JP7778413B2 - Oscillator circuits and electronic devices - Google Patents
Oscillator circuits and electronic devicesInfo
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Description
本発明は、振動子を備えた発振回路に関するものである。 The present invention relates to an oscillator circuit equipped with a vibrator.
近年、携帯電話や、あらゆるモノがインターネットに接続するＩｏＴ（Internet-of-Things）機器においてはバッテリー持続時間の長期化が求められており、そこに使われる電子回路や電子部品の低消費電力化が重要技術課題となっている。 In recent years, there has been a demand for longer battery life in mobile phones and IoT (Internet-of-Things) devices, in which all manner of objects 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.
例えば、ＩｏＴの小型通信機器に適用される通信規格ＢＬＥ（Bluetooth Low Energy）では、無線周波数２．４ＧＨｚ帯の周波数基準として数１０ＭＨｚ帯のＡＴカット水晶振動子が利用されている。発振回路としては、図２０に示すように水晶振動子Ｘ１（３００）を用いたインバータベースのピアース型の発振回路１００が広く使われている。ピアース型の発振回路１００は、発振回路ＩＣ（２００）に内蔵されたインバータＡ１、増幅素子Ａ２、発振容量素子Ｃ１ａ、Ｃ１ｂ、水晶振動子Ｘ１（３００）から構成される。周波数温度特性は３次の温度特性を有し、動作温度範囲が比較的狭い民生向け製品の場合には、温度補償をしなくてもＢＬＥ通信規格を満足する周波数温度特性を実現することができる。 For example, the Bluetooth Low Energy (BLE) communication standard applied to small IoT communication devices uses an AT-cut quartz crystal resonator in the tens of MHz band 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 quartz crystal resonator 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 quartz crystal resonator X1 (300) built into an oscillator circuit IC (200). The frequency-temperature characteristic has a third-order temperature characteristic, and in the case of 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.
しかしながら、近年の通信機器の小型化に対応して振動子の小型化が進んだため、水晶振動子の等価直列容量は小さく、等価直列抵抗は大きくなりつつある。その結果、ピアース型の発振回路の起動時間は以前より長くなっている。ＢＬＥ通信規格ではバッテリー持続時間を長くするために間欠的な通信が適用されているが、そのインターバルは最短で１０ｍｓｅｃ程度である。そこで、ピアース型の水晶発振回路では間欠動作のインターバルが短い用途に対し、発振起動時に発振電流を増加させ起動時間を短縮していた（例えば、非特許文献１参照）。 However, as oscillators have become smaller in recent years in response to the miniaturization of communication devices, the equivalent series capacitance of quartz crystal oscillators 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 increase the oscillation current when starting up the oscillation to shorten the startup time (see, for example, Non-Patent Document 1).
発振回路において発振電流を増加させると消費電力が増大するという問題がある。そのため、ＩｏＴ機器における発振回路では、消費電力を増やさずに、通信規格を満足する周波数温度特性と発振起動の高速化を両立する発振回路が望まれている。ＢＬＥ通信規格で実用上求められる発振起動時間は、～２５０μｓｅｃ、周波数温度特性は、±２０ｐｐｍである。 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 BLE communication standard requires a practical oscillation startup time of approximately 250 μsec and a frequency-temperature characteristic of ±20 ppm.
振動子としてランガサイト型圧電振動子を適用したピアース型の発振回路では、同じ発振電流でも起動時間が水晶振動子を用いた場合に比べ約１桁早い。これにより起動時の消費電力が約１桁減少するためバッテリー持続時間の長期化にも寄与するとともに、間欠動作の周期が短い用途にも対応可能となるが、ＢＬＥ通信規格を満足する周波数温度特性を有する発振回路の条件は明確になっていなかった。 In a Pierce-type oscillator circuit that uses a Langasite piezoelectric oscillator as the oscillator, the startup time is approximately one order of magnitude faster than when using a quartz oscillator, even with the same oscillation current. This reduces startup power consumption by approximately 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 clearly defined.
本発明は、上記問題を解決するためになされたものであり、消費電力を増やさずに、通信規格を満足する周波数温度特性と発振起動の高速化を両立する発振回路を提供することを目的とする。 The present invention was made to solve the above problems, and aims to provide an oscillator circuit that achieves both frequency temperature characteristics that satisfy communication standards and fast oscillation startup without increasing power consumption.
本発明の発振回路は、所定の周波数温度特性を有する圧電振動子と、前記圧電振動子に接続される能動素子と、前記能動素子に接続される発振容量素子を備えた発振回路であって、前記圧電振動子の周囲温度に応じて、前記周波数温度特性における周波数変動を補償する温度補償回路であって、サーミスタを含む受動素子によって構成され、前記圧電振動子に直列に接続された温度補償回路を備え、前記圧電振動子の前記周波数温度特性は、頂点温度が２５℃よりも高温側に設定されている負の２次係数を有する２次温度特性を有し、前記温度補償回路は、前記周波数温度特性における前記頂点温度よりも低温域における前記周波数変動を補償するように構成されている。 The oscillator circuit of the present invention comprises 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. The temperature compensation circuit compensates for frequency fluctuations in the frequency-temperature characteristic in accordance with the ambient temperature of the piezoelectric vibrator, and is 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 with a negative quadratic coefficient whose peak temperature is set higher than 25°C, and the temperature compensation circuit is configured to compensate for the frequency fluctuations in the temperature range lower than the peak temperature in the frequency-temperature characteristic.
また、本発明の発振回路の一構成例は、前記頂点温度は、＋４０℃～＋１５０℃に設定されている。 In one example configuration of the oscillator circuit of the present invention, the peak temperature is set to +40°C to +150°C.
また、本発明の発振回路の一構成例は、前記温度補償回路は、直列接続された前記サーミスタと第１の容量素子に、第２の容量素子が並列に接続されている構成と、前記サーミスタ、容量素子、および抵抗が並列に接続されている構成の何れかの構成を備える。 In one example configuration of the oscillator circuit of the present invention, the temperature compensation circuit has either a configuration in which a second capacitive element is connected in parallel to the thermistor and first capacitive element that are connected in series, or a configuration in which the thermistor, capacitive element, and resistor are connected in parallel.
また、本発明の発振回路の一構成例は、前記圧電振動子はランガサイト型圧電振動子であり、前記周波数温度特性における基準振動角周波数をω、前記ランガサイト型圧電振動子の等価直列容量をＣｍ、負荷時等価直列抵抗をＲｘ、前記発振回路の負性抵抗をＲｎ、前記温度補償回路の等価直列抵抗をＲｓとした場合に、
１／（ω2・Ｃｍ・（Ｒｎ－Ｒｘ－Ｒｓ））＜１ｅ－５
を満たすように構成されている。
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.
また、本発明の発振回路の一構成例は、前記能動素子が、前記ランガサイト型圧電振動子に並列接続されたインバータであり、前記発振容量素子は、前記インバータの入力端子および出力端子のそれぞれに接続されている。 In one example configuration 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 oscillator capacitance element is connected to each of the input and output terminals of the inverter.
また、本発明の発振回路の一構成例は、前記温度補償回路を構成する素子のうち、少なくとも前記サーミスタが、前記ランガサイト型圧電振動子と共通の保持器内に実装されている。 In one example configuration of the oscillator circuit of the present invention, among the elements constituting the temperature compensation circuit, at least the thermistor is mounted in a holder common to the Langasite-type piezoelectric vibrator.
また、本発明の発振回路の一構成例は、前記発振容量素子が、容量値が変更可能に構成されている。 In one example configuration of the oscillator circuit of the present invention, the oscillation capacitive element is configured so that its capacitance value is changeable.
また、本発明の電子機器は、上記発振回路を備える。 The electronic device of the present invention also includes the above-mentioned oscillator circuit.
本発明によれば、消費電力を増やさずに、通信規格を満足する周波数温度特性と発振起動の高速化を両立する発振回路を提供することができる。 This invention provides an oscillator circuit that achieves both frequency-temperature characteristics that meet communication standards and fast oscillation startup without increasing power consumption.
＜発振回路の構成＞
本実施の形態の発振回路では、消費電力を増やさずに、通信規格を満足する周波数温度特性と発振起動の高速化を両立する発振回路を実現するために、発振起動の高速化が可能なランガサイト型圧電振動子を適用するとともに、ＢＬＥ通信規格で実用上求められる発振起動時間（～２５０μｓｅｃ）を満たすための発振回路の条件を明らかにしたものである。
<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 can speed up oscillation startup is used, and the conditions for the oscillator circuit to satisfy the oscillation startup time (up to 250 μsec) that is practically required by the BLE communication standard are clarified.
図１は、本発明の実施の形態に係る発振回路の構成例を示す図である。図１の構成例の発振回路１０は、インバータベースのピアース（Pierce）型の発振回路１０である。図１のピアース型の発振回路１０は、発振回路ＩＣ（２０）に内蔵された能動素子（インバータ回路Ａ１、増幅回路Ａ２）、帰還抵抗Ｒ１、インバータ回路Ａ１の入力端子および出力端子のそれぞれに接続される発振容量素子（Ｃ１ａ、Ｃ１ｂ）、インバータ回路Ａ１に並列接続されたランガサイト型圧電振動子Ｘ１（３０）から構成されている。 Figure 1 is a diagram showing an example configuration of an oscillator circuit according to an embodiment of the present invention. The oscillator circuit 10 in the example configuration of Figure 1 is an inverter-based Pierce-type oscillator circuit 10. The Pierce-type oscillator circuit 10 in Figure 1 is composed of active elements (inverter circuit A1, amplifier circuit A2) built into the oscillator circuit IC (20), a feedback resistor R1, oscillation capacitance elements (C1a, C1b) connected to the input and output terminals of the inverter circuit A1, respectively, and a Langasite-type piezoelectric vibrator X1 (30) connected in parallel to the inverter circuit A1.
