Abstract:
The present invention relates to a pumping circuit. The pumping circuit comprises a first pumping block for pumping an input voltage, a first latch for latching the output of the first pumping block, a second pumping block for pumping the output of the first pumping block according to a control signal, a second latch for latching the output of the second pumping block, and a switching circuit for selectively outputting the outputs of the first and second latches according to the control signal. Thus, a program voltage and a program verify voltage of different levels are pumped. The ripple and active current can be reduced and the program efficiency can be increased.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to a pumping circuit, and more particularly to, a pumping circuit wherein a program voltage and a program verify voltage of different levels are pumped using a program verify signal, thus reducing ripples and active current.  
           [0003]    2. Description of the Prior Art  
           [0004]    In the flash memory device, program, erase and read operations are performed according to the voltage applied to the word line of a selected cell, drain/source, and the substrate. In order to perform the program operation of the flash memory cell, it is required that a pumping voltage of about 9V higher a little than the power supply voltage be generated using a pumping circuit and a regulation circuit and the generated voltage be then applied to the word line of the selected cell.          .  
           [0005]    [0005]FIG. 1A shows a common pumping circuit that is used to program the flash memory cell. The construction of the pumping circuit in FIG. 1A will be below described.  
           [0006]    A first NMOS transistor N 11  driven by an enable signal (EN) is connected between the power supply terminal VDD and a first node Q 11 . A second NMOS transistor N 12  is diode-connected between the first node Q 11  and a second node Q 12 . A third NMOS transistor N 13  is diode-connected between the second node Q 12  and a third node Q 13 . A fourth NMOS transistor N 14  is diode-connected between the third node Q 13  and a fourth node Q 14 . A fifth NMOS transistor N 15  is diode-connected between the fourth node Q 14  and an output terminal VPPI. Further, the first˜fifth capacitors C 11 ˜C 15  that are charged according to first and second clock signals (CLK 1  and CLK 2 ) are connected to the nodes Q 11 ˜Q 14  and the output terminal VPPI, respectively. In other words, the first, third and fifth capacitors C 11 , C 13  and C 15  that are charged according to the first clock signal (CLK 1 ) are connected to the first node Q 11 , the third node Q 13  and output terminal VPPI, respectively. Also, the second and fourth capacitors C 12  and C 14  that are charged according to the second clock signal (CLK 2 ) are connected to the second and fourth nodes Q 12  and Q 14 , respectively.  
           [0007]    A method of driving the pumping circuit constructed above will be described by reference to the operating waveform shown in FIG. 1B.  
           [0008]    If the enable signal (EN) is applied as a HIGH state, the first NMOS transistor N 11  is turned on. Thus, the power supply voltage (VDD) is applied and the first˜fifth capacitors C 11 ˜C 15  are charged according to the first and second clock signals (CLK 1  and CLK 2 ) having opposite phases, respectively, so that the voltage of the respective node is raised. In other words, the first, third and fifth capacitors C 11 , C 13  and C 15  are charged according to the first clock signal (CLK 1 ), so that the first and third nodes Q 11  and Q 13  and the output terminal VPPI are raised to a given voltage. Further, the second and fourth capacitors C 12  and C 14  are also charged according to the second clock signal (CLK 2 ), so that the second and fourth nodes Q 12  and Q 14  are raised to a given voltage. The voltage of the node raised such is transferred to a next stage through the second˜fifth NMOS transistors N 12 ˜N 15  that are diode-connected. Finally, the output terminal VPPI keeps a given voltage, which is determined by the power supply voltage (VDD) and the number and capacity of the capacitor.  
           [0009]    However, in order to program the flash memory cell, the program verify operation is performed to very whether the selected cell is programmed. The program operation is again performed depending on the result of the verification. The program and program verify operations are repeatedly performed by a set times. At this time, in order to perform the program verify operation, it is required to apply the program verify voltage of about 6V to the word line of the cell. The program verify voltage is one generated by a regulation circuit that changes a regulation level of the pumping voltage of about 9V generated in the pumping circuit. Therefore, as the pumping voltage must be regulated as the program verify level using the pumping circuit for generating the program voltage, many ripples may occur and the active current is also increased.  
           [0010]    [0010]FIG. 2 is a graph illustrating the ripples generating when the program verify voltage is regulated using the pumping circuit for generating the program voltage. The ripples in this program verify operation may give rise to confusion in determining whether the program operation of the cell is successful or failed. If the worst, an erroneous operation determining that the failed cell is successful as a result of the program verify operation may be generated.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention is contrived to solve the above problems and an object of the present invention is to provide a pumping circuit capable of reducing ripple and active currents in such a way that the number of a pumping stage and a capacitor are differentiated to generate different pumping voltages in program and program verify operations.  
           [0012]    Another object of the present invention is to provide a pumping circuit capable of reducing the ripple and active current by generating a program voltage and a program verify voltage using a program verify signal.  
           [0013]    In order to accomplish the above object, the pumping circuit according to the present invention is characterized in that it comprises a first pumping block for pumping an input voltage, a first latch for latching a first output of the first pumping block, a second pumping block for pumping the first output of the first pumping block, a second latch for latching a second output of the second pumping block; and a switching circuit for selectively outputting the outputs of the first and second latches according to the control signal.  
           [0014]    Further, the pumping circuit of the present invention is characterized in that it comprises a first pumping block including a plurality of diodes which are connected in series from each other through the respective connection node and a plurality of capacitors connected to the respective connection node between the diodes, respectively, wherein the plurality of the capacitors are charged according to a plurality of clock signals having opposite phases and pump an input voltage to generate a program verify voltage, a first latch for latching the program verify voltage from the first pumping block, a second pumping block including a plurality of diodes which are connected in series from each other through the respective connection node and a plurality of capacitors connected to the respective connection node between the diodes, respectively, wherein the plurality of the capacitors are charged according to a plurality of clock signals having opposite phases that are generated by an inverted signal of a program verify signal and pump the output of the first pumping block to generate a program voltage, a second latch for latching the program voltage from the second pumping block, and a switching circuit for selectively outputting the outputs of the first and second latches according to the inverted signal of the program verify signal.  
           [0015]    Meanwhile, the pumping circuit according to the present invention is characterized in that it comprises first and second clock generators for generating first and second clock signals having opposite phases, a third clock generator for logically combining the first clock signal and an inverted signal of a program verify signal to generate a third clock signal, a fourth clock generator for logically combining the second clock signal and the inverted signal of the program verify signal to generate a fourth clock signal, a plurality of diodes connected between respective nodes between an input node and an output node, for transferring the voltage of a previous node to a next node, a plurality of capacitors connected between the plurality of the diodes which are connected in series from each other through the respective connection node, respectively, and charged according to the first through fourth clock signals to raise the voltage of each of the nodes, a first latch for latching the voltage of a given node, wherein the node keeps a voltage that is raised to a program verify voltage by the capacitor charged according to the first and second clock signals, a second latch for latching the voltage of the output node, wherein that output node keeps a voltage that is raised to a program voltage by the capacitor charged according to the first through fourth clock signals, and a switching circuit for selectively outputting the voltages latched in the first and second latches according to an inverted signal of the program verify signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein:  
         [0017]    [0017]FIG. 1A and FIG. 1B illustrate a common pumping circuit and an operating waveform of the pumping circuit, respectively;  
         [0018]    [0018]FIG. 2 is a graph illustrating a ripple generated when a regulated pumping voltage of the common pumping circuit regulated is used for the program verify operation;  
         [0019]    [0019]FIG. 3 shows a pumping circuit according to a preferred embodiment of the present invention;  
         [0020]    [0020]FIG. 4A and FIG. 4B show clock generators for generating third and fourth clock signals in the pumping circuit according to the present invention;  
         [0021]    [0021]FIG. 5 illustrates an operating waveform of the pumping circuit according to the present invention;  
         [0022]    [0022]FIG. 6 shows the switching circuit in the pumping circuit according to the present invention; and  
         [0023]    [0023]FIG. 7 is a graph illustrating a result of simulating the pumping circuit according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    The present invention will be described in detail by way of a preferred embodiment with reference to accompanying drawings, in which like reference numerals are used to identify the same or similar parts.  
         [0025]    [0025]FIG. 3 shows a pumping circuit according to a preferred embodiment of the present invention. The construction of the pumping circuit according to the present invention will be below described by reference to FIG. 3.  
         [0026]    A first NMOS transistor N 21  driven by an enable signal (EN) is connected between the power supply terminal VDD and a first node Q 21 . A second NMOS transistor N 12  is diode-connected between the first node Q 21  and a second node Q 22 . A third NMOS transistor N 23  is diode-connected between the second node Q 22  and a third node Q 23 . A fourth NMOS transistor N 24  is diode-connected between the third node Q 23  and a fourth node Q 24 . A fifth NMOS transistor N 25  is diode-connected between the fourth node Q 24  and a fifth node Q 25 . Also, first and third capacitors C 21  and C 23  charged according to a first clock signal (CLK 1 ) from the first clock generator are connected to the first node Q 21  and the third node Q 23 , respectively. A second capacitor C 22  charged according to a second clock signal (CLK 2 ) from a second clock generator is connected to the second node Q 22 . Further, a fourth capacitor C 24  charged according to a third clock signal (CLK 3 ) from a third clock generator is connected to the fourth node Q 24 , as shown in FIG. 4A. A fifth capacitor C 25  charged according to by a fourth clock signal (CLK 4 ) from a fourth clock generator is connected to the fifth node Q 25 , as shown in FIG. 4B.  
         [0027]    At this time, the third clock generator comprises a first NAND gate  31  for logically combining the first clock signal (CLK 1 ) and a verify bar signal (VERIFY_b) being an inverted signal of a verify signal, and a first inverter I 31  for inverting the output of the first NAND gate  31 , as shown in FIG. 4A. Also, the fourth clock generator comprises a second NAND gate  32  for logically combining the second clock signal (CLK 2 ) and the verify bar signal (VERIFY_b) being the inverted signal of the verify signal, and a second inverter I 32  for inverting the output of the second NAND gate  32 , as shown in FIG. 4B. When the verify bar signal (VERIFY_b) is applied as a LOW state, the voltage of the third node Q 23  is latched in a first high-voltage latch  21 , depending on the program verify operation, and is then outputted through a switching circuit  21 . Also, when the verify bar signal (VERIFY_b) is applied as a HIGH state, the voltage of the fifth node Q 25  is latched in a second high-voltage latch  22 , depending on the program operation, and is then outputted through a switching circuit  23 .  
         [0028]    A method of driving the pumping circuit constructed above will be below described by reference to an operating waveform shown in FIG. 5.  
         [0029]    First, an operation in a case where the program verify voltage is pumped when the enable signal (EN) is applied as the HIGH state and the verify bar signal (VERIFY_b) is applied as the LOW state will be described.  
         [0030]    If the enable signal (EN) is applied as the HIGH state, the first NMOS transistor N 21  is turned and the power supply voltage (VDD) is thus supplied. Also, the first˜third capacitors C 21 ˜C 23  are charged according to the first and second clock signals (CLK 1  and CLK 2 ) having opposite phases, respective, so that the voltages of the first˜third nodes Q 21 ˜Q 23  are raised.  
         [0031]    Meanwhile, as the verify bar signal (VERIFY_b) is applied as the LOW state, the third clock signal (CLK 3 ) and the fourth clock signal (CLK 4 ) are applied as the LOW state, by the NAND gates  31  and  32  for logically combining the verify bar signal (VERIFY_b) and the first and second clock signals (CLK 1  and CLK 2 ) and the inverters I 31  and I 32  for inverting the verify bar signal (VERIFY_b) and the first and second clock signals (CLK 1  and CLK 2 ), as shown in FIG. 4A and FIG. 4B. Therefore, the fourth and fifth capacitors C 24  and C 25  are not charged and do not change the voltages of the fourth and fifth nodes Q 24  and Q 25 . The voltage of the node that is raised to a given level by the first˜third capacitors C 21 ˜C 23  is transferred to a next node through the second and third NMOS transistors N 22  and N 23  that are diode-connected. The voltage of the third node Q 23  is latched in the first high-voltage latch  21 .  
         [0032]    Next, an operation in a case where the program voltage is pumped when the enable signal (EN) is applied as the IGH state and the verify bar signal (VERIFY_b) is applied as the HIGH state will be described.  
         [0033]    If the enable signal (EN) is applied as the HIGH state, the first NMOS transistor N 21  is turned on and the power supply voltage (VDD) is thus supplied. Also, the first˜third capacitors C 21 ˜C 23  are charged according to the first and second clock signals (CLK 1  and CLK 2 ) having opposite phases, respectively, so that the voltages of the first˜third nodes Q 21 ˜Q 23  are raised. Further, as the verify bar signal (VERIFY_b) is applied as the HIGH state, the third clock signal (CLK 3 ) is inputted with the same phase as the first clock signal (CLK 1 ) and the fourth clock signal (CLK 4 ) is inputted with the same phase as the second clock signal (CLK 2 ), by the NAND gates  31  and  32  and the inverters I 31  and I 32  as shown in FIG. 4A and FIG. 4B, so that the fourth and fifth capacitor C 24  and C 25  are charged according to the third clock signal (CLK 3 ) and the fourth clock signal (CLK 4 ), respectively. Thereby, the fourth and fifth nodes Q 24  and Q 25  are raised to a given voltage. The voltages of the nodes raised thus are transferred to a next node through the second˜fifth NMOS transistors N 22 ˜N 25  that are diode-connected and are also latched in the second high-voltage latch  22 .  
         [0034]    The first pumping voltage (VPPI_HALF) for the program verify operation, which is latched in the first high-voltage latch  21 , and the second pumping voltage (VPPI_FULL) for the program operation, which is latched in the second high-voltage latch  22 , are switched by the switching circuit  23  driven by the verify bar signal (VERIFY_b) and then outputted to the output terminal (VPPI).  
         [0035]    Referring now to FIG. 6, a construction of a switching circuit constituting the pumping circuit according to the present invention will be described.  
         [0036]    A first PMOS transistor P 41  driven by the voltage of a second node Q 42  is connected between the output terminal of the first pumping voltage (VPPI_HALF) for the program verify operation and a first node Q 41 . A first NMOS transistor N 41  driven by a signal being a result of the verify bar signal (VERIFY_b) that is inverted through the first inverter I 41 , is connected between the first node Q 41  and the ground terminal (Vss). A second PMOS transistor P 42  driven by the voltage of the first node Q 41  is connected between the output terminal of the first pumping voltage (VPPI_HALF) for the program verify operation and the second node Q 42 . A second NMOS transistor N 42  driven by a signal being a result of the verify bar signal (VERIFY_b) that is delayed through the first and second inverters I 41  and I 42 , is connected between the second node Q 42  and the ground terminal (Vss). A third PMOS transistor P 43  driven by a fourth node Q 44  is connected between the output terminal of the second pumping voltage (VPPI_FULL) for the program operation and a third node Q 43 . A third NMOS transistor N 43  driven by the voltage of the second node Q 42  is connected between the third node Q 43  and the ground terminal (Vss). A fourth PMOS transistor P 44  driven by the voltage of the third node Q 43  is connected between the output terminal of the second pumping voltage (VPPI_FULL) for the program operation and the fourth node Q 44 . A fourth NMOS transistor N 44  driven by the verify bar signal (VERIFY_b) is connected between the fourth node Q 44  and the ground terminal (Vss). A fifth PMOS transistor P 45  driven by the voltage of the fourth node Q 44  is connected between the output terminal of the second pumping voltage (VPPI_FULL) for the program operation and the output terminal (VPPI). A fifth NMOS transistor N 45  driven by the second node Q 42  is connected between the fifth node Q 45  and the ground terminal (Vss). A sixth PMOS transistor P 46  driven by the voltage of the second node Q 42  is connected between the fifth node Q 45  and the output terminal VPPI. A seventh PMOS transistor P 47  having a gate connected to the ground terminal (Vss), for maintaining a turn-on state, and an eighth PMOS transistor P 48  driven by the voltage of the fifth node Q 45 , are serially connected between the output terminal of the first pumping voltage (VPPI_HALF) for the program very operation and the output terminal VPPI.  
         [0037]    A method of driving the switching circuit constructed above will be now described.  
         [0038]    In order to perform the program verify operation, if the verify bar signal (VERIFY_b) is applied as a LOW state, the fourth NMOS transistor N 42  is turned off. The signal is then inverted to a HIGH state through the first inverter I 41  to turn off the first NMOS transistor N 41 . Next, the signal is again inverted to the LOW state through the second inverter I 42  to turn off the second NMOS transistor N 42 . As the first NMOS transistor N 41  is turned off, the first node Q 41  keeps the LOW state. The second PMOS transistor P 42  is turned on by the voltage of the first node Q 41  that keeps the LOW state, so that the first pumping voltage (VPPI_HALF) for the program verify operation is supplied to the second node Q 42 . Thus, the second node Q 42  keeps the HIGH state, which then turns off the first PMOS transistor P 41 . As the third NMOS transistor N 43  is turned on by the voltage of the second node Q 42  that keeps the HIGH state, the third node Q 43  keeps the LOW state. As the fourth PMOS transistor P 44  is turned on by the voltage of the third node Q 43  that keeps the LOW state, the second pumping voltage (VPPI_FULL) for the program operation is supplied to the fourth node Q 44 . Thus, the fourth node Q 44  keeps the HIGH state, and the third and fifth PMOS transistors P 43  and P 45  are turned off by this voltage. As the fifth PMOS transistor P 45  is turned off, the second pumping voltage (VPPI_FULL) for the program operation is not outputted to the output terminal (VPPI). Meanwhile, the fifth NMOS transistor N 45  is turned on and the sixth PMOS transistor P 46  is turned off, by the voltage of the second node Q 42  that keeps the HIGH state. Thus, the fifth node Q 45  keeps the LOW state and the eighth PMOS transistor P 48  is turned on by this voltage. Accordingly, the first pumping voltage (VPPI_HALF) for the program verify operation is outputted to the output terminal (VPPI) through the seventh PMOS transistor (P 47 ) and the eighth PMOS transistor (P 48 ), both of which are turned on.  
         [0039]    In order to perform the program operation, if the verify bar signal (VERIFY_b) is applied as the HIGH state, the fourth NMOS transistor N 42  is turned on. The signal is then inverted to the LOW state through the first inverter I 41  to turn off the first NMOS transistor N 41 . Next, the signal is again inverted to the HIGH state through the second inverter I 42  to turn on the second NMOS transistor N 42 . As the second NMOS transistor N 42  is turned on, the second node Q 42  keeps the LOW state. The first PMOS transistor P 41  is turned on by the voltage of the second node Q 42  that keeps the LOW state, so that the first pumping voltage (VPPI_HALF) for the program verify operation is supplied to the first node Q 41 . Thus, the first node Q 41  keeps the HIGH state and the second PMOS transistor P 42  is turned off by the voltage. Also, the third and fifth NMOS transistors N 43  and N 45  are turned off and the sixth PMOS transistor P 46  is turned on, by the voltage of the second node Q 42  that keeps the LOW state. Thus, the fifth node Q 45  keeps the voltage of the output terminal (VPPI). Thereby, as the eighth PMOS transistor P 48  is turned off, the first pumping voltage (VPPI_HALF) for the program verify operation is not outputted to the output terminal (VPPI). Meanwhile, the fourth NMOS transistor N 44  is turned on the verify bar signal (VERIFY_b) applied to the HIGH state. Thus, the fourth node Q 44  keeps the LOW state. Also, the third and fifth PMOS transistors P 43  and P 45  are turned on by the voltage of the fourth node Q 44  that keeps the LOW state. Thus, the second pumping voltage (VPPI_FULL) for the program operation is outputted to the output terminal (VPPI) through the fifth PMOS transistor P 45  that is turned on.  
         [0040]    [0040]FIG. 7 is a waveform of a simulation result illustrating when the program voltage and the program verify voltage are generated using the pumping circuit according to the present invention. FIG. 7 shows a simulation result at the power supply voltage of 3.7V in the worst case of the simulation conditions for a low-voltage device.  
         [0041]    In the graph, ‘A’ indicates the pumping voltage for the program and program verify operations and ‘B’ indicates a ripple generating in this case. Also, ‘C’ indicates a waveform depending on the program signal and ‘D’ indicates the power supply voltage. In a state where the power supply voltage (D) is applied and the program signal (C) is applied, the program voltage of about 9V is pumped and the program verify voltage of about 6V is then pumped. As can be seen from the drawing, it can be seen that generation of the ripple is significantly reduced compared to the conventional circuit shown in FIG. 2.  
         [0042]    As mentioned above, according to the present invention, the program voltage and the program verify voltage of different levels are pumped using the program verify signal. Therefore, the present invention has advantageous effects that it can reduce the ripple, improve the active current and improve the program efficiency.  
         [0043]    The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof.  
         [0044]    It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention.