Patent Publication Number: US-2011069568-A1

Title: Semiconductor memory device having local sense amplifier with on/off control

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2004-0061090, filed on Aug. 3, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor memory device, and more particularly, to a semiconductor memory device with a local sense amplifier that can be turned on only if required. 
     2. Description of the Related Art 
     In a semiconductor memory device such as a dynamic random access memory (DRAM) or a synchronous random access memory (SRAM), data read in a read operation sequentially passes through a plurality of sense amplifiers and is then output. Since data read from a memory cell has a low voltage, the voltage of the data is amplified by a bit line sense amplifier. The amplified voltage of the data is amplified again by a data sense amplifier, and then the data is output.  FIG. 1  illustrates such a path of data read in a read operation. 
       FIG. 1  is a schematic circuit diagram of a conventional semiconductor memory device  100 . The semiconductor memory device  100  includes a memory cell  110  in an array block, a pair of bit lines BL and /BL connected to the memory cell  110 , an equalization circuit  120  that precharges the bit lines BL and /BL, a pair of local input/output (I/O) lines LIO and /LIO to be connected to the bit lines  13 L and /BL in response to a column selection line signal CSL, a pair of global I/O lines GIO and /GIO to be connected to the local I/O lines LIO and /LIO in response to a control signal LGIOMUX, a pair of data I/O lines DIO and /DIO to be connected to the global I/O lines GIO and /GIO in response to a control signal IOMUX, and a data sense amplifier  130 . 
     As described above, a voltage of data stored in the memory cell  110  is amplified by a bit line sense amplifier (not shown) and the data sense amplifier  130 , and then, the data is read at a high logic level or a low logic level. 
     More specifically, during a read operation of the semiconductor memory device  100 , an /RAS active command (not shown) is activated to activate a word line connected to a memory cell of a row address from which the data is to be read. When the word line is activated, data stored in all memory cells connected to the activated word line is transmitted to bit lines corresponding to the memory cells, respectively. 
     Next, the bit line sense amplifier amplifies a voltage of data output from the bit lines BL and /BL according to a logic level of the data, i.e., at a high logic level or a low level. Next, the data output from the bit lines BL and /BL is transmitted to the data I/O lines DIO and /DIO in response to the column selection line signal CSL activated in response to a /CAS active command (not shown). 
     Recent trends have seen an increase in integration density of semiconductor memory devices and a reduction of a voltage thereof. An increase in the density results in an increase in the load capacitance across each pair of data lines, and a reduction in the voltage results in a reduction in the difference between voltages of the pairs of data lines applied to corresponding amplifiers. 
     Accordingly, it becomes more and more difficult for amplifiers to detect data with a minimum voltage difference and amplify voltages of the data. Further, semiconductor memory devices are required to operate at high speeds. tRCD, which is a major parameter for high-speed operation of semiconductor memory devices, denotes a duration between an execution of an /RAS active command and a /CAS active command, i.e., an /RAS to /CAS delay time. The lower the tRCD value, the faster an operating speed of a system using a DRAM. 
       FIG. 2A  illustrates a tRCD parameter of a semiconductor memory device.  FIG. 2B  illustrates a relationship between amplification of data output from a pair of bit lines and the tRCD parameter. 
     The tRCD parameter has a minimum value when the difference in voltage or current between data output from the data I/O lines DIO and /DIO has a minimum value that the data sense amplifier  130  can detect. 
     Referring to  FIG. 2B , while the tRCD parameter can be reduced to a minimum value, in an internal operation of the semiconductor memory device  100  of  FIG. 1 , the lower the tRCD value, the more likely it is that the column selection line signal CSL will be activated before voltages of data output from the bit lines BL and /BL are completely amplified. Thus, the difference in voltage or current between data output from the data I/O lines DIO and /DIO to be applied to the data sense amplifier  130  becomes reduced. If the difference in voltage or current is too small for the data sense amplifier  130  to detect, incorrect data may be read. 
     SUMMARY OF THE INVENTION 
     It is possible to increase the tRCD parameter by adding a sense amplifier capable of amplifying a voltage of data between the data sense amplifier  130  and a bit line sense amplifier (not shown), thereby improving a performance of the semiconductor memory device. 
     Further, when the added sense amplifier can be turned on if necessary, it is possible to reduce an amount of current required to use the added sense amplifier. 