ここで、発振回路１０において、図１に示すように、ランガサイト型圧電振動子Ｘ１（３０）に直列に温度補償回路４０を挿入してもよい。所定の動作温度範囲、例えば、０℃～＋５０℃の範囲であれば、ＢＬＥ通信規格で実用上求められる周波数温度特性（±２０ｐｐｍ）を満たすことも可能であるが、温度補償回路４０を挿入することにより、ＢＬＥ通信規格で実用上求められる周波数温度特性（±２０ｐｐｍ）をより広い動作温度範囲で実現することができる。 In the oscillator circuit 10, as shown in Figure 1, a temperature compensation circuit 40 may be inserted in series with the Langasite-type piezoelectric vibrator X1 (30). It is possible to meet the frequency-temperature characteristics (±20 ppm) practically required by the BLE communication standard within a specified operating temperature range, for example, 0°C to +50°C. However, by inserting the temperature compensation circuit 40, the frequency-temperature characteristics (±20 ppm) practically required by the BLE communication standard can be achieved over a wider operating temperature range.
なお、図１および以下の実施の形態では、インバータベースのピアース型の発振回路１０を例として本発明の実施の形態を説明するが、本発明は、ピアース型の発振回路１０以外の発振回路、例えば、コルピッツ（Colpitts）型の発振回路にも適用可能である。 Note that 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.
図１において、温度補償回路４０を挿入しない場合には、発振容量素子（Ｃ１ａ、Ｃ１ｂ）の合成容量が振動子Ｘ１（３０）の負荷容量ＣＬにおいて支配的となり、振動子Ｘ１（３０）は、発振容量素子（Ｃ１ａ、Ｃ１ｂ）からなる負荷容量ＣＬの値に応じた周波数で発振する。振動子を作成する際に、圧電結晶の個片を結晶から切り出す際の結晶軸に対する切断角度を調整することで頂点温度を所望の値に調整し、所定の動作温度範囲で、周波数温度特性（±２０ｐｐｍ）を満たすように調整することができる。 In Figure 1, if the temperature compensation circuit 40 is not inserted, the combined capacitance of the oscillation capacitance elements (C1a, C1b) will dominate the load capacitance CL of the vibrator X1 (30), and the vibrator X1 (30) will oscillate at a frequency corresponding to the value of the load capacitance CL made up of the oscillation capacitance elements (C1a, C1b). When creating the vibrator, the peak temperature can be adjusted to the desired value by adjusting the cutting angle relative to the crystal axis when cutting individual pieces of piezoelectric crystal from the crystal, and can be adjusted to satisfy the frequency-temperature characteristics (±20 ppm) within the specified operating temperature range.
一方、温度補償回路４０を挿入した場合には、振動子Ｘ１（３０）の周囲温度に応じて、温度補償回路４０の容量を含む負荷容量ＣＬを変化させることにより、振動子Ｘ１（３０）と発振回路ＩＣ（２０）とで生成される発振周波数の温度による変動を補償する。これにより、温度補償回路４０を挿入しない場合と比較して、より広い動作温度範囲で、周波数温度特性（±２０ｐｐｍ）を満たす発振回路１０を実現することができる。 On the other hand, when the temperature compensation circuit 40 is inserted, the load capacitance CL, including the capacitance of the temperature compensation circuit 40, is changed according to the ambient temperature of the resonator X1 (30), thereby compensating for temperature-related fluctuations in the oscillation frequency generated by the resonator X1 (30) and the oscillator circuit IC (20). This makes it possible to realize an oscillator 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.
図２（ａ）は、振動子の等価回路である。振動子Ｘ１の等価回路は、等価直列抵抗Ｒｍ、等価直列容量Ｃｍ、等価直列インダクタンスＬｍ、等価並列容量Ｃｐから構成されている。図２（ｂ）は、圧電振動子を用いた発振回路の一般的な等価回路である。図２（ｂ）中の点線より左側は振動子の等価回路を示し、右側は発振回路の等価回路を示している。Ｒｘは、振動子側の負荷時等価直列抵抗であり、負荷容量ＣＬは、振動子側から見た発振回路側の等価直列容量、Ｒｎは、発振回路の負性抵抗である。 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 oscillator 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 oscillator circuit. Rx is the equivalent series resistance under load on the vibrator side, load capacitance CL is the equivalent series capacitance on the oscillator circuit side as seen from the vibrator side, and Rn is the negative resistance of the oscillator circuit.
＜ランガサイト型圧電振動子による高速起動＞
図２の等価回路における発振回路の発振起動時間は、等価直列インダクタンスＬｍの値に応じて増大し、負荷時等価直列抵抗Ｒｘと負性抵抗Ｒｎの差（Ｒｘ－Ｒｎ）に応じて減少する（例えば、参考文献：“Ultralow-Power Class-C Complementary Colpitts Crystal Oscillator”, IEEE SOLID-STATE CIRCUITS LETTERS, VOL. 3, 2020 参照）。等価直列インダクタンスＬｍを、基準振動角周波数ωと等価直列容量Ｃｍで表すと１／（ω２・Ｃｍ)となる。
<High-speed start-up using Langasite-type piezoelectric vibrator>
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 (see, for example, "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 becomes 1/( ω2 Cm).
本願の発明者は、鋭意検討した結果、発振回路の負性抵抗Ｒｎと振動子の負荷時等価直列抵抗Ｒｘの条件を含めて、ＭＨｚ以上の発振周波数では、以下の式（１）を満足するとき、発振起動時間が２５０μｓｅｃ未満となることを見出した。
１／（ω2・Ｃｍ・Ｒｎ）＜１ｅ－５ (ただし、Ｒｎ＞＞Ｒｘ)・・・（１）
式（１）のように、発振回路の負性抵抗Ｒｎは、振動子の負荷時等価直列抵抗Ｒｘに対して十分大きい値であることが望ましいが、少なくとも、Ｒｘ／Ｒｎ＞１０を満たせばよい。
As a result of extensive research, the inventors of the present application have found that, at an oscillation frequency of MHz or more, when the following formula (1) is satisfied, including the conditions of the negative resistance Rn of the oscillation circuit and the equivalent series resistance Rx of the vibrator under load, the oscillation startup time is less than 250 μsec.
1/( ω2 Cm 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.
水晶振動子を適用したピアース型の発振回路１００（図２０）では、例えば、３０ＭＨｚ帯の水晶発振の場合、水晶振動子における代表的な等価直列容量および負性抵抗の値、Ｃｍ＝２ｆＦ、Ｒｎ＝１０００Ωでは、式（１）を満足しない。一方、ランガサイト型圧電振動子では、等価直列容量Ｃｍは３０ｆＦ程度であるので、十分に式（１）を満足することがわかる。発明者が行った実験においても、発振起動時間が、１／Ｃｍに比例し、１００μｓｅｃ未満の高速起動を実現できることも確認できた。 In a Pierce-type oscillator circuit 100 (Figure 20) using a quartz crystal resonator, for example, in the case of 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 high-speed startup of less than 100 μsec can be achieved.
＜温度補償回路による温度補償＞
図３は、温度補償回路を挿入していない発振回路の周波数温度特性を示す図である。温度補償回路４０を挿入していない発振回路１０の周波数温度特性は、基準周波数に対応する頂点温度を有する負の２次係数を有する２次温度特性を有している。図３の縦軸のｄｆ／ｆは、２次曲線の頂点温度における振動子Ｘ１（３０）の基準周波数に対する周波数偏差の割合である。図３の点線のように室温＋２５℃近傍に頂点温度が設定された場合、０℃～＋５０℃の範囲であれば、周波数温度特性（±２０ｐｐｍ）を満たしている。
<Temperature compensation using a temperature compensation circuit>
FIG. 3 is a diagram showing the frequency-temperature characteristics of an oscillator circuit without a temperature compensation circuit. The frequency-temperature characteristics of the oscillator circuit 10 without the 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 represents the ratio of frequency deviation of the oscillator X1 (30) to the reference frequency 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.
振動子Ｘ１（３０）の周囲温度が変動した場合、発振回路１０の発振周波数は、図３の周波数温度特性に応じて変化するので、周囲温度によっては、周波数温度特性（±２０ｐｐｍ）を満たさない場合がある。その場合、温度補償回路４０を振動子Ｘ１に接続して、周囲温度の変化に応じて負荷容量ＣＬを変化させることで、振動子Ｘ１（３０）の発振周波数の周囲温度による変動を補償することができる。温度補償回路４０を接続することで、より広い動作温度範囲で、周波数温度特性（±２０ｐｐｍ）を満たすように制御することが可能となる。 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 met. In such cases, by connecting a temperature compensation circuit 40 to the resonator X1 and varying the load capacitance CL in accordance with changes in ambient temperature, it is possible to compensate for fluctuations 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 frequency-temperature characteristic (±20 ppm) to be met over a wider operating temperature range.
温度補償回路４０の接続に伴い、発振起動時間を２５０μｓｅｃ未満とするための条件は、上述した式（１）から次の式（２）に修正される。
１／（ω2・Ｃｍ・（Ｒｎ－Ｒｘ－Ｒｓ））＜１ｅ－５ ・・・（２）
ω：周波数温度特性における基準振動角周波数、Ｃｍ：ランガサイト型圧電振動子の等価直列容量、Ｒｘ：負荷時等価直列抵抗、Ｒｎ：発振回路の負性抵抗、Ｒｓ：温度補償回路の等価直列抵抗
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
２次温度特性の周波数温度特性を示す振動子では、通常の場合、図３の点線のように室温＋２５℃近傍に頂点温度が設定されている。本実施の形態では、温度補償回路４０の挿入前において頂点温度を室温より高温側に存在させ、挿入する温度補償回路４０で低温域における周波数変動を主に補償するように構成することができる。これにより、より広い動作温度範囲において、周波数温度特性（±２０ｐｐｍ）を満たすように制御することが可能となる。振動子を作成する際に、圧電結晶の個片を結晶から切り出す際の結晶軸に対する切断角度を調整することで、頂点温度を所望の値に調整することができる。 In a vibrator that exhibits a frequency-temperature characteristic of the second order, 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 the temperature compensation circuit 40 is inserted, 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 the vibrator, the peak temperature can be adjusted to the desired value by adjusting the cutting angle relative to the crystal axis when cutting individual pieces of piezoelectric crystal from the crystal.
図４は、本実施の形態における温度補償回路を挿入した際の負荷容量ＣＬの温度特性例である。低温域ほど負荷容量ＣＬが小さくなるように温度補償回路４０の補償回路定数を設定することで、低温域に進むにつれて発振周波数をより上昇させることで、低温域における周波数の低下を補償することができる。 Figure 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 constants of the temperature compensation circuit 40 so that the load capacitance CL decreases 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.
図５は、本発明の実施の形態における温度補償回路を挿入した発振回路の周波数温度特性を示す図である。温度補償回路４０によって、図４に示すような負荷容量ＣＬの温度特性を実現することで、低温域における周波数の低下が補償された周波数温度特性を実現することができる。これにより、広い温度範囲においてＢＬＥ通信規格を満足する周波数温度特性（±２０ｐｐｍ）を実現することができる。 Figure 5 shows the frequency temperature characteristics of an oscillator circuit incorporating a temperature compensation circuit according to an embodiment of the present invention. By using the temperature compensation circuit 40 to achieve the temperature characteristics of the load capacitance CL shown in Figure 4, it is possible to achieve a frequency temperature characteristic that compensates for frequency drop in the low temperature range. This makes it possible to achieve a frequency temperature characteristic (±20 ppm) that satisfies the BLE communication standard over a wide temperature range.
＜温度補償回路の構成＞
温度補償回路４０の主な構成要素はＮＴＣ（negative temperature coefficient）サーミスタＲｔｈである。温度補償回路４０を受動素子で構成することで、消費電力を増加させないように構成することができる。振動子Ｘ１（３０）と温度補償回路４０の接続形態は、温度補償後の周波数温度特性における発振容量Ｃ１ａ、Ｃ１ｂの経時変化や調整による変動影響を低減するため直列接続が望ましい。
<Configuration of temperature compensation circuit>
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 adjustments and changes over time in the oscillation capacitances C1a and C1b in the frequency-temperature characteristics after temperature compensation.
本実施の形態では、温度補償前の発振回路１０の頂点温度は室温（＋２５℃）よりも高温側に設定するが、現実的なＮＴＣサーミスタＲｔｈの特性と、室温を温度補償の中心温度としできるだけ広い温度範囲で周波数変動を補償することを考慮すると、頂点温度は、＋４０℃～＋１５０℃の範囲に設定するのが望ましい。 In this embodiment, the peak temperature of the oscillator circuit 10 before temperature compensation is set to a temperature higher than room temperature (+25°C). However, considering 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.
図６、図７に、温度補償回路の構成例を示す。図８、図９は、図６、図７の温度補償回路をそれぞれ適用した発振回路１０の周波数温度特性例である。図６の温度補償回路＃１では、直列接続されたサーミスタＲｔｈと容量素子Ｃ１（第１の容量素子）に、容量素子Ｃ２（第２の容量素子）が並列に接続されている。図７の温度補償回路＃２では、サーミスタＲｔｈ、容量素子Ｃ１、および抵抗Ｒ１が並列に接続されている。 Figures 6 and 7 show example configurations 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 applied, respectively. In temperature compensation circuit #1 of Figure 6, capacitance element C2 (second capacitance element) is connected in parallel to the series-connected thermistor Rth and capacitance element C1 (first capacitance element). In temperature compensation circuit #2 of Figure 7, thermistor Rth, capacitance element C1, and resistor R1 are connected in parallel.
これらの構成例では、３０ＭＨｚ帯で負荷容量ＣＬは約７ｐＦとし、サーミスタＲｔｈの抵抗値は、室温１００Ωとした。目標とする周波数温度特性（±２０ｐｐｍ）を満足する温度範囲は、図８では、－２５℃～＋８０℃、図９では、－３５℃～＋８５℃となり、民生機器で一般的に求められる動作温度範囲－２０℃～＋７０℃をカバーしていることがわかる。 In these configuration examples, the load capacitance CL is approximately 7 pF in the 30 MHz band, and the resistance of the thermistor Rth is 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.
ここで、動作温度範囲の値を広げるためには、温度補償前の頂点温度を調整すればよい。図８、図９によれば、温度補償回路＃２の方が温度補償回路＃１よりも補償温度範囲がやや広い。一方で、図８、９の周波数温度特性を実現した温度補償回路＃１、＃２の等価直列抵抗Ｒｓは、温度補償が効果的な低温域で増加することに留意する必要がある。 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. On the other hand, 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.
図１０は、本発明の実施の形態に係る温度補償回路の等価直列抵抗Ｒｓの温度特性を示す図である。図１０に示すように、温度補償回路４０の等価直列抵抗Ｒｓの値は、温度補償回路＃１では最大約４０Ωで留まっているのに対し、温度補償回路＃２では１００Ω以上になっていることがわかる。温度補償回路の等価直列抵抗Ｒｓの増加は、式（２）において、発振回路の負性抵抗Ｒｎに対する等価直列抵抗Ｒｓの値が大きくなり、結果として、発振回路１０の発振起動時間の増加につながる。温度補償回路４０として温度補償回路＃２を適用する場合には、発振回路の負性抵抗Ｒｎが温度補償回路４０の等価直列抵抗Ｒｓの増加に対し余裕があることを確認する必要がある。 Figure 10 is a diagram showing the temperature characteristics of the equivalent series resistance Rs of the temperature compensation circuit according to an embodiment of the present invention. As shown in Figure 10, the value of the equivalent series resistance Rs of the temperature compensation circuit 40 remains at a maximum of approximately 40 Ω in temperature compensation circuit #1, while it is 100 Ω or more in temperature compensation circuit #2. An increase in the equivalent series resistance Rs of the temperature compensation 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 the oscillator circuit 10. When using temperature compensation circuit #2 as temperature compensation circuit 40, it is necessary to confirm that the negative resistance Rn of the oscillator circuit has a margin for an increase in the equivalent series resistance Rs of the temperature compensation circuit 40.
ただし、増幅回路は高温よりも低温の方が回路利得が高くなる。一方で、サーミスタを用いた温度補償は補償が効く温度範囲において補償回路損失が増加する。よって、振動子の頂点温度を高温側に移動させ、低温域で温度補償することは、回路利得の増加と補償回路の損失増加が同時に起きて相補となるため、発振回路の動作温度範囲において発振起動時間の変動が起きにくいという利点がある。 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 vary across the operating temperature range of the oscillator circuit.
図１１に、図６の温度補償回路＃１を構成する要素の内、サーミスタＲｔｈを圧電振動子と共通の保持器内に実装した発振回路１０の構成例を示す。サーミスタＲｔｈと圧電振動子を同じ保持器に実装することで、熱結合が改善するため補償精度が向上する。また、発振回路１０を構成する素子の実装面積を削減することができる。 Figure 11 shows an example 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 holder that is shared with the piezoelectric vibrator. Mounting the thermistor Rth and the piezoelectric vibrator in the same holder improves thermal coupling, thereby increasing compensation accuracy. It also reduces the mounting area of the elements that make up the oscillator circuit 10.
本構成例では保持器に実装されない２つの容量素子（Ｃ１、Ｃ２）が存在するが、この２つの容量素子の容量値はいずれも１００ｐＦ以下であり、ＭＬＣＣ（Multi-Layer Ceramic Capacitor）では、０．４ｍｍ×０．２ｍｍ サイズが一般的になりつつあるので、実装面積の増加へ影響は少ない。なお、図１１の構成例は、温度補償回路＃２を用いる場合にも適用可能である。 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.
図１２は、図６の温度補償回路＃１を適用し、発振回路ＩＣ（２０）の発振容量（Ｃ１ａ、Ｃ１ｂ）が容量可変機能を有するピアース型の発振回路１０の構成例である。ランガサイト型圧電振動子Ｘ１（３０）は水晶振動子よりも負荷容量ＣＬに対する感度が高い。特に、発振容量（Ｃ１ａ、Ｃ１ｂ）が発振回路ＩＣ（２０）に内蔵された場合、容量値のばらつきはＭＬＣＣに比べて桁違いに大きく、例えば、公称周波数から数１０ｐｐｍ変動する場合がある。発振回路ＩＣ（２０）に内蔵された発振容量素子（Ｃ１ａ、Ｃ１ｂ）の容量値を変更可能に構成することで、発振容量素子の容量値のばらつきを調整することができる。また、ピアース型の発振回路１０中に配置された温度センサから温度情報を得ることにより、この容量可変機能を、温度補償を行うために利用してもよい。この温度センサは、温度補償回路４０に内蔵されているのが望ましい。図１２の構成例は、温度補償回路＃２を用いる場合にも適用可能である。 12 shows an example configuration of a Pierce-type oscillator circuit 10 that uses the temperature compensation circuit #1 of FIG. 6 and in which the oscillation capacitances (C1a, C1b) of the oscillator circuit IC (20) have a variable capacitance function. 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 capacitances (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, for example. By configuring the capacitance of the oscillation capacitance elements (C1a, C1b) built into the oscillator circuit IC (20) to be variable, the variation in the capacitance of the oscillation capacitance elements can be adjusted. Furthermore, this variable capacitance function may be used for temperature compensation by obtaining temperature information from a temperature sensor located in the Pierce-type oscillator circuit 10. This temperature sensor is preferably built into the temperature compensation circuit 40. The example configuration of FIG. 12 is also applicable when using the temperature compensation circuit #2.
図１３は、以上の本実施の形態に係わる検討と従来の発振回路の実績を踏まえ、従来の発振回路と本実施の形態の発振回路との特性比較した結果である。発振周波数は３０ＭＨｚ帯、動作温度範囲は－２０℃～＋７０℃とした。本実施の形態の発振回路１０は、消費電力を増やさずに、ＢＬＥ通信規格を満足する周波数温度特性と発振起動の高速化を両立した発振回路となっていることがわかる。ＩｏＴ向けの間欠動作する小型通信機器、特に、民生向けの動作温度範囲においては、従来の発振回路よりも本実施の形態の発振回路が適していることがわかる。 Figure 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-mentioned considerations related to this embodiment and the track record of conventional oscillator circuits. The oscillation frequency was set to the 30 MHz band, and the operating temperature range was set to -20°C to +70°C. It can be seen that the oscillator circuit 10 of this embodiment is an oscillator circuit that combines 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 conventional oscillator circuits for small, intermittent-operation communication devices for IoT, especially in the operating temperature range for consumer use.
＜圧電振動子を用いた検証実験＞
本発明の実施の形態の作用効果を検証するため、圧電振動子の検証サンプルを用いて実験回路による検証実験を行った。実験回路としては、図１、図２０に記載されたインバータ型の発振回路を用いた。
<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.
なお、式（２）では、温度補償回路の等価直列抵抗Ｒｓを考慮して、発振起動時間を所定の値以下とするための条件を定めている。式（２）の分母の一部を構成する［Ｒｎ－Ｒｘ－Ｒｓ］項は、負性抵抗Ｒｎと振動子、温度補償回路の損失和［Ｒｘ＋Ｒｓ］の差分であるから、発振回路の実効的な利得を表現する項と言い換えることができる。そのため、式（２）において［Ｒｎ－Ｒｘ－Ｒｓ］項の代わりに、発振回路の実効的な利得を用いることで、式（２）の妥当性を検証することが可能である。よって、検証実験における実験条件としては、温度補償回路がない、即ち、Ｒｓを考慮しない発振回路の実効的な利得である［Ｒｎ－Ｒｘ］を利用して、式（２）の妥当性を検証した。 Note that equation (2) defines the conditions for keeping the oscillation startup time below a specified 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 in 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 in place of the term [Rn - Rx - Rs] 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.
図１４、図１５は、本発明の実施の形態の効果を検証するための圧電振動子の検証サンプルの説明図である。図１４、図１５は、縦軸を式（２）における発振回路の実効的な利得である負性抵抗Ｒｎと振動子の負荷時等価直列抵抗Ｒｘの差［Ｒｎ－Ｒｘ］とし、横軸を圧電振動子の等価直列容量［Ｃｍ］とした場合の圧電振動子の検証サンプルのパラメータである。図１４は、発振回路ＩＣ（２０）の能動素子（インバータ回路Ａ１、増幅回路Ａ２）の電源電圧ＶＤＤが１．５Ｖの場合、図１５は、電源電圧ＶＤＤが２．０Ｖの場合である。 Figures 14 and 15 are explanatory diagrams of a piezoelectric vibrator verification sample used to verify the effects of an embodiment of the present invention. Figures 14 and 15 show parameters of a piezoelectric vibrator verification sample, with the vertical axis representing 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 under load Rx, and the horizontal axis representing the piezoelectric vibrator's equivalent series capacitance [Cm]. Figure 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, while Figure 15 shows the case where the power supply voltage VDD is 2.0V.
圧電振動子の検証サンプルとしては、水晶振動子（Ｑｕａｒｔｚ）、ランガサイト型圧電振動素子（ＣＴＧＳ）、セラミック振動子（Ｃｅｒａｍｉｃ）を用いた。実験回路では、圧電振動子として、図１４、図１５の検証サンプルを使用し、振動子側から見た発振回路側の等価直列容量（負荷容量）ＣＬが、所望の値（６ＰＦ、９ＰＦ、１４ＰＦ）となるように、発振容量素子（Ｃ１ａ、Ｃ１ｂ）の容量を設定した。 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 (6 pF, 9 pF, 14 pF).
図１６、図１７は、本発明の実施の形態の効果を検証するための実験回路における発振起動時間の測定結果である。図１６、図１７の縦軸は、発振起動時間（μｓｅｃ）、横軸は、式（２）の左辺［１／（ω2・Ｃｍ・（Ｒｎ－Ｒｘ））］である。 16 and 17 show the measurement results of the oscillation startup time in an experimental circuit for verifying the effects of the embodiment of the present invention. The vertical axis of each figure represents the oscillation startup time (μsec), and the horizontal axis represents the left side of equation (2) [1/( ω2 Cm (Rn-Rx))].
なお、発振起動時間は、発振回路ＩＣ（２０）に、電源電圧ＶＤＤが印加されてから、発振電圧の振幅が飽和するまでの時間である。 The oscillation startup time is the time from when the power supply voltage VDD is applied to the oscillator circuit IC (20) until the amplitude of the oscillation voltage saturates.
図１６、図１７によれば、ＢＬＥ規格で実用上求められる発振起動時間（～２５０μｓｅｃ）を満たすための、式（２）の左辺［１／（ω2・Ｃｍ・（Ｒｎ－Ｒｘ））］の値は、発振回路ＩＣ（２０）の電源電圧ＶＤＤに依存せず、１ｅ－５より小さい値とすればよいことを確認することができた。 16 and 17, it was confirmed that the value of the left side of equation (2) [1/( ω2 Cm (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 in order to satisfy the oscillation startup time (up to 250 μsec) required for practical use in the BLE standard.
図１８は、本発明の実施の形態の圧電振動子として水晶振動子を用いた場合の発振起動時間の測定結果である。図１８は、発振回路ＩＣ（２０）の能動素子の電源電圧ＶＤＤが１．５Ｖの場合の測定結果である。 Figure 18 shows the measurement results of the oscillation startup time when a quartz crystal resonator is used as the piezoelectric resonator of an embodiment of the present invention. Figure 18 shows the measurement results when the power supply voltage VDD of the active element of the oscillator circuit IC (20) is 1.5 V.
図１８によれば、負荷容量ＣＬが６ＰＦの場合には、２５０μｓｅｃより短い発振起動時間を実現できる水晶振動子がある。この場合の水晶振動子のサイズは、２．５×２．０ｍｍ２以上のものであり、駆動電極が大きいので、等価直列容量Ｃｍの大きい水晶振動子を用いることで、２５０μｓｅｃより短い発振起動時間の発振回路を実現することが確認できた。 18, when the load capacitance CL is 6 pF, there is a crystal unit that can achieve an oscillation startup time shorter than 250 μsec. In this case, the size of the crystal unit is 2.5 × 2.0 mm2 or more, and the drive electrodes are large. Therefore, it was confirmed that by using a crystal unit with a large equivalent series capacitance Cm, an oscillation circuit with an oscillation startup time shorter than 250 μsec can be realized.
図１９は、本発明の実施の形態の圧電振動子としてランガサイト型圧電振動子を用いた場合の発振起動時間の測定結果である。図１９は、発振回路ＩＣ（２０）の能動素子の電源電圧ＶＤＤが１．５Ｖの場合の測定結果である。 Figure 19 shows the measurement results for the oscillation startup time when a Langasite type piezoelectric vibrator is used as the piezoelectric vibrator according to an embodiment of the present invention. Figure 19 shows the measurement results when the power supply voltage VDD of the active element of the oscillator circuit IC (20) is 1.5 V.
図１９によれば、圧電振動子としてランガサイト型圧電振動子を用いることで、負荷容量ＣＬが、６ＰＦ、９ＰＦ、１４ＰＦのいずれの場合も、１５０μｓｅｃより短い発振起動時間の発振回路を実現することができることが分かる。 Figure 19 shows that by using a Langasite piezoelectric vibrator as the piezoelectric vibrator, it is possible to realize an oscillation circuit with an oscillation startup time of less than 150 μsec, regardless of whether the load capacitance CL is 6 pF, 9 pF, or 14 pF.
圧電振動子としてランガサイト型圧電振動子を用いた場合、振動子のサイズは、２．０×１．６ｍｍ２以下と小さく、駆動電極が小さいが、水晶振動子よりも等価直列容量Ｃｍが大きいので、１５０μｓｅｃより短い発振起動時間の発振回路を実現することが確認できた。 When a Langasite type piezoelectric vibrator is used as the piezoelectric vibrator, the size of the vibrator is small, at 2.0 × 1.6 mm² or less, and the drive electrodes are small. However, since the equivalent series capacitance Cm is larger than that of a quartz crystal vibrator, it was confirmed that an oscillation circuit with an oscillation startup time shorter than 150 μsec can be realized.
以上のように、本実施の形態によれば、消費電力を増やさずに、通信規格を満足する周波数温度特性と発振起動の高速化を両立する発振回路を提供することができる。本実施の形態の発振回路は、携帯電話機やＩｏＴ機器などの電子機器に適用することができる。 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 fast 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.
本発明の発振回路は、様々なＩｏＴ機器に組み込んで使うことができる。 The oscillator circuit of the present invention can be incorporated into a variety of IoT devices.
１０…発振回路、２０…発振回路（ＩＣ）、３０…ランガサイト型圧電振動子、４０…温度補償回路。 10...oscillation circuit, 20...oscillation circuit (IC), 30...Langasite type piezoelectric vibrator, 40...temperature compensation circuit.
Claims (6)
前記圧電振動子の周囲温度に応じて、前記周波数温度特性における周波数変動を補償する温度補償回路であって、サーミスタを含む受動素子によって構成され、前記圧電振動子に直列に接続された温度補償回路を備え、
前記圧電振動子の前記周波数温度特性は、頂点温度が２５℃よりも高温側に設定されている負の２次係数を有する２次温度特性を有し、
前記温度補償回路は、前記周波数温度特性における前記頂点温度よりも低温域における前記周波数変動を補償するように構成され、
前記圧電振動子は、水晶振動子、あるいはランガサイト型圧電振動子であり、
前記周波数温度特性における基準振動角周波数をω、前記圧電振動子の等価直列容量をＣｍ、負荷時等価直列抵抗をＲｘ、前記発振回路の負性抵抗をＲｎ、前記温度補償回路の等価直列抵抗をＲｓとした場合に、
１／（ω2・Ｃｍ・（Ｒｎ－Ｒｘ－Ｒｓ））＜１ｅ－５
を満たすように構成されている
発振回路。 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
An oscillator circuit configured to satisfy the following:
請求項１に記載の発振回路。 The oscillation circuit according to claim 1 , wherein the peak temperature is set to +40° C. to +150° C.
請求項１に記載の発振回路。 The oscillation circuit according to claim 1 , wherein the active element is an inverter connected in parallel to the piezoelectric vibrator, and the oscillation capacitive element is connected to each of an input terminal and an output terminal of the inverter.
請求項３に記載の発振回路。 The oscillation circuit according to claim 3 , wherein at least the thermistor, among the elements constituting the temperature compensation circuit, is mounted in a holder that is common to the piezoelectric vibrator.
請求項３に記載の発振回路。 The oscillation circuit according to claim 3 , wherein the oscillation capacitive element is configured so that the capacitance value thereof is changeable.
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