Abstract:
Disclosed is a level shift device. The level shift device to convert an input signal having a low-voltage level into an output signal having a high-voltage level includes a latch-type level shifter and a voltage generator. The latch-type level shifter includes two upper pull-up P channel transistors and two lower P channel transistors to prevent the gate-source voltage breakdown of the two upper pull-up P channel transistors. The two upper pull-up P channel transistors and the two lower P channel transistors form a latch structure. The voltage generator generates a voltage to prevent the gate-source voltage brake down of the two upper pull-up P channel transistors and provides the voltage to the gate electrodes of the two lower P channel transistors.

Description:
Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier date and right of priority to Korean Patent Application No. 10-2012-0098498, filed on Sep. 5, 2012, the contents of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     The embodiment relates to a level shifter to convert a low-voltage level input signal into a high-voltage level output signal and a gate driving device of an insulated gate bipolar transistor (IGBT) including the level shifter. 
     In general, in an insulated gated bipolar transistor (IGBT), if gate voltage is not sufficiently great voltage of 13V or less, the saturation voltage VCE_SAT of a device is increased. If the gate voltage is significantly low voltage of 10 V or less, the IGBT operates at an active region, so that the device may be overheated and damaged. Accordingly, in order to prevent the device from being overheated and damaged, a gate driving circuit to drive the IGBT includes a level shifter unit to convert a low-voltage level input signal (in the range of 3.3 V to 5.5 V) into a high-voltage level output signal (in the range of 15 V to 20 V), so that the IGBT is driven at the gate voltage of 15 V or more. 
     In a latch-type level shift device generally used for a gate driving circuit according to the related art, power consumption is not only increased due to static current and rising propagation delay, but also a chip price is increased due to the increase of the chip size. 
     SUMMARY OF THE INVENTION 
     The embodiment provides a level shift device capable of reducing power consumption by preventing static current from being generated. 
     The embodiment provides a level shift device capable of reducing a chip size also. 
     The embodiment provides a level shift device capable of improving a switch speed by reducing propagation delay while preventing a Vgs breakdown phenomenon. 
     According to the embodiment, there is provided a level shift device to convert an input signal having a first voltage level into an output signal having a second voltage level. The level shift device includes a latch-type level shifter comprising two upper pull-up P channel transistors having a latch structure and two lower P channel transistors to prevent a gate-source voltage breakdown phenomenon of the two upper pull-up P channel transistors, and a voltage generator to generate a voltage to prevent the gate-source voltage breakdown phenomenon of the two upper pull-up P channel transistors and provide the voltage to gate electrodes of the two lower P channel transistors. The second voltage level is higher than the first voltage level. 
     According to the embodiment, there is provided a level shift device to convert an input signal having a first voltage level into an output signal having a second voltage level. The level shift device includes a first P channel transistor, a second P channel transistor comprising a gate electrode connected to a drain electrode of the first P channel transistor and a drain electrode connected to a gate electrode of the first P channel transistor, a third P channel transistor comprising a source electrode connected to the drain electrode of the first P channel transistor, a fourth P channel transistor comprising a source electrode connected to the drain electrode of the second P channel transistor and a gate electrode connected to a gate electrode of the third P channel transistor, and a first Zener diode having an anode electrode connected to the gate electrode of the third P channel transistor. The second voltage level is higher than the first voltage level. 
     As described above, according to the level shift device of one embodiment, a Vgs breakdown phenomenon of a pull-up MOS can be prevented, and static current flowing through a Zener diode for voltage control is removed, so that undesirable power consumption can be reduced. 
     In addition, according to the level shift device of the embodiment, the PMOS for reducing pull-up time used to receive the propagation delay of the level shift device is substituted with an NMOS, so that the size of a switching device for pull-up time and the size of a bootstrap capacitor can be reduced, so that the manufacturing cost resulting from the chip size can be reduced. 
     According to the level shift device of the embodiment, the Vgs breakdown phenomenon is prevented while the propagation delay is reduced, so that the switch speed can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a circuit diagram showing a level shift device according to one embodiment. 
         FIG. 2  is a circuit diagram a level shift device according to another embodiment. 
         FIG. 3  is a circuit diagram showing the operation of the level shift device of  FIG. 2  to receive the input signal having a low level. 
         FIG. 4  is a circuit diagram showing the operation of the level shift device of  FIG. 2  to receive the input signal having a high level. 
         FIG. 5  is a circuit diagram showing a level shift device according to still another embodiment. 
         FIG. 6  is a circuit diagram showing the operation of the level shift device of  FIG. 5  to receive the input signal having a high level. 
         FIG. 7  is a circuit diagram showing the operation of the level shift device of  FIG. 5  to receive the input signal having a low level. 
         FIG. 8  is a circuit diagram showing a level shift device according to still another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a level shift device according to embodiments will be described in more detail with reference to accompanying drawings. In the following description, suffixes “module” and “unit” are only added in order to facilitate the description of the specification, and may be compatibly used with each other. 
     In the following description, when a part is connected to the other part, the parts are not only directly connected to each other, but also electrically connected to each other while interposing another part therebetween. 
       FIG. 1  is a circuit diagram showing a level shift device according to one embodiment. 
     As shown in  FIG. 1 , a level shift device  100  according to one embodiment includes a NOT gate U 1 , a NOT gate U 2 , and a latch-type level shifter unit  10 . The latch-type level shifter unit  10  includes a first NMOS NM 1  and a second NMOS NM 2  performing lower switch functions and a first PMOS PM 1  and a second PMOS PM 2  performing upper switch functions. 
     The level shift device  100  of  FIG. 1  receives a low-voltage input signal from a controller (not shown) such as a CPU (central processing unit) to output a high-voltage switching signal sufficient to drive a gate of an IGBT. 
     The low-voltage input signal is applied to an input terminal of the NOT gate U 1 . Low driving voltage VDDL is applied to the NOT gate U 1 . 
     An input terminal of the NOT gate U 2  is connected with an output terminal of the NOT gate U 1 . Low driving voltage VDDL is applied to the NOT gate U 2 . 
     The first NMOS NM 1  includes a drain electrode connected to a drain electrode of the first PMOS PM 1 , a gate electrode connected to the output terminal of the NOT gate U 2 , and a source electrode connected to the ground. 
     The second NMOS NM 2  includes a drain electrode connected to a drain electrode of the second PMOS PM 2 , a gate electrode connected to an output terminal of the NOT gate U 1 , and a source electrode connected to the ground. 
     The first PMOS PM 1  includes a source electrode to which high driving voltage VDDH is applied, a gate electrode connected to the drain electrode of the second NMOS NM 2 , and a drain electrode connected to the first NMOS NM 1 . 
     The second PMOS PM 2  includes a source electrode to which high driving voltage VDDH is applied, a gate electrode connected to the drain electrode of the first NMOS NM 1 , and a drain electrode connected to the drain electrode of the second NMOS NM 2 . 
     Hereinafter, the operation of the level shift device  100  of  FIG. 1  will be described below. 
     The NOT gate U 1  inverts the low-voltage input signal to generate a low-voltage inverted input signal. The NOT gate U 2  re-inverts the low-voltage inverted input signal generated by the NOT gate U 1  to generate a low-voltage re-inverted input signal. 
     If a High-state input signal VIN is input to the level shift device  100 , the first NMOS NM 1  placed at a lower side is turned on, and the second NMOS NM 2  is turned off, so that the state of a node OUT is shifted from ‘High’ to ‘Low’ by the first NMOS NM 1 . Accordingly, the second PMOS PM 2  placed at an upper side is turned on, so that the state of a node OUTB is shifted from ‘Low’ to ‘High’. Accordingly, the first PMOS PM 1  placed at the upper side is turned off. In this case, during the state transition of the nodes OUT and OUTB, short-circuit current is generated between the first NMOS NM 1  and the first PMOS PM 1 . 
