Abstract:
Methods can be provided for reading data from a memory device comprising a plurality of memory cells and a plurality of virtual ground lines wherein each memory cell comprises a latch circuit coupled to a read circuit and wherein each virtual ground line is coupled with read circuits of a respective group of memory cells. Methods for reading according to embodiments of the present invention can include selecting a memory cell from which data is to be read, applying a first reference voltage to a virtual ground line coupled to the selected memory cell from which data is to be read, and applying a second reference voltage to a virtual ground line not coupled to the selected memory cell. A read word line coupled to the read circuit of the selected memory cell from which data is to be read can be activated. Responsive to activating the read word line coupled to the read circuit of the selected memory cell from which data is to be read, data can be coupled from the latch circuit of the selected memory cell with a respective read bit line through the read circuit of the selected memory cell. Methods of writing are also discussed, as are related memory devices and cells.

Description:
RELATED APPLICATION 
     This application claims the benefit as a divisional of U.S. patent application Ser. No. 10/123,601, filed Apr. 16, 2002, now U.S. Pat. No. 6,674,670, issued on Jan. 6, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. This application also claims the benefit of Korean Patent Application No. 2001-24685, filed May 7, 2001, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to semiconductor devices, and more particularly, to semiconductor memory devices and related methods. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 is a diagram illustrating a conventional semiconductor memory cell connected to a write word line and a read word line. Referring to FIG. 1, the conventional semiconductor memory cell connected to a write word line AWWL 1  and a read word line ARWL 1  includes a latch circuit A 120 , a write circuit A 140 , a first read circuit A 110 , and a second read circuit A 130 . 
     The latch circuit A 120  includes two PMOS transistors AP 1  and AP 2  and two NMOS transistors AN 1  and AN 2 , thereby latching a predetermined external voltage applied to a first node AND 1 . The write circuit A 140  transmits a predetermined voltage loaded in a write bit line AWBL 1  to the first node AND 1  of the latch circuit A 120  in response to the write word line AWWL 1 . 
     The first read circuit A 110  inverts the voltage level at the first node AND 1  in response to the read word line ARWL 1  and transmits the voltage to a read bit line ARBL 1 . The second read circuit A 130  inverts the voltage level at a second node AND 2  in response to the read word line ARWL 1  and transmits the voltage to a complementary read bit line ARBLB 1 . 
     The conventional semiconductor memory device of FIG. 1 includes a plurality of semiconductor memory cells arranged in row and column directions. 
     FIG. 2 is a diagram illustrating a conventional semiconductor memory cell connected to a write word line and two read word lines. Referring to FIG. 2, the conventional semiconductor memory cell connected to a write word line AWWL 1  and two read word lines ARWL 1  and ARWL 2  includes a latch circuit A 220 , a write circuit A 240 , a first read circuit A 210 , and a second read circuit A 230 . 
     The latch circuit A 220  includes two PMOS transistors AP 1  and AP 2  and two NMOS transistors AN 1  and AN 2 , thereby latching a predetermined external voltage applied to a first node AND 1 . The write circuit A 240  transmits a predetermined voltage loaded in a write bit line AWBL 1  to the first node AND 1  of the latch circuit A 220  in response to the write word line AWWL 1 . 
     The first read circuit A 210  inverts the voltage level of the first node AND 1  in response to a first read word line ARWL 1  and/or a second read word line ARWL 2  and transmits the voltage to a first read bit line ARBL 1  and/or a second read bit line ARBL 2 . The second read circuit A 230  inverts the voltage level of a second node AND 2  in response to a first read word line ARWL 1  and/or a second read word line ARWL 2  and transmits the voltage to a first complementary read bit line ARBLB 1  and/or a second complementary read bit line ARBLB 2 . The conventional semiconductor memory device of FIG. 2 includes a plurality of semiconductor memory cells arranged in row and column directions. 
     Referring to FIG. 1, the operation of the conventional semiconductor memory cell will be described. In a case where a logic high state “H” is recorded at the first node AND 1  of the latch circuit A 120 , the write word line AWWL 1  is controlled to activate the write circuit A 140 , the first node AND 1  is charged with an electrical charge representing the state “H” of the write bit line AWBL 1  through the write circuit A 140 . 
     In a case where a logic low state “L” is recorded at the first node AND 1  of the latch circuit A 120 , the write word line AWWL 1  is controlled to activate the write circuit A 140 , and an electrical charge stored in the first node AND 1  is discharged into the write bit line AWBL 1  through the activated write circuit A 140 . 
     The voltage level at the first node AND 1  and/or the second node AND 2  of the latch circuit A 140  is output to an external device through the read bit line ARBL 1  and the complementary read bit line ARBLB 1  through the first read circuit A 110  and/or the second read circuit A 130 . 
     Responsive to a signal of the read word line ARWL 1 , the first read circuit A 110  inverts the voltage level at the first node AND 1  and transmits the voltage level to the read bit line ARBL 1 . Since the read bit line ARBL 1  is pre-charged to the state “H”, the voltage level of the read bit line ARBL 1  is not changed if the voltage level at the first node AND 1  is in the state “H”. However, if the voltage level at the first node AND 1  is in the state “L”, an electrical charge of the read bit line ARBL 1  is discharged into a supply voltage Vss through transistors AN 5  and AN 3  of the first read circuit A 110 , and thus, the first read bit line ARBL 1  represents the state “L”. 
     The second read circuit A 130  responding to a signal of the read word line ARWL 1  inverts the voltage level at the second node AND 2  and transmits the voltage to a first complementary read bit line ARBLB 1 . A method for inverting the voltage level of the second node AND 2  and transmitting the voltage to the first complementary read bit line ARBLB 1  is the same as a method for reading the voltage level at the first node AND 1  by using the first read circuit A 110 . 
     The conventional semiconductor memory cells shown in FIGS. 1 and 2, however, may have disadvantages. If the first write word line AWWL 1  is selected from a plurality of write word lines AWWL 1  through AWWLN (not shown) and is in a state “H”, for example, a plurality of latch circuits A 140  and A 240 , which are controlled by the first write word line AWWL 1 , are all activated. The voltage level of the write bit line AWBL 1  should be applied only to the latch circuits A 120  and A 220  which are connected to one write circuit from the plurality of write circuits A 140  and A 240 . However, charge re-distribution may occur even in the latch circuits A 120  and A 220  which are connected to the other write circuits. Thus, errors such as data being recorded in an unselected semiconductor memory cell may occur. 
     In a case where the read word lines ARWL 1  and/or ARWL 2  are in the state “H” during a read operation, one of the read bit line pairs ARBL 1  and/or ARBL 2  which has been already charged to the state “H” may be discharged regardless of the data stored in the latch circuits A 120  and A 220 , resulting in unnecessary power consumption. This is a reason the first node AND 1  and the second node AND 2  have opposite voltage levels. 
     In addition, if charges of the second read bit line ARBL 2  and the second complementary read bit line ARBLB 2  are increased (see FIG.  2 ), assuming that the first read word line ARWL 1  and the second read word line ARWL 2  are simultaneously in the state “H”, an effective capacitance of a third node AND 3 , which is connected to both read bit lines ARBL 1  and ARBL 2 , may increase, thereby increasing read time. 
     SUMMARY OF THE INVENTION 
     According to embodiments of the present invention, methods can be provided for reading data from a memory device comprising a plurality of memory cells and a plurality of virtual ground lines wherein each memory cell comprises a latch circuit coupled to a read circuit and wherein each virtual ground line is coupled with read circuits of a respective group of memory cells. Methods for reading according to embodiments of the present invention can include selecting a memory cell from which data is to be read, applying a first reference voltage to a virtual ground line coupled to the selected memory cell from which data is to be read, and applying a second reference voltage to a virtual ground line not coupled to the selected memory cell. A read word line coupled to the read circuit of the selected memory cell from which data is to be read can be activated. Responsive to activating the read word line coupled to the read circuit of the selected memory cell from which data is to be read, data can be coupled from the latch circuit of the selected memory cell with a respective read bit line through the read circuit of the selected memory cell. 
     According to additional embodiments according to the present invention, methods can be provided for writing data to a memory device comprising a plurality of memory cells, wherein each memory cell comprises a latch circuit having first and second complementary latch outputs and first and second write circuits respectively coupled to said first and second latch outputs. Methods for writing according to embodiments of the present invention can include selecting a memory cell to which data is to be written, activating a write word line coupled to the first and second write circuits of the selected memory cell to which data is to be written, and applying complementary write values to complementary write bit lines of a write bit line pair coupled with the first and second write circuits of the selected memory cell. Responsive to activating the write word line coupled to the first and second write circuits of the selected memory cell to which data is to be written, the first and second latch outputs of the selected memory cell can be coupled with the complementary write bit lines of the write bit line pair coupled therewith to write the complementary write values to the first and second latch outputs of the selected memory cell. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram illustrating a conventional semiconductor memory cell connected to a write word line and a read word line; 
     FIG. 2 is a diagram illustrating a conventional semiconductor memory cell connected to a write word line and two read word lines; 
     FIG. 3 is a diagram illustrating a semiconductor memory cell according to embodiments of the present invention; and 
     FIG. 4 is a diagram illustrating a semiconductor memory cell according to additional embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. It will also 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. 
     FIG. 3 is a diagram illustrating an embodiment of a semiconductor memory cell according to the present invention. Referring to FIG. 3, the semiconductor memory cell includes a latch circuit  310 , a first write circuit  320 , a second write circuit  330 , a read circuit  340 , a set circuit  350 , and a reset circuit  360 . 
     The latch circuit  310  latches two predetermined voltages which are applied to a first node ND 1  and a second node ND 2  as input/output terminals. The two voltages are logically opposite to each other, and thus the first node ND 1  and the second node ND 2  have opposite voltage levels. The latch circuit  310  includes first and second PMOS transistors P 1  and P 2  and first and second NMOS transistors N 1  and N 2 . 
     The first PMOS transistor P 1  has one source/drain connected to a supply voltage V DD , another source/drain connected to the first node ND 1 , and a gate connected to the second node ND 2 . The second PMOS transistor P 2  has one source/drain connected to a supply voltage V DD , another source/drain connected to the second node ND 2 , and a gate connected to the first node ND 1 . The first NMOS transistor N 1  has one source/drain connected to another supply voltage V ss , another source/drain connected to the first node ND 1 , and a gate connected to the second node ND 2 . The second NMOS transistor N 2  has one source/drain connected to the supply voltage V ss , another source/drain connected to the second node ND 2 , and a gate connected to the first node ND 1 . 
     The first write circuit  320  transmits a first external voltage loaded in a first write bit line WBL 1  to the first node ND 1  in response to a signal of a first write word line WWL 1 . For this purpose, the first write circuit  320  includes a fifth NMOS transistor N 5 , which has one source/drain connected to the first write bit line WBL 1 , another source/drain connected to the first node ND 1 , and a gate connected to the first write word line WWL 1 . 
     The second write circuit  330  transmits a second external voltage loaded in a first complementary write bit line WBLB 1  to the second node ND 2  in response to a signal of the first write word line WWL 1 . For this purpose, the second write circuit  330  includes a sixth NMOS transistor N 6 , which has one source/drain connected to the first complementary write bit line WBLB 1 , another source/drain connected to the second node ND 2 , and a gate connected to the first write word line WWL 1 . 
     The read circuit  340  inverts the voltage level at the second node ND 2  in response to a first read word line RWL 1  and transmits the voltage to a first read bit line RBL 1 . For this purpose, the read write circuit  340  includes a fourth NMOS transistor N 4 , which has one source/drain connected to the first read bit line RBL 1  and a gate connected to the first read word line RWL 1 , and a third NMOS transistor N 3 , which has one source/drain connected to the other source/drain of the fourth NMOS transistor N 4 , another source/drain connected to a first virtual ground VGND 1 , and a gate connected to the second node ND 2 . 
     The first virtual ground VGND 1  is supplied by a multiplexer (not shown) responding to an address (not shown) and has ground voltage in a case where the first virtual ground VGND 1  is connected to a semiconductor memory cell selected from a plurality of semiconductor memory cells and has supply voltage V DD  in a case where the first virtual ground VGND 1  is connected to an unselected semiconductor memory cell. 
     The set circuit  350  sets the first node ND 1  to a high state “H”, and the reset circuit  360  sets the second node ND 2  to a low state “L”, and the set circuit  350  and the reset circuit  360  are controlled by a control signal CTL. A plurality of semiconductor memory cells according to the present invention are arranged in a column direction and a row direction in a semiconductor memory device. 
     Operation of the semiconductor memory cell according to the present invention will be described with reference to FIG.  3 . First, operations for recording data in the latch circuit  310  will be described. If the first write word line WWL 1  is selected from a plurality of write word lines WWL 1  through WWLN (not shown) and is in the state “H”, the plurality of write circuits  320  and  330  controlled by the first write word line WWL 1  are all activated. On the other hand, only a selected write bit line WBL 1  or WBLB 1  is activated to a desired voltage level while write bit lines WBL 2  through WBLBN are maintained at a high state in the plurality of write circuits  320  and  330 . 
     In order to charge the first node ND 1  to a high state and discharge the second node ND 2  to a low state, the first write bit line WBL 1  is in the high state, and the first complementary write bit line WBLB 1  is in the low state. If the first node ND 1  is already in the high state, an electrical charge at the first node ND 1  representing the voltage level at the first node ND 1  does not change. 
     Since the size of the fifth NMOS transistor N 5  comprising the first write circuit  320  may be smaller than the first NMOS transistor N 1  of the latch circuit  310 , the first node ND 1  may not be fully charged even though the voltage level of the first write bit line WBL 1  is in the high state. If the first node ND 1  is in the low state, the first write bit line WBL 1  does not affect the first node ND 1 . However, the first node ND 1  is changed to the high state as a result of the second node ND 2  having a voltage level opposite to that of the first node ND 1 . 
     If the voltage level of the first node ND 1  is in the low state, the voltage level of the second node ND 2  is in the high state, and charging the first node ND 1  to the high state has the same meaning as charging the second node ND 2  to the low state. If the voltage level of the first write bit line WBL 1  is in the high state, the voltage level of the first complementary write bit line WBLB 1  is in the low state. Since the size of the sixth NMOS transistor N 6  comprising the second write circuit  330  may be smaller than the second NMOS transistor N 2  of the latch circuit  310 , the second node ND 2  may not be charged to the high state, but there may be no problem in discharging an electric charge of the second node ND 2 , which is pre-charged to the high state. Thus, the second node ND 2  is discharged to the low state, and the first node ND 1  is charged to the high state as a reflective effect. 
     Conversely, if the first node ND 1  is intended to be in the low state (that is, if the second node ND 2  is intended to be in the high state), the first write bit line WBL 1  is in the low state, and the first complementary write bit line WBLB 1  has the high state. Since it may be difficult to charge the second node ND 2  to the high state, the first node ND 1  having an opposite voltage level is discharged to the low state, thereby charging the second node ND 2  to the high state as a reflective effect. 
     All the other write bit lines excluding a predetermined write bit line connected to a recording circuit for recording data in the selected latch circuit are maintained at the high state, so that it may be difficult for data to be recorded in the unselected latch circuit through the recording circuit activated by the first write word line WWL 1 . 
     Second, operations for reading data recorded in the latch circuit  310  will be described. In a case where the first read word line RWL 1  is in the state “H” and instructs a read operation, only the first virtual ground VGND 1  supplied to the read circuit  340  connected to the selected latch circuit  310  is ground voltage. The other virtual grounds VGND 2  through VGNDN are in the high state. The read circuit  340  connected to the selected latch circuit  310  inverts the voltage level of the second node ND 2  and transmits the voltage to the first read bit line RBL 1 . The third NMOS transistor N 3  and the fourth NMOS transistor N 4 , which comprise the read circuit  340 , constitutes an inverter. The first read bit line RBL 1  can transmit data stored in the second node ND 2  of the latch circuit  310  to an external device. The other read bit lines RBL 2  through RBLN are maintained at the high state as previously described. Thus, only the read circuit  340  connected to the selected latch circuit  310  operates, thereby reducing the occurrence of unnecessary power consumption. 
     FIG. 4 is a diagram illustrating another embodiment of the semiconductor memory cell according to the present invention. Referring to FIG. 4, the semiconductor memory cell includes a latch circuit  410 , a first write circuit  420 , a second write circuit  430 , a read circuit  440 , a set circuit  450 , and a reset circuit  460 . 
     The latch circuit  410  latches a predetermined voltage which is applied to a first node ND 1  and a second node ND 2 , and the first node ND 1  and the second node ND 2  have opposite voltage levels. The latch circuit  410  includes two PMOS transistors P 1  and P 2  and two NMOS transistors N 1  and N 2 . 
     The PMOS transistor P 1  has one source/drain connected to a supply voltage V DD , another source/drain connected to the first node ND 1  and a gate connected to the second node ND 2 . The second PMOS transistor P 2  has one source/drain connected to a supply voltage V DD , another source/drain connected to the second node ND 2 , and a gate connected to the first node ND 1 . The first NMOS transistor N 1  has one source/drain connected to another supply voltage V ss , another source/drain connected to the first node ND 1 , and a gate connected to the second node ND 2 . The second NMOS transistor N 2  has one source/drain connected to another supply voltage V ss , another source/drain connected to the second node ND 2 , and a gate connected to the first node ND 1 . 
     The first write circuit  420  transmits a first external voltage loaded in a first write bit line WBL 1  to the first node ND 1  in response to a signal of a first write word line WWL 1 . For this purpose, the first write circuit  420  includes a fifth NMOS transistor N 5 , which has one source/drain connected to the first write bit line WBL 1 , another source/drain connected to the first node ND 1 , and a gate connected to the first write word line WWL 1 . 
     The second write circuit  430  transmits a second external voltage loaded in a first complementary write bit line WBLB 1  to the second node ND 2  in response to a signal of the first write word line WWL 1 . For this purpose, the second write circuit  430  includes a sixth NMOS transistor N 6 , which has one source/drain connected to the first complementary write bit line WBLB 1 , another source/drain connected to the second node ND 2 , and a gate connected to the first write word line WWL 1 . 
     The read circuit  440  includes a first read circuit  443  and a second read circuit  441 . The first read circuit  443  inverts the voltage level of the second node ND 2  in response to a first read word line RWL 1  and transmits the voltage to a first read bit line RBL 1 . For this purpose, the first read circuit  443  includes a fourth NMOS transistor N 4 , which has one source/drain connected to the first read bit line RBL 1  and a gate connected to the first read word line RWL 1 , and a third NMOS transistor N 3 , which has one source/drain connected to the other source/drain of the fourth NMOS transistor N 4 , another source/drain connected to first virtual ground VGND 1 , and a gate connected to the second node ND 2 . 
     The second read circuit  441  inverts the voltage level of the second node ND 2  in response to a second read word line RWL 2  and transmits the voltage to a second read bit line RBL 2 . For this purpose, the second read circuit  441  includes an eighth NMOS transistor N 8 , which has one source/drain connected to the second read bit line RBL 2  and a gate connected to the second read word line RWL 2 , and a seventh NMOS transistor N 7 , which has one source/drain connected to the other source/drain of the eighth NMOS transistor N 8 , another source/drain connected to a second virtual ground VGND 2 , and a gate connected to the second node ND 2 . 
     The first virtual ground VGND 1  and the second virtual ground VGND 2  are supplied by a multiplexer (not shown) responding to an address (not shown). The first and second virtual ground VGND 1  and VGND 2  are ground voltages in a case where the first and second virtual grounds VGND 1  and VGND 2  are connected to a semiconductor memory cell selected from a plurality of semiconductor memory cells for a read operation. The first and second virtual grounds VGND 1  and VGND 2  are supply voltages V DD  in a case where the first and second virtual grounds VGND 1  and VGND 2  are connected to an unselected semiconductor memory cell during a read operation. 
     The set circuit  450  sets the first node ND 1  to a logic high state “H”, and the reset circuit  460  sets the second node ND 2  to a logic low state “L” in response to a set/reset signal provide on the control line CTL. A plurality of the semiconductor memory cells according to the present invention can be arranged in a column direction and a row direction in a semiconductor memory device. 
     The latch circuit  410 , the first write circuit  420 , and the second write circuit  430  of FIG. 4 are the same as the latch circuit  310 , the first write circuit  320 , and the second write circuit  330 , respectively, of FIG. 3, and thus, further description thereof will be omitted. The read circuit  440  includes the first read circuit  443  and the second read circuit  441 , but operations thereof are similar to those of the read circuit  340  of FIG.  3 . Embodiments illustrated in FIG. 4 are primarily different in that two pairs of ground voltages VGND 1  and VGND 2  through VGND(N−1) and VGNDN (where N is an integer) are connected to the read circuit  440 , and there are two pairs of read bit lines RBL 1  and RBL 2  through RBL(N−1) and RBLN (where N is an integer) as a transmission path of data. 
