1. 
         [0033]    The address counter  500  may include a counter logic circuit  505 . The counter logic circuit  505  may include a NAND gate  510  configured to receive outputs Rcnt[ 13 ] and Rcnt[ 14 ] as inputs. The output of NAND gate  510  may be coupled to a delay  515 . Delay  515  may be configurable to provide a stable pulse width. The output of delay  515  and the reset signal may be coupled to inputs of AND gate  520 . The output of the AND gate  520 , RESET SIGNAL  2 , may be provided as an input to CNT[ 13 ] and CNT[ 14 ] rather than the reset signal provided to the counter cells CNT[ 0 - 12 ]. The counter logic circuit  505  may set a reset signal to logic level low (active) when both of the outputs of counter cells CNT[ 13 ] and CNT[ 14 ], which correspond to X-address bits X 13  and X 14 , respectively, become logic level high (i.e., X 13  and X 14  are 1). The logic level low reset signal RESET SIGNAL  2  provided to the counter cells CNT[ 13 ] and CNT[ 14 ] may cause the counter cells to reset such that both counter cells return to logic level low. This may cause the address counter  500  to skip addresses corresponding to refresh addresses where X 13  and X 14  are set to 1. 
         [0034]      FIG. 5  is a timing diagram of the operation of a memory including an address counter according to an embodiment of the disclosure. The memory may be implemented using the semiconductor memory device  10  illustrated in  FIG. 1 . The address counter  33  may be implemented using address counter  500  illustrated in  FIG. 4 . In response to receiving a refresh-all bank command and/or a self-refresh command, the command register  27  may provide a logic level low to an input of OR gate  32  in  FIG. 1 . In response to the logic level low of one of the inputs, the OR gate  32  may supply a clock signal OSC to address counter  33 . In response to the clock signal OSC, the counter cells of the address counter  33  may carry out counting operations. For brevity, the counting operations of only counter cells CNT[ 12 - 14 ] providing the three highest order (e.g., most significant) bits, as illustrated in  FIG. 4 , will be described. 
         [0035]    The counter logic circuit  505  may generate a reset signal RESET SIGNAL  2  at the time the outputs Rcnt[ 13 ] and Rcnt[ 14 ] of CNT[ 13 ] and CNT[ 14 ], respectively, are both logic level high. As shown in  FIG. 5 , a timing hazard may occur between the Rcnt[ 13 ] signal and the output of the counter logic circuit  505  RESET SIGNAL  2 . However, the timing hazard may be mitigated by latching signals X 13  and X 14  by an internal refresh command. The command interval corresponding to tRFC may be maintained at a minimum frequency. As a result, the delay from the additional logic of the counter logic circuit  505  may not cause a timing issue in the memory. 
         [0036]      FIG. 6A  is a timing diagram of refresh operation intervals for a memory including a conventional 15-bit address counter.  FIG. 6B  is a timing diagram of refresh operation intervals for a memory including address counter  500  according to an embodiment of the disclosure. In the refresh operation intervals shown in  FIG. 6A , during an 8K refresh period, for the period of time where both X 13 , X 14 =1, no refresh operation is performed as no corresponding memory mats exist to refresh. In contrast, as shown in  FIG. 6B , addresses corresponding to X 13 , X 14 =1 are skipped and no address count is carried out for the non-existing memory mats. This may allow for a self-refresh operation having a 6K refresh period although a 15-bit address counter is used. That is, by allowing a REF command that has been conventionally generated at 8K to be generated at 6K, the actual refresh number of times may be increased which may improve reliability. In comparison to the case where a conventional 15-bit address counter is used, the address counter  500  may reduce power consumption because the addresses having X 13  and X 14  as 1 are skipped, and any internal operations related to refreshing non-existent memory locations can be avoided. 
         [0037]    As will be described in more detail below, in some embodiments, the address to be skipped may not be from an upper counter cell, but may be from a lower counter cell so that the output from the corresponding lower cell is sent to Rcnt[ 13 ], Rcnt[ 14 ].  FIG. 7  is a schematic illustration of an address counter  900  according to an embodiment of the invention. The address counter  900  includes counter cells CNT[ 0 ]-CNT[ 14 ] and counter logic circuit  905 . As shown in  FIG. 7 , outputs from counter cells CNT[ 1 ] and CNT[ 2 ] are provided as Rcnt[ 13 ] and Rcnt[ 14 ], respectively, and may be used as inputs to the counter logic circuit  905 . 
