Abstract:
To provide a first internal voltage generating circuit that generates an internal voltage based on a first external voltage and a second internal voltage generating circuit that generates the internal voltage based on a second external voltage. The semiconductor device generates an internal voltage from a plurality of the first and second external voltages. These external voltages can be utilized efficiently depending on a load state. Therefore, even in a semiconductor device with greatly varying consumption power, it is not necessary to enlarge only a particular power supply device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device, and more particularly relates to a semiconductor device operated by a plurality of external voltages. The present invention also relates to a data processing system including a power supply device that generates different external voltages. 
         [0003]    2. Description of Related Art 
         [0004]    An internal voltage used in a semiconductor device can be different from an external voltage supplied from outside. In this case, an internal voltage generating circuit that converts the external voltage into the internal voltage is prepared for the semiconductor. That is, when the external voltage is higher than the internal voltage, the external voltage is decreased by the internal voltage generating circuit. Conversely, when the external voltage is lower than the internal voltage, the external voltage is increased by the internal voltage generating circuit. 
         [0005]    Some semiconductor devices use a plurality of internal voltages. In such semiconductor devices, a plurality of internal voltage generating circuits are provided (see Japanese Patent Application Laid-open No. 2007-13190). 
         [0006]    In addition to the semiconductor device, other semiconductor devices and various electronic components are mounted on a mounting substrate of the semiconductor device and external voltages are supplied from power supply devices on the mounting substrate. Accordingly, plural types of external voltages can exist on the mounting substrate. 
         [0007]    In the above case, when the semiconductor device with large consumption power relies on only an external voltage, the load of the power supply device that generates the corresponding external voltage becomes large. Particularly in semiconductor devices with greatly varying consumption power, the power supply device needs to be designed to supply the maximum consumption power, and thus the power supply device is difficult to be downsized. 
       SUMMARY 
       [0008]    The present invention seeks to solve one or more of the above problems, or to improve upon those problems at least in part. 
         [0009]    In one embodiment, there is provided a semiconductor device that includes a first internal voltage generating circuit that generates an internal voltage based on a first external voltage and a second internal voltage generating circuit that generates the internal voltage based on a second external voltage different from the first external voltage. 
         [0010]    In another embodiment, there is provided a data processing system that includes a first power supply device that generates a first external voltage, a second power supply device that generates a second external voltage different from the first external voltage, and a semiconductor device operated by at least the first and second external voltages. The semiconductor device includes a first internal voltage generating circuit that generates an internal voltage based on the first external voltage and a second internal voltage generating circuit that generates the internal voltage based on the second external voltage. 
         [0011]    Because the semiconductor device according to the present invention generates an internal voltage from a plurality of external voltages, it can utilize these external voltages efficiently according to the load state. Therefore, even in the semiconductor device with greatly varying consumption power, it is not necessary to enlarge only a particular power supply device. Accordingly, power supply devices used for a data processing system can be downsized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a block diagram of a data processing system according to a preferred embodiment of the present invention; 
           [0014]      FIG. 2  is a block diagram of a configuration of the semiconductor device; 
           [0015]      FIG. 3  is a circuit diagram showing an example of the internal voltage generating circuits; 
           [0016]      FIG. 4  is another example of the internal voltage generating circuits; 
           [0017]      FIG. 5  is still another example of the internal voltage generating circuits; 
           [0018]      FIGS. 6A to 6C  are waveform diagrams of the control signals; 
           [0019]      FIG. 7  is a block diagram showing an example of adding an another internal voltage generating circuit to the semiconductor device shown in  FIG. 2 ; 
           [0020]      FIG. 8  is a preferred layout of the internal voltage generating circuits when the memory cell array is divided into four banks; 
           [0021]      FIG. 9  is a circuit diagram of the sense amplifier and the sense amplifier driving circuit; 
           [0022]      FIG. 10  is a circuit diagram of the power supply control circuit; and 
           [0023]      FIG. 11  is a waveform diagram for explaining the sense operation of the semiconductor device according to the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    Preferred embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
         [0025]      FIG. 1  is a block diagram of a data processing system according to a preferred embodiment of the present invention. 
