JP5003396B2 - Semiconductor memory device - Google Patents

Description

The present invention relates to a semiconductor memory device, and more particularly to a DRAM (Dynamic Random Access Memory) device. More particularly, the present invention relates to the operation to read out data from the memory element of the DRAM device (cell), and writes the data into the storage element.

  FIG. 28 is a circuit diagram showing a main part of a conventional DRAM device. The circuit portion shown relates to a pair of bit lines BL and / BL. The DRAM device includes a sense amplifier unit 10 and two cell array units 12 and 14 connected thereto. The sense amplifier unit 10 is provided in common to the two cell array units 12 and 14. Since the configuration of the cell array unit 14 is the same as that of the cell array unit 12, it is omitted for simplification of the drawing.

  The cell array unit 12 includes a plurality of cells MC connected to a pair of bit lines BL and / BL. The cells MC are alternately connected to the bit lines BL and / BL (folded bit line configuration). Each cell MC consists of one capacitor and one transistor. In response to this signal, the transistor receiving the bit line reset signal BRST shorts the bit lines B and / BL and precharges (resets) them to VCC / 2.

  The sense amplifier unit 10 includes a flip-flop circuit 16, a data input / output circuit 18, and transfer gate circuits 20 and 22. The flip-flop circuit 16 includes four transistors, and pulls the potential of one bit line to one of the control signals PSA and NSA and pulls the other bit line to the potential of the other control signal. Transfer gate circuits 20 and 22 each have two transistors provided on bit lines BL and / BL, respectively, and one of cell array sections 12 and 14 is connected to sense amplifier section 10 in accordance with transfer control signals BT0 and BT1. Let The data input / output circuit 18 includes two transistors, and receives the column selection signal CL to connect the bit lines BL and / BL to the data lines DB and / DB, respectively.

  FIG. 29 shows a read operation of the DRAM device shown in FIG. It is assumed that the DRAM device operates in synchronization with a clock signal CLK having a period of 10 ns. One cycle of the read operation is performed in response to a row address, a column address, and a bit line precharge command ROW, COL, PRE, and is 90 ns in the illustrated case.

  In a state where the bit lines BL and / BL are precharged (reset) to VCC / 2, the row address command ROW is given from the outside. The row address is decoded by a row address decoder not shown in FIG. 28, and the word line WL is driven. Now, it is assumed that the selected word line WL is the word line WL shown in FIG. As a result, the word line WL rises from the low potential side power supply voltage VSS toward the high potential side power supply voltage VCC. The potential of the bit line on the selection side changes according to data (0 or 1) held in the cell connected to the selected word line. In the example of FIG. 29, the bit line on the selection side is the bit line BL, and data 0 is held in the memory cell MC. Therefore, the potential of the bit line BL starts to drop from VCC / 2. At this time, the unselected bit line / BL remains at VCC / 2. When the sense amplifier 16 senses the change in the relative potential between the bit lines BL and / BL, the potential of the bit line BL is pulled to the VSS side as shown in FIG. Is pulled to the VCC side.

  After the sense amplifier 16 starts the sensing operation, the column selection signal CL is activated (turned on) by the column address command COL, and the potentials of the bit lines BL and / BL determined by the sensing operation of the sense amplifier 16 are the data input / output. The data is output to the data lines DB and / DB via the circuit 18 (this timing is shown as DATA in FIG. 29). At the same time, the bit line precharge command PRE is received from the outside, the bit line reset signal BRST becomes active, and the bit lines BL and / BL are reset (precharged) to VCC / 2. This prepares for the next read operation.

  In this way, one cycle of the read operation is performed.

  However, the conventional semiconductor memory device has the following problems.

  As described above, in the read operation, it is necessary to precharge to VCC / 2 in order to always reset the bit line. One cycle of the read operation always requires time for precharging the bit lines BL and / BL to VCC / 2, which hinders the speed of the read operation.

Accordingly, an object of the present invention is to provide a semiconductor memory device that solves the above-described problems of the prior art and speeds up a read operation and a write operation .

To achieve the above object, in a semiconductor memory device including a memory element, a word line, and a bit line, in order to reset the bit line, a reset potential of the bit line is determined according to data read in the previous read cycle. Referring to FIG. 1, the word line WL rises, data (in this case, “1”) is read from the bit line BL, and the bit line BL rises to the VCC level. Therefore, the potential of the other bit line / BL is raised to the VCC level for the next read operation. That is, the bit lines BL and / BL are both set to a reset state corresponding to the read data value (precharge). In the next read cycle, data “0” is read, and the bit line BL falls to the VSS level. Therefore, the other bit line / BL is similarly lowered to the VSS level to reset the bit line.

  As described above, since the reset potential of the bit line can be set depending on the data read in the previous read cycle, it is not necessary to precharge VCC / 2 every cycle unlike the conventional case, and high speed operation is possible. It becomes.

  When writing data, if data to be masked is designated among the write data, the data bus line connected to the corresponding memory is set in a floating state. Write data to be masked can be blocked by setting the corresponding data bus in a floating state, so when writing multiple data at the same time, even if it is necessary to mask only some of the data be able to.

  As one aspect of the invention, a semiconductor device includes a memory element, a word line connected to the memory element, a bit line connected to the memory element, a sense amplifier connected to the bit line, and a previous read The reset potential determined in accordance with the value of the data read from the storage element by the sense amplifier in the cycle is set as the reset potential in the next read cycle, and the bit line is reset to the reset potential in the next read cycle. A reset circuit; a data bus pair connected to the sense amplifier via a data input / output circuit; and a control circuit that causes the data bus pair to be in a floating state. If the circuit includes a bit to be masked to inhibit writing to the storage element, the circuit includes: One data bus to respond, characterized in that in a floating state.

In one example, the bit lines are paired, and by making the potential of the other bit line coincide with one potential of the bit line pair set by reading data in the previous read cycle, To reset.

In another example, the reset potential in each read cycle is either a high power supply voltage or a low power supply voltage. This method is different from the conventional reset method for precharging to VCC / 2.

In yet another example, a dummy cell that is selectively connected to the bit line is provided, and by reading data from the dummy cell, a potential different from the potential of one bit line from which data is read from the selected cell. The other bit line is set in the above. By providing a potential difference between the bit lines in this way, data can be read by sensing the potential difference with the sense amplifier.

For example, in each read cycle, only one of the bit line pairs is driven. In a preferred operation example, the next read cycle is started before data is output to the outside in the previous read cycle. Since the high-speed read operation can be performed by setting the reset potential, such a read cycle can be realized.

A sense amplifier connected to the bit line, similar to the reset of the bit line may be configured to decide in accordance with the data read in the previous read cycle. Like the bit line, the sense amplifier also sets the reset state according to the data read in the previous read cycle.

Still another example is characterized in that each of the bit lines has sense amplifiers at both ends, and when one sense amplifier performs a sensing operation, the other sense amplifier resets the one sense amplifier. This corresponds to the first embodiment of the present invention. By alternately turning on (activating) the sense amplifiers, one can reset the other sense amplifier.

To reset the sense amplifier connected to the bit lines may be provided a circuit for the reset state of the sense amplifier in response to the data read in the previous read cycle. This circuit corresponds to, for example, the precharge circuit 130 according to the fourth embodiment of the present invention, and latches read data (the precharge circuit 130 may be referred to as a latch circuit ). The sense amplifier is reset (precharged) so that

It has a sense amplifier at both ends of the bit lines, for resetting the sense amplifier connected to the bit line, a circuit for the reset state of each of the sense amplifiers described above in accordance with the data read in the previous read cycle May be provided in common to the sense amplifiers. This circuit corresponds to, for example, the precharge circuit 130 according to the fifth embodiment of the present invention. The fifth embodiment corresponds to claim 11 and latches data read from one bit line and resets a sense amplifier connected to the bit line to the same state as the read data. The sense amplifier connected to the other bit line is reset to a different state.

