Abstract:
A semiconductor memory device with adjustable I/O bandwidth includes a plurality of data I/O buffers connected one by one to a plurality of I/O ports, a switch array including a plurality of switches for connecting the plurality of data I/O buffers to a plurality of sense amplifier arrays, and a switch control unit for receiving external control signals to control the data I/O buffer and the plurality of switches.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a semiconductor memory device, and more specifically, to a semiconductor memory device compatible with various systems having different kinds of data input/output (I/O) bandwidths. 
   2. Description of the Prior Art 
   A conventional memory device has a fixed I/O bandwidth. A system using a memory device may have different bandwidths depending on manufacturing companies or its usage. Therefore, the conventional memory device requires an additional interfacing device to be used in a system having different data bandwidth from that of the conventional memory device. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a memory device configured to control a bandwidth of I/O data. 
   According to an embodiment of the present invention there is provided a memory device, including: a plurality of data I/O buffers connected one by one to a plurality of I/O ports; a switch array including a plurality of switches for connecting the plurality of data I/O buffers to a plurality of sense amplifier arrays; and a switch controller for receiving an external control signal to control the data I/O buffers and the plurality of switches. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating a structure of a memory device according to a preferred embodiment of the present invention. 
       FIG. 2  is a structural diagram illustrating a main bitline pull-up controller, a cell array block, and a column selection controller of  FIG. 1 . 
       FIG. 3  is a structural diagram illustrating the main bitline pull-up controller of  FIG. 2 . 
       FIG. 4  is a structural diagram illustrating a main bitline load controller of  FIG. 2 . 
       FIG. 5  is a structural diagram illustrating a column selection controller of  FIG. 2 . 
       FIG. 6  is a detailed structural diagram illustrating a sub cell block of  FIG. 2 . 
       FIGS. 7   a  and  7   b  are timing diagrams illustrating read/write operations of the sub cell block of  FIG. 6 . 
       FIGS. 8   a  through  8   d  are structural diagrams illustrating a data I/O buffer and a data pad of  FIG. 1 . 
       FIGS. 9   a  through  9   b  are structural diagrams illustrating a switch array, a data I/O buffer and a sense amplifier array of  FIG. 1 . 
       FIG. 10  is a structural diagram illustrating the switch array of  FIG. 9 . 
       FIG. 11  is a structural diagram illustrating the sense amplifier array and a column decoder of  FIG. 1 . 
       FIGS. 12   a  through  12   b  are detailed structural diagrams of a switch controller of  FIG. 1 . 
       FIGS. 13   a  through  13   d  are timing diagrams illustrating operations of the switch array, the sense amplifier array and the data I/O buffer of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will be described in more detail with reference to the accompanying drawings. 
     FIG. 1  is a block diagram illustrating a structure of a memory device which can control an I/O bandwidth according to a preferred embodiment of the present invention. The memory device of the present invention comprises a cell array block  100 , a main bitline pull-up controller  11  for pulling up a main bitline included in the cell array block  100  to a positive voltage, a column selection controller  12  for connecting the main bitline to a data bus  20 , a sense amplifier array  30  connected to the data bus  20 , a switch array  400  for controlling the sense amplifier array, and a data I/O buffer  500  for exchanging data with the sense amplifier array  30 . Additionally, the memory device of the present invention comprises a column decoder  200  for controlling the switch array  400 , and a switch controller  300  for controlling the switch array  400  and the data I/O buffer  500 . The memory device further comprises I/O ports or data pads  600  connected to the data I/O buffer  500  for inputting and outputting a plurality of data bits (data signals are referred to herein as “data bits”). 
     FIG. 2  is a structural diagram illustrating a cell array block  100  of  FIG. 1 . The cell array block  100  comprises one or a plurality of main bitline load controllers  13  and a plurality of sub cell blocks  110 . 
     FIG. 3  is a structural diagram illustrating the main bitline pull-up controller  11  of  FIG. 2 . The main bitline pull-up controller  11  comprises a PMOS transistor having a gate to receive a control signal MBPUC, a source connected to a power source VPP(VCC) and a drain connected to a main bitline MBL. 
   The main bitline pull-up controller  11  pulls up the main bitline MBL to a voltage VPP(VCC) in a precharge operation. 