         [0026]    As shown in  FIG. 1 , the data processing system according to the present embodiment includes a power supply device  11  that generates an external voltage VDD 1  and a power supply device  12  that generates an external voltage VDD 2 . Both of the external voltages VDD 1  and VDD 2  are supplied to semiconductor devices  20  and  30 . The semiconductor devices  20  and  30  are operated by the two external voltages VDD 1  and VDD 2 . As an example, the semiconductor device  20  is a CPU (Central Processing Unit) and the semiconductor device  30  is a DRAM (Dynamic Random Access Memory), and these devices are connected to each other by a bus  40 . The configuration of the data processing system is not limited thereto and other devices, for example a semiconductor device such as graphic chips and a ROM, an external memory device such as a hard disk device and an optical drive, and an I/O device such as a keyboard and a speaker, can be connected to the bus  40 . 
         [0027]    Maximum current supply capabilities (current limit values) in specs of systems are determined for the power supply devices  11  and  12 , respectively. Therefore, the semiconductor devices  20  and  30  that utilize the external voltages VDD 1  and VDD 2  can be supplied with power from the power supply devices  11  and  12  within the respective ranges of the current limit values. The current limit values of the power supply devices  11  and  12  depend on constituent elements in the systems, and as the power to be supplied is increased, the power supply device is designed to be enlarged. 
         [0028]    Explanations are made below while focusing on the semiconductor device  30 , which is a DRAM. 
         [0029]      FIG. 2  is a block diagram of a configuration of the semiconductor device  30 . 
         [0030]    As shown in  FIG. 2 , the semiconductor device  30  includes an internal voltage generating circuit  41  that generates an internal voltage VOD based on the external voltage VDD 1  and an internal voltage generating circuit  42  that generates the internal voltage VOD based on the external voltage VDD 2 . The external voltage VDD 1  is different from the external voltage VDD 2 . The external voltages VDD 1  and VDD 2  are supplied from outside via terminals T 1  and T 2 , respectively. The internal voltage VOD is thus generated from the different external voltages VDD 1  and VDD 2 . The semiconductor device  30  further includes an internal voltage generating circuit  44  that generates another internal voltage VARY from the external voltage VDD 1  (or the external voltage VDD 2 ). 
         [0031]    Operations of the internal voltage generating circuits  41  and  42  are controlled by a power supply control circuit  50 . The power supply control circuit  50  selectively activates the internal voltage generating circuits  41  and  42  by control signals  41   a  and  42   a  and its selection is determined by an internal command ICMD. The internal command ICMD is an internal signal generated by a command decoder  61  that receives external commands CMD. The external command CMD is supplied from outside via terminals T 3 . For example, when the external command CMD indicates an active command, the command decoder  61  activates an active signal ACT which is one of the internal commands ICMD. When the external command CMD indicates a self refresh command, the command decoder  61  activates a refresh signal REF which is one of the internal commands ICMD. 
         [0032]    The internal command ICMD is also supplied to an access control circuit  62 . The access control circuit  62  receives the internal command ICMD from the command decoder  61  and an internal address IADD from an address buffer  63  to select a memory cell designated by the internal address IADD among memory cells MC included in a memory cell array  64 . An external address ADD is supplied from outside via terminals T 4 . As shown in  FIG. 2 , the memory cells MC are arranged at intersections of word lines WL with bit lines BLT and BLB. 
         [0033]    The memory cell MC selected by the access control circuit  62  is connected to the corresponding bit line BLT or BLB and a potential difference is amplified by a sense amplifier  65  connected to a pair of bit lines BLT and BLB. An operation voltage of the sense amplifier  65  is supplied by a sense amplifier driving circuit  66 . As shown in  FIG. 2 , at least the internal voltage VOD and the internal voltage VARY are supplied to the sense amplifier driving circuit  66 . 
         [0034]    The internal voltage VARY corresponds to the potential difference between the bit lines BLT and BLB amplified by the sense amplifier  65 . Meanwhile, the internal voltage VOD overdrives the sense amplifier  65  during an initial activation of the sense amplifier  65 . Accordingly, VOD&gt;VARY is established. The sense amplifier  65  is overdriven in an initial period of a sense operation to amplify the potential difference between the bit lines BLT and BLB more quickly to the internal voltage VARY. 
         [0035]    Read data amplified by the sense amplifier  65  is supplied to a data input/output circuit  67  and then outputted to outside the semiconductor device  30  via a terminal T 5 . Further, write data inputted from the external of the semiconductor device  30  is supplied via the terminal T 5  and data input/output circuit  67  to the sense amplifier  65  and then written in the memory cell array  64 . 
         [0036]      FIG. 3  is a circuit diagram showing an example of the internal voltage generating circuits  41  and  42 . This example shows a circuit suitable when the external voltages VDD 1  and VDD 2  are higher than the internal voltage VOD. For example, the external voltage VDD 1  is 2.0 V, the external voltage VDD 2  is 1.8 V, and the internal voltage VOD is 1.4 V. 
         [0037]    According to the example of  FIG. 3 , the internal voltage generating circuits  41  and  42  include respectively by internal voltage control units  111  and  121  that constitute differential amplifiers and voltage generation drivers  112  and  122  that output the internal voltage VOD. Specifically, the internal voltage control units  111  and  121  include respectively input transistors N 1  and N 2 , source transistors N 3  connected to sources of the input transistors N 1  and N 2 , and transistors P 1  and P 2  serially connected to the input transistors N 1  and N 2 , respectively to constitute current mirror circuits. A reference voltage VREF is supplied to gate electrodes of one input transistors N 1  and outputs (=VOD) of the voltage generation drivers  112  and  122  are returned to gate electrodes of the other input transistors N 2 . 
         [0038]    The voltage generation drivers  112  and  122  is constituted by P-channel MOS transistors and their gate electrodes are connected to drains of the input transistors N 1 . Because of such a configuration, when a level of the internal voltage VOD serving as the output becomes lower than the reference voltage VREF, the voltage generation drivers  112  and  122  are turned on and the level of the internal voltage VOD is increased. When the level of the internal voltage VOD is increased to the reference voltage VREF, the voltage generation drivers  112  and  122  are turned off. 
         [0039]    The control signals  41   a  and  42   a  are supplied respectively to the source transistors N 3  in the internal voltage control units  111  and  121 . When the control signals  41   a  and  42   a  become high level, the internal voltage control units  111  and  121  that constitute the differential amplifiers are activated, so that the above operations by the voltage generation drivers  112  and  122  are performed. On the other hand, when the control signals  41   a  and  42   a  become low level, the internal voltage control units  111  and  121  are inactivated and transistors P 3  are turned on, so that the voltage generation drivers  112  and  122  remain turned off. 
         [0040]      FIG. 4  shows another example of the internal voltage generating circuits  41  and  42 . This example shows a circuit suitable when the external voltage VDD 1  is higher than the internal voltage VOD and the external voltage VDD 2  is lower than the internal voltage VOD. For example, the external voltage VDD 1  is 1.8 V, the external voltage VDD 2  is 1.2 V, and the internal voltage VOD is 1.4 V. 
         [0041]    In this example, because the external voltage VDD 2  is lower than the internal voltage VOD, the internal voltage generating circuit  42  is provided with a booster circuit  123 . The booster circuit  123  increases the external voltage VDD 2  to an internal voltage VODP. The internal voltage VODP is an intermediate voltage for generating the internal voltage VOD and not particularly limited as long as it is higher than the internal voltage VOD, which is 1.9 V. 
         [0042]    The booster circuit  123  is activated based on a boost control signal  42   b  to generate the internal voltage VODP. The generated internal voltage VODP is supplied to the internal voltage control unit  121  and the voltage generation driver  122  for their operation voltage. Further, the internal voltage VODP is also supplied to a level shifter  124  and a level of the control signal  42   a  is shifted by the level shifter  124 . 
         [0043]    As described above, because the internal voltage generating circuit  42  shown in  FIG. 4  includes the booster circuit  123 , the internal voltage VODP needs to be increased to a predetermined value (for example, 1.9 V) when the control signal  42   a  is activated. Accordingly, the boost control signal  42   b  needs to be activated at a timing at least prior to the activation of the control signal  42   a.    
         [0044]      FIG. 5  shows still another example of the internal voltage generating circuits  41  and  42 . This example also shows a circuit suitable when the external voltage VDD 1  is higher than the internal voltage VOD and the external voltage VDD 2  is lower than the internal voltage VOD. For example, the external voltage VDD 1  is 1.8 V, the external voltage VDD 2  is 1.2 V, and the internal voltage VOD is 1.4 V. 
         [0045]    According to this example, in addition to the circuit shown in  FIG. 4 , a booster circuit  115  that increases the external voltage VDD 1  to generate an internal voltage VPP and source control circuits  116  and  126  connected respectively to the sources of the voltage generation drivers  112  and  122  are added. 
         [0046]    The booster circuit  115  is activated based on a boost control signal  41   b  to generate the internal voltage VPP. The generated internal voltage VPP is, for example, 2.7 V, and supplied to gate electrodes of N-channel MOS transistors that constitute the source control circuits  116  and  126 . When the boost control signal  41   b  is activated, the source control circuits  116  and  126  are turned on. The internal voltage can thus be outputted from the voltage generation drivers  112  and  122 . When the boost control signal  41   b  is not activated, the source control circuits  116  and  126  are turned off. The voltage generation drivers  112  and  122  are thus disconnected from power supplies. 
         [0047]    The internal voltage VPP is also applied to substrates of P-channel MOS transistors that constitute the voltage generation drivers  112  and  122 . That is, a back bias higher than the external voltages VDD 1  and VDD 2  is applied to the P-channel MOS transistors that constitute the voltage generation drivers  112  and  122 . Even if generation of the internal voltage VODP by a booster circuit  123  is delayed, a substrate (N-type) and a drain (P-type) of the P-channel MOS transistor that constitute the voltage generation driver  122  are not forward biased. 
         [0048]    Assume that a back bias of the voltage generation driver  122  is the internal voltage VODP as shown in  FIG. 4 . When the internal voltage VOD is made to rise by the internal voltage generating circuit  41  before the internal voltage VODP is generated by the booster circuit  123 , the substrate (N-type) and the drain (P-type) of the P-channel MOS transistor that constitute the voltage generation driver  122  are forward biased, so that a current flows in an opposite direction. When the back bias of the voltage generation driver  122  is the internal voltage VPP (&gt;VODP) as in this example, such current generation can be prevented, thereby reducing the consumption power. 
         [0049]    The internal voltage VPP satisfies preferably VPP-Vt&gt;VDD 1  or VODP, considering a threshold voltage Vt of the N-channel MOS transistors that constitute the source control circuits  116  and  126 . 
         [0050]      FIGS. 6A to 6C  are waveform diagrams of the control signals  41   a  and  42   a.    
         [0051]    In  FIGS. 6A to 6C , a period that the internal circuit using the internal voltage VOD (the sense amplifier driving circuit  66 ) is activated is indicated by T 1  (from a time t 1  to a time t 2 ). In the activation period T 1 , the level of the internal voltage VOD is decreased because of charge emission. By operating the internal voltage generating circuits  41  and  42 , the internal voltage returns to its original level through a recovery period T 2  (from the time t 2  to a time t 4  or from the time t 2  to a time t 5 ). 
         [0052]    According to the pattern shown in  FIG. 6A , the control signal  41   a  is activated from the time t 1  at which the activation period T 1  starts to the time t 4  at which the recovery period T 2  ends. Further, the control signal  42   a  is activated from the time t 3  at which the activation period T 1  has already ended to the time t 4 . That is, this is a pattern of activating the internal voltage generating circuit  41  longer than the internal voltage generating circuit  42 . As the internal voltage generating circuits  41  and  42  are activated during a part of the recovery period T 2  in the pattern, the internal voltage VOD can be returned to its original level quickly. Thus, the pattern shown in  FIG. 6A  is a pattern suitable in a normal operation (a read operation and a write operation). This is because the subsequent active signal ACT can be activated at a relatively early timing in the normal operation and thus the internal voltage VOD needs to be compensated earlier. 
         [0053]    The pattern shown in  FIG. 6A  is suitable when the current limit value (spec) of the external voltage VDD 1  is relatively large and the current limit value of the external voltage VDD 2  is relatively small. This pattern is also suitable when the level of the external voltage VDD 2  is lower than the internal voltage VOD and thus the booster circuit  123  needs to be used as in the examples of  FIGS. 4 and 5 . This is because losses are generated by the booster circuit  123  and a conversion efficiency of the internal voltage generating circuit  42  is lower than that of the internal voltage generating circuit  41  accordingly. By using the internal voltage generating circuit  41  with higher efficiency preferentially, the total consumption power can be suppressed. In this case, it is desirable that the internal voltage generating circuit  41  is used to the extent of satisfying the current limit value of the external voltage VDD 1  and the internal voltage generating circuit  42  is used in a complementary manner. 
         [0054]    The pattern shown in  FIG. 6B  is opposite to that shown in  FIG. 6A . The control signal  42   a  is activated from the time t 1  to the time t 4  and the control signal  41   a  is activated from the time t 3  to the time t 4 . That is, this is a pattern of activating the internal voltage generating circuit  42  longer than the internal voltage generating circuit  41 . This pattern is suitable when the current limit value of the external voltage VDD 2  is relatively large and the current limit value of the external voltage VDD 1  is relatively small. In this case, it is desirable that the internal voltage generating circuit  42  is used to the extent of satisfying the current limit value of the external voltage VDD 2  and the internal voltage generating circuit  41  is used in a complementary manner. 
         [0055]    According to the pattern shown in  FIG. 6C , the control signal  41   a  is activated during a period from the time t 1  at which the activation period T 1  starts to the time t 5  at which the recovery period T 2  ends and the control signal  42   a  is maintained inactivated. The time t 5  is a timing later than the time t 4  shown in  FIGS. 6A and 6B . The pattern shown in  FIG. 6C  is a pattern using only the internal voltage generating circuit  41  and providing the enlarged recovery period T 2 . 
         [0056]    This pattern is suitable when the internal voltage VOD does not need to be compensated early like a self-refreshing operation. Naturally, the current limit value of the external voltage VDD 1  must not be exceeded. Therefore, even if the conversion efficiency of the internal voltage generating circuit  42  is lower than that of the internal voltage generating circuit  41 , the consumption power can be minimized because only the internal voltage generating circuit  41  with higher efficiency is used. 
         [0057]      FIG. 7  is a block diagram showing an example of adding an internal voltage generating circuit  43  to the semiconductor device  30  shown in  FIG. 2 . 
         [0058]    The internal voltage generating circuit  43  generates the internal voltage VOD based on the external voltage VDD 1  and its configuration is the same as in the internal voltage generating circuit  41  shown in  FIG. 3 . An operation of the internal voltage generating circuit  43  is controlled by a control signal  43   a  supplied by the power supply control circuit  50 . The control signal  43   a  is maintained activated unless the internal voltage generating circuit  43  is in a deep power down mode (a non-access state and generation of potentials of internal power supplies is stopped). That is, unless it is in the deep power down mode, the internal voltage generating circuit  43  continues to be operated regardless of whether the internal circuit using the internal voltage VOD (the sense amplifier driving circuit  66 ) is activated or inactivated. 
         [0059]    By providing the internal voltage generating circuit  43 , a decrease in the internal voltage VOD during standby can be prevented. Because the internal voltage generating circuit  43  is provided to prevent a decrease in the internal voltage VOD during standby, a voltage generation driver (not shown) included in the internal voltage generating circuit  43  can be fabricated in smaller size than the ones in the internal voltage generating circuits  41  and  42 . 
         [0060]      FIG. 8  shows a preferred layout of the internal voltage generating circuits when the memory cell array  64  is divided into four banks BANK 0  to BANKS. 
         [0061]    As shown in  FIG. 8 , when the memory cell array  64  is divided into a plurality of banks, it is preferred that each set of the internal voltage generating circuits  41  to  44  is allocated to each bank. Such a configuration allows the sets of the internal voltage generating circuits  41  to  44  to be controlled according to activation/inactivation of the respective banks. As compared to a case of providing one set of the internal voltage generating circuits  41  to  44  for the entire DRAM, the consumption current can be reduced. 
         [0062]      FIG. 9  is a circuit diagram of the sense amplifier  65  and the sense amplifier driving circuit  66 . 
         [0063]    The sense amplifier  65  is constituted by of P-channel MOS transistors  211  and  212  and N-channel MOS transistors  213  and  214 . The P-channel MOS transistor  211  is serially connected to the N-channel MOS transistor  213  between a power supply node a and a power supply node b, their contact is connected to one signal node c, and their gate electrodes are connected to the other signal node d. Similarly, the P-channel MOS transistor  212  is serially connected to the N-channel MOS transistor  214  between the power supply node a and the power supply node b, their contact is connected to one signal node d and their gate electrodes are connected to the other signal node c. The signal node c is connected to one bit line BLT and the signal node d is connected to the other bit line BLB. 
         [0064]    Because of such a flip-flop structure, when a potential difference between a pair of bit lines BLT and BLB is generated while predetermined potentials are supplied to an upper drive wiring SAP and a lower drive wiring SAN, a potential of the upper drive wiring SAP is supplied to one of the bit line pair and a potential of the lower drive wiring SAN is supplied to the other of the bit line pair. 
         [0065]    The sense amplifier driving circuit  66  is constituted by a driver  301  that supplies the internal voltage VOD to the upper drive wiring SAP, a driver  302  that supplies the internal voltage VARY to the upper drive wiring SAP, and a driver  303  that connects the lower drive wiring SAN to a ground potential. The internal voltage VARY and the internal voltage VOD are defined by the potential difference with respect to the ground potential. The drivers  301  to  303  are controlled by activation signals SEP 1 , SEP 2 , and SEN, respectively. 
         [0066]      FIG. 10  is a circuit diagram of the power supply control circuit  50 . 
         [0067]    As shown in  FIG. 10 , the power supply control circuit  50  includes a timing circuit  51  that receives the active signal ACT and the refresh signal REF to generate an activation signal SEN and a delay circuit  52  that generates a delay signal SEND obtained by delaying the activation signal SEN. The activation signal SEN and the delay signal SEND are inputted to an OR gate  53  and its OR output is used as the control signal  41   a.  The delay signal SEND and the active signal ACT are inputted to an AND gate  54  and its AND output is used as the control signal  42   a.    
         [0068]    Because of such a configuration, when the active signal ACT is activated, the control signal  41   a  is activated to high level during a fixed period and the control signal  42   a  is activated to high level during a fixed period at the end of activation period of the control signal  41   a  as shown in  FIG. 6A . Meanwhile, when the refresh signal REF is activated, the control signal  41   a  is activated to high level during a fixed period but the control signal  42   a  is maintained inactivated as shown in  FIG. 6C . 
         [0069]      FIG. 11  is a waveform diagram for explaining the sense operation of the semiconductor device  30  according to the present embodiment. 
