Patent Publication Number: US-8120979-B2

Title: Semiconductor memory devices having hierarchical bit-line structures

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0114216, filed on Nov. 17, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments relate to semiconductor memory devices, and more particularly, to semiconductor memory devices having hierarchical bit-line structures. 
     2. Description of Related Art 
     Conventional semiconductor memory devices read data from their own memory cells and store data in the memory cells via bit lines connected to the memory cells. But, integration density of conventional semiconductor memory devices is gradually increasing. Accordingly, the number of memory cells per unit area and the number of memory cells connected by one or a pair of bit lines is also increasing. Such an increase in the number of memory cells connected to each bit line inevitably causes parasitic capacitance to increase and degrades an operating speed of the semiconductor memory device. 
     A hierarchical bit-line structure has been proposed to reduce parasitic capacitance of bit lines and reduce chip size even with increasing integration density. However, a conventional semiconductor memory device having a hierarchical bit-line structure suffers from noise caused by coupling capacitance between adjacent global bit lines. 
     SUMMARY 
     Example embodiments provide semiconductor memory devices having hierarchical bit-line structures capable of sensing and amplifying data of adjacent global bit lines in sequence. 
     At least one example embodiment provides a semiconductor memory device. According to at least this example embodiment, a memory cell array has a plurality of first memory cells connected between word lines and first local bit lines, and a plurality of second memory cells connected between the word lines and second local bit lines. A switching circuit is configured to respectively connect the first local bit lines to first global bit lines during a first sensing period of a reading operation, and to respectively connect the second local bit lines to second global bit lines during a second sensing period of the reading operation. A sensing circuit is configured to sense and amplify data from the first global bit lines during the first sensing period of the reading operation, and to sense and amplify data from the second global bit lines during the second sensing period of the reading operation. 
     According to at least some example embodiments, the sensing circuit maintains the second global bit lines at a constant or substantially constant voltage level during the first sensing period, and maintains the first global bit lines at a constant or substantially constant voltage level during the second sensing period. The sensing circuit includes: first and second sense amplifiers. The first sense amplifiers are configured to sense and amplify voltages of data from the first global bit lines during the first sensing period and to maintain the amplified voltages of the first global bit lines during the second sensing period. The second sense amplifiers are configured to sense and amplify data from the second global bit lines during the second sensing period. The sensing circuit further includes: first and second equalizers. The first equalizers are configured to precharge the first global bit lines to a precharge voltage after the reading operation. The second equalizers are configured to precharge the second global bit lines to the precharge voltage during the first sensing period and after the reading operation. 
     According to at least some example embodiments, the semiconductor memory device further includes: first and second column selection circuits. The first column selection circuit is configured to correspondingly connect the first global bit lines to data input/output lines during the second sensing period. The second column selection circuit is configured to correspondingly connect the second global bit lines to the data input/output lines during the second sensing period. 
     According to at least some example embodiments, the switching circuit respectively connects the first local bit lines to the first global bit lines during a first sub-period of the first sensing period and a third sub-period of the second sensing period, and respectively connects the second local bit lines to the second global bit lines during the second sensing period. The first sense amplifiers are enabled during a second sub-period of the first sensing period and the second sensing period, and sense and amplify data from the first global bit lines. The second sense amplifiers are enabled during the second and third sub-periods of the second sensing period, and sense and amplify data from the second global bit lines. 
     The first column selection circuit correspondingly connects the first global bit lines to the data input/output lines during the third sub-period of the second sensing period, and the second column selection circuit correspondingly connects the second global bit lines to the data input/output lines during the third sub-period of the second sensing period. 
     According to at least some example embodiments, the semiconductor memory device further includes: first and second column selection circuits. The first column selection circuit is configured to correspondingly connect the first global bit lines to first data input/output lines during the first sensing period. The second column selection circuit is configured to correspondingly connect the second global bit lines to second data input/output lines during the second sensing period. 
     According to at least some example embodiments, the switching circuit respectively connects the first local bit lines to the first global bit lines during a first sub-period of the first sensing period and a third sub-period of the second sensing period, and respectively connects the second local bit lines to the second global bit lines during the second sensing period. The first sense amplifiers are enabled during a second sub-period of the first sensing period and the second sensing period, and sense and amplify data from the first global bit lines. The second sense amplifiers are enabled in the second and third sub-periods of the second sensing period, and sense and amplify data from the second global bit lines. The first column selection circuit correspondingly connects the first global bit lines to the first data input/output lines during the third sub-period of the first sensing period, and the second column selection circuit correspondingly connects the second global bit lines to the second data input/output lines during the third sub-period of the second sensing period. 
     According to at least some example embodiments, the first and second local bit lines are formed of bit-line polycrystalline silicon and the first and second global bit lines are formed of metal. 
     According to at least some example embodiments, the first and second global bit lines are arranged alternately. The second sensing period may be subsequent to the first sensing period. The first sensing period may include at least two sub-periods, whereas the second sensing period may include at least three sub-periods. 
     In one example embodiment, the first, second and third sub-periods of the first sensing period may be sequential, and the first, second and third sub-periods of the second sensing period may also be sequential. In another example embodiment, the first and second sub-periods of the first sensing period may be sequential, and the first, second and third sub-periods of the second sensing period may also be sequential. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments are described in further detail below with reference to the accompanying drawings. It should be understood that various aspects of the drawings may have been exaggerated for clarity. 
         FIG. 1  is a schematic diagram of a semiconductor memory device having a hierarchical bit-line structure in accordance with an example embodiment. 
         FIG. 2  is a circuit diagram of a memory cell array block, a switching block, and a sensing block of the semiconductor memory device shown in  FIG. 1 . 
         FIG. 3  is a circuit diagram of a semiconductor memory device having a hierarchical bit-line structure in accordance with an example embodiment, showing a switching block, a sensing block, and a column selection block. 
         FIG. 4  is a timing diagram illustrating example operation of the semiconductor memory device shown in  FIG. 3 . 
         FIG. 5  is a circuit diagram of a semiconductor memory device having a hierarchical bit-line structure in accordance with another example embodiment, showing a switching block, a sensing block, and a column selection block. 
         FIG. 6  is a timing diagram illustrating example operation of the semiconductor memory device shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown. 
     Detailed illustrative embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. However, embodiments are not limited to those example embodiments shown and described here. Rather, example embodiments may be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. 
     Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the inventive concept. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     In order to more specifically describe example embodiments, various aspects will be described in detail with reference to the attached drawings. However, embodiments are not limited to only those example embodiments described. 
     Example embodiments of semiconductor memory devices having hierarchical bit-line structures will be described hereinafter. 
       FIG. 1  is a schematic diagram of a semiconductor memory device having a hierarchical bit-line structure in accordance with an example embodiment. According to at least this example embodiment, the semiconductor memory device includes a plurality of memory cell array blocks  10 , a plurality of switching blocks  20 , a plurality of sensing blocks  30 , and a plurality of column selection blocks  40 . In  FIG. 1 , WL denotes word lines, LBL denotes local bit lines, GBL denotes global bit lines, IO denotes data input/output lines, S denotes selection signals, CON denotes control signals, and CSL denotes column selection signals. The local bit lines LBL may be made of bit-line polycrystalline silicon and the global bit lines GBL may be formed of metal. 
     Although example embodiments are discussed herein with regard to “blocks” such as memory cell array blocks  10  and switching blocks  20 , the “blocks” may also be referred to as “circuits” or “units.” 
     Referring to  FIG. 1 , the memory cell array blocks  10  include a plurality of memory cells (not shown) coupled between the local bit lines LBL and the word lines WL. Herein, even ones of the local bit lines LBL are sometimes referred to as first local bit lines, and odd ones of the local bit lines LBL are sometimes referred to as second local bit lines. In this case, the plurality of memory cells are divided to a plurality of first memory cells and a plurality of second memory cells. The plurality of first memory cells are those memory cells coupled between the first local bit lines and the word lines WL, and the plurality of second memory cells are those memory cells coupled between the second local bit lines and the word lines WL. 
     The switching blocks  20  connect the local bit lines LBL to the global bit lines GBL in response to the selection signals S to transfer data between the local and global bit lines LBL and GBL. During a reading operation, the switching blocks  20  transfer data in sequence from the local bit lines LBL to the global bit lines GBL adjacent thereto. In one example reading operation, the switching blocks  20  are configured to connect the even members of the local bit lines LBL with the even members of the global bit lines GBL so as to transfer data from the even local bit lines to the even global bit lines. After sensing and amplifying processes of the sensing blocks  30  to the even global bit lines, the switching blocks  20  connect the odd members of the local bit lines LBL with the odd members of the global bit lines GBL to transfer data from the odd local bit lines to the odd global bit lines. 
     The sensing blocks  30  are configured to sense and amplify data, which are transferred to the global bit lines GBL, in response to the control signals CON (e.g., sensing enable signals, equalizing signals, etc.) applied thereto. The sensing blocks  30  sequentially sense and amplify data from adjacent ones of the global bit lines GBL. In one example, the sensing blocks  30  are configured to sense and amplify data from the even global bit lines after the even local bit lines are connected with the even global bit lines by the switching blocks  20 . After the odd local bit lines are connected to the odd global bit lines by the switching blocks  20 , the sensing blocks  30  sense and amplify data from the odd global bit lines. 
     The column selection blocks  40  connect the global bit lines GBL with the data input/output lines IO in response to the column selection signals CSL to transfer data between the global bit lines GBL and the data input/output lines IO. 
       FIG. 2  illustrates an example embodiment of the semiconductor memory device of  FIG. 1  in further detail. More specifically,  FIG. 2  shows example circuit configurations of the memory cell array block  10 , the switching block  20 , and the sensing block  30  shown in  FIG. 1 . 
     In  FIG. 2 , MC 1  denotes a first memory cell, MC 2  denotes a second memory cell, SAe denotes a first sense amplifier, EQe denotes a first equalizer, SAo denotes a second sense amplifier, and EQo denotes a second equalizer. WL denotes a word line as a representative of the memory cell array block, LBLAe denotes a first local bit line, LBLAo denotes a second local bit line, GBLe denotes a first global bit line, GBLo denotes a second global bit line, GBLBe denotes a first complementary global bit line, GBLBo denotes a second complementary global bit line, S_ 1 Ae denotes a first selection signal, S_ 1 Ao denotes a second selection signal, SE_e denotes a first sensing enable signal, SE_o denotes a second sensing enable signal, EQ_e denotes a first equalizing signal, and EQ_o denotes a second equalizing signal. The first and second global bit lines GBLe and GBLo are arranged alternately. 
     The semiconductor memory device shown in  FIG. 2  will be described in more detail below with regard to an example reading operation. 
     Referring to  FIG. 2 , within the memory cell array block  10 , the first memory cell MC 1  is connected between word line WL and first local bit lines LBLAe. The second memory cell MC 2  is connected between the word line WL and second local bit lines LBLAo. The memory cell array block  10  reads and writes data through charge sharing mechanisms between the first and second local bit lines LBLAe and LBLAo and the first and second memory cells MC 1  and MC 2 . In an example data reading operation, if the word line WL is activated, charge sharing occurs between the first and second local bit lines LBLAe and LBLAo and the memory cells MC coupled to the word line WL. 
     During the reading operation, the switching block  20  connects the first and second local bit lines LBLAe and LBLAo with the first and second global bit lines GBLe and GBLo in sequence to transfer data between the first and second local bit lines LBLAe and LBLAo and the first and second global bit lines GBLe and GBLo. In more detail, switching transistors ST 1 Ae, ST 1 Ao, ST 1 Be and ST 1 Bo connected between corresponding local and global bit lines are turned on/off in response to corresponding selection signals S_ 1 Ae, S_ 1 Ao, S_ 1 Be and S_ 1 Bo to transfer data between the local bit lines LBLAe and LBLAo and the global bit lines GBLe and GBLo. Thus, if the selection signals are activated in turn, the local bit lines are sequentially connected to the global bit lines and data are transferred between the local and global bit lines. 
     For example, after activation of the word line WL, the first selection signal S_ 1 Ae is enabled to turn on the switching transistor ST 1 Ae. As a result, the first local bit line LBLAe is connected to the first global bit line GBLe to transfer data between the first local bit line LBLAe and the first global bit line GBLe. 
     The second selection signal S_ 1 Ao is then enabled to turn on the switching transistor ST 1 Ao. As a result, data are transferred between the second local bit line LBLAo and the second global bit line GBLo. 
     During this example reading operation, the sensing block  30  senses and amplifies data from the first and second global bit lines GBLe and GBLo in sequence. The sensing block  30  maintains the second global bit line GBLo at a constant or substantially constant voltage level (e.g., a precharge level) while sensing and amplifying data from the first global bit line GBLe. The sensing block  30  also maintains the first global bit line GBLe at a constant or substantially constant voltage level (e.g., a high or low level) while sensing and amplifying data from the second global bit line GBLo. 
     The first sense amplifier SAe of the sensing block  30  senses and amplifies data from the first global bit line GBLe in response to the first sensing enable signal SE_e. If the first sensing enable signal SE_e is activated, the first sense amplifier SAe senses and amplifies a voltage difference between the first global bit line GBLe and the first complementary global bit line GBLBe in response to the first sensing enable signal SE_e. The second sense amplifier SAo of the sensing block  30  senses and amplifies data from the second global bit line GBLo in response to the second sensing enable signal SE_o. If the second sensing enable signal SE_o is activated, the second sense amplifier SAo senses and amplifies a voltage difference between the second global bit line GBLo and the second complementary global bit line GBLBo in response to the second sensing enable signal SE_o. In this example, the first and second sense amplifiers SAe and SAo are enabled in turn or sequentially. 
     The first equalizer EQe precharges the first global bit line GBLe to a given, desired or predetermined voltage in response to the first equalizing signal EQ_e. The second equalizer EQo precharges the second global bit line GBLo to a given, desired or predetermined voltage in response to the second equalizing signal EQ_o. 
     In the example embodiment shown in  FIG. 2 , operations of restoring the original data into memory cells coupled to an activated word line are designed to proceed at the same or substantially the same time (e.g., simultaneously or concurrently). For example, the first and second selection signals S_ 1 Ae and S_ 1 Ao may all be activated after sensing and amplifying data from the first and second global bit lines GBLe and GBLo through the first and second sense amplifiers SAe and SAo. Thus, data transmission between the first global bit line GBLe and the first local bit line LBLAe, and between the second global bit line GBLo and the second local bit line LBLAo may be performed coincidentally (e.g., simultaneously or concurrently) while the word line WL is activated. Accordingly, restoring data into the memory cells MC coupled to the activated word line WL may be performed coincidentally (e.g., simultaneously or concurrently). 
       FIG. 3  shows another example circuit configuration of a semiconductor memory device having a hierarchical bit-line structure. As shown,  FIG. 3  illustrates a switching block  20 , a sensing block  30 , and column selection blocks  41 - 1  and  41 - 2 . 
     Referring to  FIG. 3 , SAe denotes first sense amplifiers, EQe denotes first equalizers, SAo denotes second sense amplifiers, and EQo denotes second equalizers. LBL 0 Ae to LBL 3 Ae denote first local bit lines, LBL 0 Ao to LBL 3 Ao denote second local bit lines, GBL 0   e  to GBL 3   e  denote first global bit lines, GBL 0   o  to GBL 3   o  denote second global bit lines, IO 0  to IO 3  denote data input/output lines, S_ 1 Ae denotes a first selection signal, S_ 1 Ao denotes a second selection signal, CSL 1  denotes a first column section signal, and CSL 2  denotes a second column selection signal. The first global bit lines GBL 0   e  to GBL 3   e  and the second global bit lines GBL 0   o  to GBL 3   o  are arranged alternately. 
     Example function or operation of the blocks shown in  FIG. 3  will be described in more detail below. 
     Referring to  FIG. 3 , the switching block  20 , the sensing block  30 , the first and second sense amplifiers SAe and SAo of the sensing block  30 , and the first and second equalizers EQe and EQo of the sensing block  30  are functionally the same as those discussed above with regard to  FIGS. 1 and 2 . The first column selection block  41 - 1  connects the first global bit lines GBL 0   e  and GBL 1   e  to the data input/output lines IO 0  and IO 1  in response to the first column selection signal CSL 1 . The first column selection block  41 - 1  also connects the first global bit lines GBL 2   e  and GBL 3   e  to the data input/output lines IO 0  and IO 1  in response to the second column selection signal CSL 2 . 
     The second column selection block  41 - 2  connects the second global bit lines GBL 0   o  and GBL 1   o  to the data input/output lines  102  and  103  in response to the first column selection signal CSL 1 . The second column selection block  41 - 2  also connects the second global bit lines GBL 2   o  and GBL 3   o  to the data input/output lines IO 2  and IO 3  in response to the second column selection signal CSL 2 . The first and second column selection blocks  41 - 1  and  41 - 2  connect the first and second global bit lines GBL 0   e  to GBL 3   e  and GBL 0   o  to GBL 3   o , respectively, to the data input/output lines IO 0  to IO 3  at the same or substantially the same time (e.g., simultaneously or concurrently) after data sensing and amplifying operations for the first and second global bit lines are complete. 
       FIG. 4  is a timing diagram illustrating an example operation of the semiconductor memory device shown in  FIG. 3 . In the timing diagram of  FIG. 4 , WL denotes a word line as a representative of the memory cell array block, S_ 1 Ae denotes a first selection signal, S_ 1 Ao denotes a second selection signal, SE_e denotes a first sensing enable signal, SE_o denotes a second sensing enable signal, EQ_e denotes a first equalizing signal, EQ_o denotes a second equalizing signal, CSL 1  denotes a first column selection line, GBL 0   e , GBL 1   e , GBLB 0   e  and GBLB 1   e  denote first global bit lines and first complementary global bit lines, and GBL 0   o , GBL 1   o , GBLB 0   o  and GBLB 1   o  denote second global bit lines and second complementary global bit lines. 
     Referring to  FIGS. 3 and 4 , an example reading operation of the semiconductor memory device will be described below. 
     During a first sensing period ST 1  of the reading operation, data are transferred from the first local bit lines LBL 0 Ae to LBL 3 Ae to the first global bit lines GBL 0   e  to GBL 3   e , and data of the first global bit lines GBL 0   e  to GBL 3   e  are sensed and amplified. During this period, the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a precharge voltage level. 
     During a second sensing period ST 2  of the reading operation, data are transferred from the second local bit lines LBL 0 Ae to LBL 3 Ae to the second global bit lines GBL 0   o  to GBL 3   o , and data of second global bit lines GBL 0   o  to GBL 3   o  are sensed and amplified. During this period, the first global bit lines GBL 0   e  to GBL 3   e  are maintained at a high or low level. Then, as the first global bit lines GBL 0   e  and GBL 1   e  and the second global bit lines GBL 0   o  and GBL 0   o  are each connected to the data input/output lines IO 0  to IO 3 , data are transferred between the first and second global bit lines GBL 0   e , GBL 1   e , GBL 0   o  and GBL 1   o , and the data input/output lines IO 0  to IO 3 . Afterwards, data restoration for the memory cells coupled to the activated word line WL, the first local bit lines LBL 0 Ae to LBL 3 Ae, and the second local bit lines LBL 0 Ao to LBL 3 Ao is performed. 
     An example operation of the first sensing period ST 1  will be described in more detail below. 
     During a first sub-period T 11  of the first sensing period ST 1 , the word line WL is activated, the first selection signal S_ 1 Ae is enabled, and the first equalizing signal EQ_e is disabled. Because the word line WL is activated, charge sharing between the first and second local bit lines LBL 0 Ae to LBL 3 Ae and LBL 0 Ao to LBL 3 Ao and the memory cells coupled to the word line WL begins. Further, because the first selection signal S_ 1 Ae is activated, the first local bit lines LBL 0 Ae to LBL 3 Ae share charge with the first global bit lines GBL 0   e  to GBL 3   e  and data are transferred from the first local bit lines LBL 0 Ae to LBL 3 Ae to the first global bit lines GBL 0   e  to GBL 3   e . Also during the first sub-period T 11  of the first sensing period ST 1 , charge is not shared between the second local bit lines LBL 0 Ao to LBL 3 Ao and the second global bit lines GBL 0   o  to GBL 3   o  because the second selection signal S_ 1 Ao is deactivated. Thus, data is not transmitted from the second local bit lines LBL 0 Ao to LBL 3 Ao to the second global bit lines GBL 0   o  to GBL 3   o . Further, the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a given, desired or predetermined precharge voltage level because the second equalizing signal EQ_o is activated. 
     During a second sub-period T 12  of the first sensing period ST 1 , the first sensing enable signal SE_e is activated. As a result, the first sense amplifiers SAe sense and amplify data from the first global bit lines GBL 0   e  to GBL 3   e . Then, the first global bit lines GBL 0   e  to GBL 3   e  and the first complementary global bit lines GBLB 0   e  to GBLB 3   e  are charged or discharged to high or low levels. Further, the second sub-period T 12  of the first sensing period ST 1  proceeds regardless of deactivation of the first selection signal S_ 1 Ae because data has been transmitted between the first local bit lines LBL 0 Ae to LBL 3 Ae and the first global bit lines GBL 0   e  to GBL 3   e  in the first sub-period T 11  of the first sensing period ST 1 . During the second sub-period T 12  of the first sensing period ST 1 , the second equalizing signal EQ_o remains activated. Thus, the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a given, desired or predetermined precharge voltage level as in the first sub-period T 11  of the first sensing period ST 1 . 
     An example operation in the second sensing period ST 2  will now be described in more detail below. 
     During a first sub-period T 21  of the second sensing period ST 2 , the second selection signal S_ 1 Ao is activated, but the second equalizing signal EQ_o is deactivated. Charge sharing occurs between the second local bit lines LBL 0 Ao to LBL 3 Ao and the second global bit lines GBL 0   o  to GBL 3   o , and thus, data are transferred from the second local bit lines LBL 0 Ao to LBL 3 Ao to the second global bit lines GBL 0   o  to GBL 3   o . Also during the first sub-period T 21  of the second sensing period ST 2 , the first global bit lines GBL 0   e  to GBL 3   e  are maintained at high or low levels because those voltages have been amplified during the second sub-period T 12  of the first sensing period ST 1  and the first sense amplifiers SEe remain activated. 
     During a second sub-period T 22  of the second sensing period ST 2 , the second sensing enable signal SE_o is activated. As a result, the second sense amplifier SAo senses and amplifies data from the second global bit lines GBL 0   o  to GBL 3   o . Then, the second global bit lines GBL 0   o  to GBL 3   o  and the second complementary global bit lines GBLB 0   o  to GBLB 3   o  go to high or low levels. Also during the second sub-period T 22  of the second sensing period ST 2 , the first global bit lines GBL 0   e  to GBL 3   e  are maintained at high or low levels as in the first sub-period T 21  of the second sensing period ST 2 . 
     During a third sub-period T 23  of the second sensing period ST 2 , the first column selection signal CSL 1  is activated, and data are transferred from the first global bit lines GBL 0   e  and GBL 1   e  to the data input/output lines IO 0  and IO 1 . Data are also transferred from the second global bit lines GBL 0   o  and GBL 0   o  to the data input/output lines  102  and  103 . Further, because the first and second selection signals S_ 1 Ae and S_ 1 Ao are all activated, the original data are restored into the memory cells coupled to the activated word line WL by returning data from the first global bit lines GBL 0   e  and GBL 3   e  to the first local bit lines LBL 0 Ae to LBL 3 Ae and returning data from the second global bit lines GBL 0   o  and GBL 3   o  to the second local bit lines LBL 0 Ao to LBL 3 Ao. 
     During a third period T 3 , after the first and second sensing periods ST 1  and ST 2 , the word line WL, the first sensing enable signal SE_e, and the second sensing enable signal SE_o are deactivated, whereas the first equalizing signal EQ_e and the second equalizing signal EQ_o are activated. The first global bit lines GBL 0   e  to GBL 3   e , the first complementary global bit lines GBLB 0   e  to GBLB 3   e , the second global bit lines GBL 0   o  to GBL 3   o , the second complementary global bit lines GBLB 0   o  to GBLB 3   o  are set to a given, desired or predetermined voltage level. 
     According to at least the example embodiment of the semiconductor memory device having a hierarchical bit-line structure shown in  FIGS. 3 and 4 , a reading operation is executed by: transferring data to the first global bit lines GBL 0   e  to GBL 3   e ; sensing and amplifying data from the first global bit lines GBL 0   e  to GBL 3   e ; transferring data to the second global bit lines GBL 0   o  to GBL 3   o  adjacent to the first global bit lines GBL 0   e  to GBL 3   e ; sensing and amplifying data from the second global bit lines GBL 0   o  to GBL 3   o ; and outputting the data from the first and second global bit lines GBL 0   e  to GBL 1   e  and GBL 0   o  to GBL 1   o  to the input/output lines IO 0  to IO 3 . 
       FIG. 5  shows another example embodiment of a semiconductor memory device having a hierarchical bit-line structure. As shown,  FIG. 5  illustrates a switching block  20 , a sensing block  30 , and column selection blocks  42 - 1  and  42 - 2  in an example circuit configuration. 
     In  FIG. 5 , SAe denotes first sense amplifiers, EQe denotes first equalizers, SAo denotes second sense amplifiers, and EQo denotes second equalizers. LBL 0 Ae to LBL 3 Ae denote first local bit lines, LBL 0 Ao to LBL 3 Ao denote second local bit lines, GBL 0   e  to GBL 3   e  denote first global bit lines, GBL 0   o  to GBL 3   o  denote second global bit lines, IO 0   e  to IO 3   e  denote first data input/output lines, IO 0   o  to IO 3   o  denote second data input/output lines, S_ 1 Ae denotes a first selection signal, S_ 1 Ao denotes a second selection signal, CSL 1  denotes a first column section signal, and CSL 2  denotes a second column selection signal. 
     Example functions of the blocks shown in  FIG. 5  will be described in more detail below. 
     The switching block  20 , the sensing block  30 , the first and second sense amplifiers SAe and SAo of the sensing block  30 , and the first and second equalizers EQe and EQo of the sensing block  30  are functionally the same as those described above with reference to  FIGS. 1 and 2 . 
     Referring to  FIG. 5 , the first column selection block  42 - 1  connects the first global bit lines GBL 0   e  to GBL 3   e  to the first data input/output lines IO 0   e  to IO 3   e  in response to the first column selection signal CSL 1 . The second column selection block  42 - 2  connects the second global bit lines GBL 2   o  to GBL 3   o  to the second data input/output lines IO 0   o  to IO 3   o  in response to the second column selection signal CSL 2 . The first and second column selection blocks  42 - 1  and  42 - 2  correspondingly connect the global bit lines GBL 0   e  to GBL 3   e  and GBL 0   o  to GBL 3   o  to the data input/output lines IO 0   e  to IO 3   e  and IO 0   o  to IO 3   o  in sequence. For example, the first column selection block  42 - 1  connects the first global bit lines GBL 0   e  to GBL 3   e  to the first data input/output lines IO 0   e  to IO 3   e  after completing data sensing and amplifying operations for the first global bit lines GBL 0   e  to GBL 3   e . The second column selection block  42 - 2  connects the second global bit lines GBL 0   o  to GBL 3   o  to the second data input/output lines IO 0   o  to IO 3   o  after completing data sensing and amplifying operations for the second global bit lines GBL 0   o  to GBL 3   o.    
       FIG. 6  shows an example timing diagram for the semiconductor memory device shown in  FIG. 5 . In  FIG. 6 , WL denotes a word line as a representative of the memory cell array block, S_ 1 Ae denotes a first selection signal, S_ 1 Ao denotes a second selection signal, SE_e denotes a first sensing enable signal, SE_o denotes a second sensing enable signal, EQ_e denotes a first equalizing signal, EQ_o denotes a second equalizing signal, CSL 1  denotes a first column selection line, CSL 2  denotes a second column selection line, GBL 0   e  to GBL 3   e  and GBLB 0   e  to GBLB 3   e  denote first global bit lines and first complementary global bit lines, and GBL 0   o  to GBL 3   o  and GBLB 0   o  to GBLB 3   o  denote second global bit lines and second complementary global bit lines. 
     Referring to  FIGS. 5 and 6 , during a first sensing period ST 1  of a reading operation, data are transferred from the first local bit lines LBL 0 Ae to LBL 3 Ae to the first global bit lines GBL 0   e  to GBL 3   e , and data of the first global bit lines GBL 0   e  to GBL 3   e  are sensed and amplified. In addition, the amplified data are transferred from the first global bit lines GBL 0   e  to GBL 3   e  to the first data input/output lines IO 0   e  to IO 3   e . Also during the first sensing period ST 1 , the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a constant or substantially constant voltage level (e.g., a precharge voltage level). 
     During a second sensing period ST 1  of the reading operation, data are transferred from the second local bit lines LBL 0 Ao to LBL 3 Ao to the second global bit lines GBL 0   o  to GBL 3   o , and data of the second global bit lines GBL 0   o  to GBL 3   o  are sensed and amplified. The amplified data are transferred from the second global bit lines GBL 0   o  to GBL 3   o  to the second data input/output lines IO 0   o  to IO 3   o . Also during the second sensing period ST 2 , the first global bit lines GBL 0   e  to GBL 3   e  are maintained at a constant or substantially constant level (e.g., a high or low level). Afterwards, data restoration for the memory cells coupled to the activated word line WL, the first local bit lines LBL 0 Ae to LBL 3 Ae, and the second local bit lines LBL 0 Ao to LBL 3 Ao is performed in process. 
     An operation of the first sensing period ST 1  will be described in more detail below. 
     A first sub-period T 11  of the first sensing period ST 1  is the same or substantially the same as that described above with reference to  FIG. 4 . Because the word line WL is activated, charge sharing begins between the first and second local bit lines LBL 0 Ae to LBL 3 Ae and LBL 0 Ao to LBL 3 Ao and the memory cells coupled to the word line WL. And, data are transferred from the first local bit lines LBL 0 Ae to LBL 3 Ae to the first global bit lines GBL 0   e  to GBL 3   e . Also during this sub-period, the second equalizing signal EQ_o is activated, and thus, the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a given, desired or predetermined precharge voltage level. 
     A second sub-period T 12  of the first sensing period ST 1  is the same or substantially the same as that discussed above with reference to  FIG. 4 . The first sense amplifiers SAe are enabled to sense and amplify data from the first global bit lines GBL 0   e  to GBL 3   e . Then, the first global bit lines GBL 0   e  to GBL 3   e  and the first complementary global bit lines GBLB 0   e  to GBLB 3   e  are charged or discharged to high or low levels. Also during the second sub-period T 12  of the first sensing period ST 1 , the second global bit lines GBL 0   o  to GBL 3   o  are maintained at a given, desired or predetermined precharge voltage level as in the first sub-period T 11  of the first sensing period ST 1 . 
     During a third sub-period T 13  of the first sensing period ST 1 , the first column selection signal CSL 1  is activated and data are correspondingly transferred from the first global bit lines GBL 0   e  to GBL 3   e  to the first data input/output lines IO 0   e  to IO 3   e.    
     An example operation during the second sensing period ST 2  will be described in more detail below. 
     A first sub-period T 21  of the second sensing period ST 2  is the same or substantially the same as that described above with reference to  FIG. 4 . During the first sub-period T 21 , the second selection signal S_ 1 Ao is activated, whereas the second equalizing signal EQ_o is deactivated. Then, data are transferred from the second local bit lines LBL 0 Ao to LBL 3 Ao to the second global bit lines GBL 0   o  to GBL 3   o . Also during the first sub-period T 21  of the second sensing period ST 2 , the first global bit lines GBL 0   e  to GBL 3   e  are maintained at high or low levels because those voltages have been amplified during the second term T 12  of the first sensing period ST 1  and the first sense amplifiers SEe remain activated. 
     A second sub-period T 22  of the second sensing period ST 2  is also the same or substantially the same as that discussed above with reference to  FIG. 4 . The second sensing enable signal SE_o is activated, and thus, the second sense amplifier SAo senses and amplifies data from the second global bit lines GBL 0   o  to GBL 3   o . Then, the second global bit lines GBL 0   o  to GBL 3   o  and the second complementary global bit lines GBLB 0   o  to GBLB 3   o  go to high or low levels. Also during the second sub-period T 22  of the second sensing period ST 2 , the first global bit lines GBL 0   e  to GBL 3   e  are maintained at high or low levels as in the first sub-period T 21  of the second sensing period ST 2 . 
     During a third sub-period T 23  of the second sensing period ST 2 , the second column selection signal CSL 2  is activated, and data are correspondingly transferred from the second global bit lines GBL 0   o  to GBL 3   o  to the second data input/output lines IO 0   o  to IO 3   o . Further, because the first and second selection signals S_ 1 Ae and S_ 1 Ao are all activated, the original data are restored into the memory cells coupled to the activated word line WL by returning data from the first global bit lines GBL 0   e  to GBL 3   e  to the first local bit lines LBL 0 Ae to LBL 3 Ae and returning data from the second global bit lines GBL 0   o  to GBL 3   o  to the second local bit lines LBL 0 Ao to LBL 3 Ao. 
     During a third period T 3 , after the first and second sensing periods ST 1  and ST 2 , the word line WL, the first sensing enable signal SE_e, and the second sensing enable signal SE_o are deactivated, whereas the first equalizing signal EQ_e and the second equalizing signal EQ_o are activated. Then, the first global bit lines GBL 0   e  to GBL 3   e , the first complementary global bit lines GBLB 0   e  to GBLB 3   e , the second global bit lines GBL 0   o  to GBL 3   o , and the second complementary global bit lines GBLB 0   o  to GBLB 3   o  are set to a given, desired or predetermined voltage level. 
     According to at least the example embodiment shown in  FIGS. 5 and 6 , the reading operation is executed by: transferring data to the first global bit lines GBL 0   e  to GBL 3   e ; sensing and amplifying data from the first global bit lines GBL 0   e  to GBL 3   e ; outputting data from the first global bit lines GBL 0   e  to GBL 3   e  to the first data input/output lines IO 0   e  to IO 3   e ; transferring data to the second global bit lines GBL 0   o  to GBL 3   o  adjacent to the first global bit lines GBL 0   e  to GBL 3   e ; sensing and amplifying data from the second global bit lines GBL 0   o  to GBL 3   o ; and outputting data from the second global bit lines GBL 0   o  to GBL 3   o  to the second input/output lines IO 0   o  to IO 3   o.    
     While example embodiments of semiconductor memory devices having hierarchical bit-line structures are described in example configurations relevant to dynamic random access memory cells (DRAM) each formed of a cell transistor and a cell capacitor, example embodiments may also be applied to other kinds of memories including, but not limited to: phase-change RAMs, magnetic RAMs, and so on. 
     As described above, semiconductor memory devices having hierarchical bit-line structures according to example embodiments are more effective in reducing noise by coupling capacitance between adjacent global bit lines, for which data are transferred to the adjacent global bit lines, and sensed and amplified from the adjacent global bit lines in sequence. This may enlarge a voltage difference between the adjacent global bit lines during a reading operation, thereby improving operating characteristics of semiconductor memory devices. 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in example embodiments without materially departing from the novel teachings and advantages. Accordingly, all such modifications are intended to be included within the scope defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function, and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims.