Semiconductor device

Abstract: The present invention relates to overdrive circuits (12, 13, 14, and 16) for generating an operational potential of a sense amplifier (15). For example, a switch circuit (13) is used to connect a drive node (SAP) of the sense amplifier (15) with a overdrive potential generation circuit (12) for generating an overdrive potential (VIIA) to be applied to bit lines (BLt, BLc). A restoration potential generation circuit comprises a push-pull regulator circuit (14) for generating a restoration potential (VAA) to be applied to bit lines (BLt, BLc). Consequently, the restoration potential generation circuit can directly connect with the sense amplifier (15)'s drive node.

Description: The present invention relates to a semiconductor device. More specifically, the invention relates to an overdrive power supply circuit used as a power supply circuit of a sense amplifier. Conventionally, DRAM uses an overdrive power supply circuit (hereafter referred to as the overdrive circuit) for highly sensitive and fast sense operations. For a sense operation on a bit line, a sense amplifier's positive electrode is supplied with an electric potential (so-called overdrive potential) which is higher than a restoration potential for the bit line. FIG. 12 shows a configuration example of a conventional overdrive circuit. In this figure, one external power supply (VCC) 101 connects with an overdrive potential generation circuit (VIIAG) 102. The other external power supply (VCC) 103 connects with a restoration potential generation circuit (VAAG) 104. The overdrive potential generation circuit 102 and the restoration potential generation circuit 104 connect with a switch circuit 105. The switch circuit 105 connects with a sense amplifier driver (PSAD) 106. The sense amplifier driver 106 connects with a sense amplifier (S/A) 107. The sense amplifier 107 connects with a sense amplifier driver (NSAD) 108. The sense amplifier driver 108 connects with an external power supply (GND) 109. The overdrive potential generation circuit 102 generates an overdrive potential (VIIA) for overdriving (amplifying) an electric potential of the bit line during a sense operation. This overdrive potential is also used as a power for peripheral circuits. The restoration potential generation circuit 104 generates a restoration potential (VAA) for restoring an electric potential of the bit line after the overdrive. The switch circuit 105 selects one of the overdrive potential and the restoration potential, and supplies it to the sense amplifier driver 106. FIG. 13 shows a configuration of the above overdrive circuit in more detail. The overdrive circuit needs to suppress output impedance. To configure the overdrive circuit using a MOS (Metal Oxide Semiconductor) transistor, a source follower (common drain amplifier) is used. Normally, the overdrive potential generation circuit 102 and the restoration potential generation circuit 104 both generate a positive potential. Namely, the overdrive potential generation circuit 102 is configured by using an n-type MOS transistor 102a as a source follower. Namely, the restoration potential generation circuit 104 is configured by using an n-type MOS transistor 104a as a source follower. The switch circuit 105 comprises p-type MOS transistors 105a and 105b. In this example, the p-type MOS transistors 105a and 105b also work as the sense amplifier driver 106. The sense amplifier 107 comprises p-type MOS transistors 107a and 107b and n-type MOS transistors 107c and 107d. The p-type MOS transistor 107a and the n-type MOS transistor 107c share the drain and are connected serially. The p-type MOS transistor 107b and the n-type MOS transistor 107d share the drain and are connected serially. A bit line BLt is connected to a connection point between the p-type MOS transistor 107a and the n-type MOS transistor 107c and gates of the p-type MOS transistor 107b and the n-type MOS transistor 107d. A bit line BLc is connected to a connection point between the p-type MOS transistor 107b and the n-type MOS transistor 107d and gates of the p-type MOS transistor 107a and the n-type MOS transistor 107c. The bit line BLc is complementary to the bit line BLt. The power supply line 110 connects the sense amplifier 107's positive electrode (connection point between sources of the p-type MOS transistors 107a and 107b) with the switch circuit 105 (connection point between drains of the p-type MOS transistors 105a and 105b). The sense amplifier driver 108 is connected to the sense amplifier 107's negative electrode (connection point between sources of the n-type MOS transistors 107c and 107d). The sense amplifier driver 108 comprises an n-type MOS transistor 108a. FIG. 14 shows a layout structure of a DRAM memory core using the above overdrive circuit. Especially, the figure shows an arrangement of the overdrive circuit and its power supply wiring. As shown in this figure, a plurality of cell arrays (cells) 111 is arranged in a matrix. The sense amplifiers 107 are placed on and under each cell array 111 along a row direction. The segment row decoders (SRD) 112 are placed to the right and left sides of each cell array 111 along a column direction. A circuit area (SSC1) 113 is provided at each intersection point between the sense amplifier 107 and the segment row decoder 112. A memory core periphery (one end of the column direction) is provided with a main row decoder (MRD) 114 corresponding to each column for the cell array 111. A circuit area (SSC2) 115 is provided on and under each main row decoder 114 (row direction) corresponding to the circuit area 113. A memory core periphery (one end of the row direction) is provided with a plurality of overdrive potential generation circuit blocks 116 and a plurality of restoration potential generation circuit blocks 117. In this example, each circuit block 116 comprises the overdrive potential generation circuit 102 (the n-type MOS transistor 102a) and the switch circuit 105 (the p-type MOS transistor 105a). Likewise, each circuit block 117 comprises the restoration potential generation circuit 104 (the n-type MOS transistor 104a) and the switch circuit 105 (the p-type MOS transistor 105b). The circuit blocks 116 and 117 are connected to the sense amplifier 107 via the power supply line 110. The power supply line 110 comprises, say, a first-level metal wire 110a and a second-level metal wire 110b. The metal wire 110a connects with the sense amplifier 107's positive electrode. The metal wire 110b connects with the circuit blocks 116 and 117. The metal wire 110a and the metal wire 110b are connected with each other in the circuit area 115 and the sense amplifier 107. However, the above configured overdrive circuit has the following problems. 1. An operation in a long RAS cycle requires a long restoration time. At this time, the potential level creeps, causing an excessively high restoration potential. 2. In the event of an excessive overdrive, there is a limited capability of decreasing an overdrive potential. 3. The overdrive potential generation circuit 102 is also used as the power supply circuit for the peripheral circuit. Because of this, a power supply noise during a sense operation propagates to the peripheral circuit. 4. There is a long distance between the restoration potential generation circuit 104 and the sense amplifier 107. It takes time to supply a restoration potential. JP2000057764 discloses a sense amplifier for amplifying a bit-line potential, an overdrive potential needed for a sense operation of said bit-line according to said sense amplifier, a switch circuit for controlling supply of said overdrive potential to a positive electrode of said sense amplifier, and a second generation circuit providing a voltage, which is switched as a signal connected to said positive electrode of the sense amplifier, wherein the second generation circuit generates a restoration potential of said overdrive bit-line. The regulator circuit generates the restoration potential depending on said restoration potential only during a given restoration period after the overdrive started. Further JP2000057764 shows a push-pull circuit comprising a p-type MOS transistor and a n-type MOS transistor, which share the drain and are serially connected between a power supply voltage and a ground voltage. The gate of the p-type MOS transistor connects with an output terminal of an operational amplifier and the gate of the n-type MOS transistor also connects with an output terminal of another operational amplifier. Inverting input terminals of operational amplifiers are supplied with a voltage for controlling the output potential. Non-inverting input terminals of the operational amplifiers are commonly connected to the connection point of the sources of said p-type and n-type MOS transistors and the output of the push-pull circuit. JP2000057764 also discloses a push-pull circuit of the source follower type. JP9063271 discloses a semiconductor device comprising a sense amplifier for amplifying a differential bit-line potential, an overdrive potential needed for a sense operation of said bit-line according to said sense amplifier, a switch circuit for controlling supply of said overdrive potential to a positive electrode of said sense amplifier, and a second generation circuit comprising a push-pull regulator circuit connected to said positive electrode of said sense amplifier. JP9063271 further discloses a plurality of memory cell blocks arranged in a matrix; a plurality of sense amplifiers for amplifying a bit-line potential; a plurality of row decoders for controlling drive of word line; means for providing a signal for each of several memory cell blocks, a plurality of switch circuits for controlling supply of said overdrive potential to respective positive electrodes of said plurality of sense amplifiers and a plurality of second generation circuits, wherein the plurality of second generation circuits generate a restoration potential for said bit-line after overdrive. Further, the plurality of memory cell blocks and the plurality of sense amplifiers are alternately arranged in a first direction. Memory cell block controllers decode a memory cell block selection signal and control operation of a sense amplifier block and activation of a row address decoder to operate a specified memory cell block. US5398207 discloses a booster circuit as a dedicated power supply circuit for a memory cell array section in order to suppress or eliminate the occurrence of an internal noise in a highly integrated MOS DRAM device. US5398207 also shows a booster circuit, which is providing a voltage. This voltage is inputted to a word line driver and to the gate of a transistor with a voltage down converter of the bit-line restore circuit. As mentioned above, the prior art can provide highly sensitive and fast sense operations. When a bit line potential after the overdrive becomes too low or high with reference to the restoration potential, however, it is difficult to control this potential to a desired potential. An object of the invention is, to provide such a semiconductor device with the ability to speed up operations of the regulator circuit, taking the power consumption of such regulator circuit in account. In order to attain the above objects, according to a first aspect of the present invention, there is provided a semiconductor device comprising: a differential sense amplifier for amplifying a differential bit-line potential; a first generation circuit for generating an overdrive potential needed for a sense operation of the bit-lines carried out by said differential sense amplifier; a switch circuit for controlling supply of said overdrive potential to a positive electrode of said sense amplifier; and a second generation circuit comprising a push-pull regulator circuit, which push-pull regulator circuit comprising a p-type MOS transistor and a n-type MOS transistor serially connected to each other, the connection point of said p-type and n-type MOS transistor being connected to said positive electrode of said sense amplifier, wherein operational amplifiers are connected to gates of said p-type MOS transistor and said n-type MOS transistor and wherein said second generation circuit generates a restoration potential of said overdriven bit line during a restoration period. According to the invention, the operational amplifiers uses a larger bias current at an initial stage of a restoration period than a bias current at a later stage thereof. Especially, the push-pull regulator circuit may be of the source follower type. According to a second aspect of the present invention, there is provided a semiconductor device comprising: a differential sense amplifier for amplifying a differential bit-line potential; a first generation circuit for generating an overdrive potential needed for a sense operation of the bit-lines carried out by said differential sense amplifier; a switch circuit for controlling supply of said overdrive potential to a positive electrode of said sense amplifier; and a second generation circuit comprising a push-pull regulator circuit comprising a first MOS transistor and a second MOS transistor serially connected to each other, the connection of said first and second MOS transistors being connected to said positive electrode of said sense amplifier, wherein operational amplifiers are connected to gates of the first and second MOS transistors and wherein said second generation circuit generates a restoration potential of the overdriven bit line during a restoration period. According to the second aspect of the invention, the push-pull regulator circuit is of the totem pole structure, the first MOS transistor is a n-type MOS transistor of the source follower type and the second MOS transistor is a n-type MOS transistor of the source common type, and the operational amplifiers using a larger bias current at an initial stage of a restoration period than a bias current at a later stage thereof. According to the semiconductor device of the present invention, the restoration potential can be driven to be positive or negative. This can suppress potential level inconsistency of the restoration potential due to overdrive timing inconsistency. Especially, the second generation circuit can be directly connected to the sense amplifier's positive electrode. This can decrease resistance between the sense amplifier and the regulator circuit. It is possible to speed up a supply of the restoration potential to the bit line. The first generation circuit can be configured through the use of a dedicated power supply circuit which is independent of a power supply circuit for driving a peripheral circuit. In this case, it is possible to prevent a power supply noise from being propagated to the peripheral circuit during a sense operation. Since the regulator circuit is provided near the sense amplifier, it is possible to further decrease resistance between the sense amplifier and the regulator circuit. Therefore, it is possible to further speed up a supply of the restoration potential to the bit line. This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. The invention can be more fully under stood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a block diagram showing a configuration example of an overdrive circuit according to a first embodiment of the present invention; FIG. 2 is a circuit diagram showing a specific configuration of the overdrive circuit; FIG. 3 is a plan view of a DRAM memory core showing an arrangement example of the overdrive circuit and its power supply wiring; FIG. 4 shows a configuration example of a regulator circuit in the overdrive circuit; FIG. 5 is a specific circuit diagram of the regulator circuit in FIG. 4; FIGS. 6A to 6E are timing charts explaining operations of the regulator circuit; FIG. 7 is a circuit diagram showing configuration of an overdrive potential generation circuit and an internal power supply potential generation circuit using different power supply circuits in the overdrive circuit; FIG. 8 is a circuit diagram of a switch circuit when different power supply circuits are used for configuring the overdrive potential generation circuit and the internal power supply potential generation circuit; FIG. 9 is a configuration example of a regulator circuit according to a second embodiment of the present invention; FIG. 10 is a configuration example of a regulator circuit according to a third embodiment of the present invention; FIG. 11 is a configuration example of a regulator circuit according to a fourth embodiment of the present invention; FIG. 12 is a block diagram of an overdrive circuit for explaining the prior art and its problems; FIG. 13 is a circuit diagram showing a configuration example of the conventional overdrive circuit; and FIG. 14 is a plan view of a DRAM memory core showing an arrangement example of the conventional overdrive circuit and its power supply wiring. Embodiments of the present invention will now be described with reference to the accompanying drawings. (First Embodiment) FIG. 1 shows a configuration example of an overdrive power supply circuit (hereafter referred to as the overdrive circuit) according to the first embodiment of the present invention. In this example, the power supply circuit is used for a sense amplifier in DRAM. In this figure, an external power supply (VCC) 11 connects with an overdrive potential generation circuit (VIIAG) 12 as a first generation circuit. The overdrive potential generation circuit 12 connects with a switch circuit 13. The switch circuit 13 connects with a regulator circuit (second generation circuit) 14 and a sense amplifier (S/A) 15. The sense amplifier 15 connects with a sense amplifier driver (SAD) 16. The sense amplifier driver 16 connects with an external power supply (GND) 17. The overdrive potential generation circuit 12 is a dedicated power supply circuit. It generates an overdrive potential (VII) for overdriving a bit line potential during a sense operation. The switch circuit 13 provides control to supply the overdrive potential to a positive electrode (SAP) of the sense amplifier 15. The regulator circuit 14 generates a restoration potential (VAA) for restoring a bit line potential after the overdrive. The restoration potential can be driven to be positive or negative. The sense amplifier 15 applies the overdrive potential higher than the restoration potential to the bit line during a sense operation (initial sense). After the overdrive, the bit line potential is controlled with a restoration potential. FIG. 2 shows a configuration of the overdrive circuit in further detail. In this figure, the overdrive potential generation circuit 12 is configured by using an n-type MOS transistor 12a as a source follower. The switch circuit 13 comprises a p-type MOS transistor 13a and a driver 13b for driving this transistor 13a. The regulator circuit 14 is configured to be a push-pull circuit for stabilizing a restoration potential. The regulator circuit 14 will be detailed later. The sense amplifier 15 comprises p-type MOS transistors 15a and 15b and n-type MOS transistors 15c and 15d. The p-type MOS transistor 15a and the n-type MOS transistor 15c share the drain and are connected serially. The p-type MOS transistor 15b and the n-type MOS transistor 15d share the drain and are connected serially. A bit line BLt is connected to a drain connection point between the p-type MOS transistor 15a and the n-type MOS transistor 15c and gates of the p-type MOS transistor 15b and the n-type MOS transistor 15d. A bit line BLc is connected to a drain connection point between the p-type MOS transistor 15b and the n-type MOS transistor 15d and gates of the p-type MOS transistor 15a and the n-type MOS transistor 15c. The bit line BLc is complementary to the bit line BLt. The sense amplifier 15's positive electrode SAP (connection point between sources of the p-type MOS transistors 15a and 15b) is connected with the switch circuit 13 (the p-type MOS transistor 13a's drain) and the regulator circuit 14. The sense amplifier driver 16 is connected with the sense amplifier 15's negative electrode SAN (connection point between sources of the n-type MOS transistors 15c and 15d). The sense amplifier driver 16 comprises an n-type MOS transistor 16a. FIG. 3 shows a layout structure of a DRAM memory core using the above overdrive circuit. Especially, the figure shows an arrangement of the overdrive circuit and its power supply wiring. As shown in this figure, a plurality of cell arrays (cells) 21 as memory cell blocks is arranged in a matrix. The sense amplifiers 15 are placed on and under each cell array 21 along a row direction. The segment row decoders (SRD) 22 are placed to the right and left sides of each cell array 21 along a column direction. A first circuit area (first area) 23 is provided at each intersection point between the sense amplifier 15 and the segment row decoder 22. The switch circuit 13 is arranged in the first circuit area 23. A memory core periphery (one end of the column direction) is provided with a main row decoder (MRD) 24 corresponding to each column for the cell array 21. A second circuit area (second area) 25 is provided on and under each main row decoder 24 (row direction) corresponding to the first circuit area 23. The second circuit area 25 is provided with the regulator circuit 14 and a driver circuit 31. The driver circuit 31 drives a signal line SEP leading to the driver 13b of the switch circuit 13. The regulator circuit 14 is connected to a power supply line (say, a first-level metal wire) 40 leading to the switch circuit 13 (the p-type MOS transistor 13a's drain). A memory core periphery (one end of the row direction) is provided with a plurality of the overdrive potential generation circuits 12 and a plurality of internal power supply potential generation circuits 41 for the peripheral circuit. The overdrive potential generation circuit 12 is connected to the switch circuit 13 (the p-type MOS transistor 13a's source) via a power supply line (say, a second-level metal wire) 42 and a power supply line (say, a first-level metal wire) 43. This configuration allows the regulator circuit 14 to be distributively placed near the sense amplifier 15. This makes it possible to decrease resistance between the regulator circuit 14 and the sense amplifier 15. Accordingly, a restoration potential can be fast supplied to the bit lines BLt and BLc. FIG. 4 shows a configuration example of the regulator circuit 14. A p-type MOS transistor 14a and an n-type MOS transistor 14b share the drain and are serially connected between a power-supply voltage VCC and a ground voltage VSS. The p-type MOS transistor 14a's gate connects with an operational amplifier 14c's output terminal. The n-type MOS transistor 14b's gate connects with an operational amplifier 14d's output terminal. Inverting input terminals of the operational amplifiers 14c and 14d are supplied with ref potentials for controlling a restoration potential which is a circuit output. Non-inverting input terminals of the operational amplifiers 14c and 14d are commonly connected to a connection point for sources of the p-type MOS transistor 14a and the n-type MOS transistor 14b. This connection point is connected to the sense amplifier 15's positive electrode SAP. The regulator circuit 14 is configured like a push-pull circuit as mentioned above. Consequently, even if potentials of the bit lines BLt and BLc after the overdrive become too low or high with reference to the restoration potential, it is possible to easily control these potentials to a desired potential. FIG. 5 diagrams the configuration of the regulator circuit 14 in more detail. As shown in the figure, the operational amplifier 14c comprises serially connected p-type MOS transistor 14 1 , n-type MOS transistor 14 2 , 14 3 , and 14 4 and serially connected p-type MOS transistor 14 5 , n-type MOS transistor 14 6 and 141 7 . A set of the transistors 14 1 to 14 4 and a set of the transistors 14 5 to 14 7 are parallel connected between the power-supply voltage and the ground voltage. The transistor 14 1 's gate and the transistor 14 5 's gate are commonly connected. The corresponding connection point is connected to a connection point between the transistor 14 5 's drain and the transistor 14 6 's drain. A connection point is common to the transistor 14 2 's source and the transistor 14 3 's drain. A connection point is common to the transistor 14 6 's source and the transistor 14 7 's drain. A connection point between the transistor 14 1 's drain and the transistor 14 2 's drain is connected to the transistor 14a's gate. The transistor 14 2 's gate becomes an inverting input terminal of the operational amplifier 14c and is supplied with the ref potential. An output to the sense amplifier 15's positive electrode SAP is input to the transistor 14 6 's gate which becomes a non-inverting input terminal of the operational amplifier 14c. The transistors 14 3 and 14 7 control a bias current for the operational amplifier 14c. Gates of the transistors 14 3 and 14 7 are supplied with an inverting signal for the control signal which controls regulator circuit 14's operations via an inverter 14 8 . The transistor 14 4 's gate is supplied with a selection signal for turning on or off the transistor 14 4 . On the other hand, the operational amplifier 14d comprises serially connected p-type MOS transistor 14 9 , n-type MOS transistor 14 10 , 14 11 , and 14 12 and serially connected p-type MOS transistor 14 13 , n-type MOS transistor 14 14 and 141 15 . A set of the transistors 14 9 to 14 12 and a set of the transistors 14 13 to 14 15 are parallel connected between the power-supply voltage and the ground voltage. The transistor 14 9 's gate and the transistor 14 13 's gate are commonly connected. The corresponding connection point is connected to a connection point between the transistor 14 13 's drain and the transistor 14 14 's drain. A connection point is common to the transistor 14 10 's source and the transistor 14 15 's drain. A connection point is common to the transistor 14 14 's source and the transistor 14 15 's drain. The transistor 14 14 's gate becomes an inverting input terminal of the operational amplifier 14d and is supplied with the ref potential. An output to the sense amplifier 15's positive electrode SAP is input to the transistor 14 10 's gate which becomes an inverting input terminal of the operational amplifier 14d. Namely, the transistor 14 10 's gate is connected to the transistor 14a's drain. The transistors 14 11 and 14 15 control a bias current for the operational amplifier 14d. Gates of the transistors 14 11 and 14 15 are supplied with an inverting signal for the control signal which controls regulator circuit 14's operations via an inverter 14 8 . The transistor 14 12 's gate is supplied with the selection signal for turning on or off the transistor 14 12 . The regulator circuit 14 further comprises a common circuit section 14e. The common circuit section 14e comprises a polarity changeover circuit 14e-1 and a connection circuit 14e-2. The polarity changeover circuit 14e-1 comprises p-type MOS transistors 14 16 and 14 17 and an n-type MOS transistor 14 18 . The p-type MOS transistor 14 16 's gate is connected to the inverter circuit 14 8 's output terminal. The transistor 14 16 's source is connected to the power-supply voltage. The drain is connected to the connection point between the transistor 14 9 's drain and the transistor 14 10 's drain, and the p-type MOS transistor 14 17 's gate. The p-type MOS transistor 14 17 's source is connected to the power-supply voltage. The drain is connected to the n-type MOS transistor 14 18 's drain and gate. The n-type MOS transistor 14 18 's gate is connected to the transistor 14b's gate. The source is connected to the ground voltage. The connection circuit 14e-2 comprises a p-type MOS transistor 14 19 and an n-type MOS transistor 14 20 . The p-type MOS transistor 14 19 's gate is connected to the inverter circuit 14 8 's output terminal and the transistor 14 16 's gate. The transistor 14 19 's source is connected to the power-supply voltage and the transistor 14a's source. The drain is connected to the connection point between the transistor 14 1 's drain and the transistor 14 2 's drain, and the transistor 14a's gate. The n-type MOS transistor 14 20 's gate is connected to the inverter circuit 14 8 's input terminal. The gate is supplied with the control signal for controlling the regulator circuit 14's operations. The transistor 14 20 's drain is connected to the connection point between the transistor 14 18 's gate and the transistor 14b's gate. The source is connected to the transistor 14b's source and the ground voltage. As shown in FIGS. 6A to 6E, for example, the control signal controls operations of the thus configured regulator circuit 14. When the control signal has a high potential (Hi), the circuit 14's output becomes a high impedance. At this time, the regulator circuit 14 is disconnected from the sense amplifier 15 by the switch (connection circuit 14e-2). For decreasing a breakthrough current at the transistors 14a and 14b, the ref potential supplies the transistor 14 2 with a lower potential and transistor 14 14 with a higher potential than the specified restoration potential. For setting the restoration potential to 1.4V, the transistor 14 2 is supplied with the 1.38V ref potential. The transistor 14 14 is supplied with 1.42V ref potential. In this case, the restoration potential causes a dead zone of 1.4V ±20 mV. To speed up operations of the regulator circuit 14, bias currents for the operational amplifiers 14c and 14d are increased. The bias current is increased at an initial stage of the restoration and is decreased after completion of the restoration. This increases an operation speed and saves the current consumption at the same time. The regulator circuit 14 is configured so that the transistors 14 3 and 14 11 are large sized for generating a large amount of electric current. When a selection signal (high potential) turns on the transistors 14 4 and 14 12 , bias currents for the operational amplifiers 14c and 14d flow from the current paths of the transistors 14 4 and 14 12 . By contrast, when a selection signal (low potential) turns off the transistors 14 4 and 14 12 , bias currents for the operational amplifiers 14c and 14d flow from the current paths of the transistors 14 7 and 14 15 . The transistors 14 7 and 14 15 can be small-sized. This also increases an operation speed and saves the current consumption. The thus configured regulator circuit 14 provides a high impedance except when the restoration potential is supplied. The regulator circuit 14 can be directly connected to the sense amplifier 15's drive node (SAP) without using the switch circuit 13. This makes it possible to decrease resistance between the regulator circuit 14 and the sense amplifier 15. Accordingly, it is possible to shorten the time for supplying the restoration potential and shorten the restoration time. As mentioned above, the restoration potential can be driven to be positive or negative. Namely, the push-pull regulator circuit is used for generating a restoration potential. This suppresses potential level inconsistency of the restoration potential due to overdrive timing inconsistency. The restoration potential level can be stabilized even when the bit line potential becomes too higher or lower than the restoration potential after the overdrive technique is used to amplify the bit line potential. Accordingly, it is possible to easily control the bit line potential after the overdrive to a desired potential. Especially, the regulator circuit can be directly connected to the sense amplifier's positive electrode. This can decrease resistance between the sense amplifier and the regulator circuit. As a result, it is possible to shorten the time to supply the restoration potential and shorten the restoration time. Since the regulator circuit is provided near the sense amplifier, it is possible to further decrease resistance between the sense amplifier and the regulator circuit. Therefore, it is possible to further speed up a supply of the restoration potential to the bit line and further shorten the restoration time. The overdrive potential generation circuit is configured through the use of a dedicated power supply circuit which is independent of a power supply circuit (internal power supply potential generation circuit) for driving the peripheral circuit. This prevents a power supply noise from being propagated to the peripheral circuit during a sense operation. With reference to FIG. 7, the following describes a configuration example of the overdrive potential generation circuit using the dedicated power supply circuit independently of the internal power supply potential generation circuit for the peripheral circuit. For example, the dedicated power supply circuit (n-type MOS transistor 12a) is used independently of internal power supply potential generation circuit (n-type MOS transistor) 41 for generating a peripheral circuit's drive potential VII. When the overdrive potential generation circuit 12 is configured by using this dedicated power supply circuit, it is possible to isolate mutually occurring noises. Accordingly, it is possible to prevent a power supply noise during the sense operation from being propagated to the peripheral circuit. The configuration of FIG. 3 shows that the internal power supply potential generation circuit 41 is provided near the overdrive potential generation circuit 12. In this case, the overdrive potential generation circuit 12 and the internal power supply potential generation circuit 41 can share a signal line (VPPI) for potential control as shown in FIG. 7. FIG. 8 is another configuration example of the switch circuit 13. Described below is the example in which a drive potential VII of the peripheral circuit differs from an overdrive potential VIIA. In a switch circuit 13', the overdrive potential VIIA is supplied to a p-type MOS transistor 13 1 whose source is connected to a back gate. A p-type MOS transistor 13 2 controls the transistor 13 1 . The overdrive potential VIIA is supplied to the transistor 13 2 's source which is also connected to the back gate. An n-type MOS transistor 13 3 's gate is commonly connected to the transistor 13 2 's gate and is connected to the signal line SEP. The drain is commonly connected to the transistor 13 2 's drain. The drain is connected to the ground voltage and the back gate. Each source's connection point is connected to the transistor 13 1 's gate. This configuration can prevent a leak current along a forward junction direction of the transistors 13 1 , 13 2 , and 13 3 . As mentioned above, the first embodiment of the present invention configures the regulator circuit using the push-pull circuit. The regulator circuit is not limited to the configuration in FIG. 4 and can be configured by using a push-pull circuit having another configuration. (Second Embodiment) FIG. 9 relates to the second embodiment of the present invention and shows a configuration of the regulator circuit using a push-pull circuit of the source follower type. In the regulator circuit 14A, an n-type MOS transistor 14 A-1 and a p-type MOS transistor 14 A-2 share the source and are serially connected to each other between a power-supply voltage VCC and a ground voltage VSS. The n-type MOS transistor 14 A-1 's gate connects with an output terminal of an operational amplifier 14 A-3 . The p-type MOS transistor 14 A-2 's gate connects with an output terminal of an operational amplifier 14 A-4 . Non-inverting input terminals of the operational amplifiers 14 A-3 and 14 A-4 are supplied with the ref potential for controlling the restoration potential as a circuit output. Inverting input terminals of the operational amplifiers 14 A-3 and 14 A-4 are commonly connected to the connection point between the sources of the n-type MOS transistor 14 A-1 and the p-type MOS transistor 14 A-2 . This connection point is connected to the positive electrode SAP of the sense amplifier 15. When the thus configured regulator circuit 14A is used, the overdrive circuit can also provide similar effects as described for the first embodiment. (Third Embodiment) FIG. 10 relates to the third embodiment of the present invention and shows a configuration of the regulator circuit using a push-pull circuit having the totem pole structure. In this regulator circuit 14B, an n-type MOS transistor 14 B-1 of the source follower type and an n-type MOS transistor 14 B-2 of the source-common type are serially connected to form the totem pole structure between a power-supply voltage VCC and a ground voltage VSS. The n-type MOS transistor 14 B-1 's gate connects with an output terminal of an operational amplifier 14 B-3 . The n-type MOS transistor 14 B-2 's gate connects with an output terminal of an operational amplifier 14 B-4 . The operational amplifier 14 B-3 's non-inverting input terminal and the operational amplifier 14 B-4 's inverting input terminal are commonly connected. The corresponding connection point is supplied with the ref potential for controlling the restoration potential as a circuit output. The operational amplifier 14 B-3 's inverting input terminal and the operational amplifier 14 B-4 's non-inverting input terminal are commonly connected to the connection point for the n-type MOS transistors 14 B-1 and 14 B-2 . This connection point is connected to the sense amplifier 15's positive electrode SAP. When the thus configured regulator circuit 14B is used, the overdrive circuit can also provide similar effects as described for the first embodiment. (Fourth Embodiment) FIG. 11 relates to the fourth embodiment of the present invention. This configuration example uses a booster circuit (pump circuit) to control a gate potential of the n-type MOS transistor 14 B-1 of the regulator circuit 14B in FIG. 10. The n-type MOS transistor 14 B-1 of the source follower type may require a high potential as the gate potential. In this case, a regulator circuit 14B' can be configured so that a booster circuit 14 B-5 is used to control the n-type MOS transistor 14 B-1 's gate potential. As detailed above, the overdrive technique may be used to amplify a bit line potential. Even when the amplified bit line potential becomes too higher or lower than a restoration potential, the present invention can stabilize the restoration potential level. Accordingly, it is possible to provide a semiconductor device which can easily control the overdriven bit line potential to a desired potential.