     FIG. 4  is a structural diagram illustrating the main bitline load controller  13  of  FIG. 2 . The main bitline load controller  13  comprises a PMOS transistor having a gate to receive a control signal MBLC, a source connected to a power source VPP(VCC) and a drain connected to the main bitline MBL. 
   The main bitline load controller  13 , as a resistant device connected between the power source VPP(VCC) and the main bitline MBL, determines a potential of the main bitline according to the amount of current flowing through the main bitline load controller  13  in data sensing action. 
   One or more of the main bitline load controllers  13  are connected to one main bitline MBL. When two or more main bitline load controllers  13  are connected to one main bitline, the same number of sub cell blocks  110  are assigned to a main bitline load controller  13  and the main bitline load controllers  13  are evenly placed apart from each other. 
     FIG. 5  is a structural diagram illustrating the column selection controller  12  of  FIG. 2 . The column selection controller  12  is a switch for connecting the main bitline MBL to a data bus. On/off operations of the column selection controller  12  are controlled by control signals CSN and CSP. 
     FIG. 6  is a detailed structural diagram illustrating the sub cell block  110  of  FIG. 2 . 
   The sub cell block  110  comprises a sub bitline SBL, and NMOS transistors N 1 , N 2 , N 3 , N 4  and N 5 . The sub bitline SBL is connected in common to a plurality of unit cells, each of which is connected to a wordline WL&lt;m&gt; and a plateline PL&lt;m&gt;. The NMOS transistor N 1  for regulating a current has a gate connected to a first terminal of the sub bitline SBL, and a drain connected to the main bitline MBL. The NMOS transistor N 2  has a gate connected to a control signal MBSW, a drain connected to a source of the NMOS transistor N 1  and a source connected to a ground. The NMOS transistor N 3  has a gate connected to a control signal SBPD, a drain connected to a second terminal of the sub bitline SBL and a source connected to a ground. The NMOS transistor N 4  has a gate connected to a control signal SBSW 2 , a source connected to the second terminal of the sub bitline SBL and a drain connected to a control signal SBPU. The NMOS transistor N 5  has a gate connected to a control signal SBSW 1 , a drain connected to the main bitline MBL and a source connected to the second terminal of the sub bitline SBL. 
   When a unit cell is to be accessed, only the sub bitline connecting the unit cell is connected to the main bitline. Here, the sub bitline SBL is connected to the main bitline MBL by the NMOS transistor N 5 . Accordingly, memory read/write operations can be performed even with a smaller amount of load corresponding to one sub bitline rather than a larger amount of load corresponding to the whole bitline. 
   A potential of the sub bitline SBL is grounded when the control signal SBPD is activated. The control signal SBPU regulates a voltage to be provided to the sub bitline SBL. The control signal SBSW 1  regulates the flow of a signal between the sub bitline SBL and the main bitline MBL. The control signal SBSW 2  regulates the flow of a signal between the control signal SBPU and the sub bitline SBL. 
   The sub bitline SBL connected to a gate of the NMOS transistor N 1  regulates a sensing voltage of the main bitline. The main bitline MBL is connected to the power source VPP(VCC) via the main bitline load controller  13  (see  FIG. 4 ). When a control signal MBSW becomes “high”, current flows from the power source VPP(VCC), through the main bitline load controller  13 , the main bitline MBL and the NMOS transistors N 1  and N 2 , to a ground. Here, the amount of the current is determined by a voltage of the sub bitline SBL connected to the gate of the NMOS transistor N 1 . If data of a cell is “1”, the amount of the current becomes larger, thereby decreasing the voltage of the main bitline MBL. If data of a cell is “0”, the amount of the current becomes smaller, thereby increasing the voltage of the main bitline MBL. Here, the cell data can be detected by comparing the voltage of the main bitline MBL with a reference voltage. Detecting the cell data is performed in the sense amplifier array  30 . 
     FIG. 7   a  is a timing diagram illustrating a write operation of the sub cell block of  FIG. 6 . 
   If an address transits in t 1 , a chip starts a writing operation according to an address transition detection signal ATD. 
