Abstract:
A semiconductor storage device comprises a memory cell array including memory cells, and bit lines for transfer of data in the memory cells; an amplifier circuit connected to the bit lines to amplify data in the memory cells; a first switching element connected between the bit lines and the amplifier circuit; a first reference voltage source which applies to the gate of the first switching element a voltage for turning the first switching element ON; a second switching element and a third switching element connected in series between the gate of the first switching element and the first reference voltage source, said second switching element and said third switching element being connected in parallel to each other; a second reference voltage source which applies to the gates of the second and third switching elements a voltage for turning the second and third switching elements ON; and a first timing shift circuit connected between the gate of the third switching element and the second reference voltage source to delay the operation of the third switching element from the operation of the second switching element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-345655, filed on Nov. 28, 2002, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a semiconductor storage device.  
           [0004]    2. Related Background Art  
           [0005]    Along with the progress of microminiaturization of DRAMs and other semiconductor storage devices, coupling capacitance of bit line pairs is getting greater and greater. Increase of the coupling capacitance invites interference when data stored in the memory cell is amplified. Conventionally, in order to prevent noise caused by the interference, semiconductor storage devices have been configured to disconnect the bit lines from the sense amplifier when amplifying data after reading the data from the memory cell.  
           [0006]    [0006]FIG. 21 is a circuit diagram of an amplifier circuit  10  provided in a conventional semiconductor storage device. FIG. 21 illustrates a memory cell  11  on the left and a memory cell  12  on the right. One line of a bit line pair BLL/bBLL is connected to the memory cell  11 . One line of a bit line pair BLR/bBLR is connected to the memory cell  12 . A bit line pair BLS/bBLS is connected to a sense amplifier in the amplifier circuit  10 . The bit line pair BLL/bBLL is connected to bit line pair BLS/bBLS via transistors Q 9  and Q 10 . The bit line pair BLR/bBLR is connected to the bit line pair BLS/bBLS via transistors Q 11  and Q 12 .  
           [0007]    Transistors Q 9  and Q 10  are controlled by a control signal ΦL, and transistors Q 12  and Q 11  are controlled by a control signal ΦR. If the memory cell  11  has been selected, transistors Q 12  and Q 11  are switched OFF. As a result, the bit line pair BLS/bBLS is disconnected from the bit line pair BLR/bBLR. If the memory cell  12  has been selected, transistors Q 9  and Q 10  are switched OFF. As a result, the bit line pair BLS/bBLS is disconnected from the bit line pair BLL/bBLL. Disconnection of the bit line pair BLS/bBLS from the bit line pair BLR/bBLR or BLL/bBLL results in isolating the capacitance of the bit line pair BLR/bBLR or BLL/bBLL in the memory cell array CA from the bit line pair BLS/bBLS in the amplifier circuit  10 .  
           [0008]    A precharge circuit  15  in the amplifier circuit  10  precharges the respective bit line pairs BLL/bBLL, BLR/bBLR and BLS/bBLS to Vref before the memory cell  11  or  12  is selected. The sense amplifier amplifies data from the memory cell  11  or  12 .  
           [0009]    [0009]FIG. 22 is a circuit diagram of a control circuit  20  that applies the control signal ΦL to the amplifier circuit  10  shown in FIG. 21. The control circuit  20  can output one of voltage values Vpp, Vdd, Vii or Vss.  
           [0010]    A boost signal BOOST-L turns a P-channel transistor Q 39  ON and can thereby raise the voltage of the control signal ΦL to Vpp. Vpp is a voltage value of the control signal ΦL, which renders the transistors Q 9  and Q 10  a higher drive power state, and it is higher than Vdd.  
           [0011]    An isolating signal bISO-L turns a P-channel transistor Q 35  On via a NAND gate G 14 , and can thereby adjust the voltage of the control signal ΦL to Vdd. Vdd is a voltage value of the control signal ΦL during the precharge of the bit line pairs BLL/bBLL, BLR/bBLR and BLS/bBLS.  
           [0012]    In addition, the isolation signal bISO-L turns an N-channel transistor Q 36  ON via a NOR gate G 16 , and can thereby adjust the voltage of the control signal ΦL to Vii. Vii is a voltage value that turns the transistors Q 9  and Q 10  OFF. Vii is higher than Vss and lower than Vdd.  
           [0013]    A select signal SEL-R turns an N-channel transistor Q 34  ON and can thereby adjust the control signal ΦL to Vss. Vss is the ground voltage. In addition, the select signal SEL-R controls a switch composed of a P-channel transistor Q 31  and an N-channel transistor Q 32 . Thereby, a signal bBOOST-L, which is the inverted signal of the boost signal BOOST-L, is input to the NAND gate  14 , and the boost signal BOOST-L is input to the NOR gate G 16 . The select signal SEL-R is HIGH when selecting the memory cell  12  shown in FIG. 21, and LOW when selecting the memory cell  11  shown in FIG. 21.  
           [0014]    [0014]FIG. 23 is timing chart that shows operations of amplifier circuit  10  shown in FIG. 21 and the control circuit  20  shown in FIG. 22. With reference to FIG. 23, performance of the amplifier circuit  10  when amplifying data of the memory cell  11  will be explained. Before the amplifier circuit  10  reads out data, voltage of the control signal ΦL and ΦR are Vdd. Therefore, transistors Q 9 , Q 10 , Q 12  and Q 11  are ON.  
           [0015]    First, the precharge signal EQ is set LOW to turn the precharge circuit  15  OFF (point of time to). At this time, in response to the control signal ΦR being set to Vss, the transistors Q 11  and Q 12  are turned OFF. As a result, the memory cell  12  is isolated from the amplifier circuit  10 .  
           [0016]    Subsequently, the word line WLL is set HIGH to turn the N-channel transistor Q 1  ON (time t 1 ). Thereby, the sense amplifier  16  receives data of the memory cell  11 . That is, the data of the memory cell  11  is applied to the bit line pairs BLS/bBLS.  
           [0017]    Next, the isolating signal bISO-L is set LOW to turn the transistor Q 35  OFF and turn the transistor Q 36  ON (time t 2 ). Thereby, the voltage Vii is applied to the amplifier  10  in lieu of Vdd as the control signal ΦL. Since the voltage of the control signal ΦL changes from Vdd to Vii, the transistors Q 9  and Q 10  shown in FIG. 21 are switched OFF.  
           [0018]    After that, the sense amplifier  16  amplifies data of the memory cell  11 . After the data is amplified, the boost signal BOOST-L is set HIGH (time t 3 ). Then, the P-channel transistor Q 39  switches ON, and the voltage of the control signal ΦL rises to Vpp. As a result, the transistors Q 9 , Q 10  shown in FIG. 21 again turn ON, and amplified data is again written in the memory cell  11 . Since the control signal ΦL changes to Vpp higher than Vdd, sufficient charge can be accumulated in the capacitor C 1 .  
           [0019]    Subsequently, the word line WLL is set LOW (time T 4 ).  
           [0020]    Further, by setting the isolating signal bISO-L HIGH and the boost signal BOOST-L LOW, the control signals ΦL and ΦR are returned to Vdd (time T 5 ). As a result, the transistors Q 9  and Q 10  maintain the ON states, and the transistors Q 11  and Q 12  change to the ON states. Simultaneously, by setting the precharge signal EQ HIGH, the bit line pairs BLL/bBLL, BLR/bBLR and BLS/bBLS are precharged.  
           [0021]    In the conventional technique introduced above, in response to the change of the control signal ΦL to Vii, the bit line pair BLS/bBLS is isolated from the bit line pair BLL/bBLL. As a result, while the sense amplifier  16  amplifies data, noise caused by the coupling capacitance of the bit lines pair BLL/bBLL is prevented. Moreover, since the sense amplifier  16  is sufficient to amplify the potential difference between the bit lines of the bit line pair BLS/bBLS, it can amplify data quickly.  
           [0022]    However, since this technique writes data in the memory cell again, the sense amplifier  16  has to amplify the potential difference between the bit lines of the bit line pair BLL/bBLL similarly to the bit line pair BLS/bBLS after it amplifies data in the bit line pair BLS/bBLS. The point of time where the sense amplifier  16  starts amplification of the potential difference of the bit line pair BLL/bBLL is the time t 3  where the control signal ΦL rises to Vpp.  
           [0023]    At that time, since the control signal ΦL is rapidly amplified from Vii to Vpp, the transistors Q 9 , Q 10  immediately change to the ON states. As a result, capacitance of the bit line pair BLL/bBLL is suddenly added to the capacitance of the bit line pair BLS/bBLS. As a result, the voltage of the bit line bBLS amplified to the HIGH level lowers due to the connection to the bit line bBLL. On the other hand, the voltage of the bit line BLS amplified to the LOW level rises due to the connection to the bit line BLL. That is, noise occurs in the bit line pair BLS/bBLS.  
           [0024]    The noise may undesirably reverse the potential difference between the bit lines bBLS and BLS, which leads to false recognition of data.  
         SUMMARY OF THE INVENTION  
         [0025]    A semiconductor storage device comprises a memory cell array including memory cells, and bit lines for transfer of data in the memory cells; an amplifier circuit connected to the bit lines to amplify data in the memory cells; a first switching element connected between the bit lines and the amplifier circuit; a first reference voltage source which applies to the gate of the first switching element a voltage for controlling the first switching element; a second switching element and a third switching element connected in series between the gate of the first switching element and the first reference voltage source, said second switching element and said third switching element being connected in parallel to each other; a second reference voltage source which applies to the gates of the second and third switching elements a voltage for controlling the second and third switching elements; and a first timing shift circuit connected between the gate of the third switching element and the second reference voltage source to delay the operation of the third switching element from the operation of the second switching element. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a block diagram of a DRAM-type semiconductor storage device according to the first embodiment of the invention;  
         [0027]    [0027]FIG. 2 is a circuit diagram of an amplifier circuit  100  equipped in a sense amplification region S/A inside a semiconductor storage device according to the first embodiment of the invention;  
         [0028]    [0028]FIG. 3 is a circuit diagram of a control circuit  200  for controlling the amplifier circuit  100  inside the semiconductor storage device according to the first embodiment;  
         [0029]    [0029]FIG. 4 is a circuit diagram of an embodiment of a delay circuit TD;  
         [0030]    [0030]FIG. 5 is a timing chart showing operations of the amplifier circuit  100  shown in FIG. 2 and the control circuit  200  shown in FIG. 3;  
         [0031]    [0031]FIG. 6 is a circuit diagram of a control circuit  300  in the second embodiment of the invention;  
         [0032]    [0032]FIG. 7 is a timing chart showing operations according to the second embodiment;  
         [0033]    [0033]FIG. 8 is a circuit diagram of a control circuit  400  in the third embodiment of the invention;  
         [0034]    [0034]FIG. 9 is a timing chart showing operations according to the third embodiment of the invention;  
         [0035]    [0035]FIG. 10 is a circuit diagram of a control circuit  500  in the fourth embodiment of the invention;  
         [0036]    [0036]FIG. 11 is a circuit diagram of a control circuit  600  in the fifth embodiment of the invention;  
         [0037]    [0037]FIG. 12 is a timing chart showing operations according to the fifth embodiment of the invention;  
         [0038]    [0038]FIG. 13 is a circuit diagram of a control circuit  700  in the sixth embodiment of the invention;  
         [0039]    [0039]FIG. 14 is a timing chart showing operations according to the sixth embodiment of the invention;  
         [0040]    [0040]FIG. 15 is a circuit diagram as a modification of the sixth embodiment of the invention;  
         [0041]    [0041]FIG. 16 is a circuit diagram of a control circuit  800  in the seventh embodiment of the invention;  
         [0042]    [0042]FIG. 17 is a timing chart showing operations according to the seventh embodiment of the invention;  
         [0043]    [0043]FIG. 18 is a circuit diagram of a control circuit  900  in the eighth embodiment of the invention;  
         [0044]    [0044]FIG. 19 is a timing chart showing operations according to the eighth embodiment of the invention;  
         [0045]    [0045]FIG. 20 is a circuit diagram of a control circuit  1000  in the ninth embodiment of the invention;  
         [0046]    [0046]FIG. 21 is a circuit diagram of an amplifier circuit  10  equipped in a conventional semiconductor storage device;  
         [0047]    [0047]FIG. 22 is a circuit diagram of a control circuit  20  for applying a control signal ΦL to the amplifier circuit  10  shown in FIG. 21; and  
         [0048]    [0048]FIG. 23 is a timing chart showing operations of the amplifier circuit  10  shown in FIG. 21 and the control circuit  20  shown in FIG. 22. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]    Explained below are some embodiments of the invention with reference to the drawings. The embodiments, however, should not be construed to limit the invention. The embodiments explained below can be modified by using P-channel transistors instead of N-channel transistors or using N-channel transistors in lieu of P-channel transistors without losing the effects of the respective embodiments. In this case, however, levels of individual signals will need to be modified appropriately.  
