Patent Publication Number: US-9842645-B2

Title: Nonvolatile memory device including nonvolatile memory and resistance-time converter, and integrated circuit card including nonvolatile memory device

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a variable-resistance nonvolatile memory device. 
     2. Description of the Related Art 
     There has been a rapid expansion in the market for electronic commerce services carried out via the Internet, such as Internet banking and Internet shopping. Electronic money is used as a payment method at such time, and there has likewise been an expansion in the use of integrated circuit (“IC”, hereinafter the same) cards and smartphone terminals that are used as media therefor. For safety when making payments, these services ordinarily require a higher level of security technology for mutual authentication during communication and encryption of communication data. Generally, in an IC having enhanced security, confidential information is used in an encrypted manner by using an encryption circuit mounted therein and information leaks are prevented. In this case, it is essential that information regarding an encryption key (also referred to as a “secret key”) that is retained internally is not leaked to the outside. 
     In order to address these issues, physically unclonable function (PUF) technology has been proposed. PUF technology uses manufacturing variations to generate unique solid identification information that is different for each IC. Hereinafter, solid identification information generated by means of PUF technology will be referred to as “digital ID data” in the present specification. Digital ID data can be said to be random number data that is characteristic to each device and associated with variations in the physical characteristics of ICs. These physical characteristics cannot be artificially controlled for each IC, and it is therefore possible to generate data that cannot be physically replicated (for example, see Japanese Patent No. 5689571). 
     Furthermore, disposable secret keys which use true random numbers that cannot be predicted are employed when generating encryption keys (for example, see Japanese Unexamined Patent Application Publication No. 2015-212933). A true random number (physical random number) refers to a random number that is generated by using the physical phenomenon of intrinsically having random properties, such as the thermal noise within a semiconductor device, for example. In this way, a true random number is not reproducible and cannot be predicted by anyone, and therefore encryption that is carried out using a secret key generated using a true random number has a high degree of safety. 
     In Japanese Patent No. 5689571, a method is given in which variation in a resistance value inherent to a nonvolatile memory is used as digital ID data. Furthermore, in Japanese Unexamined Patent Application Publication No. 2015-212933, temporal fluctuation in a resistance value of a nonvolatile memory is used as a true random number source. 
     In order to increase the read speed when reading the resistance value of a nonvolatile memory, it is necessary for capacitance charge to be discharged quickly, and for a time measurement counter to be operated at high speed. However, with an IC card, it is necessary for various types of functions to be executed within a short period of time using power provided by a wireless power supply that is obtained during communication, and extremely low power saving and high-speed generation are required at the same time. Power consumption increases when a time measurement counter is operated at high speed, and there is a possibility that a wireless power supply will no longer be sufficient. 
     SUMMARY 
     In one general aspect, the techniques disclosed here feature a nonvolatile memory device provided with: a first nonvolatile memory that stores information in association with a resistance value thereof; a first resistance-time converter that outputs a first end signal at timing according to the resistance value of the first nonvolatile memory, the first resistance-time converter being connected to the first nonvolatile memory; and a time-digital converter that converts a first time from input of a start signal to input of the first end signal into a first digital value. The time-digital converter includes: a ring delay circuit that includes delay elements connected in a ring configuration; a counter circuit that counts the number of times of a rising edge or the number of times of a falling edge in output of one of the delay elements; a first memory circuit that stores, based on the first end signal, outputs of the delay elements as first data; and a second memory circuit that stores, based on the second end signal, a count value of the counter circuit as second data. 
     Comprehensive and specific aspects of the aforementioned may be implemented using a system, a method, and a computer program, or may be realized using a combination of a system, a method, and a computer program. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram depicting an example of a basic configuration of a nonvolatile memory device; 
         FIG. 2  is a block diagram depicting an example of a specific configuration of the nonvolatile memory device depicted in  FIG. 1 ; 
         FIG. 3  is a drawing depicting an example of a timing chart for the case where a memory is read by means of a discharging method in the nonvolatile memory device; 
         FIG. 4  is a drawing depicting an example of a timing chart for the case where a memory is read by means of a charging method in the nonvolatile memory device; 
         FIG. 5  is a block diagram depicting an example of a detailed configuration of a nonvolatile memory device according to embodiment 1; 
         FIG. 6  is a block diagram depicting an example of a detailed configuration of a delay element ring and a delay memory according to embodiment 1; 
         FIG. 7  is a drawing depicting an example of a timing chart depicting operations of the delay element ring and the delay memory depicted in  FIG. 6 ; 
         FIG. 8  is a block diagram depicting an example of a detailed configuration of a counter and a counter memory according to embodiment 1; 
         FIG. 9  is a drawing depicting an example of a timing chart depicting operations of the counter and the counter memory according to embodiment 1; 
         FIG. 10  is a drawing depicting an example of a timing chart depicting operations of the delay element ring, the delay memory, the counter, and the counter memory according to embodiment 1; 
         FIG. 11  is a block diagram depicting an example of a counter memory fetch signal generation circuit according to embodiment 2; 
         FIG. 12  is a drawing depicting an example of a timing chart depicting operations of the counter memory fetch signal generation circuit in the case where there is a delay in a delay element ring and a counter according to embodiment 2; 
         FIG. 13  is a block diagram depicting an example of a time-digital converter that includes the counter memory fetch signal generation circuit, a sampling memory, and a correction circuit according to embodiment 2; 
         FIG. 14  is a flowchart depicting a specific example of a processing flow in which the correction circuit corrects a count value according to embodiment 2; 
         FIG. 15  is a first timing chart for the case where the correction circuit does not correct the count value according to embodiment 2; 
         FIG. 16  is a second timing chart for the case where the correction circuit does not correct the count value according to embodiment 2; 
         FIG. 17  is a timing chart for the case where the correction circuit corrects the count value according to embodiment 2; 
         FIG. 18  is a third timing chart for the case where the correction circuit does not correct the count value according to embodiment 2; 
         FIG. 19  is a block diagram depicting an example of a configuration in which both the time of a time measurement start time and the time of a time measurement end time of a time-digital converter are saved and the difference is output according to embodiment 3; 
         FIG. 20  is a circuit diagram depicting an example of a configuration in which a current amount of a delay element ring can be changed according to embodiment 4; 
         FIG. 21  is a circuit diagram depicting an example of a configuration in which a voltage amount of the delay element ring can be changed according to embodiment 4; 
         FIG. 22  is a block diagram depicting an example of a configuration in which the current amount of the delay element ring is adjusted according to embodiment 4; 
         FIG. 23  is a timing chart for the case where the current amount of the delay element ring is adjusted according to embodiment 4; 
         FIG. 24  is a block diagram depicting a time-digital converter according to a modified example of embodiment 1; 
         FIG. 25  is a block diagram depicting a time-digital converter according to a modified example of embodiment 2; and 
         FIG. 26  is a block diagram depicting a time-digital converter according to a modified example of embodiment 3. 
     
    
    
     DETAILED DESCRIPTION 
     Findings Forming the Basis for the Present Disclosure 
     In Japanese Patent No. 5689571 and Japanese Unexamined Patent Application Publication No. 2015-212933, in a circuit that reads a resistance value of a nonvolatile memory, charge that has been charged in a capacitor up to a fixed voltage is discharged in a resistance of the nonvolatile memory, and the time taken for the charge to fall below a threshold voltage value is measured. In this method, the resistance value is extended as a time so to speak, and an accurate resistance value can be calculated. 
     A circuit that counts using a clock signal source is adopted as a method for measuring said time. It is also possible to adjust the discharging time by adjusting the capacitance of the capacitor. If the capacitance of the capacitor increases, the discharging time also increases, and therefore the count value increases. Furthermore, if the capacitance of the capacitor decreases, the discharging time decreases, and the count value decreases. The count interval is decided by the clock signal source, and therefore the operating frequency thereof becomes the resolution of a resistance count value. As the capacitance value of the capacitor increases, the discharging time increases, and the resolution of resistance value information with respect to the count value improves. Conversely, as the capacitance value of the capacitor decreases, the discharging time decreases; however, the resolution of the resistance value information with respect to the count value declines. 
     Furthermore, Japanese Unexamined Patent Application Publication No. 2015-212933 presents a method for generating a true random number with temporal fluctuation in the resistance value of a nonvolatile memory being used as a random property. For the method for reading the resistance value, similar to the case in the aforementioned Japanese Patent No. 5689571, a method is used where the time taken for the charge of a capacitor to be discharged is measured. However, temporal fluctuation in the resistance value of a nonvolatile memory is smaller than variation in a characteristic resistance value, and therefore, with the technology given in Japanese Unexamined Patent Application Publication No. 2015-212933, a higher resolution is required than in the case given in Japanese Patent No. 5689571. 
     In order to increase the read speed when reading the resistance value of a nonvolatile memory, it is necessary for capacitance charge to be discharged quickly, and for a time measurement counter to be operated at high speed. Mobile electronic money such as the aforementioned IC card is a card that has a semiconductor integrated circuit (IC) chip mounted thereon, and it is desirable for internal digital ID data to be read and a true random number to be generated and applied to a secret key also within the IC card. However, with an IC card, it is necessary for various types of functions to be executed within a short period of time using power provided by a wireless power supply obtained during communication, and extremely low power saving and high-speed generation of a true random number are required at the same time. Power consumption increases when a time measurement counter is operated at high speed, and there is a possibility that a wireless power supply will no longer be sufficient. 
     Furthermore, it is necessary to increase the key length in order to improve security. However, if the key length is increased, the amount of digital ID data and the amount of random number data increases, and the time for reading the resistance value and generating a random number increases. Furthermore, if mutual authentication and the encryption of communication data take time, there is a resulting deterioration in usability, and it is therefore necessary for encryption to be carried out at high speed. However, when encryption is carried out at high speed, a problem occurs in that current consumption increases. 
