Abstract:
Disclosed herein is a self refresh control device for reducing a current leakage of transistors in off-state. The apparatus for controlling a voltage used in a semiconductor memory device includes a first voltage supplying block for supplying a first voltage to the semiconductor memory device in response to an inputted control signal; and a second voltage supplying block for supplying a second voltage to the semiconductor memory device in response to the inputted control signal, wherein the first and the second voltages are used as a bulk voltage of a transistor included in the semiconductor memory device.

Description:
RELATED APPLICATIONS 
   This application is a Continuation of U.S. application Ser. No. 11/318,594, filed Dec. 28, 2005, now U.S. Pat. No. 7,327,626 claiming priority of Korean Application No. 10-2005-0075256, filed Aug. 17, 2005, the entire contents of each of which are hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a self refresh control device; and, more particularly, to a self refresh control device for reducing a current leakage in off-state of transistors during self refresh operation. 
   DESCRIPTION OF RELATED ARTS 
   A dynamic random access memory (DRAM) has an integration degree larger than other memory device. 
   Recently, according to a high-speed operation demand, various techniques are proposed so that an operation speed of DRAM is dramatically increased. 
     FIG. 1  is a circuit diagram showing a conventional circuit of a semiconductor memory device including MOS transistors. 
   Herein, a predetermined circuit including at least one MOS transistor  10  is explained. 
   As shown, the predetermined circuit including at least one MOS transistor  10  includes a PMOS transistor C_P 1  and a NMOS transistor C_N 1 . In general, the PMOS transistor C_P 1  is connected between a source voltage VDD and the NMOS transistor C_N 1 . The NMOS transistor C_N 1  is connected between the PMOS transistor C_P 1  and a ground voltage VSS. Herein, the source voltage VDD is supplied to a source and a bulk of the PMOS transistor C_P 1 , and the ground voltage VSS is supplied to a source and a bulk of the NMOS transistor C_N 1 . 
     FIG. 2  is a circuit diagram showing a conventional self refresh generating circuit block  20 . 
   The self refresh generating circuit block  20  is required to generate a self refresh signal SRFP. 
   As shown, the conventional self refresh generating circuit block  20  includes a first inverter C_IV 1 , a second inverter C_IV 2  and a NAND gate C_ND 1 . The NAND gate C_ND 1  performs a NAND operation of an internal self refresh signal ISRFP inverted by the first inverter C_IV 1  and an external self refresh signal ESRFP inverted by the second inverter C_IV 2  to output a self refresh signal SRFP. 
   If the external self refresh signal ESRFP having a logic level ‘HIGH’ is inputted to the conventional self refresh generating circuit block  20 , the self refresh signal SRFP is activated. Accordingly, a refresh operation is performed during a self refresh period. The refresh operation is performed repeatedly at a predetermined period, in general about several tens of microsecond (μs). 
   In the mean time, the self refresh operation is performed not only by the external self refresh signal ESRFP inputted from an external but also by the internal self refresh signal ISRFP which is internally generated at a predetermined period or when a specific condition is met. 
   However, as the semiconductor memory device is more integrated, a gate length of transistors becomes smaller and a threshold voltage of the transistors becomes lower. Therefore, when the transistors are in off-state, a leakage current of the transistors is increased so that there is a limitation to reduce a current consumption. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a self refresh control device for reducing a self refresh current to thereby reduce a leakage current in off-state of transistors during self refresh operation by raising a bulk voltage of a PMOS transistor and going down a bulk voltage of a NMOS transistor. 
   In accordance with an aspect of the present invention, there is provided a self refresh control device including a first voltage supplying block for supplying a first voltage to the semiconductor memory device in response to an inputted control signal; and a second voltage supplying block for supplying a second voltage to the semiconductor memory device in response to the inputted control signal. 
