Abstract:
A semiconductor device for use in a semiconductor memory device for pumping a supplying voltage according to a data access mode and an auto-refresh mode, including: a voltage level detecting means for generating a voltage level detect signal by detecting a voltage level of the supplying voltage; an auto-refresh signal detecting means for generating an auto-refresh detect signal in response to an auto-refresh signal; and a voltage pumping means for pumping the supplying voltage in response to the voltage level detect signal at the data access mode or in response to the auto-refresh detect signal at the auto-refresh mode.

Description:
FIELD OF INVENTION 
   The present invention relates to a semiconductor memory device; and, more particularly, to a semiconductor memory device which generates a stable high voltage during an auto-refresh operation. 
   DESCRIPTION OF PRIOR ART 
   Generally, a dynamic random access memory (DRAM) supplies a high voltage VPP whose voltage level is higher than that of a power supply voltage VDD to a word line during a data access operation or an auto-refresh operation because a power consumption of the DRAM is raised during those operations. Therefore, the DRAM includes a high voltage generating device for generating the high voltage VPP. 
     FIG. 1  is a block diagram showing a conventional high voltage generating device included in a semiconductor memory device. 
   As shown, the conventional high voltage generating device includes a high voltage level detecting unit  10 , a high voltage pumping control signal generating unit  20 , a high voltage pumping unit  30  and a high voltage loading unit  40 . 
   The high voltage level detecting unit  10  is enabled by a row active signal row_act for detecting a voltage level of a feed-backed high voltage signal vpp_fd, whereby the high voltage level detecting unit  10  generates a voltage level detect signal osc_en_det which is activated when a high voltage VPP is lower than a predetermined voltage level. 
   The high voltage pumping control signal generating unit  20  generates a pumping control signal pump_ctr in response to the voltage level detect signal osc_en_det. 
   The high voltage pumping unit  30  generates the high voltage VPP by performing a voltage pumping operation in response to the pumping control signal pump_ctr. The high voltage VPP is feed-backed to the high voltage level detecting unit  10  as the feed-backed high voltage signal vpp_fd. 
   The high voltage loading unit  40  consumes the high voltage VPP supplied by the high voltage pumping unit  30 . Herein, the high voltage loading unit  40  includes any circuit element which consumes the high voltage VPP. 
     FIG. 2  is a timing diagram showing an operation of the conventional high voltage generating device when performing the auto-refresh operation. 
   Referring to  FIGS. 1 and 2 , the operation of the conventional high voltage generating device is described below. 
   If the row active signal row_act is activated, an auto-refresh signal auto_ref is activated in response to the row active signal row_act. 
   Thereafter, circuit elements included in the high voltage loading unit  40  perform operations which correspond to various command signals such as a word line signal WL and bit line isolation signals BISH and BISL. Therefore, the high voltage loading unit  40  excessively consumes the high voltage VPP, and, thus, a voltage level of the high voltage VPP is lowered. 
   If the voltage level of the high voltage VPP becomes lower than an average high voltage level avg_level, the high voltage level detecting unit  10  activates the voltage level detect signal osc_en_det. Then, the high voltage pumping control signal generating unit  20  activates the pumping control signal pump_ctr in response to the voltage level detect signal osc_en_det. 
   Thereafter, the high voltage pumping unit  30  raises the voltage level of the high voltage VPP by performing a voltage pumping operation, whereby the voltage level of the high voltage VPP becomes the average high voltage level avg_level. 
   Thereafter, a row precharge signal row_pre is activated, and thus the voltage level detect signal osc_en_det and the pumping control signal pump_ctr are inactivated in response to the row precharge signal row_pre. 
   Meanwhile, the operation of the conventional high voltage generating device described above is performed when the semiconductor memory device performs an auto-refresh operation. However, the conventional high voltage generating device performs the same operation when the semiconductor memory device performs a data access operation. 
     FIG. 3  is a schematic circuit diagram showing the high voltage pumping control signal generating unit  20 . 
   As shown, the high voltage pumping control signal generating unit  20  includes a NAND gate ND 1 , a first inverter I 1  and an inverter unit  22 . 
   The NAND gate ND 1  receives the voltage level detect signal osc_en_det and an output signal from the inverter unit  22  for performing a logic NAND operation to the received two signals. 
