JP2011103636A - Method of adjusting frequency of temperature-compensated piezoelectric oscillator - Google Patents

Abstract

A temperature compensated piezoelectric oscillator capable of obtaining a stable frequency temperature characteristic with little frequency hysteresis with respect to a temperature change at the time of temperature increase or temperature decrease, and a frequency adjusting method thereof.
In a first memory and a second memory, first and second temperature compensation data for specifying frequency temperature characteristics when the temperature of a piezoelectric vibrator is increased and when the temperature is decreased, respectively. 32 and 42 are stored. The temperature change detection circuit 10 detects whether a temperature increase or a temperature decrease has occurred based on the temperature information acquired by the temperature sensor 50. The selector 20 selects the first and second temperature compensation data when the temperature rises and when the temperature falls based on the detection result of the temperature change detection circuit. The temperature compensation voltage generation circuit 60 generates the temperature compensation voltage 62 based on the first or second temperature compensation data selected by the selector. The voltage controlled oscillation circuit 70 controls the frequency of the piezoelectric vibrator based on the temperature compensation voltage.
[Selection] Figure 1

Description

  The present invention relates to a frequency adjustment method for a temperature compensated piezoelectric oscillator.

  The temperature compensated crystal oscillator (TCXO: Temperature Compensated Xtal Oscillator) can obtain high frequency stability by canceling the temperature characteristics of the oscillation frequency of the crystal oscillator, so it can be used in mobile phone terminals, base stations, and GPS (Global Positioning System). ) Widely used in equipment and systems that require highly accurate timing signals such as receivers.

  Various types of temperature compensated crystal oscillators have been proposed so far. For example, in Patent Document 1, a stable frequency characteristic with respect to a temperature change is realized by continuously correcting the frequency using an approximate cubic function generated according to the temperature characteristic of the oscillation frequency of the crystal resonator. There has been proposed a temperature compensated crystal oscillator suitable for integration and integration. Furthermore, Patent Document 2 proposes a temperature-compensated crystal oscillator that can improve temperature compensation by improving the temperature-compensated crystal oscillator described in Patent Document 1.

JP-A-9-55624 International Publication No. 98/56105

  However, since the strain stress applied to the quartz base plate cannot be recovered when the temperature changes from rising to falling, or from falling to rising, thermal distortion occurs in the adhesive, electrodes, etc. There is hysteresis that does not match when the temperature rises and when the temperature falls. In recent years, as the temperature compensated crystal oscillator has been reduced in size, the influence of this thermal distortion has been increasing. As a result, the oscillation frequency of the crystal unit may differ even at the same temperature. With conventional temperature-compensated crystal oscillators, for example, temperature compensation can be performed with high accuracy when the temperature rises, but compensation accuracy when the temperature falls There was a problem of deterioration. FIG. 13 is a diagram showing an example of frequency temperature characteristics of a conventional temperature compensated crystal oscillator. In FIG. 13, the horizontal axis represents temperature, and the vertical axis represents frequency deviation (frequency error with respect to the nominal frequency). Frequency deviation when the temperature is raised from around −25 ° C. to a temperature around + 75 ° C. (see graph A) and frequency deviation when the temperature is lowered from around + 75 ° C. to a temperature around −25 ° C. (See graph) is very different.

  The present invention has been made in view of the above problems, and according to some aspects of the present invention, there is little frequency hysteresis with respect to temperature change during temperature rise or temperature fall, and stable temperature characteristics. It is possible to provide a temperature compensated piezoelectric oscillator and a frequency adjustment method thereof.

  (1) The present invention provides a piezoelectric vibrator, first storage means for storing first temperature compensation data for specifying frequency temperature characteristics when the temperature of the piezoelectric vibrator rises, and the piezoelectric vibrator Based on the second storage means for storing the second temperature compensation data for specifying the frequency temperature characteristic at the time of temperature drop, the temperature sensor for acquiring the temperature information, and the temperature information acquired by the temperature sensor The temperature change detecting means for detecting whether the temperature rise or the temperature drop has occurred, and the first temperature compensation data is selected at the time of temperature rise based on the detection result of the temperature change detecting means, and the temperature The temperature compensation data selection means for selecting the second temperature compensation data at the time of descending, and the first temperature compensation data or the second temperature compensation data selected by the temperature compensation data selection means. Accordingly, a temperature compensation voltage generation circuit that generates a temperature compensation voltage for temperature compensation of the frequency of the piezoelectric vibrator, a voltage control oscillation circuit that controls the frequency of the piezoelectric vibrator based on the temperature compensation voltage, Is a temperature compensated piezoelectric oscillator.

  The first temperature compensation data may be, for example, a parameter that specifies a curve that represents a frequency temperature characteristic when the temperature of the piezoelectric vibrator rises, or a parameter that specifies a curve that represents the inverse characteristic of the frequency temperature characteristic. There may be.

  Similarly, the second temperature compensation data may be, for example, a parameter that specifies a curve representing the frequency temperature characteristic when the temperature of the piezoelectric vibrator is lowered, or a curve that represents the inverse characteristic of the frequency temperature characteristic. It may be a parameter.

  In the temperature compensated piezoelectric oscillator of the present invention, the frequency temperature characteristic when the temperature of the piezoelectric vibrator rises can be specified by the first temperature compensation data, and the frequency when the temperature of the piezoelectric vibrator falls by the second temperature compensation data. Temperature characteristics can be specified. In the temperature compensated piezoelectric oscillator of the present invention, the frequency of the piezoelectric vibrator is controlled by the temperature compensation voltage generated based on the first temperature compensation data when the temperature rises, and the second temperature compensation data when the temperature falls. The frequency of the piezoelectric vibrator is controlled by the temperature compensation voltage generated based on the above. Therefore, according to the present invention, it is possible to provide a temperature-compensated piezoelectric oscillator which can obtain a stable frequency-temperature characteristic with little frequency hysteresis with respect to a temperature change during temperature rise or temperature drop.

  (2) In this temperature-compensated piezoelectric oscillator, the temperature change detecting means compares delay means for delaying an output signal of the temperature sensor, an output signal of the temperature sensor and a voltage of a delay signal by the delay means, When the voltage of the output signal of the temperature sensor is higher than the voltage of the delay signal by a predetermined value or more, the first voltage value is output, and the voltage of the output signal of the temperature sensor is lower than the voltage of the delay signal by a predetermined value or more. In some cases, a second voltage value may be output, and in other cases, a voltage comparison unit that holds the output of the first voltage value or the second voltage value may be included.

  According to the temperature compensated piezoelectric oscillator of the present invention, the voltage comparison unit included in the temperature change detection unit compares the voltage value of the output signal of the temperature sensor with the voltage value of the delay signal by the delay unit, and the first voltage value One of the second voltage values is output. If the difference between the two voltages to be compared is smaller than a predetermined value, the current output voltage value is held. That is, even if there is some fluctuation in the voltage value of the output signal of the temperature sensor, the output voltage of the voltage comparison means does not change, so that the voltage comparison means does not react sensitively to subtle fluctuations in temperature. it can. Therefore, according to the temperature compensated piezoelectric oscillator of the present invention, the frequency stability can be further improved.

  (3) The present invention acquires temperature information, a piezoelectric vibrator, a first storage means for storing first temperature compensation data, a second storage means for storing second temperature compensation data, and temperature information. Based on the temperature information acquired, based on the temperature information acquired by the temperature sensor, on the basis of the temperature change detection means for detecting whether a temperature rise or a temperature drop has occurred, and on the detection result of the temperature change detection means, The temperature compensation data selection means for selecting the first temperature compensation data when the temperature rises, and the second temperature compensation data when the temperature falls, and the first compensation data selected by the temperature compensation data selection means. Based on temperature compensation data or the second temperature compensation data, a temperature compensation voltage generation circuit for generating a temperature compensation voltage for temperature compensation of the frequency of the piezoelectric vibrator, and on the basis of the temperature compensation voltage A voltage-controlled oscillation circuit for controlling a frequency of a piezoelectric vibrator, and a frequency adjustment method for a temperature-compensated piezoelectric oscillator, wherein a control voltage of the voltage-controlled oscillation circuit is supplied from outside the temperature-compensated piezoelectric oscillator, The first control voltage value acquisition step of acquiring the value of the control voltage when the frequency of the piezoelectric vibrator coincides with the target frequency by changing the control voltage at at least five different temperatures And, based on at least five control voltage values acquired in the first control voltage value acquisition step, calculate data for specifying frequency temperature characteristics at the time of temperature rise of the piezoelectric vibrator, and the data is Writing to the first storage means as first temperature compensation data; and a control power of the voltage controlled oscillation circuit from outside the temperature compensated piezoelectric oscillator. The control voltage is changed at at least five different temperatures while lowering the temperature, and the value of the control voltage when the frequency of the piezoelectric vibrator matches the target frequency is obtained. Based on at least five control voltage values acquired in the control voltage value acquisition step and the second control voltage value acquisition step, data for specifying a frequency temperature characteristic when the temperature of the piezoelectric vibrator is lowered is calculated. And writing the data into the second storage means as the second temperature compensation data.

  According to the frequency adjustment method of the present invention, the first temperature compensation data representing the frequency temperature characteristic of the piezoelectric vibrator when the temperature rises and the second temperature compensation data representing the frequency temperature characteristic of the piezoelectric vibrator when the temperature falls. Both can be calculated. Therefore, according to the frequency adjustment method of the present invention, it is possible to provide a temperature-compensated piezoelectric oscillator that can obtain a stable frequency-temperature characteristic with little frequency hysteresis with respect to a temperature change when the temperature rises or falls.

  In addition, according to the frequency adjustment method of the present invention, the temperature compensation data is calculated by acquiring the control voltage values at five or more different temperatures at the time of temperature rise and at the time of temperature fall. A temperature compensated piezoelectric oscillator capable of performing temperature compensation with higher accuracy can be provided.

The figure which shows the structure of the temperature compensation piezoelectric oscillator of this embodiment. FIG. 2A is a diagram illustrating an example of frequency temperature characteristics of a piezoelectric vibrator, and FIG. 2B is a diagram illustrating an example of a temperature compensation voltage. The figure which shows the structural example of a voltage control oscillation circuit. The figure which shows an example of the CV characteristic of MOS varicap. An example of the relationship between a reference voltage and a temperature compensation voltage is shown. The figure which shows the structural example of a temperature change detection circuit. The figure which shows an example of the output voltage of a hysteresis comparator. It is a figure which shows the structural example of a selector. The figure which shows an example of the frequency temperature characteristic of the temperature compensation piezoelectric oscillator of this embodiment. The figure which shows the structural example of the measurement system used for the frequency adjustment method of the temperature compensation piezoelectric oscillator of this embodiment. The flowchart figure of the frequency adjustment method of the temperature compensation piezoelectric oscillator of this embodiment. FIG. 12A is a diagram illustrating an example of an ideal compensation voltage when the temperature is rising, and FIG. 12B is a diagram illustrating an example of the ideal compensation voltage when the temperature is decreasing. The figure which shows an example of the frequency temperature characteristic of the conventional temperature compensation crystal oscillator.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

1. Configuration of Temperature Compensated Piezoelectric Oscillator FIG. 1 is a diagram showing a configuration of a temperature compensated piezoelectric oscillator of this embodiment.

  The temperature compensated piezoelectric oscillator 1 of the present embodiment includes a temperature change detection circuit 10, a selector 20, a first memory 30, a second memory 40, a temperature sensor 50, a temperature compensated voltage generation circuit 60, a voltage control oscillation circuit 70, a piezoelectric element. The vibrator 80 is included.

  The piezoelectric vibrator 80 is a piezoelectric element that vibrates at a constant frequency using the inverse piezoelectric effect. For example, a single crystal material such as a crystal vibrator, a ceramic vibrator, a lithium niobate vibrator, or a lithium tantalate vibrator. And vibrators using piezoelectric thin films such as zinc oxide piezoelectric thin film vibrators and aluminum oxide piezoelectric thin film vibrators.

  In particular, it is known that a frequency temperature characteristic representing a frequency deviation at each temperature of an AT-cut crystal resonator exhibits an extremely good characteristic of an approximate cubic curve over a wide temperature range. By using a cut crystal resonator, a temperature compensated crystal oscillator with extremely high frequency stability can be realized. However, as shown in FIG. 2A, the AT-cut quartz resonator has an approximate cubic curve showing the frequency temperature characteristics when the temperature is increased from a low temperature (for example, −30 ° C.) to a high temperature (for example, + 85 ° C.). (Cubic curve indicated by solid line) and approximate cubic curve (cubic curve indicated by dotted line) showing frequency temperature characteristics when temperature is lowered from high temperature (eg + 85 ° C.) to low temperature (eg −30 ° C.) do not do. That is, the frequency-temperature characteristic of the AT cut crystal resonator has hysteresis.

  Therefore, in the temperature compensated piezoelectric oscillator 1 of the present embodiment, the first memory 30 stores the first temperature compensation data 32 for correcting the frequency temperature characteristics when the temperature of the piezoelectric vibrator 80 is increased. The second memory 40 stores second temperature compensation data 42 for correcting the frequency temperature characteristic when the temperature of the piezoelectric vibrator 80 is lowered.

  For example, in the inspection process at the time of product shipment, each frequency temperature characteristic when the temperature of the piezoelectric vibrator 80 rises and falls is measured, and the first temperature compensation data 32 and the second temperature compensation data 42 according to the measurement result. Are written in the first memory 30 and the second memory 40, respectively.

  The first memory 30 and the second memory 40 can be realized by, for example, an EEPROM (Electrically Erasable Programmable Read Only Memory). The first memory 30 and the second memory 40 may be configured as two physically different storage units, or may be configured to be allocated to two storage areas having different address ranges in one storage unit. May be.

  The first temperature compensation data 32 may be a parameter for specifying a curve representing a frequency temperature characteristic when the temperature of the piezoelectric vibrator 80 is increased. Similarly, the second temperature compensation data 42 may be a parameter for specifying a curve representing a frequency temperature characteristic when the temperature of the piezoelectric vibrator 80 is lowered.

For example, if the piezoelectric vibrator 80 is an AT-cut quartz crystal vibrator, the frequency-temperature characteristic (frequency deviation Δf / f) at the time of temperature rise is approximated by a cubic curve indicated by a solid line in FIG. A cubic function corresponding to the curve can be expressed as the following equation (1). In Expression (1), f is a nominal frequency, Δf is a frequency error, T is a temperature variable, and t ₀ is a reference temperature (for example, 25 ° C.).

Equation (1) is a coefficient _A 3, _{A 1,} it is possible to identify the constants _{A 0} and the reference temperature _{t 0,} the coefficient _A 3, _{A 1,} constants _{A 0} and the reference temperature _{t 0} first temperature compensation data 32.

Similarly, if the piezoelectric vibrator 80 is an AT-cut crystal vibrator, the frequency-temperature characteristic (frequency deviation Δf / f) when the temperature drops is approximated by a cubic curve indicated by a dotted line in FIG. The cubic function corresponding to the quadratic curve can be expressed as the following equation (2). In Expression (2), f is a nominal frequency, Δf is a frequency error, T is a temperature variable, and t ₀ is a reference temperature (for example, 25 ° C.).

Equation (2) is the coefficient _B 3, _{B 1,} it is possible to identify by a constant _{B 0} and the reference temperature _{t 0,} the coefficient _B 3, _{B 1,} the constant _{B 0} and the reference temperature _{t 0} second temperature compensation data 42.

  The temperature sensor 50 detects information about the temperature in the vicinity (temperature information). The temperature sensor 50 can be realized by, for example, a thermistor that captures a temperature change as a change in electrical resistance. In the present embodiment, the output voltage 52 of the temperature sensor 50 changes linearly with a negative slope according to the temperature change. That is, the higher the temperature, the lower the output voltage 52 of the temperature sensor 50.

  The temperature change detection circuit 10 detects a change from a temperature rise to a temperature drop and a change from a temperature drop to a temperature rise based on the output voltage 52 (temperature information) of the temperature sensor 50. In this embodiment, the temperature change detection circuit 10 changes from a low level to a high level when the temperature changes from a decrease to an increase, and the control signal 12 changes from a high level to a low level when the temperature changes from an increase to a decrease. Is generated.

  Based on the control signal 12, the selector 20 is one of the first temperature compensation data 32 stored in the first memory 30 and the second temperature compensation data 42 stored in the second memory 40. Is supplied to the temperature compensation voltage generation circuit 60. In the present embodiment, the selector 20 selects the first temperature compensation data 32 when the control signal 12 is at a high level, and selects the second temperature compensation data 42 when the control signal 12 is at a low level.

  The temperature compensation voltage generation circuit 60 generates a temperature compensation voltage 62 for the voltage controlled oscillation circuit 70 based on the first temperature compensation data 32 or the second temperature compensation data 42 selected by the selector 20. In the present embodiment, the temperature compensation voltage generation circuit 60 generates the temperature compensation voltage 62 so as to be a curve similar to the curve representing the frequency temperature characteristics of the piezoelectric vibrator 80. For example, if the piezoelectric vibrator 80 is an AT-cut crystal vibrator, the temperature compensation voltage generation circuit 60 is a cubic curve indicated by a solid line in FIG. 2B based on the first temperature compensation data 32 when the temperature rises. The temperature compensation voltage 62 is generated, and when the temperature drops, the temperature compensation voltage 62 having a cubic curve indicated by the dotted line in FIG. 2B is generated based on the second temperature compensation data 42.

  The voltage controlled oscillation circuit 70 oscillates the piezoelectric vibrator 80 at a constant frequency (nominal frequency) regardless of the temperature by changing the load capacity of the piezoelectric vibrator 80 in accordance with the temperature compensation voltage 62, thereby generating an oscillation signal. 2 is generated. In the present embodiment, the voltage controlled oscillation circuit 70 increases the load capacity of the piezoelectric vibrator 80 as the temperature compensation voltage 62 increases.

  Such a voltage-controlled oscillation circuit 70 can be realized by the configuration shown in FIG. 3, for example.

  As shown in FIG. 3, the ground potential (0 V) is supplied to the sources of the NMOS transistors 77-1 to 77-p, and each NMOS transistor 77-k (1 ≦ k ≦ p) is larger as k is larger. A capacitor weighted so as to have a capacitance value is connected. Similarly, the ground potential (0 V) is supplied to the sources of the NMOS transistors 78-1 to 78 -p, and each NMOS transistor 78 -k (1 ≦ k ≦ p) has a larger capacitance value as k increases. Weighted capacitors are connected.

  A bit (k−1) of a p-bit frequency adjustment code is connected to the gate terminal of each NMOS transistor 77-k (1 ≦ k ≦ p) and the gate terminal of each NMOS transistor 78-k via an input terminal 73-k. ) Is supplied. If the bit (k-1) of the frequency adjustment code is at a low level, the NMOS transistors 77-k and 78-k are turned on, and the capacitor connected to the drain acts as a load of the piezoelectric vibrator 80.

That is, when the bit value of the p-bit frequency adjustment code increases or decreases in the range of 0 to 2 ^p −1, the load capacity of the piezoelectric vibrator 80 increases or decreases linearly. Therefore, by writing an appropriate frequency adjustment code in a nonvolatile memory (not shown), the frequency at the reference temperature (for example, 25 ° C.) of the oscillation signal 2 output via the output terminal 74 becomes a desired frequency (nominal frequency). Can be adjusted as follows.

  The gate terminal of the MOS varicap 75 is connected to one end of the piezoelectric vibrator 80, and the gate terminal of the MOS varicap 76 is connected to the other end of the piezoelectric vibrator 80.

  The temperature compensation voltage 62 is supplied to the gate terminal of the MOS varicap 75 and the gate terminal of the MOS varicap 76 via the input terminal 72. A constant reference voltage is supplied to the back gate terminal of the MOS varicap 75 and the back gate terminal of the MOS varicap 76 via the input terminal 71.

In the present embodiment, the MOS varicaps 75 and 76 have CV characteristics as shown in FIG. That is, if the potential difference between the gate terminal and the back gate terminal increases or decreases in the range of 0 to V _GB1 , the capacitance values of the MOS varicaps 75 and 76 increase or decrease substantially linearly in the range of C _{0 to} C ₁ .

  In this embodiment, a reference voltage lower than the minimum value of the temperature compensation voltage 62 is supplied in accordance with the characteristics of the MOS varicaps 75 and 76 as shown in FIG. As in FIG. 2B, also in FIG. 5, the cubic curve indicated by the solid line indicates the temperature compensation voltage 62 when the temperature rises, and the cubic curve indicated by the dotted line indicates the temperature compensation voltage 62 when the temperature decreases. ing.

  In this way, the higher the temperature compensation voltage 62 (that is, the higher the frequency of the piezoelectric vibrator 80 alone), the larger the capacitance values of the MOS varicaps 75 and 76, and the lower the temperature compensation voltage 62 (ie, the temperature compensation voltage 62). Since the capacitance value of the MOS varicaps 75 and 76 is smaller as the frequency of the piezoelectric vibrator 80 is lower, the oscillation signal 2 having a constant frequency (nominal frequency) can be generated.

  FIG. 6 is a diagram illustrating a configuration example of the temperature change detection circuit 10.

  The temperature change detection circuit 10 includes an A / D conversion circuit (ADC) 110, an N frequency divider 120, a delay circuit 130, a D / A conversion circuit (DAC) 140, and a hysteresis comparator 150.

  The N divider 120 receives the oscillation signal 2 output from the voltage controlled oscillation circuit 70 via the input terminal 102 and generates a clock signal 122 obtained by dividing the oscillation signal 2 by N.

  The A / D conversion circuit 110 receives the output voltage 52 (temperature information) of the temperature sensor 50 via the input terminal 101, performs A / D conversion processing using the clock signal 122 as a sampling clock, and outputs the output voltage of the temperature sensor 50. An m-bit digital signal 112 having a bit value linear with respect to 52 levels is generated.

  The delay circuit 130 generates an m-bit digital signal 132 obtained by delaying the m-bit digital signal 112. The delay circuit 130 can be realized, for example, as a shift register that operates by the clock signal 122 or the like.

  The D / A conversion circuit 140 performs D / A conversion processing on the m-bit digital signal 132, and outputs a voltage having a linear level with respect to the bit value of the digital signal 132.

  The hysteresis comparator 150 includes an operational amplifier 152 and resistors 154 and 156.

  The output voltage of the D / A conversion circuit 140 is supplied to one end of the resistor 154, and the other end of the resistor 154 is connected to the non-inverting input terminal (+ terminal) of the operational amplifier 152.

  Both ends of the resistor 156 are connected to the non-inverting input terminal (+ terminal) and the output terminal of the operational amplifier 152, respectively.

  The inverting input terminal (− terminal) of the operational amplifier 152 is supplied with the output voltage 52 of the temperature sensor 50 via the input terminal 101. A power supply potential and a ground potential (0 V) are supplied to a power supply terminal (not shown) and a ground terminal (not shown) of the operational amplifier 152, respectively.

Here, the resistance values of the resistors 154 and 156 are R ₁ and R ₂ , the voltage value of the output voltage of the D / A conversion circuit 140 is V _A , and the output voltage of the hysteresis comparator 150 (that is, the output of the temperature change detection circuit 10). When the voltage value of the voltage 12) and _{V O,} the voltage _{V +} is the non-inverting input terminal of the operational amplifier 152 (+ terminal) is calculated by the following equation (3).

When V _O is saturated with the power supply potential (high _level), V O _-V A> 0, so, from equation (3), the inverting input terminal of the operational amplifier 152 - than _{V A} (the pin) _{(V O} Unless a voltage higher than −V _A ) × R ₁ / (R ₁ + R ₂ ) is supplied, V _O is not inverted to the ground potential (low level). Conversely, when _{the V O} is saturated with the ground potential (low _level), V O _-V A <0, so the inverting input terminal of the operational amplifier 152 - than _{V A} (the pin) _(V A -V _O ) V _O is not inverted to the power supply potential (high level) unless a voltage lower than × R ₁ / (R ₁ + R ₂ ) is supplied.

That is, the hysteresis comparator 150 has a dead band with a voltage width of ΔV = (V _A −V _O ) × R ₁ / (R ₁ + R ₂ ) and the output voltage 52 of the temperature sensor 50 and the output voltage of the D / A conversion circuit 140. Compare

As a result, as shown in FIG. 7, if the output voltage 52 (voltage value V _B ) of the temperature sensor 50 is higher than the output voltage (voltage value V _A ) of the D / A conversion circuit 140 by a voltage width ΔV of the dead zone. The output voltage of the hysteresis comparator 150 changes from the power supply potential (high level) to the ground potential (low level). On the other hand, if the output voltage 52 (voltage value V _B ) of the temperature sensor 50 is lower than the output voltage (voltage value V _A ) of the D / A conversion circuit 140 by a dead band voltage width ΔV or more, the output voltage of the hysteresis comparator 150 Changes from the ground potential (low level) to the power supply potential (high level).

  As described above, in this embodiment, the output voltage 52 of the temperature sensor 50 changes linearly with a negative slope according to the temperature change. Therefore, the output voltage of the hysteresis comparator 150 changes from a high level to a low level when the temperature rises to a temperature fall, and changes from a low level to a high level when the temperature falls to a temperature rise.

  The output voltage of the hysteresis comparator 150 (the output voltage of the operational amplifier 152) is output as the control signal 12 to the selector 20 via the output terminal 103.

It is desirable to adjust the voltage width of the dead zone so that the hysteresis comparator 150 does not react sensitively to subtle fluctuations in temperature. For example, if R ₂ = 20R ₁ is set, the voltage width of the dead zone can be adjusted to about 5% of the voltage range. In this way, the output voltage of the hysteresis comparator 150 does not change even if there is a subtle fluctuation in temperature, so that the frequency stability can be further improved.

  FIG. 8 is a diagram illustrating a configuration example of the selector 20.

  The selector 20 includes n two-input AND circuits 210-1 to 210-n, n two-input AND circuits 220-1 to 220-n, n inverter circuits 230-1 to 230-n, n pieces. It is configured to include two-input OR circuits 240-1 to 240-n.

  The control signal 12 is commonly input to each inverter circuit 230-k (1 ≦ k ≦ n) via the input terminal 203.

  Each of the two-input AND circuits 210-k (1 ≦ k ≦ n) receives bits (k−1) of the n-bit first temperature compensation data 32 from the first memory via the input terminal 201-k at one input. ) And the control signal 12 is commonly input to the other input via the input terminal 203.

  Each of the two-input AND circuits 220-k (1 ≦ k ≦ n) receives bits (k−1) of the n-bit second temperature compensation data 42 from the second memory via the input terminal 202-k at one input. ) Is input, and the output signal of the inverter circuit 230-k (inverted signal of the control signal 12) is input to the other input.

  Each 2-input OR circuit 240-k (1 ≦ k ≦ n) receives the output signal of the 2-input AND circuit 210-k at one input and the output signal of the 2-input AND circuit 220-k at the other input. Entered. Output signals of the 2-input OR circuits 240-1 to 240-n are output to the temperature compensated voltage generation circuit 60 via the output terminals 204-1 to 204-n, respectively.

  With such a configuration, the selector 20 selects the first temperature compensation data if the control signal 12 is at a high level, and selects the second temperature compensation data if the control signal 12 is at a low level. The voltage generation circuit 60 can be supplied.

  FIG. 9 is a diagram illustrating an example of frequency temperature characteristics of the temperature compensated piezoelectric oscillator of the present embodiment. In FIG. 9, the horizontal axis is temperature, and the vertical axis is frequency deviation.

  According to the temperature compensated piezoelectric oscillator of the present embodiment, the temperature compensation voltage is generated based on the first temperature compensation data when the temperature rises, and the temperature compensation is performed based on the second temperature compensation data when the temperature falls. Temperature compensation is performed by generating a temperature compensation voltage. Therefore, as shown in FIG. 9, the frequency deviation (see the graph of A) when the temperature is raised from around -25 ° C. to around + 75 ° C. is also from about + 75 ° C. to around −25 ° C. The frequency deviation (refer to the graph of B) when lowered is also made extremely small.

  That is, according to the present embodiment, it is possible to provide a temperature-compensated piezoelectric oscillator that has a low frequency hysteresis with respect to a temperature change during a temperature rise or a temperature fall and that can obtain a stable frequency temperature characteristic.

  The temperature change detection circuit 10 and the selector 20 in this embodiment function as “temperature change detection means” and “temperature compensation data selection means” in the present invention, respectively. The first memory 30 and the second memory 40 function as “first storage means” and “second storage means” in the present invention, respectively. The circuit constituted by the A / D conversion circuit 110, the N frequency divider 120, the delay circuit 130, and the D / A conversion circuit 140 functions as “delay means” in the present invention. The hysteresis comparator 150 functions as a “voltage comparison unit” in the present invention.

2. FIG. 10 is a diagram illustrating a configuration example of a measurement system used in the frequency adjustment method of the temperature compensated piezoelectric oscillator according to the present embodiment.

  The temperature compensated piezoelectric oscillator 1 is the temperature compensated piezoelectric oscillator 1 shown in FIG. 1, and the same components as those in FIG. However, a control circuit 90, an interface (I / F) circuit 92, and switch circuits 94 and 96 are added to the temperature compensated piezoelectric oscillator 1. The temperature compensated piezoelectric oscillator 1 is installed in a thermostat (not shown) so that the temperature around the temperature compensated piezoelectric oscillator 1 can be controlled.

  The interface (I / F) circuit 92 performs interface processing with respect to the PC 300, receives a command from the personal computer (PC) 300, and transfers it to the control circuit 90.