     On the contrary, if a Low-state input signal VIN is input to the level shift device  100 , the second NMOS NM 2  placed at the lower side is turned on, and the first NMOS NM 1  is turned off, so that the state of the node OUTB is shifted from ‘High’ to ‘Low’ by the second NMOS NM 2 . Accordingly, the first PMOS PM 1  placed at the upper side is turned on, so that the state of the node OUT is shifted from ‘Low’ to ‘High’. Accordingly, the second PMOS PM 2  placed at the upper is turned off. Similarly, during the state transition of the nodes OUT and OUTB, short-circuit current is generated between the second NMOS NM 2  and the second PMOS PM 2 . 
     Hereinafter, a level shift device  200  according to another embodiment will be described with reference to  FIGS. 2 to 4 . 
       FIG. 2  is a circuit diagram a level shift device according to another embodiment. 
     As shown in  FIG. 2 , the level shift device  200  according to another embodiment includes a level shifter unit  20  to convert a level of input voltage of a circuit into a level of high voltage, which is driving voltage, voltage control units  21 - 1  and  21 - 2  to restrict Vgs of a pull-up PMOS of the level shifter unit  20  to a predetermined voltage value, thereby preventing the Vgs breakdown phenomenon of the pull-up PMOS, and pull-up time reducing units  22 - 1  and  22 - 2  to reduce pull-up time when the pull-up PMOS of the level shifter unit  20  is pull up, and a voltage output unit  23  to receive the output voltage of the level shifter unit  20  and the input voltage of the circuit, and perform buffering for the output voltage to be output. 
     The level shift device  200  of  FIG. 2  is acquired by overcoming a portion of disadvantages of the latch-type level shift circuit of  FIG. 1  by adding the voltage control units  21 - 1  and  21 - 2 , which restricts Vgs of the pull-up PMOS of the level shifter unit  20  to a predetermined voltage value so that the Vgs breakdown phenomenon of the pull-up PMOS is prevented, and the pull-up time reducing units  22 - 1  and  22 - 2 , which reduces the pull-up time when the pull-up PMOS of the level shifter unit  20  is pull up, to the latch-type level shift circuit of  FIG. 1 . 
     Hereinafter, the operation of the level shift device  200  of  FIG. 2  will be described with reference to  FIGS. 3 and 4  below. 
       FIG. 3  is a circuit diagram showing the operation of the level shift device of  FIG. 2  to receive the input signal having a low level. 
     If a Low-state input signal VIN is input to the level shift device  200 , the first NMOS NM 1  placed at a lower side is turned on, and the second NMOS NM 2  is turned off, so that the state of the node OUT is shifted from ‘High’ to ‘Low’ by the first NMOS NM 1 . Accordingly, the second PMOS PM 2  placed at an upper side is turned on, so that the state of the node OUTB is shifted from ‘Low’ to ‘High’. Accordingly, the first PMOS PM 1  placed at the upper side is turned off. In this case, the pull-up time reducing unit  22 - 2  reduces time at which the voltage at the node OUTB is charged with VDDH, and the voltage control unit  21 - 1  restricts the voltage at the node OUT to a predetermined voltage VDDH-Vz. However, as static current flows through a first Zener diode ZD 1  of the voltage control unit  21 - 1  and the first NMOS NM 1  placed at the lower side, undesirable power consumption may be caused. 
     A fifth PMOS PM 5  placed at the upper side of the voltage output unit  23  is turned off, and a third NMOS NM 3  placed at the lower side of the voltage output unit  23  is turned on, so that a terminal VOUT outputs ground voltage GND. 
       FIG. 4  is a circuit diagram showing the operation of the level shift device  200  of  FIG. 2  to receive the input signal having a high level. 