It is provided between the bit line and the data bus, and a data output circuit controlled in response to a column selection signal, located between the sense amplifier and the data bus, sense amplifier connected to the bit line It is good also as a structure which has a gate controlled according to on-off. This configuration corresponds to the sixth and seventh embodiments of the present invention. In addition to the data input / output circuit (corresponding to the data input / output circuit 140 in the sixth embodiment), the gate (the first In the sixth embodiment, the sense amplifier is activated even if, for example, the data input / output circuit is activated and the data bus and the bit line can be connected, by providing the through current blocking gate 160). Unless it is done, the data bus and the bit line are not actually connected. Therefore, the current path from the data bus through the bit line to the sense amplifier is cut off, and it is possible to prevent a through current from flowing through this route.

For example , the data input / output circuit is a direct sense circuit that indirectly connects a bit line and a data bus via a transistor, and the data bus is connected to a predetermined potential via the transistor. This configuration corresponds to the seventh embodiment of the present invention and corresponds to the direct sense circuit 180. In this case, the potential difference between the data bus and the predetermined potential is set by setting the data bus to a predetermined potential (the potential of NSA of the precharge circuit 130 in the seventh embodiment) via the transistor. And wasteful current can be prevented from flowing from the data bus.

In this case, the predetermined potential may be equal to the reset potential of the data bus when the sense amplifier is off.

  Even when a plurality of write data is temporarily held and then written simultaneously in a lump, arbitrary write data can be masked to instruct write prohibition.

  Since the reset potential of the bit line can be set depending on the data read in the previous read cycle, it is not necessary to precharge VCC / 2 every cycle unlike the conventional case, and high speed operation is possible.

  Also, since the sense amplifier can be reset efficiently and effectively, high speed operation is possible.

  Furthermore, it is possible to prevent useless current from flowing from the data bus toward the sense amplifier.

  Furthermore,

  First, the principle of the present invention will be described with reference to FIG.

  FIG. 1 is a timing diagram illustrating a read operation according to the principles of the present invention. As can be seen from comparison with FIG. 29 described above, in the present invention, when viewed from the outside of the semiconductor memory device, there is no conventionally used bit line precharge command PRE. In other words, the present invention does not precharge the bit line pair to VCC / 2 as in the prior art. Therefore, the next read cycle can be started immediately after receiving the column address command COL. Even after entering the next read cycle, the data of the previous read cycle is output to the data lines (corresponding to the data lines DB and / DB in FIG. 28). This means that the access cycle of the read operation (the time from issuing ROW to the next issue of COL) is shorter than one cycle of the read operation, and the next cell before the completion of the previous read operation. This means that the reading operation is started.

  Further, in the present invention, a new bit line reset method is proposed instead of precharging the bit line pair to VCC / 2 and resetting them internally. In the next read cycle, the potential of the bit line on the read side in the previous read cycle is reset (reset potential), and the potential of the other bit line is set to this potential. In this way, a state in which both bit lines are set to the potential of the bit line that has become the read side in the previous read cycle is referred to as a reset state. In other words, the value of the reset potential for the next reading is determined according to the previous reading information.

  The read operation will be described with reference to the timing chart shown in FIG. 1. In response to the row address command ROW, the word line WL rises. In this example, the two bit lines BL and / BL are reset to the VSS level. This means that 0 has been read to the selected bit line of the previous read operation. When the word line WL rises, the potentials of the bit lines BL and / BL start to change as illustrated. In the illustrated example, the bit line BL is on the selection side and the bit line / BL is on the non-selection side. Since data 1 is stored in the cell connected to the selected bit line BL, the potential of the bit line BL rises toward VCC. At the beginning of the rise, the non-selected bit line / BL also rises to a potential slightly higher than VSS, but is set lower than the rise potential of the bit line BL. This is due to the function of a dummy cell described later.

  In this manner, a potential difference is generated between the bit lines BL and / BL, and data can be read by sensing this with a sense amplifier. The non-selected bit line / BL is then amplified by the sense amplifier and returned to VSS. Note that it is not essential to return to VSS, and it is sufficient that the potential is lower than the potential of the bit line BL.

  After the potential difference thus generated is sensed by the sense amplifier, control is performed so that the potential of the bit line / BL on the non-selected side matches the bit line potential on the selected side. In this example, the potential of the bit line / BL is raised to VCC. When both the bit lines BL and / BL become VCC, the reset operation of the bit lines BL and / BL is completed. Therefore, the selected word line WL is lowered, and the selected word line WL ′ is raised in response to the row address command ROW in the next read cycle.

In the illustrated case, the bit line on the selection side is the bit line BL, and the potential of the bit line BL decreases toward VSS when data 0 is read from the selected memory cell (sensed by the sense amplifier). To do. In the early fall of the bit line BL, the non-selected bit line / BL is at a higher potential than the selected bit line BL due to the function of the dummy cell. Therefore, this potential difference is sensed by the sense amplifier.

  By the read operation as described above, one cycle of the read operation can be set to 60 ns, and the read operation can be speeded up.

  As a prior art of the prior art shown in FIGS. 28 and 29, there is known a method of resetting the bit line pair to the VCC level in each read cycle. However, this technique is read in the previous read cycle. The difference is that the data becomes the bit line reset potential.

  FIG. 2 is a circuit diagram showing a configuration of a main part of the DRAM device according to the first embodiment of the present invention.

The illustrated circuit configuration relates to a pair of bit lines BL0 and / BL0, and a similar circuit configuration is provided for each other bit line pair. For the bit lines BL and / BL0, a cell array unit 31, two sense amplifier units 30 ₁ and 30 ₂ , and a dummy cell unit 42 are provided.

  The cell array unit 31 includes a plurality of cells (CELL) alternately connected to the bit line pairs BL0 and / BL0 (folded bit line structure). As shown in FIG. 3, each cell is a cell MC having a one-capacitor and one-transistor configuration. Word lines WL1, WL2,... WLn are connected to the gates of the transistors.

The sense amplifier unit 30 _1, the bit line pair BL0 in the cell array portion 31, provided on one side of the / BL0, the other side of the sense amplifier 30 ₂ is the bit line pair BL0 via the dummy cell portion 42, / BL0 Is provided. The sense amplifier unit 30 ₁ includes a sense amplifier 34 ₁ , a data input / output circuit 36 ₁ , a transfer gate circuit 39 ₁ , and a bit line reset circuit 44 _1, which are internal bit line pairs BL 01 in the sense amplifier unit 30 ₁ . , / BL01.

The configuration of the sense amplifier 34 ₁ and the data output circuit 36 ₁ shown in FIG. The sense amplifier 34 ₁ has a flip-flop constituted by the transistors Q1 to Q4, further transistors Q5, Q6. In the figure, a transistor symbol with an arrow indicates a P-channel field effect transistor (for example, a MOS transistor), and a transistor symbol without an arrow indicates an N-channel field effect transistor. Transistor Q5 selectively connects power supply voltage VCC to the flip-flop according to control signal PSA1. Similarly, the transistor Q6 selectively connects the power supply voltage VSS to the flip-flop according to the control signal NSA1. Data output circuit 36 ₁ is composed of transistors Q11 and Q12 Prefecture accordance column select signal CL1, the internal bit lines BL01, / BL01, respectively data lines DB1, connected to / DB1. Incidentally, PSA1 = L (= VSS) , in the case of NSA1 = H (= VCC), the sense amplifier 34 ₁ is turned on.

Transfer gate circuits 39 ₁ has a transistor Q50 and Q51, transfer control signals BT01, / selective internal bit lines BL01, / BL01 bit line BL0 in each selectively cell array 31, respectively connected to the / BL0 accordance BT01 To do.

Bit line reset circuit 44 ₁ includes a transistor Q52, the bit line reset signal BRST1 is activated, as a short and the internal bit lines BL01 and / BL01, resets the internal bit lines BL01 and / BL01.

The sense amplifier section 30 ₂ has the same configuration as the sense amplifier section 30 ₁ . That is, the sense amplifier unit 30 ₂ includes a sense amplifier 34 ₂ , a data input / output circuit 36 ₂ , a transfer gate circuit 39 _2, and a bit line reset circuit 44 _2, which are internal bit line pairs BL 02 in the sense amplifier unit 30 ₂ . , / BL02. Configuration of the sense amplifier 34 ₂ and the data output circuit 36 ₂ has the same structure as that shown in FIG. The rereading numbers that are appended to the symbols indicating the respective units, the configuration of the sense amplifier portion _{30 2 (BL01 → BL02, /} BL01 → / BL02, DB1 → DB2, / DB1 → / DB2, CL1 → CL2, PSA1 → PSA2, NSA1 → NSA2).