   In t 2  and t 3 , data of a cell is detected by activating a wordline WL and a plateline PL. When data of the cell is “high”, the voltage of the sub bitline rises, and current flowing through the NMOS transistor N 1  becomes larger. As a result, the voltage of the main bitline MBL becomes lower than a reference level. On the other hand, if data of the cell is “low”, the voltage of the sub bitline SBL falls, and current flowing through the NMOS transistor N 1  becomes smaller. As a result, the voltage of the main bitline MBL becomes higher than a reference level. 
   In t 4 , a self-boosting operation is prepared by setting the control signal SBSW 2  at a “high” level. In t 5 , “high” level data is written into the cell. If the control signal SBSW 2  is “high”, the control signal SBSW 2 , the wordline WL and the sub bitline SBL are driven to “high” levels when the control signal SBPU becomes “high”. Voltages of these signals rise higher than the voltage VPP by the self-boosting operation. In t 5 , since the wordline WL and the bitline SBL are high, and the plateline PL is low, data “1” is automatically written into the cell. 
   In t 6 , “low” level data is written. If the control signals SBPD and SBSW 2  are inactivated, and the control signal SBSW 1  is activated, data “0” provided from the main bitline MBL is supplied to the sub bitline SBL. Here, since the voltage of the plateline PL is “high”, data “0” is written into the cell. If a signal provided from the bitline is “1”, the voltage of the plateline is “high”, and the voltage of the sub bitline SBL is also “high”. As a result, data “1” written in t 5  is maintained without change. 
   In order to improve a sensing margin by stabilizing an initial state of a cell storage node, the wordline WL is activated earlier than the plateline. Then, the wordline WL is activated in t 2 , and then the plateline PL in t 3 . In t 2 , the control signal SBPD is maintained at the “high” level, the data of the cell is initialized as “0”. After initialization, the control signal SBPD is inactivated to the “low” state, and the plateline is activated to the “high” level. After the data “0” is written in t 6 , the wordline WL is inactivated earlier than the plateline PL by inactivating the wordline WL in t 7 , and then the plateline PL in t 8  (not shown). 
     FIG. 7   b  is a timing diagram illustrating a read operation of the sub cell block of  FIG. 6 . 
   The operations in the intervals t 2  through t 6  are as described in  FIG. 7   a . The read operation is different in that data detected in a sense amplifier (not shown) is not externally outputted. 
   In t 5  and t 6 , a restore operation is performed. In the restore operation, the data detected in the sense amplifier (not shown) is temporarily stored, and then re-written into the cell. Since the data stored in the sense amplifier is provided to the cell through the bitline, the restore operation is similar to the write operation. In t 5 , the data “1” is automatically written in the same manner of the write operation. In t 6 , the data “1” written in the section t 5  is maintained if the data “1” is provided to the bitline, and the data “0” is written if the data “0” is provided to the bitline. 
     FIGS. 8   a  through  8   d  are structural diagrams illustrating a data I/O buffer and a data pad of  FIG. 1 . 
   Referring to  FIG. 8   a , data pads  610  and  620  comprise DQ_ 0  through DQ_ 15 . The data pads  610  and  620  are connected to a data I/O buffer  500  (see  FIG. 1 ). The data I/O buffer  500  is divided into a lower byte region  510  and an upper byte region  520 . DQ_ 0  through DQ_ 7  are connected to the lower byte region  510 , and DQ 8  through DQ 15  are connected to the upper byte region  520 . DQ_ 15  in the upper byte is used as an A_LSB signal which is provided to the switch controller  300  (see  FIG. 1 ). The A_LSB signal corresponds to an additional address signal. For example, when a system bus processes data by 1 byte, and a memory device processes data by 2 bytes, data of 2 bytes should be stored in a memory address for efficiency of the memory device. However, since the system processes data in 1 byte, 2 bytes should be differentiated and then processed by the memory device. Here, by using the control signal A_LSB, data inputted/outputted to and from the memory device can be processed by 1 byte. 
     FIG. 8   b  has the same structure as  FIG. 8   a . However, it is different in that the A_LSB signal is provided from one of the bits DQ_ 8  through DQ_ 14  included the upper byte except the most significant bit DQ_ 15 . 
   A preferred embodiment shown in  FIG. 8   c  comprises a plurality of upper byte regions unlike the preferred embodiments shown in  FIGS. 8   a  and  8   b . A control signal which is one of A 0     —   LSB, . . . , A n     —   LSB, exists in each of the upper byte regions. These signals are outputted from the most significant bit in each upper byte region. The control signals A 0     —   LSB through A n     —   LSB are used as additional address signals like the control signal A_LSB of  FIG. 8   a.    
