Abstract:
A level shifter includes a driving circuit, which receives an input signal and outputs a driving signal in response to a first voltage level of the input signal; a level shifting circuit, which outputs an output signal of a second voltage level in response to the driving signal; and a leakage prevention circuit, which prevents a leakage current of the driving circuit, wherein the driving circuit may include at least one native transistor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2016-0092899, filed on Jul. 21, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    The inventive concept relates to a level shifter, and more particularly, to a level shifter that outputs a second voltage level in response to a signal of a first voltage level. 
         [0003]    As process parameters shrink, the first power voltage Vdd of a level shifter is continuously decreasing. However, the threshold voltage of a high-voltage transistor does not decrease in proportion thereto. Therefore, a proper operation of a level shifter for converting a voltage level of a signal from a low first power voltage Vdd to a high second power voltage Vpp is becoming difficult to maintain. 
       SUMMARY 
       [0004]    The inventive concept provides a level shifter that may operate with an input signal having a low voltage. 
         [0005]    According to an aspect of the inventive concept, there is provided a level shifter including a driving circuit, which is configured to receive an input signal and to output a driving signal in response to a first voltage level of the input signal; a level shifting circuit, which is configured to output an output signal of a second voltage level in response to the driving signal; and a leakage prevention circuit, which is configured to prevent a leakage current of the driving circuit, wherein the driving circuit may include at least one native transistor. 
         [0006]    According to another aspect of the inventive concept, there is provided a level shifter which applies a third voltage to an output terminal in correspondence to an input signal transitioning from a first voltage to a second voltage, the level shifter including a level shifting circuit which is configured to apply the third voltage to the output terminal; a driving circuit which is configured to drive the level shifting circuit in correspondence to the input signal transitioning from the first voltage to the second voltage; and a leakage prevention circuit which is configured to prevent a leakage current of the driving circuit, wherein the level shifting circuit may include at least one first transistor having a first threshold voltage, the driving circuit may include at least one second transistor having a second threshold voltage, and the leakage prevention circuit may include at least one third transistor having a third threshold voltage, and wherein the first threshold voltage, the second threshold voltage, and the third threshold voltage may be different from one another. 
         [0007]    According to yet another aspect of the inventive concept, there is provided a device comprising: a level shifting circuit connected to an output terminal; a driving circuit connected to an input terminal and configured to receive at the input terminal an input signal and in response thereto to drive the level shifting circuit, wherein when the input signal has a first input voltage level the driving circuit drives the level shifting circuit to output at the output terminal an output voltage having a first output voltage level, and when the input signal has a second input voltage level different from the first input voltage level the driving circuit drives the level shifting circuit to output the output voltage having a second output voltage level different than the first output voltage level and different than the second input voltage level; and a leakage prevention circuit which is configured to prevent a leakage current of the driving circuit, wherein the driving circuit comprises at least one native transistor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
           [0009]      FIG. 1  is a block diagram showing an embodiment of a level shifter. 
           [0010]      FIG. 2  is a circuit diagram of an embodiment of a level shifter. 
           [0011]      FIG. 3  is a graph showing characteristics of a native transistor. 
           [0012]      FIG. 4  is a circuit diagram of an embodiment of a driving circuit. 
           [0013]      FIG. 5  is a diagram exemplifying an operation of an embodiment of a level shifter. 
           [0014]      FIG. 6  is a timing diagram showing voltages applied to the respective nodes of  FIG. 2  at various times, according to an embodiment. 
           [0015]      FIG. 7  is a block diagram showing an embodiment of a level shifter. 
           [0016]      FIG. 8A  is a circuit diagram of an embodiment of a level shifter. 
           [0017]      FIG. 8B  is a circuit diagram of an embodiment of a level shifter. 
           [0018]      FIG. 9  is a block diagram showing an embodiment of a level shifter. 
           [0019]      FIG. 10A  is a circuit diagram of an embodiment of a level shifter. 
           [0020]      FIG. 10B  is a circuit diagram of an embodiment of a level shifter. 
           [0021]      FIGS. 11A and 11B  are circuit diagrams showing embodiments of level shifters. 
           [0022]      FIG. 12  is a diagram exemplifying an operation of an embodiment of a level shifter. 
           [0023]      FIG. 13  is a flowchart showing operations of an embodiment of a level shifter. 
           [0024]      FIG. 14  is a flowchart showing operations of an embodiment of a level. 
           [0025]      FIG. 15  is a block diagram showing an embodiment of a computing system device. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]      FIG. 1  is a block diagram showing an embodiment of a level shifter. 
         [0027]    Referring to  FIG. 1 , a level shifter  100  may include a level shifting circuit  110 , a driving circuit  120 , and a leakage prevention circuit  130 . Furthermore, level shifter  100  may include an input terminal IN and an output terminal OUT, where a first voltage V 1  and a third voltage V 3  may be applied to level shifter  100 . 