The transfer gate circuit 39 ₂ includes a transistor Q53 and Q54, transfer control signals BT02, / BT02 internal bit line in accordance with BL02, / BL02 and so are selectively bit line BL0 of the cell array unit 31, respectively connected to the / BL0.

Bit line reset circuit 44 ₂ includes a transistor Q55, the bit line reset signal BRST2 is activated, as a short and the internal bit lines BL02 and / BL02, resets the internal bit lines BL02 and / BL02.

  The dummy cell section 42 includes two dummy cell transistors Q14 and Q15 shown in FIG. 5, a capacitor C, and a transistor Q16 that selectively supplies VCC / 2 to the capacitor C. The transistor Q14 is provided between the bit line BL0 and the capacitor C, and is turned on / off by the dummy cell control signal CNT1. Transistor Q15 is provided between bit line / BL0 and capacitor C, and is turned on / off by dummy cell control signal CNT2. Transistor Q16 is connected to VCC / 2 and selectively charges capacitor C.

  When data is read from the cell connected to the bit line BL0 of the sense amplifier unit 31, the dummy cell control signal CNT2 is applied so that the transistor Q15 of the dummy cell unit 42 connected to the other bit line / BL0 is turned on. When reading data from the cell connected to the bit line / BL0, the dummy cell control signal CNT1 is applied so that the transistor Q14 of the dummy cell unit 42 connected to the other bit line BL0 is turned on.

Next, the operation of the semiconductor memory device shown in FIG. 2 will be described with reference to FIG. As will be described in detail below, the sense amplifiers 30 ₁ and 30 ₂ are alternately operated in the read operation. That is, the read data is alternately output from the data line pair DB1, / DB1 and the data line pair DB2, / DB2. While reading and outputting data from the sense amplifier unit 30 ₁ performs the bit line pairs reset by the sense amplifier unit 30 _2.

State immediately before the command ROW1 enters the row address for reading the data by the operation of the sense amplifier unit 30 _1, the sense amplifier unit 30 ₁ is off, the sense amplifier unit 30 ₂ is turned on. The sense amplifier units 30 ₁ and 30 ₂ are turned on / off (more specifically, the sense amplifiers 34 ₁ and 34 ₂ are turned on / off) by the control signals PSA1, NSA1, PSA2, and NSA2. At this time, the sense amplifier unit 30 ₁ of the internal bit line pair BL01, / BL01 (in the illustrated example, a reset state is set to VSS) reset are, the transistors Q50, Q51, Q52 are turned on. The sense amplifier unit 30 ₂ is performed to read the data on and transistor Q53 is turned on and the transistors Q54, Q55 of the selected side bit line (if BL0 side) is turned off.

When the command ROW1 is input from the outside to the semiconductor memory device, the sense amplifier unit 30 ₁ is turned on and the sense amplifier unit 30 ₂ is turned off by the control signals PSA1, NSA1, PSA2, and NSA2. The command ROW1 is decoded by a decoder (not shown) to select a word line (the word line WL1 shown in FIG. 2 in the example of FIG. 6), and the potential of the word line WL1 rises toward VCC. On the other hand, falls a bit line reset signal BRST1, the transistor Q52 is the internal bit line BL01 by turning off, the reset / BL01 is released, the sense amplifier 34 ₁ is in a state capable of reading data from the cell. On the other hand, the transistor Q53 of the sense amplifier section 30 ₂ is turned off when the transfer control signal BT02 becomes low level, and the sense amplifier 34 ₂ is disconnected from the bit line BL0 of the cell array section 31.

  When the word line WL1 rises, a potential difference is generated between the bit lines BL0 and / BL0. For example, it is assumed that 1 data is stored in the cell connected to the selected word line WL1. The electric charge accumulated in this cell flows out to the bit line BL0, so that the potential of the bit line BL0 rises. On the other hand, the potential of the internal bit line / BL0 is controlled by the control signal CNT2 so that the transistor Q15 of the dummy cell circuit 42 shown in FIG. 5 is turned on, so that the charge accumulated in the capacitor C is at the VSS level. Flows out. Since the charge of the selected cell is stored at VCC, while the charge of the transistor Q15 is stored at VCC / 2, the rising potential of the bit line / BL0 is lower than the potential of the bit line BL0. Therefore, a potential difference is generated between the bit lines BL0 and / BL0.

The voltage difference is the internal bit line pair BL01, communicated to / BL01, sense amplifier 34 ₁ to sense the potential difference. At the sensed timing, the transfer control signal / BT01 is lowered, and the non-selected transistor Q51 is turned off. When the sense amplifier 34 ₁ has sensing data, it raises the column control signal CL1 by decoding the command COL1 column address and outputs a sense data data lines DB1, / to DB1.

On the other hand, the sense amplifier unit 30 _2, the transistor Q53 as described above is turned off, the bit line BL0 is disconnected from the internal bit line BL02. As a result, the internal bit line pair BL02, / BL02 enters a floating state. The sense amplifier unit 30 ₁ of the transistor Q51 is When turned off, the bit line BL0 of the cell array unit 31, starts a reset operation of the / BL0. That is, the transistors Q53, Q54, and Q55 are turned on, and the unselected bit line / BL0 is turned on by the sense amplifier 34 ₁ by the sense amplifier 34 ₁ , transistor Q50, bit line BL0, transistors Q53, Q55, transistor Q54, bit line / BL0. Is reset to the potential of the selected bit line BL0, that is, the potential of VCC in this example. In this way, after sensing read data, the potential of the non-selected bit line is reset to the potential of the selected bit line to prepare for the next read operation.

In the next reading, the word line WL2 shown in FIG. 2 is selected by the command ROW2 of the row address. In response to this, the sense amplifier unit 30 ₁ is turned off and the sense amplifier unit 30 ₂ is turned on. The data output circuit 36 ₁ of the sense amplifier portion 30 ₁ by falls column select signal CL1 is turned off, the transfer control signal BT01 by falls transistor Q50 is turned off, the selection side previous read operation The existing bit line BL0 is disconnected. In the illustrated case, 0 data is stored in the selected bit line / BL0. In this case, the non-selection side transistor Q14 of the dummy cell section 42 shown in FIG. 5 is turned on. Since the data in the cell MC connected to the word line WL2 is 0, charge flows from the bit line / BL0 to the cell capacitor, and the potential of the bit line / BL0 drops. On the other hand, since the transistor Q14 is turned on, charge flows into the capacitor C from the bit line BL0 at VCC. In this case, since C is charged with VCC / 2, the potential of the bit line BL0 does not fall below the potential of the bit line / BL0.

Potential difference of the thus bit lines BL0 and / BL0 thus generated may be transmitted to the internal bit lines BL02, / BL02, is sensed by the sense amplifier 34 _2. After sensing, it turns off the transistor Q53 which is connected to the internal bit line BL02 unselected side, and outputs data obtained by sensing by turning on the data input-output circuit 34 ₂ data lines DB2, / to DB2.

On the other hand, the sense amplifier unit 30 _1, the internal bit line pair BL01, / BL01 becomes a floating state. Transistor Q53 of the sense amplifier portion 30 ₂ When turned off, the bit line BL0 of the cell array unit 31, starts a reset operation of the / BL0. That is, the transistors Q50, Q51, Q52 are turned on, the non-selected side bit line BL0 sense amplifier 34 _2, sense amplifier 34 _2, transistor Q54, the bit line / BL0, the transistor Q51, the transistor Q52, the transistor Q50, the bit line BL0 Is reset to the potential of the selected bit line / BL0, that is, the potential of VSS in this example. In this way, after sensing read data, the potential of the non-selected bit line is reset to the potential of the selected bit line to prepare for the next read operation.

