JPH1093343A - Temperature compensation method for piezoelectric oscillating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the temperature compensation with respect to the temperature compensation of the piezoelectric oscillating circuit. SOLUTION: The piezoelectric oscillating circuit is provided with a temperature sensor 1 sensing its surrounding temperature, a crystal vibrator 14 being a frequency decision element, a varactor diode 11 whose reactance varies with a DC control voltage, a voltage controlled crystal oscillator 4 including the crystal vibrator 14 and the varactor diode 11 in its feedback loop, and a voltage generating circuit 7 which allows the varactor diode 11 to generate a desired control voltage in response to an output from the temperature sensor 1. In this case, an output control voltage of the voltage generating circuit 7 is a voltage that is realized by approximating with a plurality of line segments a 2nd voltage curve which is obtained by adding a correction voltage changed linearly at a desired gradient and a segment with respect to a temperature to a 1st voltage curve at which an output frequency of the piezoelectric oscillating circuit is constant with respect to temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensation method for a piezoelectric oscillation circuit which can be mainly used in a mobile communication system such as a portable telephone.

[0002]

2. Description of the Related Art In recent years, demand for mobile communication such as mobile phones has been increasing. Accordingly, demand for a temperature-compensated crystal oscillator serving as a reference frequency source for mobile communication has been increasing. A temperature-compensated crystal oscillator is an oscillator that uses a crystal oscillator having high frequency stability as a frequency determining element and further includes a temperature compensation circuit that stabilizes the frequency in the order of ppm even with respect to temperature. That is, since the oscillation frequency of the crystal oscillator varies depending on the ambient temperature, it is necessary to perform temperature compensation.

Therefore, as one conventional method, a temperature-compensated crystal oscillator is placed in a temperature control chamber, and the temperature inside the chamber is raised, for example, by 110 ° C. from −30 ° C. to + 80 ° C. in steps of 4 ° C. The temperature compensation can be performed by inputting the correction data every 32 lines provided in the memory.

[0004]

SUMMARY OF THE INVENTION The above-mentioned conventional method has the following problems.
In the temperature range of 10 ° C., it is necessary to adjust the internal temperature every 4 ° C., extract the correction data, and write the correction data into the memory, and the process is extremely complicated. In addition, since the quantized data is periodically output from the memory and converted into an analog signal, the oscillation frequency purity (C / N)
However, there was a problem that the steel was deteriorated.

Accordingly, an object of the present invention is to provide a high-performance piezoelectric oscillation circuit which simplifies adjustment work.

[0006]

In order to achieve this object, the present invention provides a temperature sensor for detecting an ambient temperature, a piezoelectric vibrator serving as a frequency determining element, and a reactance that is controlled by a DC control voltage. A variable reactance element that changes, an oscillation circuit that includes the piezoelectric vibrator and the variable reactance element in a feedback loop, and a voltage generation circuit that supplies a desired control voltage to the variable reactance element according to an output from the temperature sensor In a piezoelectric oscillation circuit comprising: a first voltage curve in which the output frequency of the piezoelectric oscillation circuit is substantially constant with respect to temperature as an output control voltage of the voltage generation circuit; The second voltage curve obtained by adding the correction voltage that changes linearly with the above is a voltage approximated by a plurality of straight lines. If configuration, it performs temperature compensation only in discrete temperature compensation data so linear approximation,
The temperature can be compensated for the curve in a simple and optimal manner.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a temperature sensor for detecting an ambient temperature, a piezoelectric vibrator serving as a frequency determining element, and a variable reactance whose reactance changes by a DC control voltage. A piezoelectric element comprising: an element; an oscillation circuit including the piezoelectric vibrator and the variable reactance element in a feedback loop; and a voltage generation circuit for generating a desired control voltage to the variable reactance element in accordance with an output from the temperature sensor. In the oscillation circuit, as the output control voltage of the voltage generation circuit, the output frequency of the piezoelectric oscillation circuit changes linearly with a desired slope and intercept with respect to temperature to a first voltage curve where the output frequency is substantially constant with respect to temperature. A second voltage curve obtained by adding the correction voltage to be a voltage approximated by a plurality of straight lines,
With this configuration, temperature compensation can be performed only with discrete temperature compensation data because of linear approximation, and temperature compensation can be performed in a simple and optimal form on a curve.