     FIG. 8   d  has the same structure of  FIG. 8   c . However, it is different in that the control signals A 0     —   LSB through A n     —   LSB are provided from one of the bits included in each upper byte region except the most significant bits. 
     FIGS. 9   a  through  9   b  are structural diagrams illustrating the switch array  400 , the data I/O buffer  500  and the sense amplifier array  30  of  FIG. 1 . 
   The data I/O buffer  500  is connected to an I/O bus. The I/O bus is divided into a lower byte bus LB_BUS and an upper byte bus UB_BUS. The lower byte bus LB_BUS comprises m bits, and the upper byte bus LB_BUS comprises n bits. The lower byte bus LB_BUS is connected to the lower byte region  510  of the data I/O buffer  500 . The upper byte bus UB_BUS is connected to the upper byte region  520  of the data I/O buffer. Each sense amplifier included in the sense amplifier array  30  is divided into a lower byte region  31  and an upper byte region  32 . 
   The switch array  400  comprises a first switch  410 , a second switch  420  and a third switch  430 . The first switch  410  connects the lower byte bus LB_BUS to the lower byte region  31  of the sense amplifier array  30 . The second switch  420  connects the lower byte bus LB_BUS to the upper byte region  32  of the sense amplifier array  30 . The third switch  430  connects the upper byte bus UB_BUS to the upper byte region  32  of the sense amplifier array  30 . The second switch  420  transmits n bits of sense amplifier bits to the lower byte bus LB_BUS. 
     FIG. 9   b  additionally shows control signals in the switch array  400  and the data I/O buffer  500  of  FIG. 9   a . The lower byte region  510  of the data I/O buffer  500  is controlled by ORing the control signals LB_EN and Byte_EN. The on/off operations of the first switch  410  are controlled by a control signal LB_SW_EN. The on/off operations of the second switch  420  are controlled by a control signal Byte_SW_EN. The on/off operations of the third switch  430  are controlled by a control signal UB_SW_EN. 
     FIG. 10  is a structural diagram illustrating the switch array  400  of  FIG. 9 . According to a preferred embodiment of the present invention, the first switch  410 , the second switch  420  and the third switch  430  have the same structure. Each switch comprises a predetermined number of transmission gates arranged in parallel. A transmission gate included in the first switch  410  is controlled by the control signal LB_SW_EN. A transmission gate included in the second switch  420  is controlled by the control signal Byte_SW_EN. A transmission gate included in the third switch  430  is controlled by the control signal UB_SW_EN. 
     FIG. 11  is a structural diagram illustrating the sense amplifier array  30  and a column decoder  200  of  FIG. 1 . As described above, each sense amplifier in the sense amplifier array  30  is included either in the lower byte region  31  or in the upper byte region  32 . The sense amplifier array is controlled by output signals Y&lt;0&gt;˜Y&lt;n&gt; of the column decoder  200 . 
     FIGS. 12   a  through  12   b  are detailed structural diagrams of the switch controller  300  of  FIG. 1 . The switch controller  300  receives control signals A_LSB, /Byte, /LB, /UB, and output signals of the column decoder to provide control signals LB_SW_EN, UB_SW_EN, Byte_SW_EN, LB_EN and UB_EN. 
   Referring to  FIG. 12   a , the circuit of  FIG. 12   a  generates control signals LB_EN and UB_EN provided to the data I/O buffer  500  and control signals Byte_EN, Byte_BUF, A_LSB_ 0  and A_LSB_ 1  used in the intermediate process. 
   The /Byte signal determines activation of the lower byte region. The Byte_BUF signal is generated by buffering the /Byte signal, and the Byte_EN signal is generated by inverting the Byte_BUF signal. 
   The /LB signal determines activation of lower bytes. The LB_EN signal is generated by performing an AND operation on (“ANDing”) the buffered /LB signal and the Byte_BUF signal and then by inverting the signal obtained from the AND operation. When the /Byte signal is “low”, the Byte_BUF signal is “low”. As a result, the LB_EN signal becomes “high” regardless of the level of the /LB signal. However, when the /Byte signal is “high”, the Byte_BUF signal is “high”. As a result, the level of the LB_EN signal is regulated by that of the /LB signal. 