   The inverter unit  22  includes a plurality of inverters connected in series between an input terminal and an output terminal of the NAND gate ND 1 . The output terminal of the NAND gate ND 1  is also connected to an input terminal of the first inverter I 1 . The inverter unit  22  serves to delay an output signal from the NAND gate ND 1 . 
   The first inverter I 1  receives an output signal from the NAND gate ND 1  and inverts it in order to output the pumping control signal pump_ctr. 
   The high voltage pumping control signal generating unit  20  activates the pumping control signal pump_ctr in response to the voltage level detect signal osc_en_det. Then, an active state of the pumping control signal pump_ctr is kept for a predetermined delay time corresponding to a delay quantity that the inverter unit  22  has. 
   That is, the conventional high voltage generating device raises the voltage level of the high voltage VPP if the voltage level of the high voltage VPP is lower than that of the average high voltage level avg_level so that the high voltage VPP can keep its voltage level to be equal to or higher than the average high voltage level avg_level. 
   However, when the semiconductor memory device performs the auto-refresh operation, the high voltage VPP is excessively consumed because memory banks included in the semiconductor memory device are operated simultaneously. Therefore, the voltage level of the high voltage VPP is more rapidly lowered than it is lowered during the data access operation. Therefore, it is possible that the high voltage loading unit  40  is not supplied an enough power to be normally operated. 
   SUMMARY OF INVENTION 
   It is, therefore, an object of the present invention to provide a semiconductor device to supply a stable voltage during an auto-refresh operation. 
   In accordance with an aspect of the present invention, there is provided a semiconductor device for use in a semiconductor memory device for pumping a supplying voltage according to a data access mode and an auto-refresh mode, including: a voltage level detecting means for generating a voltage level detect signal by detecting a voltage level of the supplying voltage; an auto-refresh signal detecting means for generating an auto-refresh detect signal in response to an auto-refresh signal; and a voltage pumping means for pumping the supplying voltage in response to the voltage level detect signal at the data access mode or in response to the auto-refresh detect signal at the auto-refresh mode. 
   In accordance with another aspect of the present invention, there is provided a method for pumping a supplying voltage, including a step of: detecting a voltage level of the supplying voltage; raising the voltage level of the supplying voltage if the detected voltage level of the supplying voltage is lower than a predetermined voltage level; and raising the voltage level of the supplying voltage when an auto-refresh signal is activated regardless of the detected voltage level of the high voltage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing a conventional high voltage generating device included in a semiconductor memory device; 
       FIG. 2  is a timing diagram showing an operation of the conventional high voltage generating device shown in  FIG. 1 ; 
       FIG. 3  is a schematic circuit diagram showing a high voltage pumping control signal generating unit shown in  FIG. 1 ; 
       FIG. 4  is a block diagram showing a semiconductor memory device in accordance with the present invention; 
       FIG. 5  is a schematic circuit diagram showing an auto-refresh signal detecting unit shown in  FIG. 4 ; 
       FIG. 6  is a schematic circuit diagram showing a high voltage pumping control signal generating unit shown in  FIG. 4 ; 
       FIG. 7  is a timing diagram showing an operation of the semiconductor memory device when the semiconductor memory device performs a data access operation; 
       FIG. 8  is a timing diagram showing an operation of the semiconductor memory device when the semiconductor memory device performs an auto-refresh operation; and 
       FIG. 9  is a timing diagram showing another operation of the semiconductor memory device when the semiconductor memory device performs an auto-refresh operation. 
   

   DETAILED DESCRIPTION OF INVENTION 
   Hereinafter, a semiconductor memory device in accordance with the present invention will be described in detail referring to the accompanying drawings. 
     FIG. 4  is a block diagram showing a semiconductor memory device in accordance with the present invention. 
   As shown, the semiconductor memory device includes a high voltage level detecting unit  100 , a high voltage pumping control signal generating unit  200 , a high voltage pumping unit  300 , a high voltage loading unit  400  and an auto-refresh signal detecting unit  500 . 
   The high voltage level detecting unit  100  is enabled by a row active signal row_act for detecting a voltage level of a feed-backed high voltage signal vpp_fd to thereby generate a voltage level detect signal osc_en_det. Herein, the high voltage level detecting unit  100  activates the voltage level detect signal osc_en_det as a logic high level if the voltage level of the feed-backed high voltage signal is lower than a predetermined voltage level, namely an average high voltage level avg_level. 
   The high voltage pumping control signal generating unit  200  generates a pumping control signal pump_ctr in response to the voltage level detect signal osc_en_det and an auto-refresh detect signal osc_en_auto. 
   The high voltage pumping unit  300  generates a high voltage VPP by performing a voltage pumping operation in response to the pumping control signal pump_ctr. The high voltage VPP is feed-backed to the high voltage level detecting unit  100  as the feed-backed high voltage signal vpp_fd. 
   The high voltage loading unit  400  consumes the high voltage VPP supplied by the high voltage pumping unit  300 . Herein, the high voltage loading unit  400  includes any circuit elements which consume the high voltage VPP to be operated. 
   The auto-refresh signal detecting unit  500  receives an auto-refresh signal auto_ref to generate an auto-refresh detect signal osc_en_auto. Herein, the auto-refresh signal detecting unit  500  activates the auto-refresh detect signal osc_en_auto as a logic high level if the auto-refresh signal auto_ref is activated. 
   Herein, the high voltage pumping unit  300  performs the voltage pumping operation if the pumping control signal pump_ctr is activated as a logic high level for raising a voltage level of the high voltage VPP so that the high voltage VPP can be equal to or higher than the average high voltage level avg_level. 
   The pumping control signal pump_ctr is activated if one of the voltage level detect signal osc_en_det and the auto-refresh detect signal osc_en_auto is activated. The voltage level detect signal osc_en_det is activated if the voltage level of the high voltage VPP becomes lower than the average high voltage level avg_level. On the other hand, the auto-refresh detect signal osc_en_auto is activated if the auto-refresh signal auto-ref is activated, i.e., if an auto-refresh operation starts to be performed. 
   Since a semiconductor memory device excessively consumes the high voltage VPP during the auto-refresh operation, the voltage level of the high voltage VPP is rapidly lowered. Therefore, the auto-refresh signal detecting unit  500  activated the auto-refresh detect signal osc_en_auto if the auto-refresh signal auto_ref is activated, whereby the high voltage pumping unit  300  performs the voltage pumping operation. As a result, the voltage level of the high voltage VPP is not rapidly lowered during the auto-refresh operation. 
     FIG. 5  is a schematic circuit diagram showing the auto-refresh signal detecting unit  500 . 
   As shown, the auto-refresh signal detecting unit  500  includes a first inverter I 2 , a first NAND gate ND 2  and a first delay unit  502 . 
   The first inverter I 2  serves to invert the auto-refresh signal auto_ref. The first delay unit  502  includes a plurality of inverters connected in series in order to delay an output signal from the auto-refresh signal auto_ref. 
   The first NAND gate ND 2  receives output signals from the first inverter I 2  and the first delay unit  502  for performing a logic NAND operation to the received two signals, whereby the auto-refresh detect signal osc_en_auto is outputted in a pulse shape from the first NAND gate ND 2 . 
   The auto-refresh signal detecting unit  500  activates the auto-refresh detect signal osc_en_auto as a logic high level in response to the auto-refresh signal auto_ref. Herein, a logic state of the auto-refresh detect signal osc_en_auto is kept as a logic high level for a predetermined delay time, and the predetermined delay time is determined by the number of the plurality of inverters included in the first delay unit  502 . 
     FIG. 6  is a schematic circuit diagram showing the high voltage pumping control signal generating unit  200 . 
   As shown, the high voltage pumping control signal generating unit  200  includes a NOR gate NR 1 , a second inverter I 3 , a third inverter I 4 , a second NAND gate ND 3  and a second delay unit  202 . 
   The NOR gate NR 1  receives the voltage level detect signal osc_en_det and the auto-refresh detect signal osc_en_auto for performing a logic NOR operation to the voltage level detect signal osc_en_det and the auto-refresh detect signal osc_en_auto. The second inverter I 3  receives a resultant of the logic NOR operation from the NOR gate NR 1  to invert the resultant of the logic NOR operation. 
   The second NAND gate ND 3  receives output signals from the second inverter I 3  and the second delay unit  202 . Herein, the second delay unit  202  delays an output signal from the second NAND gate ND 3  and feeds-back the delayed signal to the second NAND gate ND 3  for buffering an output signal of the second inverter I 3 . 
   The third inverter I 4  receives an output signal from the second NAND gate ND 3  for inverting the output signal from the second NAND gate ND 3 , and thus to output the pumping control signal pump_ctr. 