     An embodiment of the present invention provides a local sense amplifier that can be controlled to be turned on only if necessary. 
     According to an aspect of the present invention, there is provided a semiconductor memory device comprising a plurality of memory cells in one or more array blocks; a pair of local input/output lines comprising a local input/output line and an inverted local input/output line; a pair of global input/output lines comprising a global input/output line and an inverted global input/output line; a local sense amplifier amplifying voltages of data signals output from the local input/output lines and transmitting the data to the global input/output lines in response to a local sense control signal; and a data sense amplifier amplifying voltages of data signals output from the data input/output lines connected to the global input/output lines and outputting the data from the semiconductor memory device in response to a sensing enable signal. The data sense amplifier can be a current type sense amplifier. 
     The semiconductor memory device can further include a load transistor unit allowing current to flow through the global input/output lines in response to a load signal, and a selection switching unit connecting the data sense amplifier to one of the memory cell array blocks in response to a selection signal. The load transistor unit comprises a first load transistor having a first terminal to which a first voltage is applied, a second terminal connected to the global input/output line, and a gate to which the load signal is input; and a second load transistor having a first terminal to which the first voltage is applied, a second terminal connected to the inverted global input/output line, and a gate to which the load signal is input. 
     The semiconductor memory device can further include a local input/output line precharge controller for precharging voltages of the local input/output lines to a predetermined voltage in response to precharge control signals. 
     According to another aspect of the present invention, there is provided a semiconductor memory device including a plurality of memory cell array blocks; a bit line sense amplifier amplifying voltages of data output from a pair of bit lines connected to the memory cell array blocks and transmitting the data to a pair of local input/output lines; a local sense amplifier amplifying voltages of data output from the local input/output lines and transmitting the data to a pair of global input/output lines in response to a local sense control signal; a data sense amplifier amplifying voltages of data output from a pair of data input/output lines connected to the global input/output lines and outputting the data from the semiconductor memory device in response to a sensing enable signal; and a controller activating the local sense control signal for a predetermined duration in response to a first signal and a second signal. 
     The first signal can be activated in response to a row active command, and the local sense amplifier can be activated for a predetermined duration after the first signal is activated. 
     The first signal is a bit line sense enable signal which activates the bit line sense amplifier, and the local sense amplifier is activated for a predetermined duration after the bit line sense enable signal is activated. 
     The second signal can be activated or deactivated to be in phase with a column selection line signal that connects the bit lines and the local input/output lines. 
     The controller preferably comprises a pulse generator generating a first pulse signal activated for a predetermined duration in response to the first signal; and a local sense control signal generator activating the local sense control signal when both the first pulse signal and the second signal are activated, and deactivating the local sense control signal when the second signal is deactivated. 
     The semiconductor memory device can further include a local input/output line precharge controller for precharging the local input/output lines in response to a precharge control signal, wherein the controller can further comprise a precharge control signal generator activating the precharge control signal for a predetermined duration when the local sense control signal is deactivated. 
     The controller is preferably located in a periphery region outside a memory core. The data sense amplifier is one of a current type sense amplifier and a voltage type sense amplifier. 
     According to yet another aspect of the present invention, there is provided a semiconductor memory device comprising a plurality of memory cell array blocks; a bit line sense amplifier amplifying voltages of data output from a pair of bit lines connected to the memory cell array blocks and transmitting the data to a pair of local input/output lines; a local sense amplifier amplifying voltages of data output from the local input/output lines and transmitting the data to a pair of global input/output lines in response to a predetermined signal; a data sense amplifier amplifying voltages of data output from a pair of data input/output lines connected to the global input/output lines and outputting the data from the semiconductor memory device in response to a sensing enable signal; and a local sense amplifier controller generating the predetermined signal which controls the local sense amplifier in response to a control signal and a local sense control signal. The local sense amplifier operates in response to the local sense control signal when the control signal is activated, and does not operate when the control signal is deactivated. 
     The local sense amplifier controller performs an AND operation on the control signal and the local sense control signal to generate the predetermined signal. 
     The control signal can be activated or deactivated by one of a mode register set and a fuse unit. 