         [0028]    Driving circuit  120  may control level shifting circuit  110  according to an input signal received by the input terminal IN. For example, when the voltage level of an input signal transitions from the first voltage V 1  to a second voltage V 2 , driving circuit  120  may drive level shifting circuit  110  in correspondence thereto. According to an embodiment, the first voltage V 1  may be ground voltage Vss, whereas the second voltage V 2  may be first power voltage Vdd. In other words, in the above-stated example, driving circuit  120  may drive level shifting circuit  110  as the input signal transitions from the ground voltage Vss to the first power voltage Vdd. Hereinafter, it will be assumed that the first voltage V 1  is the ground voltage Vss. 
         [0029]    Level shifting circuit  110  may output the third voltage V 3  to the output terminal OUT under the control of driving circuit  120 . To this end, level shifting circuit  110  may be connected to the output terminal OUT. The first voltage V 1  may be applied to the output terminal OUT until the third voltage V 3  is applied thereto by the level shifting circuit  110 . As an unlimited example, the third voltage V 3  may be a voltage of a level higher than those of the first voltage V 1  and the second voltage V 2 . For example, when the first voltage V 1  is the ground voltage Vss and the second voltage V 2  is the first power voltage Vdd, the third voltage V 3  may be second power voltage Vpp, where the second power voltage Vpp may be higher than that of the first power voltage Vdd. 
         [0030]    The leakage prevention circuit  130  may prevent leakage current that may leak from driving circuit  120 . To this end, the leakage prevention circuit  130  may be connected to driving circuit  120 . 
         [0031]    As shown in  FIG. 1 , driving circuit  120  may be located between the level shifting circuit  110  and leakage prevention circuit  130 . However, the inventive concept is not limited thereto. 
         [0032]      FIG. 2  is a circuit diagram of an embodiment of a level shifter. Descriptions already given above with reference to  FIG. 1  will be omitted below. 
         [0033]    Referring to  FIG. 2 , a level shifter  100   a  may include a level shifting circuit  110   a,  a driving circuit  120   a,  and a leakage prevention circuit  130   a.    
         [0034]    Level shifting circuit  110   a  may include a first high voltage transistor Ha 1  and a second high voltage transistor Ha 2 . The first high voltage transistor Ha 1  and the second high voltage transistor Ha 2  may refer to transistors that may normally operate at high voltages. For example, the first high voltage transistor Ha 1  and the second high voltage transistor Ha 2  may be p-channel metal-oxide semiconductor (PMOS) transistors. Each of the first high voltage transistor Ha 1  and the second high voltage transistor Ha 2  may include a first terminal, a second terminal, and a gate terminal. For example, in the case of a PMOS transistor, a first terminal may be connected to a source, whereas a second terminal may be connected to a drain. 
         [0035]    In level shifting circuit  110   a,  the third voltage V 3  may be applied to the first terminals of the first high voltage transistor Ha 1  and the second high voltage transistor Ha 2 . The second terminal of the first high voltage transistor Ha 1  may be connected to driving circuit  120   a  at a node a 0 , whereas the gate terminal of the first high voltage transistor Ha 1  may be connected to driving circuit  120   a  and an output terminal OUT at a node a 1 . The second terminal of the second high voltage transistor Ha 2  may be connected to driving circuit  120   a  and the output terminal OUT at the node a 1 , whereas the gate terminal of the second high voltage transistor Ha 2  may be connected to driving circuit  120   a  at the node a 0 . Based on the connections described above, the first high voltage transistor Ha 1  and the second high voltage transistor Ha 2  may operate complementarily. 
         [0036]    Driving circuit  120   a  may include a first native transistor Na 1  and a second native transistor Na 2 . The first native transistor Na 1  and the second native transistor Na 2  may refer to transistors with threshold voltages close to 0 V, where each of the first native transistor Na 1  and the second native transistor Na 2  may include a first terminal, a second terminal, and a gate terminal. 
         [0037]    The first terminal of the first native transistor Na 1  may be connected to the second terminal of the first high voltage transistor Ha 1  and the gate terminal of the second high voltage transistor Ha 2  at the node a 0 . Furthermore, the second terminal of the first native transistor Na 1  may be connected to leakage prevention circuit  130   a,  and the gate terminal of the first native transistor Na 1  may be connected to the input terminal IN. 
         [0038]    The first terminal of the second native transistor Na 2  may be connected to the second terminal of the second high voltage transistor Ha 2 , the gate terminal of the first high voltage transistor Ha 1 , and the output terminal OUT at the node a 1 . Furthermore, the second terminal of the second native transistor Na 2  may be connected to leakage prevention circuit  130   a,  and the gate terminal of the second native transistor Na 2  may be connected to the input terminal IN via an inverter. Based on the connections described above, the first native transistor Na 1  and the second native transistor Na 2  may operate complementarily. 
         [0039]    Since threshold voltages of the first native transistor Na 1  and the second native transistor Na 2  are lower than that of a high-voltage transistor, the first native transistor Na 1  and the second native transistor Na 2  may be easily switched on or off at low voltages. Therefore, the first native transistor Na 1  and the second native transistor Na 2  may drive level shifting circuit  110   a  even at low voltages. 
         [0040]    Leakage prevention circuit  130   a  may include a first low voltage transistor La 1  and a second low voltage transistor La 2 . The first low voltage transistor La 1  and the second low voltage transistor La 2  refer to transistors operating at low voltages and may be NMOS transistors, for example. Each of the first low voltage transistor La 1  and the second low voltage transistor La 2  may include a first terminal, a second terminal, and a gate terminal. For example, in the case of an NMOS transistor, a first terminal may be connected to a drain, whereas a second terminal may be connected to a source. 
         [0041]    The first terminals of the first low voltage transistor La 1  and the second low voltage transistor La 2  may be connected to the first voltage V 1  source. The second terminal of the first low voltage transistor La 1  may be connected to the second terminal of the first native transistor Na 1 , and the gate terminal of the first low voltage transistor La 1  may be connected to the input terminal IN. The second terminal of the second low voltage transistor La 2  may be connected to the second terminal of the second native transistor Na 2 , whereas the gate terminal of the second low voltage transistor La 2  may be connected to the input terminal IN via the inverter. Based on the connections described above, the first low voltage transistor La 1  and the second low voltage transistor La 2  may operate complementarily. 
         [0042]    In some cases, the threshold voltage of a native transistor may be equal to or less than 0 V. For example, when the temperature is high, a native transistor may have a threshold voltage that is equal to or less than 0 V. In this case, leakage currents may flow between sources and drains in the first native transistor Na 1  and the second native transistor Na 2  even at 0 V. However, since the first low voltage transistor La 1  and the second low voltage transistor La 2  are OFF at low voltages, even when leakage currents of the first native transistor Na 1  and the second native transistor Na 2  flow, leakage prevention circuit  130  may prevent a leakage current from flowing through the first native transistor Na 1  and the second native transistor Na 2 . 
         [0043]      FIG. 3  is a graph showing characteristics of a native transistor. 
         [0044]      FIG. 3  shows current-voltage characteristics (I-V curves) of a native transistor Native TR and a normal transistor Normal TR. The normal transistor Normal TR may refer to a normal NMOS transistor and a normal PMOS transistor, whereas the native transistor Native TR may refer to a transistor including a thick gate-oxide layer. 
         [0045]    Regarding both the native transistor Native TR and the normal transistor Normal TR, the slope of I-V curves may rapidly increase when gate-source voltages V GS  are equal to or greater than a certain voltage level, where the certain voltage may refer to a threshold voltage. Referring to the slope characteristics of the I-V curves, when the gate-source voltage V GS  is equal to or greater than the threshold voltage, the source-drain currents I DS  of the native transistor Native TR and the normal transistor Normal TR may flow unlimitedly, and thus the native transistor Native TR and the normal transistor Normal TR may function as conducting wires having little resistances. 
         [0046]    The normal transistor Normal TR may have a threshold voltage that is higher than that of the native transistor Native TR. However, due to device characteristics, the native transistor Native TR may have a threshold voltage close to 0. Therefore, the native transistor Native TR may easily operate even when an input voltage (that is, voltage level of a signal applied to a gate terminal) is low. 
         [0047]    In the present specification, the ON state of a transistor may refer to a state wherein the source-drain current I DS  flows almost unlimitedly due to the gate-source voltage V GS  equal to or greater than a threshold voltage. Furthermore, the OFF state of a transistor may refer to a state wherein the source-drain current I DS  barely flows due to the gate-source voltage V GS  less than a threshold voltage. 
         [0048]      FIG. 4  is a circuit diagram of an embodiment of a driving circuit. 
         [0049]    Referring to  FIG. 4 , a driving circuit  120   b  may include native transistors NT 0  through NTn that are connected in series. Although  FIG. 4  shows that gates of the native transistors NT 0  through NTn are all connected to a same node as each other, the inventive concept is not limited thereto. In other words, the native transistors NT 0  through NTn may be operated by the same signal as each other, or by different signals. 
         [0050]    The native transistors NT 0  through NTn may have the same threshold voltage as each other and may be simultaneously operated, or may have different threshold voltages than each other and may be operated independently of each other. 
         [0051]      FIG. 5  is a diagram exemplifying an operation of an embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 1 and 2  will be omitted below. 
         [0052]      FIGS. 2 and 5  show an operation of a level shifter when an input signal is converted from a first voltage V 1  to a second voltage V 2 . Furthermore, although a level shifter according to the present embodiment is connected between ground voltage Vss and supply voltage Vpp, the inventive concept is not limited thereto, and the level shifter may be connected to any voltage as described above with reference to  FIG. 1 . In  FIG. 5 , a dashed circle around a transistor may denote a transistor in the ON state as described above with reference to  FIG. 3 , whereas a transistor with a “/” marked through it may denote a transistor in the OFF state as described above with reference to  FIG. 3 . 