   In accordance with another aspect of the present invention, there is provided a self refresh control device including a plurality of first circuit units, each of first circuit units including a first MOS transistor and a second MOS transistor connected between a first source voltage and a first ground voltage in series; a second circuit unit including a third MOS transistor and a fourth MOS transistor connected between the first source voltage and the first ground voltage in series; and a plurality of voltage supplying units for supplying a second source voltage higher than the first source voltage to a bulk of the first MOS transistor and a second ground voltage lower than the first ground voltage to a bulk of the second MOS transistor when starting a self refresh operation; and supplying the first source voltage to the bulk of the first MOS transistor and the first ground voltage to the bulk of the second MOS transistor when finishing the self refresh operation, wherein each of voltage supplying units is provided with each of corresponding first circuit units. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become better understood with respect to the following description of the specific embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a circuit diagram of a conventional circuit showing a semiconductor memory device including MOS transistors; 
       FIG. 2  is a circuit diagram showing a conventional self refresh generating circuit block; 
       FIG. 3  is a circuit diagram describing a self refresh control device in accordance with an embodiment of the present invention; 
       FIG. 4  is a circuit diagram depicting a self refresh control device in accordance with another embodiment of the present invention; 
       FIGS. 5A to 5C  are circuit diagrams showing self refresh control devices in accordance with the other embodiments of the present invention; 
       FIG. 6  is a timing diagram illustrating an operation of the self refresh control device shown in  FIGS. 3 to 5C ; 
       FIG. 7  is a circuit diagram showing a self refresh generating circuit block in accordance with another embodiment of the present invention; and 
       FIG. 8  is a timing diagram illustrating an operation of the self refresh generating circuit block of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, a self refresh control device in accordance with an embodiment of the present invention will be described in detail referring to the accompanying drawings. 
     FIG. 3  is a circuit diagram describing a self refresh control device in accordance with an embodiment of the present invention. 
   As shown, the self refresh control device includes a predetermined circuit including at least one MOS transistor  100  and a current control unit  200 . 
   The predetermined circuit  100  includes a first PMOS transistor P 1  and a first NMOS transistor N 1  which are connected between a first source voltage VDD and a first ground voltage VSS in series. The first source voltage VDD is supplied to a source of the first PMOS transistor P 1  and a voltage of a node A is supplied to a bulk of the first PMOS transistor P 1 . The first ground voltage VSS is supplied to a source of the first NMOS transistor N 1 , and a voltage of a node B is supplied to a bulk of the first NMOS transistor N 1 . 
   The current control unit  200  includes a second PMOS transistor P 2 , a third PMOS transistor P 3 , a second NMOS transistor N 2 , a third NMOS transistor N 3 , and a self refresh inverter SREF_IV. 
   The self refresh inverter SREF_IV inverts a self refresh flag signal SREF_F. The second PMOS transistor P 2  has a source connected to the second source voltage (VDD+α), a drain connected to the node A and a gate connected to an output of the self refresh inverter SREF_IV. The third PMOS transistor P 3  has a source connected to the first source voltage VDD, a drain connected to the node A and a gate connected to the self refresh flag signal SREF_F. The second NMOS transistor N 2  has a source connected to the first ground voltage VSS, a drain connected to the node B and a gate connected to the output of the self refresh inverter SREF_IV. The third NMOS transistor N 3  has a source connected to the second ground voltage (VSS−β), a drain connected to the node B and a gate connected to the self refresh flag signal SREF_F. 
   In this time, a pumping voltage Vpp can be used as the second source voltage (VDD+α) which is used for a voltage of a wordline. Also, a back-bias voltage VBB can be used as the second ground voltage (VSS−β) which is used for biasing a bulk voltage of cell transistors. 
     FIG. 4  is a circuit diagram depicting a self refresh control device in accordance with another embodiment of the present invention. 
   As shown, the self refresh control device includes a plurality of a predetermined circuits including at least one MOS transistor  100 _ 1  to  100 _n and a plurality of current control units  200 _ 1  to  200 _n. 
   Each of the predetermined circuits  100 _ 1  to  100 _n is corresponding to each of current control unit among the current control units  200 _ 1  to  200 _n. 
   In case that a self refresh flag signal SREF_F is activated, a second PMOS transistor P 2  and a third NMOS transistor N 3  turn on. Accordingly, a bulk voltage of a first PMOS transistor P 1  quickly comes up to a level of a second source voltage (VDD+α) and a bulk voltage of a first NMOS transistor N 1  quickly comes down to a level of a second ground voltage (VSS−β). 
   In case that the self refresh flag signal SREF_F is inactivated, the third PMOS transistor P 3  and the second NMOS transistor N 2  turn on. Accordingly, the bulk voltage of the first PMOS transistor P 1  quickly comes up to a level of the first source voltage VDD and the bulk voltage of the first NMOS transistor N 1  quickly comes down to a level of the first ground voltage VSS. 