     According to still another aspect of the present invention, there is provided a semiconductor memory device comprising a plurality of memory cell array blocks; a bit line sense amplifier amplifying voltages of data output from a pair of bit lines connected to the memory cell array blocks and transmitting the data to a pair of local input/output lines; a local sense amplifier amplifying voltages of data output from the local input/output lines and transmitting the data to a pair of global input/output lines in response to a local sense control signal; a data sense amplifier amplifying voltages of data output from a pair of data input/output lines connected to the global input/output lines and outputting the data from the semiconductor memory device in response to a sensing enable signal; and a controller deactivating the local sense control signal when a control signal is deactivated and activating the local sense control signal for a predetermined duration in response to a first signal and a second signal when the control signal is activated. 
     The control signal can be activated or deactivated by one of a mode register set and a fuse unit. The first signal is activated in response to a row active command, and the local sense amplifier is activated for a predetermined duration after the first signal is activated. The first signal is a bit line sense enable signal which activates the bit line sense amplifier, and the local sense amplifier is activated for a predetermined duration after the bit line sense enable signal is activated. 
     The control signal can be activated or deactivated to be in phase with a column selection line signal which connects the bit lines and the local input/output lines amplifier. 
     The controller comprises a third signal generator performing an AND operation on the control signal and the second signal to generate a third signal; a pulse generator generating a first pulse signal which is activated for a predetermined duration in response to the first signal; and a local sense control signal generator deactivating the local sense control signal when the third signal is deactivated and activating the local sense control signal when both the first pulse signal and the third signal are activated. 
     The semiconductor memory device can further include a local input/output line precharge controller precharging the local input/output lines in response to a precharge control signal, wherein the controller further comprises a precharge control signal generator activating the precharge control signal for a predetermined duration when the local sense control signal is deactivated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic circuit diagram of a conventional semiconductor memory device; 
         FIG. 2A  illustrates a tRCD parameter of a semiconductor memory device; 
         FIG. 2B  illustrates a relationship between amplification of data output from a pair of hit lines and the tRCD parameter; 
         FIG. 3  is a circuit diagram of a semiconductor memory device according to an embodiment of the present invention; 
         FIG. 4  is a timing diagram of a read operation of the semiconductor memory device illustrated in  FIG. 3 ; 
         FIG. 5  is a block diagram of a semiconductor memory device according to another embodiment of the present invention; 
         FIG. 6  is a mixed block and circuit diagram of a semiconductor memory device according to yet another embodiment of the present invention; 
         FIG. 7  is a circuit diagram of a controller illustrated in  FIG. 6 ; 
         FIG. 8  is a timing diagram of an operation of the semiconductor memory device illustrated in  FIG. 6 ; 
         FIG. 9  is a block diagram of a semiconductor memory device according to still another embodiment of the present invention; and 
         FIG. 10  is a circuit diagram of a controller illustrated in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals denote like elements in the drawings. 
       FIG. 3  is a circuit diagram of a semiconductor memory device  300  according to an embodiment of the present invention.  FIG. 4  is a timing diagram of a read operation of the semiconductor memory device  300  according to an embodiment of the present invention. 
     Referring to  FIGS. 3 and 4 , the semiconductor memory device  300  includes a plurality of memory cells  310  in an array block, a pair of local input/output (I/O) lines LIO and /LIO, a pair of global I/O lines GIO and /GIO, a local sense amplifier  320 , a local I/O line precharge controller  360 , and a data sense amplifier  330 . The local sense amplifier  320  amplifies voltages of data output from the local I/O lines LIO and /LIO and then transmits the data to the global I/O lines GIO and /GIO, in response to a local sense control signal LSAEN generated according to a read command. 
     The local I/O line precharge controller  360  precharges the local I/O lines LIO and /LIO to an operating voltage VINT during row activation of the memory device, and precharges them to a voltage VBL that is about half the operating voltage VINT during a precharge operation of the memory device. 
     The data sense amplifier  330 , which in this embodiment is a current type sense amplifier, amplifies and outputs the difference in current between the data I/O lines DIO and /DIO connected to the global I/O lines GIO and /GIO in response to a sensing enable signal PIOSE generated according to a read command. That is, the semiconductor memory device  300  is constructed such that the local sense amplifier  320  and the current type data sense amplifier  330  are connected. 
     Hereinafter, an operation of the semiconductor memory device  300  according to an embodiment of the present invention is described in detail with reference to  FIGS. 3 and 4 . 
     It is assumed for this example that data is read from a memory cell that stores data  1 . In a precharge state in which a row active command ACT_CMD has yet to be given, the local I/O lines LIO and /LIO are precharged by precharge controller  360  to a predetermined voltage VBL in response to a precharge control signal LIOEQP. 