         [0053]    STEP  0  in  FIG. 5  may denote a state wherein an input signal maintains a first voltage V 1 . The first voltage V 1  may be a voltage which is less than threshold voltages of a native transistor and a low voltage transistor. Therefore, when the input signal IN is a first voltage V 1 , the first native transistor Na 1  and the first low voltage transistor La 1  may be in an OFF state. On the other hand, the second native transistor Na 2  and the second low voltage transistor La 2  receive via their gate terminals an inverse input signal INB, which is an input signal inversed by an inverter INV. Therefore, when the input signal IN is the first voltage V 1 , the inverse input signal INB, which is the inversed first voltage V 1 , is input to the gate terminals of the second native transistor Na 2  and the second low voltage transistor La 2 , where the voltage level of the inverse input signal INB may be greater than the levels of the threshold voltages of the second native transistor Na 2  and the second low voltage transistor La 2 . Therefore, the second native transistor Na 2  and the second low voltage transistor La 2  may be in an ON state due to the inverse input signal INB. 
         [0054]    When the second native transistor Na 2  and the second low voltage transistor La 2  are in an ON state, the node a 1  connected to the output terminal OUT may be connected to the ground voltage Vss. Therefore, the first high voltage transistor Ha 1  may be in an ON state. Furthermore, the ground voltage Vss may be output via the output terminal OUT connected to the node a 1 . 
         [0055]    As the first high voltage transistor Ha 1  is in an ON state, second power voltage Vpp may be applied to the node a 0 . Therefore, the second power voltage Vpp may also be applied to the gate terminal of the second high voltage transistor Ha 2  connected to the node a 0 , and the gate-source voltage V GS  of the second high voltage transistor Ha 2  becomes 0 V. As a result, the second high voltage transistor Ha 2  may be maintained in an OFF state. 
         [0056]    STEP  1  may show a step in which the input signal IN transitions from the first voltage V 1  to the second voltage V 2 . The second voltage V 2  may have a voltage level which is greater than the levels of the threshold voltages of the first native transistor Na 1  and the first low voltage transistor La 1 . Therefore, when the second voltage V 2  is applied to the gate terminals of the first native transistor Na 1  and the first low voltage transistor La 1  as the input signal IN, the first native transistor Na 1  and the first low voltage transistor La 1  may transit to an ON state. As the first native transistor Na 1  and the first low voltage transistor La 1  are in an ON state, the ground voltage Vss may be applied to the node a 0 . 
         [0057]    Furthermore, since a complementary voltage of the second voltage V 2  is applied to the gate terminals of the second native transistor Na 2  and the second low voltage transistor La 2  via the inverse input signal INB, the second native transistor Na 2  and the second low voltage transistor La 2  may transit to an OFF state. 
         [0058]    STEP  2  may refer to a step after the ground voltage Vss is applied to the node a 0  in STEP  1 . Although STEP  2  is shown after STEP  1 , it is merely a logic sequence, and the steps may occur sequentially or simultaneously. 
         [0059]    In STEP  1 , when the ground voltage Vss is applied to the node a 0 , since the gate terminal of the second high voltage transistor Ha 2  is connected to the node a 0 , the ground voltage Vss may also be applied to the gate terminal of the second high voltage transistor Ha 2 . Therefore, the second high voltage transistor Ha 2  may transit to an ON state. In this case, a high voltage, which is the second power voltage Vpp, may be applied to the node a 1 . Since the output terminal OUT is connected to the node a 1 , the second power voltage Vpp may be applied to the output terminal OUT. 
         [0060]    Furthermore, when the second power voltage Vpp is applied to the node a 1 , the first high voltage transistor Ha 1 , of which the gate terminal is connected to the node a 1 , may transit to an OFF state. Therefore, the second power voltage Vpp is not applied to the node a 0  and the voltage level of the first high voltage transistor Ha 1  is maintained at the ground voltage Vss, and thus the second power voltage Vpp may be stably applied to the output terminal OUT. 
         [0061]      FIG. 6  is a timing diagram showing voltages applied to the respective nodes of  FIG. 2  at various times, according to an embodiment. Descriptions already given above with reference to  FIGS. 1, 2, and 5  will be omitted below. 
         [0062]    Referring to  FIGS. 2, 5, and 6 , t 0  may denote a time point at which the first power voltage Vdd is applied as the input signal IN. Although  FIG. 6  shows an example in which the input signal IN transitions from the ground voltage Vss to the first power voltage Vdd, the inventive concept is not limited thereto, as described above. The section before the time point t 0  is a section in which the input terminal IN is maintained at the ground voltage Vss and may correspond to STEP  0  of  FIG. 5 . The first power voltage Vdd may be applied to a node a 3 , to which the inverse input signal INB is applied, by the inverter INV. Furthermore, as shown in  FIG. 5 , the ground voltage Vss may be applied to the node a 1 , to which the output terminal OUT is connected, whereas the second power voltage Vpp may be applied to the node a 0  that complementarily operates with respect to the node a 1 . The ground voltage Vss may be applied to a node a 4  to which the first native transistor Na 1  and the first low voltage transistor La 1  are connected. 
         [0063]    When the input signal IN transitions from the ground voltage Vss to the first power voltage Vdd at the time point t 0 , the inverse input signal INB connected via the inverter INV and the node a 3  to which the inverse input signal INB is applied may transition from the first power voltage Vdd to the ground voltage Vss. Next, after STEP 1  and STEP 2  of  FIG. 5  are performed (after time t 0  in  FIG. 6 ), the second power voltage Vpp may be applied to the node al, to which the output terminal OUT is connected, whereas the ground voltage Vss may be applied to the node a 0 . 
         [0064]    Thus it may be seen from  FIG. 6  that when the input signal IN has a first input voltage level (e.g., Vss), then the driving circuit drives the level shifting circuit to output at the output terminal OUT an output voltage having a first output voltage level (e.g., Vss), and when the input signal IN has a second input voltage level (Vdd) different from the first input voltage level the driving circuit drives the level shifting circuit to output the output voltage having a second output voltage level (e.g., Vpp) different than the first output voltage level and different than the second input voltage level. In this example, the level shifter shifts the input voltage level Vdd to an output voltage level Vpp which is greater than Vdd. Thus, the output voltage range (Vss-&gt;Vpp) is greater than the input voltage range (Vss-&gt;Vdd). However, in other embodiments the level shifting may shift an input voltage level to an output voltage level which is less than the input voltage level. Also, although the first input voltage level and the first output voltage level in this example are the same as each other (e.g., Vss), it should be understood that these voltages may be different than each other, or only substantially the same as each other, where “substantially the same” means within a couple of tenths of a volt of each other. 
         [0065]      FIG. 7  is a block diagram showing an embodiment of a level shifter. Descriptions already given above with reference to  FIG. 1  will be omitted below. 
         [0066]    Referring to  FIGS. 1 and 7 , a level shifter  200  may include a level shifting circuit  210 , a driving circuit  220 , a leakage prevention circuit  230 , and a damage prevention circuit  240 . Since level shifting circuit  210 , driving circuit  220 , and leakage prevention circuit  230  are identical to those shown in  FIG. 1 , detailed description thereof will be omitted. 
         [0067]    Damage prevention circuit  240  may be connected to leakage prevention circuit  230  and prevent damage to leakage prevention circuit  230 . Leakage prevention circuit  230  may include devices vulnerable to damage. Therefore, when the input terminal IN is a high voltage, and a voltage greater than a voltage that leakage prevention circuit  230  may withstand is applied to leakage prevention circuit  230 , leakage prevention circuit  230  may be damaged. To prevent the damage, damage prevention circuit  240  may be connected to leakage prevention circuit  230 . For example, damage prevention circuit  240  may provide a path for reducing charges concentrating at leakage prevention circuit  230 . 
         [0068]    Furthermore, damage prevention circuit  240  may be connected to a device of level shifter  200  other than leakage prevention circuit  230  and prevent damage to the corresponding device. For example, damage prevention circuit  240  may be connected to driving circuit  220  and prevent damage to transistors included in driving circuit  220 . 
         [0069]      FIG. 8A  is a circuit diagram of an embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 2 and 7  will be omitted below. 
         [0070]    Referring to  FIG. 8A , a level shifter  200   a  may include a level shifting circuit  210   a,  a driving circuit  220   a,  a leakage prevention circuit  230   a,  and a damage prevention circuit  240   a . Since level shifting circuit  210   a,  driving circuit  220   a,  and leakage prevention circuit  230   a  are identical to those described above with reference to  FIG. 2 , detailed description thereof will be omitted. 
         [0071]    Damage prevention circuit  240   a  may include a first damage preventing device Db 1  and a second damage preventing device Db 2 . 
         [0072]    The first damage preventing device Db 1  may be connected to a first low voltage transistor Lb 1  in parallel between a node b 2  to which a second terminal of a first native transistor Nb 1  and a first terminal of the first low voltage transistor Lb 1  are connected, and a node b 4  to which a second terminal of the first low voltage transistor Lb 1  is connected. Furthermore, the second damage preventing device Db 2  may be connected to a second low voltage transistor Lb 2  in parallel between a node b 3  to which a first terminal of the second low voltage transistor Lb 2 , and a node b 5  to which the second terminal of the second low voltage transistor Lb 2  is connected. 
         [0073]    When both the first native transistor Nb 1  and the first low voltage transistor Lb 1  are in an OFF state due to an input signal IN, the node b 2  may be floated. Here, when voltage of the node b 2  becomes higher than the second voltage V 2  of the input signal IN due to noise interference of the third voltage V 3 , the first low voltage transistor Lb 1 , which is vulnerable to damage, may be damaged. To prevent damage to the first low voltage transistor Lb 1 , the first damage preventing device Db 1  may be connected to the first low voltage transistor Lb 1  in parallel. The first damage preventing device Db 1  may be connected to the node b 2 , preventing the node b 2  from being floated, and allowing a current to flow to the node b 4 . As a result, damage to the first low voltage transistor Lb 1  may be prevented. 
         [0074]    The second damage preventing device Db 2  may also be connected to the node b 3 , prevent the node b 3  from being floated, and allow a current to flow to the node b 5 . As a result, damage to the second low voltage transistor Lb 2  may be prevented. 