According to a second aspect of the present invention, first, a first voltage curve at which the output frequency of the piezoelectric oscillation circuit becomes substantially constant with respect to temperature is detected, and the first voltage curve is added to the temperature. The second voltage curve is calculated by adding a voltage that changes linearly with a desired slope and an intercept, and the second voltage curve is approximated by a plurality of straight lines. This is a temperature compensation method for a piezoelectric oscillation circuit. If temperature compensation is performed by this method, a voltage curve can be ideally linearly approximated.

According to a third aspect of the present invention, the intersection of a plurality of straight lines approximating the second voltage curve is set on the second voltage curve. This is a temperature compensation method for a piezoelectric oscillation circuit as described above. According to this method, it is easy and fast to calculate a plurality of approximate straight lines.

According to a fourth aspect of the present invention, the voltage compensating circuit includes a storage circuit for storing data for setting the control voltage output to the variable reactance element to a desired value. 4. The method according to claim 1, wherein
It is a temperature compensation method for a piezoelectric oscillation circuit according to any one of the above, and can be configured as a module product by mounting a storage device.

According to a fifth aspect of the present invention, when the second voltage curve is approximated by a straight line, the second voltage curve is approximated by using three to eight straight lines. A temperature compensation method for a piezoelectric oscillation circuit according to any one of the above,
If linear approximation is performed with the above number, the memory capacity does not increase and high-performance temperature compensation characteristics can be obtained.

According to a sixth aspect of the present invention, a quartz oscillator is used as the piezoelectric vibrator, and the temperature compensation of the piezoelectric oscillation circuit according to any one of the first to fifth aspects is performed. By using a quartz oscillator, a simple and high-performance temperature compensation method can be obtained for an oscillation circuit having excellent signal purity.

According to a seventh aspect of the present invention, the slope of the correction voltage straight line to be added to the first voltage curve with respect to the temperature is made positive. A temperature compensation method for a piezoelectric oscillation circuit according to
With this configuration, the positive 3
Optimal linear approximation can be performed for a piezoelectric element (for example, a quartz oscillator) having a next curve.

The invention according to claim 8 of the present invention is characterized in that the intercept with respect to the temperature of the correction voltage straight line to be added to the first voltage curve is negative. A temperature compensation method for a piezoelectric oscillation circuit according to
Optimal linear approximation can be performed for a piezoelectric element (for example, a quartz oscillator) whose characteristic inflection point is higher than 0 ° C. with respect to temperature.

According to a ninth aspect of the present invention, the slope f with respect to the temperature of the correction voltage straight line to be added to the first voltage curve is approximately f (x) =-0, where x is the number of straight lines approximating the slope. .13x + 1.18, wherein the value is represented by a function:
8. The temperature compensation method for a piezoelectric oscillation circuit according to any one of items 1 to 8, wherein, particularly when a quartz oscillator is used, a simple and high-performance temperature compensation method can be realized by using the correction voltage straight line. Obtainable.

According to a tenth aspect of the present invention, the intercept g with respect to the temperature of the correction voltage straight line to be added to the first voltage curve is approximately g (y) = g, where y is the number of approximating straight lines. 4. A value represented by a function of 4.79y-39.69.
9. The temperature compensation method for a piezoelectric oscillation circuit according to any one of items 1 to 9, wherein a simple and high-performance temperature compensation method is provided by using the above-described correction voltage straight line, particularly when a quartz oscillator is used. Obtainable.

According to an eleventh aspect of the present invention, each of the plurality of straight lines approximating the second voltage curve is formed by using an amplifier for amplifying or attenuating the output of the temperature sensor positively or negatively. 11. The method according to claim 1, wherein
In the temperature compensation method for a piezoelectric oscillation circuit according to any one of the above, the frequency is controlled without converting a digital signal into an analog signal by adopting the above configuration, so that digital noise and quantization error can be controlled. No performance degradation due to