     If a High-state input signal VIN is input to the level shift device  200 , the second NMOS NM 2  placed at a lower side is turned on, and the first NMOS NM 1  is turned off, so that the state of the node OUT is shifted from ‘High’ to ‘Low’ by the second NMOS NM 2 . Accordingly, the first PMOS PM 1  placed at an upper side is turned on, so that the state of the node OUT is shifted from ‘Low’ to ‘High’. Accordingly, the second PMOS PM 2  placed at the upper side is turned off. In this case, the pull-up time reducing unit  22 - 1  reduces time at which the voltage at the node OUTB is charged with VDDH, and the voltage control unit  21 - 2  restricts the voltage at the node OUTB to a predetermined voltage VDDH-Vz. However, as static current flows through a second Zener diode ZD 1  of the voltage control unit  21 - 2  and the second NMOS NM 2  placed at the lower side, undesirable power consumption may be caused. 
     The fifth PMOS PM 5  placed at the upper side of the voltage output unit  23  is turned on, and the third NMOS NM 3  placed at the lower side of the voltage output unit  23  is turned off, so that the terminal VOUT outputs the voltage VDDH. 
     However, following problems still remain in the level shift device according to embodiments shown in  FIGS. 1 to 4 . 
     In other words, the latch-type level shift circuit of  FIG. 1  generates short-circuit current during the state transition time of the node OUT or the node OUTB. Therefore, as the state transition time of the node OUT or the node OUTB is increased, power consumption is increased. However, when the transistor has a latch structure as described above, the state of the node OUTB (or the node OUT) is shifted from a ‘Low’ state to a ‘High’ state after the state of the opposite node OUT (or the node OUTB) is shifted from a ‘High’ state to a ‘Low’ state. Accordingly, the propagation delay required to shift the state of the node OUT or the node OUTB from ‘Low’ state to the ‘High’ state is greatly made. Accordingly, the switch speed of the level shifter may be reduced, and the power consumption may be increased. In addition, the Vgs breakdown voltage of the high-voltage transistor provided in the manufacturing company has various values depending on the manufacturing companies. However, the Vgs breakdown voltage is in the range of 12 V or less to 20 V or less. Accordingly, when the VDDH voltage is low voltage within several volts or less, problems may not occur. However, when the VDDH voltage is high voltage within several tens volts or less, the Vgs (gate-source voltage) breakdown phenomenon of the first and second PMOSs PM 1  and PM 2  is caused, so that the device may be broken. 
     The level shift device  200  of  FIG. 2  makes the Vgs of the second PMOS PM 2  and the first PMOS PM 1  smaller than the Vgs breakdown voltage by restricting the voltage at the drain electrodes of the first NMOS NM 1  and the second NMOS NM 2  to a predetermined value using a Zener diode, thereby preventing the breakdown phenomenon. The level shift device  200  of  FIG. 2  reduces the propagation delay using the first and second PMOSs PM 1  and PM 2  of the pull-up time reducing units  22 - 1  and  22 - 2  to reduce power consumption resulting from the short-circuit current as compared with the latch-type level shift of  FIG. 1 . However, when the voltage is restricted by using a Zener diode as shown in  FIG. 2 , even if the transition of the state of the node OUT or the node OUTB is completed as sown in  FIGS. 3 and 4 , that is, even if the switching operation is completed, static current continuously flows through the Zener diode, so that the undesirable power consumption occurs. Since the static current is increased proportionally to the supply voltage VDDH, as the supply voltage VDDH is increased, the power consumption is more increased. In addition, since the first and second PMOSs PM 1  and PM 2  used in the pull-up time reducing units  22 - 1  and  22 - 2  represent a great on-resistance, the first and second PMOSs PM 1  and PM 2  must have large sizes in order to drive large current capacity. Accordingly, the gate charge capacity is increased in order to drive the first and second PMOSs PM 1  and PM 2 , so that the bootstrap capacitors Cb 1  and Cb 2  to drive the first and second PMOSs PM 1  and PM 2  are increased. Accordingly, the chip size is increased, and thus the cost in the chip manufacturing is increased. 