         [0075]    As an unlimited example, each of the first damage preventing device Db 1  and the second damage preventing device Db 2  may include a diode transistor, a diode, a variable resistor, etc. A diode transistor may refer to a transistor having a gate and a drain thereof connected to each other. Although damage preventing devices are shown as diode transistors in  FIG. 8A , the inventive concept is not limited thereto. 
         [0076]      FIG. 8B  is a circuit diagram of another embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 2, 7, and 8A  will be omitted below. 
         [0077]    Referring to  FIGS. 7, 8A, and 8B , a level shifter  200   b  may include a level shifting circuit  210   b,  a driving circuit  220   b,  a leakage prevention circuit  230   b,  and a damage prevention circuit  240   b.  Since level shifting circuit  210   b,  driving circuit  220   b,  and leakage prevention circuit  230   b  are identical to those described above with reference to  FIG. 2 , detailed description thereof will be omitted. 
         [0078]    Damage prevention circuit  240   b  may include two or more damage preventing devices connected in series with each other. As shown in  FIG. 8B , a first damage preventing device Dc 1  and a second damage preventing device Dc 2  may be connected in series with each other and the series combination may be connected to a first low voltage transistor Lc 1  in parallel. Furthermore, a third damage preventing device Dc 3  and a fourth damage preventing device Dc 4  may be connected in series with each other and the series combination may operate complementarily with the first damage preventing device Dc 1  and the second damage preventing device Dc 2 . The number of damage preventing devices connected in series may be adjusted according to device characteristics of the first low voltage transistor Lc 1  and the second low voltage transistor Lc 2 . 
         [0079]    In an example where damage preventing devices are diode transistors, when n diode transistors are connected in series with each other and a voltage equal to or greater than n times of threshold voltage of the diode transistors is applied to a node c 2 , damage prevention circuit  240   b  may operate. 
         [0080]      FIG. 9  is a block diagram showing an embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 1 and 7  will be omitted below. 
         [0081]    Referring to  FIG. 9 , a level shifter  300  may include a level shifting circuit  310 , a contention preventing circuit  320 , a driving circuit  330 , a leakage prevention circuit  340 , and a damage prevention circuit  350 . Level shifting circuit  310 , driving circuit  330 , leakage prevention circuit  340 , and damage prevention circuit  350  of  FIG. 9  may be substantially identical to level shifting circuit  210 , leakage prevention circuit  230 , damage prevention circuit  240 , and damage prevention circuit  250  of  FIG. 7 . Therefore, a detailed description thereof will be omitted. 
         [0082]    Contention preventing circuit  320  may reduce contention between level shifting circuit  310  and driving circuit  330 . For example, when level shifting circuit  310  is driven, an undesired excessive current may flow to level shifting circuit  310  and driving circuit  330  due to a timing difference within driving circuit  330 . Contention preventing circuit  320  reduces such contention for faster level shifting. 
         [0083]      FIG. 10A  is a circuit diagram of an embodiment of a level shifter. Referring to  FIG. 10A , a level shifter  300   a  may include a level shifting circuit  310   a,  a contention preventing circuit  320   a,  a driving circuit  330   a,  and a leakage prevention circuit  340   a.  level shifting circuit  310   a,  contention preventing circuit  320   a,  driving circuit  330   a,  and leakage prevention circuit  340   a  of  FIG. 10A  are substantially identical to level shifting circuit  310 , contention preventing circuit  320 , driving circuit  330 , and leakage prevention circuit  340  of  FIG. 9 . Therefore, a detailed description thereof will be omitted. 
         [0084]    Contention preventing circuit  320   a  may include a first contention preventing device Cd 1  and a second contention preventing device Cd 2 . As an unlimited example, the first contention preventing device Cd 1  and the second contention preventing device Cd 2  may be high voltage transistors. 
         [0085]    A first terminal of the first contention preventing device Cd 1  may be connected to a first high voltage transistor Hd 1  at a node d 0 , whereas a second terminal of the first contention preventing device Cd 1  may be connected to a first native transistor Nd 1  at a node d 2 . Furthermore, an input signal IN may be input to a gate terminal of the first contention preventing device Cd 1 . The second contention preventing device Cd 2  may operate complementarily with the first contention preventing device Cd 1 . 
         [0086]    Since contention preventing circuit  320   a  shares a node d 6  and a node d 7  with driving circuit  330   a  and leakage prevention circuit  340   a,  contention preventing circuit  320   a,  driving circuit  330   a,  and leakage prevention circuit  340   a  may be operated together with the input terminal IN. 
         [0087]    In another example, contention preventing circuit  320   a  may be located between level shifting circuit  310   a  and a third voltage V 3  terminal. For example, in  FIG. 10A , the location of the first contention preventing device Cd 1  may be switched with the location of the first high voltage transistor Hd 1 , whereas and the location of the second contention preventing device Cd 2  may be switched with the location of the second high voltage transistor Hd 2 . 
