JP2013115496A - Oscillator and elastic surface-wave element for oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact oscillator producing a stable frequency signal over a wide temperature range, and to provide an elastic surface-wave element for this oscillator.SOLUTION: A first resonator 2 and a second resonator 3 are arranged on a common piezoelectric substrate 1, and in order to use a signal output from the second resonator 3 as a signal for temperature compensation, the resonance frequencies f1, f2 of the first resonator 2 and the second resonator 3 respectively are set to values different from each other. More specifically, a period length λ1 of an IDT electrode 12 in the first resonator 2 and a period length λ2 of the IDT electrode 12 in the second resonator 3 are set to values different from each other, and the film thicknesses t1, t2 of these IDT electrodes 12 are set to dimensions different from each other.

Description

  The present invention relates to an oscillator that outputs a set frequency signal and a surface acoustic wave device used in the oscillator.

  A piezoelectric vibrator (quartz crystal vibrator) is widely used in an oscillator as an oscillation source that outputs a reference frequency (set frequency) signal. As one of such oscillators, in order to increase the stability of the output signal, for example, a quartz resonator is housed in a thermostatic chamber equipped with a temperature sensor and a heater, so that the influence of the ambient temperature is suppressed. A temperature-controlled crystal oscillator (OCXO) is known.

  Here, with the recent downsizing and higher frequency of electronic devices, the oscillators are also required to be downsized. Therefore, an oscillator using SAW (Surface Acoustic Wave) instead of an oscillator using a crystal resonator has been studied. Specifically, for example, a 1-port SAW resonator is formed on a piezoelectric substrate, and this resonator is applied to an oscillator. However, even with a resonator using SAW, if temperature stability is to be obtained, a constant temperature bath is still required, and therefore miniaturization is difficult. In addition, when a thermostatic bath is used, it is necessary to supply power to the heater, and furthermore, the heat input efficiency to the resonator by the heater is not so good, so that it is difficult to save power in the oscillator. Furthermore, since the temperature sensor for the thermostatic chamber is arranged away from the resonator, the resonator may be at a temperature different from the temperature at which the reference frequency signal can be output.

  Patent Document 1 describes a technique in which a small-sized oscillator is configured without using a thermostatic chamber by arranging two of the crystal resonators described above and using one of these crystal resonators as a temperature detection sensor. Has been. In Patent Documents 2 and 3, a plurality of surface acoustic wave elements (resonators) M1 and M2 are arranged on a common substrate, and one of these surface acoustic wave elements is inclined with respect to the other. A technique for arranging and inputting / outputting signals in parallel to each surface acoustic wave element is described. However, these Patent Documents 1 to 3 do not describe a small oscillator having excellent temperature stability.

JP2007-108170 JP-A-53-145595 (Fig. 9) Japanese Patent Application Laid-Open No. 2004-274696 (FIG. 15)

  The present invention has been made in view of such circumstances, and an object thereof is to provide a small-sized oscillator capable of obtaining a stable frequency signal over a wide temperature range and a surface acoustic wave element for the oscillator. It is in.

The oscillator of the present invention is
A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first oscillation circuit and a second oscillation circuit respectively connected to the first resonator and the second resonator;
At least one of the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used for temperature detection.

The oscillator may be configured as follows.
A signal corresponding to the frequency of the output signal of the second oscillation circuit is used as a temperature detection signal, or the difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used. A configuration in which a corresponding signal is used as a temperature detection signal, and a temperature variation of the first oscillation frequency is compensated based on the temperature detection signal.
The oscillator is configured as a thermostatic oscillator,
A signal corresponding to the frequency of the output signal of the second oscillation circuit is used as a temperature detection signal, or the difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used. The structure which uses the corresponding signal as a temperature detection signal, and controls the power supply of the heating source of the thermostat based on the temperature detection signal.
The first resonator and the second resonator are configured such that the period lengths of the electrode fingers in each IDT electrode are set to different values. The first resonator and the second resonator are configured such that film thicknesses of electrode fingers in each IDT electrode are set to different dimensions. The first resonator and the second resonator are one of the first resonator and the second resonator so that the propagation directions of the surface acoustic waves on the piezoelectric substrate are different from each other. A configuration in which the other resonator is inclined with respect to the other resonator.

The oscillator of the present invention is
A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first oscillation circuit and a second oscillation circuit respectively connected to the first resonator and the second resonator;
A frequency difference detection unit that detects a difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit;
The present invention is characterized in that an oscillation output having a frequency corresponding to the frequency difference obtained by the frequency difference detection unit is obtained.

The surface acoustic wave device of the present invention is
A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first signal port formed on the piezoelectric substrate for connecting the first resonator to a first oscillation circuit;
A second signal port formed on the piezoelectric substrate and provided independently of the first signal port to connect the second resonator to a second oscillation circuit; It is characterized by that.

  In the present invention, the first resonator and the second resonator are disposed on a common piezoelectric substrate, and the resonance frequencies of the first resonator and the second resonator are shifted from each other. Therefore, by using at least one of the output signals of the first oscillation circuit and the second oscillation circuit connected to the first resonator and the second resonator, respectively, for temperature detection, a wide temperature range can be obtained. Thus, it is possible to obtain a small oscillator and a surface acoustic wave device that can output a stable frequency signal over a wide range.

It is a top view which shows an example of the surface acoustic wave element of this invention. It is a longitudinal cross-sectional view which shows the said surface acoustic wave element. It is a schematic diagram which shows the frequency characteristic of the said surface acoustic wave element. It is a schematic diagram which shows the temperature change of the frequency characteristic of the said surface acoustic wave element. It is a circuit diagram which shows roughly an example of the oscillator of this invention with which the said surface acoustic wave element is applied. It is a top view which shows the other example of the said surface acoustic wave element. FIG. 6 is a circuit diagram schematically showing another example of the oscillator. FIG. 5 is a circuit diagram schematically showing another example of the oscillator.

  An example of an embodiment of a surface acoustic wave element used in the oscillator of the present invention will be described with reference to FIGS. As shown in FIG. 1, the surface acoustic wave element includes two SAW resonators 2 and 3 disposed on a common piezoelectric substrate 1. As described below, these SAW resonators 2 are provided. 3 are configured such that the resonance frequencies in 3 are different from each other. In this example, the piezoelectric substrate 1 is made of quartz that is an ST cut plate. In FIG. 1, when the propagation direction of the elastic wave (surface acoustic wave) on the piezoelectric substrate 1 is referred to as the left-right direction and the direction orthogonal to the propagation direction of the elastic wave is referred to as the front-rear direction, the SAW resonator 2 and the SAW resonator 3 are On the piezoelectric substrate 1, it is arrange | positioned at the near side and the back | inner side, respectively. In the following description, these SAW resonator 2 and SAW resonator 3 will be referred to as “first resonator” and “second resonator” for convenience.

  The first resonator 2 includes an IDT (Inter Digital Transducer) electrode 12 and reflectors 13 and 13 disposed on the left and right sides of the IDT electrode 12, respectively. The IDT electrode 12 has a pair of bus bars 14 and 14 formed so as to extend in the left-right direction and be parallel to each other, and comb teeth so as to alternately cross from one side of the bus bars 14 to the other side. And a plurality of electrode fingers 15 arranged in a shape. In this example, two electrode fingers 15, 15 extending adjacent to each other are periodically arranged in the left-right direction, the width dimension of these two electrode fingers 15, 15 and the separation between the electrode fingers 15, 15. The cycle length λ1 consisting of dimensions is, for example, about 4.3 μm.

  One end side of the extraction electrode 16 extending from the end region of the piezoelectric substrate 1 is connected to, for example, the front bus bar 14 of the pair of bus bars 14, 14. The other end side of the extraction electrode 16 is connected to the end portion. It is connected to the first signal port 21a formed in the region. Similarly, the bus bar 14 on the back side is connected to the first signal port 21 b formed on the end side of the piezoelectric substrate 1 through the extraction electrode 16.

  The reflectors 13 and 13 each include a pair of grating bus bars 17 and 17 and a plurality of grating electrode fingers 18 disposed so as to connect the grating bus bars 17 and 17 to each other. The grating electrode fingers 18 are also arranged so as to have the above-described cycle length λ1. As shown in FIG. 2, the film thickness t1 of the IDT electrode 12 and the reflectors 13 and 13 is, for example, 0.14 μm. Accordingly, the resonance frequency f1 of the first resonator 2 is, for example, 315 MHz. 2 shows a longitudinal sectional view of the piezoelectric substrate 1 cut along the line AA in FIG.