  In the above read operation, there is no command PRE for bit line precharging as in the prior art, and the command ROW of the next read cycle can be brought next to the command COL of the previous read cycle. Operation becomes possible.

  FIG. 7 is a circuit diagram showing a configuration of a main part of a DRAM device according to the second embodiment of the present invention. The second embodiment is characterized in that one sense amplifier unit is provided in common in two cell array units. The same reference numerals are assigned to the same components as those of the semiconductor memory device according to the first embodiment described above.

  The illustrated circuit configuration relates to a pair of bit lines BL0 and / BL0, and a similar circuit configuration is provided for each other bit line pair. One sense amplifier section 30 and two cell array sections 32 and 33 are provided for the bit lines BL and / BL0. The sense amplifier unit 30 is provided in common to the cell array units 32 and 33. The sense amplifier unit 30 includes a sense amplifier 34, a data input / output circuit 36, and transfer gate circuits 38 and 40.

  The sense amplifier 34 includes transistors Q1 to Q4 that realize flip-flops, and further includes transistors Q5 and Q6. Transistor Q5 selectively connects power supply voltage VCC to the flip-flop according to control signal PSA. Similarly, the transistor Q6 selectively connects the power supply voltage VSS to the flip-flop according to the control signal NSA.

  Data input / output circuit 36 includes transistors Q11 and Q12, and connects bit lines BL0 and / BL0 to data lines DB and / DB, respectively, according to column selection signal CL.

  The transfer gate circuit 38 includes transistors Q7 and Q8, and selectively connects the bit lines BL0 and / BL0 to the sense amplifier unit 30 in accordance with the transfer control signals BT0 and / BT0, thereby selectively selecting the cell array unit. 32 is connected to the sense amplifier unit 30. The transfer gate circuit 40 includes transistors Q9 and Q10, and selectively connects the cell array unit 33 to the sense amplifier by selectively connecting the bit lines BL0 and / BL1 to the sense amplifier unit 30 according to the transfer control signals BT1 and / BT1. Connect to unit 30. When one of the transfer gate circuits 38 and 40 is open, the other gate is closed.

  The cell array unit 32 includes a plurality of cells (only two of MC1 and MC2 are shown in FIG. 7), a dummy cell unit 42, and a bit line reset circuit 44. Each cell has a one-capacitor, one-transistor configuration.

  The bit line reset circuit 44 includes a transistor Q13. When the bit line reset signal BRST becomes active, the bit lines BL0 and / BL0 are short-circuited and the bit lines BL0 and / BL0 are reset.

  Next, the operation of the semiconductor memory device of FIG. 7 will be described with reference to FIG.

  When the row address command ROW is externally applied to the semiconductor memory device in a state where the bit lines BL0 and / BL0 are reset to VSS, the word line WL is selected by decoding it with a decoder (not shown). The Assume that the selected word line is the word line WL1 in FIG. In order to connect the cell array unit 32 to the sense amplifier unit 30 simultaneously with the word line selection, the transfer control signals BT0 and / BT0 are activated.

  If the cell MC1 connected to the selected word line WL1 holds data 1, the charge stored in the cell MC1 flows out to the bit line BL0, and the potential of the bit line BL0 rises. On the other hand, since the transistor Q15 of the dummy cell section 42 is turned on, the electric charge accumulated in the capacitor C flows out to the bit line / BL0 at the VSS level. Since the charge of the cell MC1 is stored at VCC, while the charge of the transistor Q15 is stored at VCC / 2, the potential of the bit line / BL0 is lower than the potential of the bit line BL0.

  The sense amplifier 34 senses the potential difference between the bit lines BL0 and / BL0 formed in this way. As a result, the potential of the bit line BL0 rapidly rises toward VCC, and the potential of the bit line / BL0 moves toward VSS. Since the data of the cell MC1 is sensed by the sense amplifier 34, the transfer control signal / BT0 is lowered (off) in order to disconnect the bit line / BL0 from which the dummy cell information is read from the sense amplifier 34. The bit line BL0 from which the information in the cell MC1 is read is left connected to the sense amplifier 34.

  On the other hand, in order to output the sensed data to the data lines DB and / DB, the column address command COL is decoded to activate the column selection signal CL. As a result, the data of the cell MC1 latched by the sense amplifier 34 is output to the data lines DB and / DB.

  Next, the bit line reset signal BRST is activated to start the operation of resetting the bit lines BL0 and / BL0. As described above, the resetting of the bit lines BL0 and / BL0 is to match the non-selected bit line / BL0 to the potential of the selected bit line BL0. Since the bit line BL0 on the selection side is connected to the power supply VCC via the sense amplifier 34, the potential of the bit line / BL0 rises toward VCC. When the potentials of the bit lines BL0 and / BL0 (reset potential for the next read operation) are reached, the bit line reset signal BRST is lowered (off). Further, simultaneously with the fall of the bit line reset signal BRST, the transfer control signal BT0 is lowered, and the sense amplifier 34 and the selection side bit line BL0 are disconnected. However, in the example of FIG. 4, since the word line WL2 is continuously selected and the cell array 32 is selected, the transfer control signal BT0 is continuously selected without falling.

  After the sense amplifier 34 senses the data, the transistor Q16 is turned on by the control signal CONT3 shown in FIG. 5, and the capacitor C is charged with VCC / 2.

  In this way, the bit lines BL0 and / BL0 are set to the reset state, and the next read operation becomes possible. It is assumed that the next selected word line is WL2 in FIG. 7 and the data stored in the cell MC2 is 0. In this case, the transistor Q14 in FIG. 5 is selected. Since the data in the cell MC2 is 0, charge flows from the bit line / BL0 to the capacitor of the cell MC2, and the potential of the bit line / BL0 is lowered. On the other hand, since the transistor Q14 is turned on, charge flows into the capacitor C from the bit line BL0 at VCC. In this case, since C is charged with VCC / 2, the potential of the bit line BL0 does not fall below the potential of the bit line / BL0. The potential difference between the bit lines BL0 and / BL0 generated in this way is sensed by the sense amplifier 34. After reading, by making the potential of the non-selected side bit line BL0 coincide with the potential VSS of the selected side bit line BL0, the bit lines BL0 and / BL0 are reset to prepare for the next read operation.

  In the above read operation, there is no command PRE for bit line precharging as in the prior art, and the command ROW of the next read cycle can be brought next to the command COL of the previous read cycle. Operation becomes possible.

  In the above configuration, the configuration of resetting (precharging) the sense amplifier 34 is omitted.

  Next, a third embodiment of the present invention will be described.

  FIG. 9 is a block diagram showing a main part of a semiconductor memory device according to the third embodiment of the present invention. The same reference numerals are attached to the same components as those of the semiconductor memory devices according to the first and second embodiments described above.

  The third embodiment is characterized in that a dummy cell circuit 42 is provided in the sense amplifier section 300 so that a read operation can be performed at a higher speed. Therefore, the flip-flop circuit 34 of the sense amplifier unit 300 is configured to sense the internal bit line pair BL, / BL in the sense amplifier unit 300. When sensing, since the cell array units 320 and 330 are disconnected from the sense amplifier unit 300, the sensing operation speed depends on the loads on the internal bit lines BL and / BL. In the configuration shown in FIG. 7, the sense operation speed is slower than the configuration in FIG. 9 because it depends on the load of the bit lines BL0 and / BL0 longer than the internal bit lines BL and / BL in FIG. As a result, the power consumed in the sensing operation can be reduced.

  Since the sense amplifier unit 300 is configured as described above, the cell array units 320 and 330 connected to the sense amplifier unit 300 are also different from the configuration shown in FIG. Specifically, the cell array unit 320 includes only the bit line BL0, and the cell array unit 330 includes only the bit line / BL0. That is, one of the bit lines BL0 or / BL0 is driven for the sense amplifier 300.

  The sense amplifier section 300 includes transfer gate circuits 38A and 40A, a dummy cell circuit 42, and a bit line reset circuit 44A in addition to the flip-flop circuit 34 and the data input / output circuit 36. The transfer gate circuit 38A has a transistor Q7, and the transfer gate 40A has a transistor Q10. The dummy cell unit 42 has the configuration shown in FIG. 5, but differs from the configuration shown in FIG. 7 in that it is connected to the internal bit lines BL and / BL in the sense amplifier unit 300. The bit line reset circuit 44A resets the internal bit lines BL and / BL in the sense amplifier unit 300.