         [0038]    As illustrated in  FIG. 6A , both X 13  and X 14  equal 1 for 2K of an 8K refresh period. That is, when the address counters are successively refreshed without compensating for the non-existing memory blocks, the refresh operation is not carried out for a consecutive ¼ of the refresh period. The refresh operation is continuously carried out during the remaining consecutive ¾ of the refresh period. Having an uninterrupted 2K period of no refresh operations may not be desirable for averaging refresh currents. However, in some applications, it may not be desirable to decrease the refresh period from 8K to 6K by skipping refresh addresses that correspond to non-existing memory mats. 
         [0039]    Alternatively, an address counter may be configured so that the periods of no refresh operations may be distributed over the refresh period of 8K. One or more bits of addresses may be switched, for example, more significant bits and less significant bits of addresses may be transposed in the address counter. That is, the output of one or more counter cells forming the address counter may be switched so that periods in which refresh address bits X 13 , X 14  are both set to 1 are distributed over the refresh period. 
         [0040]      FIG. 8  is a schematic illustration of an address counter  1000  according to an embodiment of the disclosure. Address counter  1000  may be used to implement address counter  33  in  FIG. 1 . The address counter  1000  includes counter cells CNT[ 0 ]-CNT[ 14 ]. As shown in  FIG. 10 , the addresses of X 13  and X 14  may be respectively received from outputs of counter cells other than counter cells CNT[ 13 ] and CNT[ 14 ]. For example, in the embodiment illustrated in  FIG. 10 , the addresses X 13  and X 14  are provided at the outputs of the counter cells CNT[ 0 ] and CNT[ 1 ]. The rest of the Rcnt[i] is shifted onto the upper counter cells by two bits for the remaining counter cells. Since the alteration is made to the least significant two bits, of the 8K (8192) possible addresses, no refresh operation is carried for 2K (2048) addresses where both of the counter cells CNT[ 0 ] and CNT[ 1 ] of the lower two bits are set to 1. 
         [0041]      FIG. 9  is a timing diagram of refresh operation intervals for a memory including address counter  1000  according to an embodiment of the disclosure. As shown, periods during which no refresh operation is carried out (e.g., when X 13  and X 14  are both 1) may be distributed throughout the potential 8K addresses. With this configuration, because the periods when no refresh operation is performed is distributed throughout the total possible addresses, relatively long periods of time where the current consumption deviates (e.g., where X 13  and X 14  are the two most significant bits) may be avoided, and the average current consumption may be more consistent. 
         [0042]    By replacing X 13  and X 14  with the least significant bits X 0  and X 1 , the effect of current averaging process per unit time may be desirable in some applications. However, other configurations of distributing the addresses corresponding to 2K of no refresh operations throughout the 8K refresh period are possible. For example,  FIG. 10  is a schematic illustration of an alternative address counter  1200  according to an embodiment of the disclosure. Address counter  1200  may be used to implement address counter  33  in  FIG. 1 . The address counter  1200  includes counter cells CNT[ 0 ]-CNT[ 14 ]. In address counter  1200 , the outputs of CNT[ 1 ] and CNT[ 2 ] are set to Rcnt[ 13 ] and Rcnt[ 14 ], respectively. In comparison to address counter  1000 , each of Rcnt[ 13 ] and Rcnt[ 14 ] are shifted to a higher-order bit by one. 
         [0043]      FIG. 11  is a timing diagram of refresh operation intervals for a memory including address counter  1200  according to an embodiment of the disclosure. In contrast to address counter  1000 , the periods during which no refresh operation occur less frequently and are longer. For example, in comparison to the address counter  1000 , the periods of no refresh operation are twice as long and the number of periods of no refresh operations is half for address counter  1200  compared to address counter  1000 . 
         [0044]    As mentioned previously in reference to  FIG. 1 , a memory device  10  may include a mask determination circuit  34 . The mask determination circuit may include a comparison circuit to compare the address received from the register circuit  26  and the mask information storage circuit  36 .  FIG. 12  is a schematic illustration of an example comparison circuit  1400 . The comparison circuit  1400  may output a MASK signal to suppress a self-refresh operation when the refresh address RefreshAddress(Segment 0 - 7 ) received matches an address SegmentMask( 0 - 7 ) stored in the mask information storage circuit  36 . A more detailed description of a conventional mask determination circuit and its operation may be found in U.S. Pat. No. 8,363,496, issued on Jan. 29, 2013, which is incorporated herein by reference for any purpose. A mask determination circuit including the comparison circuit  1400  may not have a one-to-one correspondence for a non-Nth power of 2 memory cell array. Additional activation/deactivation logic may need to be added, which may overlap with the existing mask determination circuit. This may require an increase in the chip size. 
         [0045]      FIG. 13  is a schematic illustration of mask determination circuit  34  including a comparison circuit  1500  according to an embodiment of the disclosure. The mask determination circuit  34  may be activated by the self-refresh internal command SR, and in response to the detection that a refresh RefADD and mask information MASK match, a match signal HIT may be activated to a high logic level. The mask determination circuit  34  may receive MASK signals SegmentMasks( 0 - 7 ) from a mask information storage circuit  36 . The MASK signals SegmentMasks( 0 - 7 ) may be provided to the comparison circuit  1500 . When segment masks are used, an address decoder  342  may be included for decoding the segment to which a refresh address RefADD corresponds. The address decoder  342  may provide a decoded address to the comparison circuit  1500 . The comparison circuit  1500  may compare the decoded address to the MASK signals SegmentMasks( 0 - 7 ). The MASK signals may include BankMasks( 0 - 7 ) in addition to SegmentMasks( 0 - 7 ). For simplicity, the BankMasks( 0 - 7 ) signals are not shown in  FIG. 13 . 
         [0046]    Still referring to  FIG. 13 , the comparison circuit  1500  may be configured to provide an active match signal HIT when a segment masked by any one of SegmentMasks( 0 - 7 ) and segment information output from address decoder  342  match. The comparison circuit  1500  includes OR gates  1505 ,  1510  coupled to an input of NAND gates  1515 ,  1520 , respectively, for SegmentMask 6  and SegmentMask 7 . A first input of each OR gate  1505 ,  1510  may be MASK signal SegmentMask 6  and SegmentMask 7 , respectively, and the second input of each OR gate may be fixed to a logic level high. The outputs of the NAND gates  1515 ,  1520  for Segments  6  and  7  may be provided to a separate NAND gate  1525 . The outputs of the NAND gates for Segments  6  and  7  are coupled to the same NAND gate as Segments  4  and  5 . In the embodiment illustrated in  FIG. 15 , Segments  6  and  7  correspond to the state where both X 13  and X 14  are 1. As a result, when both of the segments are selected, an active HIT signal may be output. Regardless of the signal from the MASK, because of the fixed logic level high at the second inputs of OR gates  1505 ,  1510  SegmentMask 6  and SegmentMask 7  may be respectively fixed to a high logic level during operating of the segment mask function. As described in more detail below, fixing SegmentMask 6  and SegmentMask 7  to a high logic level may suppress refresh operations corresponding to addresses having both X 13  and X 14  equal to 1. The NAND gate  1525  may be coupled through an inverter  1530  to an input of NAND gate  1535 . NAND gate  1535  may also receive the output of NAND gate  1540 . NAND gate  1540  may receive the combined logic outputs of Segments  0 - 5  and internal self-refresh signal SR. Since NAND gate  1525  is coupled to a succeeding stage of NAND gate  1540 , the corresponding function may be made active not only at the time of a self-refresh operation, but also at the time of all-bank auto-refreshing or other refresh operations. This may allow other or all types of refresh operations on non-existent memory mats (e.g., memory mats corresponding to addresses having both X 13  and X 14  equal to 1) to be suppressed. During the corresponding address period, circuits that are operated by the internal self-refresh command (represented by the signal SR) and the refresh all bank command (represented by the signal REFADD) may be blocked and power consumption by a semiconductor memory device may be reduced. 
         [0047]    As shown in  FIG. 13 , Segments  6  and  7  are masked because these segments correspond to 2K addresses where both X 13  and X 14  of the possible 8K addresses are set to 1. However, for configurations in which the addresses where no memory mats exist correspond to other segments, the comparison circuit  1500  may be modified to mask the corresponding segments. For example, for configurations in which the addresses where no memory mats exist correspond to Segments  5 - 7 , these three segments may be masked. For configurations in which the addresses where no memory mats exist correspond to Segment  7 , only the corresponding Segment  7  may be masked. Other configurations may also be used. 
         [0048]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.