JP2011234086A - Off-set circuit for piezoelectric oscillator, piezoelectric oscillator, and temperature compensation method for piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an off-set circuit for a piezoelectric oscillator, a piezoelectric oscillator, and a temperature compensation method for a piezoelectric oscillator.SOLUTION: An off-set circuit for a piezoelectric oscillator, a piezoelectric oscillator, and a temperature compensation method for a piezoelectric oscillator comprises: an oscillatory circuit 14 which compensates the temperature of the oscillatory frequency of an oscillatory signal 66 by a temperature compensation voltage 64 in response to the temperature characteristic of the oscillatory frequency of a piezoelectric vibrator 12; a temperature sensor 16 which outputs detection voltage 62 in response to the temperature of the piezoelectric vibrator 12; a first off-set circuit 46 which is provided with the temperature compensation voltage generation circuit 18 and which offsets the temperature compensation voltage 64 in the temperature direction by offsetting the detection voltage 62 in response to the temperature characteristics of the oscillatory frequency respectively when they go up and down; a second off-set circuit 54 which is provided between the temperature compensation voltage generation circuit 18 and the oscillatory circuit 14 and which offsets the temperature compensation voltage 64 in the voltage direction in response to the temperature characteristics of the oscillatory frequency respectively when they go up and down.

Description

  The present invention relates to a piezoelectric oscillator offset circuit that constitutes a temperature compensated oscillator (TCXO) that oscillates a piezoelectric vibrator and outputs a temperature compensated voltage, and a piezoelectric oscillator incorporating the piezoelectric oscillator offset circuit. The present invention relates to a technology capable of outputting a compensation voltage.

  Conventionally, in a crystal oscillator combining a crystal resonator and an amplifier circuit, when the stability of the oscillation frequency with respect to temperature is required, a temperature compensated crystal oscillator (TCXO) with a temperature compensation circuit is used. Widely used in mobile terminal base stations, GPS receivers, and the like.

  FIG. 10 shows a circuit diagram of a temperature compensated oscillator according to the prior art. In Patent Document 1, as shown in FIG. 10, a temperature detection circuit 102 whose output changes in a linear function with respect to a temperature change, and an approximate cubic curve voltage based on the input output of the temperature detection circuit 102. Approximate cubic curve generating circuit 104 for outputting the first temperature, the first programmable gain amplifier 106 for adjusting and outputting the amplification factor of the approximate cubic curve voltage, and the temperature detection circuit 102 branched and connected from the temperature detection circuit 102 The second programmable gain amplifier 108 that adjusts and outputs the output amplification factor of the circuit 102, the constant voltage generation circuit 110, and the input amplification factor of the output from the constant voltage generation circuit 110 is adjusted and output. A third programmable gain amplifier 112 and the first, second, and third programmable gain amplifiers 106, 108, 112 are connected in parallel, and the first, second, An adder circuit 114 that outputs the temperature compensation voltage by adding the outputs from the third programmable gain amplifiers 106, 108, and 112, and a voltage controlled crystal oscillation circuit that performs temperature compensation of the oscillation frequency by the input temperature compensation voltage 116 (VCXO), and a temperature compensated oscillator 100 (TCXO).

  Here, the first programmable gain amplifier 106 is a third-order temperature compensation voltage, the second programmable gain amplifier 108 is a first-order temperature compensation voltage, and the third programmable gain amplifier 112 is a zero-order temperature compensation voltage (offset voltage). The temperature compensation of the AT-cut crystal resonator in the voltage controlled crystal oscillation circuit 116 can be continuously performed with respect to the temperature change, and a stable frequency characteristic with respect to the temperature change can be realized. By the way, the amplification factors of the first, second, and third programmable gain amplifiers 106, 108, and 112 are obtained at the time of the manufacturing inspection process. From the viewpoint of the throughput at the time of manufacturing, the temperature is increased or decreased. In general, the frequency is adjusted so that the oscillation frequency becomes the reference frequency when the temperature changes at either time.

Japanese Patent Laid-Open No. 09-55624

  By the way, the frequency-temperature characteristic of the crystal resonator has a hysteresis characteristic. Having a hysteresis characteristic means that the temperature dependence of the crystal resonator is different when the temperature rises and when it falls. This is due to the fact that the change in strain stress of the crystal resonator with respect to the temperature change cannot follow the actual temperature change, and the thermal strain change of the support structure, adhesive, welding alloy, electrode, etc. in the oscillator. It becomes more prominent as the size of the vibrator becomes smaller.

Further, in the field of high-precision electronic devices such as mobile phone terminals equipped with the GPS function described above, the allowable range of frequency deviation (Δf / f ₀ ) is very narrow, for example, a temperature of −30 ° C. to 85 ° C. In the range, the frequency deviation (Δf / f ₀ ) is required to be within ± 0.5 ppm.

  Therefore, as in the conventional method, in the method of obtaining the amplification factor when the temperature changes either when the temperature rises or when the temperature falls, only the amplification factor in one direction is stored, so the amplification factor is obtained. If the temperature changes in the opposite direction, the difference in oscillation frequency due to the hysteresis characteristic remains as a correction error even if the system is frequency corrected. Therefore, due to this, there has been a problem that it takes a long time for positioning, resulting in a positioning error or a malfunction in synchronization with the GPS satellite.

  Accordingly, the present invention pays attention to the above-mentioned problems, reduces the influence of the hysteresis characteristics of the oscillation frequency of the piezoelectric vibrator, and provides a piezoelectric oscillator offset circuit that can oscillate at a stable oscillation frequency, the piezoelectric oscillator, and the temperature of the piezoelectric oscillator. An object is to provide a compensation method.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples.
[Application Example 1] Oscillation that oscillates a piezoelectric vibrator, outputs an oscillation signal, and performs temperature compensation of the oscillation frequency of the oscillation signal by a temperature compensation voltage corresponding to the temperature characteristic of the oscillation frequency of the input piezoelectric vibrator A circuit, temperature detection means for outputting a detection voltage corresponding to the temperature of the piezoelectric vibrator, and interposed between the oscillation circuit and the temperature detection means, the temperature compensation voltage corresponding to the detection voltage An offset circuit for a piezoelectric oscillator attached to a piezoelectric oscillator having a temperature compensation voltage generation circuit for output, the temperature compensation voltage generation circuit being interposed between the temperature detection means and the temperature compensation voltage generation circuit, the temperature of the oscillation frequency A first offset circuit for offsetting the temperature compensation voltage in a temperature direction by offsetting the detection voltage in accordance with temperature characteristics at the time of rising and falling, respectively, A second circuit that is interposed between the temperature compensation voltage generation circuit and the oscillation circuit and offsets the temperature compensation voltage in the voltage direction in accordance with the temperature characteristics when the temperature of the oscillation frequency rises and falls. An offset circuit for a piezoelectric oscillator, comprising: an offset circuit.

  With the above configuration, the temperature compensation voltage output from the temperature compensation voltage generation circuit based on the detection voltage input through the first offset circuit is shifted in the temperature direction by the offset amount of the detection voltage in the first offset circuit. shift. Further, the temperature compensation voltage output from the second offset selection circuit is shifted in the voltage direction by the offset amount of the temperature compensation voltage in the second offset circuit. Therefore, the temperature compensation voltage after the shift is in contact with the temperature compensation voltage before the shift and the high temperature region and the low temperature region, and the temperature compensation voltage before the shift and the temperature compensation voltage after the shift are between the high temperature region and the low temperature region. An enclosed area occurs. As a result, a temperature characteristic very similar to the hysteresis characteristic of the piezoelectric vibrator can be obtained. Therefore, the temperature compensation voltage having one temperature characteristic is shifted according to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator when the temperature of the piezoelectric vibrator rises and falls to compensate for the hysteresis characteristic of the piezoelectric vibrator. This is an offset circuit for a piezoelectric oscillator.

  Application Example 2 It has a determination circuit that outputs a determination signal for detecting an increase or decrease in the temperature of the piezoelectric vibrator by detecting an increase or decrease in the detection voltage, and the temperature compensation voltage generation circuit includes the temperature A compensation voltage is output corresponding to one of the temperature characteristics when the temperature of the piezoelectric vibrator rises and falls, and the first offset circuit produces a temperature characteristic opposite to the one temperature characteristic. A corresponding offset amount of the detection voltage is set, the detection voltage is offset by the offset amount of the detection voltage based on the determination signal, and the second offset circuit is configured to detect the temperature corresponding to the other temperature characteristic. An offset amount of a compensation voltage is set, and the temperature compensation voltage input based on the determination signal is offset by the offset amount of the temperature compensation voltage. Piezoelectric oscillator offset circuit mounting.

  In the above-described configuration, the offset amount can be set to a constant amount when the temperature of the piezoelectric vibrator increases or decreases, and can be set to zero at the other. Therefore, the temperature compensation can be performed with high accuracy by matching the temperature coefficient input to the temperature compensation voltage generating circuit in accordance with the one temperature characteristic. In the one case, it is possible to pass the detection voltage and the temperature compensation voltage to the subsequent stage without operating the first offset circuit and the second offset selection circuit. Therefore, the first offset circuit and the second offset selection circuit do not require a configuration that realizes the offset amount when the temperature of the piezoelectric vibrator increases or decreases, and simplifies the configuration and suppresses the cost. This is an offset circuit for a piezoelectric oscillator.

  Application Example 3 The offset amounts set in the detection voltage and the temperature compensation voltage are the minimum set temperature and the maximum set temperature when the temperature of the piezoelectric vibrator is increased, and the offset amount when the temperature of the piezoelectric vibrator is decreased. In a temperature compensation voltage at a reference temperature, a minimum set temperature and a set maximum temperature when the total sum of differences in the voltage direction caused by the offset amount is minimized or when the temperature of the piezoelectric vibrator is lowered, and the piezoelectric vibrator The piezoelectric oscillator according to Application Example 2, wherein the temperature compensation voltage of the reference temperature at the time of the temperature rise is calculated so that the sum of the differences in the voltage direction caused by the offset amount is minimized. Offset circuit.

  With the above configuration, an offset circuit for a piezoelectric oscillator capable of outputting a temperature compensation voltage corresponding to the hysteresis characteristics of the piezoelectric vibrator with high accuracy in a set temperature range with the set minimum temperature as the lower limit and the set maximum temperature as the upper limit. Become.

  Application Example 4 A piezoelectric oscillator characterized in that the piezoelectric oscillator offset circuit described in any one of Application Examples 1 to 3 is incorporated in the piezoelectric oscillator.

  With the above configuration, the temperature compensation voltage with one temperature characteristic is shifted according to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator when the temperature of the piezoelectric vibrator rises and falls, and corresponds to the hysteresis characteristic of the piezoelectric vibrator Thus, a piezoelectric oscillator capable of temperature compensation can be obtained.

  Application Example 5 Oscillation that oscillates a piezoelectric vibrator, outputs an oscillation signal, and performs temperature compensation of the oscillation frequency of the oscillation signal by a temperature compensation voltage corresponding to the temperature characteristic of the oscillation frequency of the input piezoelectric vibrator A circuit, a temperature detection means for outputting a detection voltage corresponding to the temperature of the piezoelectric vibrator, and an output between the oscillation circuit and the temperature means, and outputting the temperature compensation voltage corresponding to the detection voltage. A temperature compensation method for a piezoelectric oscillator having a temperature compensation voltage generation circuit, wherein the temperature compensation voltage is voltage corresponding to temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator rises and falls, respectively. The temperature compensation is performed by offsetting the detection voltage in accordance with temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator rises and falls, respectively. Temperature compensation method of a piezoelectric oscillator, characterized by offsetting the pressure temperature direction.

  By the above method, the temperature compensation voltage input to the temperature compensation voltage generation circuit is shifted in the temperature direction by the offset amount of the detection voltage. Further, the temperature compensation voltage output from the temperature compensation voltage generation circuit is shifted in the voltage direction by the offset amount of the temperature compensation voltage. Therefore, the temperature compensation voltage after the shift is in contact with the temperature compensation voltage before the shift and the high temperature region and the low temperature region, and the temperature compensation voltage before the shift and the temperature compensation voltage after the shift are between the high temperature region and the low temperature region. An enclosed area occurs. As a result, a temperature characteristic very similar to the hysteresis characteristic of the piezoelectric vibrator can be obtained. Therefore, the temperature compensation voltage having one temperature characteristic is shifted according to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator when the temperature of the piezoelectric vibrator rises and falls to compensate for the hysteresis characteristic of the piezoelectric vibrator. Is possible.

  [Application Example 6] The temperature compensation voltage generation circuit outputs a voltage having one of temperature characteristics when the temperature of the piezoelectric vibrator rises and falls based on the detection voltage to the oscillation circuit, A detection signal for detecting an increase / decrease in the detection voltage and determining an increase / decrease in the temperature of the piezoelectric vibrator is output, and the temperature compensation voltage is determined based on the determination signal. The detected voltage is offset by the offset amount of the temperature compensation voltage set corresponding to the temperature characteristic of the detection voltage, and the detected voltage is offset based on the determination signal. The temperature compensation method for a piezoelectric oscillator according to Application Example 5, wherein the offset is offset only by the amount of time.

  In the above method, the offset amount is set to a constant amount at one of the rise and fall of the temperature of the piezoelectric vibrator, and set to zero at the other. Therefore, temperature compensation can be performed with high accuracy based on the temperature compensation voltage generation circuit adapted to the one temperature characteristic.

  Application Example 7 The offset amounts set in the detection voltage and the temperature compensation voltage are the minimum set temperature and the maximum set temperature when the temperature of the piezoelectric vibrator is increased, and the offset amount when the temperature of the piezoelectric vibrator is decreased. In a temperature compensation voltage at a reference temperature, a minimum set temperature and a set maximum temperature when the total sum of differences in the voltage direction caused by the offset amount is minimized or when the temperature of the piezoelectric vibrator is lowered, and the piezoelectric vibrator The temperature of the piezoelectric oscillator according to Application Example 6, wherein the temperature compensation voltage at the reference temperature at the time of the temperature rise is calculated so that the sum of the differences in the voltage direction caused by the offset amount is minimized. Compensation method.

  According to the above method, it is possible to output a temperature compensation voltage corresponding to the hysteresis characteristics of the piezoelectric vibrator with high accuracy in the set temperature range with the set minimum temperature as the lower limit and the set maximum temperature as the upper limit.

It is a circuit diagram of the temperature compensation circuit of this embodiment. It is a circuit diagram of the determination circuit of this embodiment. It is a circuit diagram of the 1st offset circuit of this embodiment. It is a circuit diagram of the 2nd offset circuit of this embodiment. FIG. 5A shows a concept of temperature compensation of the temperature compensation circuit of the present embodiment, FIG. 5A is a diagram showing hysteresis characteristics with respect to temperature change of the oscillation frequency of the piezoelectric vibrator, and FIG. 5B is an oscillation frequency of the piezoelectric vibrator. FIG. 5C is a diagram showing a frequency direction difference (f ₁ −f ₂ , hysteresis amount) between the temperature characteristic (f ₁ ) when the temperature rises and the temperature characteristic (f ₂ ) when the temperature drops, FIG. 6 is a diagram of a temperature characteristic (f ₁ ) when the oscillation frequency rises in temperature and a temperature characteristic (f ₁ ′) obtained by translating the temperature characteristic in the temperature direction and the frequency direction. It is a flowchart of the calculation process of the offset amount of the temperature direction of the temperature compensation voltage, and the offset amount of a voltage direction. It is a figure which shows the effect of the temperature compensation circuit of this embodiment. It is a circuit diagram of the modification of the 1st offset circuit of this embodiment. It is a circuit diagram of the modification of the 2nd offset circuit of this embodiment. The circuit diagram of the temperature compensation type | mold oscillator which concerns on a prior art is shown.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .

  FIG. 1 shows a circuit diagram of a piezoelectric oscillator incorporating a piezoelectric oscillator offset circuit according to the present embodiment. The offset circuit for a piezoelectric oscillator according to the present embodiment oscillates the piezoelectric vibrator 12 and outputs an oscillation signal 66, and the temperature compensation voltage 64 corresponding to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 inputted thereto is used. The oscillation circuit 14 that performs temperature compensation of the oscillation frequency of the oscillation signal 66, temperature detection means (temperature sensor 16) that outputs a detection voltage 62 corresponding to the temperature of the piezoelectric vibrator 12, the oscillation circuit 14 and the temperature detection A piezoelectric oscillator attached to the piezoelectric oscillator 10 having a temperature compensated voltage generation circuit 18 interposed between the means (temperature sensor 16) and outputting the temperature compensated voltage 64 corresponding to the detected voltage 62. An offset circuit interposed between the temperature detection means (temperature sensor 16) and the temperature compensation voltage generation circuit 18 to increase the temperature of the oscillation frequency. A first offset circuit 46 for offsetting the temperature compensation voltage 64 in the temperature direction by offsetting the detection voltage 62, the temperature compensation voltage generation circuit 18, and the A second offset circuit 54 interposed between the oscillation circuit 14 and for offsetting the temperature compensation voltage 64 in the voltage direction corresponding to the temperature characteristics at the time of increase and decrease of the temperature of the oscillation frequency, It is what has.

  The temperature compensated voltage generation circuit 18 outputs the temperature compensated voltage 64 corresponding to one of the temperature characteristics when the temperature of the piezoelectric vibrator 12 rises and falls, and the piezoelectric oscillator offset circuit. Includes a determination circuit 32 that detects an increase / decrease in the detection voltage and outputs a determination signal 68 for determining an increase / decrease in the temperature of the piezoelectric vibrator 12, and the first offset circuit 46 includes the first offset circuit 46. An offset amount of the detection voltage 62 corresponding to the other temperature characteristic opposite to the temperature characteristic is set, the detection voltage 62 is offset by the offset amount of the detection voltage 62 based on the determination signal 68, and the second The offset circuit 54 is set with an offset amount of the temperature compensation voltage 64 corresponding to the other temperature characteristic, and the temperature compensation voltage input based on the determination signal 68 is set. 64 by the offset amount of the temperature compensation voltage 64 is intended to offset.

  Therefore, the temperature compensation method of the piezoelectric oscillator according to the present embodiment oscillates the piezoelectric vibrator 12 and outputs the oscillation signal 66, and the temperature compensation voltage 64 corresponding to the temperature characteristic of the oscillation frequency of the inputted piezoelectric vibrator 12 is obtained. Is interposed between the oscillation circuit 14 that performs temperature compensation of the oscillation frequency of the oscillation signal 66 and the temperature sensor 16 that serves as a temperature detection unit that outputs a detection voltage 62 corresponding to the temperature of the piezoelectric vibrator 12. A temperature compensation method for the piezoelectric oscillator 10 that outputs the temperature compensation voltage 64 in correspondence with the detection voltage 62, corresponding to the temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator 12 rises and falls, respectively. The temperature compensation voltage 64 is offset in the voltage direction, and the detection voltage 62 is offset to offset the temperature compensation voltage 64 in the temperature direction. It is intended to theft.

  The temperature compensation voltage generation circuit 18 outputs a voltage having one of the temperature characteristics when the temperature of the piezoelectric vibrator 12 rises and falls based on the detection voltage 62 to the oscillation circuit 14. , Detecting a rise and fall of the detection voltage 62 and outputting a judgment signal 68 for judging the rise and fall of the temperature of the piezoelectric vibrator 12, and the temperature compensation voltage 64 is determined based on the judgment signal 68. The detected voltage 62 is offset by the offset amount of the temperature compensation voltage 64 set corresponding to the other temperature characteristic opposite to the temperature characteristic, and the detected voltage 62 is corresponding to the other temperature characteristic based on the determination signal 68. The offset is set by the set offset amount of the detection voltage 62.

  As shown in FIG. 1, in the piezoelectric oscillator 10, a temperature sensor 16 serving as a temperature detection unit, a first offset circuit 46, a temperature compensation voltage generation circuit 18, and a second offset circuit 54 connected to the oscillation circuit 14 are serially arranged in this order. It is connected to the. The determination circuit 32 has an input side connected to the temperature sensor 16 and an output side connected to the first offset circuit 46 and the second offset circuit 54.

  The piezoelectric vibrator 12 is formed of a piezoelectric material such as quartz, lithium niobate, lithium tantalate, or the like, and an AT-cut vibrator having excellent frequency temperature characteristics is desirable as long as it is quartz. Such an AT cut crystal resonator can receive an alternating voltage from the oscillation circuit 14 and oscillate at a predetermined oscillation frequency by thickness shear vibration. The oscillation frequency of the piezoelectric vibrator using the thickness shear vibration by the AT cut has a temperature characteristic that becomes a cubic curve centering on the reference temperature (around 25 ° C.).

  The oscillation circuit 14 is, for example, a Colpitts type oscillation circuit using the piezoelectric vibrator 12 as an oscillation source, and can receive temperature compensation of the oscillation frequency of the piezoelectric vibrator 12 by inputting a temperature compensation voltage 64.

  The temperature sensor 16 has a diode structure, and allows a forward current to flow, and outputs an analog detection voltage 62 that is a potential between the terminals of the diode, which varies with temperature, to the first offset circuit 46 and the determination circuit 32. It is. Here, the detection voltage 62 decreases linearly as the temperature rises, and the output detection voltage 62 corresponds to the measured temperature. The temperature sensor 16 is desirably disposed adjacent to the piezoelectric vibrator 12. Thereby, the temperature of the piezoelectric vibrator 12 can be measured while suppressing measurement errors, and the output error of the temperature compensation voltage 64 can be suppressed.

  The temperature compensation voltage generation circuit 18 includes a quaternary voltage generation circuit 20, a tertiary voltage generation circuit 22, a secondary voltage generation circuit 24, a primary voltage generation circuit 26, a 0th order voltage generation circuit 28, and an addition circuit 30. Yes.

When the piezoelectric vibrator 12 is an AT cut quartz crystal vibrator as in the present embodiment, the temperature characteristic Δf / f ₀ of the oscillation frequency of the piezoelectric vibrator 12 can be expressed by the following approximate curve.

Here, f ₀ is an oscillation frequency (reference frequency) at a reference temperature (25 ° C.), T ₀ is a reference temperature, A is a fourth-order temperature coefficient, B is a third-order temperature coefficient, C is a second-order temperature coefficient, D Is a first-order temperature coefficient, and E is a zero-order temperature coefficient (offset coefficient). Therefore, in order to perform temperature compensation of the oscillation circuit 14 (piezoelectric vibrator 12) having such temperature characteristics, the temperature compensation voltage 64 (Vh, the ideal compensation voltage described later) also has the following temperature characteristics. There is a need.
Here, Vc ₄ , Vc ₃ , Vc ₂ , Vc ₁ , and Vc ₀ correspond to −A, −B, −C, −D, and −E in Formula 1, respectively.

Therefore, the quaternary voltage generation circuit 20 stores the information of Vc ₄ in a storage area (not shown) attached thereto, and the detected voltage (temperature T ₀ ) at the reference temperature from the temperature of the piezoelectric vibrator 12, that is, the detected voltage 62 (temperature T). The voltage corresponding to the product of the fourth power of the difference (T−T ₀ ) and the information of Vc ₄ is output. The tertiary voltage generation circuit 22 stores Vc ₃ information in an attached storage area (not shown), and outputs a voltage corresponding to the product of the third power of the difference and the information of Vc ₃ . The secondary voltage generation circuit 24 stores Vc ₂ information in an attached storage area (not shown), and outputs a voltage corresponding to the product of the square of the difference and the information of Vc ₂ . The primary voltage generation circuit 26 stores Vc ₁ information in an attached storage area (not shown), and outputs a voltage corresponding to the product of the difference and the Vc ₁ information. The 0th-order voltage generation circuit 28 stores Vc ₀ information in an attached storage area (not shown), and outputs a voltage corresponding to the Vc ₀ information. Further, these voltages are added in the adding circuit 30 to generate a temperature compensation voltage 64.

  By outputting the temperature compensation voltage 64 thus generated to the oscillation circuit 14, the oscillation circuit 14 can output an oscillation signal 66 having substantially the same oscillation frequency as the reference frequency at any temperature within the operating temperature range. In the present embodiment, each temperature coefficient described above is calculated so as to correspond to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 when the temperature of the piezoelectric vibrator 12 is increased. Further, these temperature coefficients are calculated by a process described later. Furthermore, since A and C have smaller values than B, D, and E, the quaternary voltage generation circuit 20 and the secondary voltage generation circuit 24 may be omitted.

  FIG. 2 shows a circuit diagram of the determination circuit 32. The determination circuit 32 determines whether the temperature of the piezoelectric vibrator 12 increases or decreases based on the increase or decrease of the detection voltage 62 output from the temperature sensor 16. The determination circuit 32 determines that the temperature of the piezoelectric vibrator 12 decreases when the detection voltage 62 increases, and outputs a determination signal associated therewith. On the contrary, when the detection voltage 62 is lowered, it is determined that the temperature of the piezoelectric vibrator 12 is increased, and a determination signal 68 associated therewith is output.

The determination circuit 32 includes a frequency divider 34, an AD converter 36, a delay circuit 38, a DA converter 40, a hysteresis comparator 42, and a 1-bit DA converter 44.
The frequency divider 34, for example, outputs a sampling clock obtained by frequency-dividing and dividing the oscillation signal 66 from the oscillation circuit 14 to the AD converter 36.

  The AD converter 36 converts the analog detection voltage 62 output from the temperature sensor 16 into digital data for each sampling clock period, and outputs the digital data to the delay circuit 38.

  The delay circuit 38 receives the digitized detection voltage 62. Then, the delay circuit 38 holds the digitized detection voltage 62 related to the previous sampling as the past detection voltage 62a and the DA converter 40 until the digitized detection voltage 62 related to the next sampling is input. Can be output.

  The hysteresis comparator 42 compares the past detection voltage 62a that has been analogized and output by the DA converter with the current detection voltage 62, and outputs the magnitude relationship between the low voltage L and the high voltage H. The hysteresis comparator 42 has a positive differential input 42 a connected to the DA converter 40 via a resistor R 1, and a negative differential input 42 b connected to the temperature sensor 16. The positive differential input 42a is connected to the output 42c via a resistor R2 to form a positive feedback circuit. Therefore, the current detection voltage 62 connected to the negative differential input 42b has a hysteresis characteristic with respect to the past detection voltage 62a. This prevents the output 42c of the hysteresis comparator 42 from reacting sensitively to subtle fluctuations in temperature. Here, by setting R2 = 20 × R1, the current detection voltage 62 forms a dead zone of 5% in voltage ratio with respect to the past detection voltage 62a.

  Here, when the temperature of the piezoelectric vibrator 12 falls, the current detection voltage 62 becomes lower than the past detection voltage 62a, and thus the output becomes H. On the contrary, when the temperature of the piezoelectric vibrator 12 rises, the current detection voltage 62 becomes higher than the past detection voltage 62a, so the output becomes L.

  The 1-bit DA converter 44 is connected to the output 42c of the hysteresis comparator 42, and converts the output 42c into a voltage used in a first offset circuit 46 and a second offset circuit 54 described later. In this embodiment, the voltage H is converted to 1.6V, and the voltage L is converted to 0.9V. These two voltages become the determination signal 68. When the voltage is 1.6V, the temperature of the piezoelectric vibrator 12 is increased. When the voltage is 0.9V, the temperature of the piezoelectric vibrator 12 is decreased.

  FIG. 3 shows a circuit diagram of the first offset circuit 46. The first offset circuit 46 includes a differential amplifier circuit 48 that performs differential amplification between the determination signal 68 and the reference voltage (Vref: 1.2 V), and a current corresponding to the current associated with the differential amplification on the reference voltage side. And an operational amplifier 52 that offsets the detection voltage 62 to the negative side by inverting and amplifying the voltage on the current mirror circuit 50 side with the detection voltage 62 as a reference.

  The differential amplifier circuit includes a constant current source 48a, an Nch transistor 48b whose gate is connected to the determination signal 68 side, an Nch transistor 48c whose gate is connected to the reference voltage side, and a gate and a drain that are short-circuited as a diode. Pch transistors 48d and 48e that act. Here, when the voltage of the determination signal 68 is 1.6 V, that is, when the temperature of the piezoelectric vibrator 12 is rising, the Nch transistor 48 b connected to the determination signal 68 side in the differential amplifier circuit 56 is turned on. On the other hand, when the voltage of the determination signal 68 is 0.9 V, that is, when the temperature of the piezoelectric vibrator 12 is decreasing, the Nch transistor 48c connected to the reference voltage side is turned on. Therefore, the current mirror circuit 50 outputs a current 50a to the operational amplifier 52 when the temperature of the piezoelectric vibrator 12 is lowered.

  The operational amplifier 52 decodes the variable resistor 52a for adjusting the amplification ratio of the inverting amplification, the memory 52b for storing the resistance value information of the variable resistor 52a, and the resistance value information stored in the memory 52b. And a decoder (not shown) for adjusting the resistance value. Here, when the temperature of the piezoelectric vibrator 12 is rising, there is no current 50a output from the current mirror circuit 50, so the operational amplifier 52 functions as a buffer circuit. For this reason, the output (detection voltage 62b) of the operational amplifier 52 becomes the same as the input detection voltage 62, and the detection voltage 62b is not offset. On the other hand, when the temperature of the piezoelectric vibrator 12 is decreasing, the current 50a from the current mirror circuit 50 flows through the variable resistor 52a, so that a certain amount of voltage drop occurs in the output of the operational amplifier 52 (detection voltage 62b). . This voltage drop becomes an offset amount with respect to the detection voltage 62b. Here, the detection voltage 62 is offset in the voltage direction. However, since the detection voltage 62 has a linear function temperature characteristic, the detection voltage 62b is apparently offset in the temperature direction. Therefore, although the offset amount is determined by the resistance value of the variable resistor 52a, it is designed to shift the temperature compensation voltage 64 by ΔT described later in the temperature direction corresponding to the hysteresis characteristic of the oscillation frequency of the piezoelectric vibrator 12. Yes.

  FIG. 4 shows a circuit diagram of the second offset circuit 54. The second offset circuit 54 includes a differential amplifier circuit 56 that performs differential amplification between the determination signal 68 and the reference voltage (Vref: 1.2 V), and a current corresponding to the current associated with the differential amplification on the reference voltage side. And an operational amplifier 60 that offsets the temperature compensation voltage 64 to the negative side by inverting and amplifying the voltage on the current mirror circuit 58 side with the temperature compensation voltage 64 as a reference.

  The differential amplifier circuit 56 includes a constant current source 56a, an Nch transistor 56b whose gate is connected to the determination signal 68 side, an Nch transistor 56c whose gate is connected to the reference voltage side, and a short circuit between the gate and the drain. Pch transistors 56d and 56e functioning as Here, when the voltage of the determination signal 68 is 1.6 V, that is, when the temperature of the piezoelectric vibrator 12 is increased, the Nch transistor 56 b connected to the determination signal 68 side in the differential amplifier circuit 56 is turned on. On the contrary, when the voltage of the determination signal 68 is 0.9 V, that is, when the temperature of the piezoelectric vibrator 12 is lowered, the Nch transistor 56c connected to the reference voltage side is turned on. Therefore, the current mirror circuit 58 outputs a current 58a to the operational amplifier 60 when the temperature of the piezoelectric vibrator 12 is lowered.

  The operational amplifier 60 decodes the variable resistor 60a that adjusts the amplification ratio of the inverting amplification, the memory 60b that stores information on the resistance value of the variable resistor 60a, and the resistance value information that is stored in the memory 60b. And a decoder (not shown) for adjusting the resistance value. Here, when the temperature of the piezoelectric vibrator 12 is rising, there is no current 58a output from the current mirror circuit 58, and the operational amplifier 60 functions as a buffer circuit. For this reason, the output of the operational amplifier 60 (temperature compensation voltage 64a) is the same as the input temperature compensation voltage 64, and the temperature compensation voltage 64a is not offset. On the other hand, when the temperature of the piezoelectric vibrator 12 is decreasing, the current 58a from the current mirror circuit 58 flows to the variable resistor 60a, so that a certain amount of voltage drop occurs in the output of the operational amplifier 60 (temperature compensation voltage 64a). appear. This voltage drop becomes an offset amount with respect to the temperature compensation voltage 64a. The offset amount is determined by the resistance value of the variable resistor 60a, and is designed to shift the temperature compensation voltage 64 in the voltage direction by ΔV described later in accordance with the hysteresis characteristic of the oscillation frequency of the piezoelectric vibrator 12. .

  In the present embodiment, the temperature compensation voltage 64 is generated corresponding to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 when the temperature of the piezoelectric vibrator 12 rises. Therefore, the first offset circuit 46 and the second offset circuit 54 are configured such that the offset amount when the temperature rises is zero, that is, no offset is generated, and only the offset amount when the temperature falls is given a certain amount.

FIG. 5 shows the concept of temperature compensation by the temperature compensation circuit of this embodiment. FIG. 5A is a diagram showing hysteresis characteristics with respect to temperature change of the oscillation frequency of the piezoelectric vibrator. FIG. 5B shows a difference (f ₁ −f ₂ , hysteresis amount) in the frequency direction between the temperature characteristic (f ₁ ) when the oscillation frequency of the piezoelectric vibrator is increased and the temperature characteristic (f ₂ ) when the temperature is decreased. FIG. FIG. 5C is a diagram of a temperature characteristic (f ₁ ) when the oscillation frequency of the piezoelectric vibrator rises, and a temperature characteristic (f ₁ ′) obtained by translating the temperature characteristic in the temperature direction and the frequency direction. .

Temperature compensation in the piezoelectric oscillator 10 of the present embodiment will be described. As shown in FIG. 5A, the temperature characteristic (f ₁ ) at the time of temperature rise of the oscillation frequency of the AT-cut crystal resonator does not match the temperature characteristic (f ₂ ) at the time of temperature fall, so Has hysteresis characteristics. At this time, as shown in FIG. 5B, the difference (f ₁ −f) in the frequency direction between the temperature characteristic (f ₁ ) when the oscillation frequency of the piezoelectric vibrator rises and the temperature characteristic (f ₂ ) when the temperature drops. ₂ and hysteresis amount), it can be seen that it has a quadratic function shape. This difference becomes the largest at the reference temperature and becomes almost zero at the low temperature range and the high temperature range. On the other hand, as shown in FIG. 5C, the present inventor draws a temperature characteristic (f ₁ ′) obtained by translating the temperature characteristic (f ₁ ) at the time of temperature rise by a certain amount in the temperature direction and the frequency direction. It was found that hysteresis characteristics similar to 5 (a) were obtained. Further, when the difference in the frequency direction between the temperature characteristic (f ₁ ) before translation and the temperature characteristic (f ₁ ′) after translation is taken, it was found that the shape has a quadratic function shape as described above. Therefore, in the present embodiment, the temperature compensation voltage 64a corresponding to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 when the temperature rises is used as the temperature compensation voltage when the temperature rises. On the other hand, the temperature compensation voltage 64a is offset and used in the temperature direction and the voltage direction so as to approximately correspond to the temperature characteristics of the oscillation frequency of the piezoelectric vibrator 12 when the temperature drops. Therefore, each offset amount is determined by the following process.

  FIG. 6 shows a flowchart of a calculation process of the offset amount in the temperature direction and the offset amount in the voltage direction of the temperature compensation voltage. The temperature direction offset amount (ΔT) and the voltage direction offset amount (ΔV) of the temperature compensation voltage 64a are calculated as follows.

  First, a voltage generator (not shown) that outputs a predetermined voltage Vh is connected to an input terminal (not shown) of a temperature compensation voltage of the oscillation circuit 14 to which the piezoelectric oscillator 10 of the present embodiment is connected. The oscillation circuit 14 is housed in a chamber (not shown) in which an arbitrary temperature can be set, and the piezoelectric vibrator 12 is oscillated by the oscillation circuit 14.

Then, while increasing the temperature of the chamber (not shown), that is, the temperature of the piezoelectric vibrator 12, Vh is adjusted so as to oscillate at the same oscillation frequency as the reference frequency, and this is measured as an ideal compensation voltage. In the present embodiment, the first temperature point (set minimum temperature, eg: −25 ° C.), the second temperature point (eg: 0 ° C.), the third temperature point (reference temperature, eg: + 25 ° C.), the fourth temperature point ( Example: + 55 ° C.), the temperature is raised in the order of the fifth temperature point (set maximum temperature, eg: + 75 ° C.), and the ideal compensation voltage Vh is measured at each temperature point. Then, in the PC or the like, the relationship between each temperature point and Vh is input to the above equation 2 to form simultaneous equations, and the coefficients Vc ₄ , Vc ₃ , Vc ₂ , Vc ₁ , Vc ₀ corresponding to the temperature coefficients are calculated. .

In the same manner as described above, the information on Vc ₄ is stored as information on the fourth-order temperature coefficient in a storage area (not shown) attached to the fourth-order voltage generation circuit 20. The information on Vc ₃ is stored in a storage area (not shown) attached to the tertiary voltage generation circuit 22 as information on the third-order temperature coefficient. The information of Vc ₂ is stored as a secondary temperature coefficient information in a storage area (not shown) attached to the secondary voltage generation circuit 24. Information on Vc ₁ is stored in a storage area (not shown) attached to the primary voltage generation circuit 26 as information on the primary temperature coefficient. The information of Vc ₀ is stored in the storage area (not shown) attached to the 0th-order voltage generation circuit 28 as 0th-order temperature coefficient information.

  Next, the temperature of the piezoelectric vibrator 12 is lowered from + 75 ° C. to + 25 ° C. (reference temperature), and Vh is adjusted so that the oscillation frequency is the same as the reference frequency at the reference temperature at the time of the temperature rise. taking measurement.

Here, when Equation 2 is translated by ΔT in the temperature direction and ΔV in the voltage direction, the voltage Vh ′ is as follows.

Here, Vh measured at −25 ° C. at the time of temperature rise is Vh ₁ , Vh measured at + 25 ° C. at the time of temperature fall is Vh ₂ , Vh measured at + 75 ° C. at the time of temperature rise is Vh ₃ , It is assumed that T ₁ = −25 ° C., T ₂ = + 25 ° C., and T ₃ = + 75 ° C. Therefore, in a PC or the like, ΔT and ΔV are calculated so that the difference between Vh _k (k = 1, 2, 3) and Equation 3, that is, the following equation is calculated, and the value of Equation 4 is minimized.

  Since there are two variables ΔT and ΔV in Equation 4, the minimum value of Equation 4 when ΔV is swept (changed) while ΔV is fixed in a PC or the like and ΔV is fixed to a certain value. And ΔT at that time is calculated. Then, ΔV is swept (changed) in a certain range within a certain range (for example, −15 mV to +15 mV), and the minimum value and ΔT of Formula 4 corresponding to ΔV fixed for each sweep are sequentially obtained. Then, the minimum value of Expression 4 and the ΔV and ΔT at that time, at which the value of Expression 4 calculated in the entire range of ΔV becomes the minimum from the minimum value group, are extracted. Information obtained by converting ΔT calculated in this way into a corresponding resistance value is stored in the memory 52b of the first offset circuit 46, and information converted into a resistance value corresponding to ΔV is stored in the memory of the second offset circuit 54. Store in 60b.

  FIG. 7 shows the effect of the temperature compensation circuit of this embodiment. FIG. 7A shows a graph when temperature compensation is performed using a temperature compensation voltage corresponding to the temperature characteristic of the oscillation frequency when the temperature of the piezoelectric vibrator is increased. FIG. 7B shows a graph in the case where temperature compensation is performed by shifting the temperature compensation voltage corresponding to the temperature characteristic of the oscillation frequency when the temperature of the piezoelectric vibrator is raised to the temperature direction and the voltage direction when the temperature is lowered.

  The operation of the piezoelectric oscillator 10 according to the above configuration will be described. As shown in FIG. 5A, the oscillation frequency of the piezoelectric vibrator 12 does not have the same temperature characteristic when the temperature rises and falls, and has a hysteresis characteristic. Therefore, as shown in FIG. 7A, when the temperature compensation voltage 64 is generated corresponding to the temperature characteristic of the oscillation frequency when the temperature of the piezoelectric vibrator 12 is increased, the temperature of the piezoelectric vibrator 12 is increased. The temperature compensation is well performed. However, on the contrary, temperature compensation when the temperature of the piezoelectric vibrator 12 is lowered is not satisfactorily performed, and a frequency deviation of about 500 ppb occurs in the operating temperature range. When such a frequency deviation occurs in a device having a GPS function assumed in the present embodiment, the positioning performance is adversely affected as described in the prior art.

  On the other hand, as shown in FIG. 7B, in the piezoelectric oscillator 10 of the present embodiment, the temperature compensation voltage 64 (temperature compensation voltage 64a) is an inverse characteristic of the temperature characteristic when the oscillation frequency of the piezoelectric vibrator 12 rises. Therefore, the temperature compensation of the oscillation signal output from the oscillation circuit 14 can be performed satisfactorily. Further, when the temperature drops, the temperature compensation voltage 64 is shifted by ΔT in the temperature direction and ΔV in the voltage direction in order to generate a temperature compensation voltage corresponding to the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 when the temperature drops. Thereby, the temperature compensation voltage 64a corresponding to the temperature characteristic when the oscillation frequency of the piezoelectric vibrator 12 is lowered is approximately generated. Further, the temperature compensation voltage 64a generated approximately can satisfactorily compensate the temperature even when the temperature of the piezoelectric vibrator 12 is lowered.

  In the present embodiment, the temperature compensation voltage 64 is generated corresponding to the temperature characteristic when the oscillation frequency of the piezoelectric vibrator 12 is increased. Conversely, it can be generated corresponding to the temperature characteristic when the piezoelectric vibrator 12 is decreasing. is there. First, in order to obtain the temperature compensation voltage, the temperature of the piezoelectric vibrator 12 is lowered in the order of + 75 ° C., + 55 ° C., + 25 ° C., 0 ° C., and −25 ° C. as described above. Then, Vh in Expression 2 is adjusted so that the oscillation frequency of the piezoelectric vibrator 12 becomes the reference frequency of the piezoelectric vibrator 12 at the reference temperature when the temperature is lowered at each temperature, and this is measured as an ideal compensation voltage.

Next, as described above, the values of Vc ₄ , Vc ₃ , Vc ₂ , Vc ₁ , Vc ₀ in Equation 2 are calculated, and each value is stored in a storage area (not shown) attached to the corresponding temperature compensation voltage generator 18. The temperature compensation voltage 65 can be output. Then, the temperature of the piezoelectric vibrator 12 is increased to + 25 ° C., and Vh in Expression 2 is adjusted so that the oscillation frequency of the piezoelectric vibrator 12 becomes the reference frequency of the piezoelectric vibrator 12 at the reference temperature when the temperature is lowered. This is measured as an ideal compensation voltage. Then, ΔT and ΔV are calculated using the Vh at −25 ° C. when the temperature is lowered, + 25 ° C. when the temperature is raised, and + 75 ° C. when the temperature is lowered so that the value of Equation 4 is minimized as described above. After calculating ΔT and ΔV in this way, information on the resistance value corresponding to ΔT is stored in the memory 52b of the first offset circuit 46, which will be described later, and information on the resistance value corresponding to ΔV is described later. It memorize | stores in the memory 60b of the 2nd offset circuit 54 used as a modification.

  FIG. 8 shows a modification of the first offset circuit. The first offset circuit 70 includes a differential amplifier circuit 72 that performs differential amplification between the determination signal 68 and the reference voltage (Vref: 1.2 V), and a current corresponding to the current associated with the differential amplification on the reference voltage side. The first current mirror circuit 74 that generates the current, the second current mirror circuit 76 that generates the pull-in current 76a corresponding to the current output from the first current mirror circuit 74, and the pull-in based on the detection voltage 62 And an operational amplifier 78 that offsets the detection voltage 62 to the plus side by inverting and amplifying the voltage on the second current mirror circuit 76 side based on the current 76a.

  The differential amplifier circuit 72 includes a constant current source 72a, an Nch transistor 72b whose gate is connected to the determination signal 68 side, an Nch transistor 72c whose gate is connected to the reference voltage side, and a gate and a drain that are short-circuited. Pch transistors 72c and 72d functioning as Here, when the voltage of the determination signal 68 is 0.9 V, that is, when the temperature of the piezoelectric vibrator 12 is lowered, the Nch transistor 72c connected to the reference voltage side in the differential amplifier circuit 72 is turned on. On the contrary, when the voltage of the determination signal 68 is 1.6 V, that is, when the temperature of the piezoelectric vibrator 12 is rising, the Nch transistor 72b connected to the determination signal 68 side becomes conductive. Therefore, the first current mirror circuit 74 outputs a current to the second current mirror circuit 76 when the temperature of the piezoelectric vibrator 12 is lowered. At this time, the second current mirror circuit 76 generates a drawing current 76 a corresponding to the current output from the first current mirror circuit 74.

  The operational amplifier 78 decodes the variable resistor 78a for adjusting the amplification ratio of the inverting amplification, the memory 78b for storing the resistance value information of the variable resistor 78a, and the resistance value information stored in the memory 78b. And a decoder (not shown) for adjusting the resistance value. Here, when the temperature of the piezoelectric vibrator 12 is decreasing, there is no drawing current 76a to the second current mirror circuit 76, so the operational amplifier 78 functions as a buffer circuit. Therefore, the output (detection voltage 62a) of the operational amplifier 78 is the same as the input detection voltage 62, and the detection voltage 62a is not offset. On the other hand, when the temperature of the piezoelectric vibrator 12 is decreasing, a drawing current 76a to the second current mirror circuit 76 flows from the output of the operational amplifier 78 via the variable resistor 78a. For this reason, a certain amount of voltage rise occurs at the output of the operational amplifier 78 (detection voltage 62c). This voltage rise becomes an offset amount with respect to the detection voltage 62c. This offset amount is determined by the resistance value of the variable resistor 78a, and is designed to shift the temperature compensation voltage 65 by the above ΔT in the temperature direction corresponding to the hysteresis characteristic of the oscillation frequency of the piezoelectric vibrator 12. .

  FIG. 9 shows a modification of the second offset circuit. The second offset circuit 80 includes a differential amplifier circuit 82 that performs differential amplification between the determination signal 68 and the reference voltage (Vref: 1.2 V), and a current corresponding to the current accompanying the differential amplification on the reference voltage side. The first current mirror circuit 84 for generating the current, the second current mirror circuit 86 for generating the drawing current 86a corresponding to the current output from the first current mirror circuit 84, and the temperature compensation voltage 65 as a reference. And an operational amplifier 88 for offsetting the temperature compensation voltage 65 to the plus side by inverting and amplifying the voltage on the second current mirror circuit 86 side based on the drawing current 86a.

  The differential amplifier 82 includes a constant current source 82a, an Nch transistor 82b whose gate is connected to the determination signal side, an Nch transistor 82c whose gate is connected to the reference voltage side, and a gate and a drain that are short-circuited as a diode. Pch transistors 82d and 82e that act. Here, when the voltage of the determination signal 68 is 0.9 V, that is, the temperature of the piezoelectric vibrator 12 is lowered, the Nch transistor 82c connected to the reference voltage side in the differential amplifier circuit 82 is turned on. Conversely, when the voltage of the determination signal 68 is 1.6 V, that is, when the temperature of the piezoelectric vibrator 12 is rising, the Nch transistor 82b connected to the determination signal 68 side is turned on. Therefore, the first current mirror circuit 84 outputs a current to the second current mirror circuit 86 when the temperature of the piezoelectric vibrator 12 is lowered. At this time, the second current mirror circuit 86 generates a drawing current 86 a corresponding to the current output from the first current mirror circuit 84.

  The operational amplifier 88 decodes the variable resistor 88a for adjusting the amplification ratio of the inverting amplification, the memory 88b for storing the resistance value information of the variable resistor 88a, and the resistance value information stored in the memory 88b. And a decoder (not shown) for adjusting the resistance value. Here, when the temperature of the piezoelectric vibrator 12 is decreasing, there is no drawing current 86a output to the second current mirror circuit 86, so that the operational amplifier 88 functions as a buffer circuit. Therefore, the output of the operational amplifier 88 (temperature compensation voltage 65a) is the same as the input temperature compensation voltage 65, and the temperature compensation voltage 65a is not offset. On the other hand, when the temperature of the piezoelectric vibrator 12 is rising, a drawing current 86a to the second current mirror circuit 86 flows from the output of the operational amplifier 88 via the variable resistor 88a. For this reason, a certain amount of voltage rise occurs at the output of the operational amplifier 88 (temperature compensation voltage 65a). This voltage rise becomes an offset amount with respect to the temperature compensation voltage 65a. The offset amount is determined by the resistance value of the variable resistor 88a, and is designed to shift the temperature compensation voltage 65 in the voltage direction by the above-described ΔV in accordance with the hysteresis characteristic of the oscillation frequency of the piezoelectric vibrator 12. .

  In the present embodiment, the temperature compensation voltages 64 and 65 are generated corresponding to the temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator 12 rises or falls. However, for example, a temperature compensation voltage corresponding to a temperature characteristic that is an intermediate value between the temperature characteristic when rising and the temperature characteristic when falling is generated, and ΔT and ΔV when rising and ΔT and ΔV when falling are calculated. Then, the offset amount at the time of temperature rise and temperature fall is stored in the memory (not shown) of the first and second offset circuits (not shown) which can be varied, respectively, and the detection voltage 62 and The offset amount of the temperature compensation voltage may be adjusted.

  Further, in the calculation based on Equation 4, ΔV is changed in a state where ΔT is fixed in a PC or the like, and the minimum value of Equation 4 when ΔT is fixed to a certain value and ΔV at that time are calculated. Then, ΔT is swept (changed) in a certain range with a constant step size, and the minimum value and ΔV of Equation 4 corresponding to ΔT fixed for each sweep are sequentially obtained. Then, the minimum value of the value of Formula 4 that minimizes the value of Formula 4 calculated over the entire range of ΔT, and ΔV and ΔT at that time may be extracted.

  Furthermore, it goes without saying that the piezoelectric oscillator 10 capable of temperature compensation corresponding to the hysteresis characteristics of the piezoelectric vibrator 12 can be formed by incorporating the offset circuit for a piezoelectric oscillator of this embodiment into the above-described piezoelectric oscillator.

  As described above, according to the piezoelectric oscillator offset circuit and the piezoelectric oscillator temperature compensation method according to the present embodiment, firstly, based on the detection voltage 62 input via the first offset circuits 46 and 70. The temperature compensation voltages 64 and 65 output from the temperature compensation voltage generation circuit 18 shift in the temperature direction by the offset amount of the detection voltage 62 in the first offset circuit 46. Further, the temperature compensation voltages 64 a and 65 a output from the second offset selection circuits 54 and 80 are shifted in the voltage direction by the offset amount of the temperature compensation voltages 64 and 65 in the second offset circuits 54 and 80. Therefore, the temperature compensation voltages 64a and 65a after the shift are in contact with each other in the high temperature region and the low temperature region before the shift, and the temperature compensation voltages 64 and 65 before the shift between the high temperature region and the low temperature region. And a region surrounded by the temperature compensated voltages 64a and 65a after the shift occurs. For this reason, a temperature characteristic very similar to the hysteresis characteristic of the piezoelectric vibrator 12 can be obtained. Accordingly, the temperature compensation voltages 64 and 65 having one temperature characteristic are shifted in accordance with the temperature characteristic of the oscillation frequency of the piezoelectric vibrator 12 when the temperature of the piezoelectric vibrator 12 rises and falls, and the hysteresis of the piezoelectric vibrator 12 is detected. Temperature compensation corresponding to the characteristics becomes possible.

  Secondly, the offset amount can be set to a constant amount at one of the rise and fall of the temperature of the piezoelectric vibrator 12 and set to zero at the other. Therefore, the temperature compensation can be performed with high accuracy by matching the temperature coefficient input to the temperature compensation voltage generation circuit 18 in accordance with the one temperature characteristic. In the one case, it is possible to pass the detection voltage 62 and the temperature compensation voltages 64 and 65 to the subsequent stage without operating the first offset circuits 46 and 70 and the second offset selection circuits 54 and 80. . Therefore, the first offset circuits 46 and 70 and the second offset selection circuits 54 and 80 do not require a configuration that realizes one of the offset amounts when the temperature of the piezoelectric vibrator 12 increases or decreases, and the configuration is simplified. And cost can be reduced.

  Thirdly, the offset amounts (ΔT, ΔV) set in the detection voltage 62 and the temperature compensation voltage 64 are respectively the minimum set temperature and the maximum set temperature when the temperature of the piezoelectric vibrator 12 rises, and the piezoelectric vibration. In the temperature compensation voltage 64 at the reference temperature when the temperature of the child 12 is lowered, the sum of the differences in the voltage direction caused by the offset amount is minimized, or the set minimum temperature when the temperature of the piezoelectric vibrator 12 is lowered By calculating each of the set maximum temperature and the temperature compensation voltage 65 at the reference temperature when the temperature of the piezoelectric vibrator 12 is increased so that the sum of the differences in the voltage direction caused by the offset amount is minimized, A temperature compensation voltage 6 corresponding to the hysteresis characteristic of the piezoelectric vibrator 12 with high accuracy in a set temperature range with the temperature as the lower limit and the set maximum temperature as the upper limit. Thus, the piezoelectric oscillator 10 capable of outputting 4, 65 is obtained.

  In addition, according to the piezoelectric oscillator according to the present embodiment, the temperature compensation voltage having one temperature characteristic is shifted in accordance with the temperature characteristic of the oscillation frequency of the piezoelectric vibrator when the temperature of the piezoelectric vibrator 12 rises and falls. Thus, a piezoelectric oscillator capable of temperature compensation corresponding to the hysteresis characteristics of the piezoelectric vibrator is obtained.

DESCRIPTION OF SYMBOLS 10 ......... Temperature compensation circuit, 12 ......... Piezoelectric vibrator, 14 ......... Oscillation circuit, 16 ......... Temperature sensor, 18 ...... Temperature compensation voltage generation circuit, 20 ......... Fourth voltage generation circuit, 22... Tertiary voltage generation circuit 24... Secondary voltage generation circuit 26... Primary voltage generation circuit 28... 0th voltage generation circuit 30. Determining circuit 34... Divider 36... AD converter 38 38 Delay circuit 40 DA converter 42 Hysteresis comparator 42 a Differential input 42 b ...... Differential input, 42c ... Output, 44 ... 1-bit DA converter, 46 ... First offset circuit, 48 ... Differential amplifier circuit, 48a ... Constant current source, 48b ... …… Nch transistor, 48c ……… Nch transistor, 8d ... Pch transistor, 48e ... Pch transistor, 50 ... Current mirror circuit, 50a ... Current, 52 ... Operational amplifier, 52a ... Variable resistance, 52b ... Memory, 54 ... ... Second offset circuit 56 ......... Differential amplifier circuit 56a ......... Constant current source, 56b ......... Nch transistor, 56c ......... Nch transistor, 56d ...... Pch transistor, 56e ......... Pch Transistor, 58... Current mirror circuit, 58a ... Current, 60 ... Operational amplifier, 60a ... Variable resistor, 60b ... Memory, 62 ... Detection voltage, 62a ... Detection voltage, 62b ......... Detection voltage, 64 ......... Temperature compensation voltage, 64a ......... Temperature compensation voltage, 65 ......... Temperature compensation voltage, 65a ......... Temperature compensation voltage, 66 ... Oscillation signal 68 ......... determination signal, 70 ......... first offset circuit, 72 ......... differential amplifier circuit, 72a ......... constant current source,
72b... Nch transistor, 72c ... Nch transistor, 72d ... Pch transistor, 72e ... Pch transistor 74 ... First current mirror circuit, 76 ... Second current mirror circuit, 76a ......... Current drawn, 78 ......... Operational amplifier, 78a ......... Variable resistor, 78b ......... Memory, 80 ......... Second offset circuit, 82 ......... Differential amplifier circuit, 84 ......... First Current mirror circuit 86 ......... second current mirror circuit 86a ..... drawing current 88 .... op-amp, 88a .... variable resistor, 88b .... memory, 100 .... temperature compensated oscillator. 102 ......... Temperature detection circuit 104 ......... Approximate cubic curve generation circuit 106 ... First programmable gain amplifier 108 ... Second program Maburugein amplifier, 110 ......... constant voltage generating circuit, 112 ......... third programmable gain amplifier, 114 ......... adder circuit, 116 ......... voltage controlled crystal oscillator.

Claims (7)

An oscillation circuit that oscillates a piezoelectric vibrator, outputs an oscillation signal, and performs temperature compensation of the oscillation frequency of the oscillation signal by a temperature compensation voltage corresponding to a temperature characteristic of an oscillation frequency of the input piezoelectric vibrator; and the piezoelectric A temperature detection unit that outputs a detection voltage corresponding to the temperature of the vibrator, and a temperature compensation voltage that is interposed between the oscillation circuit and the temperature detection unit and outputs the temperature compensation voltage corresponding to the detection voltage. A piezoelectric oscillator offset circuit attached to a piezoelectric oscillator having a generator circuit,
The temperature compensation is interposed between the temperature detection means and the temperature compensation voltage generation circuit, and offsets the detection voltage in accordance with temperature characteristics when the oscillation frequency rises and falls, respectively. A first offset circuit for offsetting the voltage in the temperature direction;
Secondly, the temperature compensation voltage is offset between the temperature compensation voltage generation circuit and the oscillation circuit, and offsets the temperature compensation voltage in the voltage direction corresponding to the temperature characteristics when the temperature of the oscillation frequency rises and falls, respectively. And an offset circuit for the piezoelectric oscillator. A determination circuit for detecting an increase / decrease in the detection voltage and outputting a determination signal for determining an increase / decrease in temperature of the piezoelectric vibrator;
The temperature compensated voltage generation circuit includes:
The temperature compensation voltage is output corresponding to one of the temperature characteristics when the temperature of the piezoelectric vibrator rises and falls,
The first offset circuit includes:
An offset amount of the detection voltage corresponding to the other temperature characteristic opposite to the one temperature characteristic is set, and the detection voltage is offset by an offset amount of the detection voltage based on the determination signal,
The second offset circuit includes:
2. The offset amount of the temperature compensation voltage corresponding to the other temperature characteristic is set, and the temperature compensation voltage input based on the determination signal is offset by the offset amount of the temperature compensation voltage. An offset circuit for a piezoelectric oscillator according to 1. The offset amount set for the detection voltage and the temperature compensation voltage is:
In the temperature compensation voltage at the minimum set temperature and the maximum set temperature when the temperature of the piezoelectric vibrator increases and the reference temperature when the temperature of the piezoelectric vibrator drops, the sum of the differences in the voltage direction caused by the offset amount is the minimum So that
Alternatively, in the temperature compensation voltage of the set minimum temperature and the set maximum temperature when the temperature of the piezoelectric vibrator decreases and the reference temperature when the temperature of the piezoelectric vibrator rises, the sum of the differences in the voltage direction caused by the offset amount is 3. The piezoelectric oscillator offset circuit according to claim 2, wherein the offset circuits are calculated so as to be minimized.   4. A piezoelectric oscillator comprising the piezoelectric oscillator offset circuit according to claim 1 incorporated in the piezoelectric oscillator. An oscillation circuit that oscillates a piezoelectric vibrator, outputs an oscillation signal, and performs temperature compensation of the oscillation frequency of the oscillation signal by a temperature compensation voltage corresponding to a temperature characteristic of an oscillation frequency of the input piezoelectric vibrator; and the piezoelectric Temperature detection means for outputting a detection voltage corresponding to the temperature of the vibrator, and temperature compensation voltage generation that is interposed between the oscillation circuit and the temperature means and outputs the temperature compensation voltage corresponding to the detection voltage A temperature compensation method for a piezoelectric oscillator having a circuit,
The temperature compensation voltage is offset in the voltage direction corresponding to the temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator rises and falls, respectively,
A piezoelectric oscillator characterized in that the temperature compensation voltage is offset in the temperature direction by offsetting the detection voltage corresponding to the temperature characteristics of the oscillation frequency when the temperature of the piezoelectric vibrator rises and falls, respectively. Temperature compensation method. The temperature compensation voltage generation circuit outputs a voltage having one of temperature characteristics when the temperature of the piezoelectric vibrator rises and falls based on the detection voltage to the oscillation circuit,
A detection signal for detecting an increase / decrease in the detection voltage and determining an increase / decrease in temperature of the piezoelectric vibrator is output,
The temperature compensation voltage is
Offset by the offset amount of the temperature compensation voltage set corresponding to the other temperature characteristic opposite to the one temperature characteristic based on the determination signal,
The detected voltage is
6. The temperature compensation method for a piezoelectric oscillator according to claim 5, wherein an offset amount of the detected voltage set corresponding to the other temperature characteristic is offset based on the determination signal. The offset amount set for the detection voltage and the temperature compensation voltage is:
In the temperature compensation voltage at the minimum set temperature and the maximum set temperature when the temperature of the piezoelectric vibrator increases and the reference temperature when the temperature of the piezoelectric vibrator drops, the sum of the differences in the voltage direction caused by the offset amount is the minimum So that
Alternatively, in the temperature compensation voltage at the set minimum temperature and the set maximum temperature when the temperature of the piezoelectric vibrator decreases and the reference temperature when the temperature of the piezoelectric vibrator rises, the sum of the differences in the voltage direction caused by the offset amount is The temperature compensation method for a piezoelectric oscillator according to claim 6, wherein each temperature is calculated so as to be minimized.