Abstract:
A nonvolatile memory device comprises a voltage detector for generating a detection signal when the external power supply voltage is higher than a set voltage and memory chips, each comprising a memory cell unit and a content-addressable memory (CAM) cell unit and performing internal operations in response to the detection signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Priority to Korean patent application number 10-2009-0127960 filed on Dec. 21, 2009, the entire disclosure of which is incorporated by reference herein, is claimed. 
       BACKGROUND 
       [0002]    Exemplary embodiments relate to a nonvolatile memory device and a method of operating the same and, more particularly, to a nonvolatile memory device and a method of operating the same, which are capable of performing a stable operation by reading data from a content-addressable memory (hereinafter referred to as a ‘CAM’) cell after a power source stably rises up to a certain level during a power-on operation. 
         [0003]    With the recent increasing demand for mobile products, such as camcorders, digital cameras, portable phones, and MPEG-1 Layer3 (MP3) players, further improvements in performance of nonvolatile memory devices for the operation of the mobile products are desired. 
         [0004]    Designs of a nonvolatile memory device for a mobile product are determined based on the operating characteristics of a corresponding product, and the nonvolatile memory device operates in response to an application program. 
         [0005]    With the development of new technologies, the number of application programs for a mobile product increases. Accordingly, an efficient way for handling various options for a nonvolatile memory device is desired. 
         [0006]    A nonvolatile memory device may store option information in a fuse. However, because a fuse is relatively large and there is a need for high integration nonvolatile memory devices, a recent trend in nonvolatile memory devices is to store option information in a CAM cell. 
         [0007]    The nonvolatile memory device storing the option information in the CAM cell requires an operation of loading data stored in the CAM cell during a reset operation and storing the loaded data in an internal register after a power-on operation. The operation of loading the data of the CAM cell is performed when a voltage level is stabilized to some extent after supplying a power source. 
         [0008]    A typical nonvolatile memory device, when being supplied with external power source, generates a power-on signal in response to a level of the external power source and starts an operation of reading data stored in a CAM cell in response to the power-on signal. However, the power-on signal may have a varying voltage level during a power-on period since the power source is ramped up to a stable voltage with a slope. Here, if the rate with which the voltage of the power source rises is low, current consumption in reading the data stored in the CAM cell increases. Accordingly, a drop in the supplied power may occur, and the read operation may fail. 
       BRIEF SUMMARY 
       [0009]    Exemplary embodiments relate to a nonvolatile memory device and a method of operating the same, which are capable of stably reading data stored in a CAM cell by performing the read operation after an external power supply voltage rises to a certain voltage. 
         [0010]    A nonvolatile memory device according to an aspect of this disclosure comprises a voltage detector for generating a detection signal when the external power supply voltage is higher than a set voltage and memory chips, each comprising a memory cell unit and a content-addressable memory (CAM) cell unit and performing internal operations in response to the detection signal. 
         [0011]    Each of the memory chips comprises the CAM cell unit configured to store CAM cell data, a peripheral circuit unit coupled to the CAM cell unit and configured to read the CAM cell data in response to a read command, a control unit configured to generate the read command in response to the detection signal, and a register unit configured to temporarily store the read CAM cell data. 
         [0012]    A nonvolatile memory device according to another aspect of this disclosure comprises a controller configured to generate an internal command in response to an external command and memory chips operated in response to the internal command. The controller outputs a command for controlling operations of the memory chips when an external power supply voltage is higher than a set voltage. 
         [0013]    A nonvolatile memory device according to yet another aspect of this disclosure comprises memory chips, each comprising a memory cell unit and a CAM cell unit and performing internal operations in response to an internal command, a controller for generating the internal command in response to an external command, a voltage detector for comparing an external power supply voltage and a set voltage and outputting a detection signal based on a result of the comparison, and a transfer unit for transferring the internal command to the memory chips in response to the detection signal. 
         [0014]    A method of operating a nonvolatile memory device according to still yet another aspect of this disclosure comprises gradually increasing an external power supply voltage, detecting the external power supply voltage, and generating a read command when the external power supply voltage is higher than a set voltage, reading CAM cell data in response to a read command and storing the read CAM cell data, and performing program, read, and erase operations using the stored CAM cell data. 
         [0015]    A method of operating a nonvolatile memory device according to still yet another aspect of this disclosure comprises gradually increasing an external power supply voltage, inputting an external command to a controller to thereby generate an internal command, when the external power supply voltage is higher than a set voltage, transferring the internal command to memory chips, reading CAM cell data stored in the memory chips in response to the internal command, and performing program, read, and erase operations using the CAM cell data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a diagram showing the constituents of a nonvolatile memory device according to an embodiment of this disclosure; 
           [0017]      FIG. 2  is a voltage graph illustrating the operation of a voltage detector according to an embodiment of this disclosure; 
           [0018]      FIG. 3  is a flowchart illustrating the operation of the nonvolatile memory device according to an embodiment of this disclosure; and 
           [0019]      FIG. 4  is a diagram showing the construction of a nonvolatile memory device according to another embodiment of this disclosure. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    Hereinafter, exemplary embodiments of this disclosure will be described in detail with reference to the accompanying drawings. The figures are provided to facilitate understanding of the exemplary embodiments of the disclosure by those of ordinary skill in the art. 
         [0021]      FIG. 1  is a diagram illustrating the constituents of a nonvolatile memory device according to an embodiment of this disclosure. 
         [0022]    Referring to  FIG. 1 , the nonvolatile memory device  100  according to the embodiment of this disclosure includes one or more memory chips  110  and a controller  120 . 
         [0023]    Each of the memory chips  110  includes a CAM cell unit  111 , a common memory unit  112 , a peripheral circuit unit  113 , a register unit  114 , and a control unit  115 . The CAM cell unit  111  stores option information for operating the memory chip  110 . The peripheral circuit unit  113  includes a circuit for loading data stored in the CAM cell unit  111  and storing the loaded data at circuits such as a memory cell array and a page buffer which are typically included in the memory chip  110 . 
         [0024]    The register unit  114  temporarily stores option information stored in and retrieved from the CAM cell unit  111  during the operation of the memory chip  110 . The control unit  115  performs a control operation in response to a command received from the controller  120  such that option information stored in and received from the CAM cell unit  111  is loaded and stored in the register unit  114 . 
         [0025]    The controller  120  includes a voltage detector  121 . 
         [0026]    The controller  120  enables one or more memory chips  110  and outputs operation commands to the memory chips  110 . Further, the controller  120  generates the command such that option information stored in and received from the CAM cell unit  111  is loaded and stored in the register unit  114 . 
         [0027]    The voltage detector  121  detects an external power supply voltage Vext and, when the power supply voltage Vext is higher than a certain voltage, outputs a detection signal V_det. The control unit  115  of the memory chip  110  loads option information stored in and received from the CAM cell unit  111  in response to the detection signal V_det and stores the loaded option information in the register unit  114 . 
         [0028]      FIG. 2  is a voltage graph illustrating the operation of the voltage detector  121  according to an embodiment of this disclosure. 
         [0029]    Referring to  FIG. 2 , when the external power supply voltage Vext rises during a power-on period, the voltage detector  121  outputs the detection signal V_det when the external power supply voltage Vext is higher than a set voltage (indicated by ‘A’). Here, the set voltage according to an example may be set to be equal to or greater than a voltage of the power source at which data stored in the CAM cell unit  111  can be read more stably. 
         [0030]      FIG. 3  is a flowchart illustrating the operation of the nonvolatile memory device according to an embodiment of this disclosure. 
         [0031]    The operation of the nonvolatile memory device is described below with reference to  FIGS. 1 to 3 . 
         [0032]    First, the external power supply voltage Vext which gradually rises is supplied to the nonvolatile memory device  100  and powers on the nonvolatile memory device  100  at step S 110 . 
         [0033]    When the external power supply voltage Vext is supplied, the controller  120  is reset from a standby state at step S 120 . 
         [0034]    The voltage detector  121  of the controller  120  detects the external power supply voltage Vext at step S 130 . The voltage detector  121  compares the detected external power supply voltage Vext and a set voltage and outputs the detection signal V_det based on a result of the comparison at step S 140 . If, as a result of the comparison, the external power supply voltage Vext is determined to be equal to or less than the set voltage, the voltage detector  121  does not output the detection signal V_det. If, as a result of the comparison, the external power supply voltage Vext is determined to be higher than the set voltage, the voltage detector  121  outputs the detection signal V_det. 
         [0035]    Since the external power supply voltage Vext gradually rises, the voltage detector  121  eventually outputs the detection signal V_det when the external power supply voltage Vext becomes higher than the set voltage. 
         [0036]    The control unit  115  of the memory chip  110  inputs a read command for reading data stored in and retrieved from a CAM cell of the CAM cell unit  111  to the peripheral circuit unit  113  in response to the detection signal V_det at step S 150 . 
         [0037]    The peripheral circuit unit  113  reads the data stored in the CAM cell of the CAM cell unit  111  and stores the read data in the register unit  114  via the control unit  115  at step S 160 . 
         [0038]    Next, the nonvolatile memory device performs operations (e.g., program, erase, and read operations) based on the data stored in the register unit  114  at step S 170 . 
         [0039]    As described above, according to the embodiments of this disclosure, data stored in a CAM cell of the CAM cell unit  111  are read when the external power supply voltage Vext is higher than a set voltage, and then stored in the register unit  114 . Accordingly, CAM cell data can be stably read, and so reliability of the operations of the nonvolatile memory device can be improved. 
         [0040]      FIG. 4  is a diagram showing the construction of a nonvolatile memory device according to another embodiment of this disclosure. 
         [0041]    Referring to  FIG. 4 , a nonvolatile memory device according to another embodiment of this disclosure includes one or more memory chips  210 , a controller  220 , a transfer unit  230 , and a voltage detector  240 . 
         [0042]    Each of the memory chips  210  includes a CAM cell unit  211 , a common memory unit  212 , a peripheral circuit unit  213 , a register unit  214 , and a control unit  215 . The CAM cell unit  211  stores option information for operating the memory chip  210 . The peripheral circuit unit  213  includes a circuit for loading data stored in the CAM cell unit  211  and storing the loaded data into circuits such as a memory cell array and a page buffer which are typically included in the memory chip  210 . 
         [0043]    The register unit  214  temporarily stores option information stored in the CAM cell unit  211  during the operation of the memory chip  210 . The control unit  215  loads information stored in the CAM cell unit  211  in response to an internal command generated by the controller  220  and received via a transfer unit  230 , and stores the loaded information in the register unit  214 . 
         [0044]    The controller  220  generates the internal command for operating the one or more memory chips  110  in response to an external command. 
         [0045]    The transfer unit  230  transfers the internal command generated by the controller  220  to the memory chips  210  in response to a detection signal V_det generated by the voltage detector  240 . 
         [0046]    The voltage detector  240  detects an external power supply voltage Vext. When the external power supply voltage is higher than a certain voltage, the voltage detector  240  outputs the detection signal V_det. 
         [0047]    The operation of the nonvolatile memory device according to another embodiment of this disclosure shown in  FIG. 4  is described below. 
         [0048]    First, the external power supply voltage Vext which gradually rises is supplied to the nonvolatile memory device and powers on the nonvolatile memory device. When the external power supply voltage Vext is supplied, the controller  220  is reset from a standby state. In response to the external command, the controller  220  generates the internal command for operating the memory chips  210 . 
         [0049]    The voltage detector  240  determines whether the external power supply voltage Vext is higher than a certain voltage and generates the detection signal V_det based on a result of the determination. For example, if the external power supply voltage Vext is equal to or less than the set voltage, the voltage detector  240  does not output the detection signal V_det. If the external power supply voltage Vext is determined to be higher than the set voltage, the voltage detector  240  outputs the detection signal V_det. 
         [0050]    If the detection signal outputted by the voltage detector  240  is deactivated, the transfer unit  230  is disabled from transferring the internal command generated by the controller  220  to the memory chips  210 . If the external power supply voltage Vext is higher than the set voltage, the voltage detector  240  outputs the detection signal V_det. The transfer unit  230  is enabled to transfer the internal command to the memory chips  210  in response to the detection signal. 
         [0051]    The control unit  215  of the memory chips  210  inputs a read command for reading data, where the read command is stored in a CAM cell of the CAM cell unit  211 , to the peripheral circuit unit  213  in response to the internal command received via the transfer unit  230 . 
         [0052]    The peripheral circuit unit  213  reads the data stored in the CAM cell of the CAM cell unit  211  and stores the read data in the register unit  214  via the control unit  215 . Next, the nonvolatile memory device performs operations (e.g., program, erase, and read operations) using the data stored in the register unit  214 . 
         [0053]    As described above, according to an exemplary embodiment, the internal command is sent to the control unit  215  of the memory chip  210  when the external power supply voltage is higher than a set voltage. Data stored in a CAM cell of the CAM cell unit  211  are read and stored in the register unit  214 . Accordingly, data stored in a CAM cell can be read more stably, and so reliability of the operations of the nonvolatile memory device can be improved. 
         [0054]    As described above, according to exemplary embodiments of this disclosure, an external power supply voltage higher than a certain voltage is detected, and the detection signal is generated in response thereto. The memory chip including the CAM cell unit reads data stored in the CAM cell unit in response to the detection signal. Accordingly, data stored in a CAM cell can be read more stably.