   The /UB signal regulates activation of upper bytes. The UB_EN signal is generated by ANDing the Byte_BUF signal and a signal generated by buffering and then inverting the /UB signal. When the /Byte signal is “low”, the Byte_BUF signal is “low”. As a result, the UB_EN signal becomes “low” regardless of the level of the /LB signal. However, when the /Byte signal is “high”, the Byte_BUF signal is “high”. As a result, the level of the UB_EN signal is regulated by that of the /UB signal. 
   The A_LSB signal converts data of upper bytes into data of lower bytes. The A_LSB_ 1  signal is generated by ANDing the A_LSB signal and the Byte_EN signal. The A_LSB_ 0  signal is generated by ANDing the A_LSB signal and the Byte_EN signal and then inverting the signal obtained by the AND operation. When the /Byte signal is “low”, the Byte_EN signal is “high”, one of the A_LSB_ 1  or the A_LSB_ 0  signals becomes “high”, and the other signal becomes “low”. However, when the /Byte signal is “high”, the Byte_EN signal is “low”. As a result, the level of the A_LSB_ 0  signal becomes “high”, and the level of the A_LSB_ 1  signal becomes “low” regardless of the level of the A_LSB signal. 
   The circuit of  FIG. 12   b  outputs control signals LB_SW_EN, UB_SW_EN and Byte_SW_EN by using the signals A_LSB_ 0 , A_LSB_ 1 , UB_EN and Byte_EN of  FIG. 12   a  and the output Y&lt;n&gt; of the column decoder  200 . 
   The control signal LB_SW_EN for controlling the on/off operation of the first switch  410   FIG. 9   b  is obtained by ANDing the A_LSB_ 0  signal and the output Y&lt;n&gt; of the column decoder  200 . The control signal Byte_SW_EN for controlling the on/off operations of the second switch  420  of  FIG. 9   b  is obtained by ANDing the signals A_LSB_ 1  and Byte_EN and the output Y&lt;n&gt; of the column decoder  200 . The control signal UB_SW_EN for controlling the on/off operations of the third switch  430  of FIG.  9   b  is obtained by ANDing the inverted Byte_EN signal, the UB_EN signal and the output Y&lt;n&gt; of the column decoder  200 . The function of each signal is as follows. 
     FIGS. 13   a  through  13   d  are timing diagrams illustrating operations of the switch array  400 , the sense amplifier array  30  and the data I/O buffer  500 . 
     FIG. 13   a  shows the timing diagram when the first switch  410  is activated, and data in the lower byte region  31  of the sense amplifier array  30  is provided to the lower byte region  510  of the data I/O buffer  500 . In this state, the /Byte signal is inactivated to the “high” level, the /LB signal is activated to the “low” level, and the /UB signal is inactivated to the “high” level. Here, the Byte_EN signal becomes “low”, the Byte_BUF signal becomes “high”, the LB_EN signal becomes “high”, the UB_EN signal becomes “low”, and the A_LSB_ 0  becomes “high”, and the A_LSB_ 1  becomes “low” (see  FIG. 12   a ). 
   Since the A_LSB_ 0  signal is “high”, the LB_SW_EN signal becomes “high”. Since the UB_EN signal is “low”, the UB_SW_EN becomes “low” (see  FIG. 12   b ). As a result, the upper byte region  520  of the data I/O buffer  500  is inactivated (see  FIG. 9   b ). If the LB_EN signal becomes “high”, a signal obtained by performing an OR operation on (“ORing”) the signals LB_EN and Byte_EN becomes “high”. As a result, the lower byte region  510  of the data I/O buffer  500  is activated (see  FIG. 9   b ). Here, data in the lower byte region  31  of the sense amplifier array  30  is outputted into the lower byte region  510  of the data I/O buffer  500 . 
     FIG. 13   b  shows the timing diagram when the third switch  430  is activated, and data in the lower byte region  32  of the sense amplifier array  30  is provided to the lower byte region  520  of the data I/O buffer  500 . In this state, the /Byte signal is inactivated to the “high” level, the /LB signal is inactivated to the “high” level, and the /UB signal is activated to the “low” level. Here, the Byte_EN signal becomes “low”, the Byte_BUF signal becomes “high”, the LB_EN signal becomes “low”, the UB_EN signal becomes “high”, and the A_LSB_ 0  becomes “high”, and the A_LSB_ 1  becomes “low” (see  FIG. 12   a ). 