         [0050]    [0050]FIG. 1 is a block diagram of a DRAM-type semiconductor storage device according to the first embodiment of the invention. The semiconductor storage device includes a memory cell array CAL, memory cell array CAR and a sense amplification region S/A. The memory cell arrays CAL and CAR include memory cells MC, bit lines BL and word lines WL. The sense amplification region S/A is connected to the bit lines BL. The sense amplification region S/A includes a sense amplifier  116  (see FIG. 2) for amplifying data in memory cells MC. The sense amplifier  116  is a shared sense amplifier for common use with both the memory cells CAL, CAR. The semiconductor storage device has buffers RAB, CAB and DQB for temporally storing externally applied signals RAS bar, CAS bar and WE bar, respectively; decoders RD and CD for decoding them; and an internal voltage generating circuit VG.  
         [0051]    [0051]FIG. 2 is a circuit diagram of an amplifier circuit  100  equipped in the sense amplification region S/A. The memory cell  11  and the bit line pair BLL/bBLL shown on the left side of FIG. 2 belong to the memory cell array CAL. The memory cell  12  and the bit line pair BLR/bBLR shown on the right side of FIG. 2 belong to the memory cell array CAR. The bit line pair BLS/bBLS belong to the sense amplification region S/A. The bit line pair BLL/bBLL is connected to the memory cell  11 . The bit line pair BLR/bBLR is connected to the memory cell  12 . The bit line pair BLS/bBLS is connected to the sense amplifier  116  in the amplifier circuit  100 . The bit line bBLL functions to transport the inverted signal of BLL, and it means BLL bar. The set of BLR and bBLR and the set of BLS and bBLS have the same relationship, respectively.  
         [0052]    An N-channel transistor Q 109  is connected between the bit lines BLL and BLS, and an N-channel transistor Q 110  is connected between the bit lines bBLL and bBLS. An N-channel transistor Q 112  is connected between the bit lines BLR and BLS, and an N-channel transistor Q 111  is connected between the bit lines bBLR and bBLS. The transistors Q 109  and Q 110  are controlled by the control signal ΦL. The transistors Q 102  and Q 110  are controlled by the control signal ΦR. In case the memory cell  11  is selected, the transistors Q 112  and Q 111  are switched OFF, and accordingly, the bit lines BLS and bBLS are disconnected from the bit lines BLR and bBLR, respectively. In case the memory cell  12  is selected, the transistors Q 109  and Q 110  are switched OFF.  
         [0053]    A precharge circuit  115  includes N-channel transistors Q 113 , Q 114  and Q 115 . Gates of the transistors Q 113 , Q 114  and Q 115  are connected to the precharge signal EQ. Accordingly, the transistors Q 113 , Q 114  and Q 115  are controlled by the precharge signal EQ and can precharge the bit lines pairs BLL/bBLL, BLR/bBLR and BLS/bBLS to Vref.  
         [0054]    The sense amplifier  116  includes N-channel transistors Q 103 , Q 104  and P-channel transistors Q 106 , Q 107 . For amplifying data of the memory cell  11  or  12 , an N-channel sense amplifier control signal SEN is set HIGH, and a P-channel sense amplifier control signal bSEP is set LOW. Accordingly, the sense amplifier  116  is activated and amplifies data received from the memory cell.  
         [0055]    [0055]FIG. 3 is a circuit diagram of a control circuit  200  for controlling the amplifier circuit  100  inside the semiconductor storage device according to the instant embodiment. The control circuit  200  can output any of voltage values Vpp, Vss, Vdd or Vii as the control signal ΦL to the amplifier circuit  100 . Vpp is the voltage of a first reference voltage source. Vss is the voltage of a second reference voltage source. Vdd is the voltage of a third reference voltage source. Vii is the voltage of a fourth reference voltage source.  
         [0056]    Vdd is the voltage that turns the transistors Q 109  and Q 110  ON. Vdd is used as the control signal ΦL when the bit lines pairs BLL/bBLL, BLR/bBLR and BLS/bBLS are precharged.  
         [0057]    Vpp is the voltage that turns the transistors Q 109 , Q 110  On to a high driving state. Vpp is higher than Vdd. By adjusting the control signal ΦL to Vpp when amplified data is written again in the memory cell  111  or  112 , sufficient electric charge can be given to the capacitor C 1  or C 2 .  
         [0058]    Vii is the voltage that turns the transistors Q 102 , Q 110  OFF. By adjusting the control signal ΦL to Vii when the sense amplifier  116  amplified data, the bit line pair BLS/bBLS is isolated from the bit line pair BLL/bBLL. As a result, the sense amplifier  116  can amplify the data in the bit line pair BLS/bBLS without influences of noise caused by the coupling capacitance of the bit line par BLL/bBLL.  
         [0059]    Vss is the ground voltage. When the control signal ΦL is Vss, the transistors Q 109 , Q 110  turn OFF completely. Vii is higher than Vss and lower than Vdd.  
         [0060]    A P-channel transistor Q 139  is connected in series between the first reference voltage source and the gates of the transistors Q 109  and Q 110  shown in FIG. 2. The source of the transistor Q 139  is connected to the first reference voltage source, and its drain is connected to gates of the transistors Q 109  and Q 110 . The size of the transistor Q 139  is smaller than the transistor Q 39  (see FIG. 22).  
         [0061]    A P-channel transistor Q 140  is connected in series between the first reference voltage source and gates of the transistors Q 109  and Q 110  shown in FIG. 2, and further connected in parallel to the transistor Q 139 . The source of the transistor Q 140  is connected to the first reference voltage source, and its drain is connected to the gates of the transistors Q 109 , Q 110 . The size of the transistor Q 140  is larger than the transistor Q 139 .  
         [0062]    The gate of the transistor Q 139  is connected to an inverter G 111 . The gate of the transistor Q 140  is connected to the inverter G 111  via a delay circuit TD. The inverter G 111  inverts the boost signal BOOST-L to a boost signal bBOOST-L 1 . Therefore, when the boost signal BOOST-L is HIGH, Vss (LOW) is output as the boost signal bBOOST-L 1 . When the boost signal BOOST-L is LOW, Vpp (HIGH) is output as the boost signal bBOOST-L 1 .  
         [0063]    Since the delay circuit TD is connected to the gate of the transistor  140 , a boost signal bBOOST-L 2  is given to the transistor Q 140  with a time delay after the point of time where the boost signal bBOOST-L 1  is given to the transistor Q 139 . Therefore, operation of the transistor Q 140  is behind the operation of the transistor Q 139 .  
         [0064]    A P-channel transistor Q 135  and an N-channel transistor  136  are connected in series between the third reference voltage source and the fourth reference voltage source. The node N 1  between the transistors Q 135  and Q 136  is connected to the second reference voltage source via the N-channel transistor Q 134 .  
