Oscillator circuits and electronic devices

Abstract

To provide an oscillation circuit that achieves both frequency-temperature characteristics satisfying communication standards and speeding up of oscillation startup without increasing power consumption.SOLUTION: An oscillation circuit (10) according to the present invention is equipped with a piezoelectric vibrator (30) having a predetermined frequency-temperature characteristic, an active element connected to the piezoelectric vibrator, and an oscillation capacitive element connected to the active element. The oscillation circuit includes a temperature compensation circuit (40) that compensates for frequency fluctuations in the frequency-temperature characteristic according to the ambient temperature of the piezoelectric vibrator, is composed of passive elements including a thermistor and is connected in series with the piezoelectric vibrator. The frequency-temperature characteristic of the piezoelectric vibrator (30) has a secondary temperature characteristic with a negative secondary coefficient with an apex temperature set at higher than 25°C. The temperature compensation circuit (40) is configured to compensate for the frequency fluctuations at lower temperatures than the apex temperature in the frequency-temperature characteristic.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oscillator circuit including a vibrator. [Background technology]

[0002] In recent years, there has been a demand for longer battery life in mobile phones and IoT (Internet-of-Things) devices, in which all kinds of things are connected to the Internet, and reducing the power consumption of the electronic circuits and electronic components used in these devices has become an important technological challenge.

[0003] For example, the Bluetooth Low Energy (BLE) communication standard applied to compact IoT communication devices uses an AT-cut crystal unit with a frequency band of several tens of megahertz as a frequency reference for the 2.4 GHz radio frequency band. As shown in Figure 20, an inverter-based Pierce-type oscillator circuit 100 using a crystal unit X1 (300) is widely used as an oscillator circuit. The Pierce-type oscillator circuit 100 is composed of an inverter A1, an amplifier element A2, oscillation capacitance elements C1a and C1b, and a crystal unit X1 (300) built into an oscillator circuit IC (200). The frequency-temperature characteristic has a third-order temperature characteristic, and for consumer products with a relatively narrow operating temperature range, it is possible to achieve a frequency-temperature characteristic that meets the BLE communication standard without temperature compensation.

[0004] However, as resonators have become smaller in recent years in response to the miniaturization of communication devices, the equivalent series capacitance of quartz crystal resonators has become smaller and the equivalent series resistance has become larger. As a result, the startup time of Pierce-type oscillator circuits has become longer than before. The BLE communication standard applies intermittent communication to extend battery life, but the shortest interval is approximately 10 msec. Therefore, for applications with short intervals between intermittent operations, Pierce-type crystal oscillator circuits have shortened the startup time by increasing the oscillation current when starting up the oscillation (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Masaya Miyahara, Yukiya Endo, Kenichi Okada, and Akira Matsuzawa, “A 64μs Start-Up 26 / 40 MHz Crystal Oscillator with Negative Resistance Boosting Technique Using Reconfigurable Multi-Stage Amplifier”, Proc. IEEE Symp. VLSI Circuits, 2018 Summary of the Invention [Problem to be solved by the invention]

[0006] Increasing the oscillation current in an oscillator circuit increases power consumption. Therefore, there is a demand for oscillator circuits in IoT devices that combine frequency-temperature characteristics that meet communication standards with fast oscillation startup without increasing power consumption. The practical requirements for the BLE communication standard are an oscillation startup time of approximately 250 μsec and a frequency-temperature characteristic of ±20 ppm.

[0007] In a Pierce-type oscillator circuit that uses a Langasite piezoelectric resonator as the oscillator, the startup time is about one order of magnitude faster than when using a quartz crystal resonator, even with the same oscillation current. This reduces power consumption at startup by about one order of magnitude, contributing to longer battery life and enabling use in applications with short intermittent operation cycles. However, the conditions for an oscillator circuit with frequency-temperature characteristics that meet the BLE communication standard had not been clarified.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide an oscillator circuit that achieves both frequency temperature characteristics that satisfy communication standards and high-speed oscillation startup without increasing power consumption. [Means for solving the problem]

[0009] The oscillation circuit of the present invention is an oscillation circuit comprising a piezoelectric vibrator having a predetermined frequency-temperature characteristic, an active element connected to the piezoelectric vibrator, and an oscillation capacitive element connected to the active element, and is a temperature compensation circuit that compensates for frequency fluctuations in the frequency-temperature characteristic depending on the ambient temperature of the piezoelectric vibrator, the temperature compensation circuit being composed of passive elements including a thermistor and connected in series to the piezoelectric vibrator, the frequency-temperature characteristic of the piezoelectric vibrator having a quadratic temperature characteristic with a negative quadratic coefficient whose peak temperature is set on the higher side than 25°C, and the temperature compensation circuit is configured to compensate for the frequency fluctuations in the temperature range below the peak temperature in the frequency-temperature characteristic.

[0010] In one configuration example of the oscillation circuit of the present invention, the peak temperature is set to +40°C to +150°C.

[0011] In addition, in one configuration example of the oscillator circuit of the present invention, the temperature compensation circuit has either a configuration in which a second capacitance element is connected in parallel to the thermistor and first capacitance element that are connected in series, or a configuration in which the thermistor, capacitance element, and resistor are connected in parallel.

[0012] In addition, in one configuration example of the oscillation circuit of the present invention, the piezoelectric vibrator is a Langasite type piezoelectric vibrator, and when the reference vibration angular frequency in the frequency temperature characteristics is ω, the equivalent series capacitance of the Langasite type piezoelectric vibrator is Cm, the equivalent series resistance under load is Rx, the negative resistance of the oscillation circuit is Rn, and the equivalent series resistance of the temperature compensation circuit is Rs, 1 / (ω 2 Cm (Rn-Rx-Rs)<1e-5 It is configured to satisfy the following.

[0013] In addition, in one configuration example of the oscillator circuit of the present invention, the active element is an inverter connected in parallel to the Langasite type piezoelectric vibrator, and the oscillation capacitive element is connected to each of the input terminal and output terminal of the inverter.

[0014] In one configuration example of the oscillation circuit of the present invention, at least the thermistor, among the elements constituting the temperature compensation circuit, is mounted in a holder that is common to the Langasite type piezoelectric vibrator.

[0015] In one configuration example of the oscillation circuit of the present invention, the oscillation capacitive element is configured so that the capacitance value thereof is changeable.

[0016] Moreover, an electronic device according to the present invention includes the above-described oscillator circuit. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an oscillator circuit that achieves both frequency temperature characteristics that satisfy communication standards and high-speed oscillation startup without increasing power consumption. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an oscillator circuit according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of an equivalent circuit of a vibrator and an oscillation circuit. [Figure 3] FIG. 3 is a diagram showing the frequency temperature characteristics of the oscillation circuit before the temperature compensation circuit is inserted. [Figure 4] FIG. 4 is a diagram showing the temperature dependency of the load capacitance according to the embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing the frequency temperature characteristics of the oscillation circuit according to the embodiment of the present invention. [Figure 6] FIG. 6 shows an example of the configuration of a temperature compensation circuit according to an embodiment of the present invention. [Figure 7] FIG. 7 shows another example of the configuration of the temperature compensation circuit according to the embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing the frequency temperature characteristics of the oscillation circuit according to the embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing the frequency temperature characteristics of the oscillation circuit according to the embodiment of the present invention. [Figure 10]FIG. 10 is a diagram showing the temperature characteristics of the equivalent series resistance of the temperature compensation circuit according to the embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing an example of the configuration of an oscillator circuit according to an embodiment of the present invention. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of an oscillator circuit according to an embodiment of the present invention. [Figure 13] FIG. 13 shows the results of a comparison of the characteristics of a conventional oscillator circuit and the oscillator circuit of this embodiment. [Figure 14] FIG. 14 is an explanatory diagram of a verification sample of a piezoelectric vibrator for verifying the effects of the embodiment of the present invention. [Figure 15] FIG. 15 is an explanatory diagram of a verification sample of a piezoelectric vibrator for verifying the effects of the embodiment of the present invention. [Figure 16] FIG. 16 shows the measurement results of the oscillation startup time in an experimental circuit for verifying the effects of the embodiment of the present invention. [Figure 17] FIG. 17 shows the measurement results of the oscillation startup time in an experimental circuit for verifying the effects of the embodiment of the present invention. [Figure 18] FIG. 18 shows the measurement results of the oscillation startup time when a quartz crystal resonator is used as the piezoelectric resonator according to the embodiment of the present invention. [Figure 19] FIG. 19 shows the measurement results of the oscillation startup time when a Langasite type piezoelectric vibrator is used as the piezoelectric vibrator according to the embodiment of the present invention. [Figure 20] FIG. 20 is a diagram showing an example of the configuration of a conventional oscillator circuit. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Configuration of oscillator circuit> In the oscillator circuit of this embodiment, in order to realize an oscillator circuit that achieves both frequency-temperature characteristics that satisfy the communication standard and fast oscillation startup without increasing power consumption, a Langasite type piezoelectric vibrator that enables fast oscillation startup is used, and the conditions for the oscillator circuit to satisfy the oscillation startup time (up to 250 μsec) practically required by the BLE communication standard are clarified.

[0020] Fig. 1 is a diagram showing an example of the configuration of an oscillator circuit according to an embodiment of the present invention. The oscillator circuit 10 in the example configuration of Fig. 1 is an inverter-based Pierce-type oscillator circuit 10. The Pierce-type oscillator circuit 10 in Fig. 1 is composed of active elements (inverter circuit A1, amplifier circuit A2) built into an oscillator circuit IC (20), a feedback resistor R1, oscillation capacitance elements (C1a, C1b) connected to the input terminal and output terminal of the inverter circuit A1, respectively, and a Langasite-type piezoelectric vibrator X1 (30) connected in parallel to the inverter circuit A1.

[0021] 1, a temperature compensation circuit 40 may be inserted in series with the Langasite type piezoelectric vibrator X1 (30) in the oscillator circuit 10. Although it is possible to satisfy the frequency temperature characteristic (±20 ppm) practically required by the BLE communication standard within a predetermined operating temperature range, for example, a range of 0°C to +50°C, by inserting the temperature compensation circuit 40, it is possible to achieve the frequency temperature characteristic (±20 ppm) practically required by the BLE communication standard over a wider operating temperature range.

[0022] In FIG. 1 and the following embodiments, an embodiment of the present invention will be described using an inverter-based Pierce-type oscillator circuit 10 as an example, but the present invention can also be applied to oscillator circuits other than the Pierce-type oscillator circuit 10, such as a Colpitts-type oscillator circuit.

[0023] 1, if the temperature compensation circuit 40 is not inserted, the combined capacitance of the oscillation capacitance elements (C1a, C1b) becomes dominant in the load capacitance CL of the resonator X1 (30), and the resonator X1 (30) oscillates at a frequency corresponding to the value of the load capacitance CL consisting of the oscillation capacitance elements (C1a, C1b). When creating the resonator, the apex temperature can be adjusted to a desired value by adjusting the cutting angle relative to the crystal axis when cutting out individual pieces of piezoelectric crystal from the crystal, and can be adjusted to satisfy the frequency-temperature characteristics (±20 ppm) within a specified operating temperature range.

[0024] On the other hand, when the temperature compensation circuit 40 is inserted, the temperature-dependent fluctuation of the oscillation frequency generated by the resonator X1 (30) and the oscillation circuit IC (20) is compensated for by changing the load capacitance CL, including the capacitance of the temperature compensation circuit 40, according to the ambient temperature of the resonator X1 (30). This makes it possible to realize an oscillation circuit 10 that satisfies the frequency-temperature characteristics (±20 ppm) over a wider operating temperature range than when the temperature compensation circuit 40 is not inserted.

[0025] Figure 2(a) is the equivalent circuit of a vibrator. The equivalent circuit of vibrator X1 consists of equivalent series resistance Rm, equivalent series capacitance Cm, equivalent series inductance Lm, and equivalent parallel capacitance Cp. Figure 2(b) is a general equivalent circuit of an oscillation circuit using a piezoelectric vibrator. The left side of the dotted line in Figure 2(b) shows the equivalent circuit of the vibrator, and the right side shows the equivalent circuit of the oscillation circuit. Rx is the equivalent series resistance under load on the vibrator side, the load capacitance CL is the equivalent series capacitance on the oscillation circuit side as seen from the vibrator side, and Rn is the negative resistance of the oscillation circuit.

[0026] <High-speed start-up using Langasite-type piezoelectric vibrators> The oscillation startup time of the oscillator circuit in the equivalent circuit of Figure 2 increases according to the value of the equivalent series inductance Lm, and decreases according to the difference (Rx-Rn) between the equivalent series resistance under load Rx and the negative resistance Rn (for example, see the reference document "Ultralow-Power Class-C Complementary Colpitts Crystal Oscillator", IEEE SOLID-STATE CIRCUITS LETTERS, VOL. 3, 2020). When the equivalent series inductance Lm is expressed in terms of the reference oscillation angular frequency ω and the equivalent series capacitance Cm, it is expressed as 1 / (ω 2 ·Cm).

[0027] As a result of extensive research, the inventors of the present application have found that, at an oscillation frequency of MHz or more, including the conditions of the negative resistance Rn of the oscillation circuit and the equivalent series resistance Rx of the vibrator under load, when the following formula (1) is satisfied, the oscillation startup time is less than 250 μsec. 1 / (ω 2Cm Rn)<1e-5 (where Rn>>Rx) (1) As in equation (1), it is desirable that the negative resistance Rn of the oscillation circuit be a value that is sufficiently large relative to the equivalent series resistance Rx of the vibrator under load, but it is sufficient if at least Rx / Rn>10 is satisfied.

[0028] In a Pierce-type oscillator circuit 100 (FIG. 20) using a quartz crystal resonator, for example, in the case of a 30 MHz band quartz crystal oscillation, the typical equivalent series capacitance and negative resistance values ​​for a quartz crystal resonator, Cm=2 fF and Rn=1000 Ω, do not satisfy equation (1). On the other hand, in a Langasite-type piezoelectric resonator, the equivalent series capacitance Cm is approximately 30 fF, so it is clear that equation (1) is fully satisfied. Experiments conducted by the inventors also confirmed that the oscillation startup time is proportional to 1 / Cm, and that a fast startup of less than 100 μsec can be achieved.

[0029] <Temperature compensation using a temperature compensation circuit> FIG. 3 is a diagram showing the frequency-temperature characteristics of an oscillation circuit without a temperature compensation circuit. The frequency-temperature characteristics of the oscillation circuit 10 without a temperature compensation circuit 40 have a quadratic temperature characteristic with a negative quadratic coefficient having a peak temperature corresponding to the reference frequency. df / f on the vertical axis of FIG. 3 is the ratio of frequency deviation to the reference frequency of the oscillator X1 (30) at the peak temperature of the quadratic curve. When the peak temperature is set near room temperature +25°C as shown by the dotted line in FIG. 3, the frequency-temperature characteristics (±20 ppm) are satisfied within the range of 0°C to +50°C.

[0030] When the ambient temperature of the resonator X1 (30) fluctuates, the oscillation frequency of the oscillator circuit 10 changes according to the frequency-temperature characteristic shown in Figure 3. Therefore, depending on the ambient temperature, the frequency-temperature characteristic (±20 ppm) may not be satisfied. In such cases, by connecting a temperature compensation circuit 40 to the resonator X1 and varying the load capacitance CL according to changes in the ambient temperature, it is possible to compensate for the fluctuation in the oscillation frequency of the resonator X1 (30) due to ambient temperature. Connecting the temperature compensation circuit 40 makes it possible to control the resonator so that the frequency-temperature characteristic (±20 ppm) is satisfied over a wider operating temperature range.

[0031] With the connection of the temperature compensation circuit 40, the condition for making the oscillation startup time less than 250 μsec is modified from the above-mentioned formula (1) to the following formula (2). 1 / (ω 2 ·Cm·(Rn-Rx-Rs))<1e-5 ···(2) ω: Reference vibration angular frequency in frequency temperature characteristics, Cm: Equivalent series capacitance of Langasite type piezoelectric vibrator, Rx: Equivalent series resistance under load, Rn: Negative resistance of oscillation circuit, Rs: Equivalent series resistance of temperature compensation circuit

[0032] In a resonator exhibiting a frequency-temperature characteristic of quadratic temperature characteristics, the peak temperature is typically set near room temperature + 25°C, as shown by the dotted line in Figure 3. In this embodiment, the peak temperature is set to be higher than room temperature before inserting the temperature compensation circuit 40, and the inserted temperature compensation circuit 40 can be configured to primarily compensate for frequency fluctuations in the low-temperature range. This makes it possible to control the frequency-temperature characteristic (±20 ppm) to be satisfied over a wider operating temperature range. When creating a resonator, the peak temperature can be adjusted to the desired value by adjusting the cutting angle relative to the crystal axis when cutting a piece of piezoelectric crystal from the crystal.

[0033] 4 shows an example of the temperature characteristics of the load capacitance CL when the temperature compensation circuit of this embodiment is inserted. By setting the compensation circuit constant of the temperature compensation circuit 40 so that the load capacitance CL becomes smaller in the lower temperature range, the oscillation frequency increases as the temperature decreases, thereby compensating for the decrease in frequency in the low temperature range.

[0034] Fig. 5 is a diagram showing the frequency-temperature characteristic of an oscillator circuit incorporating a temperature compensation circuit according to an embodiment of the present invention. By using temperature compensation circuit 40 to achieve the temperature characteristic of load capacitance CL as shown in Fig. 4, it is possible to achieve a frequency-temperature characteristic in which the decrease in frequency in the low temperature range is compensated for. This makes it possible to achieve a frequency-temperature characteristic (±20 ppm) that satisfies the BLE communication standard over a wide temperature range.

[0035] <Temperature compensation circuit configuration> The main component of the temperature compensation circuit 40 is an NTC (negative temperature coefficient) thermistor Rth. By configuring the temperature compensation circuit 40 using passive elements, it is possible to configure it so as not to increase power consumption. The resonator X1 (30) and the temperature compensation circuit 40 are preferably connected in series to reduce the influence of fluctuations due to changes over time in the oscillation capacitances C1a and C1b and adjustments in the frequency-temperature characteristics after temperature compensation.

[0036] In this embodiment, the peak temperature of the oscillation circuit 10 before temperature compensation is set to a temperature higher than room temperature (+25°C). However, taking into consideration the realistic characteristics of the NTC thermistor Rth and the need to compensate for frequency fluctuations over as wide a temperature range as possible with room temperature as the center temperature for temperature compensation, it is desirable to set the peak temperature in the range of +40°C to +150°C.

[0037] Figures 6 and 7 show configuration examples of temperature compensation circuits. Figures 8 and 9 show examples of frequency-temperature characteristics of oscillator circuit 10 to which the temperature compensation circuits of Figures 6 and 7 are respectively applied. In temperature compensation circuit #1 of Figure 6, a capacitance element C2 (second capacitance element) is connected in parallel to a thermistor Rth and capacitance element C1 (first capacitance element) that are connected in series. In temperature compensation circuit #2 of Figure 7, a thermistor Rth, capacitance element C1, and resistor R1 are connected in parallel.

[0038] In these configuration examples, the load capacitance CL is set to approximately 7 pF in the 30 MHz band, and the resistance of the thermistor Rth is set to 100 Ω at room temperature. The temperature range that satisfies the target frequency-temperature characteristics (±20 ppm) is -25°C to +80°C in Figure 8, and -35°C to +85°C in Figure 9, which shows that the operating temperature range of -20°C to +70°C generally required for consumer devices is covered.

[0039] To widen the operating temperature range, the peak temperature before temperature compensation can be adjusted. Figures 8 and 9 show that temperature compensation circuit #2 has a slightly wider compensation temperature range than temperature compensation circuit #1. However, it should be noted that the equivalent series resistance Rs of temperature compensation circuits #1 and #2, which achieve the frequency-temperature characteristics shown in Figures 8 and 9, increases in the low-temperature range where temperature compensation is effective.

[0040] FIG. 10 is a graph showing the temperature characteristics of the equivalent series resistance Rs of the temperature-compensated circuit according to the embodiment of the present invention. As shown in FIG. 10, the value of the equivalent series resistance Rs of the temperature-compensated circuit 40 remains at a maximum of approximately 40 Ω in temperature-compensated circuit #1, whereas it reaches 100 Ω or more in temperature-compensated circuit #2. An increase in the equivalent series resistance Rs of the temperature-compensated circuit increases the value of the equivalent series resistance Rs relative to the negative resistance Rn of the oscillator circuit in equation (2), which ultimately leads to an increase in the oscillation startup time of oscillator circuit 10. When temperature-compensated circuit #2 is used as temperature-compensated circuit 40, it is necessary to ensure that the negative resistance Rn of the oscillator circuit has a sufficient margin to accommodate an increase in the equivalent series resistance Rs of the temperature-compensated circuit 40.

[0041] However, the circuit gain of an amplifier circuit is higher at low temperatures than at high temperatures. On the other hand, temperature compensation using a thermistor increases compensation circuit loss in the temperature range where compensation is effective. Therefore, moving the peak temperature of the resonator to the high temperature side and performing temperature compensation in the low temperature range has the advantage that the increase in circuit gain and the increase in compensation circuit loss occur simultaneously and complement each other, making it less likely that the oscillation start-up time will fluctuate within the operating temperature range of the oscillator circuit.

[0042] Figure 11 shows an example of the configuration of an oscillator circuit 10 in which the thermistor Rth, one of the elements that make up the temperature compensation circuit #1 in Figure 6, is mounted in a common holder together with the piezoelectric vibrator. Mounting the thermistor Rth and the piezoelectric vibrator in the same holder improves thermal coupling, thereby improving compensation accuracy. In addition, the mounting area of ​​the elements that make up the oscillator circuit 10 can be reduced.

[0043] In this configuration example, there are two capacitance elements (C1, C2) that are not mounted on the holder, but the capacitance values ​​of these two capacitance elements are both 100 pF or less, and since MLCCs (Multi-Layer Ceramic Capacitors) are becoming more common with a size of 0.4 mm x 0.2 mm, there is little impact on the increase in mounting area. Note that the configuration example in Figure 11 can also be applied when using temperature compensation circuit #2.

[0044] FIG. 12 shows a configuration example of a Pierce-type oscillator circuit 10 that uses the temperature compensation circuit #1 of FIG. 6 and has variable capacitance functions for the oscillation capacitors (C1a, C1b) of the oscillator circuit IC (20). The Langasite-type piezoelectric resonator X1 (30) is more sensitive to the load capacitance CL than a quartz crystal resonator. In particular, when the oscillation capacitors (C1a, C1b) are built into the oscillator circuit IC (20), the capacitance variation is orders of magnitude larger than that of an MLCC, and may fluctuate by several tens of ppm from the nominal frequency. By configuring the capacitance values ​​of the oscillation capacitors (C1a, C1b) built into the oscillator circuit IC (20) to be variable, the variation in the capacitance values ​​of the oscillation capacitors can be adjusted. Furthermore, this variable capacitance function may be used for temperature compensation by obtaining temperature information from a temperature sensor installed in the Pierce-type oscillator circuit 10. This temperature sensor is preferably built into the temperature compensation circuit 40. The configuration example of FIG. 12 is also applicable when the temperature compensation circuit #2 is used.

[0045] 13 shows the results of a comparison of the characteristics of a conventional oscillator circuit and the oscillator circuit of this embodiment, based on the above-described considerations related to this embodiment and the track record of conventional oscillator circuits. The oscillation frequency is set to the 30 MHz band, and the operating temperature range is set to -20°C to +70°C. It can be seen that the oscillator circuit 10 of this embodiment is an oscillator circuit that achieves both frequency-temperature characteristics that satisfy the BLE communication standard and fast oscillation startup without increasing power consumption. It can be seen that the oscillator circuit of this embodiment is more suitable than the conventional oscillator circuit for small communication devices that operate intermittently for IoT, especially in the operating temperature range for consumer use.

[0046] <Verification experiment using piezoelectric vibrators> In order to verify the effects of the embodiment of the present invention, a verification experiment was carried out using a verification sample of a piezoelectric vibrator with an experimental circuit. The inverter-type oscillation circuit shown in Figures 1 and 20 was used as the experimental circuit.

[0047] Equation (2) defines the conditions for keeping the oscillation startup time below a predetermined value, taking into account the equivalent series resistance Rs of the temperature compensation circuit. The term [Rn-Rx-Rs], which forms part of the denominator of equation (2), is the difference between the negative resistance Rn and the sum of the losses of the resonator and temperature compensation circuit [Rx+Rs], and can therefore be rephrased as a term expressing the effective gain of the oscillator circuit. Therefore, the validity of equation (2) can be verified by using the effective gain of the oscillator circuit instead of the [Rn-Rx-Rs] term in equation (2). Therefore, the validity of equation (2) was verified using [Rn-Rx], the effective gain of an oscillator circuit without a temperature compensation circuit, that is, without considering Rs, as the experimental condition in the verification experiment.

[0048] 14 and 15 are explanatory diagrams of a verification sample of a piezoelectric vibrator for verifying the effects of an embodiment of the present invention. In Fig. 14 and Fig. 15, the vertical axis represents the difference [Rn-Rx] between the negative resistance Rn, which is the effective gain of the oscillator circuit in Equation (2), and the vibrator's equivalent series resistance Rx under load, and the horizontal axis represents the equivalent series capacitance [Cm] of the piezoelectric vibrator. Fig. 14 shows the case where the power supply voltage VDD of the active elements (inverter circuit A1, amplifier circuit A2) of the oscillator circuit IC (20) is 1.5V, and Fig. 15 shows the case where the power supply voltage VDD is 2.0V.

[0049] The piezoelectric vibrator verification samples used were a quartz crystal vibrator (Quartz), a Langasite type piezoelectric vibrator element (CTGS), and a ceramic vibrator (Ceramic).In the experimental circuit, the verification samples shown in Figures 14 and 15 were used as piezoelectric vibrators, and the capacitance of the oscillation capacitance elements (C1a, C1b) was set so that the equivalent series capacitance (load capacitance) CL on the oscillation circuit side as seen from the vibrator side was the desired value (6PF, 9PF, 14PF).

[0050] 16 and 17 show the measurement results of the oscillation startup time in an experimental circuit for verifying the effect of the embodiment of the present invention. The vertical axis of FIG. 16 and FIG. 17 represents the oscillation startup time (μsec), and the horizontal axis represents the oscillation startup time [1 / (ω 2 ·Cm·(Rn-Rx))].

[0051] The oscillation startup time is the time from when the power supply voltage VDD is applied to the oscillation circuit IC (20) until the amplitude of the oscillation voltage is saturated.

[0052] According to Figures 16 and 17, the left side of equation (2) [1 / (ω 2 It was confirmed that the value of (Rn-Rx)) does not depend on the power supply voltage VDD of the oscillator circuit IC (20) and should be set to a value smaller than 1e-5.

[0053] 18 shows the measurement results of the oscillation startup time when a quartz crystal resonator is used as the piezoelectric resonator of the embodiment of the present invention, where the power supply voltage VDD of the active element of the oscillator circuit IC (20) is 1.5V.

[0054] According to Figure 18, when the load capacitance CL is 6PF, there is a crystal unit that can achieve an oscillation startup time of less than 250 μsec. The size of the crystal unit in this case is 2.5 × 2.0 mm. 2 As described above, it was confirmed that an oscillation circuit with an oscillation startup time of less than 250 μsec can be realized by using a quartz crystal resonator with a large equivalent series capacitance Cm because the drive electrodes are large.

[0055] Fig. 19 shows the measurement results of the oscillation startup time when a Langasite type piezoelectric vibrator is used as the piezoelectric vibrator according to the embodiment of the present invention, where the power supply voltage VDD of the active element of the oscillator circuit IC (20) is 1.5V.

[0056] According to FIG. 19, by using a Langasite type piezoelectric vibrator as the piezoelectric vibrator, it is possible to realize an oscillation circuit with an oscillation startup time shorter than 150 μsec regardless of whether the load capacitance CL is 6 PF, 9 PF, or 14 PF.

[0057] When a Langasite type piezoelectric vibrator is used as the piezoelectric vibrator, the size of the vibrator is 2.0 x 1.6 mm. 2 Although the driving electrodes are small, the equivalent series capacitance Cm is larger than that of a quartz crystal unit, so it has been confirmed that an oscillation circuit with an oscillation startup time of less than 150 μsec can be realized.

[0058] As described above, according to this embodiment, it is possible to provide an oscillator circuit that achieves both frequency temperature characteristics that satisfy communication standards and high-speed oscillation startup without increasing power consumption. The oscillator circuit of this embodiment can be applied to electronic devices such as mobile phones and IoT devices. [Industrial Applicability]

[0059] The oscillator circuit of the present invention can be incorporated into various IoT devices. [Explanation of symbols]

[0060] 10...oscillation circuit, 20...oscillation circuit (IC), 30...Langasite type piezoelectric vibrator, 40...temperature compensation circuit.

Claims

1. An oscillation circuit including a piezoelectric vibrator having a predetermined frequency temperature characteristic, an active element connected to the piezoelectric vibrator, and an oscillation capacitive element connected to the active element, a temperature compensation circuit that compensates for frequency fluctuations in the frequency-temperature characteristics in accordance with the ambient temperature of the piezoelectric vibrator, the temperature compensation circuit being configured with passive elements including a thermistor and connected in series to the piezoelectric vibrator; the frequency-temperature characteristic of the piezoelectric vibrator has a quadratic temperature characteristic having a negative quadratic coefficient with a peak temperature set on the higher side than 25°C, the temperature compensation circuit is configured to compensate for the frequency variation in a temperature range lower than the peak temperature of the frequency temperature characteristic, the piezoelectric vibrator is a quartz crystal vibrator or a Langasite type piezoelectric vibrator, When the reference vibration angular frequency in the frequency temperature characteristics is ω, the equivalent series capacitance of the piezoelectric vibrator is Cm, the equivalent series resistance under load is Rx, the negative resistance of the oscillation circuit is Rn, and the equivalent series resistance of the temperature compensation circuit is Rs, 1 / (ω 2 ・Cm・(Rn-Rx-Rs))<1e-5 It is configured to satisfy Oscillator circuit.

2. The peak temperature is set to +40°C to +150°C.

2. The oscillator circuit according to claim 1.

3. The active element is an inverter connected in parallel to the piezoelectric vibrator, and the oscillation capacitive element is connected to each of the input terminal and the output terminal of the inverter.

2. The oscillator circuit according to claim 1.

4. Among the elements constituting the temperature compensation circuit, at least the thermistor is mounted in a holder that is common to the piezoelectric vibrator.

4. The oscillator circuit according to claim 3.

5. The oscillation capacitance element is configured so that the capacitance value can be changed.

4. The oscillator circuit according to claim 3.

6. 6. An electronic device comprising the oscillator circuit according to claim 1.

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