  FIG. 10 is a timing chart showing the operation of the circuit configuration of FIG.

  Now, when the bit line BL, / BL is reset to VSS and a row address command ROW is externally applied to the semiconductor memory device, the word line WL is decoded by decoding it with a decoder (not shown). Selected. Assume that the selected word line is the word line WL1 in FIG. In order to connect the cell array unit 320 to the sense amplifier unit 30 simultaneously with the word line selection, the transfer control signal BT0 is activated.

  If the cell MC1 connected to the selected word line WL1 holds data 1, the charge stored in the cell MC1 flows out to the bit line BL0, and the potential of the bit line BL0 rises. Therefore, the potential of the internal bit line BL in the sense amplifier unit 300 also rises. On the other hand, since the transistor Q15 of the dummy cell portion 42 is turned on, the electric charge accumulated in the capacitor C flows out to the internal bit line / BL at the VSS level. Since the charge of the cell MC1 is stored at VCC, while the charge of the transistor Q15 is stored at VCC / 2, the potential of the internal bit line / BL is lower than the potential of the internal bit line BL.

The flip-flop circuit 34 senses the potential difference between the internal bit lines BL0 and / BL0 formed in this way. At this time, the cell array unit 320 turns off the transistor Q7 to keep it disconnected from the sense amplifier unit 300. As a result, the potential of the internal bit line BL rises rapidly toward VCC, and the potential of the internal bit line / BL goes toward VCC.

  On the other hand, in order to output the sensed data to the data lines DB and / DB, the column address command COL is decoded to activate the column selection signal CL. As a result, the data in the cell MC1 latched in the flip-flop circuit 34 is output to the data lines DB and / DB.

  Next, the bit line reset signal BRST is activated to start the operation of resetting the internal bit lines BL and / BL. The internal bit lines BL0 and / BL0 are reset by matching the non-selected side internal bit line / BL0 to the potential of the selected side internal bit line BL0. Therefore, in this case, the potential of the bit line / BL0 rises toward VCC. When the potentials of the internal bit lines BL0 and / BL0 become VCC (reset potential for the next read operation), the bit line reset signal BRST is lowered (off).

  After the sense amplifier 34 senses the data, the transistor Q16 is turned on by the control signal CONT3 shown in FIG. 5, and the capacitor C is charged with VCC / 2.

  If the bit lines BL and / BL are reset, the next read operation can be executed immediately. Therefore, commands related to external reading can be arranged as shown in FIG. Since the sensing operation can be performed at a higher speed, commands can also be arranged and arranged.

  In FIG. 9, the bit lines extend in both directions of the sense amplifier unit 300, but may be configured to extend in one direction.

  In the above configuration, the configuration of resetting (precharging) the sense amplifier 34 is omitted.

The sense amplifiers 34 ₁ and 34 ₂ used in the first to third embodiments are composed of six transistors. As shown in FIG. 11, two P-channel transistors and two N-channel transistors are used. A total of four transistors may be used. In the configuration of FIG. 11, when the control signals PSA and NSA are at a high level and a low level, respectively, the sense amplifier is turned on. Therefore, the configuration of FIG. 11 is the reverse of the operation of the sense amplifier composed of 6 transistors.

  Next, a fourth embodiment of the present invention will be described.

In the first embodiment described above, the two sense amplifiers 34 ₁ and 34 ₂ provided on both sides of the bit lines BL 0 and / BL 0 are used, and while one sense amplifier reads data, the other The bit line pair BL0, / BL0 is precharged (reset) by the sense amplifier and the bit line (node) in the one sense amplifier is reset (floating state) after data is read to release the latched state It is the structure to do.

  When an actual semiconductor memory device is configured using this configuration, sense amplifiers S / A1 and S / A2 can be arranged on both sides of a pair of bit lines as shown in FIG. It is extremely difficult to realize the relaxed layout shown in FIG. In the relax method, a plurality of bit line pairs share the sense amplifiers S / A1 and S / A2. Therefore, a configuration that enables the arrangement of the sense amplifiers in FIG. 12B is required.

In the fourth embodiment of the present invention, means for precharging bit lines and sense amplifiers (bit lines therein) is provided to enable a layout as shown in FIG. Further, this means can be applied to the second and third embodiments described above and used to reset the bit line in the sense amplifier.

  FIG. 13 is a circuit diagram showing a fourth embodiment of the present invention. The configuration of FIG. 13 relates to a pair of bit lines, and includes a plurality of memory cells, the dummy cell circuit 42 described above, a sense amplifier 110 having a 4-transistor configuration, a precharge control circuit 120, a precharge circuit 130, and a data input / output circuit 140. It comprises. The precharge circuit 130 precharges the bit line pair BLX (BL), BLZ (BL) and the bit lines BLX (LA), BLZ (LA) on the sense amplifier 110 side simultaneously. Since the precharge circuit 130 has the same circuit configuration as the sense amplifier 110, it also has a function of latching data. The precharge control circuit 120 includes a bit line reset circuit 121 composed of one N-channel MOS transistor and a transfer gate 122 composed of two N-channel MOS transistors, and a bit line pair BLX (BL), BLZ (BL) And precharge of the bit lines BLX (LA) and BLZ (LA).

Next, the operation of FIG. 13 will be described with reference to FIG. Below, the operation | movement is demonstrated for every area shown by the alphabet AF in the figure.
Section A
First, when the word line WL1 rises while the bit lines BLX (BL) and BLZ (BL) are precharged to the high level H, data is output from the memory cells connected to the word line WL1. come. In this example, it is assumed that “L” appears. At the same time, data comes out of the dummy cell 42. As described above, half of the power supply voltage VCC is stored in the dummy cell 42. Therefore, the bit line BLX (BL) connected to the selected memory cell has a faster fall than the bit line BLZ (BL) connected to the dummy cell 42. The sense amplifier 110 is turned on by inverting the control signals NSA1 and PSA1, and amplifies a slight potential difference between the bit lines BLX (BL) and BLZ (BL).
Section B
Next, the precharge control circuit 120 transfers the data amplified by the sense amplifier 110 to the precharge circuit 130. After the sense amplifier 110 is latched, the transfer control signals BT0 and / BT0 rise, both the two transistors of the transfer gate 122 are turned on, and the latched data is transferred to the precharge circuit 130.
Section C
The control signals PSA and NSA are inverted, and the precharge circuit 130 is turned on. At this time, the control signals PSA1 and NSA1 are inverted, and the sense amplifier 110 is turned off. This is because the sense amplifier 110 and the bit line are precharged next, but at that time, the sense amplifier 110 cannot be precharged unless it is turned off in advance.
Section D
The sense amplifier 110 is precharged (that is, the bit line pair BLX (BL), BLZ (BL) is precharged) and the bit line pair BLX (LA), BLZ (LA) is precharged. In section D, first of all, the bit lines connected to the selected memory cell (in this case, the memory cell connected to the word line WL1) among the transfer control signals BT0 and / BT0 simultaneously raised in section B, that is, non- In order to disconnect the selected bit line (in this case, the bit line BLZ (BL)) from the precharge circuit 130, the transfer control signal BT0 is lowered. Then, the bit line reset signal BRST is raised, the transistor of the bit line short circuit 121 is turned on, the bit lines BLX (BL) and BLZ (BL) are short-circuited, and the non-selected bit line BLZ (BL) is set to low. Precharge to level. That is, the bit line BLX (LA) of the precharge circuit 130 is at a low level, and the bit line BLZ (BL) of the sense amplifier 110 is at a high level. Therefore, the charge of the bit line BLZ (BL) flows into the NSA through the bit line short circuit 121, the / BT0 side transistor, the bit line BLX (LA), and the N channel MOS transistor.

