Temperature-compensated piezoelectric oscillator

Abstract

This temperature-compensation-type piezoelectric actuator (100) has a rock crystal vibration element (111) in which frequency temperature characteristics change according to at least a tertiary function, a temperature compensation circuit (130) that outputs a tertiary-function electrical signal for compensating for the frequency temperature characteristics of the rock crystal vibration element (111), and an oscillation circuit (112) to which the rock crystal vibration element (111) and a variable-capacitance element are connected and via which an output electrical signal from the temperature compensation circuit (130) is inputted to the variable-capacitance element. The temperature compensation circuit (130): generates a pseudo-tertiary-function electrical signal; and calculates an electrical signal that represents the difference between the pseudo-tertiary-function electrical signal and an ideal tertiary-function electrical signal, in which the pseudo-tertiary-function electrical signal is approximated using a tertiary function. A difference correction electrical signal corresponding to the electrical signal that represents the difference is added to the temperature compensation circuit (130).

Description

[Technical Field]

[0001] The present invention relates to a temperature compensated piezoelectric oscillator. [Background technology]

[0002] Piezoelectric oscillators, such as quartz crystal oscillators, have inherent frequency-temperature characteristics that cause their oscillation frequency to change in response to temperature. When an oscillation circuit is configured using such a piezoelectric oscillator, the output frequency of the oscillation circuit also changes in response to the piezoelectric oscillator. Therefore, a temperature-compensated piezoelectric oscillator has been known in the past that performs temperature compensation to suppress frequency changes in the oscillation circuit due to temperature changes by changing the capacitance (load capacitance) of the oscillation circuit to cancel out the frequency-temperature characteristics of the piezoelectric oscillator (see, for example, Patent Document 1).

[0003] A temperature-compensated piezoelectric oscillator includes, for example, a piezoelectric vibrator whose frequency-temperature characteristics change at least n-order (n is 2 or 3), a temperature-compensation circuit (signal generating circuit) that outputs an n-order electrical signal (e.g., voltage) that compensates for the frequency-temperature characteristics of the piezoelectric vibrator, and an oscillation circuit to which the piezoelectric vibrator and a variable capacitance element are connected and to which the output electrical signal from the temperature-compensating circuit is input. In a temperature-compensated piezoelectric oscillator, the temperature-compensating circuit generates an electrical signal that changes with temperature and applies it to a variable capacitance element in the oscillation circuit, thereby changing the load capacitance of the oscillation circuit with temperature, thereby performing temperature compensation. A tuning-fork piezoelectric vibrator is a typical example of a piezoelectric vibrator whose frequency-temperature characteristics change quadratically, while an AT-cut thickness-shear piezoelectric vibrator is a typical example of a piezoelectric vibrator whose frequency-temperature characteristics change cubically. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-219738 Summary of the Invention [Problem to be solved by the invention]

[0005] In the temperature-compensated piezoelectric oscillator described above, it is difficult for the temperature compensation circuit to generate an ideal electrical signal of n-th order function using a simple circuit configuration, and instead an electrical signal adjusted to be a pseudo-n-th order function is generated. As a result, a discrepancy (approximation error) occurs between the electrical signal corresponding to the frequency-temperature characteristics of the piezoelectric vibrator (ideal n-th order function) and the electrical signal generated by the temperature compensation circuit (pseudo-n-th order function), which raises concerns about a deterioration in temperature compensation accuracy.

[0006] In addition, because there is variation in the frequency-temperature characteristics of individual piezoelectric vibrators, the gain of each order component of the temperature compensation circuit is adjusted to suppress frequency changes in the oscillation circuit. However, if the gain of the nth order component is increased, the approximation error of the nth order component mentioned above also increases, which may result in a deterioration in temperature compensation accuracy.

[0007] The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a temperature-compensated piezoelectric oscillator that can reduce the approximation error of the nth-order component generated in the temperature compensation circuit and improve the temperature compensation accuracy. [Means for solving the problem]

[0008] The present invention provides a means for solving the above-mentioned problems as follows: That is, the present invention provides a temperature-compensated piezoelectric oscillator having a piezoelectric vibrator whose frequency-temperature characteristic changes at least n-th order (n is 2 or 3), a signal generating circuit that outputs an n-th order electric signal that compensates for the frequency-temperature characteristic of the piezoelectric vibrator, and an oscillation circuit to which the piezoelectric vibrator and a variable capacitance element are connected and to which the output electric signal of the signal generating circuit is input to the variable capacitance element, wherein the signal generating circuit generates a pseudo-n-th order electric signal, calculates an electric signal that is a difference between the pseudo-n-th order electric signal and an ideal n-th order electric signal that is an approximation of the pseudo-n-th order electric signal by an n-th order function, and applies a difference correction electric signal corresponding to the electric signal that is the difference to the signal generating circuit. The differential correction electrical signal corresponds to and suppresses an approximation error of an n-th order component between the ideal n-th order functional electrical signal and the pseudo-n-th order functional electrical signal, and by adding the differential correction electrical signal to the signal generating circuit, the approximation error of the n-th order component contained in the pseudo-n-th order functional electrical signal is canceled by the differential correction electrical signal. An example of a piezoelectric vibrator whose frequency-temperature characteristic changes quadratically (when n=2) is a tuning fork crystal vibrator, and an example of a piezoelectric vibrator whose frequency-temperature characteristic changes cubically (when n=3) is an AT-cut crystal vibrator.

[0009] According to the above configuration, the difference (approximation error) between the electrical signal (ideal n-th order function) corresponding to the frequency-temperature characteristics of the piezoelectric vibrator and the electrical signal (pseudo n-th order function) generated by the signal generating circuit can be canceled by the differential correction electrical signal, thereby reducing the approximation error of the n-th order component generated by the signal generating circuit. This allows the electrical signal corrected by the differential correction electrical signal to be as close as possible to the temperature compensation voltage (ideal n-th order function) corresponding to the frequency-temperature characteristics of the piezoelectric vibrator, thereby improving the temperature compensation accuracy of the temperature-compensated piezoelectric oscillator.

[0010] In conventional signal generating circuits (temperature compensation circuits), the gain was adjusted for each order component of the electrical signal. Therefore, increasing the gain of the nth-order component of the electrical signal also increased the approximation error of the nth-order component contained in the electrical signal, resulting in a deterioration in temperature compensation accuracy. However, with the above configuration, the approximation error of the nth-order component contained in the electrical signal can be canceled out by the differential correction electrical signal, thereby reducing the approximation error of the nth-order component, thereby preventing deterioration in temperature compensation accuracy. Furthermore, the circuit configuration of the signal generating circuit can be simplified, and the circuit area can be minimized. This allows for reduced power consumption and cost.

[0011] In the above configuration, it is preferable to apply the differential correction electrical signal only to the n-th order component of the signal generating circuit. With this configuration, by applying the differential correction electrical signal only to the n-th order component of the signal generating circuit, it is possible to accurately cancel out the approximation error of the n-th order component generated in the signal generating circuit and reduce the approximation error of the n-th order component.

[0012] In the above configuration, the signal generation circuit preferably includes an n-th order function generation circuit that generates a pseudo-n-th order function electric signal, a difference correction generation circuit that generates the difference correction electric signal, and an amplifier circuit that adjusts the gain of the n-th order component, and the difference correction generation circuit is preferably provided between the circuit that generates the n-th order component of the n-th order function generation circuit and the amplifier circuit. In this case, the circuit that generates the n-th order component of the n-th order function generation circuit preferably includes a constant current circuit and a differential amplifier circuit. Furthermore, the signal generation circuit preferably adds the difference correction electric signal, which is an inverse component generated by the constant current circuit and the differential amplifier circuit, to the maximum and minimum values ​​of the electric signal that constitutes the difference. With these configurations, difference correction is performed on the electric signal before it is input to the amplifier circuit, thereby efficiently reducing the approximation error of the n-th order component contained in the electric signal output from the amplifier circuit.

[0013] In the above configuration, it is preferable that the signal generation circuit is configured to apply the difference correction electrical signal from the difference correction generation circuit to the n-th order function generation circuit, and also to apply the difference correction electrical signal from the difference correction generation circuit to higher-order function generation circuits (for example, an n+1th order function generation circuit, an n+2nd order function generation circuit).With this configuration, by applying the difference correction electrical signal from the difference correction generation circuit to the higher-order function generation circuits as well, highly accurate temperature compensation by the signal generation circuit can be achieved. [Effects of the Invention]

[0014] According to the temperature-compensated piezoelectric oscillator of the present invention, the difference (approximation error) between the electrical signal corresponding to the frequency-temperature characteristics of the piezoelectric vibrator (ideal n-th order function) and the electrical signal generated by the signal generating circuit (pseudo n-th order function) can be canceled out by the difference correction electrical signal, thereby reducing the approximation error of the third-order component generated by the signal generating circuit, thereby improving the temperature compensation accuracy of the temperature-compensated piezoelectric oscillator. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator according to an embodiment of the present invention. [Figure 2] 10 is a graph showing an outline of the reduction in approximation error of the third-order component generated in the temperature compensation circuit. [Figure 3] 10 is a graph showing an example of an anticomponent generated near a temperature T1. [Figure 4] 10 is a graph showing an example of an anticomponent generated near a temperature T2. [Figure 5] 10 is a graph showing an example of an anticomponent generated near a temperature T3. [Figure 6] FIG. 1 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator according to a comparative example. [Figure 7] FIG. 10 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator according to another embodiment. [Figure 8]10 is a graph showing an outline of the reduction in approximation error of the second-order component generated in the temperature compensation circuit. [Figure 9] 10 is a graph showing an example of an anticomponent generated near a temperature T4. [Figure 10] 10 is a graph showing an example of an anticomponent generated near a temperature T5. [Figure 11] FIG. 10 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator according to a first modification. [Figure 12] FIG. 10 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator according to a second modification. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] The present invention provides a temperature-compensated piezoelectric oscillator having a piezoelectric vibrator whose frequency-temperature characteristic changes at least n-th order (n is 2 or 3), a signal generating circuit that outputs an n-th order electrical signal that compensates for the frequency-temperature characteristic of the piezoelectric vibrator, and an oscillation circuit to which the piezoelectric vibrator and a variable capacitance element are connected and to which the output electrical signal of the signal generating circuit is input to the variable capacitance element, wherein the signal generating circuit generates a pseudo-n-th order electrical signal, calculates an electrical signal that is a difference between the pseudo-n-th order electrical signal and an ideal n-th order electrical signal that is an approximation of the pseudo-n-th order electrical signal by an n-th order function, and applies a difference correction electrical signal corresponding to the difference electrical signal to the signal generating circuit. In the following embodiments, the piezoelectric vibrator is an AT-cut thickness-shear piezoelectric vibrator (n=3).

[0018] The temperature compensated crystal oscillator 100 according to this embodiment includes a piezoelectric vibrator whose frequency-temperature characteristic changes at least cubically, a signal generating circuit that outputs a cubic electrical signal (voltage in this embodiment) that compensates for the frequency-temperature characteristic of the piezoelectric vibrator, and an oscillation circuit to which the piezoelectric vibrator and a variable capacitance element are connected and to which the output electrical signal of the signal generating circuit is input to the variable capacitance element. Specifically, as shown in Fig. 1, the temperature compensated crystal oscillator 100 includes a crystal oscillator 110 as a piezoelectric oscillator, a temperature sensor 120 as temperature detection means, a temperature compensation circuit 130 as a signal generating circuit, a ROM 140 as storage means, etc.