  The control circuit 90 performs open / close control of the switch circuits 94 and 96 and a process of writing temperature compensation data in the first memory 30 and the second memory 40.

  The switch circuit 94 is disposed between the output of the temperature compensation voltage generation circuit 60 and the input of the voltage control oscillation circuit 70. By opening and closing the switch circuit 94, the output voltage of the temperature compensation voltage generation circuit 60 is changed to a voltage control oscillation circuit. 70 can be selected.

  The switch circuit 96 is disposed between the output of the voltage generator 320 and the input of the voltage controlled oscillation circuit 70, and supplies the output voltage of the voltage generator 320 to the voltage controlled oscillation circuit 70 by opening and closing the switch circuit 96. It is possible to select whether or not.

  The switching circuit 94 and the switching circuit 96 are opened and closed exclusively. The voltage controlled oscillation circuit 70 is supplied with the output voltage of the voltage generator 320 during frequency adjustment, and the temperature compensated voltage generating circuit during normal operation. 60 output voltages are supplied.

  The PC 300 instructs the temperature-compensated piezoelectric oscillator 1 to open / close the switch circuits 94 and 96, and instructs the voltage generator 320 to write temperature-compensated data to the first memory 30 and the second memory 40. On the other hand, a process of controlling to generate a voltage of a desired level is performed.

  The frequency counter 310 performs processing for counting the frequency of the oscillation signal 2 output from the voltage controlled oscillation circuit 70 and transmitting the count value to the PC 300.

  The digital multimeter 330 performs a process of measuring the level of the output voltage of the voltage generator 320 and transmitting the measurement value to the PC 300.

  Next, an example of a method for adjusting the frequency of the temperature compensated piezoelectric oscillator of the present embodiment using the measurement system shown in FIG. 10 will be described. FIG. 11 is a flowchart of the frequency adjustment method for the temperature compensated piezoelectric oscillator of the present embodiment. Before each process of the flowchart of FIG. 11, the switch circuit 94 is opened and the switch circuit 96 is closed in accordance with an instruction from the PC 300.

  First, the internal temperature of the thermostat is lowered to a first temperature (for example, −25 ° C.) to obtain an ideal compensation voltage at the first temperature point (step S10). Specifically, the PC 300 monitors the count value of the frequency counter 310 while changing the output voltage of the voltage generator 320, and the measured value of the digital multimeter 330 when the frequency of the oscillation signal 2 matches the nominal frequency. Obtained as an ideal compensation voltage at the first temperature point.

  Next, the internal temperature of the thermostat is raised to a second temperature (for example, 0 ° C.), and an ideal compensation voltage at the second temperature point is obtained in the same manner (step S20).

  Next, the internal temperature of the thermostat is raised to a third temperature (for example, + 25 ° C.), and the ideal compensation voltage at the third temperature point is obtained in the same manner (step S30).

  Next, the internal temperature of the thermostatic oven is raised to a fourth temperature (for example, + 55 ° C.), and the ideal compensation voltage at the fourth temperature point is obtained in the same manner (step S40).

  Next, the internal temperature of the thermostatic oven is raised to the fifth temperature (for example, + 75 ° C.), and the ideal compensation voltage at the fifth temperature point is obtained in the same manner (step S50).

Next, temperature compensation data (first temperature compensation data) at the time of temperature rise is calculated from the ideal compensation voltage at the first temperature point to the fifth temperature point acquired in steps S <b> 10 to S <b> 50, and stored in the first memory 30. Write (step S60). Specifically, first, as shown in FIG. 12A, the error with respect to five ideal compensation voltages (indicated by white circles) at the first to fifth temperature points is minimized by using a minimum approximation method or the like. A cubic function representing a cubic curve (shown by a solid line) is obtained. Next, this cubic function is converted into a cubic function represented by the equation (1), for example, with the third temperature as the reference temperature t ₀ . Then, the coefficients A ₃ and A ₁ , the constant A ₀ and the reference temperature t ₀ in the equation (1) are written in the first memory 30 as the first temperature compensation data 32.

  Next, the ideal compensation voltage at the fifth temperature point is again acquired in the same manner (step S70).

  Next, the internal temperature of the thermostatic oven is lowered to the fourth temperature, and the ideal compensation voltage at the fourth temperature point is similarly obtained (step S80).

  Next, the internal temperature of the thermostat is lowered to the third temperature, and the ideal compensation voltage at the third temperature point is obtained in the same manner (step S90).

  Next, the internal temperature of the thermostatic oven is lowered to the second temperature, and the ideal compensation voltage at the second temperature point is similarly obtained (step S100).

  Next, the internal temperature of the thermostat is lowered to the first temperature, and the ideal compensation voltage at the first temperature point is obtained in the same manner (step S110).

Finally, temperature compensation data (second temperature compensation data) at the time of temperature decrease is calculated from the ideal compensation voltage at the first temperature point to the fifth temperature point obtained in steps S70 to S110, and the second memory 40 stores the temperature compensation data. Write (step S120). Specifically, first, as shown in FIG. 12B, the error with respect to five ideal compensation voltages (indicated by white circles) at the first temperature point to the fifth temperature point is minimized using a minimum approximation method or the like. A cubic function representing a cubic curve (shown by a solid line) is obtained. Next, this cubic function is converted into a cubic function represented by the equation (2), for example, with the third temperature as the reference temperature t ₀ . Then, the coefficients B ₃ and B ₁ , the constant B ₀ and the reference temperature t ₀ in Expression (2) are written in the second memory 40 as the second temperature compensation data 42.

  According to the frequency adjustment method of the present embodiment, the first temperature compensation data 32 representing the frequency-temperature characteristics of the piezoelectric vibrator 80 when the temperature rises and the second temperature-temperature characteristics of the piezoelectric vibrator 80 when the temperature falls. Both temperature compensation data 42 can be calculated. Therefore, according to the frequency adjustment method of the present embodiment, it is possible to provide a temperature-compensated piezoelectric oscillator that can obtain a stable frequency-temperature characteristic with little frequency hysteresis with respect to a temperature change when the temperature rises or falls.

  In addition, according to the frequency adjustment method of the present embodiment, ideal compensation voltages at five temperature points are acquired and temperature compensation data is calculated both when the temperature rises and when the temperature falls, so that the accuracy can be improved over a wide temperature range. It is possible to provide a temperature compensated piezoelectric oscillator capable of performing high temperature compensation.

  In addition, this invention is not limited to this embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 Temperature compensation piezoelectric oscillator, 2 Oscillation signal, 10 Temperature change detection circuit, 12 Control signal, 20 Selector, 30 1st memory, 32 1st temperature compensation data, 40 2nd memory, 42 2nd temperature compensation data 50 temperature sensor, 52 temperature sensor output voltage, 60 temperature compensation voltage generation circuit, 62 temperature compensation voltage, 70 voltage control oscillation circuit, 71-72 input terminal, 73-1 to 73-p input terminal, 74 output terminal, 75-76 MOS varicap, 77-1 to 77-p NMOS transistor, 78-1 to 78-p NMOS transistor, 80 piezoelectric vibrator, 90 control circuit, 92 interface (I / F) circuit, 94 switch circuit, 96 Switch circuit, 101-102 input terminal, 103 output terminal, 110 A / D conversion circuit ADC), 112 digital signal, 120 N frequency divider, 122 clock signal, 130 delay circuit, 132 digital signal, 140 D / A conversion circuit (DAC), 150 hysteresis comparator, 152 operational amplifier, 154 resistance, 156 resistance, 201 -1 to 201-n input terminal, 202-1 to 202-n input terminal, 203 input terminal, 204-1 to 204-n output terminal, 210-1 to 210-n 2-input AND circuit, 220-1 to 220 -N 2-input AND circuit, 230-1 to 230-n inverter circuit, 240-1 to 240-n 2-input OR circuit, 300 personal computer (PC), 310 frequency counter, 320 voltage generator, 330 digital multimeter

Claims (1)

A piezoelectric vibrator;
First storage means for storing first temperature compensation data;
Second storage means for storing second temperature compensation data;
A temperature sensor for acquiring temperature information;
Based on the temperature information acquired by the temperature sensor, temperature change detection means for detecting whether a temperature rise or a temperature drop has occurred;
Temperature compensation data selection means for selecting the first temperature compensation data when the temperature rises and selecting the second temperature compensation data when the temperature falls based on the detection result of the temperature change detection means;
A temperature compensation voltage for generating a temperature compensation voltage for temperature compensation of the frequency of the piezoelectric vibrator based on the first temperature compensation data or the second temperature compensation data selected by the temperature compensation data selection means. Generating circuit;
A voltage-controlled oscillation circuit that controls the frequency of the piezoelectric vibrator based on the temperature-compensated voltage, and a frequency adjustment method for a temperature-compensated piezoelectric oscillator,
The control voltage of the voltage-controlled oscillation circuit is supplied from the outside of the temperature-compensated piezoelectric oscillator, and the temperature of the piezoelectric vibrator is changed to a target frequency by changing the control voltage at at least five different temperatures while increasing the temperature. A first control voltage value acquisition step of acquiring a value of the control voltage when it coincides with
Based on at least five control voltage values acquired in the first control voltage value acquisition step, data for specifying a frequency temperature characteristic at the time of temperature rise of the piezoelectric vibrator is calculated, and the data is calculated as the first control voltage value. Writing to the first storage means as temperature compensation data of
The control voltage of the voltage-controlled oscillation circuit is supplied from the outside of the temperature-compensated piezoelectric oscillator, and the control voltage is changed at at least five different temperatures while lowering the temperature, so that the frequency of the piezoelectric vibrator becomes a target frequency. A second control voltage value acquisition step of acquiring a value of the control voltage when it coincides with
Based on at least five control voltage values acquired in the second control voltage value acquisition step, data for specifying a frequency temperature characteristic when the temperature of the piezoelectric vibrator is lowered is calculated, and the data is calculated as the second control voltage value. A method of adjusting the frequency of the temperature compensated piezoelectric oscillator, the method comprising: writing to the second storage means as temperature compensation data of