         [0065]    Drains of the transistors Q 135  and Q 136  are connected to the node N 1 . The source of the transistor Q 135  is connected to the third reference voltage source. The source of the transistor Q 136  is connected to the fourth reference voltage source. The source of the transistor Q 134  is connected to the second reference voltage source, and its drain is connected to the gate of the transistor Q 109  and Q 110 .  
         [0066]    Furthermore, the node N 1  is connected to the gates of the transistors Q 109  and Q 110  shown in FIG. 2. Therefore, the control circuit  200  can output Vss (second reference voltage source), Vdd (third reference voltage source) or Vii (fourth reference voltage source) as the control signal ΦL from the node N 1 . Vpp (first reference voltage source) can be output through the transistor Q 139  or Q 140 .  
         [0067]    The output of a NAND gate G 114  is connected to the gate of the transistor Q 135 . The output of a NOR gate G 116  is connected to the gate of the transistors Q 136 . The NAND gate G 114  and the NOR gate G 116  commonly introduce the isolation signal bISO-L and the boost signal bBOOST-L 1 . However, the NOR gate G 116  introduces the boost signal bBOOST-L 1  in the inverted form.  
         [0068]    Transistors Q 131  and Q 132  are connected between the input of the NAND gate G 114  and the output of the inverter G 111 . An N-channel transistor Q 133  is connected between the input of the NAND gate G 114  and the second reference voltage source.  
         [0069]    The transistors Q 131 , Q 132 , Q 134  and Q 134  are controlled by the select signal SEL-R. The select signal SEL-R is given to the gate of the transistor Q 132  via an inverter G 112 . Therefore, the gate of the transistor Q 132  is supplied with the inverted signal of the select signal SEL-R. The select signal SEL-R is given to the gate of the transistor Q 134  via the inverters G 112  and G 113 . Therefore, the gate of the transistor Q 134  is supplied with the select signal SEL-R.  
         [0070]    The select signal SEL-R is set HIGH when the memory cell  12  is selected. At that time, the transistors Q 131  and Q 132  are OFF, and the transistors Q 133  and Q 134  are ON. Therefore, voltage of the control signal ΦL becomes Vss.  
         [0071]    On the contrary, the select signal SEL-R is set LOW when the memory cell  11  is selected. At that time, the transistors Q 131  and Q 132  are ON, and the transistors Q 133  and Q 134  are OFF. Therefore, voltage of the control signal ΦL becomes Vdd, Vii or Vpp, when the memory cell  11  is selected.  
         [0072]    Aspects of individual signals in case of setting the control signal ΦL to Vdd, Vii or Vpp will be explained below.  
         [0073]    To set the voltage of the control signal ΦL to Vpp, the boost signal bBOOST-L 1  may be set LOW. Thereby, the transistors Q 139  and Q 140  turn ON.  
         [0074]    At that time, the NAND gate G 114  is supplied with LOW as the boost signal bBOOST-L 1 . The NOR gate G 116  is supplied with HIGH as the inverted signal of the boost signal bBOOST-L 1 . Responsively, irrespectively of the level of the isolating signal bISO-L, the transistors Q 135  and Q 136  turn OFF. Therefore, the gate of the transistor Q 109  is connected to the first reference voltage source, and detached from the third reference voltage source and the fourth reference voltage source. As a result, voltage of the control signal ΦL becomes Vpp.  
         [0075]    To set the voltage of the control signal ΦL to Vdd, the boost signal bBOOST-L 1  and the isolating signal bISO-L may be set HIGH. Since the boost signal bBOOST-L 1  is HIGH, the transistors Q 139  and Q 140  are OFF.  
         [0076]    At that time, the NAND gate G 114  is supplied with HIGH as the boost signal bBOOST-L 1 . The NOR gate G 116  is supplied with LOW as the inverted signal of the boost signal bBOOST-L 1 . Furthermore, since the isolating signal bISO-L is HIGH, the transistor Q 135  turns ON, and the transistor Q 136  turns OFF. Therefore, the gate of the transistor Q 109  is connected to the third reference voltage source, and detached from the first reference voltage source and the fourth reference voltage source. As a result, voltage of the control signal ΦL becomes Vdd.  
         [0077]    To set the voltage of the control signal ΦL to Vii, the boost signal bBOOST-L 1  may be set HIGH and the isolating signal bISO-L LOW. Responsively, the transistor Q 135  turns OFF, and the transistor Q 136  turns ON. Therefore, the gate of the transistor Q 109  is connected to the fourth reference voltage source, and detached from the first reference voltage source and the third reference voltage source. As a result, voltage of the control signal ΦL becomes Vii.  
         [0078]    [0078]FIG. 4 is a circuit diagram of an embodiment of the delay circuit TD. The delay circuit TD includes resistors R 11  and R 12  connected in series between the first reference voltage source and the second reference voltage source. A transistor Q 37  is connected between the first reference voltage source and the resistor R 11 . A transistor Q 38  is connected between the second reference voltage source and the resistor R 12 . The boost signal bBOOST-L 1  is input to the gate of the transistor Q 37  and the gate of the transistor Q 38 .  
         [0079]    An inverter G 17  is connected to the node N 2  between the resistors R 11  and R 12 , and the boost signal bBOOST-L 2  is output from the inverter G 17 . A capacitor C 11  is connected between the node N 2  and the second reference voltage source. An RC delay circuit is composed of the capacitor C 11  and the resistor R 11  and R 12 .  
         [0080]    In case the boost signal bBOOST-L 1  is LOW, Vpp is output from the delay circuit TD. Responsively, the capacitor C 1  is charged by the first reference voltage source.  
         [0081]    In case the boost signal bBOOST-L 1  is switched HIGH, Vss is output from the delay circuit TD instead of Vpp. Responsively, the electric charge accumulated in the capacitor C 11  is discharged to the second reference voltage source via the resistor R 12 . The output of the boost signal bBOOST-L 2  is delayed for the length of time required for discharging the electric charge from the capacitor C 11 .  
         [0082]    [0082]FIG. 5 is a timing chart showing operations of the amplifier circuit  100  shown in FIG. 2 and the control circuit  200  shown in FIG. 3. With reference to FIGS. 2, 3 and  5 , operations of the amplifier circuit  100  for amplifying data of the memory cell  11  will be explained.  
         [0083]    Before the amplifier circuit  100  reads out data, voltage of the control signals ΦL and ΦR is Vdd. Accordingly, the transistors Q 109 , Q 110 , Q 112  and Q 111  are ON. When the amplifier circuit  100  reads out data of the memory cell  11 , the select signal SEL-R is LOW.  