     When the row active command ACT_CMD is given, the local I/O lines LIO and /LIO are precharged by precharge controller  360  to the operating voltage VINT in response to a precharge control signal LIOEQA. Also, data output from a memory cell  310  connected to an activated word line in a memory block is transmitted to the bit lines BL and /BL, and data output from the bit lines BL and /BL is amplified by a bit line sense amplifier  315  in response to a bit line sense amplification control signal BLSAEN. 
     When a read command RD_CMD is given, precharging of the local I/O lines LIO and /LIO in response to the precharge control signal LIOEQA is stopped, and the local I/O lines LIO and /LIO are floated at the operating voltage VINT. Next, a column selection line signal CSL is activated, and then data output from the bit lines BL and /BL is transmitted to the local I/O lines LIO and /LIO, thereby performing charge sharing. The local I/O line LIO is maintained at the operating voltage VINT, and the voltage of the inverted local I/O line /LIO becomes lower than the operating voltage VINT (i). The column selection line signal CSL may be continuously activated depending on a burst length. The local sense amplifier  320  amplifies voltages of data output from the local I/O lines LIO and /LIO in response to the local sense control signal LSAEN and transmits the data to the global I/O lines GIO and /GIO (ii). The local sense amplifier  320  maintains the local I/O line LIO at the operating voltage VINT and amplifies the voltage of the inverted local I/O line /LIO to a ground voltage VSS. 
     Transistors CTR 1  and CTR 2 , which are both connected to respond to the control signal IOMUX, connect the global I/O lines GIO and /GIO to the local I/O lines LIO and /LIO respectively during a write operation, and are turned off during a read operation. 
     A selection switching unit  350  connects the global I/O lines GIO and /GIO to the data I/O lines DIO and /DIO in response to a selection signal SELS. That is, the selection switching unit  350  selects a bank (not shown) to be connected to the data I/O lines DIO and /DIO. 
     When the selection signal SELS is activated at a low logic level, transistors SSTR 1  and SSTR 2  are turned on to connect the global I/O lines GIO and /GIO to the data I/O lines DIO and /DIO (iii). 
       FIG. 3  illustrates the global I/O lines GIO and /GIO connected to the selection switching unit  350  for convenience. However, according to the present invention, a plurality of global I/O lines (not shown) and a plurality of memory arrays (not shown) may be connected to the data I/O lines DIO and /DIO. A load transistor unit  340  includes a first load transistor LTR 1  and a second load transistor LTR 2 . A first voltage V 1  is applied to a first terminal of the first load transistor LTR 1 , a second terminal of which is connected to the global I/O line GIO, and a load signal LOADS is input to its gate. The first voltage V 1  is a predetermined voltage. 
     The first voltage V 1  is applied to a first terminal of the second load transistor LTR 2 , a second terminal of which is connected to the inverted global I/O line /GIO, and the load signal LOADS is input to its gate. 
     The first and second load transistors LTR 1  and LTR 2  supply a predetermined current to the global I/O lines GIO and /GIO and the data I/O lines DIO and /DIO in response to the load signal LOADS. The current supplied to the inverted global I/O line /GIO is conducted to the ground voltage VSS via the local sense amplifier  320 , and thus, a small amount of current is supplied to the inverted data I/O line /DIO. In contrast, since the current supplied to the global I/O line GIO is not conducted to the ground voltage VSS via the local sense amplifier  320 , the current is supplied to the data I/O line DIO. 
     The data sense amplifier  330  detects the difference in current between the data I/O lines DIO and /DIO, amplifies the detected difference in current, transforms the amplified difference in current into a voltage, and outputs the voltage outside the semiconductor memory device  300  via output nodes NOUT 1  and NOUT 2 , in response to the sensing enable signal PIOSE. 
     The local I/O lines LIO and /LIO must be precharged to the operating voltage VINT again to continuously activate the column selection line signal CSL to read data according to a burst length when a read command is given. Specifically, when the column selection line signal CSL is disabled, the local sense control signal LSAEN is also disabled and the local I/O lines LIO and /LIO are precharged again to the operating voltage VINT in response to the precharge control signal LIOEQA. The precharge control signal LIOEQA is activated at a high logic level to control a precharging operation when the column selection line signal CSL is deactivated, that is, when the local sense control signal LSAEN is deactivated. Then, a read operation is performed as described above. 
