Temperature compensation crystal oscillator

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a temperature-compensated crystal oscillator (hereinafter referred to as a temperature-compensated oscillator) as an industrial technical field, and particularly relates to a temperature-compensated oscillator with reduced noise and power consumption.

【0002】

[Conventional technology]

(Background of the Invention) Since a temperature-compensated oscillator compensates for the frequency-temperature characteristics of a crystal oscillator and maintains a constant oscillation frequency, it is widely used in mobile communication devices such as mobile phones used in a dynamic environment. ing. In recent years, a temperature-compensated oscillator with low noise and low power consumption (low voltage operation) has been demanded from the viewpoint of high-quality communication of information and energy saving.

【0003】

(Example of Conventional Technology) FIG. 4 is a block circuit diagram of a temperature-compensated oscillator for explaining one conventional example. The temperature compensation oscillator basically consists of a crystal oscillator 1 and a temperature compensation circuit 2. The crystal oscillator 1 includes, for example, a crystal oscillator 3 as an inductor component, and an oscillation circuit unit 4 in which a capacitor forming a resonance circuit (not shown), a feedback amplifier for oscillation, and the like are integrated (IC). These form an oscillating closed loop. Then, for example, when the crystal oscillator 3 is AT-cut, the frequency temperature characteristic of the crystal oscillator 1 becomes a cubic curve having an inflection point near room temperature mainly due to the crystal oscillator 3 (Fig. 5, for example, curve a).

【0004】

As shown in FIG. 6, the temperature compensation circuit 2 includes, for example, each parallel circuit of the thermistor 5 and the capacitor 6. Then, based on the resistance value of the thermistor 5, which decreases exponentially in response to the temperature, the change in the inter-terminal capacitance (equivalent series capacitance) in each parallel circuit is used. This is commonly known as the direct method. Normally, an adjusting resistor 7 is inserted in series or in parallel to adjust the temperature resistance characteristics of the thermistor 5 (see Japanese Patent Publication No. 64-1969). Then, the high temperature part and the low temperature part compensation circuit 2 (ab) based on the normal temperature are connected in series, and the high temperature part and the low temperature part of the frequency temperature characteristic are independently temperature-compensated, respectively.

【0005】

In such a case, since the capacitance between the terminals of the temperature compensation circuit 2 changes depending on the temperature, the series equivalent capacitance (so-called load capacitance) on the circuit side as seen from both terminals of the crystal oscillator 3 also changes. Therefore, by setting each element value of the temperature compensation circuit 2, the frequency temperature characteristic of the crystal oscillator 1 is compensated and flattened within the standard temperature range.

【0006】

Generally, in order to adjust the oscillation frequency (nominal frequency) of the crystal oscillator 1 at room temperature, a frequency adjustment circuit 8 mainly composed of a capacitor is inserted into the oscillation closed loop (previous Fig. 4). In addition, in order to correct the variation in frequency temperature characteristics before temperature compensation (Fig. 5, curve B, C) mainly due to the crystal oscillator 3, the temperature characteristics are in the oscillation closed loop, for example, in the frequency adjustment circuit 8 or separately. A capacitor 9 having a temperature (referred to as a temperature capacitor 9) is applied.

【0007】

For example, if a thermocouple capacitor 9 having a negative temperature characteristic whose capacitance value decreases with temperature is applied (Fig. 7, curve a), the capacitance value decreases above the reference temperature (normal temperature), so the oscillation frequency rises with temperature. To do. Then, when the temperature is below the reference temperature, the capacitance value becomes large, so that the oscillation frequency drops. Therefore, the frequency temperature characteristic of the crystal oscillator 1 rotates counterclockwise around room temperature.

【0008】

On the contrary, when the thermocouple capacitor 9 having a positive temperature characteristic is applied (figure, curve b), the frequency temperature characteristic is rotated clockwise. As a result, for example, the temperature can be compensated by making the curves b and c in FIG. 5 above close to the reference frequency temperature characteristic (reference temperature characteristic) curve a, that is, reducing the degree of variation. In reality, the thermocouple capacitor 9 having a negative temperature characteristic is mainly used, and the correction is performed counterclockwise.

【0009】

In this case, since the frequency temperature characteristic of each crystal oscillator is close to the reference temperature characteristic and the value of each element of the temperature compensation circuit does not differ significantly, the design of the temperature compensation circuit 2 is facilitated and the assortment of each element is assorted. To reduce. Further, even if the frequency temperature characteristic cannot be compensated within the standard due to a large variation in the setting of each element value, the frequency temperature characteristic can be compensated within the standard because it is compensated after approaching the reference temperature. Therefore, it is possible to improve productivity by eliminating waste due to poor frequency temperature characteristics before compensation of the crystal oscillator. The variation in frequency-temperature characteristics depends on the temperature characteristics of each circuit element, but is particularly due to the cutting angle of the crystal oscillator 3.

【0010】

[Problems to be Solved by the Invention]

(Problems of the prior art) However, the temperature-compensated oscillator having the above configuration requires the thermocouple capacitor 9 because it corrects the variation in the frequency-temperature characteristics of the crystal oscillator 1. However, there are few types of this type of thermal capacitor 9, and it takes a long time to obtain them, and the price is high, which reduces productivity.

【0011】

Further, when the thermal capacitor 9 is not used, it is necessary to select and compensate each element value according to the variable frequency and temperature characteristics of each crystal oscillator 1. However, in this case, it is necessary to increase the assortment of each element (thermistor 5, capacitor 6 and adjusting resistor 7), and the design becomes complicated and the productivity is lowered. Further, in any case, the direct method using the thermistor 5 including a resistor and the capacitor 6 requires a frequency adjustment circuit 8, and there is a problem that the total number of parts is increased and miniaturization is hindered.

【0012】

On the other hand, as shown in FIG. 8, the so-called indirect method is used as the temperature compensation means, and the oscillation circuit unit 4 excluding the crystal oscillator 3 and the temperature compensation mechanism 10 are integrated in the IC 11 shown by the alternate long and short dash line frame. There is a temperature-compensated oscillator. In the indirect method, a compensation voltage is applied to a voltage variable capacitance element 12 such as a varicap diode inserted in an oscillation closed loop composed of a crystal oscillator 3 and an oscillation circuit unit 4, and the load capacitance seen from the crystal oscillator 3 is changed. To compensate for the temperature. Reference numeral 19 is a high frequency blocking resistor.

【0013】

The temperature compensation mechanism 10 includes a compensation voltage generation circuit 13 and a storage circuit 14. The compensation voltage generation circuit 13 includes, for example, a constant term, a linear function term, and a cubic function term voltage generation circuit 13 (abc). Then, the compensation voltage Vs (T) of the cubic function approximated by the following equation (1) is generated by the temperature detection signal of the temperature sensor (not shown) provided inside the IC. However, T₀Is the reference temperature, and α, β, and γ are the coefficients of each degree term. The temperature sensor consists of, for example, a resistor having a linear and positive temperature coefficient. Vs (T) = α (TT)₀)³ + β (TT)₀) + γ (1) [0014]

The storage circuit 14 receives compensation data based on the frequency temperature characteristics measured by each crystal oscillator 1 from the write terminal and holds it. Then, for example, the amplification factor of the operational amplifier provided in each voltage generation circuit 13 (abc) is controlled to determine the coefficients α, β, and γ of each order. As a result, the compensation voltage Vs (T) corresponding to each frequency temperature characteristic is obtained and the temperature is compensated.

【0015】

In such a case, even if there is a variation in the frequency and temperature characteristics of each crystal oscillator 1, it can be compensated by setting α and β based on the compensation data, so that the heating capacitor 9 as described above is not required. Further, since the coefficient γ sets the compensation voltage (reference voltage that becomes the nominal frequency) at room temperature, the frequency adjustment circuit 8 itself is basically excluded. In the indirect method, in order to widen the temperature compensation range, a frequency temperature characteristic having a maximum value in a low temperature part and a minimum value in a high temperature part is usually applied (Fig. 5, curve d).

【0016】

However, in the indirect method using such an IC, the temperature coefficient of the resistor provided in the IC is used to generate the compensation voltage of the linear and cubic function terms from the weak temperature detection signal, so an amplifier or the like is required. Power consumption increases. In addition, there is a problem that the internal noise of the IC becomes relatively large with respect to the temperature detection signal, and the noise characteristics deteriorate.

【0017】

(Purpose of the Invention) An object of the present invention is to provide a temperature-compensated oscillator with improved productivity and reduced power consumption and noise.

【0018】

[Means for solving problems]

(Point of interest) The present invention has focused on the fact that the frequency temperature characteristic can be rotated with reference to room temperature by controlling the linear coefficient β of the compensation voltage in the indirect method. That is, if a voltage that is a linear function is applied to the voltage variable capacitance element with reference to normal temperature, the capacitance value decreases and the oscillation frequency increases above room temperature, and the capacitance value increases and the oscillation frequency decreases below room temperature. As a result, we focused on the fact that the frequency temperature characteristics can be rotated and corrected.

【0019】

According to the present invention, a correction voltage corresponding to a temperature is generated by a temperature sensor provided inside an IC, and a frequency temperature characteristic mainly caused by a crystal oscillator is corrected to a reference temperature characteristic, and then a reference temperature characteristic is obtained. The basic solution is to compensate the temperature by a temperature compensation mechanism outside the IC.

【0020】

[Action]

In the present invention, since the frequency temperature characteristic of each crystal oscillator is brought close to the reference temperature characteristic by the correction voltage, the heating capacitor 9 is not required. Further, since the coefficient α of the cubic function term is not controlled, the cubic function voltage generation circuit is not required, the noise generation source is reduced, and the noise characteristics can be improved. Hereinafter, an embodiment of the present invention will be described.

【0021】

[Example]

FIG. 1 is a block circuit diagram of a temperature-compensated oscillator for explaining an embodiment of the present invention. In addition, the same number is given to the same part as the previous conventional example drawing, and the description thereof will be simplified or omitted. As described above, the temperature compensating oscillator includes a crystal oscillator 1 having a frequency temperature characteristic of a cubic curve, a direct temperature compensating circuit 2 as a parallel circuit of the thermistor 5 and a capacitor 6, and a temperature compensating mechanism unit peculiar to the present invention. It consists of 15. Then, the oscillation circuit unit 4 including the voltage variable capacitance element 12 and the temperature compensation unit 15 are integrated inside the IC 11 indicated by the alternate long and short dash line frame, and the crystal oscillator 3 and the temperature compensation circuit 2 are outside the IC.

【0022】

The temperature correction mechanism unit 15 includes a correction voltage generation circuit 13A and a storage circuit 14. The correction voltage generation circuit 13A includes the constant term voltage generation circuit 13a that sets the oscillation frequency (nominal frequency) at room temperature described above, and the linear function term voltage generation circuit 13b that operates based on the resistance change depending on the temperature sensor described above. Consists of. Then, the correction voltage Vs of the following equation (2)₁(T) is generated. Vs₁(T) = β₁(TT₀) + Gamma (2) [0023]

The storage circuit 14 stores the correction data based on the difference between the measured frequency temperature characteristic and the reference temperature characteristic (previous Fig. 5, curve a) of each crystal oscillator. That is, this is corrected (proximity) according to the difference from the reference temperature characteristic, and the correction data for setting the linear coefficient β is stored.

【0024】

In such a case, for example, for frequency temperature characteristics that deviate from the reference temperature characteristics due to the cutting angle (Fig. 5, curve B and C), the linear function is corrected according to each frequency temperature characteristic. Voltage Vs₁Close to the reference temperature characteristic by (T). Then, the frequency temperature characteristic close to the reference temperature characteristic is temperature-compensated by the external temperature compensation circuit 2, that is, the temperature compensation circuit 2 of the direct method including the thermistor 5 including the adjusting resistor 7 and the parallel circuit circuit of the capacitor 6. The oscillation frequency at room temperature is controlled by the constant term voltage from the constant term voltage generation circuit 13a.

【0025】

With such a configuration, the frequency temperature characteristic is close to the reference temperature characteristic, so that the conventional hard-to-find and expensive thermal capacitor is not required. Moreover, since the design of the temperature compensation circuit 2 is generally standardized, the product lineup of each temperature compensation element (thermistor, capacitor, adjustment resistor) can be reduced. Therefore, productivity can be increased.

【0026】

The correction voltage generation circuit 13A inside the IC is limited to the constant term and the linear function term voltage generation circuit 13 (ab), and the cubic function term voltage generation circuit 13c is excluded. Therefore, as compared with the temperature compensation oscillator of the IC using the indirect method of the conventional example, the number of circuits for amplifying the temperature detection signal and the noise generation source are reduced, so that the power consumption is suppressed and the noise characteristics are improved.

【0027】

Further, in this embodiment, since the oscillation frequency at room temperature is adjusted by the constant term voltage, the frequency adjustment circuit 8 of the conventional example in the direct method is not required. Therefore, miniaturization can be promoted.

【0028】

[Other matters]

In the above embodiment, the oscillation frequency at room temperature is adjusted by the constant term voltage generation circuit 13a in the correction voltage generation circuit 13A, and the frequency adjustment circuit 8 outside the IC is removed. The constant term voltage generation circuit 13a may be removed from the IC, and the frequency adjustment circuit 8 described above may be provided outside the IC. In this case, since the constant term voltage generation circuit 13a is removed from the inside of the IC, the noise component contained in the voltage source can be eliminated, and the noise characteristics are further improved.

【0029】

In addition, the temperature compensation circuit 2 outside the IC is a direct method in which two parallel circuits, one for high temperature and one for low temperature, which consist of a parallel circuit of the thermistor and a capacitor, are connected in series, but basically the capacitor is shared and parallel to this. Thermistors for high temperature and low temperature may be connected in parallel (not shown).

【0030】

Although the temperature compensation circuit (mechanism) is a direct method, as shown in Fig. 3, the voltage variable capacitance element 16 is inserted in the oscillation closed loop outside the IC and the compensation voltage from the compensation voltage generation circuit 17 is applied. You may try to do it. Here, the compensation voltage generation circuit 17 is composed of a thermistor network including an adjustment resistor provided outside the IC. Reference numeral 18 in the figure is a DC blocking capacitor. In this case, since the frequency temperature characteristic having the maximum value in the low temperature portion and the minimum value in the high temperature portion is targeted, the compensation temperature range can be expanded as compared with the direct method as described above. However, since the number of parts of the temperature compensation circuit itself increases, the direct method is preferable in this respect.

【0031】

Further, although the voltage variable capacitance element 16 to which the compensation voltage from the compensation voltage generation circuit 17 is applied is provided outside the IC, it may be provided inside the IC in order to promote miniaturization. In this case, the voltage variable capacitance element 12 can be shared and unified. On the contrary, since discrete is better in terms of characteristics, the voltage variable capacitance element 12 may be provided outside the IC, and when the temperature compensation circuit 2 is indirect (Fig. 3 above), it may be provided. , The voltage variable capacitance element 16 can be shared and unified.

【0032】

Further, although the temperature compensation circuit of the direct method is formed from the thermistor 5, the capacitor 6 and the adjusting resistor 7, only the thermistor 5 and the capacitor 6 may be used, or a composite element of the thermistor and the capacitor may be used. In this case, of course, miniaturization is promoted. Further, although the temperature sensor is a resistor having a temperature coefficient, for example, the temperature characteristic of the forward voltage drop in the transistor may be used, and a detection signal corresponding to the temperature may be obtained. However, all of these detection signals are small signals and require amplification.

【0033】

Further, although the voltage variable capacitance element 12 is a varicap diode, for example, as a parallel circuit of CMOS and a capacitor, the capacitance between terminals of the parallel circuit may be changed by changing the resistance of CMOS due to the correction voltage, in short, depending on the correction voltage. It suffices as long as the capacity value changes substantially. Further, although only the correction voltage is applied to the voltage variable capacitance element 12, the AFC voltage by the automatic frequency control circuit may be applied.

【0034】

[Effect of the invention]

In the present invention, a correction voltage corresponding to the temperature is generated by a temperature sensor provided inside the IC, the frequency temperature characteristic mainly caused by the crystal oscillator is corrected to the reference base temperature characteristic, and then the reference temperature characteristic is corrected outside the IC. Since the temperature is compensated by the temperature compensation mechanism, it is possible to provide a temperature compensation oscillator with improved productivity and reduced power consumption and noise.

[Simple explanation of drawings]

[Figure 1]

It is a block circuit diagram of the temperature compensation oscillator explaining one Embodiment of this invention.

[Figure 2]

It is a block circuit diagram of the temperature compensation oscillator explaining another embodiment of this invention.

[Fig. 3]

It is a block circuit diagram of the temperature compensation oscillator explaining another embodiment of this invention.

[Fig. 4]

It is a block circuit of a temperature compensation oscillator for explaining a conventional example.

[Fig. 5]

It is a frequency temperature characteristic figure of a crystal oscillator explaining a conventional example.

[Fig. 6]

It is a temperature compensation circuit diagram of the direct method explaining a conventional example.

[Fig. 7]

It is a characteristic diagram of the thermal capacitor which explains the conventional example.

[Fig. 8]

It is a block circuit of a temperature compensation oscillator by IC conversion using an indirect method temperature compensation mechanism (circuit) for explaining a conventional example.

[Explanation of symbols]

1 Crystal oscillator, 2 Temperature compensation circuit, 3 Crystal oscillator, 4 Oscillator circuit, 5 Thermista, 6 Capacitor, 7 Adjustment resistor, 8 Frequency adjustment circuit, 9 Thermocoupler, 10 Temperature compensation mechanism, 11 IC, 12, 16 Voltage Variable capacitance element, 13, 17 Compensated voltage generation circuit, 13A correction voltage generation circuit, 14 storage circuit, 15 correction mechanism, 18 DC blocking capacitor, 19 AC blocking resistor.