         [0084]    First, the precharge signal EQ is set LOW to turn OFF the precharge circuit  115  (time t 10 ). At that time, in response to the change of the voltage of the control signal ΦR to Vss, the transistors Q 111  and Q 112  are switched OFF. Accordingly, the memory cell  12  is isolated from the amplifier circuit  100 .  
         [0085]    Next, the word line WLL is set HIGH to turn the transistor Q 1  ON (time t 11 ). Responsively, the sense amplifier  116  receives data of the memory cell  11 . That is, the data of the memory cell  11  is applied to the bit line pairs BLS/bBLS.  
         [0086]    Subsequently, the isolating signal bISO-L is set LOW (time t 12 ). Responsively, the voltage of the control signal ΦL changes from Vdd to Vii. Therefore, the transistors Q 109  and Q 110  shown in FIG. 2 are switched OFF. As a result, the bit line pair BLS/bBLS is separated from the bit line pair BLL/bBLL. That is, the isolating signal bISO-L determines the timing of separation of the bit line pair BLS/bBLS from the bit line pair BLL/bBLL.  
         [0087]    After the time t 12 , the sense amplifier  116  amplifies data of the memory cell  11 .  
         [0088]    After the data is amplified, the boost signal BOOST-L is set HIGH (time t 13 ). That is, the boost signal bBOOST-L 1  is set LOW. The rising of the control signal ΦL in the instant embodiment is more moderate than that of the conventional circuit. This is because the transistor Q 139  is relatively small-sized than the transistor Q 140 , and it takes time to raise the voltage of the gates of the transistors Q 109 , Q 110 .  
         [0089]    Because of the modest rising of the control signal ΦL, the transistors Q 109  and Q 110  are gradually switched ON. Therefore, the bit line pair BLL/bBLL is gradually connected to the bit line pair BLS/bBLS. Thus, it is prevented that the capacitance of the bit line pair BLL/bBLL is suddenly added to the capacitance of the bit line pair BLS/bBLS. Therefore, the sense amplifier  116  can amplify the data of the bit line pair BLL/bBLL gradually to the same potential as that of the bit line pair BLS/bBLS. As a result, generation of noise in the bit line pair BLS/bBLS can be prevented. In addition, inversion of the potential difference between the bit lines bBLS and BLS does not occur.  
         [0090]    Subsequently, the boost signal bBOOST-L 2  delayed by the delay circuit TD becomes LOW (time t 14 ). Responsively, the transistor Q 140  is switched ON. Since both transistors Q  139  and Q 140  are currently ON, the control signal ΦL is rapidly raised to Vpp.  
         [0091]    However, at the time t 14 , data of the bit line pair BLL/bBLL is already amplified. Therefore, noise generated by the rapid increase of the control signal ΦL to Vpp does not matter. Rather, since the voltage of the control signal ΦL rises to Vpp quickly, the amplified data can be written quickly in the memory cell  11 . Thus, the semiconductor storage device according to the instant embodiment will be speeded up.  
         [0092]    In response to the change of the control signal ΦL to Vpp, the transistors Q 109 , Q 110  again switch ON (time t 15 ). As a result, the amplified data is again written in the memory cell  11 . At that time, since the voltage of the control signal ΦL is Vpp which is higher than Vdd, sufficient electric charge can be accumulated in the capacitor C 1 .  
         [0093]    After that, the word line WLL is set LOW (time t 16 ).  
         [0094]    Further, by setting the isolating signal bISO-L HIGH and the boost signal BOOST-L LOW, the control signals ΦL and ΦR are returned to Vdd (time t 17 ). As a result, the transistors Q 109  and Q 110  remain ON. The transistors Q 111  and Q 112 , however, switch ON. Simultaneously, by setting the precharge signal EQ HIGH, the bit line pairs BLL/bBLL, BLR/bBLR and BLS/bBLS are precharged.  
         [0095]    According to the instant embodiment, when the sense amplifier  116  amplifies data, the control signal ΦL starts rising modestly from Vii to Vpp. Therefore, noise caused by the capacitance of the bit line pair BLL/bBLL can be prevented.  
         [0096]    In addition, according to the instant embodiment, once the sense amplifier  116  completes amplification of data, the control signal ΦL is rapidly raised. Therefore, the sense amplifying operation can be speeded up.  
         [0097]    Since the transistors Q 139  and Q 140  are P-channel transistors, they can be driven without the need of adding voltage sources other than the first to fourth reference voltage sources.  
         [0098]    [0098]FIG. 6 is a circuit diagram of a control circuit  300  in the second embodiment of the invention. This embodiment is different from the first embodiment in the feature that a voltage control circuit VC is connected between the gate of the transistor Q 139  and the node N 3 . The node N 3  is the node of the delay circuit TD and the inverter G 111 .  
         [0099]    The voltage control circuit VC includes an N-channel transistor Q 142  connected between the first reference voltage source and the second reference voltage source. The gate and the drain of the transistor Q 142  are short-circuited, and they are connected to the gate of the transistor Q 139 .  
         [0100]    A P-channel transistor Q 141  is connected between the drain of the transistor Q 142  and the first reference voltage source. An N-channel transistor Q 143  is connected between the source of the transistor Q 142  and the second reference voltage source. Further, an inverter G 118  is connected between the gate of the transistors Q 141 , Q 143  and the output of the inverter G 111 .  
         [0101]    Operations of the control circuit  300  will be explained below. The voltage control circuit VC operates to introduce the voltage signal bBOOST-L 1  and output a boost signal bBOOST-Ld.  
         [0102]    Since the P-channel transistor Q 141  and N-channel transistor Q 143  share a common gate, one of the transistors Q 141 , Q 143  is ON and the other is OFF.  
         [0103]    In case the boost signal bBOOST-L 1  is set HIGH, the transistor Q 141  turns ON, and the transistor Q 143  turns OFF. Therefore, the boost signal bBOOST-Ld becomes Vpp (HIGH). The boost signal bBOOST-Lb under this condition is the same as the boost signal bBOOST-L 1  of the first embodiment.  
         [0104]    On the other hand, in case the boost signal bBOOST-L 1  is set LOW, the transistor Q 143  turns ON, and the transistor Q 141  turns OFF. Since the second reference voltage source is connected to the source of the transistor Q 142 , the voltage of the boost signal bBOOST-Ld becomes the sum of Vss and the threshold value of the transistor Q 142 . That is, the voltage of the bBOOST-Ld becomes Vss+Vth(Q 142 ).  