         [0088]      FIG. 10B  is a circuit diagram of an embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 2 and 10A  will be omitted below 
         [0089]    Referring to  FIGS. 10A and 10B , a level shifter  300   b  may include a level shifting circuit  310   b,  a contention preventing circuit  320   b,  a driving circuit  330   b,  and a leakage prevention circuit  340   b.  Since level shifting circuit  310   b,  contention preventing circuit  320   b , and driving circuit  330   b  are identical to those described above with reference to  FIG. 10A , detailed description thereof will be omitted. 
         [0090]    Contention preventing circuit  320   b  may include a first contention preventing device Ce 1  and a second contention preventing device Ce 2 . A first terminal of the first contention preventing device Ce 1  may be connected to a first high voltage transistor He 1 , whereas second terminal of the first contention preventing device Ce 1  may be connected to a first native transistor Ne 1 . Furthermore, a bias signal BIAS may be applied to a gate terminal of the first contention preventing device Ce, 1  instead of an input signal IN as in level shifter  300   a  shown in  FIG. 10A . The second contention preventing device Ce 2  may operate complementarily with the first contention preventing device Ce 1 , where an inverse bias signal BIASB may be applied to a gate terminal of the second contention preventing device Ce 2 . The bias signal BIAS may be a signal that is pre-set in order to reduce contention between level shifting circuit  310   b  and contention preventing circuit  320   b.  Furthermore, the inverse bias signal BIASB may be a signal obtained by inversing the bias signal BIAS via an inverter. 
         [0091]      FIGS. 11A and 11B  are circuit diagrams showing level shifters according to embodiments. Descriptions already given above with reference to  FIGS. 2, 8A, 8B, and 10A  will be omitted below. 
         [0092]    Referring to  FIGS. 11A and 11B , level shifters  300   c  and  300   d  may include level shifting circuits  310   c  and  310   d,  contention preventing circuits  320   c  and  320   d,  driving circuits  330   c  and  330   d,  leakage prevention circuits  340   c  and  340   d,  and damage prevention circuits  350   c  and  350   d,  respectively. 
         [0093]    As described above with reference to  FIGS. 8A and 8B , damage prevention circuits  350   c  and  350   d  may prevent damage to leakage prevention circuits  340   c  and  340   d.  As shown in  FIG. 11A , damage prevention circuit  350   c  may include a pair of damage preventing devices Df 1  and Df 2  that operate complementarily with each other. Furthermore, as shown in  FIG. 11B , the damage prevention circuit  350   d  may include two or more damage preventing devices Dg 1 , Dg 2 , Dg 3 , and Dg 4  that are connected in series with each other. 
         [0094]      FIG. 12  is a diagram exemplifying an operation of an embodiment of a level shifter. Descriptions already given above with reference to  FIGS. 5 and 10A  will be omitted below. 
         [0095]      FIGS. 5, 10A, and 12  may show an operation of a level shifter when an input signal is converted from a first voltage V 1  to a second voltage V 2 . Furthermore, although a level shifter according to these embodiments is connected between ground voltage Vss and supply voltage Vpp, the inventive concept is not limited thereto, and the level shifter may be connected to any voltage as described above with reference to  FIG. 1 . In  FIG. 12 , a dashed circle around a transistor may denote a transistor in the ON state as described above with reference to  FIGS. 3 and 5 , whereas a transistor with a “/” marked through it may denote a transistor in the OFF state as described above with reference to  FIGS. 3 and 5 . 
         [0096]    STEP  0  may denote a state wherein an input signal IN maintains a first voltage V 1 . The first voltage V 1  may be a voltage which is less than the threshold voltages of a native transistor and a low voltage transistor. Therefore, when the input signal IN is the first voltage V 1 , the first native transistor Nd 1  and the first low voltage transistor Ld 1  may be in an OFF state and the first contention preventing device Cd 1  may be in an ON state. On the other hand, the second native transistor Nd 2  and the second low voltage transistor Ld 2  receive an inverse input signal INB, which is an input signal inverted by an inverter INV, via gate terminals. Therefore, when the input signal IN is the first voltage V 1 , the inverse input signal INB, which is the inverted first voltage V 1 , is input to the gate terminals of the second native transistor Nd 2  and the second low voltage transistor Ld 2 , where the voltage level of the inverse input signal INB may be greater than the threshold voltages of the second native transistor Nd 2  and the second low voltage transistor Ld 2 . Therefore, the second native transistor Nd 2  and the second low voltage transistor Ld 2  may be in an ON state due to the inverse input signal INB, and the second contention preventing device Cd 2  may be in an OFF state due to the inverse input signal INB. 
         [0097]    When the ground voltage Vss is applied to a node d 3  and the first high voltage transistor Hd 1  is in an ON state, second power voltage Vpp may be applied to a node d 0  and a node d 2 . Therefore, the second power voltage Vpp may also be applied to a gate terminal of the second high voltage transistor Hd 2  connected to the node d 0 , and thus the second high voltage transistor Hd 2  may be maintained in an OFF state. 
