Abstract:
A semiconductor memory device having a uniform bit line sensing margin time independent on an external voltage variation, includes: a memory cell coupled to a bit line and a word line; an amplifier for amplifying an electric potential of the bit line; a first control signal generator to which an external voltage is supplied for activating the word line; and a second control signal generator to which a core voltage is supplied for controlling an execution of the amplifier by receiving the first control signal.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a semiconductor memory device; and, more particularly, to a memory device and a method sensing bit line with a uniform sensing margin time regardless of variation of an external supply voltage. 
   DESCRIPTION OF RELATED ART 
   Generally, a memory device such as a dynamic random access memory has a bit line sense amplifier for amplifying a delicate electric potential difference between a pair of bit lines in order to execute a read operation or a write recovery operation. 
   After a bit line floating operation is performed that a bit line precharging operation is disabled, a word line is activated. Then, the bit line sense amplifier waits performing an amplification of an electric potential difference of a bit line pair until enough amount of electric potential difference is charged between a bit line pair in order to execute a stable sensing operation. Herein, an amount of time between the activation of the word line and the amplification of the electric potential difference of the bit line pair is called ‘sensing margin time’. 
     FIG. 1  is a circuit diagram showing a conventional bit line sense amplifier and a convention driving voltage generator. 
   Referring to  FIG. 1 , a memory cell  110  is coupled to a bit line and a sense amplifier  120  is coupled to a bit line pair BL and /BL. The sense amplifier  120  has a latch structure and amplifies an electric potential difference between the bit line pair BL and /BL. Driving voltages RTO and SB are generated from a driving voltage generator  130  and supplied to the sense amplifier  120 . 
   The supply voltage generator  130  includes a precharging unit  131 , a PMOS transistor  132  and an NMOS transistor  133 . 
   The precharging unit  131  precharges and equalizes a pair of driving voltage terminals by using a precharge voltage with responding to a precharge control signal bleq. The PMOS transistor  132  of the driving voltage is to perform a pull up operation of sources of PMOS transistors in the sense amplifier  120 , with a power supply voltage VDD level with responding to an enable signal rtoen. The NMOS transistor  133  is to perform a pull down operation of sources of NMOS transistors in the sense amplifier  120  to a ground voltage VSS level with responding to an enable signal sben. 
     FIG. 2  is a timing diagram showing a conventional bit line sensing operation in the conventional sense amplifier. A bit line sensing operation will be described. 
   As shown, as an active signal rasatv is activated with a logic high level and the bit line precharge signal bleq is inactivated with a logic low level, the bit line precharging unit is disabled and a bit line pair becomes a floating state. A word line WL of a memory cell selected by performing a row decoding operation is activated to a logic high level and enable signals rtoen and sben are activated to start an operation of the sense amplifier  120  after a predetermined sensing margin time. The sensing margin time is determined to have enough amount of electric potential difference between the bit line pair. Finally, the sense amplifier  120  is operated and the delicate electric potential difference of the bit line pair BL and /BL is amplified to a supply voltage and a ground voltage. 
     FIG. 3  is a block diagram showing control flows of a conventional word line and a bit line sense amplifier. 
   As shown in  FIG. 3 , an active signal generator  310  generates an active signal pxact by combining external inputs to a chip. The active signal pxact is enabled during an active operation and disabled during a precharge operation. 
   A word line timing controller  320  generates a control signal wlstd and a sensing timing controller  330  generates a control signal sest with responding to the active signal pxact. The control signal sest is a timing control signal for controlling timing of sense amplifier enable signals rtoen and sben. 
   A row address rowadd is decoded in a row decoder  340  with responding to the control signal wlstd and a word line selected by a sub word line driver  350  is activated. 
   A sense amplifier  360  generates enable signals rtoen and sben with responding to the control signal sest. A supply voltage generator  370  generates driving voltages RTO and SB with responding to the enable signals rtoen and sben and a bit line sense amplifier  380  amplifies data supplied to the bit line. The word line timing controller  320  and the sensing timing controller  330  are typical CMOS delay circuits and a predetermined amount of delay is set to a corresponding specification of the CMOS delay circuit. 
   It is broadly known that a constant core voltage Vcore generated in a chip is used for a core circuit unit and an external voltage Vext is used for peripheral circuits. That is, the external voltage Vext is supplied to the peripheral circuits of the active signal generator  310 , the word line timing controller  320 , the sensing timing controller  330 , the sense amplifier controller  360  and the supply voltage generator  370 . 
   However, the external voltage Vext varies with many reasons. It is a problem that the sensing margin time obtained from the delay circuit of the sensing timing controller  330  varies according to the external voltage Vext. 
   Therefore, in a modified conventional art, the core voltage Vcore is used as a supply voltage to a delay circuit of the sensing timing controller  330 . 
     FIG. 4  is a timing diagram showing control signals of a modified conventional art. 
   Referring to  FIG. 4 , the active signal pxact is enabled and with responding to the active signal pxact, a delay is given for an amount of a first delay generated by the word line timing controller  320  to which the external voltage Vext is supplied. Then, the control signal wlstd is enabled. 
   With responding to the active signal pxact, a delay is given for an amount of a second delay generated by the sensing timing controller  330  to which the core voltage Vcore is supplied. Then, the control signal sest is enabled. 
   However, the modified conventional art has a problem that variation of the external voltage Vext still largely affects the sensing margin time, which is the time between the activation of word line and the start of the bit line sense amplification. 
   The problem mentioned above is explained in details as follows. 
   The word line control signal wlstd largely varies according to the variation of the external voltage Vext because the word line control signal is generated by the delay circuit to which the external voltage Vext is supplied. 
   However, the control signal sest which controls the operation of the sense amplifier is constantly activated because the control signal sest is generated by the delay circuit to which the core voltage Vcore is supplied. 
     FIG. 5  is a timing diagram illustrating control signals of the convention art according to external voltages, e.g., 2V, 2.5V and 4V. 
   Referring to  FIG. 5 , the sensing margin time which is the time between the activation of the word line and the bit line amplification varies according to the variations of the external voltage. 
   SUMMARY OF THE INVENTION 
   Therefore, it is an object of the present invention to provide a memory device and a bit line sensing method having a uniform sensing margin time regardless of variations of an external supply voltage. 
   In accordance with one aspect of the present invention, there is provided a semiconductor memory device having a uniform bit line sensing margin time independent on an external voltage variation, including: a memory cell coupled to a bit line and a word line; an amplifier for amplifying an electric potential of the bit line; a first control signal generator to which an external voltage is supplied for activating the word line; and a second control signal generator to which a core voltage is supplied for controlling an execution of the amplifier by receiving the first control signal. 
   Further, in accordance with another aspect of the present invention, there is provided an operating method of a semiconductor memory device having a memory cell coupled to a word line and a bit line, including the steps of: a) generating a first control signal by supplying an external voltage in order to activate the word line; and b) generating a second control signal by supplying a core voltage in order to amplifying an electric potential of the bit line by receiving the first control signal. 
   Further, in accordance with still another aspect of the present invention, there is provided a semiconductor memory device, including: a memory cell coupled to a bit line and a word line; an amplifier unit which is coupled to the bit line for amplifying an electric potential of the bit line; an active signal generating unit to which an external voltage is supplied for generating an active signal that is activated during an active operation and inactivated during a precharge operation; a word line timing controller to which the external voltage is supplied for generating a first control signal in order to activate a word line by receiving the active signal; 
   a row decoder/driver for activating a chosen word line with responding to the first control signal; a sensing timing controller to which a core voltage is supplied for generating a second control signal in order to control the amplifier unit by receiving the first control signal; and a sense amplifier controller for generating an enable signal of the amplifier unit with responding to the second control signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a circuit diagram showing a conventional bit line sense amplifier and a convention driving voltage generator; 
       FIG. 2  is a timing diagram showing a conventional bit line sensing operation in the conventional sense amplifier; 
       FIG. 3  is a block diagram showing control flows of a conventional word line and a bit line sense amplifier; 
       FIG. 4  is a timing diagram showing control signals of a modified conventional art; 
       FIG. 5  is a timing diagram illustrating control signals of the convention art according to external voltages, e.g., 2V, 2.5V and 4V; 
       FIG. 6  is a block diagram showing control flows of a word line and a bit line sense amplifier of a synchronous dynamic random access memory (SDRAM) in accordance with a preferred embodiment of the present invention; 
       FIG. 7  is a circuit diagram illustrating the active signal generating unit and the word line timing controller in accordance with the present invention; 
       FIG. 8  is a block diagram showing a sensing timing controller for performing a level-shifting operation in accordance with the present invention; 
       FIG. 9  is a circuit diagram illustrating the sensing timing controller having the delay circuit and the level-shifter in accordance with the present invention; 
       FIG. 10  is a timing diagram showing control signals for a bit line sensing operation in accordance with the present invention; and 
       FIG. 11  is a timing diagram showing control signals in accordance with the present invention when an external voltage is varied to 2V, 2.5V and 4V. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. 
     FIG. 6  is a block diagram showing control flows of a word line and a bit line sense amplifier of a synchronous dynamic random access memory (SDRAM) in accordance with a preferred embodiment of the present invention. 
   Referring to  FIG. 6 , a memory cell MC including one transistor and one capacitor is coupled to a word line WL and a bit line BL. A bit line sense amplifier  680  is coupled to a bit line pair BL and /BL in order to amplify an electric potential of a bit line. An external voltage Vext is supplied to a driving voltage generator  670  and driving voltages RTO and SB are generated. The driving voltages RTO and SB are supplied to the bit line sense amplifier  680 . 
   The memory device of the present invention includes an active signal generator  610 , a word line timing controller  620 , a sensing timing controller  630 , a row decoder  640 , a sub-word line driver  650 , a sense amplifier controller  660  and a driving voltage generator  670 . 
   An active signal pxact is generated from the active signal generator  610  to which the external voltage is supplied. The active signal pxact is enabled at an active operation and disabled at a precharge operation. If the word line timing controller  620  receives the active signal pxact, a word line control signal wlstd is generated from the word line timing controller  620  to which the external voltage is supplied. The row decoder  640  and the sub-word line driver  650  activate a chosen word line WL with responding to the word line control signal wlstd. A control signal wlstd_ses is outputted from the word line timing controller  620  and inputted to the sensing timing controller  630 . The control signals wlstd and wlstd_ses are outputted from the word line timing controller  620 . 
   The sensing timing controller  630  receives the control signal wlstd_ses and generates a control signal sest in order to control the sense amplifier controller  660 . The sense amplifier controller  660  generates enable signals rtoen and sben with responding to the control signal sest. 
     FIG. 7  is a circuit diagram illustrating the active signal generating unit  610  and the word line timing controller  620  in accordance with the present invention. 
   As shown, the active signal generating unit  610  receives a word line clear signal wlc, a word line enable signal rast 10  and a power-up signal, and generates the active signal pxact. The word line clear signal wlc is to disable the word line in a precharge operation and the word line enable signal rast 10  is to enable the word line, wherein the word line enable signal rast 10  becomes a logic high level in an active mode. The power up signal pwrup is to remove a floating node in the active signal generating unit  610 . 
   The word line timing controller  620  receives the active signal from the active signal generating unit  610  and generates the control signals wlstd_ses and wlstd. The word line timing controller  620  is a delay circuit for notifying an activation of the word line. 
     FIG. 8  is a block diagram showing a sensing timing controller  630  for performing a level-shifting operation in accordance with the present invention. 
   Referring to  FIG. 8 , the sensing timing controller  630  includes a delay circuit  632  to which the core voltage Vcore is supplied and a level-shifter  634  to which the external voltage Vext is supplied. The delay circuit  632  receives the control signal wlstd_ses and performs a delay operation according to the sensing margin time. Then, the level-shifter  634  performs a level-shifting operation of the signal received from the delay circuit  632  to thereby generate the control signal sest 30 . The power up signal pwrup applied to the level-shifter  634  is to remove a floating node. 
   The level-shifter  634  can be implemented in an input unit of the sense amplifier controller  660  or in a circuit block between the sensing timing controller  630  and the sense amplifier controller  660 . 
     FIG. 9  is a circuit diagram illustrating the sensing timing controller  630  having the delay circuit  632  and the level-shifter  634  in accordance with the present invention. 
   As shown, the sensing timing controller  630  receives the control signal wlstd_ses from the word line timing controller  620  and generates the control signal sest 30 . The delay circuit  632  is configured with a plurality of inverters, resistors and transistors coupled in series each other. 
   The control signal sest is generated by delaying the active signal pxact in the conventional art in  FIG. 3 . However, the control signal sest 30  is generated by delaying the control signal wlstd_ses in the present invention. Also, the control signal wlstd_ses is generated by the word line timing controller  620  to which the external voltage is supplied and the control signal sest 30  is generated by the sensing timing controller  630  to which the core voltage is supplied. 
     FIG. 10  is a timing diagram showing control signals for a bit line sensing operation in accordance with the present invention. 
   Referring to  FIG. 10 , the control signals wlstd and wlstd_ses are generated by the word line timing controller  620  to which the external voltage is supplied and the control signal wlstd_ses is generated by the sensing timing controller  630  to which the core voltage is supplied. 
   Because the sensing timing controller  630  uses the core voltage and the control signal sest 30  outputted from the sensing timing controller  630  is inputted to the sense amplifier controller  660 , it is preferred that the control signal sest 30  is level-shifted corresponding to a power level of the external voltage through a level shifter  700  in the sensing timing controller  630 . 
     FIG. 11  is a timing diagram showing control signals in accordance with the present invention when an external voltage is varied to 2V, 2.5V and 4V. 
   Referring to  FIG. 11 , the sensing margin times are uniform although the external voltage is varied to 2V, 2.5V and 4V. That is, a stable bit line sensing operation is performed because the bit line amplification is started if data are supplied to the cell for a uniform duration after the word line is activated. 
   The present invention can provide a stable data sensing operation by keeping a uniform sensing margin time regardless of the variation of the external supply voltage. 
   While the present invention has been shown and described with respect to the particular embodiments, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.