   The high voltage pumping control signal generating unit  200  activates the pumping control signal pump_ctr when the auto-refresh detect signal osc_en_auto or the voltage level detect signal osc_en_det is activated so that the voltage level of the high voltage VPP can be raised. 
     FIG. 7  is a timing diagram showing an operation of the semiconductor memory device when the semiconductor memory device performs a data access operation according to an inputted command. 
   As shown, when the semiconductor memory device consumes the high voltage VPP for performing the data access operation in response to the row active signal row-act, the voltage level of the high voltage VPP is lowered than the average high voltage level avg_level. 
   Thereafter, the high voltage level detecting unit  100  activates the voltage level detect signal osc_en_det after detecting that the voltage level of the high voltage VPP is lowered than the average high voltage level avg_level. 
   Then, the high voltage pumping control signal generating unit  200  activates the pumping control signal pump_ctr in response to the voltage level detect signal osc_en_det. Therefore, the high voltage pumping unit  300  raises the voltage level of the high voltage VPP by performing the voltage pumping operation in response to the pumping control signal pump_ctr. Thereafter, a row precharge signal row_pre is activated. 
   Herein, since the auto-refresh signal auto_ref is not activated, the auto-refresh signal detecting unit  500  is not enabled. 
     FIG. 8  is a timing diagram showing an operation of the semiconductor memory device when the semiconductor memory device performs the auto-refresh operation. 
   As shown, the auto-refresh signal auto_ref is activated in response to the row active signal row_act. 
   Thereafter, the auto-refresh signal detecting unit  500  actives the auto-refresh detect signal osc_en_auto. Herein, the auto-refresh detect signal osc-en_auto is activated for a first predetermined activation time T 1 . Then, the high voltage pumping control signal generating unit  200  activates the pumping control signals pump_ctr. The first predetermined activation time T 1  is determined by the number of the plurality of inverters included in the first delay unit  502  of the auto-refresh signal detecting unit  500 . 
   Therefore, the high voltage pumping unit  300  raises the voltage level of the high voltage VPP by performing the voltage pumping operation in response to the pumping control signal pump_ctr. Thereafter, as the high voltage loading unit  400  consumes the high voltage VPP in order to perform operations which correspond to command signals such as a world line signal WL and bit line isolation signals BISH and BISL for performing the auto-refresh operation, the voltage level of the high voltage VPP starts to be lowered. However, since the voltage level of the high voltage VPP is raised before the auto-refresh operation is performed, the voltage level of the high voltage VPP is not lowered below the average high voltage level avg_level. 
     FIG. 9  is a timing diagram showing another operation of the semiconductor memory device when the semiconductor memory device performs the auto-refresh operation. 
   In this case, the auto-refresh signal detecting unit  500  actives the auto-refresh detect signal osc_en_auto, and the auto-refresh detect signal osc_en_auto is activated for a second predetermined activation time T 2 . Then, the high voltage pumping control signal generating unit  200  activates the pumping control signal pump_ctr. Like the first predetermined activation time T 1 , the second predetermined activation time T 2  is determined by the number of the plurality of inverters included in the first delay unit  502  of the auto-refresh signal detecting unit  500 . 
   However, the number of the plurality of inverters included in the first delay unit  502  for the operation shown in  FIG. 9  is smaller than that for the operation shown in  FIG. 8 . Therefore, the second predetermined activation time T 2  is shorter than the first predetermined activation time T 1 . 
   As shown in  FIG. 9 , the voltage level of the high voltage VPP is lowered than the average high voltage level avg_level while the semiconductor memory device consumes the high voltage VPP for performing the auto-refresh operation. 
   However, since the high voltage level detecting unit  100  activates the voltage level detect signal osc_en_det, the voltage level of the high voltage VPP is raised to the average high voltage level avg_level again. 
   Herein, although the voltage level of the high voltage VPP is lowered than the average high voltage level avg_level, the high voltage VPP is raised to the average high voltage level avg_level fast compared to that of the conventional high voltage generating device because the voltage pumping operation is performed prior to consumption of the high voltage VPP. 
   Therefore, the semiconductor memory device in accordance with the present invention can supply a stable high voltage by raising the voltage level of the high voltage VPP before consumption of the high voltage VPP for the auto-refresh operation. 
   The present application contains subject matter related to Korean patent application No. 2003-83324, filed in the Korean Patent Office on Nov. 22, 2003, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to the particular 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.