     For example, the level shift circuit of the gate driving circuit may include a latch-type level shift device as shown in  FIG. 1 . In the above structure, power consumption occurs due to the great propagation delay and the short-circuit current. In addition, when the supply voltage VDDH is small voltage within several volts, problems may not occur. However, when the supply voltage VDDH is high voltage within several tens volts, a Vgs breakdown phenomenon occurs in the first PMOS PM 1 , the second PMOS PM 2 , and the third PMOS PM 3  placed at the upper side, so that the device may be broken. In order to solve the above problem, the drain voltage of the first and second NMOSs NM 1  and NM 2  is restricted to a predetermined value by using the Zener diode as shown in  FIG. 2 , thereby preventing the Vgs breakdown phenomenon of the second and first PMOSs PM 2  and PM 1 . In addition, the propagation delay is reduced by using the first and second PMOSs PM 1  and PM 2  of the pull-up time reducing unit  22 - 1  and  22 - 2  to reduce the power consumption resulting from the short-circuit current. In this case, undesirable power consumption occurs due to the static current flowing through the Zener diode, and the chip size is increased due to the first and second PMOSs PM 1  and PM 2  of the pull-up time reducing units  22 - 1  and  22 - 2 , so that the cost in the chip manufacturing is increased. 
     Hereinafter, a level shift device  300  according to still another embodiment will be described with reference to  FIGS. 5 to 7 . 
       FIG. 5  is a circuit diagram showing a level shift device  300  according to still another embodiment. 
     As shown in  FIG. 5 , the level shift device  300  according to the embodiment includes a NOT gate U 1 , a NOT gate U 2 , a NOT gate U 3 , a NOT gate U 4 , a latch-type level shifter unit  30 , a voltage generator  31 , a pull-up time reducing unit  32 - 1 , a pull-up time reducing unit  32 - 2 , and a voltage output unit  33 . 
     The  1   a  latch-type level shifter unit  30  converts the level of the input signal of the level shift device  300  into the level of high voltage which is driving voltage. 
     The voltage generator  31  restricts Vgs of a pull-up PMOS of the latch-type level shifter unit  30  to a predetermined voltage value to prevent the Vgs breakdown phenomenon of the pull-up PMOS. 
     When the pull-up PMOS PM 1  of the latch-type level shifter unit  30  is pulled up, the pull-up time reducing unit  32 - 1  reduces the pull-up time. When the pull-up PMOS PM 2  of the latch-type level shifter unit  30  is pulled up, the pull-up time reducing unit  32 - 2  reduces the pull-up time. 
     The voltage output unit  33  receives the output voltage of the latch-type level shifter unit  30  and the input signal of the level shift device  300  and performs buffering the output voltage and the input signal to be output. 
     The latch-type level shifter unit  30  includes a first PMOS PM 1 , a second PMOS PM 2 , a first NMOS NM 1 , a second NMOS NM 2 , a third PMOS PM 3 , and a fourth PMOS PM 4 . The first PMOS PM 1  and the second PMOS PM 2  placed at the upper side of the latch-type shifter unit  30  construct a latch structure together with the first NMOS NM 1  and the second NMOS NM 2  placed at the lower side of the latch-type shifter unit  30 . The third and fourth PMOSs PM 3  and PM 4  are transistors to prevent Vgs breakdown phenomenon of the first and second PMOSs PM 1  and PM 2  which are pull-up PMOSs. 
     The voltage generator  31  includes a Zener diode ZD 3 , a constant current source ICC, and a capacitor Cc. 
     The pull-up time reducing unit  32 - 1  includes a Zener diode ZD 1 , a third NMOS NM 3 , and a bootstrap capacitor Cb 1 . 
     The pull-up time reducing unit  32 - 2  includes a Zener diode ZD 2 , a fourth NMOS NM 4 , and a bootstrap capacitor Cb 2 . 
     The voltage output unit  33  includes a fifth PMOS PM 5  placed at the upper side thereof and a fifth NMOS NM 5  placed at the lower side thereof. 
     The NOT gate U 1  has input and output terminals. The low-voltage level input signal is applied to the input terminal of the NOT gate U 1 . 
     The NOT gate U 2  has input and output terminals. The input terminal of the NOT gate U 2  is connected to the output terminal of the NOT gate U 1 . 
     The NOT gate U 3  has input and output terminals. The input terminal of the NOT gate U 3  is connected to the output terminal of the NOT gate U 2 . 