     As described above, the semiconductor memory device  300  is capable of increasing the tRCD parameter using the local sense amplifier  320  and the current type data sense amplifier  330 . That is, the tRCD parameter is increased by amplifying a difference in voltage between data using the local sense amplifier  320  before the data is transmitted to the sense amplifier  330 . The current type data sense amplifier  330  does not additionally require precharging and equalizing for a data operation and is thus helpful to operate the semiconductor memory device  300  at a high speed compared to a voltage type data sense amplifier. Accordingly, an operating frequency of the semiconductor memory device  300  is also increased. 
       FIG. 5  is a block diagram of a semiconductor memory device  500  according to another embodiment of the present invention. The semiconductor memory device  500  includes a plurality of memory cells  510 , a bit line sense amplifier  520 , a local I/O line precharge controller  525 , a local sense amplifier  530 , a data sense amplifier  540 , and a local sense amplifier controller  550 . 
     The constructions and operations of the memory cell arrays  510 , the bit line sense amplifier  520 , and the data sense amplifier  540  are the same as those of the memory cell arrays  310 , the bit line sense amplifier  315 , and the data sense amplifier  330  of the semiconductor memory device  300  of  FIG. 3 , respectively. However, unlike in the semiconductor memory device  300 , the data sense amplifier  540  can be either a voltage type or a current type. The local sense amplifier controller  550  generates a signal LSAEN 1  that determines whether the local sense amplifier  530  must be activated by performing an AND operation on a control signal CON input to a mode register set (MRS) (not shown) or a fuse unit (not shown), and a local sense control signal LSAEN generated according to a read command. The local sense amplifier controller  550  can include an AND gate. To increase the tRGD parameter when operating the semiconductor memory device  500 , the control signal CON input to the MRS or the fuse unit is enabled and the local sense control signal LSAEN is generated according to a read command so as to operate the local sense amplifier  530 . 
     To reduce the consumption of current regardless of the tRCD parameter when operating the semiconductor memory device  500 , the control signal CON can be disabled so that the local sense amplifier  530  is kept off, i.e., non-amplifying. The construction and operation of the local sense amplifier controller  550  that generates the control signal CON to be maintained in an activation or deactivation state by the MRS or the fuse unit, are known to those skilled in the art, and therefore will not be described. 
       FIG. 6  is a diagram of a semiconductor memory device  600  according to another embodiment of the present invention. The semiconductor memory device  600  includes a plurality of memory cells  610 , a bit line sense amplifier  620 , a local I/O line precharge controller  660 , a local sense amplifier  630 , a data sense amplifier  640 , and a controller  650 . 
     The bit line sense amplifier  620  amplifies voltages of data output from a pair of bit lines BL and /BL connected to the memory cell arrays  510  and transmits the data to a pair of local I/O lines LIO and /LIO. 
     The local sense amplifier  630  amplifies voltages of data output from the local I/O lines LIO and /LIO and transmits the data to a pair of global I/O lines GIO and /GIO in response to a local sense control signal LSAEN. 
     The data sense amplifier  640  amplifies voltages of data output from a pair of data I/O lines DIO and /DIO connected to the global I/O lines GIO and /GIO and outputs the data from the semiconductor memory device  600  in response to a sensing enable signal PIOSE. The data sense amplifier  640  can be a current type sense amplifier or a voltage type sense amplifier. 
     The constructions and operations of the array of memory cells  610 , the bit line sense amplifier  620 , the local I/O line precharge controller  660 , the local sense amplifier  630 , and the data sense amplifier  640  are the same as those of memory cell arrays, a bit line sense amplifier, a local I/O line precharge controller, a local sense amplifier, and a data sense amplifier of a semiconductor memory device as described above. 
     The controller  650  activates the local sense control signal LSAEN only under predetermined conditions in response to a first signal S 1  and a second signal S 2 . That the local sense control signal LSAEN is activated only under the predetermined conditions must be understood that the local sense amplifier  630  operates only under the same predetermined conditions. 
     The first signal S 1  is activated in response to a row active command. In particular, in this embodiment, the first signal S 1  is a bit line sense enable signal that activates the bit line sense amplifier  620  in response to a row active command ACT_CMD, and the second signal S 2  is generated to be in phase with a column selection line signal generated according to a read command. 
