JP2009232304A - Crystal oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystal oscillator capable of securely switching a terminal function and preventing an error due to noise. <P>SOLUTION: Each of function blocks (109, 111) is connected to a first terminal 105 via a first connection switching circuit 113, and connected to a second terminal 107 via a second connection switching circuit 115. Then a signal for switching the function blocks connected to the first terminal 105 and a signal for switching the function blocks connected to the second terminal 107 are produced by signals which are simultaneously input into these first and second terminals. Since simultaneous inputs of signals into a plurality of terminals themselves which are subjected to switching involve signal generation for switching terminal functions in the crystal oscillator, it eliminates using a voltage of a power source terminal for determination of terminal function switching in switching the terminal functions, thereby eliminating instability in operation which attributes to the use of a single power supply voltage for determination of switching. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystal oscillator, and more particularly to a crystal oscillator capable of reliably switching terminal functions while preventing malfunction due to noise.

  A crystal oscillator is a device that is frequently used as a high-precision time source and frequency source. However, when the crystal oscillator itself has insufficient frequency accuracy, it is used with higher accuracy using a frequency control circuit. Sometimes. A temperature-compensated crystal oscillator (hereinafter abbreviated as “TCXO”) mounted on a cellular phone is a typical example, and the temperature characteristics of an AT-cut crystal resonator are compensated by a temperature compensation circuit, and the oscillation frequency is highly accurate. Is supposed to be retained.

  Early TCXOs were “direct compensation” products that consisted of a number of discrete components. However, since the configuration is unsuitable for downsizing and cost reduction, the TCXO of “indirect compensation method” composed of one crystal resonator and one chip of semiconductor integrated circuit (IC) has become the mainstream recently. It has become.

  The IC used for the TCXO of the indirect compensation method is equipped with an electrically rewritable nonvolatile memory or a one-time ROM, and correction data for manufacturing variation such as a crystal resonator and a temperature sensor is written in the memory. Temperature compensation accuracy of oscillation frequency is ensured. However, since the manufacturing variation differs for each product, the correction data cannot be written unless the crystal resonator and the IC are mounted in one package and the characteristics are measured as a unit. For this reason, the TCXO package of the indirect compensation method is provided with a write terminal for the memory on the side surface or the like.

  When terminals are provided on the side of the package, a sufficiently large writing terminal can be secured if the package size is large, but it is difficult to provide a sufficiently large writing terminal as miniaturization progresses in recent years. And problems such as poor contact are likely to occur. Such a situation is the same when the write terminal is provided on the lower surface of the package.

  In view of this, there has been proposed a method of performing writing to the memory by eliminating the writing terminal to the memory and switching the terminal function of the user terminal (see, for example, Japanese Patent Application Laid-Open No. 11-136032).

  In general TCXO, four user terminals are provided, which are two power supply terminals, an oscillation output terminal, and a frequency adjustment terminal that changes the frequency by applying a voltage. Some TCXOs do not have a frequency adjustment function, but even in that case, they are apparently provided with four terminals.

  Patent Document 1 discloses a method of switching the terminal function so that the frequency adjustment terminal can be used as a write terminal to the memory by setting the power supply voltage input to the power supply terminal to a certain unsteady state. The signal input terminal for switching the terminal function provided in the temperature compensated oscillator described in this publication is only one power supply terminal.

  In addition, although patent document 1 also mentions that a signal may be input into terminals other than a power supply terminal and a terminal function may be switched, the specific method is not described. This publication details only the method of switching the terminal function by detecting the power supply voltage. In fact, only a method using one power supply terminal as the input of the switching signal of the terminal function is disclosed. .

However, there are various noise sources around the IC, and unexpected noise may jump into each terminal of the IC. In particular, in the case of TCXO, the power supply voltage fluctuates due to its own oscillation operation, and a strong radio wave generation source exists in the vicinity, so that the operating environment is quite severe. For this reason, there is a problem that the terminal function is arbitrarily switched due to a malfunction due to noise, although it is not necessary to switch the terminal function after being incorporated in the mobile phone.
JP-A-11-136032

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a crystal oscillator capable of reliably switching the terminal function and free from malfunction due to noise. .

  In order to solve the above-described problem, a crystal oscillator according to a first aspect of the invention includes first and second terminals other than a power supply terminal, and a plurality of functional blocks connectable to the first and second terminals, The switching signal of the functional block connected to the first terminal and the switching signal of the functional block connected to the second terminal are generated by signals simultaneously input to the first and second terminals. Features.

  The crystal oscillator according to the second invention is connected to the first and second terminals other than the power supply terminal, a plurality of functional blocks connectable to the first and second terminals, and the first terminal. A first connection switching circuit for switching function blocks to be switched, a second connection switching circuit for switching function blocks connected to the second terminal, and the first and second connection switching circuits. A switching control circuit for controlling, and a power-on reset circuit for controlling the operation of the switching control circuit when the power source is activated, wherein the first and second terminals are connected to an input of the switching control circuit. Features.

The switching control circuit detects a magnitude relationship between the voltage (V ₁ ) of the first terminal and the first threshold voltage (V _1th ), and outputs a reverse signal when V ₁ > V _1th . A second voltage detection circuit for detecting a magnitude relationship between the voltage (V ₂ ) of the second terminal and the second threshold voltage (V _2th ) and outputting an inverted signal when V ₂ > V _2th And a latch circuit that detects and holds the simultaneous inversion of the outputs of the first and second voltage detection circuits.

  The first and second voltage detection circuits may be configured to include an integration circuit in at least one of input and output.

The first and second threshold voltages (V _1th , V _2th ) are input / output operations of functional blocks that are preferentially connected to the first and second terminals when the power is turned on among the plurality of functional blocks. It is preferable to be outside the voltage range.

_Further , it is preferable that at least one of the first and second threshold voltages (V _1th , V _2th ) is a voltage exceeding a power supply voltage.

  Further, among the plurality of functional blocks, the functional block that is preferentially connected to the first and second terminals at the time of power activation by the control of the power-on reset circuit is a crystal oscillation circuit including a temperature compensation circuit, The other functional block may be a nonvolatile memory circuit that controls the operation of the temperature compensation circuit.

  In the conventional configuration, the signal for switching the terminal function is input to a terminal different from the terminal to be switched, whereas in the crystal oscillator of the present invention, a plurality of terminals to be switched are supplied to the terminal itself. Since simultaneous signal input is signal generation for switching the terminal function, it is not necessary to use the voltage of the power supply terminal to determine the switching of the terminal function when switching the terminal function, and one power supply voltage is used for the determination of switching. Instability of operation due to use can be eliminated, and even with a crystal oscillator that has only two terminals other than the power supply terminal, the disadvantage of the conventional technology that the fluctuation of the power supply voltage is likely to malfunction due to the superposition of noise. Can be resolved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram for explaining a configuration of a crystal oscillator according to the present invention. In this figure, reference numerals 101 and 103 are two power supply terminals (Vcc101, Gnd102), and reference numerals 105 and 107 are a first terminal 105 and a second terminal 107, respectively. That is, the crystal oscillator shown in this figure includes a power supply terminal (101, 103) and two terminals (105, 107). The crystal oscillator is provided with a plurality of functional blocks (a first functional block 109, a second functional block 111, and the like) that can be connected to the first terminal 105 and the second terminal 107.

  The feature of this crystal oscillator is a signal for switching a functional block (first functional block 109, second functional block 111, etc.) connected to the first terminal 105 and a function connected to the second terminal 107. Signal input terminals for switching blocks (the first functional block 109, the second functional block 111, and the like) are a plurality of terminals such as a first terminal 105 and a second terminal 107.

  In the mode shown in FIG. 1, each of the functional blocks (the first functional block 109, the second functional block 111, and the like) is connected to the first terminal 105 via the first connection switching circuit 113. The second connection switching circuit 115 is connected to the second terminal 107. Therefore, switching of the functional block connected to the first terminal 105 is performed by the first connection switching circuit 113, and switching of the functional block connected to the second terminal 107 is performed by the second connection switching circuit 115. It is.

  The operation control of the two connection switching circuits (113, 115) is performed by the switching control circuit 117, and the first terminal 105 and the second terminal 107 are connected to the input of the switching control circuit 117. Furthermore, the switching control circuit 117 is controlled by a power-on reset circuit 119 that controls the operation of the switching control circuit when the power source is activated.

  A feature of the crystal oscillator of the present invention is that it is connected to a signal for switching a functional block (first functional block 109, second functional block 111, etc.) connected to the first terminal 105 and the second terminal 107. The signal input terminals for switching the functional blocks (the first functional block 109, the second functional block 111, etc.) are a plurality of terminals such as a first terminal 105 and a second terminal 107. As described above, switching a functional block connected to a terminal is the same as changing the role of the terminal when viewed from the outside. Therefore, switching the functional block involves switching the terminal function. means.