     The NOT gate U 4  has input and output terminals. The input terminal of the NOT gate U 4  is connected to the output terminal of the NOT gate U 3 . 
     The first PMOS PM 1  has a source electrode, a gate electrode, and a drain electrode. High-voltage level driving voltage VDDH is applied to the source electrode of the first PMOS PM 1 . 
     The second PMOS PM 2  has a source electrode, a gate electrode, and a drain electrode. High-voltage level driving voltage VDDH is applied to the source electrode of the second PMOS PM 2 . The gate electrode of the second PMOS PM 2  is connected to the drain electrode of the first PMOS PM 1 . The drain electrode of the second PMOS PM 2  is connected to the gate electrode of the first PMOS PM 1 . 
     The third PMOS PM 3  has a source electrode, a gate electrode, and a drain electrode. The source electrode of the third PMOS PM 3  is connected to the drain electrode of the first PMOS PM 1 . 
     The fourth PMOS PM 4  has a source electrode, a gate electrode, and a drain electrode. The source electrode of the fourth PMOS PM 4  is connected to the drain electrode of the second PMOS PM 2 . The gate electrode of the fourth PMOS PM 4  is connected to the gate electrode of the third PMOS PM 3 . 
     The first NMOS NM 1  has a drain electrode, a gate electrode, and a source electrode. The drain electrode of the first NMOS NM 1  is connected to the drain electrode of the third PMOS PM 3 . The gate electrode of the first NMOS NM 1  is connected to the output terminal of the NOT gate U 2 . The source electrode of the first NMOS NM 1  is connected to the ground. 
     The second NMOS NM 2  has a drain electrode, a gate electrode, and a source electrode. The drain electrode of the second NMOS NM 2  is connected to the drain electrode of the fourth PMOS PM 4 . The gate electrode of the second NMOS NM 2  is connected to the output terminal of the NOT gate U 1 . The source electrode of the second NMOS NM 2  is connected to the ground. 
     The third NMOS NM 3  has a drain electrode, a gate electrode, and a source electrode. High-voltage level driving voltage VDDH is applied to the drain electrode of the third NMOS NM 3 . The source electrode of the third NMOS NM 3  is connected to the drain electrode of the first PMOS PM 1 . 
     The Zener diode ZD 1  has an anode electrode and a cathode electrode. The high-voltage level driving voltage VDDH is applied to the cathode electrode of the Zener diode ZD 1 . The anode electrode of the Zener diode ZD 1  is connected to the gate electrode of the third NMOS NM 3 . 
     The bootstrap capacitor Cb 1  has one end connected to the anode electrode of the Zener diode ZD 1  and an opposite end connected to the gate electrode of the third NMOS NM 3 . 
     The fourth NMOS NM 4  has a drain electrode, a gate electrode, and a source electrode. The high-voltage level driving voltage VDDH is applied to the drain electrode of the fourth NMOS NM 4 . The source electrode of the fourth NMOS NM 4  is connected to the drain electrode of the second PMOS PM 2 . 
     The Zener diode ZD 2  has an anode electrode and a cathode electrode. The high-voltage level driving voltage VDDH is applied to the cathode electrode of the Zener diode ZD 2 . The anode electrode of the Zener diode ZD 2  is connected to the gate electrode of the fourth NMOS NM 4 . 
     The bootstrap capacitor Cb 2  has one end connected to the anode electrode of the Zener diode ZD and an opposite end connected to the gate electrode of the fourth NMOS NM 4 . 
     The fifth PMOS PM 5  has a source electrode, a gate electrode, and a drain electrode. The high-voltage level driving voltage VDDH is applied to the source electrode of the fifth PMOS PM 5 . The gate electrode of the fifth PMOS PM 5  is connected to the drain electrode of the second PMOS PM 2 . The drain electrode of the fifth PMOS PM 5  outputs the high-voltage level output signal that has been buffered. 