         [0070]    As shown in  FIG. 11 , when the sense operation starts at a time t 11 , the activation signals SEP 1  and SEN are activated. As described above, the activation signal SEP 1  controls the driver  301  and the activation signal SEN controls the driver  303 . The internal voltage VOD is thus supplied between the power supply nodes a and b of the sense amplifier  65 . The internal voltage VOD higher than the internal voltage VARY is used in the initial period of the sense operation, because the potential difference between the bit lines BLT and BLB is amplified more quickly by overdrive. 
         [0071]    Thereafter, the activation signal SEP 1  is inactivated at a time t 12  and overdrive ends. The activation signal SEP 2  is then activated and thus the internal voltage VARY is supplied between the power supply nodes a and b of the sense amplifier  65 . The activation signal SEP 2  is inactivated at a time t 15  and the activation signal SEN is inactivated at a time t 14 . 
         [0072]    Meanwhile, as the delay signal SEND which is activated from a time t 13  to a time t 16  is generated by the power supply control circuit  50  shown in  FIG. 10 , the control signal  41   a  is activated from the time t 11  to the time t 16 . The internal voltage generating circuit  41  is activated during this period and the reduced internal voltage VOD is compensated. 
         [0073]    The waveform of the control signal  42   a  varies depending on whether the sense operation is due to the active signal ACT or the refresh signal REF. When the sense operation is due to the active signal ( 42   a  (ACT)), the control signal  42   a  is activated from the time t 13  to the time t 16  by the power supply control circuit  50  shown in  FIG. 10 . That is, the internal voltage generating circuit  42  is activated during this period and the reduced internal voltage VOD is compensated. As the internal voltage VOD reduced by the sense operation is compensated by the two internal voltage generating circuits  41  and  42  (three internal voltage generating circuits when the internal voltage generating circuit  43  is added), the voltage is recovered quickly. 
         [0074]    When the sense operation is due to the refresh signal ( 42   a  (REF)), the control signal  42   a  is maintained inactivated. The internal voltage generating circuit  42  is not activated and the internal voltage VOD reduced by the sense operation is compensated by only one internal voltage generating circuit  41  (two internal voltage generating circuits when the internal voltage generating circuit  43  is added). The voltage is thus recovered relatively gently. 
         [0075]    As described above, according to the present embodiment, when the sense operation is performed due to the active signal ACT, that is, in the normal read or write operation, the internal voltage VOD is driven by the internal voltage generating circuits  41  and  42 . Meanwhile, when the sense operation is performed due to the refresh signal REF, the internal voltage VOD is driven only by the internal voltage generating circuit  41 . That is, in a normal operation that the internal voltage VOD reduced by the sense operation needs to be recovered quickly, the compensation is performed by the two internal voltage generating circuits  41  and  42 . In a self-refreshing operation that the internal voltage VOD reduced by the sense operation does not need to be recovered quickly, the compensation is performed only by the internal voltage generating circuit  41 . With this arrangement, the consumption power during the self-refreshing operation can thus be reduced while successive high speed accesses can be realized. 
         [0076]    Furthermore, as the compensation is performed by the internal voltage generating circuits  41  and  42  using different external voltages VDD 1  and VDD 2  in the normal operation, the load is not centralized only on a particular external power supply. 
         [0077]    It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention. 
         [0078]    For example, in the above embodiment, while the internal voltage generating circuits  41  and  42  that generate the internal voltage VOD by using different external voltages VDD 1  and VDD 2  are selectively activated, three or more internal voltage generating circuits that use three or more external voltages with different levels can be selectively activated. 
         [0079]    In the above embodiment, while the operation of the internal voltage generating circuits  41  and  42  during the activation of the active signal ACT is different from the operation during the activation of the refresh signal REF, the operation of the internal voltage generating circuits  41  and  42  can be controlled according to other signals (for example, a pre-charge signal). 
         [0080]    Further, the activation period of the internal voltage generating circuits  41  and  42  does not need to be fixed, and can be varied freely by changing, for example, the delay amount of the delay circuit  52 .