  In the conventional configuration, a signal for switching the function (terminal function) of a certain terminal is input to one power supply terminal different from the terminal to be switched. On the other hand, according to the present invention, as is apparent from the block diagram shown in FIG. 1, a plurality of terminals, ie, the first terminal 105 and the second terminal 107 to be switched, switch the terminal function. The signal input terminal for switching the terminal function is the simultaneous input of the signals to the plurality of terminals to be switched.

  With such a configuration, it is not necessary to use the voltage of the power supply terminal for the determination of the switching of the terminal function when switching the terminal function, so that the instability of the operation caused by using one power supply voltage for the determination of the switching is eliminated. Even in the case of a crystal oscillator having only two terminals other than the power supply terminal, it is possible to eliminate the disadvantage of the prior art that the fluctuation of the power supply voltage is likely to malfunction by superimposing the noise on the noise.

  As shown in FIG. 1, since the signals from the first terminal 105 and the second terminal 107 are always input to the switching control circuit 117, the power-on reset circuit 119 gives priority to the first control when the power is turned on. The voltage in the voltage range of the input / output operation of the functional block connected to the first terminal 105 or the second terminal 107 is always input to the switching control circuit 117.

  For example, in the case of a TCXO having specifications of a power supply voltage of 2.4 ± 0.1 V, an oscillation output of 0 to 1.2 V, 26 MHz, and a frequency adjustment voltage input of 1.1 ± 0.8 V, the configuration is shown in FIG. Then, an AC voltage of 0 to 1.2 V and a DC voltage of 1.1 ± 0.8 V are always input to the switching control circuit 117 during a normal state in which switching is not performed. Therefore, the switching control circuit 117 must not respond to a voltage in such a range.

FIG. 2 is a diagram for explaining the configuration of the switching control circuit 117 included in the crystal oscillator according to the present embodiment. The switching control circuit 117 includes the voltage (V ₁ ) of the first terminal 105 and its own threshold voltage ( The first voltage detection circuit 201 that detects the magnitude relationship with V _1th ) and outputs an inverted signal when V ₁ > V _1th , the voltage (V ₂ ) at the second terminal 107, and its threshold voltage ( V _2th ) is detected, and when V ₂ > V _2th , the second voltage detection circuit 203 that outputs an inverted signal and the output of these two voltage detection circuits are inverted simultaneously, the state Has a latch circuit 205 for detecting and holding the signal.

Then, these first threshold voltage at which the output is inverted of the voltage detection circuit 201 (V _1th) and the threshold voltage at which the output is inverted in the second voltage detecting circuit 203 (V _2th), in the normal state, the first terminal 105 and the second terminal 107 are set outside the possible voltage range. In other words, the first and second threshold voltages (V _1th , V _2th ) of the functional blocks that are preferentially connected to the first and second terminals when the power is turned on among the plurality of functional blocks. It is out of the voltage range of input / output operation.

For example, when the voltage ranges in the normal state of the first terminal 105 and the second terminal 107 are an AC voltage of 0 to 1.2 V and a DC voltage of 1.1 ± 0.8 V, respectively, If any threshold voltage (V _1th , V _2th ) of the voltage detection circuits (201, 203) of 2 is set to 2V, the output will not be inverted in the normal state. By setting in this way, it is possible to use the terminal itself for which the terminal function is switched as an input terminal for the switching signal.

  When switching the terminal function, voltages exceeding the threshold voltages of the first voltage detection circuit 201 and the second voltage detection circuit 203 are applied to the first terminal 105 and the second terminal 107, respectively. For example, when both threshold voltages are set to 2 V, 2.4 V that is the same as the power supply voltage may be applied to the first terminal 105 and the second terminal 107. As a result, the outputs of the first voltage detection circuit 201 and the second voltage detection circuit 203 are inverted. As a result, the state of the latch circuit 205 is also changed, and thereafter the state is maintained until the power is turned off.

  Then, due to a change in the signal from the latch circuit 205, the first switching circuit 113 and the second switching circuit 115 shown in FIG. 1 switch the functional blocks connected to the first terminal 105 and the second terminal 107. I do. The state in which the terminal function is switched in this way is maintained until the power is turned off.

  By the way, the output state of the latch circuit 205 changes only when the outputs of the first voltage detection circuit 201 and the second voltage detection circuit 203 are inverted at the same time, but “simultaneous” is “synchronized”. ”Means that“ the time zone in which the output of the first voltage detection circuit 201 is inverted and the time zone in which the output of the second voltage detection circuit 203 is inverted have an overlap ”. . A disturbance such as noise is usually applied to the terminal as a beard-like pulse having a time width of the order of nsec. However, it is rare that such a short pulse is simultaneously applied to a plurality of terminals. A crystal oscillator based on a technique for detecting simultaneous inversion of two voltage detection circuits including a simple switching control circuit has a very high ability to prevent malfunction of switching of functional blocks.

  The present embodiment is a crystal oscillator provided with a switching control circuit for making it possible to further suppress malfunction due to noise. As described above, disturbances such as noise are usually applied to the terminals as whisker-like pulses with a time width of the order of nsec, and such short pulses are rarely applied to a plurality of terminals at the same time. However, since the probability that noise is simultaneously applied to the first terminal 105 and the second terminal 107 is not zero, even if such a rare phenomenon is taken, measures are taken to prevent malfunction of functional block switching. It is desirable to keep it.

  FIG. 3 is a diagram for explaining the configuration of the switching control circuit 117 included in the crystal oscillator of the present embodiment. The difference from that shown in FIG. 2 is that the output of the first voltage detection circuit 201 is the first. That is, the output of the second voltage detection circuit 203 is connected to the latch circuit 205 via the integration circuit 207 and the second integration circuit 209, respectively. As already described, since the pulse width of noise is on the order of nsec, if the time constant of these integration circuits is set to the order of μsec, changes in the input of the latch circuit 205 due to noise can be suppressed to a level that can be ignored. can do.

  In the example shown in FIG. 3, the integration circuit is provided on the output side of the voltage detection circuit. However, the integration circuit may be provided on the input side of the voltage detection circuit, or may be provided on both sides. Further, the method for improving the ability to prevent the switching malfunction due to disturbance such as noise is not limited to the method using the integration circuit. For example, the threshold voltages of the first voltage detection circuit 201 and the second voltage detection circuit 203 are set to the input / output operations of the functional blocks connected to the first terminal 105 and the second terminal 107 in the normal state. It is also effective to keep it as far as possible from the voltage range.

  As described above, when the threshold voltage is set to 2 V with respect to the DC voltage of 1.1 ± 0.8 V in the normal state, the voltage difference between the two is only 0.1 V, and the viewpoint of preventing malfunction. Is not enough. This is because even if the pulse width of the noise is narrow near the peak, the noise often has a long tail, so even if an integration circuit is provided on the input side of the voltage detection circuit, the integrated value of the noise voltage is 0. This is because it is sufficiently possible to exceed 1V.

  Therefore, when the difference between the voltage of the first terminal 105 or the second terminal 107 in the normal state and the power supply voltage is small, it is desirable to set the threshold voltage of the voltage detection circuit to a value exceeding the power supply voltage. . In TCXO, the oscillation output voltage has a large difference from the power supply voltage, but the frequency adjustment voltage has a small difference from the power supply voltage. Therefore, at least the threshold voltage of the voltage detection circuit on the frequency adjustment terminal side exceeds the power supply voltage. It is desirable to set. However, if the power supply voltage is greatly exceeded, a large current flows from the terminal to which the voltage is applied through the protection circuit to the power supply side, causing the power supply voltage to fluctuate, affecting the operation of the voltage detection circuit. There is a problem that it ends up. Therefore, it is desirable to set the threshold voltage so that it does not exceed 1-2 V from the power supply voltage.

  By the way, as a configuration of the voltage detection circuit, a voltage comparator that compares an applied voltage and an internal reference voltage by using an operational amplifier is generally used. It is not suitable as a voltage detection circuit. Therefore, in the crystal oscillator of the present invention, it is preferable to employ a simple circuit such as a combination of two resistors and an inverter.

  FIG. 4 is a diagram for explaining such a voltage detection circuit. As shown in FIG. 4, the voltage applied by the resistor 301 and the resistor 303 is divided by resistance, and the division point is connected to the input of the inverter 305. Thus, a voltage detection circuit is configured. The threshold voltage of the voltage detection circuit is set by the combination of the resistance ratio of the resistor 301 and the resistor 303 and the threshold voltage of the inverter 305.

  For example, in the case of a crystal oscillator with a power supply voltage of 2.4 V and the threshold voltage of the inverter 305 is ½ of the power supply voltage, the resistance ratio between the resistor 301 and the resistor 303 is 2 to 3 or 2 to 1. Then, the threshold voltage of the voltage detection circuit is 2V or 3.6V, respectively.

  Since the voltage detection circuit shown in FIG. 4 does not have a function of maintaining the state, when switching the terminal function, a voltage equal to or higher than the threshold voltage is applied to each of the two voltage detection circuits in overlapping time zones. There is a need. When the application is performed with the time shifted, the latch circuit 205 shown in FIG. 2 or FIG. The strict switching conditions contribute to the prevention of malfunction due to noise and other disturbances, and the reason why a circuit configuration without a feedback system is suitable as a voltage detection circuit used in the present invention. It is.

  This embodiment is another configuration example of the crystal oscillator (TCXO) of the present invention.

  FIG. 5 is a block diagram of the TCXO of this embodiment. The crystal oscillation circuit 401 connected to the temperature compensation circuit 403 corresponds to the first functional block shown in FIG. And connected to the second terminal 107. The nonvolatile memory circuit 405 for controlling the operation of the temperature compensation circuit 403 corresponds to the second functional block shown in FIG. 1, and only when the terminal function switching signal is input, the first terminal 105 and the second Connected to terminal 107. That is, this TCXO is a crystal oscillation circuit including a temperature compensation circuit, among the above-described plurality of functional blocks, the functional block that is preferentially connected to the first and second terminals at the time of power-on under the control of the power-on reset circuit. The other functional block is a crystal oscillator which is a nonvolatile memory circuit that controls the operation of the temperature compensation circuit. The configuration of the other circuit parts is the same as in FIG. 1, and the same reference numerals as in FIG.

  The function that final products such as mobile phones equipped with TCXO require TCXO is to output an accurate crystal oscillation frequency that is temperature compensated, and it is not possible to use non-volatile memory mounted inside from the outside. Absent. Therefore, the functional block connected to the first terminal 105 and the second terminal 107 preferentially at the time of power activation must always include the crystal oscillation circuit 401 and the temperature compensation circuit 403. In this state, the first terminal 105 and the second terminal 107 are an oscillation output terminal and a frequency adjustment terminal, respectively.

  By the way, the conventional TCXO is provided with four terminals in most cases for writing to the nonvolatile memory. The breakdown is a chip select terminal (hereinafter abbreviated as “CS”), a clock input terminal (hereinafter abbreviated as “CLK”), and a data input / output terminal (hereinafter abbreviated as “Di / o”). ), A write voltage application terminal (hereinafter abbreviated as “Vpp”).

  In the crystal oscillator according to the present invention, there are only two terminals, the oscillation output terminal and the frequency adjustment terminal, that can be used for memory writing by switching the terminal function. For this reason, it is necessary to play the role of the conventional four terminals only by the two terminals.

  Of the four conventional terminals, CS serves to inform the IC chip of the start of access to the memory. Therefore, in the present invention, the output of the latch circuit 205 shown in FIGS. 2 and 3 can be substituted. That is, inputting a terminal function switching signal to the first terminal 105 and the second terminal 107 corresponds to inputting a signal to CS.

  Of the remaining three terminals, CLK and Di / o are terminals that are used at the same time, but Vpp is a terminal that is used after the input of the write data and is used at least simultaneously with Di / o. There is nothing. Therefore, the first terminal 105 and the second terminal 107 after the terminal function switching are initially used as CLK and Di / o, respectively, and automatically from Di / o to Vpp at the stage when the input of the write data is completed. The terminal function may be switched.

  Of course, since the write voltage of the memory is usually much higher than the power supply voltage, it is necessary to specially devise a protection circuit on the side of the first terminal 105 or the second terminal 107 that is used as Vpp. Needless to say.

  However, it goes without saying that switching from Di / o to Vpp is unnecessary in the TCXO in which the write voltage to the memory is generated by the internal booster circuit, and in that case, no special device for the protection circuit is necessary. .

  In any case, according to the present invention, only the first terminal 105 and the second terminal 107, that is, the oscillation output terminal and the frequency adjustment terminal, serve as the four terminals for writing provided in the conventional TCXO. And writing to the non-volatile memory becomes possible.

  As described above, the application of the present invention to TCXO has been mainly described. However, the effectiveness of the present invention is not limited to TCXO, and can be applied to various crystal oscillators. For example, in a simple crystal oscillator called a clock generator, there is an increasing demand for a product called a high-precision product with high frequency accuracy. Conventionally, however, a nonvolatile memory is used because of changes in package shape and manufacturing equipment. High precision has been postponed. Therefore, conventionally, high-precision products can only be produced by selecting products after production, and the yield cannot be increased. Since the package of the clock generator has two terminals in addition to the power supply terminal, the terminal function switching method according to the present invention can be applied, and high accuracy by the nonvolatile memory can be easily realized.

  As described above, the crystal oscillator according to the present invention determines whether to switch one power supply voltage by switching the terminal function of two terminals other than the power supply terminal by simultaneous input of signals to the two terminals themselves. The instability of operation due to the use of the terminal can be eliminated, and the terminal function can be reliably switched while preventing malfunction due to disturbance. If the present invention is applied to the TCXO, terminals other than user terminals can be removed, so that further miniaturization can be realized, and the effect is very great.

It is a block diagram for demonstrating the structure of the crystal oscillator by this invention. FIG. 3 is a diagram for explaining a configuration of a switching control circuit included in the crystal oscillator according to the first embodiment. It is a figure for demonstrating the structure of the switching control circuit with which the crystal oscillator of Example 2 is provided. It is a figure for demonstrating the voltage detection circuit of a simple circuit structure by the combination of two resistances and an inverter. 6 is a block diagram of a TCXO of Example 3. FIG.

Explanation of symbols

101, 103 Power supply terminal 105 First terminal 107 Second terminal 109 First functional block 111 Second functional block 113 First connection switching circuit 115 Second connection switching circuit 117 Switching control circuit 119 Power-on reset circuit 201 First voltage detection circuit 203 Second voltage detection circuit 205 Latch circuit 207 First integration circuit 209 Second integration circuit 301, 303 Resistor 305 Inverter 401 Crystal oscillation circuit 403 Temperature compensation circuit 405 Nonvolatile memory circuit

Claims (7)

  The first and second terminals other than the power supply terminal, and a plurality of functional blocks connectable to the first and second terminals, the switching signal of the functional block connected to the first terminal and the second A crystal oscillator, wherein a switching signal of a functional block connected to a terminal is generated by a signal input simultaneously to the first and second terminals.   First and second terminals other than the power supply terminal, a plurality of functional blocks connectable to the first and second terminals, and a first connection for switching the functional blocks connected to the first terminal A switching circuit, a second connection switching circuit that switches a functional block connected to the second terminal, a switching control circuit that controls the first and second connection switching circuits, and a switching control circuit A crystal oscillator comprising: a power-on reset circuit that controls an operation at the time of power supply startup, wherein the first and second terminals are connected to an input of the switching control circuit. The switching control circuit detects a magnitude relationship between the voltage (V ₁ ) of the first terminal and the first threshold voltage (V _1th ), and outputs a reverse signal when V ₁ > V _1th . A second voltage detection circuit for detecting a magnitude relationship between the voltage (V ₂ ) of the second terminal and the second threshold voltage (V _2th ) and outputting an inverted signal when V ₂ > V _2th The crystal oscillator according to claim 2, further comprising: a voltage detection circuit for detecting the simultaneous inversion of the outputs of the first voltage detection circuit and the second voltage detection circuit.   4. The crystal oscillator according to claim 3, wherein each of the first voltage detection circuit and the second voltage detection circuit includes an integration circuit in at least one of an input and an output. The first and second threshold voltages (V _1th , V _2th ) are input / output operations of functional blocks that are preferentially connected to the first and second terminals when the power is turned on among the plurality of functional blocks. The crystal oscillator according to claim 3, wherein the crystal oscillator is out of the voltage range. 6. The crystal oscillator according to claim 5, wherein at least one of the first and second threshold voltages (V _1th , V _2th ) is a voltage exceeding a power supply voltage.   Among the plurality of functional blocks, the functional block that is preferentially connected to the first and second terminals at the time of power activation by the control of the power-on reset circuit is a crystal oscillation circuit including a temperature compensation circuit, 3. The crystal oscillator according to claim 2, wherein the functional block is a nonvolatile memory circuit that controls the operation of the temperature compensation circuit.