         [0105]    [0105]FIG. 7 is a timing chart showing operations according to the second embodiment. The second embodiment is different from the first embodiment in the feature that, at the time t 13 , the boost signal bBOOST-Ld decreases only to Vss+Vth(Q 142 ) and does not decrease to Vss as the boost signal bBOOST-L 1  does.  
         [0106]    Therefore, the rising of the control signal ΦL from the time t 13  to the time t 14  is more moderate than that of the first embodiment. Thus, the instant embodiment can prevent noise generated in the bit line pair BLS/bBLS more reliably than the first embodiment.  
         [0107]    [0107]FIG. 8 is a circuit diagram of a control circuit  400  in the third embodiment of the invention. This embodiment is different from the first embodiment in the use of a timing shift circuit TS different from the delay circuit TD instead of the delay circuit TD. The timing shift circuit TS includes P-channel transistors Q 144 , Q 146 , N-channel transistors Q 145 , Q 147  and inverter G 119 .  
         [0108]    The source of the transistor Q 146  is connected to the third reference voltage source. The drain of the transistor Q 146  is connected to the gate of the transistor Q 140  via the transistor Q 145 .  
         [0109]    The source of the transistor Q 147  is connected to the second reference voltage source. Similarly to the drain of the transistor Q 146 , the drain of the transistor Q 147  is connected to the gate of the transistor Q 140  via the transistor Q 145 . Both the gate of the transistor Q 146  and the gate of the transistor Q 147  are connected to the gates of the transistors Q 109  and Q 110 .  
         [0110]    The source of the transistor Q 144  is connected to the first reference voltage source. The drain of the transistor Q 144  is connected to the gate of the transistor Q 140 . The source of the transistor Q 145  is connected to the drains of the transistors Q 146  and Q 147 . Similarly to the drain of the transistor Q 144 , the drain of the transistor Q 145  is connected to the gate of the transistor Q 140 . The gates of the transistors Q 144  and Q 145  are both connected to the node between the inverter G 111  and the gate of the transistor Q 139  via the inverter G 119 .  
         [0111]    Next explained are operations of the control circuit  400 .  
         [0112]    In case the boost signal bBOOST-L 1  is set HIGH, the transistor Q 144  turns ON, and the transistor Q 145  turns OFF. Therefore, Vpp is output as the boost signal bBOOST-L 2 . This operation is the same as the first embodiment.  
         [0113]    In case the boost signal bBOOST-L 1  is set LOW, the transistor Q 145  turns ON and the transistor Q 144  turns OFF. Therefore, the voltage at the node N 4  of the drain of the transistor Q 146  and the drain of the transistor Q 147  is output as the boost signal bBOOST-L 2 .  
         [0114]    At the point of time (see the time t 13  of FIG. 9) where the boost signal bBOOST-L 1  is switched from HIGH to LOW, the voltage of the control signal ΦL is Vii. Therefore, the transistor Q 146  is ON with the feedback of the control signal ΦL, and the transistor Q 147  is OFF with the feedback of the control signal ΦL. Therefore, the voltage at the node N 4 , i.e. the voltage of the boost signal bBOOST-L 2 , becomes Vdd. As a result, the transistor Q 140  remains OFF.  
         [0115]    When the voltage of the control signal ΦL reaches from vii to Vdd−Vth(Q 146 ) (called the set voltage Vset hereunder), the transistor Q 146  is switched OFF. Threshold value of the transistor Q 147  is set lower than Vset. Therefore, at the point of time where the transistor Q 146  is switched OFF, the transistor Q 147  is already ON. Accordingly, the voltage at the node N 4 , i.e. the voltage of the boost signal bBOOST-L 2 , becomes Vss, and it results in turning the transistor Q 140  ON.  
         [0116]    [0116]FIG. 9 is a timing chart showing operations according to the third embodiment of the invention. This embodiment is different from the first embodiment in that the transistor Q 140  switched ON when the control signal ΦL reaches the set voltage Vset. Operations of this embodiment from the time t 10  to the time t 12  are identical to those of the first embodiment.  
         [0117]    At the time t 13 , the boost signal bBOOST-L 1  is switched from HIGH to LOW. Then, the transistor Q 144  turns OFF and the transistor Q 145  turns ON. At that time, the transistor Q 146  is ON, and the transistor Q 147  is OFF. Therefore, the boost signal bBOOST-L 2  is reduced from Vpp to Vdd.  
         [0118]    At the time t 14 , the control signal ΦL reaches the set voltage Vset. Responsively, the transistor Q 146  turns OFF, and the transistor Q 147  turns ON. Therefore, the voltage of the boost signal bBOOST-L 2  is reduced from Vdd to Vss. At that time, since the transistor Q 140  turns ON, the control signal ΦL rapidly rises to Vpp.  
         [0119]    As already explained, the first embodiment uses the RC delay circuit as the timing shift circuit. Resistors and capacitors, in general, are elements subject to variance depending upon their manufacturing process. Therefore, there is the possibility that the transistor Q 140  turns ON approximately simultaneously with the transistor Q 139 . In contrast, there is also the possibility that a long time required for the transistor Q 140  to turn ON disturbs the high-speed operation of the amplifier circuit.  
         [0120]    In the instant embodiment, however, since the timing shift circuit is entirely composed of transistors, variance by the manufacturing process is relatively small. Moreover, the transistor Q 140  turns ON under the condition that the control signal ΦL exceeds the set voltage Vset. Therefore, the transistor Q 140  does not turn ON before the control signal ΦL is raised to the set voltage Vset via the transistor Q 139 . Moreover, when the control signal ΦL is raised to exceed the set voltage Vset via the transistor Q 139 , the transistor Q 140  turns ON reliably.  
         [0121]    As such, the instant embodiment can determine the timing for raising the control signal ΦL to Vpp without worrying about variance by the manufacturing process.  
         [0122]    [0122]FIG. 10 is a circuit diagram of a control circuit  500  in the fourth embodiment of the invention. This embodiment is a combination of the second and third embodiments. The instant embodiment can provide both effects of the second and third embodiments.  
         [0123]    The timing shift circuit TS may be replaced by the delay circuit TD. In this case, both effects of the first and second embodiments can be obtained.  
         [0124]    [0124]FIG. 11 is a circuit diagram of a control circuit  600  in the fifth embodiment of the invention. This embodiment is different from the fourth embodiment in the use of an N-channel transistor Q 148  inside the voltage control circuit VC. The transistor Q 148  is connected in parallel with the transistor  142 . The gate of the transistor Q 148  is connected to the gates of the transistor Q 109  and Q 110 . To operate the transistor Q 139  at an earlier timing than the transistor Q 140 , the threshold voltage of the transistor Q 148  is preferably lower than the threshold voltage of the transistor  147 .  