In addition, by raising (turning on) the column selection signal CL in the section D, the read data can be output to the data buses DBX and DBZ.
Section E
In this state, the precharge of the bit line pair BLZ (BL), BLX (BL) of the sense amplifier 110 is completed. In the precharge circuit 130, the bit line BLX (LA) is at the low level and the bit line BLZ (LA) is at the high level, and the read data is latched. Then, the transfer control signal / BT0 is lowered, and the bit line reset signal BRST is lowered.
Section F
Then, the control signals PSA and NSA are inverted, and the precharge circuit 130 is turned off. As a result, there is a margin in the timing margin when the next new data is latched.

  As described above, since the bit line pair BLZ (BL) and BLX (BL) extending from the sense amplifier 110 can be precharged by the precharge circuit 130, the circuit can be simplified as compared with the configuration shown in FIG. The arrangement shown in FIG. 12B can be realized by using the circuit configuration shown in FIG.

  FIG. 15 is a circuit diagram showing a relaxation type semiconductor memory device realized by using the circuit configuration shown in FIG. Hereinafter, the configuration of FIG. 15 will be described as a fifth embodiment of the present invention. In FIG. 15, the same components as those shown in FIG. 13 are denoted by the same reference numerals. The circuit shown in FIG. 15 is characterized in that one precharge circuit 130 is provided in common for the left sense amplifier 110 and the right sense amplifier 140, and both sense amplifiers are precharged by the precharge circuit 130. In the following description, in order to distinguish the left and right components from the precharge circuit 130, L (left) is used to represent signals, bit lines, and word lines among the reference numbers shown in FIG. Add R (right). For example, the word lines arranged on the left side (upper side for convenience in FIG. 15) are WLL1 and WLL2, and the word lines arranged on the right side (lower side for convenience in FIG. 15) are WLR1 and WLR2.

  The circuit configuration on the upper side of FIG. 15 is the same as the circuit configuration shown in FIG. 15 includes a cell array, a dummy cell 142, a right sense amplifier 140, and a right precharge control circuit 150. The right sense amplifier 140 has the same configuration as the left sense amplifier 110. The right precharge control circuit 150 has the same configuration as the left precharge control circuit 120 and includes a bit line short circuit 151 and a transfer gate 152. The data bus lines DBX and DBZ and the data input / output circuit 140 are the same.

  Next, the operation of the configuration shown in FIG. 15 will be described with reference to FIGS. 16 and 17. 16 is an operation timing chart of the left circuit located on the left side with respect to the precharge circuit 130, and FIG. 17 is an operation timing chart of the right circuit located on the right side. 16 and 17 show the sections A to F corresponding to the sections A to F shown in FIG.

  First, in FIG. 16, it is assumed that a cell connected to the word line WLL1 is selected. The operation of the left circuit in this case is the same as the circuit operation described with reference to FIG. That is, the operation of each part in the section A to the section F in FIG. 16 is the same as the operation of the corresponding part in the section A to the section F in FIG. Therefore, the description of the operation of the left circuit here is omitted.

  The right precharge control circuit 150 in the right circuit operates differently from the left precharge control circuit 120. In FIG. 17, in the standby state (at 0 (ns)), the right sense amplifier 140 is at a precharge level opposite to that of the left sense amplifier 110. That is, the bit lines BLRX (BL) and BLRZ (BL) in the right sense amplifier 140 are at a low level. When the memory cell of the left circuit is selected and the left circuit is performing a sensing operation (section C in FIG. 16), both transfer control signals BTR0 and / BTR0 of the right precharge control circuit 150 are at a low level. Therefore, the right sense amplifier 140 is disconnected from the precharge circuit 130, that is, in a floating state. When the sensing operation of the left circuit is completed and the precharge operation is started (section D in FIG. 16), the right circuit enters the precharge operation at the same time (section D in FIG. 17). In this precharge operation, if the left side performs a precharge operation in the VSS direction so as not to increase the load of the precharge circuit 130, the right side performs a precharge operation in the VCC direction. That is, in FIG. 16, the transfer control signal / BTL0 is ON in the section D, and the precharge circuit 130 precharges the bit line BLLZ (BL) potential of the left sense amplifier 110 to the potential VSS of the bit line BLX (LA). To work. Therefore, in the section of FIG. 17, the transfer control signal BTR0 is turned on simultaneously with the bit line reset signal BRSTR, and the precharge circuit 130 changes the bit lines BLRX (BL) and BLRZ (BL) of the right sense amplifier 140 to BLZ (LA). It operates so as to be precharged to the potential VCC. As a result, the bit line does not enter a floating state when inactive (off).

  As described above, the arrangement shown in FIG. 12B can be realized with the circuit configuration of FIG. 15, and the precharge circuit can be shared by the right side circuit and the left side circuit, which is advantageous in terms of layout area.

  Next, a sixth embodiment of the present invention will be described with reference to FIG. In FIG. 18, the same reference numerals are given to the same components as those shown in the above-described drawings. In the sixth embodiment of the present invention, a through current blocking gate 160 is provided in the circuit configuration according to the fourth embodiment of the present invention shown in FIG. This through current blocking gate 160 can also be applied to the circuit configuration shown in FIG.

  In FIG. 13, the column selection signal CL is turned on when the memory cell array is in an inactive state (none is selected; hereinafter, the memory cell array in this state is referred to as an inactive array) and the precharge circuit 130 is in a latched state. In this case, when the data latched in the precharge circuit 130 is different from the precharge level of the data bus lines DBX and DBZ, the PSA or NSA of the precharge circuit 130 is connected from the data bus DBX or DBZ via the data input / output circuit 140. Through current will flow through. Normally, the through current flows when a plurality of sense amplifiers as shown in FIG. 15 share a data bus. In FIG. 15, for example, the memory cell array of the left circuit is inactive and the memory cell array of the right circuit is active (a word line rises and a memory cell is selected; hereinafter, the memory cell array in this state is referred to as an active array). In some cases, when the column selection signal CL is raised to output the data to the data buses DBX and DBZ, the above through current flows.

  The through current blocking gate 160 is composed of two N-channel MOS transistors. A control signal CLD is applied to the gates of the two transistors. When the word line is selected and the sense amplifier operates, the through current blocking gate 160 must be open. Therefore, the gate control signal CLD must be turned on before or simultaneously with the column selection signal CL being turned on. In the present embodiment, the gate control signal CLD is synchronized with the control signals PSA and NSA, and the gate control signal CLD is turned on before the column selection signal CL is turned on.

  FIG. 19 is a timing chart showing the active array operation of the configuration of FIG. When the control signals PSA and NSA are inverted and the precharge circuit 130 is turned on, the gate control signal CLD is turned on and the gate of the through current blocking gate 160 is opened. Thereafter, the column selection signal CL is turned on, and the data latched in the precharge circuit 130 is transferred to the data bus lines DBX and DBZ.

  FIG. 20 is a diagram showing an inactive array operation of the configuration of FIG. When the memory cell is not selected, the gate control signal CLD remains at a low level (off). Therefore, even if the column selection signal CL is subsequently turned on, the data bus lines DBX and DBZ are disconnected from the precharge circuit 130, and no through current flows.

  The data input / output circuit 140 may be a circuit having a configuration other than the two-transistor configuration shown in FIG. FIG. 21 shows a configuration including a direct sense circuit 180. In FIG. 21, the same components as those described above are denoted by the same reference numerals. The configuration shown in FIG. 21 will be described below as a seventh embodiment of the present invention. In the following description, it is assumed that the data bus lines DBX and DBZ are precharged to the VCC level.

  Direct sense circuit 180 includes transistors Q21 to Q28. Bit lines BLZ (LA) and BLX (LA) are received by the gates of transistors Q25 and Q26, respectively, and their drains are connected to data bus lines DBX and DBZ. Data read from the memory cell and latched by the precharge circuit 130 is transferred to the data bus lines DBX and DBZ by controlling on / off of the transistors Q25 and Q26. At the time of writing data, the column selection signal WCLE is turned on at the time of writing and the transistors Q23 and Q24 are turned on. Write data on the data bus lines DBX and DBZ is supplied to the precharge circuit 130 through the transistors Q21 to Q24.

