Patent Publication Number: US-2022222339-A1

Title: Low voltage attack detector, secure element and electronic system including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims benefit of priority to Korean Patent Application No. 10-2021-0005408 filed on Jan. 14, 2021 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present inventive concept relates to a low voltage attack detector. 
     Various types of hardware security system have been developed to prevent hacking accidents caused by physical attacks of semiconductor chips. However, even in the case of semiconductor chips to which a hardware security system is applied, information inside a security chip may be exposed by various physical attacks. 
     A semi-invasive attack, among the physical attacks on a semiconductor chip, refers to an attack method of injecting an error without direct physical access to a chip and analyzing a resultant malfunction. Among the semi-invasive attacks, there is a method of causing an error by abnormally changing a voltage, and in order to prevent the same, a device that may detect an occurrence of an abnormal operating environment would be beneficial. 
     SUMMARY 
     An aspect of the present inventive concept is to provide a low voltage attack detector maintaining a level of a low voltage detection flag signal when a power supply voltage is lowered to a voltage level in a voltage region in which an analog circuit malfunctions. 
     According to an aspect of the present inventive concept, a low voltage attack detector includes: a low voltage detector configured to output a low voltage detection flag signal having a high level when a first power supply voltage reaches a first voltage level using a bandgap reference (BGR) circuit including a PMOS transistor and a first bipolar junction transistor (BJT) connected in series between the first power supply voltage and a second power supply voltage; a BGR operation region detector configured to output a malfunction detection flag signal having a high level when the first power supply voltage reaches a second voltage level lower than the first voltage level; and a logic gate configured to output a final low voltage detection flag signal having a high level when at least one of the low voltage detection flag signal and the malfunction detection flag signal has a high level. 
     According to an aspect of the present inventive concept, a low voltage attack detector includes: a low voltage detector configured to detect whether a first power supply voltage reaches a first voltage level using a bandgap reference (BGR) circuit in a first reliability region in which the first power supply voltage belongs to a first range, and output a low voltage detection flag signal having a high level when the first power supply voltage reaches the first voltage level; a BGR operation region detector configured to output a malfunction detection flag signal having a high level in a second reliability region in which the first power supply voltage belongs to a second range different from the first range; and a power on reset (POR) circuit configured to output a first POR signal having a low level in a third reliability region in which the first power supply voltage belongs to a third range different from the first range and the second range. Each voltage level belonging to the first range is greater than each voltage level belonging to the second range, and each voltage level belonging to the second range is greater than each voltage level belonging to the first range. 
     According to an aspect of the present inventive concept, a low voltage attack detector includes: a bandgap reference (BGR) operation region detector configured to detect a decrease in a first power supply voltage, wherein the BGR operation region detector may include: a first resistor and a bipolar junction transistor (BJT) connected in series between the first power supply voltage and a second power supply voltage; a second resistor and a third resistor connected in series between the first power supply voltage and the second power supply voltage; and a comparator including a first input terminal connected to a first node between the first resistor and the BJT and a second input terminal connected to a second node between the second resistor and the third resistor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features, and advantages of the present inventive concept will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a low voltage attack detector according to an embodiment of the present inventive concept. 
         FIG. 2  illustrates operation waveforms of a low voltage attack detector according to an embodiment of the present inventive concept. 
         FIG. 3  is a diagram schematically illustrating a low voltage detector according to an embodiment of the present inventive concept. 
         FIG. 4  illustrates a bandgap reference (BGR) circuit according to an embodiment of the present inventive concept. 
         FIG. 5  illustrates a BGR operation region detector according to an embodiment of the present inventive concept. 
         FIG. 6  illustrates a low voltage attack detector according to an embodiment of the present inventive concept. 
         FIG. 7  illustrates a power on reset (POR) circuit according to an embodiment of the present inventive concept. 
         FIG. 8  illustrates operation waveforms of a POR circuit according to an embodiment of the present inventive concept. 
         FIGS. 9 and 10  are graphs illustrating a guaranteed region of a low voltage attack detector according to an embodiment of the present inventive concept. 
         FIG. 11  is a block diagram illustrating a secure element according to an embodiment of the present inventive concept. 
         FIG. 12  is a flowchart illustrating a method of operating a secure element according to embodiments of the present inventive concept. 
         FIG. 13  is a block diagram illustrating an electronic system according to embodiments of the present inventive concept. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments of the present inventive concept will be described with reference to the accompanying drawings. 
       FIG. 1  illustrates a low voltage attack detector according to an embodiment of the present inventive concept, and  FIG. 2  illustrates operation waveforms of a low voltage attack detector according to an embodiment of the present inventive concept. 
     Referring to  FIGS. 1 and 2  together, a low voltage attack detector  10  may include a low voltage detector (LVD)  100 , a bandgap reference (BGR) operation region detector (BORD)  200 , and a logic gate  300 . 
     Each of the low voltage detector  100  and the BGR operation region detector  200  may receive a power supply voltage AVDD. The power supply voltage AVDD may be a voltage used to drive an arbitrary electronic device and/or system (hereinafter, referred to as a “system”), and may be, for example, an analog power supply voltage. When the power supply voltage AVDD is lowered to a target voltage V TG , the low voltage attack detector  10  may generate a final low voltage detection flag signal and maintain the final low voltage detection flag signal until the power supply voltage AVDD reaches 0V. When the low voltage attack detector  10  informs the system of the final low voltage detection flag signal, the system may be disabled. 
     The low voltage detector  100  may detect whether the power supply voltage AVDD reaches the target voltage V TG , and output a detection result as a low voltage detection flag signal V LVDET . The target voltage V TG  may refer to a voltage of a region in which various components constituting the system may malfunction. For example, the target voltage V TG  may be a voltage lower than a voltage V TYP  (e.g., 1.2V) for the system to operate normally. 
     When the power supply voltage AVDD reaches the target voltage V TG  at a time point t 1 , the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a high level ‘H’. The low voltage detection flag signal V LVDET  has to be able to maintain the high level ‘H’ as shown in graph ‘a’ when the power supply voltage AVDD continues to decrease. 
     The system may be disabled based on the low voltage detection flag signal V LVDET  having the high level ‘H’. Therefore, the system cannot operate in an abnormal power supply region and may operate only in a normal power supply region. 
     The low voltage detector  100  may detect whether the power supply voltage AVDD reaches the target voltage V TG  using a reference voltage generated by a BGR circuit. The BGR circuit may be used as a current source or voltage source that generates a reference current or a reference voltage in analog and digital systems. The power supply voltage AVDD of the analog and digital systems tends to gradually decrease due to the development of a process technology, so BGR circuits used in the analog and digital systems have to be able to operate well at low voltages. 
     Meanwhile, in order for an analog circuit such as an operational amplifier or a comparator to operate normally, a minimum voltage required for a bias circuit of the analog circuit to operate normally has to be applied. For example, a minimum voltage is required for transistors included in the analog circuit to operate normally. However, as the power supply voltage AVDD gradually decreases, the bias circuit of the analog circuit may not operate normally at a malfunction voltage V ERR  at a time point t 2 . That is, if the power supply voltage AVDD is lowered to the malfunction voltage V ERR , the analog circuit may malfunction. 
     When the power supply voltage AVDD in the low voltage detector  100  is lowered to the malfunction voltage V ERR , the BGR circuit may malfunction. When the BGR circuit malfunctions, the reference voltage may have an unpredictable value. 
     If the reference voltage has an unpredictable value, the low voltage detector  100  may not be able to maintain the high level ‘H’ of the low voltage detection flag signal V LVDET  even though the power supply voltage AVDD continues to decrease. As shown in graph ‘b’, when the power supply voltage AVDD reaches the malfunction voltage V ERR  at the time point t 2 , the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a low level ‘L’. The system may be enabled based on the low voltage detection flag signal V LVDET  having the low level ‘L’. Thus, the system may operate in an abnormal power supply region. 
     When the low voltage detector  100  is a low voltage detector for preventing hacking, a hacker may hack the system after artificially applying various voltages that may cause malfunction of the analog circuit. Therefore, the low voltage detector  100  has to be able to maintain the low voltage detection flag signal V LVDET  at the high level ‘H’ even at a voltage level in a voltage region in which the analog circuit malfunctions. 
     When the power supply voltage AVDD is lowered to a voltage level in the voltage region in which the BGR circuit malfunctions, the low voltage attack detector  10  according to an embodiment of the present inventive concept may output a malfunction detection flag signal V BGRDET  having a high level in advance using the BGR operation region detector  200  before the BGR circuit malfunctions. Therefore, even if the BGR circuit malfunctions, since the BGR operation region detector  200  generates the malfunction detection flag signal V BGRDET  having a high level, the same effect as maintaining the high level of the low voltage detection flag signal V LVDET  may be obtained. 
     The logic gate  300  may receive the low voltage detection flag signal V LVDET  from the low voltage detector  100  and the malfunction detection flag signal V BGRDET  from the BGR operation region detector  200 . When the power supply voltage AVDD reaches the target voltage V TG , the low voltage detection flag signal V LVDET  may have a high level, and when the power supply voltage AVDD decreases to the malfunction voltage V ERR , the low voltage detection flag signal V LVDET  may have a low level and the malfunction detection flag signal V BGRDET  may have a high level. When the logic gate  300  is an OR gate, the logic gate  300  may perform an OR operation on the low voltage detection flag signal V LVDET  and the malfunction detection flag signal V BGRDET . When at least one of the low voltage detection flag signal V LVDET  and the malfunction detection flag signal V BGRDET  has a high level, the logic gate  300  may output a final low voltage detection flag signal V LVDET_MERGED  having a high level. 
     When the low voltage attack detector  10  informs the system of the final low voltage detection flag signal V LVDET_MERGED  of the high level, the system may be disabled. For example, when at least one of the low voltage detection flag signal V LVDET  and the malfunction detection flag signal V BGRDET  has a high level, the system does not operate. Therefore, even if the BGR circuit malfunctions, the same effect as maintaining the high level of the low voltage detection flag signal V LVDET  may be obtained. 
       FIG. 3  is a diagram illustrating a simplified low voltage detector according to an embodiment of the present inventive concept. 
     Referring to  FIG. 3 , the low voltage detector  100  according to an embodiment of the present inventive concept may include a BGR circuit  110 , a first power supply voltage detection circuit  120 , and a comparator  130 . The BGR circuit  110  may generate a reference voltage V REF  having a stable level regardless of a process-voltage-temperature (PVT) fluctuation. 
     The first power supply voltage detection circuit  120  may generate a first detection voltage V SENSE   1  from the power supply voltage AVDD. For example, the first power supply voltage detection circuit  120  may include a first resistor R 1  and a second resistor R 2  connected in series between the power supply voltage AVDD and a ground voltage, and generate a first detection voltage V SENSE1  by resistance-dividing the power supply voltage AVDD. The power supply voltage AVDD may be defined as a first power supply voltage, and the ground voltage may be defined as a second power supply voltage. 
     The comparator  130  may receive a detection voltage V SENSE1  from the first power supply voltage detection circuit  120  and may receive a reference voltage V REF  from the BGR circuit  110 . The comparator  130  may compare the first detection voltage V SENSE1  to the reference voltage V REF , and when the first detection voltage V SENSE1  reaches the reference voltage V REF , the comparator  130  may output a low voltage detection flag signal V LVDET  having a high level. 
     For example, when the power supply voltage AVDD is too low, the BGR circuit  110  cannot operate normally. When a hacker artificially applies a voltage that may cause malfunction of the BGR circuit  110 , the reference voltage V REF  generated by the BGR circuit  110  may have an unpredictable value. Therefore, a normal operation of the low voltage detector  100  cannot be guaranteed. 
       FIG. 4  illustrates a BGR circuit according to an embodiment of the present inventive concept. 
     Referring to  FIG. 4 , the BGR circuit  110  may generate a reference voltage V REF  having a stable level regardless of PVT fluctuation. The BGR circuit  110  may include an operational amplifier (OPAMP), first to third PMOS transistors P 1  to P 3 , third to sixth resistors R 3  to R 6 , a first bipolar junction transistor (BJT) Q 1 , and a second BJT Q 2 . A size of the second BJT Q 2  may be N times a size of the first BJT Q 1 . 