         [0125]    [0125]FIG. 12 is a timing chart showing operations according to the fifth embodiment of the invention. The fourth embodiment has been explained as the control signal ΦL rising from Vii to Vpp while changing its inclination twice. In the instant embodiment, however, the control signal ΦL rises from Vii to Vpp while changing its inclination three times.  
         [0126]    Operations of the fifth embodiment from the time t 10  to the time t 13  are identical to those of the second embodiment. At the time t 13 , since the voltage of the boost signal bBOOST-Ld is lowered from Vpp to Vss+Vth(Q 142 ), the transistor Q 139  switches ON. Therefore, inclination of the control signal ΦL from the time t 13  to the time t 14a  in the instant embodiment (called the first inclination hereunder) is identical to the inclination of the control signal ΦL from the time t 13  to the time t 14  in the second embodiment (see FIG. 7).  
         [0127]    Since the control signal ΦL is fed back to the gate of the transistor Q 148 , the transistor Q 148  turns ON when the voltage of the control signal ΦL rises to the threshold value Vth(Q 148 ) of the transistor Q 148 (time t 14a ). Since the gate voltage of the transistor Q 139  becomes Vss responsively, the channel resistance of the transistor Q 139  further decreases, and the driving power of the transistor Q 139  is enhanced. As a result, the control signal ΦL rises with a second inclination larger than the first inclination.  
         [0128]    Further, when the voltage of the control signal ΦL rises from Vii and reaches the set voltage Vset, the transistor Q 146  is switched OFF, and the transistor Q 147  is switched ON (time t 14b ). Accordingly, the voltage of the control signal ΦL rises up to Vpp with a third inclination larger than the second inclination. The third inclination is identical to the inclination of the control signal ΦL from the time t 14  to the time t 15  in the third embodiment (see FIG. 9). Operations of the instant embodiment after arrival of the voltage of the control signal ΦL to Vpp, that is, operations as from the time t 15 , are identical to those of the third embodiment.  
         [0129]    The control circuit  600  changes the inclination of the control signal in three steps. The second inclination of the control signal ΦL is larger than the first inclination and smaller than the third inclination. Therefore, the control circuit  600  can raise the voltage of the control signal ΦL from Vii to Vpp relatively smoothly. In other words, upon amplification of data, the instant embodiment can connect the bit line pair BLL/bBLL shown in FIG. 2 to the bit line pair BLS/bBLS more smoothly that the first to fourth embodiments. As a result, the sense amplifier of this embodiment can perform its amplifying operation with less noise and higher sensitivity than the first to fourth embodiments. The instant embodiment can additionally obtain the same effects as those of the fourth embodiment.  
         [0130]    [0130]FIG. 13 is a circuit diagram of a control circuit  700  in the sixth embodiment of the invention. This embodiment is different from the fifth embodiment in the use of an N-channel transistor Q 149  inside the voltage control circuit VC. The transistor Q 149  is connected between the transistors Q 142  and Q 143 . The gate of the transistor Q 149  is connected to the drain of the transistor Q 149  and the source of the transistor Q 148 .  
         [0131]    [0131]FIG. 14 is a timing chart showing operations according to the sixth embodiment of the invention. This embodiment is similar to the fifth embodiment in that the control signal ΦL rises from Vii to Vpp while changing its inclination three times.  
         [0132]    In the instant embodiment, however, the transistor Q 149  is interposed between the source of the transistor Q 148  and the second reference voltage source. Therefore, at the time t 13 , the voltage of the boost signal bBOOST-Ld is reduced from Vpp to Vss+Vth(Q 142 )+Vth(Q 149 ). Thus, the first inclination of the control signal ΦL in the instant embodiment is smaller than the first inclination of the control signal ΦL in the fifth embodiment.  
         [0133]    At the time t 14a , the voltage of the boost signal bBOOST-Ld is further reduced from Vss+Vth(Q 142 )+Vth(Q 149 ) to Vss+Vth(Q 149 ). Therefore, the second inclination of the control signal ΦL in the instant embodiment is smaller than the second inclination of the control signal ΦL in the fifth embodiment. Operations of the instant embodiment as from the time t 14b  are identical to those of the fifth embodiment. Vth(Q 142 ) and Vth(Q 149 ) can be set independently for adjusting the gate voltage of the transistor Q 139 , i.e. for adjusting the inclination of the control signal ΦL.  
         [0134]    According to the instant embodiment, since the first and second inclinations of the control signal ΦL are smaller than those of the first embodiment, the control circuit  700  can raise the voltage of the control signal ΦL smoothly from Vii to Vpp. In other words, upon amplification of data, the instant embodiment can connect the bit line pair BLL/bBLL shown in FIG. 2 to the bit line pair BLS/bBLS more smoothly than the first to fifth embodiments. As a result, the sense amplifier in this embodiment can perform its amplifying operation with less noise and higher sensitivity than the first to fifth embodiments. Furthermore, the instant embodiment can obtain the same effects as those of the fifth embodiment.  
         [0135]    A control circuit (not shown) connecting the source of the transistor Q 148  to the source of the transistor Q 149  will be also acceptable as a modification of the control circuit  700  shown in FIG. 13. In this modification, the voltage of the boost signal bBOOST-Ld changes from Vss+Vth(Q 142 )+Vth(Q 149 ) to Vss at the time t 14a  shown in FIG. 14. Therefore, the first inclination of the control signal ΦL is as small as that of the sixth embodiment, and the second inclination of the control signal ΦL is equal to that of the third embodiment.  
         [0136]    The numbers of the transistors Q 142  and Q 149  connected in series between the transistor Q 139  and the second reference voltage source are not limitative. For example, when assuming that the numbers of the transistors Q 142  and Q 149  are m and n, respectively, the voltage of the boost signal bBOOST-Ld from the time t 13  to the time t 14a  is Vss+m*Vth(Q 142 )+n*Vth(Q 149 ). The voltage of the boost signal bBOOST-Ld from the time t 14a  to the time t 17  is Vss+n*Vth(Q 149 ).  
         [0137]    The number of the transistor Q 148  is not limitative either. As shown in FIG. 15 for example, a transistor Q 148 ′ is connected in parallel to the transistors Q 142  and Q 149 . The transistor Q 1481  shares a common gate with the transistor Q 148 . Further, Vth(Q 148 ′) is higher than Vth(Q 148 ). This modification can raise the control signal ΦL from Vii to Vpp while changing the inclination four times. If the number of transistor Q 148  is further increased, it will be possible to raise the control signal ΦL from Vii to Vpp while changing its inclination five or more times.  