  Here, when the memory cell is not selected, the control signal NSA of the precharge circuit 130 is set to a high level. Focusing on this point, the sources of the transistors Q27 and Q28 are connected to the node of the control signal NSA of the precharge circuit 130. Therefore, even if the column selection signal CL is turned on and the transistors Q25 and Q26 are turned on, the through current does not flow from the data bus lines DBX and DBZ to the NSA node of the precharge circuit 130.

  FIG. 22 is a timing chart showing an active array operation of the configuration of FIG. In this case, the control signals NSA and PSA of the precharge circuit 130 are set to low level and high level, respectively. Then, the column selection signal CL is turned on. In the case of FIG. 22, since the bit line BLZ (LA) is at a high level, the transistor Q25 is turned on, a current flows from the data bus line DBX to the NSA node of the precharge circuit 130, and the potential of the data bus line DBX is changed from VCC. Descend. On the other hand, since the bit line BLX (LA) is at a low level, the transistor Q26 is turned off. Therefore, the potential of the data bus line DBZ remains at a high level.

  FIG. 23 is a timing chart showing an inactive array operation of the configuration of FIG. In this case, the control signals NSA and PSA of the precharge circuit 130 are at a high level and a low level, respectively. Transistor Q25 is on and transistor Q26 is off. Therefore, even if the column selection signal CL rises and the transistors Q27 and Q28 are turned on, the data bus lines DBX and DBZ and the NSA node of the precharge circuit 130 are at the same level (high level), so no through current flows. .

  In the circuit configuration shown in FIG. 21, the sources of the transistors Q27 and Q28 are directly connected to the NSA node of the precharge circuit 130, but may be connected to another circuit that changes similarly to the NSA.

  In FIGS. 21 to 23, the data bus lines DBX and DBZ are precharged to VCC. However, when precharged to the VSS level, the sources of the transistors Q27 and Q28 are used as the PSA node. Just connect. Further, when the data bus lines DBX and DBZ are VCC / 2, the sources of the transistors Q27 and Q28 may be connected to a node (circuit) that changes to 0V during the active array operation and VCC / 2 during the inactive operation. .

  FIG. 24 is a block diagram showing a configuration of a synchronous DRAM (SDRAM) as an example of a semiconductor memory device to which the first to seventh embodiments can be applied. The SDRAM illustrated in FIG. 24 includes a clock buffer 200, a command decoder 210, an address buffer / register 220, an I / O data buffer / register 230, a memory cell array 240, a row decoder 250, a sense amplifier unit 260, and a column decoder 270. The clock buffer 200 receives the clock signal CLK and the clock enable signal CKE from the outside, generates an internal clock signal necessary for the internal circuit, and sends it to the command decoder 210, the address buffer / register 220, the I / O data buffer / register 230, and the like. Output. The command decoder 210 receives a chip select signal / CS, a row address strobe signal / RAS, a column address strobe signal / CAS, and a write enable signal / WE from the outside, and decodes these signals to perform various types required by the internal circuit. Signals such as the bit line reset signal BRST, transfer control signal BT, control signals NSA, and PSA described above are generated. In addition, although not shown in FIG. 24, the control signal CNT, the gate control signal CLD, and the like are also generated by the command decoder 210. The address buffer / register 220 decodes external address signals A0 to Am to generate a row address and a column address. The I / O data buffer / register 230 is connected to data buses DB and / DB (also corresponding to the above-described DBX and DBZ), temporarily stores write data from the outside, and temporarily stores read data to the outside. The memory cell array 240 is a circuit including a large number of memory cells, word lines, and bit lines. The row decoder 250 decodes the row address and generates a signal (such as WL1 described above) for driving the word line. The column decoder 270 decodes the column address and generates the above-described column selection signal CL and the like. The sense amplifier unit 260 includes all circuit parts between the memory cell array and the data buses DB and / DB. For example, in the configuration of FIG. 13, the sense amplifier 110, the precharge control circuit 120, the precharge circuit 130, and A data input / output circuit 140 is included.

  Here, the arrangement relationship between the memory cell array 240 and the sense amplifier unit 260 in the block diagram of FIG. 24 directly corresponds to the fourth embodiment shown in FIG. However, the arrangement relationship between the memory cell array 240 and the sense amplifier unit 260 in FIG. 24 is merely an example, and includes other embodiments, modifications, and improvements. For example, the configuration of FIG. 16 does not directly correspond to the arrangement relationship between the memory cell array 240 and the sense amplifier unit 260 of FIG. 24, but the configuration of FIG. 16 is included in the block composed of the memory cell array 240 and the sense amplifier unit 260 of FIG. It can be considered that it has been realized. In addition, the memory cell array 240 in FIG. 24 may of course have a configuration having a plurality of banks.

  Here, the semiconductor memory device shown in FIG. 24 can have a characteristic configuration described below with respect to a data write operation. In an actual semiconductor memory device, data of a plurality of bits is written at once. At this time, writing may be prohibited by masking a part of the write data. For example, when writing data on a data bus to a memory cell at a time via a corresponding sense amplifier, the data to be masked may be masked.

  FIG. 25 is a diagram for explaining a write operation and a mask operation for one (1 bit) data bus line of a certain data bus. Data H, L, H, L... Are sequentially written into the memory cells in synchronization with the rising edge of the write clock. In this case, when the writing of the second data L is prohibited, the data L may be masked at this timing to prohibit the data L from being output to the data bus line connected to the corresponding memory cell. . Usually, a mask signal is generated for this mask operation.

  On the other hand, a plurality of 1-bit data of a certain data bus line are accumulated (for example, when four sense amplifiers are selected at the same time, the data is accumulated on the data bus lines connected to each), and the memory cells are stored at a time. There is a write operation. This write operation is also called a batch write operation. For example, in the example of FIG. 25, the write operation is not performed until four 1-bit data of H, L, H, and L are collected, and once four data are collected. To the memory cell. In this case, when the second data L needs to be masked, it is necessary to specify that the second data is masked data in order to write four data to the memory cell at a time. . Therefore, the mask operation for writing data in a lump cannot be realized in the mask operation for writing data in synchronization with each rising edge of the write clock as shown in FIG.

  The configuration of FIG. 26 is characterized in that even when the plurality of 1-bit data are written at a time, the data therein can be masked. More specifically, the configuration of FIG. 26 sets the data bus line corresponding to the data to be masked to the floating state, thereby specifying the data to be masked and prohibiting the write operation. The configuration shown in FIG. 26 will be described below as an eighth embodiment of the present invention.

  FIG. 26 shows portions corresponding to the cell array 240 and the sense amplifier unit 260 in FIG. 24, and assumes a case where four bits are written into the memory cells at once. A plurality of sense amplifiers (S / A) 310 and 320 are provided on both sides of the cell array 300, and bit line pairs are alternately extended from the sense amplifiers 310 and 320 on both sides in accordance with the relaxation method described above. In FIG. 26, only one pair of bit line pairs extending from each sense amplifier is shown for easy understanding. Each of sense amplifiers 310 and 320 is connected to a data bus. In FIG. 26, four pairs of data bus lines DB0X, DB0Z; DB1X, DB1Z; DB2X, DB2Z; DB3X, DB3Z are connected as illustrated. The column decoder 270 selects four data input / output circuits (corresponding to the data input / output circuit 140 described above, but not shown in FIG. 26) at a time when data is written, and corresponding four sense amplifiers. Are connected to the data bus line.

Data bus control circuits 330 ₁ , 330 ₂ , 330 ₃ , 330 ₄ are provided for each of the four pairs of data bus lines DB0X, DB0Z; DB1X, DB1Z; DB2X, DB2Z; DB3X, DB3Z. The data bus control circuits 330 ₁ , 330 ₂ , 330 ₃ , and 330 ₄ respectively include write instruction signal lines WDM0, WDM1, WDM2, and WDM3, data bus lines WDB0X, WDB0Z, WDB1X, WDB1Z, WDB2X, WDB2Z, WDB3X, and WDB3Z, and Data bus precharge instruction signal line DBP is connected as shown. The write instruction signal lines WDM0, WDM1, WDM2, and WDM3 are generated by the write instruction signal generation circuit 340. The write instruction signal generation circuit 340 performs a predetermined logical operation on the write enable signal WE and the data mask signals DQM0, DQM1, DQM2, and DQM3 to generate the write instruction signals WDM0, WDM1, WDM2, and WDM3.