     The first PMOS transistor P 1  may be connected between the power supply voltage AVDD and a first input terminal (−) of an operational amplifier OPAMP and include a gate connected to an output terminal of the operational amplifier OPAMP. The second PMOS transistor P 2  may be connected between the power supply voltage AVDD and a second input terminal (+) of the operational amplifier OPAMP and include a gate connected to the output terminal of the operational amplifier OPAMP. The third PMOS transistor P 3  may be connected between the power supply voltage AVDD and an output terminal OUT and include a gate connected to the output terminal of the operational amplifier OPAMP. 
     The gate of the first PMOS transistor P 1 , the gate of the second PMOS transistor P 2 , and the gate of the third PMOS transistor P 3  are commonly connected to the output terminal of the operational amplifier OPAMP. The sizes of the first transistor P 1  and the second PMOS transistor P 2  may be the same, and a ratio of the size of the second PMOS transistor P 2  and the size of the third PMOS transistor P 3  may be 1:M. Here, M is a positive integer greater than 1. 
     The third resistor R 3  may be connected between the first input terminal (−) of the operational amplifier OPAMP and the ground voltage, and the first BJT Q 1  may be connected between the first input terminal (−) of the operational amplifier OPAMP and the ground voltage. The fourth resistor R 4  and the second BJT Q 2  may be connected in series between the second input terminal (+) of the operational amplifier OPAMP and the ground voltage. The fifth resistor R 5  may be connected between the second input terminal (+) of the operational amplifier OPAMP and the ground voltage, and the sixth resistor R 6  may be connected between the output terminal OUT and the ground voltage. 
     Since the first transistor P 1  and the second PMOS transistor P 2  have the same size and the gate of the first transistor P 1  and the gate of the second PMOS transistor P 2  are commonly connected to the output terminal of the operational amplifier OPAMP, a first current I 1  flowing through the first PMOS transistor P 1  and a second current I 2  flowing through the second PMOS transistor P 2  may be substantially the same. 
     Turn-on degrees of the first PMOS transistor P 1  and the second PMOS transistor P 2  may change according to an output voltage of the operational amplifier OPAMP. Accordingly, the amounts of the first current I 1  and the second current I 2  may be adjusted. Such an operation continues until a level of a voltage VN at the first input terminal (−) of the operational amplifier OPAMP and a voltage VP at the second input terminal (+) of the operational amplifier OP AMP are the same. 
     The voltage VN at the first input terminal (−) of the operational amplifier OPAMP may be inversely proportional to temperature due to complementary to absolute temperature (CTAT) characteristics of a base-emitter voltage V BE  of the first BJT Q 1 . Since the voltage VP at the second input terminal (+) of the operational amplifier OPAMP is the same as the voltage VN at the first input terminal (−) of the operational amplifier OPAMP, a current flowing through the fifth resistor R 5  may have characteristics inversely proportional to an absolute temperature. 
     A level of a base-emitter voltage V BEN  of the second BJT Q 2  is also lowered as a temperature increases. Since a size of the second BJT Q 2  is N times a size of the first BJT Q 1 , a variation of the base-emitter voltage V BEN  of the second BJT Q 2  according to a temperature is greater than a variation of the base-emitter voltage V BE  of the first BJT Q 1  according to a temperature. Here, N is a positive integer greater than 1. Accordingly, as the temperature increases, a voltage difference at both ends of the fourth resistor R 4  may increase. Accordingly, a current flowing through the fourth resistor R 4  may have characteristics proportional to the absolute temperature (PTAT). 
     PTAT characteristics of the current flowing through the fourth resistor R 4  may be canceled by CTAT characteristics of a current flowing through the fifth resistor R 5 . 
     When a ratio of the size of the second PMOS transistor P 2  and the size of the third PMOS transistor P 3  is 1:M, a magnitude of a third current I 3  flowing through the third PMOS transistor P 3  may be M times a magnitude of a second current I 2  flowing through the second PMOS transistor P 2 . When a level of the voltage VN at the first input terminal (−) of the amplifier OPAMP and a level of the voltage VP at the second input terminal (+) of the operational amplifier OPAMP are the same, the reference voltage VREF having a constant level may be applied to on the terminal OUT. 
     For example, the first PMOS transistor P 1  connected between the power supply voltage AVDD and the first BJT Q 1  has to operate in a saturation region. A drain-source voltage V DS  of the first PMOS transistor P 1  has to be sufficiently secured so that the first PMOS transistor P 1  may operate in the saturation region. For example, if the drain-source voltage V DS  of the first PMOS transistor P 1  is lower than 10% of the power supply voltage AVDD, the first PMOS transistor P 1  may not operate in the saturation region. In this case, a desirable voltage of the drain-source voltage V DS  of the first PMOS transistor P 1  may be 10% or less of the power supply voltage AVDD. The base-emitter voltage V BE  of the BJT may increase to 0.9V in a low-temperature environment (for example, −55° C.) due to the CTAT characteristics, and thus, when the power supply voltage AVDD is lowered to 1V in the low-temperature environment, the drain-source voltage V DS  of the first PMOS transistor P 1  reaches the desirable voltage. Accordingly, the first PMOS transistor P 1  may fail to operate in the saturation region. If the first PMOS transistor P 1  fails to operate in the saturation region, a voltage gain of a loop formed by the first PMOS transistor P 1  may be lowered. When the voltage gain of the loop formed by the first PMOS transistor P 1  is lowered, the reference voltage V REF  may have an unpredictable value. That is, if the power supply voltage AVDD continues to decrease in the low-temperature environment, the BGR circuit  110  may malfunction. 
     In the above, an embodiment in which the desirable voltage of the drain-source voltage V DS  of the first PMOS transistor P 1  is 10% or less of the power supply voltage AVDD has been described. However, this is only an example and the desirable voltage of the drain-source voltage V DS  of the first PMOS transistor P 1  may be set to be different. 
     The low-voltage attack detector according to an embodiment of the present inventive concept may include a BGR operation region detector outputting a malfunction detection flag signal having a high level in advance before the BGR circuit  110  malfunctions when the power supply voltage AVDD is lowered to a voltage level in a voltage region in which the BGR circuit  110  malfunctions in a low-temperature environment. Therefore, even if the BGR circuit  110  malfunctions, since the BGR operation region detector generates the malfunction detection flag signal V BGRDET  having a high level, the same effect as that when the high level of the low voltage detection flag signal is maintained may be obtained. 
       FIG. 5  illustrates a BGR operation region detector according to an embodiment of the present inventive concept. 