         [0138]    [0138]FIG. 16 is a circuit diagram of a control circuit  800  in the seventh embodiment of the invention. This embodiment is different from the first embodiment in the use of a sync circuit SC and a resistor R 13 .  
         [0139]    The sync circuit SC is connected to the input of the NAND gate G 114  and the input of the NOR gate G 116 . The sync circuit SC includes a NAND gate  120 . The NAND gate  120  introduces a sense amplifier activation signal SEN (see FIG. 2) and the inverted signal of the isolating signal bISO-L′, and outputs its result of its arithmetical operation to the NAND gate G 114 .  
         [0140]    The control circuit  800  having the sync circuit SC can actuate the transistors Q 109  and Q 110  (see FIG. 2) in synchronism with the sense amplifier activation signal SEN. Responsively, the bit line pair BLS/bBLS is isolated from the bit line pair BLL/bBLL substantially concurrently with activation of the sense amplifier.  
         [0141]    If the sense amplifier  116  is activated under the condition where the bit line pair BLS/bBLS is fully isolated from the bit line pair BLL/bBLL like the conventional circuit, then the data is more likely to be influenced by noise caused by the capacitance difference between the bit lines BLS+BLL and bBLS+bBLL, and this may result in inverting the data when the sense amplifier is activated.  
         [0142]    In the instant embodiment, however, since the bit line pair BLS/bBLS is isolated from the bit line pair BLL/bBLL substantially at the same time as activation of the sense amplifier  116 , data is less likely to be influenced by noise caused by the capacitance difference between the bit line BLS+BLL and bBLS+bBLL.  
         [0143]    The control circuit  800  further includes a resistor R 13  connected in series between the transistor Q 136  and the node N 1 . The resistor R 13  and a parasitic capacitance constitute an RC delay circuit. Further, the voltage of the control signal ΦL in above-mentioned embodiments transit slowly. As a result, when the sense amplifier  116  is activated, the bit line pair BLS/bBLS is gradually isolated from the bit line pair BLL/bBLL. Therefore, the sense amplifier  116  is less likely to detect the noise caused by the capacitance difference between the bit lines BLS+BLL and bBLS+bBLL. As a result, the sense amplifier  116  can amplify the correct data. The instant embodiment additionally has the same effects as those of the first embodiment. The parasitic capacitance may be, for example, the wiring capacitance between the resistor R 13  to the gates of the transistor Q 109  and Q 110 .  
         [0144]    [0144]FIG. 17 is a timing chart showing operations according to the eighth embodiment of the invention. At the time t 12  where the sense amplifier activation signal SEN changes from LOW to HIGH, the voltage of the control signal ΦL begins to decrease. This demonstrates that the control circuit  800  synchronizes with the sense amplifier  116 . At that time, ISO-L′ is maintained LOW.  
         [0145]    In the period from the time t 12  to the time t 13 , the control signal ΦL gradually decreases from Vdd to Vii. This demonstrates that the bit line pair BLS/bBLS is gradually isolated from the bit line pair BLL/bBLL. The other operations of this embodiment are identical to those of the first embodiment.  
         [0146]    [0146]FIG. 18 is a circuit diagram of a control circuit  900  in the eighth embodiment of the invention. This embodiment is different from the first embodiment in the use of a delay circuit TD′ NOR gate G 117  and N-channel transistor Q 150 . In addition, this embodiment is different from the first embodiment in that the transistor Q 136 ′ is smaller in size than the transistor Q 136 .  
         [0147]    The transistor Q 150  is connected in series between the second reference voltage source and the node N 1 . The NOR gate G 117  introduces the same signal as that introduced into the NOR gate G 116 . The NOR gate G 117 , however, introduces the isolating signal bISO-L through the delay circuit TD′. The output of the NOR gate G 117  is connected to the gate of the transistor Q 150 . Accordingly, the transistor Q 150  operates after a delay from the transistor Q 136 ′. Configuration of the delay circuit TD′ may be identical to the configuration of the delay circuit TD. The NOR gate G 117  is used for the purpose of delaying the operation of the transistor Q 150  than the operation of the transistor Q 136 ′ and preventing that the transistor Q 139  turns ON earlier than the transistor Q 150  is switched OFF.  
         [0148]    The control circuit  900  includes the sync circuit SC similarly to the control circuit  800 . Thus, the control circuit  900  can activate the transistors Q 109  and Q 110  in synchronism with the sense amplifier activation signal SEN.  
         [0149]    [0149]FIG. 19 is a timing chart showing operations according to the eighth embodiment of the invention. At the time t 12a , since the isolating signal ISO-L 1  changes from LOW to HIGH, the transistor Q 136 ′ turns ON. Responsively, the voltage of the control signal ΦL gradually decreases from Vdd. Since the transistor Q 136 ′ has a relatively small size, the voltage of the control signal ΦL in this embodiment begins to decrease more slowly than the seventh embodiment.  
         [0150]    At the time t 12b , since the isolating signal ISO-L 2  changes from LOW to HIGH, the transistor Q 150  turns ON later than the transistor Q 136 ′. Thereby, the voltage of the control signal rapidly decreases toward Vii.  
         [0151]    In the instant embodiment, isolation of the bit line pair BLS/bBLS and the bit line pair BLL/bBLL occurs after activation of the sense amplifier  116 . Therefore, this embodiment can reliably exclude noise caused by the capacitance difference between the bit lines BLS+BLL and bBLS+bBLL. Additionally, the instant embodiment has the same advantages as those of the seventh embodiment.  
         [0152]    The signs “S” and “D” shown at individual transistors in the drawings denote their sources and drains.  
         [0153]    In the fourth to sixth embodiments, the timing shift circuit TS may be replaced by the RC delay circuit TD. In the seventh and eighth embodiments, the RC delay circuit may be replaced by the timing shift circuit TS.  
         [0154]    [0154]FIG. 20 is a circuit diagram of a control circuit  1000  in the ninth embodiment of the invention. This embodiment uses the timing shift circuit TS in lieu of the RC delay circuit TD used in the eighth embodiment. The timing chart of this embodiment appears identical to that of FIG. 19. The embodiment shown in FIG. 20 also ensures the same effects as those of the eighth embodiment.  
         [0155]    The seventh and eighth embodiments may additionally include a voltage change circuit (VC) between the gate of the transistor Q 139  and the inverter G 111 . Although the foregoing embodiments are directed to DRAM-type semiconductor storage devices, the invention is not limitative to those embodiments, but it is applicable to other storage devices.  
         [0156]    The semiconductor storage devices heretofore explained can amplify data quickly, and can prevent noise caused by the capacitance difference of bit lines during amplification of data.