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a temperature sensor;
Is a voltage amplifier, 3 is a voltage adder, 4 is a voltage-controlled crystal oscillator (hereinafter referred to as VCXO) that can change the frequency by voltage, 5 is a memory that stores a control amount,
Reference numeral 6 denotes a digital / analog converter (hereinafter referred to as a D / A converter), and reference numeral 7 denotes a voltage generation circuit for generating an offset voltage. The temperature sensor 1 outputs the temperature information to the memory 5 as temperature information, and the memory 5 outputs a digital signal based on the temperature information. The digital signal is converted by a D / A converter 6 into an analog amount, for example, a resistance or a voltage, and output to the voltage amplifier 2 and the voltage generation circuit 7. The voltage amplifier 2 amplifies the output voltage of the temperature sensor 1 at a predetermined gain according to the output of the D / A converter 6,
Output to the voltage adder 3. Further, the output voltage of the voltage generation circuit 7 for adjusting the offset amount based on the output of the D / A converter 6 is determined and output to the voltage adder 3. Voltage adder 3 adds the output voltage from voltage amplifier 2 and the output voltage from voltage generation circuit 7 and outputs the result to VCXO 4. The temperature sensor 1, the voltage amplifier 2, the voltage adder 3, the VCXO 4, the memory 5, the D / A converter 6, and the voltage generating circuit 7 are modularized to constitute a temperature compensated crystal oscillator.

As shown in FIG. 2, the VCXO 4 is a control terminal 9 to which the output of the voltage adder 3 is applied, a buffer resistor 10, a variable capacitance diode 11, a DC cut capacitor 12, a feedback capacitor 13, a crystal oscillator. 14, an active element 15, a feedback resistor 16, and an output terminal 17.

The temperature sensor 1 is, as shown in FIG.
Three series-connected diodes 18, a resistor 19 and a DC
A 3V application terminal 20 and an output terminal 21;
Since the junction voltage of the diode 18 varies depending on the temperature, the output from the output terminal 21 falls linearly as shown in FIG.

Here, the frequency deviation obtained from the VCXO 4 is determined by the frequency deviation of the quartz oscillator 14 used. The commonly used quartz oscillator 14 is cut out at an angle called an AT cut. FIG. 5 shows the temperature characteristics of the AT-cut quartz resonator. As shown in FIG.
It is known that the temperature characteristics of a cut quartz resonator have a substantially cubic curve with respect to temperature. Accordingly, the characteristic obtained from the VCXO 4 also becomes a cubic curve, and the control voltage applied to the control terminal 9 to keep the frequency constant with respect to temperature has the opposite characteristic. FIG. 6 shows this state. In FIG. 6, A to C each have an oscillation output frequency of ± 0 pp.
The control voltages at m, +1 ppm and -1 ppm are also shown.

In order to generate the control voltage shown in FIG. 6, the configuration of the present invention employs a method of approximating the curve of FIG. 6 with a plurality of straight lines. That is, a circuit in which the output voltage changes linearly with temperature in the temperature sensor 1 shown in FIG.
Using a circuit as shown in FIG. 3, the output is optimized by a voltage amplifier for slope and intercept to generate a plurality of straight lines. However, here, when the curve shown in FIG. 6 is simply approximated by a straight line, the result is as shown in FIG. In general, a straight line approximation of a curve is based on the joint of the approximating straight lines (where it bends)
Is on a curve to be approximated, it can be obtained by a very simple mathematical formula, and is obtained from the following (Equation 1). That is, the coordinates (x
If (1, y1) and (x2, y2) are on the approximated curve, then

[0023]

(Equation 1)

Is an equation of a straight line passing through the two coordinates. Hereinafter, in the present invention, an approximate straight line will be obtained using the equation (Equation 1).

FIG. 7 shows a case in which approximation is made by five straight lines as an example. From FIG. 7, it is understood that the given straight line passes through the inside of the curve. That is, in an area where the curve is convex downward (approximately −25 ° C. or less), an approximate straight line passes above the curve, and an area where the curve is convex upward (approximately −25 ° C.).
In the above, the approximate straight line passes below the curve.

Therefore, in the present invention, a predetermined correction straight line is added to the given ideal control curve (FIG. 6), and a straight line approximation is performed on the added curve. FIG. 8 shows this. 8, the line A is the ideal control curve shown also in FIGS. 6 and 7, and the temperature on the line A is t,
The added voltage (correction voltage) is Vadd, and becomes (Equation 2).

[0027]

(Equation 2)

The line B to which the added voltage is applied is the line B, and the line C is an approximation of the line B by five straight lines in the same manner as in FIG. What is important here is that although the C-line is a linear approximation to the B-line, the C-line is ultimately an optimal linear approximation to the A-line. In the present invention,
The above-mentioned added voltage Vadd can be generated by the voltage generation circuit 7 in FIG. 1, and is not shown in FIG. 1, but when the temperature sensor 1 generates a voltage that changes linearly with temperature, The output can be used to amplify or attenuate appropriately.

When the above contents are examined in more detail,
It was found that there is an important relationship between the coefficient of t in (Equation 2) and the number of straight lines used for approximation. The contents will be described below.

FIG. 9A shows the relationship between the slope a of the correction voltage straight line and the number of straight lines used for approximation, and FIG. 9B shows the relationship between the intercept b of the correction voltage straight line and the number of straight lines used for approximation. In both figures, if the number of straight lines increases, a
And b asymptotically approach 0, but when approximating by 3 to 8 straight lines as a realistic number, the relationship between a and b and the number L of approximate straight lines is expressed by (Equation 3) and (Equation 4)

[0031]

(Equation 3)

[0032]

(Equation 4)

FIGS. 10 (a) to 10 (f) show the results of the temperature frequency stability when the number of approximate straight lines is changed from 3 to 8 using the method of the present invention. For comparison, each drawing also shows a case where the correction voltage obtained from (Equation 3) and (Equation 4) is not used. When the correction voltage is used, it can be seen that the maximum frequency deviation range is smaller than when the correction voltage is not used, and higher performance can be achieved.

As described above, by adding a desired correction voltage straight line to the ideal control voltage according to the number of approximating straight lines and performing linear approximation on the resulting curve, a large memory 5 is not required. Thus, it is possible to obtain a simple and high-performance temperature-compensated piezoelectric oscillator.

As the voltage amplifier 2, an operational amplifier as shown in FIG. 11 can be used as an example of the constituent means. The output terminal 21 of the temperature sensor 1 is connected to the input terminal 23 of the inverting amplifier 22. As feedback resistors, n sets of resistors (R1, R2... Rn) and switches (Sw1, Sw)
2... Sw3) are connected, and which switch Sw1
傾 き Swn can be turned on to change the slope of the voltage appearing at the output terminal 24. Also, the switch Sw1
As a method for storing the states of Swn, an EEPROM, a flash memory, a fuse ROM, or the like can be used. Reference numeral 23a is a reference terminal for adjusting the offset amount of the output voltage. When using a fuse ROM, it is preferable to use a multiplexer as shown in FIG. In the multiplexer shown in FIG. 12, the connection destination of the voltage application terminal 25 can be changed by the switch control terminal 26, and a desired fuse (R1, R2,
Rn), an excess voltage is applied to the voltage application terminal 25 to burn out the fuses (R1, R2, Rn). By doing so, the number of terminals drawn out can be reduced. As a method of knowing the optimum combination in advance, a switch (Sw1, Sw2, S2
wn) is effective. That is, it is turned on by a digital signal in series with the fuses (R1, R2, Rn).
By connecting switches (Sw1, Sw2, Swn) capable of / off, fuses (R1, R2, Rn)
You can know the optimal switch status before burning out.

[0036]

As described above, according to the present invention, the temperature of the piezoelectric oscillator which adds a correction voltage straight line according to the number of straight lines approximating the ideal control voltage curve and performs linear approximation on the obtained curve is obtained. This is a compensation method, and a correction voltage straight line and a method of linear approximation can be obtained by simple mathematical expressions. Therefore, a simple and high-performance temperature-compensated piezoelectric oscillation circuit can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of the voltage-controlled crystal oscillator.

FIG. 3 is a circuit diagram of the temperature sensor.

FIG. 4 is a characteristic diagram of the temperature sensor shown in FIG. 3;

FIG. 5 is a temperature characteristic diagram of the crystal resonator.

FIG. 6 is a characteristic diagram showing an ideal voltage curve when performing temperature compensation of the voltage controlled crystal oscillator.

FIG. 7 is a characteristic diagram showing a state in which the ideal voltage curve shown in FIG. 6 is approximated by five straight lines by a simple method.

FIG. 8 is a characteristic diagram showing a state in which a curve obtained by adding a correction voltage straight line to the ideal control voltage curve shown in FIG. 6 is subjected to linear approximation;

9A and 9B are characteristic diagrams showing the relationship between the slope and intercept of the correction voltage straight line and the number of straight lines used for approximation, respectively.

FIGS. 10A to 10F are frequency-temperature characteristic diagrams of a crystal oscillator when temperature compensation is performed using the method of the present invention, respectively.

FIG. 11 is a circuit diagram showing an example of a voltage amplifier that can be used in the present invention.

FIG. 12 is a circuit diagram illustrating an example of a multiplexer that can be used as a memory of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature sensor 2 Voltage amplifier 3 Voltage adder 4 VCXO 5 Memory 6 D / A converter 7 Voltage generation circuit 8 Temperature compensation crystal oscillator

Claims (11)

[Claims] 1. A temperature sensor for detecting an ambient temperature, a piezoelectric vibrator serving as a frequency determining element, a variable reactance element whose reactance changes according to a DC control voltage, and feedback of the piezoelectric vibrator and the variable reactance element. An oscillation circuit included in a loop, and a piezoelectric oscillation circuit including a voltage generation circuit that supplies a desired control voltage to the variable reactance element in accordance with an output from the temperature sensor, wherein an output control voltage of the voltage generation circuit is: A second voltage curve obtained by adding a correction voltage that changes linearly with a desired slope and intercept to temperature to a first voltage curve at which the output frequency of the piezoelectric oscillation circuit is substantially constant with temperature. A voltage approximated by a plurality of straight lines. 2. First, a first voltage curve at which the output frequency of the piezoelectric oscillation circuit becomes substantially constant with respect to temperature is detected, and the first voltage curve is linearly formed with a desired slope and intercept with respect to temperature. 2. The temperature compensation method for a piezoelectric oscillation circuit according to claim 1, wherein a second voltage curve is calculated by adding the changing voltages, and the second voltage curve is approximated by a plurality of straight lines. 3. The temperature compensation method for a piezoelectric oscillation circuit according to claim 1, wherein intersections of a plurality of straight lines approximating the second voltage curve are set on the second voltage curve. 4. The voltage compensating circuit includes a storage circuit,
4. A temperature compensation method for a piezoelectric oscillation circuit according to claim 1, wherein data for setting a control voltage output to said variable reactance element to a desired value is stored therein. . 5. When approximating the second voltage curve with a straight line,
5. The temperature compensation method for a piezoelectric oscillation circuit according to claim 1, wherein the approximation is performed using three to eight straight lines. 6. The temperature compensation method for a piezoelectric oscillation circuit according to claim 1, wherein a quartz oscillator is used as the piezoelectric oscillator. 7. The temperature compensation of the piezoelectric oscillation circuit according to claim 1, wherein a slope of the correction voltage straight line to be added to the first voltage curve with respect to the temperature is made positive. Method. 8. The temperature compensation of a piezoelectric oscillation circuit according to claim 1, wherein an intercept with respect to a temperature of a correction voltage straight line to be added to the first voltage curve is negative. Method. 9. A function of approximately f (x) = − 0.13x + 1.18, where the slope f with respect to the temperature of the correction voltage line to be added to the first voltage curve is represented by x, where x is the number of approximate lines. 2. A value which is set to a value to be set.
9. The temperature compensation method for a piezoelectric oscillation circuit according to any one of items 1 to 8. 10. The intercept g with respect to the temperature of a correction voltage straight line to be added to the first voltage curve is represented by a function of approximately g (y) = 4.79y-39.69, where y is the number of approximating straight lines. 2. A value represented by the following expression:
10. The temperature compensation method for a piezoelectric oscillation circuit according to any one of items 1 to 9. 11. The method according to claim 1, wherein each of the plurality of straight lines approximating the second voltage curve is formed by using an amplifier for amplifying or attenuating the output of the temperature sensor to positive or negative. A temperature compensation method for a piezoelectric oscillation circuit according to any one of the preceding claims.