         [0098]    STEP  1  may show a step in which the input signal IN transitions from the first voltage V 1  to the second voltage V 2 . The second voltage V 2  may have a voltage level which is greater than the threshold voltages of the first native transistor Nd 1  and the first low voltage transistor Ld 1 . Therefore, when the second voltage V 2  is applied to the gate terminals of the first native transistor Nd 1  and the first low voltage transistor Ld 1  as the input signal IN, the first native transistor Nd 1  and the first low voltage transistor Ld 1  may transition to an ON state. As the first native transistor Nd 1  and the first low voltage transistor Ld 1  are in an ON state, the ground voltage Vss may be applied to the node d 2 . Furthermore, when the second voltage V 2  is applied as an input signal IN, the first contention preventing device Cd 1  may transition to an OFF state. When the input signal IN is switched to the second voltage V 2 , the first high voltage transistor Hd 1  may maintain the ON state. When the input signal IN transitions to the second voltage V 2 , the first contention preventing device Cd 1  may transition to an OFF state together with the first native transistor Nd 1  and the first low voltage transistor Ld 1 , thereby preventing a concentration of contention. 
         [0099]    Furthermore, since a voltage complementary with the second voltage V 2  is applied to the gate terminals of the second native transistor Nd 2  and the second low voltage transistor Ld 2  as an inverse input signal INB, the second native transistor Nd 2  and the second low voltage transistor Ld 2  may transition to an OFF state. Accordingly, the second contention preventing device Cd 2  may transition to an ON state. 
         [0100]    STEP  2  may refer to a step after the ground voltage Vss is applied to the node a 0  in STEP  1 . Although STEP  2  is shown after STEP  1 , it is merely a logic sequence, and the steps may occur sequentially or simultaneously. 
         [0101]    In STEP  1 , when the ground voltage Vss is applied to the node d 2 , since the gate terminal of the second high voltage transistor Hd 2  is connected to the node d 2 , the ground voltage Vss may also be applied to the gate terminal of the second high voltage transistor Hd 2 . Therefore, the second high voltage transistor Hd 2  may transition to an ON state. In this case, a high voltage, which is the second power voltage Vpp, may be applied to the node d 1 . Furthermore, as described above, since the second contention preventing device Cd 2  is in an ON state, the second power voltage Vpp may also be applied to the node d 3 . Since the output terminal OUT is connected to the node d 3 , the second power voltage Vpp may be applied to the output terminal OUT. 
         [0102]    Furthermore, when the second power voltage Vpp is applied to the node d 3 , the first high voltage transistor Hd 1 , of which the gate terminal is connected to the node d 3 , may transition to an OFF state. Therefore, the second power voltage Vpp may be stably applied to the output terminal OUT. 
         [0103]      FIG. 13  is a flowchart showing operations of an embodiment of a level shifter. 
         [0104]    Referring to  FIG. 13 , when an input signal transitions from a first voltage V 1  to a second voltage V 2  (operation S 10 ), a driving circuit may drive a level shifting circuit (operation S 20 ). Next, a level shifting circuit may apply a third voltage V 3  to an output node (operation S 30 ). 
         [0105]      FIG. 14  is a flowchart showing operations of an embodiment of a level shifter. 
         [0106]    Referring to  FIGS. 2 and 14 , as an input signal transitions from a first voltage V 1  to a second voltage V 2  (operation S 110 ), a native transistor and a low voltage transistor, which receive the input signal via gate terminals thereof, may transition to an ON state (operation S 120 ). Next, the ground voltage Vss may be applied to a gate terminal of a high voltage transistor (operation S 130 ), and thus the high voltage transistor may transition to an ON state (operation S 140 ). As a result, the second power voltage Vpp may be applied to the output node (operation S 150 ). 
         [0107]      FIG. 15  is a block diagram showing an embodiment of a computing system device. 
         [0108]    Referring to  FIG. 15 , a computing system device  500  may include a memory system device  510 , which includes a memory controller  512  and a memory device  511 , and a power supply device  520 . A level shifter  513  may be included in memory device  511 . Level shifter  513  may be a level shifter according to the above-stated embodiment. Level shifter  513  may change voltage level of a voltage applied by power supply device  520  and apply the voltage with changed voltage level to other circuits in memory device  511 . Also, level shifter  513  may output the voltage with changed voltage level to a device other than memory device  511 . Although  FIG. 15  shows that level shifter  513  and memory controller  512  as separate devices, memory controller  512  may include level shifter  513 , or level shifter  513  memory controller  512  may be embodied as separate devices. 
         [0109]    Computing system device  500  may further include a microprocessor  530 , a user interface  550 , a RAM  540 , and power supply device  520  that are electrically connected to bus  560 . Computing system device  500  may comprise a mobile device, a camera, a computer, etc. 
         [0110]    When computing system device  500  according to an embodiment is a mobile device, a battery for supplying a voltage for operating computing system device  500  and a modem, such as a baseband chipset, may be additionally provided. Furthermore, computing system device  500  according to an embodiment may further include an application chipset, a camera image processor (CIS), and a mobile DRAM. 
         [0111]    For example, memory controller  512  and memory device  511  may constitute a solid state drive/disk (SSD) that uses a non-volatile memory for storing data. 
         [0112]    While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.