[0019] In this embodiment, the crystal oscillator 110 is configured as a voltage-controlled crystal oscillator (VCXO). The crystal oscillator 110 includes a crystal resonator 111 as a piezoelectric resonator and an oscillation circuit 112. The crystal resonator 111 has a frequency-temperature characteristic that varies at least cubically, and for example, an AT-cut crystal resonator equipped with an AT-cut crystal diaphragm can be used. The oscillation circuit 112 includes a variable capacitance element whose capacitance varies with the application of voltage, and the frequency of the crystal oscillator 110 can be controlled by the change in capacitance of this variable capacitance element. For example, a variable capacitance diode (varicap) or a MOS varactor can be used as the variable capacitance element.

[0020] The temperature compensation circuit 130 generates a temperature compensation voltage that compensates for the frequency-temperature characteristic of the crystal unit 111 based on the temperature information output from the temperature sensor 120, and applies this temperature compensation voltage to the variable capacitance element of the oscillation circuit 112. In this embodiment, the temperature compensation circuit 130 applies a temperature compensation voltage set so as to reduce the frequency deviation of the crystal unit 111 with respect to temperature changes to the variable capacitance element of the oscillation circuit 112, performing analog control by continuously changing the capacitance of the variable capacitance element with respect to temperature. In this way, by the temperature compensation circuit 130 applying the temperature compensation voltage to the variable capacitance element of the oscillation circuit 112, the load capacitance changes so as to cancel out the frequency-temperature characteristic of the crystal unit 111, and the oscillation circuit 112 can obtain a frequency-temperature characteristic with reduced frequency change with temperature.

[0021] 1, the temperature compensation circuit 130 includes a linear function generating circuit 131, a cubic function generating circuit 132, a difference correction generating circuit 133, gain amplifiers 134 and 135, an adder circuit 137, etc. The linear function generating circuit 131 generates a linear component of a temperature compensation voltage for the temperature compensation circuit 130 based on temperature information output from the temperature sensor 120. A gain amplifier 134 serving as an amplifier circuit is connected to the circuit that generates the linear component of the linear function generating circuit 131, and the gain amplifier 134 amplifies the linear component of the temperature compensation voltage for the temperature compensation circuit 130. The linear component of the temperature compensation voltage for the temperature compensation circuit 130 amplified by the gain amplifier 134 is input to the adder circuit 137.

[0022] Cubic function generating circuit 132 generates a third-order component of a temperature-compensated voltage for temperature compensation circuit 130 based on the temperature information output from temperature sensor 120. Gain amplifier 135, which serves as an amplifier, is connected to the circuit that generates the third-order component of cubic function generating circuit 132, and the third-order component of the temperature-compensated voltage for temperature compensation circuit 130 is amplified by gain amplifier 135. A difference correction generating circuit 133 is interposed between the circuit that generates the third-order component of cubic function generating circuit 132 and gain amplifier 135, as will be described later. The third-order component of the temperature-compensated voltage for temperature compensation circuit 130 amplified by gain amplifier 135 is input to adder circuit 137. Adder circuit 137 adds the first-order and third-order components of the temperature-compensated voltage for temperature compensation circuit 130 input from gain amplifiers 134 and 135, and outputs the result to oscillator circuit 112.

[0023] In this embodiment, attention is focused on the temperature compensation voltage generated by the temperature compensation circuit 130, and in particular, the error component of the third-order component of the temperature compensation voltage is improved, thereby improving the frequency-temperature characteristics of the temperature-compensated crystal oscillator 100. In more detail, in the temperature-compensated crystal oscillator 100, the temperature compensation circuit 130 generates a pseudo-cubic function temperature compensation voltage, calculates an ideal cubic function temperature compensation voltage obtained by approximating this pseudo-cubic function temperature compensation voltage with a cubic function, and calculates a compensation voltage that is the difference between the pseudo-cubic function temperature compensation voltage and the pseudo-cubic function temperature compensation voltage, and applies a difference-corrected compensation voltage corresponding to the compensation voltage that is the difference to the temperature compensation circuit 130. This point will be explained below.

[0024] As described above, in the temperature compensation circuit 130, since it is difficult to generate an ideal cubic function temperature compensation voltage using a simple circuit configuration, the cubic function generating circuit 132 generates a temperature compensation voltage that is adjusted to be a pseudo cubic function. In detail, the circuit that generates the cubic component of the cubic function generating circuit 132 is configured, for example, with a constant current circuit and a differential amplifier circuit, and three sets of constant current circuits and differential amplifier circuits are connected in series to generate a pseudo cubic function temperature compensation voltage. For this reason, a deviation (approximation error of the cubic component) occurs between the temperature compensation voltage corresponding to the frequency-temperature characteristics of the crystal resonator 111 (ideal cubic function) and the temperature compensation voltage generated by the cubic function generating circuit 132 (pseudo cubic function). In other words, when the ideal cubic function temperature compensation voltage is [Vc=A3×T 3 ], the pseudo-cubic function temperature compensation voltage generated by the cubic function generating circuit 132 is expressed as [Vc=A3×T 3 +α], which includes the approximation error α of the third-order component (A3 is a coefficient, and T is temperature).