     More specifically, a predetermined delay time after the bit line sense enable signal S 1  is activated is set to a minimum tRCD value, and the local sense amplifier  630  operates only when a column selection line signal CSL is activated within the delay time according to a read command. If the local sense amplifier  630  operates only when the column selection line signal CSL is activated within the delay time, it is possible to reduce a consumption of current compared to when the local sense amplifier  630  always operates. 
       FIG. 7  is a circuit diagram of the controller  650  of  FIG. 6  according to an embodiment of the present invention.  FIG. 8  is a timing diagram illustrating an operation of the semiconductor memory device  600  according to an embodiment of the present invention. The operation of the semiconductor memory device  600  according to this embodiment of the present invention will now be described in greater detail with reference to  FIGS. 6 through 8 . 
     The controller  650  includes a pulse generator  710  and a local sense control signal generator  730 . The pulse generator  710  generates a first pulse signal PRCD that is activated for a predetermined duration in response to the first signal S 1  (i). As described above, the first signal S 1  is a bit line sense enable signal that activates the bit line sense amplifier  620  after a row active command is given. 
     More specifically, the pulse generator  710  includes a first delayer D 1  that delays the first signal S 1 , a first inverter INV 1  that inverts an output of the first delayer D 1 , and a first AND gate unit  720  that performs an AND operation on an output of the first inverter INV 1  and the first signal S 1  and outputs the result as the first pulse signal PRCD. The first OR gate unit  720  can include a NAND gate N 1  and an inverter I 1 . 
     The delayer D 1  determines the duration for which the first pulse signal PRCD is to be activated. The pulse generator  710  is an automatic pulse generator that is activated for a predetermined duration in response to the first signal S 1 . The construction of the pulse generator  710  according to the present invention is not limited to the circuit shown. 
     The local sense control signal generator  730  activates a local sense control signal LSAEN when both the first pulse signal PRCD and the second signal S 2  are activated, and deactivates it when the second signal S 2  is deactivated. The second signal S 2  is activated or deactivated to be in phase with the column selection line signal CSL that connects the bit lines BL and /BL to the local I/O lines LIO and /LIO. It is possible to synchronize the local sense control signal LSAEN with the column selection line signal CSL by associating the first pulse signal PRCD with the second signal S 2 . The local sense control signal generator  730  includes a first transmission gate TRM 1  that transmits or blocks the first pulse signal PRCD in response to the second signal S 2 , a latch unit  735  that latches an output of the first transmission gate TRM 1  and includes inverters I 2  and I 3 , a second transmission gate TRM 2  that transmits or blocks an output of the latch unit  735  in response to the second signal S 2 , a second inverter INV 2  that inverts an output of the second transmission gate TRM 2 , and a second AND gate unit  740  that performs an AND operation on an output of the second inverter INV 2  and the second signal S 2  and outputs the result as the local sense control signal LSAEN. 
     The second AND gate unit  740  can include a NAND gate N 2  and an inverter I 4 . When the second signal S 2  is at a low logic level, the first pulse signal PRCD is stored in the latch unit  735 . When the second signal S 2  is at a high logic level, the first pulse signal PRCD sequentially passes through the second transmission gate TRM 2  and the second AND gate unit  740 , and is then output as the local sense control signal LSAEN from the second AND gate unit  740 . While the first pulse signal PRCD is activated, data is transmitted to the local I/O lines LIO and /LIO in response to the column selection line signal CSL, and the local sense control signal LSAEN is activated in response to the second signal S 2  activated in phase with the column selection line signal CSL (iii). 
     Then, referring to  FIG. 6 , a voltage of the data output from the local I/O lines LIO and /LIO is amplified by the local sense amplifier  630 , the data is transmitted to the global I/O lines GIO and /GIO (iv). Next, the data sense amplifier  640  activated in response to the sensing enable signal PIOSE amplifies a voltage of data transmitted to the data I/O lines DIO and /DIO from the global I/O lines GIO and /GIO, and outputs the data from the semiconductor memory device  600  (v). 
     When the first pulse signal PRCD is activated for a predetermined time and then deactivated, the local sense control signal LSAEN is not activated even if the second signal S 2  is activated. Therefore, the local sense amplifier  630  operates for a predetermined time after the first signal S 1 , that is, the bit line sense enable signal, is activated. 
