Abstract:
A semiconductor memory device configured to share a local I/O line is described herein. The device includes: a memory cell array including a plurality of memory cells; a plurality of bit line sense amplifiers configured to sense and to amplify data stored in the plurality of memory cells; a plurality of bit lines configured to transmit transmitting the data stored in the plurality of memory cells to the plurality of bit line sense amplifiers, respectively; a plurality of bit line dividing circuits configured to selectively divide the plurality of bit lines; and a plurality of column selecting circuits configured to sequentially transmit the data amplified by the plurality of bit line sense amplifiers to corresponding I/O lines.

Description:
TECHNICAL FIELD 
     The present disclosure relates to semiconductor memory devices, and more particularly, to a semiconductor memory device configured to share a local I/O (input/output) line. 
     BACKGROUND 
     A conventional memory core structure minimizes distance between memory cell arrays to maximize memory cell efficiency. In particular, the conventional memory core structure requires a maximum of 16 bits of data outputs, and thus shares a local I/O line. 
     On the other hand, a high speed memory such as a double data rate (DDR), a DDR-II and a graphic memory outputs a maximum of 32 bits of data. The high speed memory is required to have high speed burst operation, and thus the core must read data as many as a number of the bursts in advance. This function is a prefetch function. The DDR uses 2 bit prefetch and the DDR-II uses 4 bit prefetch. For example, the X16 DDR-II operates at 400MHz with 4 bursts, uses 4 bit prefetch, and reads 64 bits of data by one core access. 
     However, because the conventional core structure gradually increases an operation speed and widens a bandwidth, it cannot share the local I/O line. As a result, a spatial efficiency cannot be achieved. 
     SUMMARY OF THE DISCLOSURE 
     A semiconductor memory device configured to share a local I/O line by sequentially outputting data in a pipeline form is disclosed herein. 
     The semiconductor memory device includes: a memory cell array including a plurality of memory cells; a plurality of bit line sense amplifiers configured to sense and to amplify data stored in the plurality of memory cells; a plurality of bit lines configured to transmit the data stored in the plurality of memory cells to the plurality of bit line sense amplifiers, respectively; a plurality of bit line dividing circuits configured to selectively divide the plurality of bit lines; and a plurality of column selecting circuits configured to sequentially transmit the data amplified by the plurality of bit line sense amplifiers to corresponding I/O lines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The disclosure will be described in terms of several embodiments to illustrate its broad teachings. Reference is also made to the attached drawings. 
     FIG. 1 is a block diagram illustrating a semiconductor memory device using a pipeline fetch structure; and 
     FIGS. 2 a  and  2   b  are timing diagrams of operation signals to explain the operation of the semiconductor memory device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a block diagram illustrating a semiconductor memory device  100  using a pipeline fetch structure. In the semiconductor memory device  100 , a bit line dividing unit  20  is formed at the center portion of a memory cell array  10  composed of a plurality of memory cells  11 ,  12 ,  13  and  14 . Sense amplifier arrays  30  and  40  composed of a plurality of sense amplifiers with two shown as  31  and  41 , respectively, are connected to both ends of the memory cell array  10 . Here, the bit line dividing unit  20  including NMOS transistors NM 1 , NM 2 , NM 3  and NM 4  that perform switching operation, according to an up bit line switching signal UBL and a down bit line switching signal DBL for dividing bit lines. 
     In the operation of reading data from memory cells  11  and  12  connected to an enabled word line WLO, the up bit line switching signal UBL is at a low level to turn off the NMOS transistors NM 1  and NM 2  when the data stored in the memory cell  11  connected to the upper sense amplifier array  30  are read. Accordingly, a length of the bit line pair BL and /BL is decreased and a bit line capacitance is reduced, and thereby improving sensing efficiency of the sense amplifiers. 
     On the other hand, when the data stored in the memory cell  12  connected to the lower sense amplifier array  40  are read, the down bit line switching signal DBL is at a high level to turn on the NMOS transistors NM 3  and NM 4 . The bit line pair BL and /BL of the memory cell  12  positioned in the upper memory cell array  30  of the bit line dividing unit  20  is connected to the lower sense amplifier array  40 . Accordingly, the reading speed of the data stored in the memory cell  11  connected to the upper sense amplifier array  30  is higher than that of the data stored in the memory cell  12  connected to the lower sense amplifier array  40  to sequentially perform the operations for reading the data stored in the two memory cells  11  and  12 . As a result, local I/O line LIO can be shared by using the aforementioned operation property. To illustrate this concept, column selecting units  50  and  60  sequentially transmit the data amplified by the sense amplifiers  31  and  41  to the local I/O line LIO by using a column select signal YI, an up column select signal UYI and a down column select signal DYI. 
     To read the data from memory cells  11  and  12 , the data stored in the memory cell  11  connected to the upper sense amplifier array  30  are transmitted to a bit line BL 0 . Here, the up bit line switching signal UBL becomes a low level to turn off the NMOS transistors NM 1  and NM 2 . 
     The data on the bit line BL 0  are sensed and amplified by the bit line sense amplifier  31 . Here, the column select signal YI becomes a high level to turn on NMOS transistors NM 5  and NM 6 . Accordingly, the data amplified by the bit line sense amplifier  31  are transmitted to the local I/O line LIO through a data bus DB. Here, the up column select signal UYI becomes a high level to turn on NMOS transistors NM 9  and NM 10  to form a path for outputting the data amplified by the bit line sense amplifier  31  to the data bus DB. 
     Thereafter, the data stored in the memory cell  12  connected to the lower sense amplifier array  40  are transmitted to a bit line BL 1 . The down bit line switching signal DBL becomes a high level to turn on the NMOS transistors NM 3  and NM 4 . The data on the bit line BL 1  are sensed and amplified by the bit line sense amplifier  41 . Here, the column select signal YI becomes a high level to turn on NMOS transistors NM 7  and NM 8 . 
     Therefore, the data are transmitted to the local I/O line LIO through the data bus DB. The down column select signal DYI becomes a high level to turn on NMOS transistors NM 11  and NM 12  to form a path for outputting the data amplified by the bit line sense amplifier  41  to the data bus DB. 
     Further, the data stored in the memory cell  14  connected to the lower sense amplifier array  40  are transmitted to the bit line BL 1  to read the data from the memory cells  13  and  14  connected to an enabled word line WL 1 . The down bit line switching signal DBL becomes a low level to turn off the NMOS transistors NM 3  and NM 4 . 
     The data on the bit line BL 1  are sensed and amplified by the bit line sense amplifier  41 . Here, the column select signal YI becomes a high level to turn on the NMOS transistors NM 7  and NM 8 . Accordingly, the data amplified by the bit line sense amplifier  41  are transmitted to the local I/O line LIO through the data bus DB. The down column select signal DYI becomes a high level to turn on the NMOS transistors NM 11  and NM 12  to form a path for outputting the data amplified by the bit line sense amplifier  41  to the data bus DB. 
     Thereafter, the data stored in the memory cell  13  connected to the upper sense amplifier array  30  are transmitted to the bit line BL 0 . Here, the up bit line switching signal UBL becomes a high level to turn on the NMOS transistors NM 1  and NM 2 . The data on the bit line BL 0  are sensed and amplified by the bit line sense amplifier  31 . The column select signal YI becomes a high level to turn on the NMOS transistors NM 5  and NM 6 . 
     Therefore, the data are transmitted to the local I/O line LIO through the data bus DB. The up column select signal UYI becomes a high level to turn on the NMOS transistors NM 9  and NM 10  to form a path for outputting the data amplified by the bit line sense amplifier  31  to the data bus DB. 
     FIGS. 2 a  and  2   b  are timing diagrams of operation signals to explain the operation of the semiconductor memory device of FIG.  1 . Here, the column select signal YI is inputted with a frequency twice as fast as the general column select signal, and a wave pipe delay time T has a time less than 10 nanoseconds. 
     FIG. 2 a  is a timing diagram of the read operation of the data stored in the memory cells  11  and  12  connected to the enabled world line WL 0 . The data stored in the memory cell  11  connected to the upper sense amplifier array  30  are transmitters the sense amplifier  31  through the bit line pair BL 0  and /BL 0 , and the sense amplifier  31  senses and amplifies the data. The column select signal YI has a high level in a period when the up column select signal UYI is becomes a high level to transmit the data amplified by the sense amplifier  31  to the data bus DB. 
     Thereafter, the data stored in the memory cell  12  connected to the lower sense amplifier array  40  are transmitted to the sense amplifier  41  through the bit line pair BL 1  and /BL 1 , and the sense amplifier  41  senses and amplifies the data. The column select signal YI has a high level in a period when the down column select signal DYI becomes a high level to transmit the data amplified by the sense amplifier  41  to the data bus DB. 
     FIG. 2 b  is a timing diagram of the read operation of the data stored in the memory cells  13  and  14  connected to the enabled world line WL 1 . The data stored in the memory cell  14  connected to the lower sense amplifier array  40  are transmitted to the sense amplifier  41  through the bit line pair BL 1  and /BL 1 , and the sense amplifier  41  senses and amplifies the data. The column select signal YI has a high level in a period when the down column select signal DYI becomes a high level to transmit the data amplified by the sense amplifier  41  to the data bus DB. 
     Thereafter, the data stored in the memory cell  13  connected to the upper sense amplifier array  30  are transmitted to the sense amplifier  31  through the bit line pair BL 0  and /BL 0 , and the sense amplifier  31  senses and amplifies the data. The column select signal YI has a high level in a period when the up column select signal UYI becomes a high level to transmit the data amplified by the sense amplifier  31  to the data bus DB. 
     As mentioned above, efficiency of the core structure is improved with the I/O bandwidth in the high speed memory device by using the pipeline fetch function. Moreover, the semiconductor memory device disclosed herein reduces the bit line capacitance and improves the sensing speed of the sense amplifiers by using the switch element for dividing the bit lines. Thus, the semiconductor memory device sequentially senses the data stored in the memory cells connected to the same word line with the sense amplifiers to share the local I/O line. 
     Many changes and modifications to the embodiments described herein could be made. The scope of some changes is discussed above. The scope of others will become apparent from the appended claims.