     In a nonvolatile memory device according to an aspect of the present disclosure described hereinafter, it is possible to suppress an increase in current consumption while also improving the digital ID data read speed and the random number generation speed. Furthermore, errors do not occur in acquired resistance value data. Thus, it is possible for digital ID data having excellent security to be generated at high speed and with low power consumption. 
     A nonvolatile memory device according to an aspect of the present disclosure is provided with: a nonvolatile memory that stores data by determining a resistance value with at least one threshold value; a first conversion circuit that converts the resistance value stored in the nonvolatile memory into time information; and a second conversion circuit that converts the time information into a digital value, in which the second conversion circuit is provided with: a ring delay circuit in which a plurality of delay elements are connected; a counter circuit that measures the number of times that a rising edge or a falling edge occurs in data that is output from any delay element from among the plurality of delay elements; a first memory circuit that saves data that is output from each of the plurality of delay elements; and a second memory circuit that saves data retained in the counter circuit, and the second conversion circuit, on the basis of a time difference from the time at which a time measurement start signal is input to the time at which a time measurement end signal is input, refers to the data saved in the first memory circuit and the data saved in the second memory circuit, and acquires resistance value information relating to the resistance value of the nonvolatile memory. 
     Thus, it is possible for digital ID data having excellent security to be generated at high speed and with low power consumption. 
     Furthermore, the ring delay circuit may be provided with an inversion circuit that inverts the output of any of the connected plurality of delay elements, and the output of any of the plurality of delay elements inverted by the inversion circuit may be connected to the input of the first-stage delay element from among the plurality of delay elements. 
     In addition, there may be provided: a counter memory fetch signal generation circuit that, after data retained in the counter circuit has changed due to a rising edge or a falling edge of the data that is output from any delay element from among the plurality of delay elements, generates an edge that is the inverse of the rising edge or the falling edge of the data that is output from any delay element from among the plurality of delay elements, or delays the rising edge or the falling edge of the data that is output by any delay element from among the plurality of delay elements; a third counter memory circuit that saves the data retained in the counter circuit on the basis of the time measurement end signal; and a correction circuit that refers to the data saved in the first memory circuit, the data saved in the second memory circuit, and the data saved in the third memory circuit, and corrects the data saved in the third memory circuit on the basis of predetermined determination criteria. 
     Furthermore, the first memory circuit may save data that is output from each of the plurality of delay elements in accordance with the time measurement start signal, and output the saved data in accordance with the time measurement end signal, the second memory circuit and the third memory circuit may output the data saved in each of the second memory circuit and the third memory circuit in accordance with the time measurement end signal, and the correction circuit may, on the basis of the data that is output from the first memory circuit, the second memory circuit, and the third memory circuit, calculate the time from the time measurement start signal being input to the time measurement end signal being input. 
     Furthermore, the ring delay circuit may be provided with: a change circuit that changes the voltage or current applied to the delay elements, to at least any of a power source side and a ground side of the delay elements; and an adjustment circuit for changing delay times of the delay elements. 
     Furthermore, the time measurement start signal and the time measurement end signal may be generated in accordance with a reference signal that is input from outside, and the adjustment circuit may change the delay times of the delay elements in such a way that the time difference from the time at which the time measurement start signal is input to the time at which the time measurement end signal is input becomes a predetermined target value. 
     Furthermore, an integrated circuit card according to an aspect of the present disclosure is provided with a nonvolatile memory device having the aforementioned features. 
     First, to aid understanding of the nonvolatile memory device and the like according to the present disclosure, the basic configuration of the nonvolatile memory device will be described. 
       FIG. 1  is a block diagram depicting an example of a basic configuration of a variable-resistance nonvolatile memory device  100 . 
     As depicted in  FIG. 1 , the nonvolatile memory device  100  is configured of a variable-resistance nonvolatile memory cell (hereinafter, simply referred to as a “nonvolatile memory”)  101  and a reading device  102 . The reading device  102  is configured of a resistance-time converter  103  and a time-digital converter  104 . The nonvolatile memory device  100  has at least one variable-resistance nonvolatile memory  101 . The nonvolatile memory  101  stores data by determining a resistance value with at least one threshold value. 
     The nonvolatile memory  101  is connected to the resistance-time converter  103 , and when a time measurement start signal is input to the resistance-time converter  103 , a resistance value of a variable-resistance element  210  provided in the nonvolatile memory  101  is converted into time information and a time measurement end signal is output. The time-digital converter  104  counts the time between the time measurement start signal and the time measurement end signal, and outputs this as time data. That is, the resistance value of the variable-resistance element  210  provided in the nonvolatile memory  101  is output as time data, and therefore, if the value of the time data is confirmed, the resistance value of the variable-resistance element  210  provided in the nonvolatile memory  101  is consequently understood. 
       FIG. 2  is an example of a specific configuration of the nonvolatile memory device  100  depicted in  FIG. 1 . The reading device  102  has a discharging-type resistance-time converter  103 . The resistance-time converter  103  is provided with a comparator  202 , a load PMOS transistor  203 , a precharge PMOS transistor  204 , a clamp circuit  206  configured of a clamp NMOS transistor  205 , and a charging capacitor  201 . 
     The time-digital converter  104  is configured of a time measurement counter  207  and a VCO  208 . The output of the comparator  202  is connected to the time measurement counter  207 . The time measurement counter  207  starts counting by means of a clock signal CLK after a count value within the time measurement counter is initialized by RST becoming low-level. 
     The clock signal CLK is a signal that is output from the VCO  208 , and is a signal that becomes a reference for when a discharging time that changes depending on the resistance value of the variable-resistance element  210  is converted into a count value. The clock signal CLK is a square wave that maintains a fixed frequency, for example. Each time the clock signal CLK rises,  1  is added to the count value of the time measurement counter  207 , the counting up of the time measurement counter  207  stops when a node SEN falls below a VREF, and the count value at such time is maintained at COUNT_OUT. At such time, a threshold value is input to the VREF. 
     In the precharge PMOS transistor  204 , a precharge control signal PRE is input to the gate terminal, a VDD is input to the source terminal, and the node SEN is connected to the drain terminal. 
     In the load PMOS transistor  203 , a load control signal LOAD is input to the gate terminal, the VDD is input to the source terminal, and the node SEN is connected to the drain terminal. 
     In the clamp NMOS transistor  205 , a clamp control signal CLMP is input to the gate terminal, and the node SEN is connected to either one of the source terminal or the drain terminal with a memory cell selected by way of a column decoder circuit being connected to the other. It should be noted that the column decoder circuit is omitted in  FIG. 2 . 
     Here, an operation in which the reading device  102  outputs the count value (an example of the resistance count value) will be specifically described using  FIGS. 2, 3, and 4 .  FIG. 3  is an example of a timing chart for the case where a memory is read by means of a discharging method in the nonvolatile memory device  100 .  FIG. 4  is an example of a timing chart for the case where a memory is read by means of a charging method in the nonvolatile memory device  100 . 
       FIG. 3  is a timing chart for the case where a memory stored in the selected memory cell is read by means of a discharging method. 
     In the precharge period of T 1 , the control signal PRE becomes low-level, and the precharge PMOS transistor  204  enters an on state. Meanwhile, the control signal LOAD becomes high-level, and the load PMOS transistor  203  enters an off state. The potential of a selection word line WLs is low-level and a transistor  209  is in an off state. 
     Here, a VCLMP voltage is applied to the gate terminal of the clamp NMOS transistor  205  of the clamp circuit  206 , and therefore the potential of a selection bit line BLs is precharged to a potential obtained by subtracting VT (threshold value for the clamp NMOS transistor  205 ) from VCLMP. Furthermore, a selection source line SLs is fixed to GND. The node SEN is precharged up to the VDD. Furthermore, the control signal RST for the time measurement counter connected to the output of the comparator becomes high-level. A fixed value of 0 is thereby output for the time measurement counter output terminal COUNT_OUT. 
     In the sensing period of T 2 , the control signal PRE is made high-level. Thus, the precharge PMOS transistor  204  enters an off state, and the control signal LOAD becomes low-level. Thus, the load PMOS transistor  203  enters an on state. Furthermore, the potential of the selection word line WLs is made high-level. Thus, the NMOS transistor  209  enters an on state. 
     A voltage is then applied from the selection bit line BLs to the selection source line SLs by way of the selected variable-resistance element  210 . In other words, discharging is started. At the same time as the start of discharging, the RST of the time-digital converter  104  becomes low-level, and counting is started. Then, at each single count, the potential of the node SEN and the voltage of the reference voltage VREF are compared by the comparator  202 , and the count value continues to be added until the node SEN falls below the reference voltage VREF. As the resistance value of the variable-resistance element  210  during reading increases, the discharging time increases and the count value increases. 
     Furthermore, it is possible to also adjust the discharging time by adjusting the capacitance of the charging capacitor  201 . If the capacitance of the charging capacitor  201  increases, the discharging time of the node SEN also increases and the count value consequently increases, and if the capacitance decreases, the discharging time of the node SEN decreases and the count value decreases. 
     Using the charging capacitor  201  is effective when there is a desire to improve detection accuracy for a low resistance level at which the discharging time is fast, for example. The count interval is decided by the clock signal CLK, and therefore the operating frequency of the clock signal CLK serves as the resolution of the count value when the resistance value of the variable-resistance element  210  is converted as a time. However, in the case of a low resistance value, there is a possibility that the discharging time exceeds the resolution of the count value, in other words, that the discharging time is shorter than the time taken for a single count value, and may therefore become indistinguishable. Thus, by adding a capacitance load to the node SEN and causing a delay, it becomes possible to deliberately implement an adjustment to achieve discharge characteristics of a level at which detection is possible at the resolution of the count value. 
     However, in principle, in the case of the discharging method, as the resistance increases, the discharging time increases and accordingly the discharge amount with respect to time changes gradually, and therefore the resolution of the resistance value information with respect to the count value improves. That is, in the case of the discharging method, highly accurate information can be obtained for a resistance value on the high resistance side of the variable-resistance element  210 . 
     In the latch period of T 3 , after discharging has started, the count value of the time-digital converter  104  when the node SEN has fallen below the reference voltage VREF is latched. The latched count value is output to the COUNT_OUT. 
     In the reset period of T 4 , when data output has been completed, the potential of the selection word line WLs is made low-level, the transistor  209  of the nonvolatile memory  101  selected turns off, and the read operation ends. 
       FIG. 4  is a timing chart for the case where a memory stored in the selected memory cell is read by means of a charging method. 
     In the discharge period of T 1 , the control signal PRE becomes high-level together with the LOAD, and both the precharge PMOS transistor  204  and the load PMOS transistor  203  enter an off state. Furthermore, the potential of the selection word line WLs is low-level and the transistor  209  is also in an off state. 
     Here, as a result of the VCLMP voltage being applied to the gate terminal of the clamp NMOS transistor  205  of the clamp circuit, and the potential of the selection word line WLs being made high-level, the NMOS transistor  209  enters an on state. Thus, the node SEN and the selection bit line BLs are connected to GND by way of the variable-resistance element  210 , and are discharged to a GND level. Furthermore, the control signal RST for the time measurement counter connected to the output of the comparator becomes high-level. A fixed value of 0 is thereby output for the time measurement counter output terminal COUNT_OUT. 
     In the sensing period of T 2 , the control signal LOAD becomes low-level, and the load PMOS transistor  203  therefore enters an on state. Thus, a current path of the load PMOS transistor  203 , the clamp NMOS transistor  205 , and the selected nonvolatile memory  101  is formed, and charging is started to the node SEN and the selection bit line BLs. At the same time as charging is started, the control signal RST of the time-digital converter  104  becomes low-level, and counting is started. Then, at each single count, the potential of the node SEN and the voltage of the reference voltage VREF are compared by the comparator  202 , and the count value continues to be added until the node SEN exceeds the reference voltage VREF. As the resistance value of the variable-resistance element  210  during reading decreases, the charging time increases and the count value increases. 
     Furthermore, using the charging capacitor  201 , it is possible to adjust the charging time in the charging method in the same manner as when adjusting the discharging time in the discharging method. A detailed explanation thereof is the same as the explanation for the discharging method, and is therefore omitted. 
     In principle, in the case of the charging method, as the resistance decreases, the charging time increases and accordingly the charge amount with respect to time changes gradually, and therefore the resolution of the resistance value information with respect to the count value improves. That is, in the case of the charging method, highly accurate information can be obtained for a resistance value on the low resistance side of the variable-resistance element  210 . 
     In the latch period of T 3 , after charging has started, the count value of the time-digital converter  104  when the node SEN has exceeded the reference voltage VREF is held. The held count value is output to the COUNT_OUT, and is treated as a count value that expresses the resistance value information of the variable-resistance element  210 . 
     In the reset period of T 4 , when data output has been completed, the potential of the selection word line WLs is made low-level, the transistor  209  of the nonvolatile memory  101  selected turns off, and the read operation ends. 
     In this way, the resolution with respect to the resistance value information differs depending on the reading method, and therefore, in the case where there is a desire to obtain resistance value information in a highly accurate manner, it is desirable to use the discharging method when digital ID data is saved using a high resistance value range, and, conversely, it is desirable to use the charging method when digital ID data is saved using a low resistance value range. 
     However, meanwhile, the counter range of the time-digital converter  104  depicted in  FIG. 2  is a finite amount due to hardware constraints. That is, when the discharging time or charging time such as the aforementioned is too long, the range of the counter is exceeded, and there is a problem in that accurate resistance value information is not obtained. 
     Therefore, in the case where a reduction in circuit scale is to be achieved with the necessary counter bit width being reduced, it is desirable for the discharging method to be used when digital ID data is saved using a low resistance value range, and, conversely, it is desirable for the charging method to be used when digital ID data is saved using a high resistance value range. 
     Embodiment 1 
     Hereinafter, a nonvolatile memory device according to embodiment 1 will be described using  FIGS. 5 to 10 . 
     To begin, a configuration of the nonvolatile memory device according to the present embodiment will be described.  FIG. 5  is a block diagram depicting a configuration of the nonvolatile memory device according to the present embodiment.  FIG. 6  is a block diagram depicting an example of a detailed configuration of a delay element ring  501  and a delay memory  503  according to the present embodiment. 
     As depicted in  FIG. 5 , a nonvolatile memory device  100   a  according to the present embodiment is provided with the variable-resistance nonvolatile memory  101  and a reading device  102   a.    
     The reading device  102   a  has the resistance-time converter  103  and a time-digital converter  104   a.  The variable-resistance nonvolatile memory  101  and the resistance-time converter  103  have the same configurations as those of the variable-resistance nonvolatile memory  101  and resistance-time converter  103  depicted in  FIG. 2 . Furthermore, the time-digital converter  104   a  has a different internal configuration from that of the time-digital converter  104  depicted in  FIG. 2 . 
     The time-digital converter  104   a  is configured of: the delay element ring  501 ; the delay memory  503 , which saves the phase state (retained data, specifically A to H described in detail later on) of the delay element ring  501 ; a counter  502 ; a counter memory  504  that records the state (retained data, specifically a count value) of the counter  502 ; and a decoder  505  that decodes output of the delay memory  503  and the counter memory  504 . Here, the phase state of the delay element ring  501  refers to data retained by the delay element ring  501 , specifically output data A to H described in detail later on. Furthermore, the state of the counter  502  refers to data retained by the counter  502 , specifically a count value described in detail later on. 
     As depicted in  FIG. 6 , the delay element ring  501  is configured of delay elements  602  in which the input and output have the same logic, represented by buffers or the like, and a NAND element  601 , for example. In the delay element ring  501 , the plurality of delay elements  602  are linked in series, and any of the delay elements from among said plurality of delay elements  602  is connected to the NAND element  601  that constitutes input. For example, the final-stage delay element  602  is connected to the input NAND element  601  that constitutes input. It should be noted that  FIG. 6  depicts the delay element ring  501  having the delay elements  602  linked in four stages as an example. Furthermore, the output data corresponding to each delay element  602  is also referred to as bits. It should be noted that the output data corresponding to the counter  502  described later on is also referred to as bits. 
     Furthermore, the delay memory  503  is configured of a plurality of delay flip-flops  603  linked in series.  FIG. 6  depicts the delay memory  503  having the delay flip-flops  603  linked in four stages as an example. The delay flip-flops  603  are respectively connected to the outputs of the four-stage delay elements  602 . 
     It should be noted that the resistance-time converter  103  and the time-digital converter  104   a  are respectively examples of a first conversion circuit and a second conversion circuit in the present disclosure. Furthermore, the delay element ring  501  is an example of a ring delay circuit in the present disclosure. The counter  502  is an example of a counter circuit in the present disclosure. The delay memory  503  and the counter memory  504  are respectively examples of a first memory circuit and a second memory circuit in the present disclosure. Furthermore, the NAND element  601  is an example of an inversion circuit in the present disclosure. 
     Next, operations of the nonvolatile memory device  100   a  in the present embodiment will be described.  FIG. 7  is a timing chart depicting operations of the delay element ring  501  and the delay memory  503  depicted in  FIG. 6 . 
     It should be noted that, hereinafter, a “rising edge” refers to a boundary where an output signal changes from low to high, in other words, a boundary where output data changes from 0 to 1. Furthermore, a “falling edge” refers to a boundary where an output signal changes from high to low, in other words, a boundary where output data changes from 1 to 0. 
     As depicted in  FIG. 7 , when a time measurement start signal is input in the delay element ring  501 , falling edges are transmitted in the order of from the first-stage delay element  602  to the second, third, and fourth-stage delay elements  602 . If the data that is output from each of the delay elements  602  from the first stage to fourth stage is taken as D 0 , D 1 , D 2 , and D 3 , the data that is output from each of the delay elements  602  in the intervals of T 1 →T 2 →T 3 →T 4 →T 5  depicted in  FIG. 7  changes in the order of (D 0 , D 1 , D 2 , D 3 )=(1, 1, 1, 1)→(0, 1, 1, 1)→(0, 0, 1, 1)→(0, 0, 0, 1)→(0, 0, 0, 0). The falling edge transmitted to the fourth-stage delay element  602  is transmitted to the NAND element  601  of the delay element ring  501 , and is converted into a rising edge at the NAND. 
     Following on, rising edges are transmitted from the first-stage delay element  602  to the second, third, and fourth-stage delay elements  602 , and the data that is output from each of the delay elements  602  in the intervals of T 5 →T 6 →T 7 →T 8 →T 9  changes in the order of (D 0 , D 1 , D 2 , D 3 )=(0, 0, 0, 0)→(1, 0, 0, 0)→(1, 1, 0, 0)→(1, 1, 1, 0)→(1, 1, 1, 1). The rising edge transmitted to the fourth-stage delay element  602  is transmitted to the NAND element  601  of the delay element ring  501 , and is converted into a falling edge at the NAND. Hereinafter, the same operation as that which is first carried out is repeated. 
     As mentioned above, the output data (DO, D 1 , D 2 , D 3 ) of the delay elements  602  expressed by four bits does not result in a simple increase of a binary number. Thus, if it is assumed that (1, 1, 1, 1)=A, (0, 1, 1, 1)=B, (0, 0, 1, 1)=C, (0, 0, 0, 1)=D, (0, 0, 0, 0)=E, (1, 0, 0, 0)=F, (1, 1, 0, 0)=G, and (1, 1, 1, 0)=H, the delay element ring  501  performs the operation of a three-bit counter that repeats the output of eight types of data from A to H. 
     As mentioned above, in the delay element ring  501 , when the time measurement start signal is input, rising edges and falling edges are alternately transmitted in the order of from the first-stage delay element  602  to the second, third, and fourth-stage delay elements  602 . A delay flip-flop  603  is connected to the output side of each of the delay elements  602 . When a time measurement end signal is input to the delay memory  503 , output data (1 or 0) from the delay elements  602  is saved in the delay flip-flops  603 . By referring to the output data saved in the delay memory  503 , it is possible to determine the time from the time measurement start signal being input to the time measurement end signal being input. For example, in the case where the delay amount per one delay element  602  is  100  picoseconds and (D 0 , D 1 , D 2 , D 3 )=(0, 0, 0, 1), it is understood that the time from the time measurement start signal being input to the time measurement end signal being input is 300 picoseconds. 
     However, until the time measurement end signal is input to the delay memory  503 , the rising edges and falling edges continue within the delay element ring  501  in an alternating manner indefinitely. Consequently, it is difficult to determine how many times a rising edge and a falling edge has occurred up to the time measurement end signal being input to the delay memory  503 . Thus, as depicted in  FIG. 5 , the output of the final-stage delay element  602  of the delay element ring  501  is connected to the input of the counter  502  as a count-up signal. 
       FIG. 8  is a block diagram depicting an example of a detailed configuration of the counter  502  and the counter memory  504  according to the present embodiment.  FIG. 9  is an example of a timing chart depicting operations of the counter  502  and the counter memory  504  according to the present embodiment. 
     The counter  502  is configured of a plurality of flip-flops  803  linked in series.  FIG. 8  depicts the counter  502  having the flip-flops  803  linked in four stages as an example. 
     The counter memory  504  is configured of a plurality of counter flip-flops  802  linked in series.  FIG. 8  depicts the counter memory  504  having the counter flip-flops  802  linked in four stages as an example. The counter flip-flops  802  are respectively connected to the outputs of the four-stage flip-flops  803 . 
     For the counter  502 , a synchronous counter may be used rather than the asynchronous counter depicted in  FIG. 8 . The counter  502  adds 1 to a count value each time a count-up signal is input. That is, 1 is added to the count value each time the output D 3  of the final-stage delay element  602  of the delay element ring  501  changes from low to high. 
     Specifically, the outputs (C 0 , C 1 , C 2 , C 3 ) of the flip-flops  803  increase by 1 at a time as in (0, 0, 0, 0), (1, 0, 0, 0), (0, 1, 0, 0), and (1, 1, 0, 0). The outputs of the flip-flops  803  are connected to the counter memory  504 . When a time measurement end signal is input to the counter flip-flops  802 , count values are stored in the counter flip-flops  802 . By referring to the count values stored in the counter memory  504 , the delay element ring  501  can determine how many times a rising edge or falling edge has occurred in the delay element ring  501 . 
     In addition, the aforementioned values acquired by the delay memory  503  and the count values acquired by the counter memory  504  are decoded by the decoder  505  and summed up, and it is thereby possible to determine how many stages of delay elements are equivalent to the time that has elapsed. If the delay amount per one delay buffer stage is several picoseconds to several nanoseconds, and a conventional method in which time is measured by a counter is adopted, a resolution is consequently obtained that is the same as that obtained when a counter is operating at several hundred megahertz to several hundred gigahertz. 
     For example, in the case where the delay element ring  501  and delay memory  503  depicted in  FIG. 6  and the counter  502  and counter memory  504  depicted in  FIG. 8  are combined, when the delay elements  602  in the delay element ring  501  constitute four stages and the flip-flops  803  in the counter  502  are configured of four bits, consequently the delay buffers can constitute eight stages and the counter can perform  16  counts, and measurement can be performed with 8×16=128 stages in total. 
       FIG. 10  is an example of a timing chart depicting operations of the delay element ring  501 , the delay memory  503 , the counter  502 , and the counter memory  504  according to the present embodiment. 
     When the time measurement end signal is input, the output of the delay element ring  501  is stored in the delay memory  503 , and the output of the counter  502  is stored in the counter memory  504 . For example, in the case where the time measurement end signal is input at the timing of time TA indicated in the timing chart depicted in  FIG. 10 , D is stored in the delay memory  503 , and 9 is stored in the counter memory  504  as a decimal number. D that is output from the delay memory  503  corresponds to three of the delay elements  602 . 
     In addition, the decoder  505  calculates and outputs how many of the delay elements  602  are equivalent to the delay time, namely the time from the time measurement start to the time measurement end, on the basis of the output of the delay memory  503  and the output of the counter memory  504 . In the case where the delay element ring  501  and delay memory  503  depicted in  FIG. 6  and the counter  502  and counter memory  504  depicted in  FIG. 8  are combined, a count value of 1 of the counter  502  corresponds to eight of the delay elements  602 , and therefore there are 3+8×9=75 stages when expressing the number of stages of all of the delay elements  602 . In addition, when the processing time of the delay elements  602  is taken as having been 100 picoseconds per one stage, it is understood that the time from the time measurement start to the time measurement end was 7.5 nanoseconds. From a time obtained in this manner, it is possible to acquire the resistance value (resistance value information) of the variable-resistance element  210  provided in the nonvolatile memory  101 . 
     The delay element ring in  FIG. 6  is configured of the NAND element  601 , the delay elements  602 , and the delay flip-flops  603 ; however, it should be noted that an AND element may be used instead of the NAND element  601 . Furthermore, the delay element ring may be configured of only the delay elements  602  and the delay flip-flops  603  without using the NAND element  601 . In these cases, a mechanism with which the outputs of the delay elements  602  are returned to the original state may be newly provided. 
     Hereinabove, according to a nonvolatile memory device according to an aspect of the present disclosure, the time-digital converter  104  is configured using the delay element ring  501 , the counter  502 , the delay memory  503 , the counter memory  504 , and the decoder  505 , and it is thereby possible to obtain a high temporal resolution without increasing the counter operating speed. Since the counter operating speed is not increased, it is possible to suppress an increase in power consumption. 
       FIG. 24  depicts a time-digital converter  104   d  according to a modified example of embodiment 1. 
     The time-digital converter  104   d  includes the delay element ring  501 , the counter  502 , delay memories  503   a  and  503   b,  counter memories  504   a  and  504   b , and decoders  505   a  and  505   b.  The delay memory  503   a,  the counter memory  504   a , and the decoder  505   a  constitute a first channel, and the delay memory  503   b,  the counter memory  504   b,  and the decoder  505   b  constitute a second channel. 
     The configurations of the delay memories  503   a  and  503   b  are the same as that of the aforementioned delay memory  503 , for example. The configurations of the counter memories  504   a  and  504   b  are the same as that of the aforementioned counter memory  504 , for example. The configurations of the decoders  505   a  and  505   b  is the same as that of the aforementioned decoder  505 , for example. 
     The operations in the channels of the time-digital converter  104   d  are the same as those described above as the operations of the delay memory  503 , the counter memory  504 , and the decoder  505 , for example. 
     The time-digital converter  104   d,  for example, receives a time measurement start signal from outside, receives a first time measurement end signal from a first resistance-time converter (not depicted), and receives a second time measurement end signal from a second resistance-time converter (not depicted). Each of these resistance-time converters has the same configuration as that of the aforementioned resistance-time converter  103 , for example. A resistance value of a first nonvolatile memory (not depicted), for example, is reflected in the first time measurement end signal, and a resistance value of a second nonvolatile memory (not depicted), for example, is reflected in the second time measurement end signal. 
     The first channel outputs information regarding the time from the time measurement start time to the first time measurement end time as first decoder output. The second channel outputs information regarding the time from the time measurement start time to the second time measurement end time as second decoder output. The time-digital converter  104   d  is thereby able to output a plurality of items of time information in parallel on the basis of different time measurement end signals. Therefore, for example, a reading device that includes the time-digital converter  104   d  and a plurality of resistance-time converters is able to acquire information regarding the resistance values of a plurality of nonvolatile memories in parallel. 
     It should be noted that the time-digital converter  104   d  may be provided with three or more channels. The time-digital converter  104   d  would thereby able to acquire three or more items of time information. In the time-digital converter  104   d,  a decoder does not have to be provided for each channel, and a decoder may be shared by a plurality of channels. In this case, for example, the decoder selectively acquires one set of delay memory output and counter memory output from a plurality of channels, and generates one item of decoder output on the basis thereof. Thus, a plurality of items of decoder output can be output from one decoder. 
     Based on the above, with the nonvolatile memory device  100   a  according to the present embodiment, it is possible for digital ID data having excellent security to be generated at high speed and with low power consumption. 
     Embodiment 2 
     Next, a nonvolatile memory device according to the present embodiment will be described using  FIGS. 11 to 18 .  FIG. 11  is a block diagram depicting an example of a counter memory fetch signal generation circuit according to the present embodiment.  FIG. 12  is an example of a timing chart depicting operations of the counter memory fetch signal generation circuit in the case where there is a delay in a delay element ring and a counter according to the present embodiment.  FIG. 13  is a block diagram depicting an example of a time-digital converter that includes the counter memory fetch signal generation circuit, a sampling memory, and a correction circuit according to the present embodiment.  FIG. 14  is a flowchart depicting a specific example of a processing flow in which the correction circuit corrects a count value according to the present embodiment. 
     In practice, when there is an operation delay in the delay elements  602 , there are cases where the nonvolatile memory device  100   a  does not operate as envisaged. In particular, in the case of the asynchronous counter  502  such as that depicted in  FIG. 8 , the extent to which the circuit delay effect of the flip-flops  803  accumulates increases with higher-order bits (output from the later stages from among the plurality of flip-flops  803 ), and the bits do not change at the same time. If the counter  502  were configured of a synchronous counter, the delay of the flip-flops  803  would not accumulate, however, variations produced during manufacture, parasitic resistance, parasitic capacitance, and the like would accompany the output elements of each bit, and the bits would not change at the same time. 
     For example, as depicted in  FIG. 12  described later on, the bit outputs C 1 , C 2 , C 3 , and C 4  of the counter  502  do not operate at the same timing as a count-up signal, and are output delayed with respect to the count-up signal. At the timing of time TB, the change of each bit of the counter  502  has completed, and therefore a normal value is acquired by the counter memory  504  even if a time measurement end signal is input. However, when a time measurement end signal is input at the timing of time TC, the change (for example, bit output C 1 ) of each bit of the counter  502  has not completed, and therefore an erroneous value is saved in the counter memory  504 . 
     Furthermore, deviation in the operation timings of the delay element ring  501  and the counter  502  become a problem. For example, as depicted in  FIG. 12 , the count-up signal rises at the timing when the output from the delay element ring  501  switches from 7 to 0, and 1 is added to the value of the counter  502 . However, in practice, C 0 , which is the 0 th  bit of the counter  502 , changes after the elapse of the delay time of the time TD from the rise of the count-up signal. This causes an erroneous value to be input to the counter memory  504  even if a time measurement end signal is input in the period of time TD. 
     In order to prevent this kind of problem, in the nonvolatile memory device according to the present embodiment, a counter memory fetch signal generation circuit (in  FIG. 11 , simply depicted as a “signal generation circuit”)  1101  such as that depicted in  FIG. 11  is provided. 
     The counter memory fetch signal generation circuit  1101  is a circuit that delays the time measurement end signal. In detail, after data retained in the counter circuit has changed due to a rising edge or a falling edge of data that is output from any of the plurality of delay elements  602 , the counter memory fetch signal generation circuit  1101  generates an edge that is the inverse of the rising edge or the falling edge of the data that is output from any of the plurality of delay elements  602 . Alternatively, the counter memory fetch signal generation circuit  1101  delays the rising edge or the falling edge that is output from any of the plurality of delay elements  602 . 
     As depicted in  FIG. 11 , the counter memory fetch signal generation circuit  1101  is configured of an inversion element  1102  and a flip-flop circuit  1103 . The counter memory fetch signal generation circuit  1101 , when installed in a time-digital converter  104   b  as depicted in  FIG. 13 , performs an operation in which the time measurement end signal is resampled when the count-up signal is inverted. 
     Specifically, as depicted in the timing chart of  FIG. 12 , after the time measurement end signal has been input at the time TC, the counter memory fetch signal generation circuit  1101  generates a counter memory fetch signal at the falling edge (time TE) of the first count-up signal. The counter  502  adds 1 to the count value at the rising edge of the count-up signal. 
     When the time measurement end signal has been input, the counter memory  504  saves the count value by means of the subsequent counter memory fetch signal. If the time taken for each bit output of the counter  502  to stabilize is shorter than a half period of the count-up signal, consequently the count value is always saved in the counter memory  504  after each bit output by the counter  502  has completed operating. Thus, it is possible to prevent an erroneous operation caused by operation variations of each bit of the counter output. 
     It should be noted that the aforementioned counter memory fetch signal generation circuit  1101  does not have to be configured of the inversion element  1102  and the flip-flop circuit  1103 , for example, as long as the operation of the counter  502  and the timing of the counter memory  504  are offset. Instead of the counter memory fetch signal generation circuit  1101 , a circuit may be provided in which the delay elements  602  are connected in a plurality of stages and the time measurement end signal is delayed, for example. 
     However, in the aforementioned method, the time at which the counter memory  504  acquires a value is later than the time at which the time measurement end signal is input, and therefore there exists the condition that the counter memory  504  acquires a value after 1 has been added to the count value for the time at which the time measurement end signal was input, and there is a risk of an erroneous value being acquired. 
     In order to avoid this, in the time-digital converter  104   b  in the nonvolatile memory device according to the present embodiment, a sampling memory  1302  and a correction circuit  1303  have been added, as depicted in  FIG. 13 . 
     The sampling memory  1302  acquires the value of the least significant bit (output from the first-stage flip-flop  803 ) of the counter  502  at the same time as when the time measurement end signal is input. It should be noted that the sampling memory  1302  corresponds to a third memory circuit in the present disclosure. 
     Furthermore, the correction circuit  1303  corrects a count value on the basis of predetermined determination criteria, from the delay memory  503 , the counter memory  504 , and the sampling memory  1302 . It should be noted that the predetermined determination criteria, as an example, as described hereinafter, refers to the case where the time measurement end signal changes from 0 to 1, the output of the counter memory  504  (in other words, the data saved in the counter memory  504 ) is not 0, the output of the delay memory  503  (in other words, the data saved in the delay memory  503 ) is a value that is in the latter half of one period (for example, E, F, G, and H depicted in  FIG. 6 ), and the value of the least significant bit of the counter memory  504  and the value of the sampling memory  1302  are not the same. 
     The processing procedure therefor is given in the flowchart of  FIG. 14 . When the time measurement end signal that is input to the time-digital converter  104   b  changes from 0 to 1 (yes in step S 11 ), after values have been acquired by the delay memory  503 , the counter memory  504 , and the sampling memory  1302 , the correction circuit  1303  confirms whether the output of the counter memory  504  is not 0 (to be accurate,  0000  in the case of four bits) (step S 12 ). 
     If the output of the counter memory  504  is not 0 (no in step S 12 ), the correction circuit  1303  refers to the value of the delay memory  503 , and confirms whether it is within the range of the latter half (E, F, G, or H constituting the latter half of the output of one period of A to H indicated in embodiment 1, provided the delay elements  602  are constituted by four stages as in  FIG. 6 ) (step S 13 ). 
     If within the range of the latter half (yes in step S 13 ), the correction circuit  1303  compares the value of the least significant bit of the counter memory  504  and the value of the sampling memory  1302 , and confirms whether the value of the least significant bit of the counter memory  504  and the value of the sampling memory  1302  are different (step S 14 ). 
     Here, if the value of the least significant bit of the counter memory  504  and the value of the sampling memory  1302  are not the same (no in step S 14 ), and the entirety of the aforementioned condition is met, the counter memory  504  consequently acquires a value having 1 added to the count value for the time at which the time measurement end signal is input. Thus, the correction circuit  1303  performs a correction with which 1 is subtracted from the count value of the counter memory  504  (step S 15 ). Thereafter, the correction circuit  1303  outputs the corrected count value to the decoder  505  (step S 17 ). 
     Furthermore, in the case where the aforementioned condition is not met at all, the correction circuit  1303  takes the count value for the time at which the time measurement end signal is input, as it is as the count value of the counter memory  504  (step S 16 ), and outputs the count value to the decoder  505  (step S 17 ). 
     It should be noted that, in the aforementioned counter memory  504 , a case has been given in which the value of the least significant bit in the counter memory  504  is acquired by the sampling memory  1302 ; however, a bit other than the least significant bit may be acquired by the sampling memory  1302  and used for a determination. 
     Next, the effect of the correction circuit  1303  will be described by actually using a timing chart. An example of the case where the delay element ring  501  uses four bits (A to H), the counter  502  uses four bits, and the sampling memory  1302  uses the least significant one bit of the counter  502  is depicted in  FIGS. 15 to 18 .  FIG. 15  is a first timing chart for the case where the correction circuit does not correct the count value according to the present embodiment.  FIG. 16  is a second timing chart for the case where the correction circuit does not correct the count value according to the present embodiment.  FIG. 17  is a timing chart for the case where the correction circuit corrects the count value according to the present embodiment.  FIG. 18  is a third timing chart for the case where the correction circuit does not correct the count value according to the present embodiment. Here, more realistic timing charts are depicted, with a time delay being present in the count-up signal, the counter output, and the counter memory fetch signal. 
     In the timing chart depicted in  FIG. 15 , at the timing at which the time measurement end signal is input, the delay element ring output=D, the counter output=09, and the sampling memory output=1. Since the delay memory output=D, the counter memory output=09 (least significant bit=1), the delay memory  503  is in the first half (A to D), and the sampling memory output value and the least significant bit of the counter memory output match, the correction circuit  1303  outputs the value of the counter memory output as it is without subtracting 1 therefrom. 
     Next, in the timing chart depicted in  FIG. 16 , at the timing at which the time measurement end signal is input, the delay element ring output=F, the counter output=09, and the sampling memory output=1. Since the delay memory output=F, the counter memory output=09 (least significant bit=1), the delay memory  503  is in the latter half (E to H), and the sampling memory output value and the least significant bit of the counter memory output match, the correction circuit  1303  outputs the value of the counter memory output as it is without subtracting 1 therefrom. 
     Next, in the timing chart depicted in  FIG. 17 , at the timing at which the time measurement end signal is input, the delay element ring output=G, the counter output=09, and the sampling memory output =1. Since the delay memory output=G, the counter memory output=10 (least significant bit=0), the delay memory  503  is in the latter half (E to H), and the sampling memory output and the least significant bit of the counter memory output are different, the correction circuit  1303  outputs a value obtained by subtracting  1  from the value of the counter memory output. 
     Next, in the timing chart depicted in  FIG. 18 , at the timing at which the time measurement end signal is input, the delay element ring output=A, the counter output=10, and the sampling memory output=1. The reason the counter output=09 but the counter memory output=10 at the timing at which the time measurement end signal is input is because there is a delay in the counter output compared to the delay element ring output, and originally the correct value is the counter output=10. Since the delay memory output=0, the counter memory output=10 (least significant bit=0), the sampling memory output=1, and the delay memory is in the first half (A to D), the correction circuit outputs the value of the counter memory output as it is without subtracting 1 therefrom. 
     In this way, the correction circuit  1303  subtracts the value of the counter memory output in an appropriate manner, and a correct time is obtained. 
     Based on the above, according to the nonvolatile memory device according to the present embodiment, the effect of an operation delay of each bit of the counter  502  and an operation delay of the delay element ring  501  and counter  502  can be eliminated, and an accurate time measurement can be performed. It is possible to acquire an accurate resistance value (resistance value information) of the nonvolatile memory  101  from an accurate time obtained in this manner. 
     It should be noted that the method for eliminating the effect of the aforementioned operation delay is able to demonstrate said effect in all systems using the delay element ring  501  and counter  502 , regardless of a variable-resistance nonvolatile memory. 
       FIG. 25  depicts a time-digital converter  104   e  according to a modified example of embodiment 2. 
     The time-digital converter  104   e  includes the delay element ring  501 , the counter  502 , counter memory fetch signal generation circuits  1101   a  and  1101   b , the delay memories  503   a  and  503   b,  sampling memories  1302   a  and  1302   b,  the counter memories  504   a  and  504   b,  correction circuits  1303   a  and  1303   b,  and the decoders  505   a  and  505   b.  The counter memory fetch signal generation circuit  1101   a,  the delay memory  503   a,  the sampling memory  1302   a,  the counter memory  504   a,  the correction circuit  1303   a,  and the decoder  505   a  constitute a first channel. The counter memory fetch signal generation circuit  1101   b,  the delay memory  503   b , the sampling memory  1302   b,  the counter memory  504   b,  the correction circuit  1303   b,  and the decoder  505   b  constitute a second channel. 
     The configurations of the counter memory fetch signal generation circuits  1101   a  and  1101   b  are the same as that of the aforementioned counter memory fetch signal generation circuit  1101 , for example. The configurations of the delay memories  503   a  and  503   b  are the same as that of the aforementioned delay memory  503 , for example. The configurations of the sampling memories  1302   a  and  1302   b  are the same as that of the aforementioned sampling memory  1302 , for example. The constituent operations of the counter memories  504   a  and  504   b  are the same as that of the aforementioned counter memory  504 , for example. The configurations of the correction circuits  1303   a  and  1303   b  are the same as that of the aforementioned correction circuit  1303 , for example. The configurations of the decoders  505   a  and  505   b  is the same as that of the aforementioned decoder  505 , for example. 
     The operations in the channels of the time-digital converter  104   e  are the same as that described above as the operations of the counter memory fetch signal generation circuit  1101 , the delay memory  503 , the sampling memory  1302 , the counter memory  504 , the correction circuit  1303 , and the decoder  505 , for example. 
     The first channel outputs information regarding the time from the time measurement start time to the first time measurement end time as first decoder output on the basis of the time measurement start signal and the first time measurement end signal. The second channel outputs information regarding the time from the time measurement start time to the second time measurement end time as second decoder output on the basis of the time measurement start signal and the second time measurement end signal. The time-digital converter  104   e  is thereby able to output a plurality of items of time information in parallel on the basis of different time measurement end signals. Therefore, for example, a reading device that includes the time-digital converter  104   e  and a plurality of resistance-time converters is able to acquire information regarding the resistance values of a plurality of nonvolatile memories in parallel. 
     It should be noted that the time-digital converter  104   e  may be provided with three or more channels. The time-digital converter  104   e  is thereby able to acquire three or more items of time information. It should be noted that, in the time-digital converter  104   e,  a decoder does not have to be provided for each channel, and may be shared by a plurality of channels. In this case, for example, the decoder selectively acquires one set of delay memory output and counter memory output from a plurality of channels, and generates one item of decoder output on the basis thereof. Thus, a plurality of items of decoder output can be output from one decoder. 
     Embodiment 3 
     Next, a nonvolatile memory device according to embodiment  3  will be described using  FIG. 19 .  FIG. 19  is a block diagram depicting an example of a configuration in which both the time of a time measurement start time and the time of a time measurement end time of a time-digital converter are saved and the difference is output according to the present embodiment. 
     In the nonvolatile memory device according to the aforementioned embodiment, the delay element ring  501  and the counter  502  start operating from the time measurement start signal being input, the states (saved data) of the delay element ring  501  and the counter  502  when the time measurement end signal is input are saved in the delay memory  503 , the counter memory  504 , and the sampling memory  1302 , and reference is made to said states to thereby measure the time from the time measurement start to the time measurement end. As a result, there have been cases where a phenomenon occurs in which the delay amount changes for a while after the delay element ring  501  has started operating, and then stabilizes after a fixed time. Therefore, for an accurate time measurement, it is desirable for the time measurement to be started once the operation of the delay element ring  501  has stabilized. 
     Thus, in the nonvolatile memory device according to the present embodiment, as depicted in  FIG. 19 , a configuration is adopted in which a memory that saves the time measurement start time and a memory that saves the time measurement end time are provided separately in a time-digital converter  104   c . The stability of the time measurement can thereby be improved. 
     As depicted in  FIG. 19 , the time-digital converter  104   c  is provided with, as a configuration for saving the time measurement start time, a start delay memory  1901 , a start counter memory  1902 , a start counter memory fetch signal generation circuit  1903 , a start sampling memory  1904 , a start correction circuit  1905 , and a start decoder  1912 . Furthermore, the time-digital converter  104   c  is provided with, as a configuration for saving the time measurement end time, a stop delay memory  1906 , a stop counter memory  1907 , a stop counter memory fetch signal generation circuit  1908 , a stop sampling memory  1909 , a stop correction circuit  1910 , and a stop decoder  1913 . In addition, the time-digital converter  104   c  is provided with a difference calculation circuit  1911  that calculates and outputs the difference between a saved time measurement start time and time measurement end time. 
     In the time-digital converter  104   c,  when a delay element ring start signal is input to the delay element ring  501 , the delay element ring  501  and the counter  502  start operating. After the operation of the delay element ring  501  has stabilized, the time measurement start signal is input to the time-digital converter  104   c.  Thus, the state of the delay element ring  501  is saved in the start delay memory  1901 , and the state of the counter  502  is saved in the start sampling memory  1904  and the start counter memory  1902 . Then, in a similar manner to the correction circuit  1303  indicated in embodiment  2 , the counter memory output for when the time measurement start signal was input is corrected by the start correction circuit  1905 . In addition, the corrected counter memory output is output to the start decoder  1912  as a start correction circuit output. 
     Thereafter, in the time-digital converter  104   c,  when the time measurement end signal is input, the state of the delay element ring  501  is saved in the stop delay memory  1906 , and the state of the counter  502  is saved in the stop sampling memory  1909  and the stop counter memory  1907 . Then, in a similar manner to the correction circuit  1303  indicated in embodiment  2 , the counter memory output for when the time measurement end signal was input is corrected by the stop correction circuit  1910 , and the corrected counter memory output is output to the start decoder  1912  as a stop correction circuit output. 
     In addition, the start decoder output is input from the start decoder  1912  and the stop decoder output is input from the stop decoder  1913  to the difference calculation circuit  1911 . The difference calculation circuit  1911  calculates the difference between a correction value for the time at which the start decoder output, in other words, the time measurement start signal was input and a correction value for the time at which the time measurement end signal was input, and outputs the difference as a difference calculation output. Thus, it is possible to start a time measurement after the operation of the delay element ring  501  has stabilized, and it is therefore possible to obtain a more accurate time. It is possible to acquire an accurate resistance value (resistance value information) of the nonvolatile memory  101  from an accurate time obtained in this manner. 
       FIG. 26  depicts a time-digital converter  104   f  according to a modified example of embodiment  3 . 
     The time-digital converter  104   f  includes the delay element ring  501 , the counter  502 , the start counter memory fetch signal generation circuit  1903 , the start delay memory  1901 , the start sampling memory  1904 , the start counter memory  1902 , the start correction circuit  1905 , the start decoder  1912 , stop counter memory fetch signal generation circuits  1908   a  and  1908   b,  stop delay memories  1906   a  and  1906   b,  stop sampling memories  1909   a  and  1909   b,  stop counter memories  1907   a  and  1907   b,  stop correction circuits  1910   a  and  1910   b , stop decoders  1913   a  and  1913   b,  and difference calculation circuits  1911   a  and  1911   b.  The start counter memory fetch signal generation circuit  1903 , the start delay memory  1901 , the start sampling memory  1904 , the start counter memory  1902 , the start correction circuit  1905 , and the start decoder  1912  constitute a start channel. The stop counter memory fetch signal generation circuit  1908   a,  the stop delay memory  1906   a,  the stop sampling memory  1909   a,  the stop counter memory  1907   a,  the stop correction circuit  1910   a,  and the stop decoder  1913   a  constitute a first stop channel. The stop counter memory fetch signal generation circuit  1908   b , the stop delay memory  1906   b,  the stop sampling memory  1909   b,  the stop counter memory  1907   b,  the stop correction circuit  1910   b,  and the stop decoder  1913   b  constitute a second stop channel. 
     The configurations of the stop counter memory fetch signal generation circuits  1908   a  and  1908   b  are the same as that of the aforementioned stop counter memory fetch signal generation circuit  1908 , for example. The configurations of the stop delay memories  1906   a  and  1906   b  are the same as that of the aforementioned stop delay memory  1906 , for example. The configurations of the stop sampling memories  1909   a  and  1909   b  are the same as that of the aforementioned stop sampling memory  1909 , for example. The configurations of the stop counter memories  1907   a  and  1907   b  are the same as that of the aforementioned stop counter memory  1907 , for example. The configurations of the stop correction circuits  1910   a  and  1910   b  are the same as that of the aforementioned stop correction circuit  1910 , for example. The configurations of the stop decoders  1913   a  and  1913   b  are the same as that of the aforementioned stop decoder  1913 , for example. The configurations of the difference calculation circuit  1911   a  and  1911   b  are the same as that of the aforementioned difference calculation circuit  1911 , for example. 
     The operations in the stop channels of the time-digital converter  104   f  are the same as that described above as the operations of the stop counter memory fetch signal generation circuit  1908 , the stop delay memory  1906 , the stop sampling memory  1909 , the stop counter memory  1907 , the stop correction circuit  1910 , and the stop decoder  1913 , for example. 
     The start channel outputs information regarding the time from the start time of the delay element ring to the time measurement start time as start decoder output on the basis of a delay element ring start signal and the time measurement start signal. The first stop channel outputs information regarding the time from the start time of the delay element ring to the first time measurement end time as first stop decoder output on the basis of the delay element ring start signal and the first time measurement end signal. The difference calculation circuit  1911   a  outputs information regarding the time from the time measurement start time to the first time measurement end time as first difference calculation output on the basis of the start decoder output and the first stop decoder output. The second stop channel outputs information regarding the time from the start time of the delay element ring to the second time measurement end time as second stop decoder output on the basis of the delay element ring start signal and the second time measurement end signal. The difference calculation circuit  1911   b  outputs information regarding the time from the time measurement start time to the second time measurement end time as second difference calculation output on the basis of the start decoder output and the second stop decoder output. The time-digital converter  104   f  is thereby able to output a plurality of items of time information in parallel on the basis of different time measurement end signals. Therefore, for example, a reading device that includes the time-digital converter  104   f  and a plurality of resistance-time converters is able to acquire information regarding the resistance values of a plurality of nonvolatile memories in parallel. 
     It should be noted that the time-digital converter  104   f  may be provided with three or more channels. The time-digital converter  104   f  is thereby able to acquire three or more items of time information. It should be noted that, in the time-digital converter  104   f,  a decoder does not have to be provided for each channel, and may be shared by a plurality of channels. In this case, for example, the decoder selectively acquires one set of delay memory output and counter memory output from a plurality of channels, and generates one item of decoder output on the basis thereof. Thus, a plurality of items of decoder output can be output from one decoder. 
     Embodiment 4 
     Next, a nonvolatile memory device according to embodiment  4  will be described using  FIGS. 20 to 23 .  FIG. 20  is a circuit diagram depicting an example of a configuration in which a current amount of a delay element ring can be changed according to the present embodiment.  FIG. 21  is a circuit diagram depicting an example of a configuration in which a voltage amount of a delay element ring can be changed according to the present embodiment.  FIG. 22  is a block diagram depicting an example of a configuration in which the current amount of the delay element ring is adjusted according to the present embodiment.  FIG. 23  is a timing chart for the case where the current amount of the delay element ring is adjusted according to the present embodiment. 
     It is ideal for the delay elements  602  of the delay element ring  501  to always have the same delay amount; however, in practice, there are cases where the delay time (delay amount) of a signal that is output from the delay element ring  501  changes due to manufacturing variations and temperature fluctuations. Thus, as disclosed in  FIG. 20 , a configuration is adopted in which current sources  2001  are provided on the source side and the ground side of the delay elements  602  so that the current amount can be changed. For example, when the current amount flowing to the delay elements  602  is decreased, the delay amount increases. By adjusting the current amount that flows to the delay elements  602  by means of the current sources  2001 , it is possible to obtain a desired delay amount in the delay element ring  501 . 
     Furthermore, a method in which a voltage is supplied from a voltage source  2101  to the source side and the ground side of the delay elements  602  as in  FIG. 21  is also feasible. For example, when the source voltage or the ground voltage of the delay elements  602  is restricted, the delay amount increases. By adjusting the magnitude of the voltage supplied to the delay elements  602  by means of the voltage source  2101 , it is possible to obtain a desired delay amount in the delay element ring  501 . 
     In addition, the nonvolatile memory device may be provided with an adjustment circuit  2201  that can adjust the current amount or the voltage amount, instead of the aforementioned current sources  2001  and voltage source  2101 . The adjustment circuit  2201  changes the delay time of the delay elements  602  in such a way that the time difference from the time at which the time measurement start signal is input to the time at which the time measurement end signal is input becomes a predetermined target value. At such time, the time measurement start signal and the time measurement end signal may be generated according to the reference signal that is input from outside. Specifically, this may be performed as follows. 
       FIG. 22  depicts a block diagram for the case where the delay amount is to be adjusted. Here, the case where the current amount is to be adjusted will be described. In this case, it is assumed that the time-digital converter depicted in  FIG. 13  is used for the time-digital converter  104 , and the adjustment circuit  2201  is mounted with the configuration capable of adjusting the current amount depicted in  FIG. 20 . Furthermore,  FIG. 23  depicts a timing chart for the case where the delay elements  602  are to be adjusted to have a desired delay amount. 
     An output value of the decoder  505  that serves as the target value is equal to or greater than 10 and equal to or less than 15, for example. The reference signal is a clock signal having a stable period of a crystal oscillator or the like, and is used in the adjustment circuit  2201 . The adjustment circuit  2201  outputs a current setting and a time measurement start signal at the same time as when the reference signal rises, and inputs a time measurement end signal at the clock signal that is immediately subsequent to the reference signal or a clock signal that is a few signals subsequent to the reference signal. Decoder output is thereby obtained from the decoder  505  of the time-digital converter  104   b.  In the case where the decoder output from the decoder  505  is not the target value (equal to or greater than 10 and equal to or less than 15), the adjustment circuit  2201 , at the same time as when the reference signal rises once again, outputs a current setting that is different from the aforementioned and a time measurement start signal, and inputs a time measurement end signal at the clock signal that is immediately subsequent to the reference signal or a clock signal that is a few signals subsequent to the reference signal. New decoder output is thereby obtained from the decoder  505  of the time-digital converter  104   b.  The aforementioned is repeated, and the adjustment is finished when the decoder output reaches the target value. 
     If the aforementioned method is used, it is possible to adjust the delay amount of the delay elements  602  of the delay element ring  501 , and to obtain a desired delay amount. If the current amount is adjusted immediately prior to a time being converted into a digital value by the time-digital converter  104 , deviations in delay amounts caused by not only manufacturing variations of the delay elements  602  but also temperature and source voltage fluctuations can also be corrected, and a target delay amount can be obtained. 
     Hereinabove, a nonvolatile memory device according to embodiments of the present disclosure has been described; however, the present disclosure is not restricted to these embodiments. 
     For example, the counter circuit may measure the number of times that a rising edge occurs or may measure the number of times that a falling edge occurs in the output of any of a plurality of delay elements. 
     Furthermore, an AND element may be used instead of a NAND element in the delay element ring. Furthermore, the delay element ring may be configured of only a delay element and a delay flip-flop without using a NAND element. In these cases, a mechanism with which the output of the delay element is returned to the original state may be newly provided. 
     Furthermore, the aforementioned counter memory fetch signal generation circuit does not have to be configured of an inversion element and a flip-flop circuit, and may delay a time measurement end signal with delay elements being connected in a plurality of stages, for example. 
     Furthermore, in the aforementioned embodiments, one threshold value for determining a resistance value has been given; however, there may be a plurality of threshold values for determining a resistance value. In the aforementioned embodiments, data of 1 or 0 is stored in a nonvolatile memory; however, other data may be stored due to increasing the threshold values for determining a resistance value. 
     Furthermore, a nonvolatile memory device has been described in the aforementioned embodiments; however, an integrated circuit card provided with a nonvolatile memory device having the aforementioned features is also included in the present disclosure. 
     Furthermore, the method for eliminating the effect of the aforementioned operation delays may be used for all systems that use a delay element ring and a counter, regardless of a variable-resistance nonvolatile memory. 
     Hereinabove, a nonvolatile memory device according to one or more aspects has been described on the basis of the embodiments; however, the present disclosure is not restricted to these embodiments. Modes in which various modifications conceived by a person skilled in the art have been implemented in the present embodiments, and modes constructed by combining the constituent elements in different embodiments may also be included within the scope of one or more aspects provided they do not depart from the purpose of the present disclosure. 
     Supplement 
     In  FIG. 5 , the nonvolatile memory device  100   a  is provided with the nonvolatile memory  101 , the resistance-time converter  103 , and the time-digital converter  104   a.    
     The nonvolatile memory  101  stores predetermined information (for example, 0 or 1) corresponding to a resistance value thereof. 
     The resistance-time converter  103  outputs a time measurement end signal at a timing corresponding to the resistance value of the nonvolatile memory  101 . The resistance-time converter  103  includes the capacitor  201  and the comparator  202 . The capacitor  201  is able to electrically connect to the nonvolatile memory  101 . Charge corresponding to the resistance value of the nonvolatile memory  101  is accumulated in the capacitor  201 . Therefore, the potential of the capacitor  201  decreases at a speed corresponding to the resistance value of the nonvolatile memory  101 , due to discharging of the capacitor  201 . Alternatively, the potential of the capacitor  201  increases at a speed corresponding to the resistance value of the nonvolatile memory  101 , due to charging of the capacitor  201 . The comparator  202  compares the potential of the capacitor  201  and a reference potential VREF, and outputs a time measurement end signal in accordance with the result thereof. It should be noted that the “capacitor” in the present disclosure is not restricted to a device and may be parasitic capacitance, for example. 
     The time measurement start signal and the time measurement end signal are input to the time-digital converter  104   a.  The time-digital converter  104   a  converts the time from the time measurement start signal being input to the time measurement end signal being input into a digital value. 
     The time-digital converter  104   a  includes the delay element ring  501 , the counter  502 , the delay memory  503 , the counter memory  504 , and the decoder  505 . 
     As depicted in  FIG. 6 , the delay element ring  501  includes the plurality of delay elements  602 , and these are connected in a ring form. Each of the plurality of delay elements  602  is a digital buffer, for example. The plurality of delay elements  602  output the outputs D 0  to D 3 . In  FIG. 6 , the delay element ring  501  includes the NAND element  601 . In accordance with the time measurement start signal, the NAND element  601  inverts the output D 3  from the final-stage delay element  602 , and outputs the inverted value to the first-stage delay element  602 . Thus, the outputs D 0  to D 3 , for example, sequentially change each time a predetermined delay period elapses from the time measurement start signal being input to the first-stage delay element  602 . It should be noted that this delay period may vary slightly. The delay element ring  501 , for example, outputs the output D 3  from the final-stage delay element  602  as a count-up signal. The delay memory  503  stores the outputs D 0  to D 3  of the plurality of delay elements  602  on the basis of the time measurement end signal. 
     As depicted in  FIG. 8 , the counter  502  counts the number of times that a rising edge occurs or the number of times that a falling edge occurs in the count-up signal. The counter memory  504  stores the outputs C 0  to C 3  of the counter  502  on the basis of the time measurement end signal. 
     The decoder  505  generates decoder output on the basis of the data D 0  to D 3  and the data C 0  to C 3 . In the present disclosure, “on the basis of X” and “based on X” each mean X is directly or indirectly used. 
     The time measurement start signal is an example of a “start signal” in the present disclosure, and the time measurement end signal is an example of a “first end signal” in the present disclosure. The delay element ring  501  is an example of a “ring delay circuit” in the present disclosure, and the counter  502  is an example of a “counter circuit” in the present disclosure. The NAND element  601  is an example of an “inversion circuit” in the present disclosure. The delay memory  503  is an example of a “first memory circuit” in the present disclosure, and the counter memory  504  is an example of a “second memory circuit” in the present disclosure. The outputs D 0  to D 3  of the plurality of delay elements  602  are an example of “first data” in the present disclosure, and the outputs C 0  to C 3  of the counter  502  are an example of “second data” in the present disclosure. The decoder output of the decoder  505  is an example of “first digital data” in the present disclosure. 
     In  FIG. 13 , the time-digital converter  104   b  is additionally provided with the counter memory fetch signal generation circuit  1101 , the sampling memory  1302 , and the correction circuit  1303  in addition to the configuration of the time-digital converter  104   a.    
     The counter memory fetch signal generation circuit  1101  causes the data C 0  to C 3  of the counter  502  to be acquired by the counter memory  504  after a predetermined period has elapsed from the time measurement end signal being input. 
     In the example depicted in  FIG. 12 , at the timing at which the output D 3  of the final-stage delay element  602  rises, the count-up signal rises, and the counter  502  counts up. Then, after the time measurement end signal has been input, the counter memory fetch signal rises at the timing at which the output D 3  falls. In this case, the counter memory  504  acquires the data C 0  to C 3  from the counter  502  in accordance with the counter memory fetch signal. 
     Alternatively, in a separate example, the time-digital converter  104   b  is provided with a delay circuit (not depicted) instead of the counter memory fetch signal generation circuit  1101 . This delay circuit causes a time measurement end signal to be delayed by a predetermined delay time and then output to the counter memory  504 . In this case, the counter memory  504  acquires the data C 0  to C 3  from the counter  502  in accordance with the delayed time measurement end signal. 
     The sampling memory  1302  receives a time measurement end signal not via the counter memory fetch signal generation circuit  1101 , and, in accordance therewith, stores the output CO of the first-stage flip-flop  803  of the counter  502 . 
     The correction circuit  1303  generates data of the original count value or a corrected count value from the output of the delay memory  503 , the sampling memory  1302 , and the counter  502 . The decoder  505  generates decoder output from the output of the delay memory  503  and the correction circuit  1303 . 
     The counter memory fetch signal generation circuit  1101  and the aforementioned delay circuit are both examples of a “first delay circuit” in the present disclosure, the sampling memory  1302  is an example of a “first sampling memory circuit” in the present disclosure, and the correction circuit  1303  is an example of a “first correction circuit” in the present disclosure. The counter memory fetch signal is an example of a “fetch signal” in the present disclosure. 
     In  FIG. 19 , the time-digital converter  104   c  is provided with the delay element ring  501 , the counter  502 , the start counter memory fetch signal generation circuit  1903 , the start delay memory  1901 , the start sampling memory  1904 , the start counter memory  1902 , the start correction circuit  1905 , the start decoder  1912 , the stop counter memory fetch signal generation circuit  1908 , the stop delay memory  1906 , the stop sampling memory  1909 , the stop counter memory  1907 , the stop correction circuit  1910 , the stop decoder  1913 , and the difference calculation circuit  1911 . 
     The start counter memory fetch signal generation circuit  1903  is an example of a “first delay circuit” in the present disclosure, and the stop counter memory fetch signal generation circuit  1908  is an example of a “second delay circuit” in the present disclosure. The start delay memory  1901  is an example of a “first memory circuit” in the present disclosure, and the stop delay memory  1906  is an example of a “third memory circuit” in the present disclosure. The start sampling memory  1904  is an example of a “first sampling memory circuit” in the present disclosure, and the stop sampling memory  1909  is an example of a “second sampling memory circuit” in the present disclosure. The start counter memory  1902  is an example of a “second memory circuit” in the present disclosure, and the stop counter memory  1907  is an example of a “fourth memory circuit” in the present disclosure. The start correction circuit  1905  is an example of a “first correction circuit” in the present disclosure, and the stop correction circuit  1910  is an example of a “second correction circuit” in the present disclosure. The start decoder  1912  is an example of a “first decoder” in the present disclosure, and the stop decoder  1913  is an example of a “second decoder” in the present disclosure. The difference calculation circuit  1911  is an example of a “first generation circuit” in the present disclosure. 
     In  FIGS. 20 to 22 , the current sources  2001 , the voltage source  2101 , or the adjustment circuit  2201  are connected to the delay element ring  501 . Thus, the delay times of each of the plurality of delay elements  602  can be adjusted. The current sources  2001 , the voltage source  2101 , and the adjustment circuit  2201  are all examples of an “adjustment circuit” in the present disclosure. 
     In  FIG. 22 , the adjustment circuit  2201  generates a time measurement start signal for testing and a time measurement end signal for testing on the basis of a reference signal, and outputs the time measurement start signal and the time measurement end signal to the time-digital converter  104   b.  The time-digital converter  104   b  outputs the time from the time measurement start signal being input to the time measurement end signal being input as decoder output. The adjustment circuit  2201  determines whether or not the value of the decoder output is within a predetermined range. If the value of the decoder output is not within the predetermined range, the adjustment circuit  2201  adjusts the delay times of each of the plurality of delay elements  602 . 
     The time measurement start signal for testing is an example of a “first test signal” in the present disclosure, and the time measurement end signal for testing is an example of a “second test signal” in the present disclosure. Decoder output that is output from the time-digital converter  104   b  to the adjustment circuit  2201  is an example of a “digital value” in the present disclosure. 
     In  FIG. 24 , the time-digital converter  104   d  includes the delay element ring  501 , the counter  502 , the delay memories  503   a  and  503   b,  the counter memories  504   a  and  504   b,  and the decoders  505   a  and  505   b.    
     The first time measurement end signal is an example of a “first end signal” in the present disclosure, and the second time measurement end signal is an example of a “second end signal” in the present disclosure. The delay memory  503   a  is an example of a “first memory circuit” in the present disclosure, and the delay memory  503   b  is an example of a “third memory circuit” in the present disclosure. The counter memory  504   a  is an example of a “second memory circuit” in the present disclosure, and the counter memory  504   b  is an example of a “fourth memory circuit” in the present disclosure. Data that is output from the delay element ring  501  to the delay memory  503   a  is an example of “first data” in the present disclosure, and data that is output from the counter  502  to the counter memory  504   a  is an example of “second data” in the present disclosure. Data that is output from the delay element ring  501  to the delay memory  503   b  is an example of “third data” in the present disclosure, and data that is output from the counter  502  to the counter memory  504   b  is an example of “fourth data” in the present disclosure. The decoder output of the decoder  505   a  is an example of a “first digital data” in the present disclosure, and the decoder output of the decoder  505   b  is an example of a “second digital data” in the present disclosure. 
     In  FIG. 25 , the time-digital converter  104   e  is additionally provided with the counter memory fetch signal generation circuits  1101   a  and  1101   b,  the sampling memories  1302   a  and  1302   b,  and the correction circuits  1303   a  and  1303   b  in addition to the configuration of the time-digital converter  104   d.    
     The counter memory fetch signal generation circuit  1101   a  is an example of a “first delay circuit” in the present disclosure, and the counter memory fetch signal generation circuit  1101   b  is an example of a “second delay circuit” in the present disclosure. The sampling memory  1302   a  is an example of a “first sampling memory circuit” in the present disclosure, and the sampling memory  1302   b  is an example of a “second sampling memory circuit” in the present disclosure. The correction circuit  1303   a  is an example of a “first correction circuit” in the present disclosure, and the correction circuit  1303   b  is an example of a “second correction circuit” in the present disclosure. 
     In  FIG. 26 , the time-digital converter  104   f  is provided with the delay element ring  501 , the counter  502 , the start counter memory fetch signal generation circuit  1903 , the start delay memory  1901 , the start sampling memory  1904 , the start counter memory  1902 , the start correction circuit  1905 , the start decoder  1912 , the stop counter memory fetch signal generation circuits  1908   a  and  1908   b,  the stop delay memories  1906   a  and  1906   b,  the stop sampling memories  1909   a  and  1909   b,  the stop counter memories  1907   a  and  1907   b,  the stop correction circuits  1910   a  and  1910   b,  the stop decoders  1913   a  and  1913   b,  and the difference calculation circuits  1911   a  and  1911   b.    
     The stop delay memory  1906   a  is an example of a “third memory circuit” in the present disclosure. The stop delay memory  1906   b  is an example of a “fifth memory circuit” in the present disclosure. The stop sampling memory  1909   a  is an example of a “second sampling memory circuit” in the present disclosure, and the stop sampling memory  1909   b  is an example of a “third sampling memory circuit” in the present disclosure. The stop counter memory  1907   a  is an example of a “fourth memory circuit” in the present disclosure, and the stop counter memory  1907   b  is an example of a “sixth memory circuit” in the present disclosure. The stop correction circuit  1910   a  is an example of a “second correction circuit” in the present disclosure, and the stop correction circuit  1910   b  is an example of a “third correction circuit” in the present disclosure. The stop decoder  1913   a  is an example of a “second decoder” in the present disclosure, and the stop decoder  1913   b  is an example of a “third decoder” in the present disclosure. The difference calculation circuit  1911   a  is an example of a “first generation circuit” in the present disclosure, and the difference calculation circuit  1911   b  is an example of a “second generation circuit” in the present disclosure. 
     The nonvolatile memory device according to the present disclosure is useful mounted in an IC, SoC, or the like which implements the access that accompanies authentication for data encryption, host computers, and servers.