  The data mask signals DQM0, DQM1, DQM2 and DQM3 and the data bus precharge signal DBP are supplied from the command decoder 210 in FIG. The data bus lines WDB0X, WDB0Z, WDB1X, WDB1Z, WDB2X, WDB2Z, WDB3X, and WDB3Z are connected to the I / O data buffer / register 230 of FIG.

  The write instruction signal generation circuit 340 includes four NAND gates 341 to 344 and four inverters 345 to 348. The NAND gates 341 to 344 perform NAND logic operations on the write enable signal WE and the data mask signals DQM0, DQM1, DQM2, and DQM3, respectively. Output as WDM3. The data mask signals DQM0, DQM1, DQM2, and DQM3 are at a low level when a mask is instructed.

Each of the data bus control circuits 330 _{1 to} 330 ₄ includes a precharge circuit 331, a data bus drive circuit 332, NAND gates 333 and 334, and inverters 336 to 338. FIG. 26 shows only the structure of the data bus control circuit 330 ₁ as an example. The NAND gate 334 takes the NAND logic of the write instruction signal WDM0 and the write data WDB0X, and outputs the output of the P channel MOS transistor of the CMOS inverter on the data bus line DB0X side of the data bus driver 337 via the two inverters 336 and 337. Give to the gate. The output of the inverter 336 is applied to the gate of the N channel MOS transistor of the CMOS inverter on the data bus line DB0Z side of the data bus driving unit 337. The NAND gate 333 takes the NAND logic of the write instruction signal WDM0 and the write data WDB0Z and outputs the output of the P channel MOS transistor of the CMOS inverter on the data bus line DB0Z side of the data bus driver 337 via the two inverters 335 and 338. Give to the gate. The output of the inverter 335 is applied to the gate of the N channel MOS transistor of the CMOS inverter on the data bus line DB0X side of the data bus driving unit 337. The outputs of the two CMOS inverters are connected to data bus lines DB0X and DB0Z, respectively.

  When all four transistors of the data bus driving circuit 332 are turned off, the data bus lines DB0X and DB0Z are in a floating state.

  The precharge circuit 331 includes two P channel MOS transistors 331. These gates receive the data bus precharge instruction signal, and their drains are connected to data bus lines DB0X and DB0Z, respectively. In the illustrated configuration, the data bus lines DB0X and DB0Z are precharged to a high level (VCC).

  Next, the operation of FIG. 26 will be described with reference to the timing chart of FIG.

At the time of writing data in which four sense amplifiers are selected at a time, the data bus precharge signal DBP and the write enable signal WE rise and the write operation is enabled. In the example of FIG. 27, the data mask signals DQM0 to DQM2 rise to instruct the writing of the corresponding data, but the data mask signal DQM3 remains at the low level and the corresponding data mask is instructed. In this case, the write instruction signal generation circuit 340 includes the write instruction signals WDM0, WDM1, and WDM.
2 is set to the high level, and the write instruction signal WDM3 is set to the low level.

All four transistors of the data bus driver circuit 332 of the data bus control circuit 330 _4, which has received the write instruction signal WDM3 is turned off. That is, since the write instruction signal WDM3 is at a low level, the outputs of the inverters 335 and 336 are at a low level and the outputs of the inverters 337 and 338 are at a high level. Therefore, the data bus lines DB3X and DB3Z are set to a high level floating state. Since this high level floating state corresponds to the above-described data reading state of the sense amplifier, data cannot be written.

In the other data bus control circuits 330 _{1 to} 330 ₃ , the data bus lines DB0X to DB2Z are driven according to the write data WDB0X, WDB0Z, WDB1X, WDB1Z, WDB2X, and WDB2Z.

  As described above, by setting a data bus line corresponding to data to be masked to a floating state, writing of data to be masked can be prohibited despite simultaneous writing of a plurality of data.

  The embodiment of the present invention has been described above. The present invention includes all DRAM devices, and is particularly suitable for application to SDRAM (synchronous DRAM) capable of high-speed operation, which is currently attracting attention.

It is a timing diagram for demonstrating the principle of this invention. 1 is a circuit diagram showing a main part of a semiconductor device according to a first embodiment of the present invention. It is a circuit diagram which shows the structure of a cell. FIG. 3 is a circuit diagram showing configurations of a sense amplifier circuit and a data output circuit shown in FIG. 2. FIG. 3 is a circuit diagram showing a configuration example of a dummy cell circuit shown in FIG. 2. FIG. 6 is a timing chart showing the operation of the second circuit. FIG. 6 is a circuit diagram showing a main part of a semiconductor memory device according to a second embodiment of the present invention. FIG. 8 is a timing chart showing an operation of the circuit shown in FIG. 7. FIG. 6 is a circuit diagram showing a main part of a semiconductor memory device according to a third embodiment of the present invention. FIG. 10 is a timing chart showing an operation of the circuit shown in FIG. 9. It is a figure which shows another structural example of a sense amplifier. It is a figure which shows the example of an arrangement | sequence of a sense amplifier. FIG. 10 is a circuit diagram showing a main part of a semiconductor memory device according to a fourth embodiment of the present invention. FIG. 14 is a timing diagram illustrating an operation of the configuration illustrated in FIG. 13. FIG. 9 is a circuit diagram showing a main part of a semiconductor memory device according to a fifth embodiment of the present invention. FIG. 16 is a timing diagram (part 1) illustrating the operation of the configuration illustrated in FIG. 15; FIG. 16 is a timing diagram (part 2) illustrating the operation of the configuration illustrated in FIG. 15. It is a circuit diagram which shows the principal part of the semiconductor memory device by the 6th Embodiment of this invention. FIG. 19 is a timing diagram (part 1) illustrating the operation of the configuration illustrated in FIG. 18; FIG. 19 is a timing diagram (part 2) illustrating the operation of the configuration illustrated in FIG. 18. It is a circuit diagram which shows the principal part of the semiconductor memory device by the 7th Embodiment of this invention. FIG. 22 is a timing diagram (part 1) illustrating the operation of the configuration illustrated in FIG. 21; FIG. 23 is a timing diagram (part 2) illustrating the operation of the configuration illustrated in FIG. 22; 1 is a block diagram showing an overall configuration of a semiconductor memory device of the present invention. FIG. 25 is a diagram illustrating an example of a data write operation of the apparatus of FIG. 24. It is a circuit diagram which shows the principal part of the semiconductor memory device by the 8th Embodiment of this invention. FIG. 27 is a timing chart showing the operation of the configuration shown in FIG. 26. It is a circuit diagram which shows the principal part of the conventional semiconductor memory device. FIG. 29 is a timing diagram illustrating an operation of the circuit diagram illustrated in FIG. 28.

Explanation of symbols

30, 30 ₁ , 30 ₂ , 310 , 320 sense amplifier units 31, 32, 33, 300 cell array unit 42 dummy cell unit
330 Data Bus Control Circuit

Claims (1)

A storage element;
A word line connected to the storage element;
A pair of bit lines connected to the storage element;
A sense amplifier connected to the bit line pair ;
When the output potential on the bit line pair side of the sense amplifier in the previous read cycle is a low power supply potential, the bit line pair is reset to the low power supply potential as a reset potential in the next read cycle, When the output potential on the bit line pair side of the sense amplifier is a high power supply potential, a reset circuit that resets the bit line pair to the high power supply potential as a reset potential for the next read cycle;
A plurality of data bus pairs connected to the sense amplifier via a data input / output circuit;
A control circuit for bringing a predetermined data bus pair among the plurality of data bus pairs into a floating state,
The reset circuit includes a latch circuit that holds a reset potential of a selected bit line of the bit line pair, and a precharge that matches a non-selected bit line of the bit line pair with the reset potential held in the latch circuit. Control circuit,
The control circuit sets a corresponding data bus pair to a floating state among the plurality of data bus pairs when the data includes a bit to be masked in order to inhibit writing to the corresponding storage element. A semiconductor memory device.

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