     Referring to  FIG. 5 , the BGR operation region detector  200  according to an embodiment of the present inventive concept may include a BJT voltage generator  210 , a second power supply voltage detection circuit  220 , and a comparator  230 . As described above with reference to  FIG. 4 , as the power supply voltage AVDD decreases, the drain-source voltage of the PMOS transistor P 1  included in the BGR circuit decreases. When the drain-source voltage of the PMOS transistor P 1  reaches the desirable voltage, the operation region of the PMOS transistor P 1  is outside the saturation region. When the operation region of the PMOS transistor P 1  is outside the saturation region, the BGR circuit may malfunction. For example, when the PMOS transistor P 1  is outside the saturation region, the first current I 1  flowing through the first PMOS transistor P 1  may not flow linearly. The BGR operation region detector  200  may detect a decrease in the drain-source voltage of the PMOS transistor P 1  included in the BGR circuit by detecting the decrease in the power supply voltage AVDD. Accordingly, the BGR operation region detector  200  may detect whether the drain-source voltage of the PMOS transistor P 1  reaches a desirable voltage. 
     The BJT voltage generator  210  may include a seventh resistor R 7  and a BJT Q connected in series between the power supply voltage AVDD and the ground voltage. The BJT voltage generator  210  may output a base-emitter voltage V BJT  of the BJT Q based on the power supply voltage AVDD. The BJT voltage generator  210  may include the seventh resistor R 7  instead of a transistor (e.g., the PMOS transistor P 1  in  FIG. 4 )). The seventh resistor R 7  may allow a current to flow linearly based on the power supply voltage AVDD and the base-emitter voltage V BJT  of the BJT Q (V IN1 ). For example, the base-emitter voltage V BJT  of the BJT Q may maintain at a predetermined level based on a current flowing through the seventh resistor R 7 . 
     The second power supply voltage detection circuit  220  may output a second detection voltage V SENSE2  based on the power supply voltage AVDD. For example, the second power supply voltage detection circuit  220  may include an eighth resistor R 8  and a ninth resistor R 9  connected in series between the power supply voltage AVDD and the ground voltage, and the second power supply voltage detection circuit  220  may generate the second detection voltage V SENSE2  by resistance-dividing the power supply voltage AVDD. 
     For example, in the BGR circuit  110 , if the drain-source voltage of the PMOS transistor is equal to or lower than 10% of the power supply voltage AVDD, the BGR circuit  110  may malfunction. The BGR operation region detector  200  may detect a decrease in the power supply voltage AVDD and detect a case in which the drain-source voltage of the PMOS transistor included in the BGR circuit  110  is lower than 10% of the power supply voltage AVDD. The drain-source voltage of the PMOS transistor included in the BGR circuit  110  may correspond to a difference between the power supply voltage AVDD and the base-emitter voltage V BE  of the BJT Q in the BGR operation region detector  200 . As described above in  FIG. 4 , since the base-emitter voltage V BE  of the BJT Q increases to 0.9V in a low-temperature environment, the drain-source voltage of the PMOS transistor P 1  may be 100 mV when the power supply voltage AVDD is 1V in the BGR circuit  110 . If the drain-source voltage of the PMOS transistor P 1  is equal to or lower than 100 mV, the BGR circuit  110  may malfunction. Therefore, when a ratio of a size of the eighth resistor R 8  and a size of the ninth resistor R 9  in the BGR operation region detector  200  is 1:9, the BGR operation region detector  200  may detect a decrease in the power supply voltage AVDD and detect a case in which the drain-source voltage of the PMOS transistor P 1  included in the BGR circuit  110  is equal to or lower than 10% of the power supply voltage AVDD. The ratio of the size of the eighth resistor R 8  and the size of the ninth resistor R 9  may vary according to a drain-source voltage of the PMOS transistor P 1  to be detected. 
     The comparator  130  may include a first input terminal connected to a first node IN 1  between the seventh resistor R 7  and the BJT Q and a second input terminal connected to a second node IN 2  between the eighth resistor R 8  and the ninth resistor R 9 . The comparator  130  may receive the base-emitter voltage V BJT  of the BJT Q from the BJT voltage generator  210  through the first input terminal and may receive the second detection voltage V SENSE2  from the second power supply voltage detection circuit  220  through the second input terminal. The comparator  130  may compare the base-emitter voltage V BJT  of the BJT Q to the second detection voltage V SENSE2 , and when the base-emitter voltage V BJT  of the BJT (Q reaches the second detection voltage V SENSE2 , the comparator  130  may output a malfunction detection flag signal V BGRDET  having a high level. For example, in a low-temperature environment, when the base-emitter voltage V BJT  of BJT Q increases to 0.9V and the power supply voltage AVDD decreases to 1V, the base-emitter voltage V BJT  of BJTQ and the reference voltage V REF  from the BGR circuit  110  is 0.9V, respectively. Accordingly, the comparator  130  may output a malfunction detection flag signal V BGRDET  having a high level. 
     The BGR operation region detector  200  may output a malfunction detection flag signal V BGRDET  having a high level in advance before the BGR circuit malfunctions. For example, even if the low voltage detector  100  cannot maintain the high level of the low voltage detection flag signal V LVDET , the BGR operation region detector  200  may output the malfunction detection flag signal V BGRDET  having a high level. Therefore, even if the BGR circuit  110  malfunctions, the same effect as continuously maintaining the high level of the low voltage detection flag signal V BGRDET  may be obtained. 
     However, if the power supply voltage AVDD is continuously lowered in a low-temperature environment, a bias circuit of an analog circuit such as an operational amplifier or a comparator may not operate normally. For example, if the power supply voltage AVDD continues to decrease in the low-temperature environment, the bias circuit of the comparator included in the BGR operation region detector  200  may malfunction and the BGR operation region detector  200  may malfunction. Accordingly, even if the voltage region in which the BGR circuit  110  malfunctions is covered using the BGR operation region detector  200 , it may not be able to maintain the high level of the low voltage detection flag signal in the voltage region in which another analog circuit malfunctions. 
     In addition, since a threshold voltage of a transistor decreases as a temperature increases, a voltage at which an analog circuit malfunctions may decrease. For example, in a high-temperature environment (e.g., 150° C.), a voltage at which the BGR circuit  110  malfunctions may be lowered. However, in a high-temperature environment, the low voltage detector  100  may malfunction because the bias circuit of the operational amplifier included in the BGR circuit  110  does not operate normally rather than due to the effect of the base-emitter voltage V BE  of the BJT Q 1  included in the BGR circuit  110 . Accordingly, in a voltage region in which the analog circuit malfunctions, it may not be possible to maintain the high level of the low voltage detection flag signal V BGRDET . 
     The low voltage attack detector according to an embodiment of the present inventive concept may include a power on reset (POR) circuit capable of detecting a region in which an analog circuit malfunctions at the entire temperatures. Accordingly, the effect that the high level of the low voltage detection flag signal is continuously maintained in the entire low voltage region may be provided. 
       FIG. 6  illustrates a low voltage attack detector according to an embodiment of the present inventive concept. 
     Referring to a difference from  FIG. 1 , a low voltage attack detector  20  of  FIG. 6  may further include a POR circuit  400  and an inverter  500 . The POR circuit  400  may output a first POR signal V POR , and the inverter  500  may output a second POR signal V POR′  by inverting a level of the first POR signal V POR . The second POR signal V POR′  may be input to the logic gate  300 . The POR circuit  400  outputs a reset signal when the power supply voltage AVDD is lower than a predetermined voltage so that the system maintains a reset state, and when the power supply voltage AVDD is equal to or higher than the predetermined voltage, the system may operate normally. 
     As described above, when the power supply voltage AVDD reaches the target voltage, the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a high level. However, in a low-temperature environment, when the power supply voltage AVDD is lowered to a voltage level in a voltage region in which the BGR circuit  110  may malfunction, the high level of the low voltage detection flag signal V LVDET  may not be maintained. 
     The BGR operation region detector  200  may detect a decrease in the power supply voltage AVDD in a low-temperature environment to detect whether the operation region of the PMOS transistor of the BGR circuit  110  is outside a saturation region. Accordingly, the BGR operation region detector  200  may detect whether the power supply voltage AVDD reaches a voltage level in the voltage region in which the BGR circuit  110  malfunctions, and may output a malfunction detection flag signal V BGRDET  having a high level before the BGR circuit  110  malfunctions. Even if the level of the low voltage detection flag signal V LVDET  decreases to be low, the BGR operation region detector  200  may output the malfunction detection flag signal V BGRDET  having a high level, and thus, a final low voltage detection flag signal V LVDET_MERGED  having a high level may be output through the logic gate  300 . Accordingly, even if the BGR circuit  110  malfunctions, the same effect as continuously maintaining the high level of the low voltage detection flag signal V LVDET  may be obtained. 
     However, when the level of the power supply voltage AVDD decreases to a voltage level in the voltage region in which the bias circuit of the comparator included in the BGR operation region detector  200  does not operate normally in a low-temperature environment, the BGR operation region detector  200  may malfunction. In addition, even in a high-temperature environment, if the level of the power supply voltage AVDD decreases to a voltage level in the voltage region in which the bias circuit of the operational amplifier included in the BGR circuit  110  does not operate normally, the low voltage detector  100  may malfunction. Accordingly, the low voltage attack detector  20  according to an embodiment of the present inventive concept may generate the second POR signal V POR′  having a high level before the analog circuit malfunctions at the entire temperatures. A voltage at which the first POR signal V POR  has a low level may be adjusted by changing the size of a resistor and a transistor included in the POR circuit  400 . 
     The POR circuit  400  may output the first POR signal V POR  having a low level when the power supply voltage AVDD reaches a voltage level in a voltage region in which the analog circuit malfunctions. The inverter  500  may output the second POR signal V POR′  having a high level by inverting the low level of the first POR signal V POR . 
     Even if the level of the low voltage detection flag signal V LVDET  falls to a low level, the POR circuit  400  may output the second POR signal V POR′  having a high level through the inverter  500 , so that a final low voltage detection flag signal V LVDET_MERGED  having a high level may be output through the logic gate  300 . Accordingly, even if the analog circuits malfunction, the same effect as continuously maintaining the high level of the low voltage detection flag signal V LVDET  may be obtained. 
       FIG. 7  illustrates a POR circuit according to an embodiment of the present inventive concept, and  FIG. 8  illustrates operation waveforms of a POR circuit according to an embodiment of the present inventive concept. 
     Referring to  FIG. 7 , the POR circuit  400  may include a tenth resistor R 10 , an eleventh resistor R 11 , an NMOS transistor N, and an inverter INV The tenth resistor R 10 , the eleventh resistor R 11 , and the NMOS transistor N may be connected in series between the power supply voltage AVDD and the ground voltage. A gate of the NMOS transistor N may be connected to a first node ND 1  between the tenth resistor R 10  and the eleventh resistor R 11 . An input terminal of the inverter INV may be connected to a second node ND 2  between the eleventh resistor R 11  and the NMOS transistor N to receive a voltage from the second node ND 2 . The inverter INV may invert the voltage from the second node ND 2  and output an inverted voltage. 
     When the power supply voltage AVDD is very low, a gate voltage of the NMOS transistor N may be lower than a threshold voltage (e.g., a threshold voltage V LTH  in  FIG. 8 ). Accordingly, when the gate voltage of the NMOS transistor N is lower than the threshold voltage, the NMOS transistor N may be turned off. When the NMOS transistor N is turned off, current may not flow through the tenth resistor R 10  and the eleventh resistor R 11 . Accordingly, the voltage of the first node ND 1  follows the power supply voltage AVDD. 
     The power supply voltage AVDD may gradually increase so that a current may flow through the tenth resistor R 10  and the eleventh resistor R 11 . When a current flows through the tenth resistor R 10  and the eleventh resistor R 11 , the voltage at the second node ND 2  may gradually decrease and the voltage at the first node ND 1  may gradually increase. When the gate voltage of the NMOS transistor N is greater than the threshold voltage, the NMOS transistor N may be turned on. When the NMOS transistor N is turned on, the voltage at the second node ND 2  may drop to the ground voltage. 
     As shown in  FIG. 8 , when the power supply voltage AVDD increases, a voltage V ND1  at the first node ND 1  may reach a threshold voltage V TH  of the NMOS transistor N at a time point t 1  and continue to follow the power supply voltage AVDD. When the voltage V ND1  of the first node ND 1  reaches the threshold voltage V TH  of the NMOS transistor N, the NMOS transistor N may be turned on. The voltage V ND2  at the second node ND 2  may decrease to a logic threshold voltage of the inverter INV and the inverter INV may output the first POR signal V POR  having a high level ‘H’ based on the logic threshold voltage of the inverter INV. 
     Conversely, when the power supply voltage AVDD decreases, the voltage V ND1  at the first node ND 1  may reach the threshold voltage V TH  of the NMOS transistor N at a time point t 2  and continue to follow the power supply voltage AVDD. When the voltage V ND1  of the first node ND 1  reaches a voltage level lower than the threshold voltage V TH  of the NMOS transistor N, the NMOS transistor N may be turned off. The voltage V ND2  at the second node ND 2  may increase to the logic threshold voltage of the inverter INV and the inverter INV may output the first POR signal V POR  having a low level ‘L’ based on the logic threshold voltage of the inverter INV. 
     The logic threshold voltage may refer to a threshold voltage of an input signal capable of transitioning a level of an output signal of an inverter. For example, when the input signal of the inverter has a voltage level greater than a first level, the output of the inverter has a low level, and when the input signal of the inverter has a voltage level lower than the first level, the output of the inverter has a high level. In this case, the logic threshold voltage of the inverter may have the first level and may be variable based on a level of the power supply voltage. 
     The power supply voltage at which the level of the first POR signal V POR  is high may be adjusted by changing the size of a resistor and a transistor. 
     Meanwhile, the analog circuit may operate normally only when an appropriate bias is applied and the transistors operate in the saturation region. The POR circuit  400  is a logic, and transistors constituting the logic may operate well even if they are not in the saturation region. For example, the POR circuit  400  is a detection circuit that does not need a bias. However, the POR circuit  400  is highly influenced by a threshold voltage of a transistor and thus has a large distribution. Therefore, before the power supply voltage AVDD reaches a reliability region of the POR circuit  400 , the BGR circuit may malfunction. Accordingly, in a low-temperature environment, the BGR operation region detector may cover a malfunction voltage region of the BGR circuit, and the POR circuit  400  may cover a voltage region in which the BGR operation region detector malfunctions. In the low-temperature environment, the POR circuit  400  may detect whether the power supply voltage AVDD reaches a voltage level in the voltage region in which the BGR operation region detector  200  malfunctions, by detecting whether the bias circuit of the analog circuit included in the BGR operation region detector  200  operates normally. 
     For example, as a temperature increases, a reliability region of the BGR operation region detector may gradually decrease and a reliability region of the POR circuit  400  may gradually increase. Therefore, in a high-temperature environment, the POR circuit  400  may cover a voltage region in which the low voltage detector malfunctions. The POR circuit  400  may detect whether the power supply voltage AVDD reaches a voltage level in a voltage region in which the low voltage detector malfunctions by detecting whether the bias circuit of the analog circuit included in the low voltage detector operates normally. The voltage region in which the POR circuit  400  malfunctions may be determined by a threshold voltage distribution range of the NMOS transistor included in the POR circuit  400 . 
       FIGS. 9 and 10  are graphs illustrating a reliability region of a low voltage attack detector according to an embodiment of the present inventive concept. In the graphs of  FIGS. 9 and 10 , the X-axis represents the power supply voltage AVDD and the Y-axis represents flag voltages that the low voltage detector, the BGR operation region detector, and the POR circuit output in corresponding reliability regions. For example, the flag voltages may be the final low voltage detection flag signal V LVDET_MERGED . Levels of the flag voltages may vary according to the power supply voltage AVDD. 
       FIG. 9  is a graph illustrating a reliability region of a low voltage attack detector in a low-temperature environment. 
     Referring to  FIGS. 6 and 9  together, the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a high level when the power supply voltage AVDD is within a low voltage detection specification range SPEC. For example, when the power supply voltage AVDD is a first voltage Va, the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a high level. The low voltage detection flag signal V LVDET  has to be able to maintain the high level even if the power supply voltage AVDD continues to decrease. 
     However, when the power supply voltage AVDD is lower than a second voltage Vb in a low-temperature environment, the BGR circuit  110  may malfunction. A first section D 1  in which the power supply voltage AVDD falls within a first range from the first voltage Va to the second voltage Vb may be defined as a first reliability region in which the low voltage detection flag signal V LVDET  output from the low voltage detector  100  maintains the high level. Since the BGR circuit  110  operates normally in the first reliability region, a final low voltage detection flag signal V LVDET_MERGED  may maintain a high level by the low voltage detection flag signal V LVDET . 
     When the power supply voltage AVDD is lower than the second voltage Vb in the low-temperature environment, for example, when the power supply voltage AVDD is outside the first reliability region of the low voltage detector  100 , the BGR operation region detector  200  may output a malfunction detection flag signal V BGRDET  having a high level. Accordingly, regardless of whether the low voltage detection flag signal V LVDET  maintains the high level, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the malfunction detection flag signal V BGRDET . 
     When the power supply voltage AVDD is lower than a third voltage Vc in the low-temperature environment, the BGR operation region detector  200  may malfunction. A second section D 2  in which the power supply voltage AVDD falls within a second range from the second voltage Vb to a third voltage Vc may be defined as a second reliability region in which the malfunction detection flag signal V BGRDET  output from the BGR operation region detector  200  may maintain the high level. Since the BGR operation region detector  200  operates normally in the second reliability region, a final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the malfunction detection flag signal V BGRDET , regardless of whether the low voltage detection flag signal V LVDET  maintains the high level. 
     When the power supply voltage AVDD is lower than the third voltage Vc in the low-temperature environment, for example, when the power supply voltage AVDD is outside the second reliability region of the BGR operation region detector, the POR circuit  400  may output a POR signal V POR  having a low level. A third section D 3  in which the power supply voltage AVDD falls within a third range from the third voltage Vc to 0V may be defined as a third reliability region in which the POR signal V POR  output from the POR circuit  400  maintains a low level. Since the POR circuit  400  operates normally in the third reliability region, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the POR signal V POR  having a low level ‘L’, regardless of whether the low voltage detection flag signal V LVDET  maintains a high level. 
       FIG. 10  is a graph illustrating a reliability region of a low voltage attack detector in a high-temperature environment. 