     The fifth NMOS NM 5  has a drain electrode, a gate electrode, and a source electrode. The drain electrode of the fifth NMOS NM 5  is connected to the drain electrode of the fifth PMOS PM 5 . The gate electrode of the fifth NMOS NM 5  is connected to the output terminal of the NOT gate U 4 . The source electrode of the fifth NMOS NM 5  is connected to the ground. 
     The Zener diode ZD 3  has an anode electrode and a cathode electrode. The high-voltage level driving voltage VDDH is applied to the cathode electrode of the Zener diode ZD 3 . 
     The constant current source Icc has a current input terminal connected to the anode electrode of the Zener diode ZD 3  and a current output terminal connected to the ground. 
     The capacitor Cc has one terminal connected to the anode electrode of the Zener diode ZD 3  and an opposite end connected to the ground. 
     The bias voltage VDDH-Vz generated from the voltage generator  31  is applied to the gate electrodes of the third and fourth PMOSs PM 3  and PM 4 . 
     The bias voltage VDDH-Vz is applied to the gate electrodes of the third and fourth PMOSs PM 3  and PM 4  of the latch-type level shifter unit  30 . 
     Hereinafter, the operation of the level shift device  300  of  FIG. 5  will be described with reference to  FIGS. 6 and 7 . 
       FIG. 6  is a circuit diagram showing the operation of the level shift device to receive the high-level input signal. 
     If a high-level input signal VIN is input, the first NMOS NM 1  provided at the lower portion of the level shift device  300  is turned on, and the second NMOS NM 2  is turned off, so that the state of the node OUT is shifted from a ‘High’ state to a ‘Low’ state by the first NMOS NM 1 . Accordingly, the second PMOS PM 2  placed at the upper side of the level shift device  300  is turned on to shift the state of the node OUTB from a ‘Low’ state to a ‘High’ state, so that the first PMOS PM 1  placed at the upper side of the level shift device  300  is turned off. In this case, the voltage at the node C is reduced from the voltage VDD-Vz+VDDL to the voltage VDD-Vz by the first bootstrap capacitor Cb 1 , the third NMOS NM 3  of the pull-up time reducing time  32 - 1  is turned off, and the voltage at the node D is increased from voltage VDD-Vz to voltage VDD-Vz+VDDL by the second bootstrap capacitor Cb 2 , so that the fourth NMOS NM 4  of the pull-up time reducing unit  32 - 2  is turned on. Accordingly, the time at which the voltage at the node OUTB is charged with VDDH is reduced. In this case, if the voltage at the node E is constantly maintained to the bias voltage VDDH-Vz supplied by the voltage generator  31 , so that the voltage at the node OUT is reduced to predetermined voltage VDDH-Vz+Vth or less, the third PMOS PM 3  is turned off, so that the voltage at the node OUT is increased again. If the voltage at the node OUT is increased to the predetermined voltage VDDH-Vz+Vth or more, the third PMOS PM 3  is turned on, and the feedback operation to reduce the drain voltage of the first PMOS PM 1  again is performed, so that the voltage at the node OUT is restricted to the predetermined voltage VDDH-Vz+Vth. Accordingly, even if the supply voltage VDDH is increased, the Vgs of the first and second PMOSs PM 1  and PM 2 , which serve as pull-up PMOSs of the latch-type level shifter unit  30 , is maintained to the predetermined voltage Vz-Vth to prevent the Vgs breakdown phenomenon of the pull-up PMOS resulting to the increase of the supply voltage VDDH. In addition, different from the related art, since the Zener diode is not used, so that the undesirable static current is not generated. 
     The fifth PMOS PM 5  placed at the upper side of the voltage output unit  33  is turned off by the latch-type level shifter unit  30 , and the fifth NMOS NM 5  placed at the lower side of the voltage output unit  33  is turned on, so that the terminal VOUT outputs voltage GND. 
       FIG. 7  is a circuit diagram showing the operation of the level shift device of  FIG. 5  to receive the input signal having a low level of  FIG. 5 . 