  Similar to the first resonator 2, the second resonator 3 includes an IDT electrode 12 and reflectors 13 and 13 disposed on both the left and right sides of the IDT electrode 12. The bus bar 14 on the back side of the IDT electrode 12 in the second resonator 3 is connected to the second signal port 22 a provided on the end side of the piezoelectric substrate 1 through the extraction electrode 16. Similarly, the bus bar 14 on the near side of the IDT electrode 12 in the second resonator 3 is connected to the second signal port 22b provided on the end side of the piezoelectric substrate 1 through the extraction electrode 16 in the same manner. Yes. Therefore, these second signal ports 22a and 22b are provided independently of the first signal ports 21a and 21b (so as not to conduct). An oscillation circuit 23 (24), which will be described later, is connected to the signal ports 21a and 21b (22a and 22b) via, for example, a wire (not shown).

  In the second resonator 3, the period length λ2 of the electrode finger 15 and the grating electrode finger 18 is different from the period length λ1 of the first resonator 2, for example, 4.5 μm. The film thickness t2 of the IDT electrode 12 in the second resonator 3 is a dimension different from the film thickness t1 in the first resonator 2, for example, 0.15 μm. Therefore, the resonance frequency f2 of the second resonator 3 is, for example, 300 MHz (≠ f1) as shown in FIG. At this time, since the two first resonators 2 and the second resonator 3 are formed on the common piezoelectric substrate 1, the temperature of the atmosphere in which the resonators 2 and 3 are placed is almost the same. Therefore, as shown in FIG. 4, the temperature characteristics of each of the resonators 2 and 3 (the degree to which the resonance frequency changes with respect to the temperature change) are also aligned with each other. 3 and 4 schematically show the characteristics of the respective resonators 2 and 3.

  Next, a method for manufacturing such a surface acoustic wave element will be briefly described by taking as an example the case of using a lift-off technique. First, for example, a second resonator 3 is formed by a photolithography method in which a metal film made of, for example, aluminum (Al) is formed on the piezoelectric substrate 1 and then dry etching is performed through a resist mask. Then, another resist mask is formed on the piezoelectric substrate 1 so as to cover the second resonator 3, and the first resonator 2, the extraction electrode 16, and the signal port 21 are formed by exposure processing and development processing. , 22 are formed in the other resist mask so that the regions corresponding to. Thereafter, for example, a metal film is embedded in the opening by vapor deposition of aluminum, and then the piezoelectric substrate 1 is immersed in an organic solvent or an alkaline aqueous solution to remove the resist mask together with an unnecessary metal film above the resist mask. As a result, the surface acoustic wave device shown in FIG. 1 is formed.

  At this time, when a surface acoustic wave device is manufactured using etching instead of the lift-off technique, the resonators 2 and 3 are first formed so as to have the same film thickness by photolithography. Subsequently, for example, a resist mask is formed so as to cover the second resonator 3 and expose the first resonator 2, and then the film thickness t 1 of the first resonator 2 becomes the above-described dimension. Then, the first resonator 2 is wet-etched with an etching solution.

Next, an example of an oscillator including the surface acoustic wave element described above will be described with reference to FIG. This oscillator (TCXO: Tempered Compensated Crystal Oscillator) is a circuit for outputting a signal having a set frequency f ₀ to the outside, and does not depend on the temperature change outside the TCXO or suppresses the influence of the temperature change outside the TCXO. It is configured so as to output the set frequency f _0. The set frequency f ₀ is an output frequency obtained when a reference voltage V ₀ is applied to a first oscillation circuit 23 described below at a reference temperature T _0, for example, 29 ° C.

The first resonator 2 is connected to the first oscillation circuit 23 via the first signal ports 21a and 21b, and the second resonator 3 is similarly connected to the second signal port 22a, A second oscillation circuit 24 for using the second resonator 3 as a temperature sensor is connected via 22b. Between the oscillation circuits 23 and 24, the temperature of the surface acoustic wave element described above is estimated based on the temperature compensation frequency signal input from the second oscillation circuit 24. At this temperature, the first A control voltage supply unit 41 for calculating a control voltage V _c (V _c = V ₀ −ΔV) at which the set frequency f ₀ is obtained by the oscillation circuit 23 is provided as a signal output unit. 5 of 42 is an input terminal of the control voltage V ₁₀ to the second oscillation circuit 24 is inputted, 43 is an output end of the oscillator. In FIG. 5, reference numeral 44 denotes a varicap diode.

Specifically, the control voltage supply unit 41 includes a frequency detection unit 45 including, for example, a frequency counter for measuring the frequency f from the frequency signal input from the second oscillation circuit 24, and the frequency detection unit 45 A temperature estimation unit 46 that estimates the temperature T based on the measured frequency f, a compensation voltage calculation unit 47 that calculates the compensation voltage ΔV based on the temperature T estimated by the temperature estimation unit 46, and a compensation voltage calculation unit 47 It includes a mixer 48 for outputting a control voltage V _c to the computed compensation voltage ΔV is subtracted from the reference voltage V ₀ to the first oscillation circuit 23, the at. The temperature estimation unit 46 stores a frequency temperature characteristic (for example, a cubic function) of the second oscillation circuit 24 expressed by the following equation (1), and this temperature characteristic and the oscillation frequency of the second oscillation circuit 24 are stored. Based on f, the temperature of the surface acoustic wave element is obtained.
f = f ₁₀ {1 + α ₂ (T−T ₁₀ ) ³ + β ₂ (T−T ₁₀ ) + γ ₂ } (1)

Further, the compensation voltage calculation unit 47 includes, for example, a cubic function generator that is a temperature characteristic of the first oscillation circuit 23, and the compensation voltage is calculated based on the following equations (2) to (4) and the temperature T. It is comprised so that (DELTA) V may be calculated | required.
ΔV = V ₀ (Δf / f ₀ ) (2)
Δf / f ₀ = α ₁ (T−T ₀ ) ³ + β ₁ (T−T ₀ ) + γ ₁ (3)
ΔV = V ₀ {α ₁ (T−T ₀ ) ³ + β ₁ (T−T ₀ ) + γ ₁ } (4)
α ₁ , β ₁ , γ ₁ and α ₂ , β ₂ , γ ₂ are constants specific to the first oscillating circuit 23 and the second oscillating circuit 24, respectively. It is obtained by measuring. Δf = f−f ₀ , and f ₁₀ is an output frequency obtained when the reference voltage V ₁₀ is applied at the reference temperature T ₁₀ in the second oscillation circuit 24.

When inputting the control voltage V ₁₀ to the input end 42 in the oscillator, the second oscillator circuit 24, based on the temperature T of the surface acoustic wave element, the fundamental wave at the oscillation frequency f obtained by the above equation (1) Oscillates with thickness-slip vibration. The oscillation frequency f is input to the temperature estimation unit 46 via the frequency detection unit 45 as described above, and the temperature estimation unit 46 estimates the temperature T of the surface acoustic wave element. Then, the compensation voltage calculation unit 47 calculates the compensation voltage ΔV based on the temperature T obtained by the temperature estimation unit 46, and the control voltage V _c is applied to the first oscillation circuit 23 via the mixer 48. The The first oscillation circuit 23 vibrates with thickness shear vibration at an oscillation frequency f corresponding to the temperature T of the surface acoustic wave element and the control voltage V _c , that is, a set frequency f ₀ . That is, at the temperature T, the first oscillation circuit 23 causes the oscillation frequency f to follow the cubic function of the frequency temperature characteristic of the first oscillation circuit 23 by the difference (T−T _o ) from the reference temperature T _0. but when you Zureyo from the set frequency f _0. However, since the control voltage V _c for obtaining the set frequency f ₀ is applied to the first oscillation circuit 23, that is, the control voltage V lower (or higher) than the reference voltage V ₀ by the amount corresponding to the difference. _{Since c} is applied, an output frequency (set frequency f ₀ ) in which the difference is canceled is obtained.

  According to the above-described embodiment, the first resonator 2 and the second resonator 3 are disposed on the common piezoelectric substrate 1, and the resonance frequency (output signal) of the second resonator 3 is temperature compensated. Therefore, the resonance frequencies of the resonators 2 and 3 are shifted from each other. For this reason, the temperature difference between these resonators 2 and 3 disappears or becomes extremely small, and a stable frequency signal can be output over a wide temperature range. Since the constant temperature bath described above is not used in performing temperature compensation, the SAW resonator (first first) can be further downsized than a quartz crystal resonator in which electrode films are formed on both upper and lower surfaces of a quartz substrate. Since the resonator 2 and the second resonator 3) are used, a small oscillator and a surface acoustic wave element can be obtained. In addition, since the small oscillator is configured as described above, and since the thermostatic bath is not used as described above, a resonator excellent in power saving can be obtained.

  At this time, the period lengths λ1 and λ2 and the film thicknesses t1 and t2 are different from each other between the first resonator 2 and the second resonator 3, but when the resonance frequencies f1 and f2 are set to different values. Only at least one of the period length λ and the film thickness t may be changed. In addition, regarding the film thickness t, the film thickness of the reflector 13 may be made uniform between the resonators 2 and 3, and only the film thickness of each IDT electrode 12 may be changed, or the film of the electrode finger 15 of the IDT electrode 12 Only the thicknesses may be changed. Further, with respect to the periodic length λ, the periodic lengths λ of the reflectors 13 and 13 may be made uniform between the resonators 2 and 3, and only the periodic length λ of the IDT electrode 12 may be changed.

  Next, another example of the surface acoustic wave element will be described with reference to FIG. In this example, the first resonator 2 and the second resonator 3 are formed such that the periodic length λ and the film thickness t are aligned with each other, and the resonance frequencies f1 and f2 are shifted from each other. The other resonator 3 (2) is disposed so as to be inclined with respect to the child 2 (3). Specifically, when “L1” and “L2” are attached to the straight lines (straight lines orthogonal to the direction of the electrode fingers 15) extending along the bus bar 14 in the resonators 2 and 3, respectively, The angle θ formed by the straight line L2 is 45 °, for example. In FIG. 6, parts having the same configuration as in FIG.

  That is, the first resonator 2 is formed so that the straight line L1 is parallel to the X-axis direction (the left-right direction of the piezoelectric substrate 1) in the crystal axis of the piezoelectric substrate 1. The second resonator 3 is disposed such that the straight line L2 is inclined by 45 ° with respect to the X axis of the piezoelectric substrate 1. Therefore, in the first resonator 2 and the second resonator 3, the elastic wave propagates along the straight line L1 and the straight line L2, respectively. Therefore, the elastic wave in the first resonator 2 and the second resonator 3 is obtained. Are different from each other. That is, it can be said that the period length λ2 of the second resonator 3 is formed longer than the period length λ1 of the first resonator 2 when viewed from the elastic wave. Therefore, in the first resonator 2 and the second resonator 3, the resonance frequencies f1 and f2 are different from each other. Also in this surface acoustic wave element, the oscillator shown in FIG. 5 is configured, and the same effect can be obtained.

  The angle θ in FIG. 6 may be any angle, specifically, 0 ° <θ <180 ° (θ ≠ 90 °). Further, the first resonator 2 may be arranged such that the straight line L1 is inclined with respect to the X axis of the piezoelectric substrate 1. In this case, the straight lines L1 and L2 are respectively the Y axis (X It may be configured such that it is inclined with respect to the axis orthogonal to the axis and the angle θ ≠ 0 ° (180 °). That is, the resonators 2 and 3 are arranged so that elastic waves propagate.

  In addition, the second resonator 3 is inclined with respect to the first resonator 2 as shown in FIG. 6, and the period length λ and the film thickness t are set in these resonators 2 and 3 as shown in FIG. They may be shifted from each other. Further, in setting the resonance frequencies f1 and f2 to different values, instead of adjusting the period length λ, the film thickness t, and the inclination angle θ, or together with the period length λ, the film thickness t, and the inclination angle θ, The crossing length of the electrode finger 15 in the IDT electrode 12 (the dimension in which the electrode finger 15 extending from one bus bar 14 and the electrode finger 15 extending from the other bus bar 14 adjacent to the electrode finger 15 intersect) is defined as the resonator 2, 3. It may be changed between each other.

At this time, when two crystal resonators are formed on a common crystal substrate and one of these crystal resonators is used for temperature compensation (Patent Document 1 described above), resonance occurs between these crystal resonators. If the frequency is to be shifted, a method of adjusting the film thickness and size (surface area) of the electrode films formed on the upper and lower surfaces of the quartz substrate has to be taken. On the other hand, when the resonators 2 and 3 are used, as described above, the resonance frequencies f1 and f2 are set to different values not only for the film thickness t but also for the period length λ and the inclination angle θ. In other words, it can be used as a parameter. Accordingly, the resonance frequencies f1 and f2 of the resonators 2 and 3 can be easily set to different dimensions. In other words, by using the resonators 2 and 3, it is possible to widen the parameter adjustment range when setting the resonance frequencies f1 and f2 to different values.
The above-described resonator 2 (3) has a configuration in which a pair of reflectors 13 and 13 are arranged so as to sandwich one IDT electrode 12, but a plurality of IDT electrodes 12 are provided between the reflectors 13 and 13. It may be arranged.

Hereinafter, other examples of the oscillator of the present invention will be described. FIG. 7 shows an example in which a mixer 48 is connected to the oscillation circuits 23 and 24 as a frequency difference detection unit in order to obtain the difference between the output signals of the first oscillation circuit 23 and the second oscillation circuit 24. ing. That is, since the frequency temperature characteristics of the resonators 2 and 3 are uniform, the difference (f1-f2) between the frequency signals output from the oscillation circuits 23 and 24 hardly changes with an external temperature change. may be used as a set frequency f _0. In FIG. 7, reference numeral 25 denotes a multiplier circuit for multiplying the difference between the frequency signals.

  FIG. 8A shows an example in which a signal ((f1−f2) / f1) corresponding to the difference between the resonance frequencies f1 and f2 of the resonators 2 and 3 is used as a temperature sensor. That is, the difference hardly changes with an external temperature change, but when viewed microscopically, it changes only slightly with an external temperature change. Therefore, in FIG. 8A, an external temperature is detected based on the difference, and the temperature compensation of the frequency synthesizer 50 is performed using the detection result.

  Specifically, the first oscillation circuit 23 is connected to the frequency synthesizer 50 in order to supply a driving clock signal to a DDS (Direct Digital Synthesizer) described later in the frequency synthesizer 50. The oscillation circuits 23 and 24 are connected to a difference detection unit 51 for detecting a signal ((f2−f1) / f1) corresponding to the difference between the oscillation frequencies f1 and f2. Is connected to a compensation amount calculation unit 52 for obtaining a temperature compensation amount.

  Since the relationship between the environmental temperature and (f2−f2) / f1 and the relationship between the environmental temperature and the compensation value for the set value input to the mixer 53 are known in advance, the compensation amount calculation unit 52 Stores relationship data or a relational expression indicating the relationship between (f2−f1) / f1 and the compensation value, and therefore, the compensation value calculation unit 52 outputs a compensation value corresponding to the temperature. That is, since the output signal of the first oscillation circuit 23 is used as the clock signal for driving the DDS described above, the signal output from the DDS is set according to the temperature change of the surface acoustic wave element. This value is compensated for, but the deviation is compensated.

  In this frequency synthesizer 50, a reference clock signal corresponding to the input value of the mixer 53 is output from a DDS (Direct Digital Synthesizer), and this reference signal is output to one input terminal of a phase comparison unit of a PLL (Phase Locked Loop) circuit. To enter. Thus, a frequency signal corresponding to the frequency of the reference signal is output.

  FIG. 8B shows an example in which the surface acoustic wave element of the present invention is applied to an oscillator with a thermostatic chamber (not shown). A surface acoustic wave element (piezoelectric substrate 1 on which resonators 2 and 3 are formed) is installed in a thermostatic chamber provided with a heater 31 as a heating source. The first oscillation circuit 23 is connected to the frequency synthesizer 50 as in FIG. In FIG. 8B, reference numeral 32 denotes a control circuit for the heater 31, and the difference detection unit 51 is connected to the control circuit 32. The control circuit 32 stores correlation data between the difference between the resonance frequencies and the temperature, and is configured to be able to adjust the power supplied to the heater 31 based on the correlation data.

  In the case of an oscillator having such a configuration, each of the resonators 2 and 3 oscillates at a resonance frequency corresponding to an external temperature, and the difference detection unit 51 calculates a difference between these resonance frequencies. In the control circuit 32, the temperature of the heater 31 is adjusted according to the difference. Therefore, the influence of the external temperature on the clock signal for driving the DDS output from the first oscillation circuit 23 to the frequency synthesizer 50 is suppressed. Therefore, when a set value is input to the frequency synthesizer 50 as described above, a frequency signal corresponding to the frequency of the reference signal is output with almost no influence of temperature. In this oscillator, since the output of the heater 31 is adjusted using the difference between the resonance frequencies of the resonators 2 and 3, an extremely stable clock signal can be obtained.

Even when the frequency synthesizer 50 is used, the resonance frequency f2 of the second resonator 3 may be used as a temperature sensor, as in FIG. 5 described above. That is, in the case of FIG. 8A, the temperature is calculated based on the resonance frequency f2 and the compensation amount is set. The compensation amount is added to the set value input to the mixer 53 in order to cancel the fluctuation of the output signal of the first oscillation circuit 23 used for driving the DDS due to an external temperature change. . 8B, a control circuit 32 is connected to the second oscillation circuit 24. In this control circuit 32, the external temperature is calculated based on the resonance frequency f2, and the heater 31 is used. The power supplied to is adjusted. Therefore, as in the above-described example, the output signal of the first oscillation circuit 23 is not dependent on the temperature change or hardly affected by the temperature with respect to the DDS. Supplied as
In FIGS. 8A and 8B, a third resonator is provided on the piezoelectric substrate 1 separately from the resonators 2 and 3 used as temperature sensors as clock signals for driving the DDS. Instead of the output signal output from the first oscillation circuit 23, an output signal output from the third resonator via a third oscillation circuit (both not shown) may be used.

DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 1st resonator 3 2nd resonator 21 1st signal port 22 2nd signal port 23 1st oscillation circuit 24 2nd oscillation circuit

Claims (8)

A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first oscillation circuit and a second oscillation circuit respectively connected to the first resonator and the second resonator;
At least one of the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used for temperature detection.   A signal corresponding to the frequency of the output signal of the second oscillation circuit is used as a temperature detection signal, or the difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used. 2. The oscillator according to claim 1, wherein a corresponding signal is used as a temperature detection signal, and a temperature variation of the first oscillation frequency is compensated based on the temperature detection signal. The oscillator is configured as a thermostatic oscillator,
A signal corresponding to the frequency of the output signal of the second oscillation circuit is used as a temperature detection signal, or the difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit is used. 2. The oscillator according to claim 1, wherein a corresponding signal is used as a temperature detection signal, and power supplied to a heating source of the thermostatic bath is controlled based on the temperature detection signal.   The said 1st resonator and the said 2nd resonator are set to the value from which the period length of the electrode finger in each IDT electrode differs from each other. The oscillator described.   The first resonator and the second resonator are set such that film thicknesses of electrode fingers in each IDT electrode are set to different dimensions. The oscillator described.   The first resonator and the second resonator are one of the first resonator and the second resonator so that the propagation directions of the surface acoustic waves on the piezoelectric substrate are different from each other. 6. The oscillator according to claim 1, wherein the other resonator is inclined with respect to the other resonator. A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first oscillation circuit and a second oscillation circuit respectively connected to the first resonator and the second resonator;
A frequency difference detection unit that detects a difference between the frequency of the output signal of the first oscillation circuit and the frequency of the output signal of the second oscillation circuit;
An oscillator configured to obtain an oscillation output having a frequency corresponding to the frequency difference obtained by the frequency difference detection unit. A first resonator comprising an IDT electrode formed on a piezoelectric substrate and reflectors disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode;
An IDT electrode formed on the piezoelectric substrate, and a reflector disposed on one side and the other side of the propagation direction of the surface acoustic wave in the IDT electrode, each having a resonance frequency different from that of the first resonator A second resonator set to a value;
A first signal port formed on the piezoelectric substrate for connecting the first resonator to a first oscillation circuit;
A second signal port formed on the piezoelectric substrate and provided independently of the first signal port to connect the second resonator to a second oscillation circuit; A surface acoustic wave device.

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