     Embodiments illustrated in FIG. 4 can be carried out in a case where a user intends to read a plurality of same data from the latch circuit  410  in which arbitrary data are stored. A plurality of read word lines RWL 1  and RWL 2  can be enabled simultaneously or at different times. The date stored in the second node ND 2  of the latch circuit  410  can be read in response to the enabled read word lines RWL 1  and/or RWL 2 . In a case where the same data is transmitted to different devices, a number of read bit lines can be increased by as much as the number of the same data to read from the same latch circuit. 
     Assuming that a user-intends to read the same data twice from the same latch circuit, for comparison with the prior art, a case where the first read word line RWL 1  and the second read word line RWL 2  are simultaneously in the high logic state “H” will be described. Referring to FIG. 4, the capacitance of a third node ND 3  of the first read circuit  443  and a fourth node ND 4  of the second read circuit  441  is the same and is determined by the size of the third NMOS transistor N 3  and the fourth NMOS transistor N 4  and the size of the seventh NMOS transistor N 7  and the eighth NMOS transistor N 8 , respectively. 
     Referring to FIG. 2, the substantial capacitance of the third node ND 3  and the fourth node ND 4  of the read circuit of the conventional semiconductor memory cell may be increased by as much as the number of added NMOS transistors AN 8  and AN 9  compared to the capacitance of read circuits of the semiconductor memory cells according to embodiments of the present invention. Thus, the semiconductor memory cells according to embodiments of the invention, as illustrated in FIG. 4, may have a plurality of read bit lines and may reduce read times as compared with conventional semiconductor memory cells. 
     As described above, the semiconductor memory cells according to embodiments of the present invention can reduce power consumption and reduce read time of data when writing/reading data. 
     According to embodiments of the present invention, a plurality of semiconductor memory cells can be arranged in column and row directions in a semiconductor memory device. Each semiconductor memory cell can be coupled to at least one write word line, at least one write bit line, at least one read word line, at least one read bit line, and at least one virtual ground, and each memory cell can include a latch circuit, a first write circuit, and a read circuit. 
     The latch circuit can latch a predetermined voltage and can include first and second nodes having opposite voltage levels. The first write circuit can transmit a first external voltage loaded in a first write bit line of the at least one write bit line to the first node in response to a signal of a first write word line of the at least one write word line. The read circuit can invert the voltage level of the second node in response to a signal of a first read word line of the at least one read word line and in response to the at least one virtual ground and can transmit the voltage to a first read bit line of the at least one read bit line. 
     The virtual ground can latch a first voltage in a case where the virtual ground is connected to a semiconductor memory cell selected from the plurality of semiconductor memory cells, and the virtual ground can latch a second voltage, which is logically opposite to the first voltage, in a case where the virtual ground is connected to an unselected semiconductor memory cell. More particularly, the first voltage can be a ground voltage for the device, and the second voltage can be a supply voltage for the device. 
     The first write circuit can include a first NMOS transistor, which has one source/drain connected to the first write bit line, and another source/drain connected to the first node, and a gate connected to the first write word line. 
     The read circuit can include a second NMOS transistor, which has one source/drain connected to the first read bit line and a gate connected to the first read word line, and a third NMOS transistor, which has one source/drain connected to the other source/drain of the second NMOS transistor, another source/drain connected to a first virtual ground, and a gate connected to the second node. 
     Each semiconductor memory cell may also include a second write circuit for transmitting a second external voltage loaded in a second write bit line of the at least one write bit line to the second node in response to the first write word line. The first external voltage and the second external voltage have logically opposite voltage levels. 
     The second write circuit can includes a fourth NMOS transistor, which has one source/drain connected to the second node, another source/drain connected to the second write bit line, and a gate connected to the write word line. 
     The semiconductor memory cell may further include a set circuit for setting the first node and a reset circuit for resetting the second node. The read circuit may further include a fifth NMOS transistor, which has one source/drain connected to a second read bit line of the at least one read bit line and a gate connected to a second read word line of the at least one read word line, and a sixth NMOS transistor, which has one source/drain connected to the other source/drain of the fifth NMOS transistor, another source/drain connected to a second virtual ground, and a gate connected to the second node. 
     According to embodiments of the present invention, a semiconductor memory cell may be provided such that integration densities and/or performance can be maintained while providing that data is not recorded in an unselected semiconductor memory cell, read time and write time are reduced, and/or power consumption and leakage current can be reduced. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.