     The semiconductor memory device  600  further includes a local I/O line precharge controller  660  that precharges the local I/O lines LIO and /LIO in response to a precharge control signal LIOEQA. The controller  650  as shown in  FIG. 7  further includes a precharge control signal generator  750  that activates the precharge control signal LIOEQA for a predetermined time when the local sense control signal LSAEN is deactivated. 
     The local I/O line precharge controller  660  precharges the local I/O lines LIO and /LIO when the column selection line signal CSL is deactivated, that is, while the local sense amplifier  630  does not operate. 
     The precharge control signal generator  750  includes a third inverter INV 3  that inverts the local sense control signal LSAEN, a second delayer D 2  that delays an output of the third inverter INV 3 , a fourth inverter INV 4  that inverts an output of the second delayer D 2 , and a third AND gate unit  760  that performs an AND operation on the output of the third inverter INV 3  and an output of the fourth inverter INV 4  to generate the precharge control signal LIOEQA. 
     The third AND gate unit  760  can include a NAND gate N 3  and an inverter I 5 . The precharge control signal LIOEQA is activated for a predetermined duration when the local sense control signal LSAEN is deactivated (vi). The duration for which the precharge control signal LIOEQA is activated is determined by the second delayer D 2 . 
     As described above, use of the controller  650  allows the local sense amplifier  630  of the semiconductor memory device  600  to operate only for a predetermined time after the bit line sense enable signal is activated, thereby increasing the tRCD parameter and reducing the consumption of current. The controller  650  is arranged in a periphery region outside a memory core. 
       FIG. 9  is a block diagram of a semiconductor memory device  900  according to still another embodiment of the present invention.  FIG. 10  is a circuit diagram of a controller  910  of  FIG. 9 . 
     Referring to  FIGS. 9 and 10 , the semiconductor memory device  900  includes a plurality of memory cells  610 , a bit line sense amplifier  620 , a local I/O line precharge controller  660 , a local sense amplifier  630 , a data sense amplifier  640 , and the controller  910 . The controller  910  deactivates a local sense control signal LSAEN when a control signal CON is deactivated, and activates the local sense control signal LSAEN only in a certain case in response to first and second signals S 1  and S 2  when the control signal CON is activated. 
     The controller  910  performs both the functions of the local sense amplifier controller  550  of  FIG. 5  and the controller  650  of  FIG. 6 . To reduce a consumption of current regardless of the tRCD parameter when operating the semiconductor memory device  900 , the controller  910  deactivates the local sense control signal so that the local sense amplifier  630  does not operate in response to the control signal CON. 
     In contrast, to increase the tRCD parameter and reduce the consumption of current in operating the semiconductor memory device  900 , the controller  910  receives the activated control signal CON, and activates the local sense control signal LSAEN for certain cases in response to the first and second signals S 1  and S 2 , similar to the controller  650  of  FIG. 6 . Referring to  FIG. 10 , the controller  910  includes a third signal generator  1010 , a pulse generator  710 , and a local sense control signal generator  730 . The third signal generator  1010  generates a third signal S 3  by performing an AND operation on the control signal CON and the second signal S 2 . The pulse generator  710  generates a first pulse signal PRCD activated for a predetermined duration in response to the first signal S 1 . 
     The local sense control signal generator  730  deactivates the local sense control signal LSAEN when the third signal S 3  is deactivated, and activates it when both the first pulse signal PRCD and the third signal S 3  are activated. 
     The third signal generator  1010  includes a NAND gate N 4  and an inverter I 6 . When the control signal CON is at a low logic level, the third signal S 3  is always at a low logic level, and then, the local sense control signal generator  730  deactivates the local sense control signal LSAEN. When the control signal CON is at a high logic level, the logic level of the third signal S 3  becomes equal to that of the second signal S 2 . That is, the third signal generator  1010  inputs the third signal S 3  to the local sense control signal generator  730  in the same manner in which the second signal S 2  is input to the local sense control signal generator  730  of  FIG. 7 . In this case, the operation of the third signal generator  1010  is the same as that of the controller  650  of  FIG. 6 . 
     As described above, a semiconductor memory device according to the present invention is capable of turning on or off a local sense amplifier according to operating conditions, thereby increasing a tRCD parameter and reducing a consumption of current. Also, a local sense amplifier is combined with a current type data sense amplifier that does not require precharging and equalizing during a read operation, thus improving an operating speed of the semiconductor memory device. 
     While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.