     If a low-level input signal VIN is input, the second NMOS NM 2  provided at the lower portion of the level shift device  300  is turned on, and the first NMOS NM 1  is turned off, so that the state of the node OUTB is shifted from a ‘High’ state to a ‘Low’ state by the second NMOS NM 2 . Accordingly, the first PMOS PM 1  placed at the upper side of the level shift device  300  is turned on to shift the state of the node OUT from a ‘Low’ state to a ‘High’ state, so that the second PMOS PM 2  placed at the upper side of the level shift device  300  is turned off. In this case, the voltage at the node D is reduced from the voltage VDD-Vz+VDDL to the voltage VDD-Vz by the second bootstrap capacitor Cb 2 , the fourth NMOS NM 4  of the pull-up time reducing time  32 - 2  is turned off, and the voltage at the node C is increased from voltage VDD-Vz to voltage VDD-Vz+VDDL by the first bootstrap capacitor Cb 1 , so that the third NMOS NM 3  of the pull-up time reducing unit  32 - 1  is turned on. Accordingly, the time at which the voltage at the node OUT is charged with VDDH is reduced. In this case, the voltage at the node OUTB is restricted to predetermined voltage VDD-Vz+Vth through the above-described principle, so that the Vgs of the first PMOS PM 1  placed at the upper side of the level shift device  300  is maintained to predetermined voltage Vz-Vth. Accordingly, the Vgs breakdown phenomenon of the pull-up PMOS resulting from the increase of the supply voltage VDDH does not occur, and the Zener diode is not used different from the related art, so that the undesirable static current does not occur. 
     The fifth PMOS PM 5  placed at the upper side of the voltage output unit  33  is turned on by the latch-type level shifter unit  30 , and the fifth NMOS NM 5  placed at the lower side of the voltage output unit  33  is turned off, so that the terminal VOUT outputs the supply voltage VDDH. 
     Hereinafter, still another embodiment will be described with reference to  FIG. 8 . 
       FIG. 8  is a circuit diagram showing a level shift device  400  according to still another embodiment. 
     As shown in  FIG. 8 , the level shift device  400  according to still another embodiment includes a NOT gate U 1 , a NOT gate U 2 , a NOT gate U 3 , a NOT gate U 4 , a latch-type level shifter unit  40 , a voltage generator  41 , a pull-up time reducing unit  42 - 1 , a pull-up time reducing unit  42 - 2 , and a voltage output unit  43 . 
     As shown in  FIG. 8 , the Zener diode of the voltage generator  31  of  FIG. 5  may be substituted with N diodes connected in series. In this case, the voltage at the node E is constantly maintained to the voltage VDDH-n*VD, so that the Vgs of the first and second PMOSs PM 1  and PM 2  placed at the upper side is maintained to predetermined voltage n*VD-Vth. 
     As shown in  FIG. 8 , the Zener diode of the pull-up time reducing units  32 - 1  and  32 - 2  of  FIG. 5  may be substituted with N diodes connected in series. Anodes of N diodes connected in series receive high-voltage level driving voltage, and cathodes of the N diodes may be connected to a node C. 
     The number n of diodes of the pull-up time reducing units  42 - 1  and  42 - 2  is the same as the number n of diodes of the voltage generator  41 . If the number n of diodes of the pull-up time reducing units  42 - 1  and  42 - 2  is smaller than or larger than the number n of diodes of the voltage generator  41 , the third NMOS NM 3  and the fourth NMOS NM 4  of the pull-up time reducing units  42 - 1  and  42 - 2  may not be normally turned on or turned off. Accordingly, the propagation delay may not be reduced or the static current may be generated. 
     In order to prevent voltages at the nodes OUT and OUTB from being increased to VDDH+VD or more, the first and second diodes D 1  and D 2  are inversely arranged in parallel to N diodes. 
     According to one embodiment, the above method may be realized in the form of process-readable codes in a medium having a program recoded therein. Process-readable media may include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disc, and an optical data storage device, and may be implemented in the form of a carrier wave (transmission through the Internet). 
     The level shift device described above is applied without limitation to the constitution and the method according to the above embodiment. The whole embodiments or parts of the embodiments can be selectively combined so that various variations and modifications are possible.