Abstract:
Ramping voltage circuits are described for augmenting or supplying a higher power-up slope upon initial power-up or a wake-up transition from a period of dormancy to a semiconductor memory device. Such ramping voltage circuits are responsive to a power-up signal, and are capable of increasing by at least two orders of magnitude the power-up slope, thereby enabling far quicker device turn-on. In one embodiment, a level shifter is used to ramp up the power-on voltage. In another embodiment, the internal voltage line is effectively shorted to an external voltage line via a power-up turned-on PMOS or depletion-type NMOS transistor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of this Invention  
           [0002]    This disclosure relates to a semiconductor memory device, and more particularly, to a semiconductor memory device having an internal supply voltage driver to provide internal supply voltage.  
           [0003]    As the integration density of semiconductor memory devices increases and the high power up speed is required, the structure of internal supply voltage generating means of a memory cell array is very important especially in hand-held systems. Namely, when the internal supply voltage rises with the external supply voltage, the internal supply voltage reaches a level where the memory device can operate in a stabilized state after the external supply voltage reaches the appropriate level. This difference in rising time of the voltage level causes various problems.  
           [0004]    For example, when a system accesses the semiconductor memory device, if the system accesses the memory device only according to the external supply voltage level, there is a possibility that the system uses the internal supply voltage that has not yet reached the minimum voltage level for operating the memory device. It means that the semiconductor memory device will incur errors.  
           [0005]    2. Description of Prior Art  
           [0006]    [0006]FIG. 1 is a block diagram of the conventional memory device. In this figure, the memory device will be considered as a flash memory device.  
           [0007]    The memory device comprises an internal circuit  60 , an Internal Voltage Converter (IVC)  500 , a standby IVC driver  200 , a power level detector  120 , a CE buffer  140  and a CMD buffer  160 . During the power-up period, the power level detector  120  generates a signal PDT with the external supply voltage. The signal PDT inputs to the internal circuits  60  and the CMD register  160  to reset the level in the memory device. The standby IVC driver  200  converts the external supply voltage to the internal supply voltage according to the level of reference voltage Vref. The standby IVC driver  200  always provides the internal voltage to the internal circuits after power up.  
           [0008]    In FIG. 1, the IVC  500  comprises an active IVC controller and an active IVC driver. The active IVC controller ( 550  in FIG. 3) is activated only when CE buffer  140  and CMD register  160  generate an enable and busy signal, respectively. Those of skill in the art will appreciate that a standby IVC driver  200  is used in the standby mode for reducing the power consumption and the active IVC driver ( 550 ) is used during periods of active device operation to supply a sufficiently high voltage quickly to the memory device even when power consumption is high.  
           [0009]    The circuit depicted in FIG. 2 is generally used in standby IVC driver  200 . In FIG. 2, during power up, the standby IVC driver  200  receives a reference voltage Vref and an external supply voltage Vext to generate the internal voltage Vint. In the standby IVC driver, no signals are input to the driver  200  except the reference voltage Vref. Vref itself does not comprise other signals. Vref is controlled only by external voltage Vext. Because the standby IVC driver  200  always operates during the period of active device operation, driver  200  must generate an internal supply voltage Vint according to the level of reference voltage Vref. During that time, the power-up slopes of Vext and Vint are different from one another, as shown in FIG. 4. If the internal supply voltage is supplied to the memory device according to the external supply voltage, whereby Vext goes to the saturational level Vext at t 1 , the internal supply voltage remains lower than the minimum operating voltage Vdet over the time range A. As a consequence, an error may occur in the memory device.  
           [0010]    Generally, the rise time of Vint for providing minimum operating voltage Vdet has taken approximately 6 μs. But recently, especially in hand-held systems, the IVC driver  200  is required to provide the internal supply voltage Vint to the memory device within 1 μs. As shown FIG. 3, because there is no power-up signal input to the active IVC controller  550 , the internal voltage in accordance with the prior art is provided only by the standby IVC driver during the power-up period.  
           [0011]    Accordingly, present invention provides an internal supply voltage far more quickly than the prior art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a block diagram of a conventional memory device.  
         [0013]    [0013]FIG. 2 illustrates a conventional standby IVC driver.  
         [0014]    [0014]FIG. 3 illustrates a conventional active IVC controller for producing an active IVC enable signal.  
         [0015]    [0015]FIG. 4 is a timing diagram corresponding to FIG. 2.  
         [0016]    [0016]FIG. 5 is a block diagram of a memory device according to the present invention.  
         [0017]    [0017]FIG. 6 illustrates a first embodiment of the present invention.  
         [0018]    [0018]FIG. 7 illustrates a power level detector.  
         [0019]    [0019]FIG. 8 is a timing diagram of FIG. 7.  
         [0020]    [0020]FIG. 9 illustrates an active IVC driver controller.  
         [0021]    [0021]FIG. 10 illustrates an active IVC driver.  
         [0022]    [0022]FIG. 11 illustrates another active IVC drivers.  
         [0023]    [0023]FIG. 12 illustrates a voltage regulator.  
         [0024]    [0024]FIG. 13 is a timing diagram corresponding to FIG. 6.  
         [0025]    [0025]FIG. 14 illustrates a second embodiment of present invention.  
         [0026]    [0026]FIG. 15 is the third embodiment of present invention.  
         [0027]    [0027]FIG. 16 illustrates a Vint and Vext short circuit.  
         [0028]    [0028]FIG. 17 is a timing diagram corresponding to FIGS. 14 and 15. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    Referring to FIG. 5, the memory device comprises a power level detector  120 , an Internal Voltage Converter (IVC)  600  and internal circuits  60 . The internal circuits  60  will be understood to be the same as those of FIG. 1. Upon power up, a power level detector  120  generates a power-up signal PDT. The signal PDT activates the IVC  600  to produce internal supply voltage Vint. The IVC  600  provides the required internal supply voltage Vint to internal circuits  60 .  
         [0030]    Power-up is used broadly herein to refer to any intended ramping up of power from a nominal zero volts to a nominal supply voltage, whether such occurs at initial power-up or start-up, for example, of a hand-held, flash memory-based device such as a digital camera or after initial start-up but after a dormant (or so-called sleep) period wherein the power supplied to the device&#39;s internal circuits has been either diminished (e.g. to a standby level) or removed.  
         [0031]    [0031]FIG. 6 is a block diagram illustrating a first embodiment of this invention. FIG. 6 comprises a power level detector  120 , a CE Buffer  140 , a CMD register  160 , a Voltage Regulator  400  and an IVC  600 . In accordance with the prior art, the active IVC controller  650  is activated only when the CE Buffer. 140  or the CMD register  160  is enabled. The CE Buffer  140  provides chip enable information and the CMD Register  160  provides read, program, and erase information. The power-up signal PDT of the power level detector  120  does not input to the IVC controller  650  but inputs instead to the CMD register  160  and internal circuits  60  only for resetting the memory device. In contrast to the prior art teachings by which no power up signal PDT inputs to the IVC controller  650 , in accordance with the present invention, the signal PDT inputs to the IVC controller  650  during the power up period.  
         [0032]    In other words, novel IVC controller  650  is activated whenever one of the three signals, the chip enable signal from CE buffer  140 , the chip busy signal from CMD register  160  or the power up signal from power level detector  120 , is active.  
         [0033]    The power level detector  120  of the present invention is shown in FIG. 7. There are many types of power level detectors. Although other power level detectors are contemplated as being within the spirit and scope of the invention, the featured power level detector  120  has a p-mos and an n-mos depletion transistor that are serially connected to each other, in accordance with the present invention. The gates of the two transistors are connected in common to ground. The source of the p-mos transistor MP 3  is connected to the external voltage Vext, and the drain thereof is connected to node N 1  and to the drain of the n-mos transistor MN 3 . An n-type well which is used for the bulk of the p-mos transistor MP 3  is connected to the external supply voltage Vext having high potential. The source of the n-mos transistor MN 3  is connected to ground. The n-mos transistor MN 3  connected between the node N 1  and ground is a depletion type and has a long channel, thus providing high resistance.  
         [0034]    As shown in FIG. 7 and  8 , the level of node Ni is ground level because of an n-mos depletion transistor MN 3 . When the external supply voltage Vext reaches to the threshold voltage Vth of p-mos transistor MP 3 , the p-mos transistor MP 3  turns on at t 1 . After time t 1 , the node N 1  ramps up from ground to the external supply voltage but does not reach the voltage Vext because of the n-mos depletion transistor MN 3 . At the same time, the power up signal PDT ramps up from ground to the voltage Vext and reaches the voltage Vext in a short time because n-mos transistor (not shown) of inverter INV 1  is turned off. When the gate-to-source voltage Vgs of n-mos and p-mos transistor (not shown) in the inverter INV 1  are the same, the power up signal PDT goes down toward ground level. In other words, when the node N 1  level reaches a certain trip-point level Va at t 2 , the PDT goes logical LOW level. In general, the PDT is logical HIGH level before t 2  and logical LOW level after t 2 . As a result, the power up period is finished after time t 2 .  
         [0035]    During the power-up period, the power-up signal PDT goes HIGH and inputs to the IVC controller. The IVC ( 600  in FIG. 6)—which comprises an active IVC Controller ( 650 ), active IVC drivers ( 300 ) and standby IVC driver ( 200 )—receives the power-up signal PDT from power level detector ( 120 ).  
         [0036]    As shown in FIGS. 5 and 9, the active IVC Controller  650  (see FIG. 9) receives the power-up signal PDT which is a logic HIGH. The active IVC controller  650  generates an active IVC enable signal AIVCen. The active IVC Controller  650  comprises control logic  800  (coupled to the internal supply voltage Vint) and a level shifter  850 . The control logic  800  includes a NOR gate  101  and an inverter  103 . The NOR gate  101  receives a power-up signal PDT, a chip enable signal ChipEnable and chip busy signal ChipBusy. According to this invention, because the power level detector ( 120  in FIG. 5) generates a power-up signal PDT at a logic HIGH, the output of the NOR gate  101  goes to a logic LOW. The level of the gate of the n-mos transistor  106  is a logic HIGH, which turns on the transistor  106  when the output of the inverter  103  goes HIGH. So the node N 4  goes LOW and turns on the p-mos transistor  107 . As a result, the external supply voltage Vext is provide to the node N 5 . Specifically, the output of the control logic  800  is shifted to the other level Vext, the same as the level of the active IVC enable signal AIVCen through the level shifter  850 .  
         [0037]    There are many types of level shifters  850 . In this invention, the level shifter uses an external voltage Vext as a voltage source. Namely, the active IVC enable signal AIVCen is raised to the level of Vext. Those of skill in the art will appreciate that, within the spirit and scope of the invention, other types may be used.  
         [0038]    When the active IVC enable signal AIVCen (which is the output of the active IVC controller  650 ) inputs to the active IVC Drivers ( 300  in FIG. 6), the drivers ( 300 ) generate an internal voltage Vint at node N 7 . A representative one of the active IVC drivers is shown in FIG. 10. There are many types of active IVC drivers. In this invention, two such driver types will be described. Those of skill in the art will appreciate that, within the spirit and scope of the invention, other types may be used.  
         [0039]    One of the active IVC drivers is shown in FIG. 10 and the other is shown in FIG. 11. The active IVC driver  310  of FIG. 10 operates as follows. The external supply voltage Vext is supplied to the node N 7  as an internal supply voltage Vint through the p-mos transistor P 1 . Similarly, the external supply voltage Vext is supplied to node N 7  in active IVC driver  320  of FIG. 11 as an internal supply voltage Vint through the n-mos transistor M 1 . Each of the two active IVC drivers ( 310  of FIG. 10, 320 of FIG. 11) receives and is controlled by the active IVC enable signal AIVCen. In both cases, the driver ( 310 ,  320 ) receives a reference voltage signal Vref as well as the active IVC enable signal AIVCen.  
         [0040]    The reference voltage signal is generated by a Voltage Regulator  400 , as illustrated in FIG. 12. Because any one of many known Voltage Regulators  400  can be used in this invention, it will not be further explained.  
         [0041]    Referring next to FIG. 13, it will be appreciated that the active IVC driver ( 310  of FIG. 10, 320 of FIG. 11) has a high charge driving capability compared with the standby IVC driver ( 200  in FIG. 6). Accordingly, when the internal supply voltage Vint passes the external supply voltage Vext by way of the active IVC driver, the slope of the internal supply voltage Vint is greater than that of the standby IVC driver ( 200 ). Moreover, The slope of the internal supply voltage Vint is nearly as great as that of the external supply voltage Vext.  
         [0042]    It is possible to use several active IVC drivers ( 300  in FIG. 6) to provide the internal supply voltage to the node N 7 . Preferably, plural active IVC drivers ( 300 ) are used to provide the internal supply voltage Vint. This increases the internal supply voltage ramping-up speed (slope) and minimizes the speed difference between the external supply voltage Vext and the internal supply voltage Vint. Thus, the internal supply voltage Vint can be provided to the internal circuits within the required shorter time in the newer and more demanding hand-held systems.  
         [0043]    Indeed, the invention makes it possible to achieve power-up voltage ramp slopes up to at least two orders of magnitude higher than has been conventionally possible, rendering memory device turn-on times far less than the required 1 μs maximum. This permits use of the invention in the most demanding digital camera applications, which may require as low as 1 microsecond power-up timing, rather than the several microsecond to millisecond ramp-up timing that conventional standby power techniques provided.  
         [0044]    In FIGS. 6, 7 and  13 , during the power-up operation, the power level detector ( 120  in FIGS. 6 and 7) generates the power-up signal PDT of a logic HIGH.  
         [0045]    According to the level of the power level detector, the IVC generates the internal supply voltage. The internal supply voltage Vint ramps up quickly, closely following the ramp of the external supply voltage Vext, until the internal supply voltage reaches the minimum operating voltage Vdet, as shown in FIG. 13.  
         [0046]    As a result, the internal supply voltage rapidly goes to the Vdet level. After the power level detector ( 120  of FIG. 7) generates a logic LOW and the level of the node Ni of FIG. 7 exceeds the Va level, the IVC driver ( 310  of FIG. 10, 320 of FIG. 11) stops providing the internal supply voltage Vint to the node N 7 . Thereafter, the internal supply voltage connected to the node N 7  is supplied only the external supply voltage Vext from the standby IVC driver. As shown in FIG. 13, after passing the time t 1  when the level of Vdet is reached, the slope of supplied voltage is equal to the slope of the internal supply voltage Vint from the standby IVC driver ( 200  of FIG. 6). Even though the slope of the internal supply voltage Vint after time t 1  follows that of the standby IVC driver, because the internal supply voltage Vint already has achieved the minimum operating voltage Vdet within the required time, the system operates properly and without errors.  
         [0047]    In contrast, the active IVC driver of the prior art operates only when the memory device receives the chip enable signal or chip busy signal (see FIG. 1). Moreover, the standby IVC Driver ( 200  of FIG. 1) provides only an internal voltage to the internal circuits during the power-up period. So, it is impossible to provide the internal supply voltage to the internal circuits within 1 μs, which is the required time in recent systems.  
         [0048]    [0048]FIG. 14 illustrates a second embodiment of the present invention.  
         [0049]    In this embodiment, the IVC  600  further comprises a Vint/Vext short circuit  130 . The power-up signal PDT of the power level detector  120  does not input to the active IVC controller  650  but it does input to the Vint/Vext short circuit  130 . The active IVC controller is activated by the CE Buffer  140  and CMD Register  160 , as in the prior art. But, in important contrast, the internal supply voltage Vint is supplied to the node N 7  by way of the Vint/Vext short circuit controlled by the power-up signal PDT. The Vint/Vext short circuit is shown in FIG. 16. As may be seen from FIG. 16, the power-up signal PowerUp (PDT) inputs to an inverter INV 2  to turn on p-mos transistor MP 4 , effectively shorting Vext to Vint. (During the power-up period, the power-up signal PowerUp (PDT) goes to a logic HIGH. The gate of the p-mos transistor goes to logic LOW via an inverter INV 2 . The p-mos transistor MP 4  turns on and the external supply voltage Vext is connected to the internal supply voltage Vint via the on transistor, effectively shorting Vext to Vint.).Within the spirit and scope of the invention, the p-mos transistor MP 4  may change to an n-mos transistor (depletion or enhancement type.)  
         [0050]    The beneficial result of electrically shorting the two voltages Vext and Vint is illustrated in FIG. 17. During the power up, the internal supply voltage Vint ramps up and precisely tracks the external supply voltage Vext until time t 1 . At that time, the internal supply voltage reaches the minimum operating voltage Vdet. After the power-up signal PDT goes to a logic LOW, as described above in connection with the first embodiment of invention, the slope of the internal supply voltage Vint tracks that of the standby IVC driver ( 200  of FIG. 14).  
         [0051]    As a result, it is possible to provide a quickly ramped-up internal supply voltage Vint within the system required time.  
         [0052]    [0052]FIG. 15 is a third embodiment of the present invention. In this figure, the power-up signal PDT of the power-up detector  120  inputs to the active WVC controller and Vext/Vint short circuit  130 . According as the power-up signal PDT concurrently inputs to the active IVC controller and Vext/Vint short circuit  130 , the internal supply voltage Vint generated from the external supply voltage Vext ramps up more rapidly. In this hybrid embodiment, active IVC controller  650  has three inputs, PowerUp , ChipEnable and ChipBusy, as shown in FIG. 9 and as described above.  
         [0053]    A person skilled in the art will be able to practice the present invention in view of the description present in this document, which is to be taken as a whole. Numerous details have been set forth in order to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail in order not to obscure unnecessarily the invention.  
         [0054]    While the invention has been disclosed in its preferred embodiments, the specific embodiments as disclosed and illustrated herein are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art in view of the present description that the invention may be modified in numerous ways. The inventor regards the subject matter of the invention to include all combinations and sub-combinations of the various elements, features, functions and/or properties disclosed herein.  
         [0055]    The following claims define certain combinations and sub-combinations, which are regarded as novel and non-obvious. Additional claims for other combinations and sub-combinations of features, functions, elements and/or properties may be presented in this or a related document.