[0025] In this embodiment, the temperature compensation voltage obtained by the temperature compensation circuit 130 is [Vc=A3×T 3 +α'(α-β)], and by adding an anticomponent β (differential compensation voltage) that corresponds to and suppresses the cubic component approximation error α to the temperature compensation voltage, the temperature compensation voltage approaches the ideal cubic function characteristic (α'<α). In FIG. 2, the ideal cubic temperature compensation voltage (vertical axis in units of [V]) is shown by a solid line, the pseudo-cubic temperature compensation voltage (vertical axis in units of [V]) generated by the cubic function generator circuit 132 is shown by a two-dot chain line, and the cubic component approximation error α (vertical axis in units of [mV]), which is the difference between the two, is shown by a dashed line. Although the ideal cubic temperature compensation voltage and the pseudo-cubic temperature compensation voltage generated by the cubic function generator circuit 132 appear to overlap in FIG. 2, strictly speaking, there is a cubic component approximation error α that varies as shown by the dashed line. As shown in FIG. 2, the cubic component approximation error α fluctuates on both the positive and negative sides of 0 [mV].

[0026] In this embodiment, the approximation error α of the third-order component is reduced by adjusting the anticomponent β so as to cancel out the approximation error α of the third-order component, bringing the approximation error α of the third-order component closer to 0 [mV]. Specifically, as shown in FIG. 2 , the approximation error α of the third-order component exhibits a maximum value (maximum value) or a minimum value (minimum value) near temperatures T1, T2, and T3. Based on the approximation error α of the third-order component near temperatures T1, T2, and T3, the anticomponent β is adjusted to cancel out the approximation error α of the third-order component. The anticomponent β is adjusted to reduce its maximum value at the temperature where the approximation error α of the third-order component reaches its maximum value (maximum value). On the other hand, the anticomponent β is adjusted to increase its minimum value at the temperature where the approximation error α of the third-order component reaches its minimum value (minimum value). In other words, the anticomponent β is adjusted to reduce the absolute value of the approximation error α of the third-order component. Such adjustment of the anticomponent β as a differential correction electrical signal is performed by the differential correction generating circuit 133. The difference correction generating circuit 133 adjusts the inverse component β (a component whose positive and negative polarities are opposite to those of the approximation error α of the third-order component) produced by the constant current circuit and the differential amplifier circuit based on the approximation error α of the third-order component near temperatures T1, T2, and T3.

[0027] 3 to 5 are graphs showing examples of the anticomponent β. FIG. 3 is a graph of the anticomponent β adjusted to vary quadratically near temperature T1. The anticomponent β varies in a downward convex shape so as to reach a minimum value (local minimum value) at temperature T1, and is 0 at temperatures other than near T1. The anticomponent β (minimum value) at temperature T1 corresponds to the maximum value (local maximum value) of the approximation error α of the third-order component at temperature T1.

[0028] Figure 4 is a graph of the anticomponent β, which has been adjusted to vary quadratically near temperature T2. The anticomponent β varies in an upward convex shape so that it reaches a maximum value (local maximum value) at temperature T2, and is 0 outside the vicinity of temperature T2. The anticomponent β (maximum value) at temperature T2 corresponds to the minimum value (local minimum value) of the approximation error α of the third-order component at temperature T2.

[0029] Figure 5 is a graph of the anticomponent β, which has been adjusted to vary quadratically near temperature T3. The anticomponent β varies in a downward convex shape so that it reaches a minimum value (local minimum value) at temperature T3, and is 0 at temperatures other than near T3. The anticomponent β (minimum value) at temperature T3 corresponds to the maximum value (local maximum value) of the approximation error α of the third-order component at temperature T3.

[0030] Then, the anti-component β (see FIGS. 3 to 5) adjusted by the difference correction generating circuit 133 is added to the approximation error α of the third-order component. As a result, as shown by the arrows in FIG. 2, the approximation error α of the third-order component can be reduced near temperatures T1, T2, and T3, and the approximation error α of the third-order component can be brought closer to 0 [mV]. The voltage at which the approximation error α of the third-order component peaks can be suppressed by adding the anti-component β.

[0031] As described above, in this embodiment, the approximation error α of the third-order component generated in the temperature compensation circuit 130 can be reduced by canceling out the approximation error α of the third-order component generated between the temperature compensation voltage (ideal cubic function) corresponding to the frequency-temperature characteristic of the crystal resonator 111 and the temperature compensation voltage (pseudo cubic function) generated by the cubic function generating circuit 132 with the anti-component β adjusted by the difference correction generating circuit 133. This allows the temperature compensation voltage output from the difference correction generating circuit 133 (the temperature compensation voltage input to the gain amplifier 135) to be as close as possible to the temperature compensation voltage (ideal cubic function) corresponding to the frequency-temperature characteristic of the crystal resonator 111, thereby improving the temperature compensation accuracy of the temperature-compensated crystal oscillator 100.

[0032] In conventional temperature compensation circuits, the gain was adjusted for each order component of the temperature compensation voltage, so increasing the gain of the third-order component of the temperature compensation voltage also increased the approximation error α of the third-order component included in the temperature compensation voltage, degrading the temperature compensation accuracy. However, according to this embodiment, the approximation error α of the third-order component included in the temperature compensation voltage can be reduced by canceling it out with the anticomponent β, thereby suppressing the deterioration of the temperature compensation accuracy.

[0033] For example, in a temperature compensation circuit 130' of a temperature compensated crystal oscillator 100' according to a comparative example shown in Figure 6, a signal correction circuit 133' is provided in parallel with a linear function generating circuit 131 and a cubic function generating circuit 132, and gain amplifiers 134, 135, and 136 are connected to each circuit. In the temperature compensation circuit 130', an approximation error α of a third-order component generated between a temperature compensation voltage (ideal cubic function) corresponding to the frequency-temperature characteristics of the crystal resonator 111 and a temperature compensation voltage (pseudo cubic function) generated by the cubic function generating circuit 132 is input directly to the gain amplifier 135. The approximation error α of the third-order component is amplified by the gain amplifier 135, resulting in a deterioration in temperature compensation accuracy.

[0034] In contrast to this, in this embodiment, the difference correction generation circuit 133 that adjusts the anti-component β that cancels the approximation error α of the third-order component is interposed between the circuit that generates the third-order component in the cubic function generation circuit 132 of the temperature compensation circuit 130 and the gain amplifier 135. Therefore, difference correction is performed on the temperature compensation voltage before it is input to the gain amplifier 135, and it is possible to efficiently reduce the approximation error α of the third-order component included in the temperature compensation voltage output from the gain amplifier 135. This makes it possible to suppress deterioration of the temperature compensation accuracy.

[0035] Furthermore, in this embodiment, the anti-component β is added only to the third-order component of the temperature compensation voltage of the temperature compensation circuit 130, so that the approximation error α of the third-order component generated in the temperature compensation circuit 130 can be accurately canceled out, and the approximation error α of the third-order component can be reduced. Furthermore, the circuit configuration of the temperature compensation circuit 130 can be simplified, and the circuit area can be made as small as possible. This allows for reduced power consumption and cost.

[0036] The present invention can be embodied in various other forms without departing from its spirit, essence, or main features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and variations within the equivalent range of the claims are within the scope of the present invention.

[0037] In the above embodiment, an AT-cut quartz crystal resonator, whose frequency-temperature characteristic varies at least cubically, is used as the piezoelectric resonator, but a quartz crystal resonator other than an AT-cut quartz crystal resonator may also be used. For example, as shown in Figure 7, a tuning fork-type quartz crystal resonator, whose frequency-temperature characteristic varies at least quadratically, such as an X-cut or Y-cut, may also be used. Furthermore, as the piezoelectric resonator, a resonator using a single crystal material, such as a ceramic resonator, a lithium niobate resonator, or a lithium tantalate resonator, or a resonator using a piezoelectric thin film, such as a zinc oxide piezoelectric thin film resonator or an aluminum oxide piezoelectric thin film resonator, may also be used.

[0038] 7 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator 200 according to another embodiment. In the following embodiment, a case will be described in which the piezoelectric vibrator used in the temperature compensated piezoelectric oscillator 200 is a tuning fork type piezoelectric vibrator whose frequency-temperature characteristics change at least quadratically (when n=2).

[0039] A temperature compensated crystal oscillator 200 according to another embodiment includes a piezoelectric resonator whose frequency-temperature characteristic changes at least quadratically, a signal generating circuit that outputs a quadratically functioning electrical signal (voltage in this embodiment) that compensates for the frequency-temperature characteristic of the piezoelectric resonator, and an oscillation circuit to which the piezoelectric resonator and a variable capacitance element are connected and to which the output electrical signal of the signal generating circuit is input to the variable capacitance element. Specifically, as shown in Fig. 7, the temperature compensated crystal oscillator 200 includes a crystal oscillator 210 as a piezoelectric oscillator, a temperature sensor 220 as temperature detection means, a temperature compensation circuit 230 as a signal generating circuit, a ROM 240 as storage means, etc.

[0040] In this embodiment, the crystal oscillator 210 is configured as a voltage-controlled crystal oscillator (VCXO). The crystal oscillator 210 includes a crystal resonator 211 as a piezoelectric resonator and an oscillation circuit 212. The crystal resonator 211 has a frequency-temperature characteristic that varies at least quadratically, and for example, a tuning-fork crystal resonator including a tuning-fork crystal diaphragm can be used. The oscillation circuit 212 includes a variable capacitance element whose capacitance varies with the application of voltage, and the frequency of the crystal oscillator 210 can be controlled by the change in capacitance of this variable capacitance element. For example, a variable capacitance diode (varicap) or a MOS varactor can be used as the variable capacitance element.

[0041] The temperature compensation circuit 230 generates a temperature compensation voltage that compensates for the frequency-temperature characteristic of the crystal unit 211 based on the temperature information output from the temperature sensor 220, and applies this temperature compensation voltage to the variable capacitance element of the oscillation circuit 212. In this embodiment, the temperature compensation circuit 230 applies a temperature compensation voltage set so as to reduce the frequency deviation of the crystal unit 211 with respect to temperature changes to the variable capacitance element of the oscillation circuit 212, performing analog control by continuously changing the capacitance of the variable capacitance element with respect to temperature. In this way, by the temperature compensation circuit 230 applying the temperature compensation voltage to the variable capacitance element of the oscillation circuit 212, the load capacitance changes so as to cancel out the frequency-temperature characteristic of the crystal unit 211, and the oscillation circuit 212 can obtain a frequency-temperature characteristic with reduced frequency change with temperature.

[0042] As shown in FIG. 7 , the temperature compensation circuit 230 includes a quadratic function generating circuit 232, a difference correction generating circuit 233, a gain amplifier 235, an adder circuit 237, etc. The quadratic function generating circuit 232 generates a quadratic component of a temperature compensation voltage for the temperature compensation circuit 230 based on temperature information output from the temperature sensor 220. A gain amplifier 235 serving as an amplifier circuit is connected to a circuit for generating the quadratic component of the quadratic function generating circuit 232, and the gain amplifier 235 amplifies the quadratic component of the temperature compensation voltage for the temperature compensation circuit 230. A difference correction generating circuit 233 is interposed between the circuit for generating the quadratic component of the quadratic function generating circuit 232 and the gain amplifier 235. The quadratic component of the temperature compensation voltage for the temperature compensation circuit 230, amplified by the gain amplifier 235, is input to the adder circuit 237. The adder circuit 237 outputs the second-order component of the temperature compensation voltage of the temperature compensation circuit 230 input from the gain amplifier 235 to the oscillator circuit 112 .

[0043] In this embodiment, attention is focused on the temperature compensation voltage generated by the temperature compensation circuit 230, and in particular, the error component of the quadratic component of the temperature compensation voltage is improved to improve the frequency-temperature characteristics of the temperature compensated crystal oscillator 200. In more detail, in the temperature compensated crystal oscillator 200, the temperature compensation circuit 230 generates a pseudo-quadratic temperature compensation voltage, calculates an ideal quadratic temperature compensation voltage obtained by approximating this pseudo-quadratic temperature compensation voltage with a quadratic function, and calculates a compensation voltage that is the difference between the pseudo-quadratic temperature compensation voltage, and a difference-corrected compensation voltage that corresponds to the compensation voltage that is the difference is applied to the temperature compensation circuit 230. This point will be explained below.

[0044] As described above, in the temperature compensation circuit 230, since it is difficult to generate an ideal quadratic temperature compensation voltage with a simple circuit configuration, the quadratic function generating circuit 232 generates a temperature compensation voltage that is adjusted to be a pseudo quadratic function. In detail, the circuit that generates the quadratic component of the quadratic function generating circuit 232 is configured, for example, with a constant current circuit and a differential amplifier circuit, and the constant current circuit and the differential amplifier circuit are connected in series to generate a pseudo quadratic temperature compensation voltage. For this reason, a deviation (approximation error of the quadratic component) occurs between the temperature compensation voltage (ideal quadratic function) corresponding to the frequency-temperature characteristics of the crystal resonator 211 and the temperature compensation voltage (pseudo quadratic function) generated by the quadratic function generating circuit 232. In other words, when the ideal quadratic temperature compensation voltage is [Vc=A2×T 2 ], the pseudo-quadratic temperature compensation voltage generated by the quadratic function generating circuit 232 is expressed as [Vc=A2×T 2 +γ], which includes the approximation error γ of the second-order component (A2 is a coefficient, and T is temperature).

[0045] In this embodiment, the temperature compensation voltage obtained by the temperature compensation circuit 230 is [Vc=A2×T 2 +γ'(γ-δ)], and by adding an anticomponent δ (differential correction voltage) that corresponds to and suppresses the quadratic component approximation error γ to the temperature compensation voltage, the temperature compensation voltage approaches the ideal quadratic function characteristics (γ'<γ). In FIG. 8, the ideal quadratic temperature compensation voltage (vertical axis in [V]) is shown by a solid line, the pseudo-quadratic temperature compensation voltage (vertical axis in [V]) generated by the quadratic function generator circuit 232 is shown by a two-dot chain line, and the quadratic component approximation error γ (vertical axis in [mV]), which is the difference between the two, is shown by a dashed line. Although the ideal quadratic temperature compensation voltage and the pseudo-quadratic temperature compensation voltage generated by the quadratic function generator circuit 232 appear to overlap in FIG. 8, strictly speaking, there is a quadratic component approximation error γ that varies as shown by the dashed line. As shown in FIG. 8, the quadratic component approximation error γ fluctuates on both the positive and negative sides of 0 [mV].

[0046] In this embodiment, the approximation error γ of the second-order component is reduced by adjusting the anticomponent δ so as to cancel out the approximation error γ of the second-order component, bringing the approximation error γ closer to 0 mV. Specifically, as shown in FIG. 8 , the approximation error γ of the second-order component exhibits a maximum value (maximum value) or a minimum value (minimum value) near temperatures T4 and T5. Based on the approximation error γ of the second-order component near temperatures T4 and T5, the anticomponent δ is adjusted to cancel out the approximation error γ of the second-order component. The anticomponent δ is adjusted to reduce its maximum value at the temperature where the approximation error γ of the second-order component reaches its maximum value (maximum value). On the other hand, the anticomponent δ is adjusted to increase its minimum value at the temperature where the approximation error γ of the second-order component reaches its minimum value (minimum value). In other words, the anticomponent δ is adjusted to reduce the absolute value of the approximation error γ of the third-order component. This adjustment of the anticomponent δ as a differential correction electrical signal is performed by the differential correction generating circuit 233. The difference correction generating circuit 233 adjusts the inverse component δ of the inverse component (the component whose sign is opposite to that of the approximation error γ of the second-order component) produced by the constant current circuit and the differential amplifier circuit based on the approximation error γ of the second-order component near temperatures T4 and T5.

[0047] 9 and 10 are graphs showing examples of the anticomponent δ. FIG. 9 is a graph of the anticomponent δ adjusted to vary quadratically near temperature T4. The anticomponent δ varies in a downward convex shape so as to reach a minimum value (local minimum value) at temperature T4, and is 0 at temperatures other than near T4. The anticomponent δ (minimum value) at temperature T4 corresponds to the maximum value (local maximum value) of the quadratic component approximation error γ at temperature T4.

[0048] Figure 10 is a graph of the anticomponent δ adjusted to vary quadratically near temperature T5. The anticomponent δ varies in an upward convex shape so that it reaches a maximum value (local maximum value) at temperature T5, and is 0 at temperatures other than near T5. The anticomponent δ (maximum value) at temperature T5 corresponds to the minimum value (local minimum value) of the quadratic component approximation error γ at temperature T5.

[0049] Then, the anti-component δ (see FIGS. 9 and 10) adjusted by the difference correction generating circuit 233 is added to the approximation error γ of the second-order component. As a result, as shown by the arrows in FIG. 8, the approximation error γ of the second-order component can be reduced near temperatures T4 and T5, and the approximation error γ of the second-order component can be brought closer to 0 [mV]. The voltage at which the approximation error γ of the second-order component peaks can be suppressed by adding the anti-component δ.

[0050] As described above, in this embodiment, the approximation error γ of the quadratic component generated in the temperature compensation circuit 230 can be reduced by canceling out the approximation error γ of the quadratic component generated between the temperature compensation voltage (ideal quadratic function) corresponding to the frequency-temperature characteristic of the crystal resonator 211 and the temperature compensation voltage (pseudo-quadratic function) generated by the quadratic function generating circuit 232 with the anti-component δ adjusted by the difference correction generating circuit 233. This allows the temperature compensation voltage output from the difference correction generating circuit 233 (the temperature compensation voltage input to the gain amplifier 235) to be as close as possible to the temperature compensation voltage (ideal quadratic function) corresponding to the frequency-temperature characteristic of the crystal resonator 211, thereby improving the temperature compensation accuracy of the temperature-compensated crystal oscillator 200.

[0051] Furthermore, as described above, in conventional temperature compensation circuits, the gain was adjusted for each order component of the temperature compensation voltage, so increasing the gain of the second-order component of the temperature compensation voltage also increased the approximation error γ of the second-order component included in the temperature compensation voltage, degrading the temperature compensation accuracy. However, according to this embodiment, the approximation error γ of the second-order component included in the temperature compensation voltage can be reduced by canceling it out with the anticomponent δ, thereby suppressing the deterioration of the temperature compensation accuracy.

[0052] Furthermore, in this embodiment, the difference correction generation circuit 233 that adjusts the anti-component δ that cancels the approximation error γ of the second-order component is interposed between the circuit that generates the second-order component of the quadratic function generation circuit 232 in the temperature compensation circuit 230 and the gain amplifier 235, so that difference correction is performed on the temperature compensation voltage before it is input to the gain amplifier 235, making it possible to efficiently reduce the approximation error γ of the second-order component included in the temperature compensation voltage output from the gain amplifier 235. This makes it possible to suppress deterioration in temperature compensation accuracy.

[0053] Furthermore, in this embodiment, the anti-component δ is added only to the second-order component of the temperature compensation voltage of the temperature compensation circuit 230, so that the approximation error γ of the second-order component generated in the temperature compensation circuit 230 can be accurately canceled out, and the approximation error γ of the second-order component can be reduced. Furthermore, the circuit configuration of the temperature compensation circuit 230 can be simplified, and the circuit area can be made as small as possible. This allows for reduced power consumption and cost.

[0054] In the above embodiment, the anticomponent β adjusted by the difference correction generating circuit 133 has a waveform that changes convexly like a quadratic function (see FIGS. 3 to 5), but the waveform of the anticomponent β may be triangular, trapezoidal, rectangular, etc. Furthermore, the peak value (maximum or minimum value) of the anticomponent β corresponds to the peak value (maximum or minimum value) of the approximation error α of the third-order component, but the peak value of the anticomponent β may be set proportionally to the peak value of the approximation error α of the third-order component, or may be set in stages depending on the peak value of the approximation error α of the third-order component.

[0055] 9 and 10 show that the anticomponent δ adjusted by the difference correction generating circuit 233 has a waveform that changes convexly like a quadratic function, but the waveform of the anticomponent δ may be triangular, trapezoidal, rectangular, etc. Also, the peak value (maximum or minimum value) of the anticomponent δ corresponds to the peak value (maximum or minimum value) of the approximation error γ of the second-order component, but the peak value of the anticomponent δ may be set proportionally to the peak value of the approximation error γ of the second-order component, or may be set in stages depending on the peak value of the approximation error γ of the second-order component.

[0056] In the above embodiment, differential correction is performed by adding the inverse component β at three points near temperatures T1, T2, and T3 where the approximation error α of the third-order component reaches its peak value (see FIG. 2). However, differential correction may be performed at one, two, or four or more points depending on the number of points where the approximation error α of the third-order component reaches its peak value. Note that it is desirable to add a complete inverse differential signal that has an axisymmetric waveform with respect to the approximation error α of the third-order component.

[0057] Similarly, differential correction was performed by adding the inverse component δ at two points near temperatures T4 and T5 where the approximation error γ of the second-order component peaks as shown in Fig. 8, but differential correction may be performed at one point or three or more points depending on the number of points where the approximation error γ of the second-order component peaks. Note that it is desirable to add a complete inverse differential signal whose waveform is axisymmetric to the approximation error γ of the second-order component.

[0058] In the above embodiment, the temperature compensation circuit 130 includes the linear function generating circuit 131 and the cubic function generating circuit 132 (see FIG. 1), but the temperature compensation circuit 130 may include only the cubic function generating circuit 132. Alternatively, the temperature compensation circuit 130 may also include a higher-order function generating circuit (a quartic function generating circuit, a quintic function generating circuit, a sextic function generating circuit, ...) in addition to the linear function generating circuit 131 and the cubic function generating circuit 132, as shown in FIG. 11, for example. FIG. 11 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator 101 according to the first modification. 11, temperature compensation circuit 130A of temperature compensated piezoelectric oscillator 101 is configured to include linear function generating circuit 131, cubic function generating circuit 132, higher-order function generating circuits (quaternary function generating circuit 141, quintic function generating circuit 151), difference correction generating circuits 133, 142, 152, gain amplifiers 134, 135, 143, 153, and adder circuit 137. Temperature compensation circuit 130A is configured to apply a difference correction electrical signal from difference correction generating circuit 133 to cubic function generating circuit 132, and also to high-order quartic function generating circuit 141 and quintic function generating circuit 151, from difference correction generating circuits 142, 152. As a result, highly accurate temperature compensation can be achieved by the temperature compensation circuit 130A by applying the difference correction electrical signals from the difference correction generating circuits 142 and 152 to the higher-order function generating circuits (quartic function generating circuit 141, quintic function generating circuit 151). Note that a configuration may also be adopted in which the difference correction electrical signal from the difference correction generating circuit is applied to the low-order linear function generating circuit 131.

[0059] 7 includes only the quadratic function generating circuit 232, but the temperature compensation circuit 230 may also include higher-order function generating circuits (cubic function generating circuit, quartic function generating circuit, quintic function generating circuit, ...) in addition to the quadratic function generating circuit 232, as shown in FIG. 12, for example. FIG. 12 is a block diagram showing a schematic configuration of a temperature compensated piezoelectric oscillator 201 according to Modification 2. As shown in FIG. 12, the temperature compensation circuit 230A of the temperature compensated piezoelectric oscillator 201 includes the quadratic function generating circuit 232, higher-order function generating circuits (cubic function generating circuit 241, quartic function generating circuit 251), difference correction generating circuits 233, 242, 252, gain amplifiers 235, 243, 253, adder circuit 137, etc. In addition to being configured to apply a difference correction electrical signal from difference correction generating circuit 233 to quadratic function generating circuit 232, temperature compensation circuit 230A is also configured to apply difference correction electrical signals from difference correction generating circuits 242, 252 to higher-order cubic function generating circuit 241 and quartic function generating circuit 251. In this way, by applying difference correction electrical signals from difference correction generating circuits 242, 252 to the higher-order function generating circuits (cubic function generating circuit 241, quartic function generating circuit 251), highly accurate temperature compensation can be achieved by temperature compensation circuit 230A.

[0060] This application claims priority from Japanese Patent Application No. 2022-089202, filed on May 31, 2022, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0061] 100 Temperature-compensated crystal oscillator (temperature-compensated piezoelectric oscillator) 110 Crystal oscillator (piezoelectric oscillator) 111 Quartz crystal oscillator (piezoelectric oscillator) 112 Oscillator Circuit 120 Temperature Sensor 130 Temperature compensation circuit (signal generation circuit) 132 Cubic Function Generator 133 Differential correction generation circuit 135 Gain amplifier (amplifier circuit) α Approximation error (differential electrical signal) β anticomponent (differential correction electrical signal)

Claims

1. a piezoelectric vibrator whose frequency-temperature characteristics change at least n-th order (n is 2 or 3); a signal generating circuit that outputs an n-order functional electric signal that compensates for the frequency temperature characteristics of the piezoelectric vibrator; a temperature-compensated piezoelectric oscillator having an oscillation circuit to which the piezoelectric vibrator and a variable capacitance element are connected and to which an output electrical signal from the signal generating circuit is input to the variable capacitance element, the signal generating circuit generates a pseudo-n-th order functional electric signal, calculates an electric signal that is a difference between an ideal n-th order functional electric signal obtained by approximating the pseudo-n-th order functional electric signal with an n-th order function, and the pseudo-n-th order functional electric signal; a differential correction electrical signal corresponding to the differential electrical signal is applied to the signal generating circuit; the differential correction electrical signal corresponds to and suppresses an approximation error of an n-th order component between the ideal n-th order functional electrical signal and the pseudo n-th order functional electrical signal, a temperature-compensated piezoelectric oscillator, characterized in that by adding the differential correction electrical signal to the signal generating circuit, the approximation error of the nth-order component contained in the pseudo-nth-order function-like electrical signal is canceled out by the differential correction electrical signal.

2. 2. The temperature compensated piezoelectric oscillator according to claim 1, a temperature-compensated piezoelectric oscillator, characterized in that the difference correction electrical signal is applied only to the n-th order component of the signal generating circuit;

3. 3. The temperature compensated piezoelectric oscillator according to claim 1, the signal generating circuit includes an n-order function generating circuit that generates a pseudo-n-order function electric signal, a difference correction generating circuit that generates the difference correction electric signal, and an amplifier circuit that adjusts the gain of the n-order component; a temperature-compensated piezoelectric oscillator, characterized in that the difference correction generating circuit is provided between a circuit for generating an nth-order component of the nth-order function generating circuit and the amplifier circuit;

4. 4. The temperature compensated piezoelectric oscillator according to claim 3, A temperature compensated piezoelectric oscillator, wherein the circuit for generating the nth-order component of the nth-order function generating circuit comprises a constant current circuit and a differential amplifier circuit.

5. 5. The temperature compensated piezoelectric oscillator according to claim 4, The signal generating circuit adds the difference correction electrical signal of the inverse component generated by a constant current circuit and a differential amplifier circuit to the maximum and minimum values ​​of the electrical signal that is the difference.

6. 3. The temperature compensated piezoelectric oscillator according to claim 1, The temperature-compensated piezoelectric oscillator is characterized in that the piezoelectric vibrator is an AT-cut quartz crystal vibrator.

7. 3. The temperature compensated piezoelectric oscillator according to claim 1, 10. A temperature compensated piezoelectric oscillator, wherein the piezoelectric vibrator is a tuning fork type crystal vibrator.

8. 4. The temperature compensated piezoelectric oscillator according to claim 3, a signal generating circuit configured to apply the differential correction electrical signal generated by the differential correction generating circuit to the n-th order function generating circuit, and also to apply differential correction electrical signals generated by differential correction generating circuits to higher-order function generating circuits of higher orders than the n-th order function generating circuit;

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