Claims: A semiconductor device, comprising: a differential sense amplifier for amplifying a differential bit-line potential; a first generation circuit (12) for generating an overdrive potential needed for a sense operation of the bit-lines (BLc, BLt) carried out by said differential sense amplifier (15); a switch circuit (13) for controlling supply of said overdrive potential to a positive electrode (SAP) of said differential sense amplifier (15); and a second generation circuit comprising a push-pull regulator circuit (14; 14 A ), which push-pull regulator circuit (14; 14 A ) comprising a p-type MOS transistor (14a; 14 A-2 ) and a n-type MOS transistor (14b; 14 A-1 ) serially connected to each other, the connection point of said p-type and n-type MOS transistor (14a, 14b; 14 A-2 , 14 A-1 ) being connected to said positive electrode (SAP) of said sense amplifier (15), wherein operational amplifiers (14c, 14d; 14 A-4 , 14 A-3 ) are connected to gates of said p-type MOS transistor (14a; 14 A-2 ) and said n-type MOS transistor (14b; 14 A-1 ) and wherein said second generation circuit generates a restoration potential of said overdriven bit lines during a restoration period; characterized in that said operational amplifiers (14c, 14d) use a larger bias current at an initial stage of a restoration period than a bias current at a later stage thereof. The semiconductor device according to claim 1, wherein the push-pull regulator circuit (14A) being of the source follower type. A semiconductor device, comprising: a differential sense amplifier for amplifying a differential bit-line potential; a first generation circuit (12) for generating an overdrive potential needed for a sense operation of the bit-lines (BLc, BLt) carried out by said differential sense amplifier (15); a switch circuit (13) for controlling supply of said overdrive potential to a positive electrode (SAP) of said differential sense amplifier (15); and a second generation circuit comprising a push-pull regulator circuit (14B) comprising a first MOS transistor (14 B-1 ) and a second MOS transistor (14 B-2 ) serially connected to each other, the connection of said first and second MOS transistors (14 B-1 , 14 B-2 ) being connected to said positive electrode (SAP) of said sense amplifier (15), wherein operational amplifiers (14 B-3 , 14 B-4 ) are connected to gates of said first and second MOS transistors (14 B-1 , 14 B-2 ) and wherein said second generation circuit generates a restoration potential of said overdriven bit lines during a restoration period; characterized in that said push-pull regulator circuit (14B) is of the totem pole structure, said first MOS transistor being a n-type MOS transistor (14 B-1 ) of the source follower type and said second MOS transistor being a n-type MOS transistor (14 B-2 ) of the source common type, and said operational amplifiers (14 B-3 , 14 B-4 ) use a larger bias current at an initial stage of a restoration period than a bias current at a later stage thereof. The semiconductor device according to one of the preceding claims, characterized in that said first generation circuit (12) is a dedicated power supply circuit (12a) . The semiconductor device according to one of the preceding claims, characterized in that said second generation circuit generates said restoration potential only during a given restoration period after said overdrive and outputs a high impedance otherwise. The semiconductor device according to one of the preceding claims, characterized in that said operational amplifiers have first transistors (14 3 , 14 11 ) for a flow of the bias current at an initial stage of a restoration period and second transistors (14 7 , 14 15 ) smaller than said first transistors (14 3 , 14 11 ) for a flow of the bias current at a later stage of a restoration period. The semiconductor device according to one of the preceding claims, characterized by further comprising: a plurality of memory cell blocks (21) arranged in a matrix; a plurality of said differential sense amplifiers (15); a plurality of main row decoders (24) for controlling drive of one main word line for controlling selection of a plurality of word lines; a plurality of segment row decoders (22) driven by selecting a specific word line from said plurality of word lines corresponding to said one main word line; a plurality of said first generation circuits (12); a plurality of said switch circuits (13); and a plurality of said second generation circuits, the push-pull regulator circuits (14) of which being respectively connected to the positive electrodes of said plurality of sense amplifiers (15); wherein said plurality of memory cell blocks (21) and said plurality of sense amplifiers (15) are alternately arranged in a first direction; said plurality of segment row decoders (22) are arranged respectively adjacent to said plurality of memory cell blocks (21) in a second direction orthogonal to said first direction; said plurality of main row decoders (24) are arranged at one end of said second direction; said plurality of switch circuits (13) are arranged in a plurality of first regions (23) adjacent to said plurality of sense amplifiers (15); said plurality of first generation circuits (12) are arranged at one end of said first direction; and said plurality of second generation circuits are arranged in a plurality of second regions (25) adjacent to said plurality of main row decoders (24).

Inventors: TAKEUCHI ATSUSHI, TSUCHIDA KENJI, WADA MASAHARU, TAKEUCHI, ATSUSHI, TSUCHIDA, KENJI, WADA, MASAHARU
Applicants: FUJITSU LTD, TOSHIBA KK, FUJITSU LIMITED, KABUSHIKI KAISHA TOSHIBA
Application year: 2001
Main classification: G11C7
IPC codes: G11C11, G11C7