   Since the A_LSB_ 0  signal is “high”, the LB_SW_EN signal becomes “high”. Since the UB_EN signal is “high”, the UB_SW_EN becomes “high” (see  FIG. 12   b ). As a result, the upper byte region  520  of the data I/O buffer  500  is activated (see  FIG. 9   b ). If the LB_EN signal becomes “low”, a signal obtained by ORing the signals LB_EN and Byte_EN becomes “low”. As a result, the lower byte region  510  of the data I/O buffer  500  is inactivated (see  FIG. 9   b ). Here, data in the upper byte region  32  of the sense amplifier array  30  is outputted into the upper byte region  520  of the data I/O buffer  500 . 
     FIG. 13   c  shows the timing diagram when the first switch  410  and the third switch  430  are activated, data in the lower byte region  31  of the sense amplifier array  30  is provided to the lower byte region  510  of the data I/O buffer  500 , and data in the upper byte region  32  of the sense amplifier array  30  is outputted into the upper byte region  520  of the data I/O buffer  500 . The detailed operation is omitted because it is similar to the above-described operation. 
     FIG. 13   d  shows the timing diagram when the first switch  410  and the second switch  420  are activated in turn. In this state, the /Byte signal is inactivated to the “low” level, and the /LB signal and the /UB signal are inactivated to the “high” level. Here, the Byte_EN signal becomes “high”, the Byte_BUF signal becomes “low”, the LB_EN signal becomes “high”, the UB_EN signal becomes “low”, and the A_LSB_ 0  becomes a signal obtained by inverting the A_LSB signal, and the A_LSB_ 1  becomes the same value of the A_LSB signal (see  FIG. 12   a ). 
   Since the output Y&lt;n&gt; of the column decoder  200  is activated, the Byte_EN signal is “high”, the UB_SW_EN signal is “low”, the LB_SW_EN is at the same level with the A_LSB_ 0 , and the Byte_SW_EN is at the same level with the A_LSB_ 1 . If the A_LSB signal is “high”, the LB_SW_EN becomes “low”, and the Byte_SW_EN becomes “high”. If the A_LSB signal is “low”, the LB_SW_EN signal becomes “high”, and the Byte_SW_EN signal becomes “low” (see  FIG. 12   b ). As a result, the upper byte region  520  of the data I/O buffer  500  is inactivated, and the lower byte region  510  is activated (see  FIG. 9   b ). 
   An example is described where data of a memory device is processed by 2 bytes, and data of a system bus is processed by 1 byte. Here, an address of a system bus is designated every 1 byte of data, and an address of a memory device is designated every 2 bytes of data. The number of address bits used in the system should be one more than that used in the memory device. The data bit A_LSB in the upper byte region is used as an address bit in order to compensate for the insufficient address bit (see  FIGS. 8   a  through  8   d ). 
   The process of storing data into a memory is as follows. An address of a system bus is designated every 1 byte of data, and the system bus is provided to the lower byte region  510  of the data I/O buffer  500 . Here, if the A_LSB_ 0  signal becomes “high”, the A_LSB_ 1  becomes “high”, the LB_SW_EN becomes “low”, and the Byte_SW_EN becomes “high”. As a result, the lower byte region  510  of the data I/O buffer  500  becomes connected to the lower byte region  31  of the sense amplifier array  30  via the first switch  410  (see  FIGS. 9   b ,  12   a  and  12   b ). If the A_LSB signal becomes “low”, the A_LSB_ 0  signal becomes “high”, the LB_SW_EN becomes “high”, and the Byte_SW_EN signal becomes “low”. As a result, the lower byte region  510  of the data I/O buffer  500  becomes connected to the upper byte region  32  of the sense amplifier array  30  via the second switch  420 . 
   The process of reading data from the sense amplifier array  30  to the data I/O buffer  500  is performed as described above. 
   Accordingly, the semiconductor memory device of the present invention does not need extra interfacing devices by effectively changing the data I/O bandwidth of the memory device. 
   While the present invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims.