JPH06291550A - Digital type temperature compensation piezoelectric oscillator and communication equipment - Google Patents

Abstract

PURPOSE:To decrease the memory, and also, to execute the temperature compensation with high accuracy by constituting a compensation data generating part of a first temperature compensating part, and a second temperature compensating part with an offset memory, and sending out compensation data to a first temperature compensating part, based on temperature data by a second temperature compensating part. CONSTITUTION:In a compensation data generating part 3, an offset corresponding to each temperature data is stored in advance in an offset memory 11 of a second temperature compensating part, and based on the temperature data subjected to analog- to-digital conversion, offset data is sent out to a first temperature compensating part. In a first temperature compensating part, compensation data is generated by executing an operation of a polynomial expression, based on temperature data and the contents of a coefficient memory 9, and also, to this compensation data, the offset data sent out of a second temperature compensating part is added, and it becomes final compensation data 7. According to this constitution, the memory quantity can be decreased, and formation of the oscillator and its cost-up caused by an increase of the memory quantity can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature-compensated oscillator, and more particularly to a temperature-compensated piezoelectric oscillator for compensating the temperature of a piezoelectric oscillator with a digital temperature compensation circuit.

[0002]

2. Description of the Related Art In a general digital temperature-compensated piezoelectric oscillator, as shown in the block diagram of FIG. 9, a temperature detector 1 detects the temperature in the vicinity of a voltage-controlled piezoelectric oscillator 5, and an analog-digital converter 2 is used to detect the temperature. The information is digitally encoded and converted into temperature data 6, the compensation data creation unit 3 creates compensation data 7 for compensating the frequency-temperature characteristics of the voltage controlled piezoelectric oscillator 5, and the digital-analog converter 4 creates the compensation data 7 Is converted into a compensation voltage and applied to the voltage-controlled piezoelectric oscillator 5 to output a stable frequency with respect to temperature.

The compensation data creating section 3 is conventionally composed of a memory 8 which stores compensation data 7 corresponding to the temperature data 6 for each temperature data as shown in FIG. This structure is disclosed in Japanese Patent Application Laid-Open No. 48-25463.

As another configuration of the compensation data creating section 3, a compensation voltage-temperature curve of the voltage controlled piezoelectric oscillator 5 is approximated by a polynomial as shown in FIG. 11, and the coefficient of the polynomial is constructed by a semiconductor or the like. There is a configuration in which the compensation data 7 is generated by storing it in the coefficient memory 9 and performing a polynomial calculation in the arithmetic processing unit 10 every time the temperature data 6 changes.

[0005]

However, the above-mentioned FIG.
The configuration of the compensation data creating unit 3 has a drawback that a large amount of memory is required to obtain high frequency accuracy. The use of a large amount of memory leads to an increase in the chip area of the IC, which poses a problem regarding miniaturization and cost reduction.

On the other hand, in the case of the configuration of the compensation data generating section 3 of FIG. 11, the amount of the coefficient memory 9 for storing the frequency temperature coefficient of the voltage controlled piezoelectric oscillator 5 is about 40 bits, and therefore the method of FIG. Although the amount of memory can be significantly reduced compared to the above, due to frequency fluctuations caused by distortion during processing of the piezoelectric vibrator and errors during data acquisition when calculating the coefficients of the polynomial, the polynomial cannot be sufficiently approximated and the necessary temperature compensation is required. Accuracy may not be obtained.

In the case of the configuration of FIG. 11, the compensation data 7 in each temperature data is associated with the coefficient data in the coefficient memory 9. Therefore, if it becomes clear that the frequency deviation does not fall within the specified frequency deviation at a specific temperature, it is impossible to correct the compensation data at that specific temperature, which significantly increases the productivity of the digital temperature-compensated crystal oscillator. It was a loss.

[0008]

A digital temperature-compensated crystal oscillator according to the present invention comprises a temperature detector for detecting temperature, and compensation data for transmitting temperature compensation data according to temperature data output from the temperature detector. A digital temperature-compensated piezoelectric oscillator including a creation unit, a variable reactance whose electrostatic capacitance is changed according to the compensation data from the creation unit, and a piezoelectric oscillator whose frequency is controlled by the variable reactance. The compensation data creation unit is composed of a first temperature compensation unit and a second temperature compensation unit having an offset memory, and the second temperature compensation unit has a first temperature compensation unit based on temperature data from a temperature detector. It is characterized in that the compensation data is sent to the temperature compensation unit.

The second temperature compensator is characterized by including an index memory, a spare memory and a spare decoder.

[0010]

According to the above configuration of the present invention, the frequency temperature characteristic of the piezoelectric oscillator is compensated by the first temperature compensating section, and further the first temperature compensating section is used.
By compensating the residual difference that cannot be compensated by the temperature compensating unit of No. 2 by the offset data of the second temperature compensating unit,
It is possible to perform temperature compensation with high accuracy and a small memory.

Further, by compensating in the second temperature compensating section only at a specific temperature or a limited temperature range, it is possible to further reduce the memory.

[0012]

EXAMPLES Examples of the present invention will be described below.

FIG. 3 shows an example of frequency-temperature characteristics of the piezoelectric oscillator. In the figure, the horizontal axis represents the temperature of the piezoelectric oscillator and the vertical axis represents the frequency deviation Δf / f _O when the oscillation frequency of the piezoelectric oscillator at T _O ° C is f _O, and the solid line in the figure represents the frequency of the piezoelectric oscillator. The result of having acquired the temperature characteristic at every 0.5 degreeC is shown. This Δf / f _O is generally a polynomial (1)
Can be expressed as

Δf / f _O = K _O + K ₁ (T-T _O ) + K ₂ (T-T _O ) ² + K ₃ (T-T _O ) ³ + ··· + Kn (T-T _O ) ⁿ ··· ( 1) However, Kn (n = 0, 1, 2, 3 ...) Represents an nth-order temperature coefficient.

The broken line in FIG. 3 shows the frequency-temperature characteristic of the piezoelectric oscillator shown by the solid line, which is approximated by a third-order polynomial, for example. Thus, the frequency temperature characteristic of the piezoelectric oscillator is
Since it can be expressed relatively well in (1), a large amount of frequency fluctuation of the frequency temperature characteristic of the piezoelectric oscillator can be compensated by the conventional configuration shown in the compensation data generating unit of FIG. This FIG.
FIG. 4 shows the temperature compensation result obtained by the compensation data creating unit.
From the figure, it can be seen that the frequency temperature characteristic of the piezoelectric oscillator has a frequency variation of about ± 0.8 ppm that cannot be canceled by the compensation data creation unit of FIG. 11 because it cannot be approximated by a polynomial. This occurs due to frequency fluctuations caused by distortion during processing of the piezoelectric vibrator, errors during data acquisition when calculating the coefficients of the polynomial, and the like.

According to the present invention, the temperature compensation of the piezoelectric oscillator is performed by making the offset K _O of the frequency variation that cannot be approximated by this polynomial variable and changing it according to the temperature data. That stores the K _O of formula (1) corresponding to each temperature data, and to assist compensated by the second temperature compensating section.

FIG. 1 shows a block diagram of a temperature-compensated piezoelectric oscillator for explaining an embodiment of the present invention. In FIG. 1, the first temperature compensating unit has the same configuration as the compensation data creating unit of FIG. 11, and the offset memory 11 of the second temperature compensating unit according to the present invention is a storage device composed of a semiconductor or the like. Is. The offset memory 11 of the second temperature compensating unit stores offset data corresponding to K _O of the equation (1) in each temperature data, and the first temperature is calculated based on the analog-digital converted temperature data. The offset data is sent to the compensator.

FIG. 5 shows an example of the contents of the offset memory 11 shown in FIG. 1. The vertical axis shows the offset data in the offset memory, and the horizontal axis shows the temperature corresponding to the temperature data. Arithmetic processing unit 1 in the first temperature compensation unit
At 0, a polynomial operation is performed based on the temperature data 6 and the contents of the coefficient memory 9 to create compensation data, and the offset data K _O sent from the second temperature compensation section is added to the compensation data to finally obtain the compensation data. Compensation data 7.

FIG. 6 shows an example of the temperature compensation result of the temperature-compensated piezoelectric oscillator according to the embodiment of the present invention shown in FIG. 1. The compensation result by the first temperature compensator of FIG. Offset data K _O sent from the temperature compensating unit 2
It has been corrected by. As is apparent from FIG. 6, the frequency-temperature characteristic of the digital temperature-compensated crystal oscillator can be made extremely highly accurate by using the compensation data creation unit having the above-described configuration of the present invention. According to the above configuration, the amount of memory required for compensation is, for example, the coefficient memory of the first temperature compensating unit is 40 bits, and the offset memory compensates the temperature range of −30 ° C. to + 85 ° C. by 3 bits every 0.5 ° C. [40] + [[{85 − (− 30)} / 0.5 + 1] × 3]
= 733 bits.

FIG. 12 shows an example of a result obtained by the configuration of the conventional compensation data creating unit 3 of FIG. 10 with the same frequency accuracy as that of FIG. In the case of FIG. 12, the amount of memory 8 required for compensation is 0.5 ° C. in the temperature range of −30 ° C. to + 85 ° C.
Since 8 bits are compensated for each time, [[{85 − (− 30)} / 0.5 + 1] × 8] = 18
It is 48 bits.

As is apparent from the above, the method according to the configuration of FIG. 1 of the present invention can reduce the memory amount to 1/2 or less as compared with the method according to FIG.
It is possible to suppress an increase in the size and cost of the oscillator due to an increase in the amount of memory.

FIG. 2 is a block diagram of a temperature compensated piezoelectric oscillator for explaining another embodiment of the present invention. FIG. 2 shows a configuration for supplementarily compensating in the second temperature compensating unit by the offset information at a specific temperature or a limited temperature range. 2, the first temperature compensating unit has the same configuration as the compensation data creating unit of FIG. 11, and the index memory 12 and the spare memory 13 of the second temperature compensating unit according to the present invention are composed of semiconductors or the like. It is a storage device. The operation will be described below. In the index memory 12 shown in FIG. 2, whether offset compensation corresponding to K _O in equation (1) is necessary when inputting compensation data (“1” or “
0 ") is written in advance. For example, the required frequency accuracy is ± 0.6 p as shown by the broken line in FIG.
In the case of pm, the index data corresponding to the temperature data of the temperature ranges a, b, c and d in which the frequency deviation of FIG. Write offset data that fits inside.

An example of the index data in the index memory 12 and the offset data in the spare memory 13 is shown in FIG. In FIG. 8, the horizontal axis indicates the temperature corresponding to the temperature data. The spare decoder 14 selects presence / absence of offset compensation by the second temperature compensating unit based on the temperature data from the analog-digital converter and the index data in the index memory 12 of the second temperature compensating unit. That is, when the index data in the index memory 12 is the temperature data other than the temperature ranges a, b, c and d in which the index data is “0”, the temperature compensation by the second temperature compensating unit is not performed and the index data is “1”. In the case of temperature data in the temperature ranges a, b, c and d
The offset data K _O in the spare memory 13 is sent to the first temperature compensator. The arithmetic processing unit 10 in the first temperature compensating unit performs a polynomial calculation based on the temperature data and the contents of the coefficient memory to create compensation data, and further the offset data sent from the second temperature compensating unit to the compensation data. Is added to obtain the final compensation data 7.

FIG. 7 shows an example of frequency-temperature characteristics of the temperature-compensated piezoelectric oscillator according to FIG. 2 which is an embodiment of the present invention. FIG. 7 shows the compensation result by the first temperature compensator of FIG. FIG. 9 shows results obtained by correcting the temperature ranges a, b, c and d with the offset data of FIG. 8 in the spare memory 13 of the second temperature compensation unit of FIG. As is apparent from FIG. 7, the frequency-temperature characteristic of the digital temperature-compensated crystal oscillator compensated by the compensation-data creating unit of FIG. 2 of the present invention can be kept within the required frequency accuracy ± 0.6 ppm. .

According to the above configuration, the required memory amount is the minimum required memory amount for keeping the frequency within the compensation accuracy. For example, assuming that the amount of spare memory is 20 points of temperature data, the required amount of memory is represented by the sum of the coefficient memory, index memory, and spare memory. Therefore, [40] + [{85 − (− 30)} /0.5+1]+[20
X2] = 311 bits.

FIG. 13 shows an example of the result obtained by the configuration of the conventional compensation data creating unit 3 of FIG. 10 with the same frequency accuracy as that of FIG. In the case of FIG. 13, the amount of memory 8 required for compensation is 0.5 ° C. in the temperature range of −30 ° C. to + 85 ° C.
Since 6 bits are compensated for each time, [[{85 − (− 30)} / 0.5 + 1] × 6] = 13
It will be 86 bits.

As is apparent from the above, the method according to the configuration of FIG. 2 of the present invention can reduce the memory amount to 1/4 or less as compared with the method of FIG.
It is possible to suppress an increase in the size and cost of the oscillator due to an increase in the amount of memory.

Further, according to the configuration of FIGS. 1 and 2 which is the present invention, since the compensation by the second temperature compensating unit can be carried out completely independently of the temperature data before and after, the conventional temperature compensating unit of FIG. It is possible to correct compensation data at a specific temperature, which was difficult with the method, and high productivity can be realized.

The means for converting the temperature into temperature data is
Not limited to the temperature detector and the A / D converter, when the temperature detector is a frequency output type, it can be configured with a temperature detector and a counter. Also, the variable reactance of the piezoelectric oscillator is a variable voltage reactance. It is needless to say that the structure is not limited to the element, and a variable reactance configuration using a capacitive array group is also possible.

It goes without saying that the offset memory, the index memory and the spare memory may be separated from each other and used in the same memory.

[0031]

According to the above-mentioned structure of the present invention, the frequency temperature characteristic of the piezoelectric oscillator is compensated by the first temperature compensating section, and the residual difference compensation which cannot be compensated by the first temperature compensating section is performed by the second temperature compensating section.
By compensating with the offset data of the temperature compensating unit, the temperature can be compensated with high accuracy and with less memory.

Further, the memory in the second temperature compensating section can be further reduced by setting the operation to a specific temperature or a limited temperature range.

As described above, in the temperature-compensated piezoelectric oscillator, which serves as a frequency reference source for various communication devices that require miniaturization and high accuracy, a temperature-compensated piezoelectric oscillator having a small size, high accuracy, and high productivity is provided. Since the oscillator is provided, it has a great effect on the performance improvement of various communication devices.

[Brief description of drawings]

FIG. 1 is a diagram showing a compensation data creation unit of a temperature-compensated piezoelectric oscillator that is an embodiment of the present invention.

FIG. 2 is a diagram showing a compensation data creation unit of a temperature-compensated piezoelectric oscillator that is another embodiment of the present invention.

FIG. 3 is a diagram showing an example of frequency-temperature characteristics of a piezoelectric oscillator.

FIG. 4 is a diagram showing an example of a temperature compensation result of the piezoelectric oscillator according to the conventional configuration of FIG.

5 is a diagram showing an example of offset data in the offset memory of FIG. 1 which is an embodiment of the present invention.

FIG. 6 is a diagram showing an example of a temperature compensation result of the temperature-compensated piezoelectric oscillator according to FIG. 1, which is an embodiment of the present invention.

FIG. 7 is a diagram showing an example of temperature compensation results of the temperature-compensated piezoelectric oscillator according to FIG. 2, which is an embodiment of the present invention.

FIG. 8 is a diagram showing an example of index data in the index memory of FIG. 2 and offset data in the spare memory of one embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a general digital temperature-compensated piezoelectric oscillator.

FIG. 10 is a diagram showing an example of a memory configuration of a conventional compensation data creation unit.

FIG. 11 is a diagram showing an example of a configuration of a conventional compensation data creation unit based on polynomial approximation.

FIG. 12 is a diagram showing an example of a frequency compensation result by 8-bit compensation data in the conventional configuration of FIG.

13 is a diagram showing an example of a frequency compensation result by 6-bit compensation data in the conventional configuration of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Temperature detector 2 ... Analog-digital converter 3 ... Compensation data creation part 4 ... Digital-analog converter 5 ... Voltage-controlled piezoelectric oscillator 6 ... Temperature data 7 ... Compensation data 8 ... Memory 9 ... Coefficient memory 10 ... Calculation processing Unit 11 ... Offset memory 12 ... Index memory 13 ... Spare memory 14 ... Spare decoder

Claims (4)

[Claims] 1. A temperature detector that detects at least a temperature, a compensation data creation unit that sends compensation data in accordance with temperature data output from the temperature detector, and a compensation data output from the compensation data creation unit. In a digital temperature-compensated piezoelectric oscillator including a variable reactance whose electrostatic capacity is changed by a variable reactance, and a piezoelectric oscillator whose frequency is controlled by the variable reactance, the compensation data creation unit includes a first temperature compensation unit and an offset. A digital temperature-compensated piezoelectric oscillator, comprising a second temperature compensation unit having a memory, wherein the second temperature compensation unit sends compensation data to the first temperature compensation unit based on temperature data. 2. The digital temperature-compensated piezoelectric oscillator according to claim 1, wherein the second temperature compensator comprises an index memory, a spare memory and a spare decoder. 3. The digital temperature-compensated piezoelectric oscillator according to claim 1, wherein the piezoelectric element of the piezoelectric oscillator is a crystal oscillator or a surface acoustic wave element. 4. A communication device comprising the digital temperature-compensated piezoelectric oscillator according to claim 1, claim 2, or claim 3.