     Referring to  FIGS. 6 and 10  together, the low voltage detector  100  may output a low voltage detection flag signal V LVDET  when the power supply voltage AVDD is within the low voltage detection specification range SPEC. For example, when the power supply voltage AVDD is a fourth voltage Vd, the low voltage detector  100  may output a low voltage detection flag signal V LVDET  having a high level. The low voltage detection flag signal V LVDET  has to be able to maintain the high level even if the power supply voltage AVDD continues to decrease. 
     When a temperature increases, the voltage at which the low voltage detector  100  malfunctions may be lowered, but when the power supply voltage AVDD is lower than a fifth voltage Ve, the bias circuit of the operational amplifier included in the BGR circuit  110  may malfunction. In the high-temperature environment, a fourth section D 4  in which the power supply voltage AVDD falls within a fourth range from the fourth voltage Vd to the fifth voltage Ve may be defined as a fourth reliability region in which the low voltage detection flag signal V LVDET  maintains a high level. Since the BGR circuit  110  operates normally in the fourth reliability region, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the low voltage detection flag signal V LVDET  having a high level ‘H’. 
     When the power supply voltage is lower than the fifth voltage Ve in the high-temperature environment, for example, when the power supply voltage is outside the fourth reliability region of the low voltage detector  100 , the POR circuit  400  may output a POR signal V POR  having a low level ‘L’. Accordingly, regardless of whether the low voltage detection flag signal V LVDET  maintains the high level, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the POR signal V POR  having a low level ‘L’. 
     As the temperature increases, the reliability region of the BGR operation region detector gradually decreases, the reliability region of the POR circuit  400  gradually increases, and the POR circuit  400  does not malfunction to 0V, so in the high-temperature environment, the POR circuit  400  may cover all the malfunction regions of the low voltage detector  100 . In the high-temperature environment, a fifth section D 5  in which the power supply voltage AVDD falls within a fifth range from the fifth voltage Ve to 0V may be defined as a fifth reliability region in which the POR signal V POR  may maintain a low level. The fifth reliability region may be determined by a threshold voltage distribution range of the NMOS transistor included in the POR circuit  400 . According to an embodiment, at room temperature (e.g., 25° C.), the BGR operation region detector  200  and the POR circuit  400  may complement each other in order to cover the malfunction region of the low voltage detector  100 . 
     In example embodiments, a sixth section D 6  between the fourth section D 4  and the fifth section D 5  may be disposed. The sixth section D 6  (not shown) in which the power supply voltage AVDD falls to a voltage level within a sixth range from the fifth voltage Ve to a sixth voltage Vf (not shown) may be defined as a sixth reliability region in which the malfunction detection flag signal V BGRDET  output from the BGR operation region detector  200  may maintain the high level. Since the BGR operation region detector  200  operates normally in the sixth reliability region, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level by the malfunction detection flag signal V BGRDET , regardless of whether the low voltage detection flag signal V LVDET  maintains the high level. 
       FIG. 11  is a block diagram illustrating a secure element according to an embodiment of the present inventive concept. 
     Referring to  FIG. 11 , the secure element  1000  may include a secure memory  1100 , a secure processor  1200 , a low voltage attack detector  1300 , and a reset signal generator  1400 . For example, the secure element  1000  may be a smart card, a secure element (SE), or the like. 
     The secure memory  1100  stores secure data SDAT, and the secure processor  1200  processes secure data SDAT. For example, the secure processor  1200  may write secure data SDAT in the secure memory  1100  and read secure data SDAT from the secure memory  1100 . For example, the secure data SDAT may include a cryptographic key, sensitive data, a key code, and the like. For example, the secure memory  1100  and the secure processor  1200  may operate based on a power supply voltage VDD. However, the disclosure is not limited thereto. For example, the secure memory  1100  and the secure processor  1200  may be provided the power supply voltage AVDD. For example, the power supply voltage VDD may be generated based on the power supply voltage AVDD. In an embodiment, a voltage level of the power supply voltage AVDD may be higher than a voltage level of the power supply voltage VDD. 
     In an embodiment, the secure memory  1100  may include a non-volatile memory such as an electrically erasable programmable read-only memory (EEPROM), a flash memory, a phase change random access memory (PRAM), a resistance random access memory (RRAM), a nano floating gate memory (NFGM), a polymer random access memory (PoRAM), a magnetic random access memory (MRAM), a ferroelectric random access memory (FRAM) and/or a volatile memory such as a dynamic random access memory (DRAM) and a static random access memory (SRAM). 
     In an embodiment, the secure processor  1200  may include any processing device such as a central processing unit (CPU), a microprocessor, or the like. 
     In an embodiment, the secure element  1000  may have a tamper-resistant function so as to be protected from a tampering attack such as microprobing, software attack, eavesdropping, fault injection, etc. 
     Microprobing may be used to directly access a chip surface. Software attacks may use a processor&#39;s general communication interface and may take advantage of security vulnerabilities, cryptographic algorithms, or algorithm executions that occur in a protocol. Eavesdropping may measure analog characteristics of all supply and interface connections and electromagnetic radiation generated by a processor during a normal operation. Error injection may create malfunction of a processor that provides additional access using abnormal environmental conditions. Microprobing is a direct invasive attack technique and requires a lot of time. The other techniques are non-invasive attack techniques. 
     As an indirect attack technique, a voltage change indicates hacking the secure element  1000  by abnormally changing a signal or power applied from the outside so that the secure element  1000  operates unpredictably. For example, a method of leaking the secure data SDAT from the secure memory  1100  by abnormally changing a voltage (e.g., the power supply voltage AVDD) for driving internal components of the secure element  1000  may be attempted. 
     The low voltage attack detector  1300  may output a final low voltage detection flag signal V DET_MERGED  having a high level when the power supply voltage AVDD reaches a target voltage, and may maintain the high level of the final low voltage detection flag signal until the power supply voltage AVDD reaches 0V. The low voltage attack detector  1300  may be the low voltage attack detector previously described according to embodiments of the present inventive concept, and may be implemented as described above with reference to  FIGS. 1 to 10 . The low voltage attack detector  1300  may detect a low voltage even if the power supply voltage AVDD reaches a voltage level in a voltage region in which the analog circuit malfunctions. 
     The reset signal generator  1400  generates a reset signal RST based on the final low voltage detection flag signal V DET_MERGED . The reset signal RST is provided to the secure processor  1200 , and the secure processor  1200  is reset based on the reset signal RST. Accordingly, the secure element  1000  may protect the secure data SDAT from leakage, destruction, or alteration of the secure data SDAT caused by an external attack, and security performance of the secure element  1000  may be improved. 
     For example, in  FIG. 11 , it is illustrated that the reset signal RST is provided only to the secure processor  1200 , but the present inventive concept may not be limited thereto. For example, the reset signal RST may be provided to the secure memory  1100  as well, and the secure memory  1100  may also be reset based on the reset signal RST. 
       FIG. 12  is a flowchart illustrating a method of operating a secure element according to embodiments of the present inventive concept. 
     Referring to  FIGS. 11 and 12 , when the power supply voltage AVDD reaches the target voltage, the low voltage detector may output a low voltage detection flag signal having a high level in operation S 110 . 
     When the power supply voltage AVDD is lowered to a voltage at which the BGR circuit malfunctions in a low-temperature environment, the BGR operation region detector may output a malfunction detection flag signal having a high level in operation S 120 . In the high-temperature environment, when the power supply voltage AVDD is lowered to the voltage at which the BGR circuit malfunctions, the POR circuit may output a POR signal having a high level through an inverter in operation S 130 . 
     When the power supply voltage AVDD is lowered to a voltage at which the BGR operation region detector malfunctions in a low-temperature environment, the POR circuit may output the POR signal having a high level through an inverter in operation S 130 . 
     The logic gate (e.g., OR gate) may receive the low voltage detection flag signal, the malfunction detection flag signal, and the POR signal through an inverter (i.e., the second POR signal V POR′ ). If any of the low voltage detection flag signal, the malfunction detection flag signal, and the POR signal through the inverter has a high level (YES in operation S 140 ), the low voltage attack detector  1300  may output a final low voltage detection flag signal V LVDET_MERGED  having a high level. Therefore, regardless of whether the low voltage detection flag signal maintains the high level, the final low voltage detection flag signal V LVDET_MERGED  may maintain the high level in the entire low voltage region. 
     The reset signal detector  1400  generates the reset signal RST based on the final low voltage detection flag signal V DET_MERGED . The secure processor  1200  may be reset based on the reset signal RST (S 150 ). However, when the low voltage detection flag signal, the malfunction detection flag signal, and the POR signal through the inverter all have low levels (NO in operation S 140 ), the secure processor  1200  may operate normally in operation S 160 . 
     Therefore, even if a hacker artificially applies a voltage that may cause a malfunction of an analog circuit, the system cannot operate normally, so an effect of preventing a hacker&#39;s attack may be obtained. 
     For example, the embodiments of the present inventive concept may be implemented in the form of a product including a computer-readable program code stored in a computer-readable medium. The computer-readable program code may be provided by processors of various computers or other data processing devices. The computer-readable medium may be a computer-readable signal medium or a computer-readable recording medium. The computer-readable recording medium may be any tangible medium that may store or contain a program in an instruction execution system, equipment, or device or may be connected thereto to store or contain a program. For example, the computer-readable medium may be provided in the form of a non-transitory storage medium. Here, non-transitory means that the storage medium does not contain a signal and is tangible, but does not distinguish that data is semi-permanently or temporarily stored in the storage medium. 
       FIG. 13  is a block diagram illustrating an electronic system according to embodiments of the present inventive concept. 
     Referring to  FIG. 13 , the electronic system  2000  may include a processor  2100 , a memory device  2200 , a secure element  2300 , an input/output device  2400 , a power supply  2500 , and a display device  2600 . The electronic system  2000  may further include various ports capable of communicating with a video card, a sound card, a memory card, a USB device, or the like, or with other systems. 
     The processor  2100  may control an overall operation of the electronic system  2000  and execute an operating system, an application, and the like. The memory device  2200  may store data necessary for the operation of the electronic system  2000 . The input/output device  2400  may include an input means such as a keyboard, a keypad, a touch pad, a touch screen, a mouse, and a remote controller, and an output means such as a speaker or a printer. The power supply  2500  may supply power required for the operation of the electronic system  2000 . The display device  2060  may display an image. 
     The processor  2100  may control a normal operation, and the secure element  2300  may control a secure operation. The secure element  2300  may be a secure element according to embodiments of the present inventive concept, and may be implemented as described above with reference to  FIGS. 11 and 12 . The secure element  2300  may detect a low voltage in the entire low voltage regions even if a low voltage that may cause an analog circuit to malfunction is applied to the system. 
     The secure element  2300  may protect secure data from leakage, destruction, or alteration of secure data by an external attack, and security performance of the secure element  2300  and the electronic system  2000  including the same may be improved. 
     In an embodiment, the electronic system  2000  may be a security-related system, and the low voltage attack detector  2310  may be used as a detector for preventing hacking. In another embodiment, the electronic system  2000  may be a mobile system such as an application processor (AP) or a wearable device, and the low voltage attack detector  2310  may be used as a detector for preventing hacking which operates at low power. In another embodiment, the electronic system  2000  may be an automotive system, and the low voltage attack detector  2310  may be used as a safety related detector. 
     The embodiments of the present inventive concept may be advantageously used in any electronic device and system including a low voltage attack detector and a secure element. For example, the embodiments of the present inventive concept may be more usefully applied to a personal computer (PC), a server computer, a data center, a workstation, a laptop, a cellular phone, and a smartphone, an MP3 player, a personal digital assistant (PDA), a portable multimedia player (PMP), a digital TV, a digital camera, a portable game console, a navigation device, a wearable device, an Internet of things (IoT) device, an Internet of everything (IoE) device, e-book, a virtual reality (VR) device, an augmented reality (AR) device, a drone, an automotive, etc. 
     According to an embodiment of the present inventive concept, even if the level of the power supply voltage decreases to a voltage level in the voltage region in which the analog circuit malfunctions, the level of the low voltage detection flag signal is maintained, and thus, the system may not operate in the entire low voltage region. Therefore, even if a hacker artificially applies a voltage that may cause a malfunction of the analog circuit, the hacker&#39;s attack may be prevented. 
     Various and beneficial advantages and effects of the present inventive concept are not limited to the above description, and the present inventive concept will be more easily understood in the course of describing specific embodiments. 
     While example embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.