JP5213845B2 - Temperature compensated crystal oscillator - Google Patents

Description

  The present invention relates to a crystal oscillator in which temperature compensation is performed based on a detection value of a temperature detector.

Crystal oscillation circuits are mounted on many electronic devices such as mobile phones because of their relatively high oscillation accuracy. However, the crystal resonator has a so-called frequency temperature characteristic in which the oscillation frequency fluctuates according to the temperature change when the ambient temperature changes. This frequency-temperature characteristic differs for each crystal resonator due to variations in the cutting angle and thickness of the crystal pieces constituting the crystal resonator. The solid line graph in FIG. 4 shows an example of the frequency-temperature characteristics of a crystal resonator made of an AT-cut crystal piece that is not temperature compensated. Assuming that the target oscillation frequency is f and the deviation between the frequency (f ′) and f at a certain temperature is Δf, the vertical axis of the graph is Δf / f, and the horizontal axis is the ambient temperature T of the crystal resonator. Each shows. This frequency deviation Δf / f is known to be approximated as the following equation (1) that is a cubic function of the ambient temperature T.
Δf / f = α (T−T ₀ ) ³ + β (T−T ₀ ) + γ (1)
T ₀ is a reference temperature when designing the crystal oscillator, and is set to 29 ° C., for example. This reference temperature is not limited to 29 ° C. Since Delta] f / f in T ₀ is therefore 0, T ₀ is the inflection point of the cubic function represented by equation (1). α, β, and γ are constants specific to the crystal piece.

A temperature-compensated crystal oscillator (hereinafter referred to as TCXO) having a function for compensating for the influence of the frequency-temperature characteristic is obtained when the crystal resonator has a frequency-temperature characteristic indicated by a solid line in FIG. Is configured to have a frequency temperature characteristic indicated by a reverse dotted line on the control voltage side. That is, since the control voltage applied to the crystal resonator and the oscillation frequency of the crystal resonator are in a proportional relationship as shown in FIG. 5, the temperature is T ₁ shifted from T ₀ as shown in FIG. The frequency is shifted by Δf. Therefore, if the temperature is increased from T ₀ , for example, temperature compensation is performed so that the control voltage V ₀ at which the crystal resonator has a set frequency at the temperature T ₀ is increased by ΔV corresponding to Δf. Specifically, assuming that the control voltage for obtaining the target oscillation frequency at the reference temperature T ₀ is V ₀ and V _C is the compensation voltage, Δf / f = V _C / V ₀ , so V _C / V ₀ is ( 1) becomes the right side of the equation, thus _{V C} is expressed by equation (2).
V _C = V ₀ {α (T−T ₀ ) ³ + β (T−T ₀ ) + γ}
= Α ′ (T−T ₀ ) ³ + β ′ (T−T ₀ ) + γ ′ (2)
α ′ = V ₀ · α, β ′ = V ₀ · β, and γ ′ = V ₀ · γ. α, β, and γ are obtained by installing a TCXO in a thermostat and measuring the frequency by changing the temperature in the thermostat variously.

Further, the temperature T is obtained, for example, by storing the relationship between the output voltage of the temperature detector and the temperature in the memory of the control unit and reading the temperature based on the output voltage. When the temperature and the output voltage are proportional to each other as the temperature detector 28, the output voltages of the temperature detector at the temperatures T and T ₀ are V _T and V _T0 , respectively, corresponding to the equation (1) (3 ) To obtain the compensation voltage V _C (corresponding to the above ΔV).
V _C (ΔV) = α ₁ (V _T −V _T0 ) ³ + β ₁ (V _T −V _T0 ) + γ ₁ (3)
Note that α ₁ , β ₁ , and γ ₁ are obtained by installing a TCXO in a thermostat and measuring the frequency by changing the temperature in the thermostat variously.

  On the other hand, as shown in FIGS. 7A and 7B, the TCXO 1 includes a substrate 11, a crystal resonator 21 including an AT-cut crystal piece provided on the substrate 11, and an oscillation control unit that is an IC chip. 22 and a cover 12 that covers the crystal unit 21 and the oscillation control unit 22 on the substrate 11. FIG. 7B shows a state where the cover 12 is removed from the substrate 11.

Here, since the oscillation control unit 22 and the crystal resonator 21 are provided in a space surrounded by the same cover 12 and substrate 11, the temperature detected by the temperature detector included in the oscillation control unit 22 is the same as that of the crystal resonator 21. It has been considered equal to ambient temperature. However, in reality, the oscillation control unit 22 which is an IC generates heat by the supplied electric power, and the temperature detected by the temperature detector due to the generated heat is slightly higher than the ambient temperature of the crystal resonator. When the TCXO 1 is used after determining each constant as described above, a voltage corresponding to a temperature deviated from the ambient temperature of the crystal resonator 21 due to the heat generation is applied to the cubic function generator. a compensation voltage V _C required to suppress the frequency change, error and compensation voltage V _C to be actually applied occurs. This error causes a minute frequency fluctuation in the change in the ambient temperature in the TCXO1.

  In recent years, mobile terminals such as mobile phones are sometimes configured as GPS receivers equipped with a GPS (Global Positioning System) function. This GPS is a system that detects the current position of the mobile terminal based on a signal transmitted from GPS hygiene and a signal output from an oscillator mounted on the GPS receiver, and a TCXO is used as this oscillator. Is being considered. In this GPS, in order to detect the position of the mobile terminal with high accuracy, TCXO is required to have particularly high oscillation accuracy, and therefore it is required to suppress frequency fluctuations due to heat generation of the IC.

Although Patent Document 1 and Patent Document 2 describe the configuration of TCXO, the above problem is not described, and the problem cannot be solved.
JP-A-6-326516 JP 2004-172831 A

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a temperature-compensated crystal oscillator that suppresses fluctuations in oscillation frequency due to changes in ambient temperature and has high oscillation accuracy.

Ｋ_２＝０で表される電圧Ｖ_ＣをＶ₀に加算した制御電圧を出力するように構成されていることを特徴とする。前記温度検出器、発振回路及び電圧制御部は例えば集積回路チップに設けられている。 The temperature compensated crystal oscillator of the present invention is
A quartz crystal provided in a container;
An oscillation circuit provided in the container for oscillating a crystal resonator;
A temperature detector provided in the container;
A voltage controller for applying a control voltage to the crystal unit;
With
The voltage control unit detects the temperature detected by the temperature detector as T, the reference temperature as T ₀ , and the voltage at which the set frequency of the crystal resonator is obtained at the reference temperature T ₀ as V ₀ , as detected by the temperature detector. ΔT, a set temperature difference corresponding to the temperature difference between the measured temperature and the temperature of the crystal unit
If K _j is a preset constant, it is expressed by the following equation:

A control voltage obtained by adding a voltage V _C represented by K ₂ = 0 to V ₀ is output. The temperature detector, the oscillation circuit, and the voltage control unit are provided in, for example, an integrated circuit chip.

  According to the present invention, a control voltage calculated based on a temperature detected by a temperature detector and a preset temperature difference between the temperature detected by the temperature detector and the crystal resonator is applied to the crystal resonator. When applied, its oscillation is controlled. Therefore, since the influence of the temperature difference is suppressed, the oscillation of the crystal resonator can be controlled with high accuracy, and fluctuations in the oscillation frequency can be suppressed.

FIG. 1 is a circuit configuration diagram of a TCXO 2 according to an embodiment of the present invention. Reference numeral 22 denotes an oscillation control unit that controls the oscillation of the crystal resonator 21 and is constituted by, for example, an IC chip. _{Reference numeral} 23 is a DC voltage (V _CC ) supply terminal, and 24 is an output terminal for oscillation output. As described in the background art section, the oscillation controller 22 cancels the frequency change Δf corresponding to the difference between the temperatures T and T ₀ to the control voltage V _{0 at} which the target frequency f is obtained at the reference temperature T ₀ . The compensation voltage V _C is configured to be added. The oscillation control unit 22 includes an oscillation circuit 25 that constitutes the crystal oscillation circuit 20 together with the crystal resonator 21, a variable capacitance diode 26, a cubic function generator 27 that constitutes a voltage control unit, a temperature detector 28, and a memory 29. Yes.

As a difference between the TCXO 2 shown in FIG. 1 and the conventional TCXO 1, the cubic function generator 27 of the oscillation control unit 22 performs the calculation represented by the equation (4), and the compensation voltage V _C that is the calculation result, The reference _value T ₀ is set so that an addition value to the control voltage V _{0 at} which the crystal resonator has a set frequency is applied to the crystal oscillation circuit 20 including the crystal resonator 21 and the oscillation circuit 25.
V _C = α ′ (T−T ₀ −ΔT) ³ + β ′ (T−T ₀ −ΔT) + γ ′ (4)
In this equation (4), T is the ambient temperature of the crystal resonator detected by the temperature detector 28, and this temperature T is controlled to oscillate to the actual ambient temperature of the crystal resonator as described in the background art section. The temperature increase due to the heat generation of the portion 22 is included. T ₀ is a reference temperature that is the temperature of the inflection point in the frequency temperature characteristics of the crystal resonator, similarly to T _{0 in} equations (1) and (2), and is, for example, 29 ° C. T ₀ and α ′, β ′, and γ ′ are constants obtained from measurement. These α ′, β ′, and γ ′ are not necessarily the same values as α ′, β ′, and γ ′ in the formula (2) described in the background art section, but the same reference numerals are used for convenience.

Here, the correspondence relationship between the output voltage of the temperature detector 28 and the temperature, for example, a table or algorithm is stored in the memory 29 in advance, and the temperature T is obtained based on the output voltage and the correspondence relationship in the memory 29. Therefore, a cubic function is generated by the cubic function generator 27 using this temperature T, and V _C is obtained thereby. However if the output voltage of the temperature detector 28 is proportional to the temperature, without a corresponding relationship between the temperature and the output voltage as described above is stored in the memory 29, obtains the V _C using the output voltage be able to. FIG. 1 shows such a case. Since the output voltage of the temperature detector 28 becomes an input signal of the cubic function generator 27, the compensation voltage V _C obtained by the cubic function generator 27 is as follows. It is represented by the formula (5).
V _C = α ₁ (V _T −V _T0 −V _ΔT ) ³ + β ₁ (V _T −V _T0 −V _ΔT ) + γ ₁ (5)
V _T is an output voltage of the temperature detector 28 at the temperature T, and V _T0 is an output voltage of the temperature detector 28 at the reference temperature T ₀ . V _ΔT is an output voltage fluctuation amount of the temperature detector 28 corresponding to the temperature difference ΔT between the crystal resonator 21 and the oscillation controller 22. These α ₁ , β ₁ , γ ₁ , V _T0 and V _ΔT are stored in the memory 29. The compensation voltage V _C calculated in this way is added to the control voltage V ₀ for obtaining the set frequency f at the reference temperature T ₀ to obtain the control voltage V ₁ of the crystal resonator 21. In the function generator 27, the calculation of the equation (5) and the calculation of the compensation voltages V _C and V ₀ are performed and output to the crystal unit 21.

A procedure for determining the constant of the equation (5) will be described. First, after assembling TCXO2, it is carried into a thermostat. Then, for example, each value of α _{1 to} γ ₁ , V _T0, and V _ΔT is input in advance to the memory 29 at the time of carrying into the thermostat. This constant temperature bath can freely change the temperature inside, and can maintain the said temperature uniformly. The temperature detector 28 of the TCXO 2 carried into the thermostat is connected to, for example, a display screen provided outside the thermostat, and the temperature detection value is displayed on the display screen. The TCXO 2 is connected to a frequency measuring device, and the measurement result is displayed on the display screen.

  Subsequently, the temperature in the thermostatic chamber is set to an arbitrary temperature. After the temperature in the bath reaches that temperature and the temperature has stabilized, for example, the TCXO 2 is powered on, and the crystal oscillation circuit 20 oscillates. After the power supply to the TCXO 2 is turned on, the oscillation control unit 22 generates heat due to the current flowing through the oscillation control unit 22, and the temperature gradually increases. The operator records the temperature measured by the temperature detector 28 every time a predetermined time elapses, for example. The temperature in the thermostatic chamber and the temperature of the oscillation control unit 22 are gradually balanced, the temperature rise of the oscillation control unit 22 is suppressed, and the temperature detected by the temperature detector 28 becomes constant. The operator confirms that the detected temperature has become constant, subtracts the temperature in the thermostat from the constant temperature, and determines the subtracted temperature value as a temperature difference ΔT. In TCXO2, for example, the temperature difference ΔT is 0.8 ° C.

  In the step of determining the temperature difference ΔT, the measurement does not have to be continued until the temperature detected by the temperature detector 28 becomes constant. For example, if the temperature is measured several times at predetermined intervals after the TCXO 2 is turned on, From the measurement result, the temperature at which the temperature rise detected by the temperature detector 28 stops and becomes constant may be predicted, and the temperature in the thermostatic bath may be subtracted from the predicted value to determine ΔT.

After determining the temperature difference ΔT, the operator changes, for example, α ₁ , β ₁ , γ ₁ , T ₀ and the oscillation frequency of the crystal oscillator 20 measured by the frequency measuring instrument, and the set temperature of the thermostat. Are stored in a computer connected to the frequency measuring device and the thermostat.

Subsequently, the operator changes the temperature in the thermostatic chamber, and when the temperature in the bath stabilizes, the oscillation frequency obtained by changing α ₁ , β ₁ , γ ₁ , T ₀ of the crystal oscillator 20 at that time And the temperature in a thermostat is similarly memorize | stored in a computer. Such temperature change of the thermostat and the storage of the temperature and oscillation frequency of the thermostat after the change are repeatedly performed a predetermined number of times. Since the compensation voltage V _C necessary for changing the oscillation frequency of the crystal resonator 21 at each temperature to the set frequency is known from FIG. 5, α can be obtained by establishing the above equation (5) for each temperature. Simultaneous equations with ₁ , β ₁ , and γ ₁ as unknowns are obtained. For this reason, α ₁ , β ₁ , γ ₁ , and T ₀ that minimize the frequency change at each temperature are obtained. The quartz oscillator 21 from the variation of just the manufacturing process slight frequency occurs, for example, gamma ₁ not set to zero, it is set to a value that is taking into account the variation in frequency between the quartz resonator 21 However, it may be zero.

Now consider the above formula (5) and the conventional formula (2). Conventionally, grounds decided as the temperature compensation voltage V _C (2) expression is due to being treated as the temperature detected by the temperature detector T in represents the temperature characteristic of the frequency (1). On the other hand, in the above-described embodiment, when T is a temperature detection value of the temperature detector, Δf / f is handled as expressed by the following equation (6).
Δf / f = α (T−T ₀ −ΔT) ³ + β (T−T ₀ −ΔT) + γ (6)

By the way, if this equation (6) is subtracted from the conventional equation (1), the third-order influence on (T−T ₀ ) is small, so that it is expressed by the following equation (7) as an approximate equation (T−T): _A quadratic function for ₀ ) is obtained.
(Δf / f) ≈A (T−T ₀ ) ² + B (T−T ₀ ) + C (7)
A, B, and C are constants determined by α, β, γ, and ΔT.
2 and 3 show examples of the cubic function of the expression (1) and the quadratic function of the expression (7) when ΔT is 0.8 ° C., for example. That is, in this example, since the degree of scale of the vertical axis is greatly different, the temperature characteristics are shown separately in FIG. 2 and FIG. 3, but in the past, only the characteristic of the cubic function shown in FIG. This means that the characteristic component of the quadratic function shown in FIG. 3 is not compensated. The reason is that the temperature of the temperature detector 28 and the temperature of the crystal unit 21 are different as described repeatedly.

Therefore, by setting based on a temperature compensation voltage V _C to (5), characteristic portion of a quadratic function is also to be compensated. That is, to cancel the temperature characteristics obtained by combining the FIG. 2 and FIG. 3, the compensation voltage V _C of TCXO2 are set.

According to this TCXO2, based on the ambient temperature T detected by the temperature detector 28, and the temperature difference ΔT which is the temperature difference between the temperature detected by the preset temperature detector 28 and the crystal oscillator, The cubic function generator 27 determines a compensation voltage V _C to be applied to the oscillation circuit 25, and a control voltage V ₁ corresponding to the compensation voltage V _C is applied to the crystal oscillation circuit 20. Therefore, due to the temperature difference ΔT at the time when the ambient temperature T is changed, the deviation between the compensation voltage V _C to be actually applied to the crystal oscillation circuit 20 and the compensation voltage V _C required to suppress the frequency fluctuations can be suppressed. As a result, the frequency fluctuation can be suppressed, and the crystal resonator can be oscillated with high accuracy.

この式（８）でＫ_ｊは予め設定した定数であるが、ただしＫ_２＝０である。つまり、既述の例では（８）式においてｎ＝３である場合について説明しており、上記の（４）式と対応させると、Ｋ_３＝α’、Ｋ_１＝β’、Ｋ_０＝γ’である。そして、（８）式においてｎは４以上の整数として設定されてもよく、例えばｎ＝４である場合、ｎ＝５である場合にはＶ_Ｃは夫々下記の（９）式、（１０）式で表すことができる。
Ｖ_Ｃ＝Ｋ₄(Ｔ−Ｔ₀−ΔＴ)⁴＋Ｋ₃(Ｔ−Ｔ₀−ΔＴ)³＋Ｋ₁(Ｔ−Ｔ₀−ΔＴ)＋Ｋ₀
・・・（９）
Ｖ_Ｃ＝Ｋ₅(Ｔ−Ｔ₀−ΔＴ)⁵＋Ｋ₄(Ｔ−Ｔ₀−ΔＴ)⁴＋Ｋ₃(Ｔ−Ｔ₀−ΔＴ)³
＋Ｋ₁(Ｔ−Ｔ₀−ΔＴ)＋Ｋ₀
・・・（１０） By the way, an example in which the compensation voltage V _C is a cubic function for (T−T ₀ −ΔT) has been described, but V _C is not limited to such a cubic function, and a quartic function, a quintic function, or the like. May be set as a higher-order function of the third or higher order. The _{V C} can be expressed by the following equation (8).

In this equation (8), K _j is a preset constant, but K ₂ = 0. That is, in the above-described example, the case where n = 3 in the equation (8) is described, and when corresponding to the above equation (4), K ₃ = α ′, K ₁ = β ′, K ₀ = γ ′. In the equation (8), n may be set as an integer equal to or greater than 4. For example, when n = 4, when n = 5, _VC is represented by the following equations (9) and (10), respectively. It can be expressed by a formula.
V _C = K ₄ (T−T ₀ −ΔT) ⁴ + K ₃ (T−T ₀ −ΔT) ³ + K ₁ (T−T ₀ −ΔT) + K ₀
... (9)
V _C = K ₅ (T−T ₀ −ΔT) ⁵ + K ₄ (T−T ₀ −ΔT) ⁴ + K ₃ (T−T ₀ −ΔT) ³
+ K ₁ (T−T ₀ −ΔT) + K ₀
... (10)

It is a circuit block diagram of TCXO which concerns on embodiment of this invention. It is the graph which showed the part for the cubic function of the temperature characteristic of the crystal oscillator provided in the TCXO. FIG. 6 is a graph showing a quadratic function portion of the temperature characteristics of the crystal resonator. It is the graph which showed the temperature characteristic for the cubic function of a crystal oscillator, and the change of the compensation voltage which compensates it. It is the graph which showed the relationship between the control voltage applied to an oscillation circuit, and an oscillation frequency. It is the graph which showed the relationship between ambient temperature and a frequency deviation. It is an external appearance perspective view of TCXO.

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Cover 20 Crystal oscillation circuit 21 Crystal oscillator 22 Oscillation control part 25 Oscillation circuit 27 Tertiary function generator 28 Temperature detector 29 Memory 1, 2 TCXO (temperature compensation crystal oscillator)

Claims (2)

A quartz crystal provided in a container;
An oscillation circuit provided in the container for oscillating a crystal resonator;
A temperature detector provided in the container;
A voltage controller for applying a control voltage to the crystal unit;
With
The voltage control unit detects the temperature detected by the temperature detector as T, the reference temperature as T ₀ , and the voltage at which the set frequency of the crystal resonator is obtained at the reference temperature T ₀ as V ₀ , as detected by the temperature detector. ΔT, a set temperature difference corresponding to the temperature difference between the measured temperature and the temperature of the crystal unit
If K _j is a preset constant, then

Represented by the relationship
A temperature-compensated crystal oscillator configured to output a control voltage obtained by adding a compensation voltage V _C expressed by K ₂ = 0 to V ₀ .   2. The temperature compensated crystal oscillator according to claim 1, wherein the temperature detector, the oscillation circuit, and the voltage control unit are provided in an integrated circuit chip.

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