   As described above, if the self refresh flag signal SREF_F is activated, the bulk voltage of the first PMOS transistor P 1  comes up to the second source voltage (VDD+α). Accordingly, a threshold voltage of the first PMOS transistor P 1  is increased in proportion to α. As a result, a leakage current of the first PMOS transistor P 1  during an off-state can be reduced. 
   Likewise, if the self refresh flag signal SREF_F is activated, the bulk voltage of the first NMOS transistor N 1  comes down to the second ground voltage (VSS−β). Accordingly, the threshold voltage of the first NMOS transistor N 1  is increased in proportion to β. As a result, a leakage current of the first NMOS transistor N 1  during the off-state can be reduced. 
     FIGS. 5A to 5C  are circuit diagrams showing self refresh control devices in accordance with other embodiments of the present invention. 
     FIGS. 5A to 5C  describe self refresh control devices in case that predetermined circuits including at least one MOS transistor are classified into their own functions. 
   More particularly,  FIG. 5A  shows a row access block  300  having a row access current control unit  400  and  FIG. 5B  shows a column access block  310  having a column access current control unit  410 . 
   Also, a predetermined circuit including at least one MOS transistor in  FIG. 5C  is for controlling a current of a bulk in a non-critical block such as a test-mode block  420 . Herein, a self refresh flag signal SREF_F is not applied to the test-mode block  420 . On the other hand, a second source voltage (VDD+α) is supplied to a bulk of a first PMOS transistor P 1  and a second ground voltage (VSS−β) is supplied to a bulk of a first NMOS transistor N 1  in the test-mode block  420 . 
     FIG. 6  is a timing diagram illustrating an operation of the self refresh control device shown in  FIGS. 3 to 5C . 
   As shown, first, in a normal operation, if the self refresh flag signal SREF_F becomes a logic level ‘LOW’, the third PMOS transistor P 3  whose source is connected to the first source voltage VDD turns on. Accordingly, the bulk voltage of the first PMOS transistor P 1  in the predetermined circuit including at least one MOS transistor  100 , i.e., the voltage of the node A, comes up to the first source voltage VDD. 
   Then, in a self refresh operation, the self refresh flag signal SREF_F becomes a logic level ‘HIGH’, the third PMOS transistor P 3  turns off; and, at the same time, the second PMOS transistor P 2  whose source is connected to the second source voltage (VDD+α) turns on. Accordingly, the bulk voltage of the first PMOS transistor P 1  in the predetermined circuit including at least one MOS transistor  100 , i.e., the voltage of the node A, comes up to the second source voltage (VDD+α). 
   As s result, the threshold voltage of the first PMOS transistor P 1  is increased in proportion to α. Hence, a leakage current of the first PMOS transistor P 1  in an off-state can be reduced. 
   Likewise, in the normal operation, if the self refresh flag signal SREF_F becomes the logic level ‘LOW’, the second NMOS transistor N 2  whose source is connected to the first ground voltage VSS turns on. Accordingly, the bulk voltage of the first NMOS transistor N 1  in the predetermined circuit including at least one MOS transistor  100 , i.e., the voltage of the node B, comes down to the first ground voltage VSS. 
   Then, in the self refresh operation, the self refresh flag signal SREF_F becomes the logic level ‘HIGH’, the second NMOS transistor N 2  turns off; and, at the same time, the third NMOS transistor N 3  whose source is connected to the second ground voltage (VSS−β) turns on. Accordingly, the bulk voltage of the first NMOS transistor N 1  in the predetermined circuit including at least one MOS transistor  100 , i.e., the voltage of the node B, comes down to the second ground voltage (VSS−β). 
   As a result, the threshold voltage of the first NMOS transistor N 1  is increased in proportion to β. Hence, a leakage current of the first NMOS transistor N 1  in the off-state can be reduced. 
   In the mean time, if the self refresh operation is finished, an active command ‘ACT’ can be inputted after a ‘tRC’. Then, if the active command ‘ACT’ was inputted, a writable or readable command ‘WT/RD’ can be inputted after a ‘tRCD’. Wherein, the ‘tRC’ means a ‘RAS cycle time’ in order to finish precharging a sense amplifier of a bitline and a wordline to thereby precharge a core of a DRAM. The ‘tRCD’ means a ‘RAS to CAS delay time’ in order to read or write a data, in reality, after the active command ‘ACT’ is performed. 
   In case that the self refresh operation is finished and the active command ‘ACT’ is inputted, in the row access block  300  of  FIG. 5A , the first source voltage VDD of the row access current control unit  400  is supplied to a bulk of a first PMOS transistor P 1 . At the same time, the first ground voltage VSS of the row access current control unit  400  is supplied to a bulk of a first NMOS transistor N 1 . 
   Continuously, after the ‘tRCD’, the writable command or the readable command ‘WT/RD’ can be inputted. Hence, in the column access block  310  of  FIG. 5B , the first source voltage VDD of the column access current control unit  410  is inputted to a bulk of a first PMOS transistor P 1 . At the same time, the first ground voltage VSS of the column access current control unit  410  is supplied to a bulk of a first NMOS transistor N 1 . 
     FIG. 7  is a circuit diagram showing a self refresh generating circuit block  500  in accordance with another embodiment of the present invention. 
   As shown, the self refresh generating circuit block  500  includes a first logic gate  510  and a second logic gate  520 . 
   The first logic gate  510  includes a first inverter IV 1 , a second inverter IV 2  and a first NAND gate ND 1 . The second logic gate  520  includes a third inverter IV 3 , a fourth inverter IV 4  and a second NAND gate ND 2 . 
   In the first logic gate  510 , the first NAND gate ND 1  performs a nand operation of an inverted self refresh flag signal SREF_F inverted by the first inverter IV 1  and an external self refresh signal ESRFP. The second inverter IV 2  inverts an output of the first NAND gate ND 1 . Accordingly, in case that the self refresh flag signal SREF_F is activated, even if the external self refresh signal ESRFP is inputted as a logic level ‘HIGH’, the external self refresh signal ESRFP is outputted as a logic level ‘LOW’. 
   In the second logic gate  520 , the third inverter IV 3  inverts an output of the first logic gate  510  and the fourth inverter IV 4  inverts an internal self refresh signal ISRFP. Then, the second NAND gate ND 2  performs a nand operation of an output of the third inverter IV 3  and an output of the fourth inverter IV 4  to output a self refresh signal SRFP. Accordingly, in case that any one of the internal self refresh signal ISRFP and the output of the first logic gate  510  is a logic level ‘HIGH’, the self refresh signal SRFP is outputted as a logic level ‘HIGH’. 
   As above described, in a conventional self refresh generating circuit block  20  shown in  FIG. 2 , it is possible to activate the self refresh signal SRFP in case that any of the internal self refresh signal ISRFP and the external self refresh signal ESRFP is activated. Accordingly, the refresh operation is performed repeatedly at a predetermined period, e.g., about several tens of microsecond (μs). 
   On the other hand, in the self refresh generating circuit block  500  shown in  FIG. 7  according to the present invention, a corresponding signal to the external self refresh signal ESRFP is selectively activated. Namely, the corresponding signal to the external self refresh signal ESRFP is activated only if the self refresh flag signal SREF_F is inactivated. Accordingly, if the self refresh flag signal SREF_F is activated, whether the self refresh signal SRFP is activated or not depends on the internal self refresh signal ISRFP. 
   More particularly,  FIG. 8  is a timing diagram illustrating an operation of the self refresh generating circuit block  500  shown in  FIG. 7 . 
   As shown, in the self refresh generating circuit block  500 , if the external self refresh signal ESRFP is inputted during an active section of the self refresh flag signal SREF_F, the self refresh operation is not performed at once. 
   Hence, it is possible to supply a pumping voltage VPP to a bulk voltage of the first PMOS transistor P 1  in the predetermined circuit including at least one MOS transistor  100  and supply a back-bias voltage VBB to a bulk voltage of the first NMOS transistor N 1  before the internal self refresh signal ISRFP is activated. Then, in case that the internal self refresh signal ISRFP is activated, the self refresh signal SRFP is activated so that the refresh operation is performed. 
   In accordance with the specific embodiment of the present invention, during a self refresh operation, it is possible to reduce a self refresh current by raising a bulk voltage of a PMOS transistor and going down a bulk voltage of a NMOS transistor. As a result, when the transistors are in the off-state, a leakage current of the transistors can be reduced. 
   The present application contains subject matter related to the Korean patent application No. KR 2005-75256, filed in the Korean Patent Office on Aug. 17, 2005, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to certain specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.