KR100322936B1 - A digital controlled oscillation circuit of a portable telephone, a method of calculating an oscillation frequency of a crystal oscillator, and an output frequency correction method - Google Patents

Abstract

In a portable telephone using a CPU, a storage device, a temperature sensor, a D / A converter, and an A / D converter as control elements and having an oscillation circuit including a crystal oscillator and a variable capacitance diode, Lt; / RTI > The storage device previously stores control information for correcting the output frequency drift of the portable telephone set caused by the temperature change. The temperature of the oscillation circuit is sensed by the temperature sensor and converted into a digital value by the A / D converter. The CPU reads the control information corresponding to the sensed temperature from the storage device and applies it to the variable capacitance diode of the oscillation circuit through the D / A converter to maintain the output frequency at a certain level. Also disclosed is a method for efficiently calculating an oscillation frequency of a quartz crystal with a reduced number of measurement points relative to a temperature characteristic of the quartz crystal. A method for accurately performing the temperature compensation described above is also disclosed.

Description

A digital controlled oscillation circuit of a portable telephone, a method of calculating an oscillation frequency of a crystal oscillator, and an output frequency correction method

The present invention relates to a digital control type oscillation circuit of a portable telephone, and also relates to a quartz crystal oscillation frequency calculation method and a frequency correction method suitable for use in an oscillation circuit.

FIG. 1 shows an example of the arrangement of a conventional digital temperature-compensated crystal oscillator. As illustrated in the figure, the digital temperature compensated crystal oscillator 60 includes an oscillation circuit 61 using a crystal oscillator 45 (see FIG. 2), a temperature sensor 62, an A / D converter 63 A central processing unit (CPU) 64, a D / A converter 65, an integrating circuit 66, and a storage circuit (storage device)

The crystal oscillator has a temperature characteristic in which the oscillation frequency changes with temperature change. Therefore, in the oscillation circuit 61 using the crystal oscillator as the oscillation device, the oscillation frequency is corrected by applying the control voltage corresponding to the temperature change, and the output frequency is maintained at a constant level. For this purpose, the memory circuit 67 stores control information (voltage value) in advance in order to correct the resonance frequency drift caused by the temperature change. The temperature of the oscillation circuit 61 is sensed by the temperature sensor 62. The sensed temperature is converted into a digital value by the A / D converter 63 and output to the CPU 64. [ The CPU 64 outputs a control signal (digital signal) corresponding to the sensed temperature to the D / A converter 65 by referring to the correction information stored in the storage circuit 67. [ The D / A converter 65 converts the control signal into an analog signal and outputs it to the oscillation circuit through the integration circuit 66 to maintain the output frequency at a predetermined level.

The digital temperature compensated crystal oscillator 60 includes a temperature sensor 62, an A / D converter 63, a CPU 64, a D / A converter 65, an integrating circuit 66, (67) is necessary, so that the arrangement is complex and must be large.

Further, the digital temperature-compensated crystal oscillator 60 performs temperature compensation corresponding to the temperature characteristic of the crystal oscillator 45. [ Therefore, when the digital temperature-compensated crystal oscillator 60 is used as the oscillation circuit of the portable telephone, when the crystal oscillator fails, not all of the crystal oscillator 45 is replaced with a new one, which is costly.

Further, when the digital temperature compensated crystal oscillator 60 is used as the oscillator of the portable telephone, the control object of the temperature compensation is the frequency at the output terminal of the oscillation circuit 61. [ Therefore, the output frequency of the antenna of the portable telephone has an undesirable error caused by the high frequency part, that is, the VCO.

FIG. 2 shows an example of the arrangement of the oscillation circuit shown in FIG. The oscillation frequency of the oscillation circuit 61 is determined by the capacitance of the quartz crystal resonator 45, the capacitors 43, 44, and 46, and the variable capacitance diode 42. The frequency signal oscillated from the crystal oscillator 45 is amplified by the transistor 50 and output from the output terminal T _out via the capacitor 56. [

The quartz crystal vibrator 45 has a temperature characteristic in which the frequency changes (about ± 10 ppm) in accordance with a change in temperature. Therefore, the voltage applied to the variable capacitance diode 42 (i.e., the voltage applied to the input terminal T _in ) is controlled to correct a change in the resonant frequency of the quartz crystal oscillator 45 caused by the temperature change. The change in the resonant frequency of the quartz crystal vibrator 45 caused by the temperature changing with a high degree of accuracy should be calculated in order to perform frequency correction with a high degree of accuracy. Further, for example, the frequency deviation of the crystal vibrator of the AT plate is represented by a polynomial, as described later. Therefore, the data measured at various measurement points are needed to accurately calculate the change in resonant frequency caused by the temperature change. That is, an unmanageable action must be performed to prepare such measurement data.

Further, in the conventional oscillation circuit, as described above, by controlling the voltage applied to the variable capacitance diode 42, the change in the resonance frequency of the quartz crystal caused by the temperature change is corrected. Moreover, each of the variable capacitance diodes has its own control voltage versus variable capacitance diode characteristic. As shown in FIG. 3, there are various control voltage versus frequency deviation characteristics in which the slope K is different. The conventional practice is to select a variable capacitance diode having a slope K close to a predetermined slope and to store the value in the storage device 67 as the slope K of the variable capacitance diode 42 in advance. Thus, it takes a lot of time to select an appropriate variable capacitance diode. Moreover, since the slope of the control voltage vs. frequency deviation characteristic is not accurate, an error occurs in the control voltage (correction voltage). In addition, the linear slope K indicating the control voltage vs. frequency deviation characteristic is not uniform in the entire control voltage range, as shown in Fig. That is, the control voltage versus frequency deviation characteristic of each variable capacitance diode is given by a linear root equation. Therefore, if correction is not performed using the control voltage given by the linear form with the slope K obtained at a proper control voltage, an error will occur.

It is an object of the present invention to provide a portable telephone in which the temperature compensation of a quartz crystal resonator is made by effectively using a control element which has been conventionally used in a portable telephone and a control object of temperature compensation is an output frequency of an antenna of a portable telephone, And to provide a digital controlled oscillation circuit.

In order to achieve the above object, the present invention provides a digital controlled oscillation circuit for use in a portable telephone using a CPU, a storage device, a temperature sensor, a D / A converter, and an A / D converter as control elements. As shown in FIG. 4, the memory device 20 previously stores control information for correcting the drift of the output frequency of the portable telephone set caused by the temperature change.

The temperature of the oscillation circuit 22 is sensed by the temperature sensor 23. The detected temperature is converted into a digital signal in the A / D converter 24, and the digital signal is input to the CPU 1. [ The CPU 1 outputs a correction signal corresponding to the control information stored in the storage device 20. [ The correction signal is converted into an analog value in the D / A converter 21 and then inputted to the oscillation circuit 22 as a control voltage to control the output frequency of the portable telephone to a predetermined constant level. That is, the temperature sensor 23, the A / D converter 24, the CPU 1, the memory device 20, and the D / A converter 21, which have been conventionally installed in the portable telephone, Can be used. The object of temperature compensation control is the output frequency of the antenna 9 and can be used as temperature compensation data.

It is still another object of the present invention to provide a method of efficiently calculating the oscillation frequency of a quartz crystal with the number of reduced measurement points with respect to the temperature characteristic of the quartz crystal.

In order to achieve the above object, the present invention provides a method of calculating the oscillation frequency of a quartz crystal by obtaining each temperature coefficient of characteristic of a quartz crystal expressed in the form of n-degree polynomial with respect to temperature. The temperature characteristic expressed by n-th order polynomial to temperature is approximated as a cubic. The average value is used as a third order coefficient and a second order coefficient of the third order. The oscillation frequency is calculated by determining the first order coefficient and the constant as frequency data measured at three temperature points and three temperature points. That is, by using an average value as the third-order coefficient, the oscillation frequency deviation can be calculated with sufficiently high accuracy from the data measured at three measurement points, while the data measured at four or more measurement points can be calculated as third, It is necessary to obtain first order coefficients and constants and to calculate the oscillation frequency deviation.

The oscillation frequency calculating method can be executed as follows. The average value is used for each of the cubic and quadratic coefficients of the cubic equation representing the temperature characteristics. The first coefficient and the constant are determined as the frequency data measured at two temperature points and two temperature points, and the oscillation frequency is calculated. Thus, the number of data points can be reduced and the number and cost of manhour can be reduced.

It is still another object of the present invention to provide a frequency correction method for a digital controlled oscillation circuit that obtains a line form representing a relationship between a frequency deviation and a control voltage for each variable capacitance diode to be used for temperature compensation to cause voltage control, Thereby improving frequency accuracy.

In order to achieve the above object, as shown in FIG. 10, the frequency deviation characteristic proportional to the control voltage is expressed in a linear form with respect to a linear region including a point having a frequency deviation of 0 for each variable capacitance diode And the linear coefficients of the linear form and the temperature characteristics of the quartz crystal are stored in advance in the storage device. The CPU computes the frequency deviation from the temperature characteristic of the quartz crystal corresponding to the temperature sensed by the temperature sensor, obtains the control voltage applied to the variable capacitance diode from the line form represented by the first coefficient, and outputs the control voltage to the variable capacitance diode And controls the output frequency to a predetermined constant level. That is, by the method of the present invention, the frequency deviation characteristic proportional to the control voltage is expressed in the form of a linear equation for a linear region including a point where the frequency deviation is zero for each variable capacitance diode used, and the slope K It is set according to the measured value. Therefore, accurate frequency control can be performed without errors caused by characteristic deviations.

Yet another object of the present invention is to provide a frequency control method for a digital controlled oscillation circuit which makes it possible to easily use a quartz oscillator having different frequency versus temperature characteristics from various reference contents.

In order to achieve the above-mentioned object, the present invention controls a resonance frequency of a digital controlled oscillation circuit having a control unit that is controlled by detecting a temperature change of a quartz crystal by a temperature sensor and correcting a resonance frequency drift of a quartz oscillator caused by a temperature change , A method of controlling the voltage applied to the variable capacitance diode is provided to control the resonance frequency of the oscillation circuit to a certain level. The control unit is provided with a memory circuit. At least three suitable temperature points are selected and a control voltage for correcting the frequency deviation of the quartz crystal is measured at the selected temperature point. Then, the third calibration curve is determined from the measured value at the measurement point, and the coefficients of the calibration curve are stored in advance in the memory circuit. The control voltage corresponding to the temperature measured by the temperature sensor is calculated from the third calibration curve and the control voltage is applied to the variable capacitance element to control the capacitance of the variable capacitance element to maintain the oscillation frequency of the oscillation circuit at a certain level do.

The frequency control method can be performed as follows. Three suitable temperature points are selected, and a control voltage for correcting the frequency deviation of the crystal oscillator is measured at each of the three temperature points. Then, a calibration curve represented by a cubic equation is determined from values measured at three temperature points, and the coefficients of the cubic calibration curve are stored in advance in the memory circuit. A control voltage corresponding to the temperature measured by the temperature sensor is calculated from the third calibration curve and a control voltage is applied to the variable capacitance element to control the capacitance of the variable capacitance diode element so that the oscillation frequency of the oscillation circuit is maintained at a constant level .

With the above method, the frequency correction curve is calculated from the values measured at three measurement points, and the coefficient (temperature coefficient) of the frequency correction curve is stored in the memory circuit. Therefore, the required storage capacity is minimized, and the number of insights is also reduced. Therefore, it becomes possible to make an oscillation circuit capable of accurate temperature compensation at a reduced cost. In addition, since the calibration curve of each quartz vibrator is directly obtained, a quartz crystal having different frequency temperature characteristics from the reference characteristic to various contents can be used easily. That is, the frequency control method is superior to the prior art in terms of flexibility.

It is a further object of the present invention to provide a variable capacitance diode that divides the control voltage versus frequency deviation characteristic of the variable capacitance diode into a plurality of control regions and provides a controllable variable that is used for temperature compensation in a manner controlled based on data stored for a particular control region And to provide a frequency correction method for a digital controlled oscillation circuit which controls the control voltage to be applied to the capacitance diode to improve the frequency accuracy.

In order to achieve the above object, as shown in FIG. 19, the control voltage vs. frequency deviation characteristic of the variable capacitance diodes used for temperature compensation is appropriately divided into a plurality of control areas (three parts in the example described) . The frequency deviation in each control region is given in a linear form with respect to the control voltage, and the linear coefficient of the linear form and the temperature characteristic of the quartz crystal are stored in the storage device in advance. The CPU calculates the frequency deviation from the temperature characteristic of the quartz crystal according to the temperature sensed by the temperature sensor, obtains the control voltage to be applied to the variable capacitance diode by using the first coefficient in the corresponding control region, And controls the output frequency to a predetermined constant level.

That is, by the above method, the control voltage versus frequency deviation characteristic of the variable capacitance diodes used for temperature compensation is divided into a plurality of control regions, and the slope K of the variable capacitance diodes is calculated for each control region Respectively. Therefore, the frequency deviation (error) decreases in all control areas, and accurate frequency control can be possible.

One embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 4 is a block diagram showing an example of the arrangement of the portable telephone used in the digital controlled oscillation circuit according to the present invention. As described in the drawings, a portable telephone using a digital controlled oscillation circuit according to the present invention includes a CPU (Central Processing Unit) 1, a data signal processing apparatus 2, a base band unit 3 for transmission and reception, A mixer 5 serving as a frequency converter, an amplifier 6, an output controller 7, an antenna multiplexer 8, an antenna 9, an amplifier 10, a mixer 11, an amplifier 12, A mixer 13, a demodulator 14, a PLL 15, a VCO 16, a PLL 17, a VCO 18, an automatic output controller 19, A D / A converter 21, an oscillation circuit 22, a temperature sensor 23, an A / D converter 24, a display device 30, a keypad 31 for inputting a data signal, An external device connection interface 32, a telephone transmitter 33, and a telephone receiver 34. The oscillating circuit 22 is the same as that shown in Fig.

The dial signal input from the keypad 31 is processed by the CPU 1 and displayed on the display device 30. [ The signal processed by the CPU 1 is further processed and transmitted by the data signal processing apparatus 2 and the baseband unit 3 in accordance with the data. The signal is then modulated in the modulator 4, frequency converted in the mixer 5, amplified in the amplifier 6 and fed to the antenna 9 through the output control 7 and antenna multiplexer 8 . The voice signal to be transmitted is supplied from the telephone transmitter 33 to the baseband unit 3 and similarly processed and transmitted.

A signal from the outside is received by the antenna and fed to the amplifier 10 through the antenna multiplexer. The signals amplified in the amplifier 10 are frequency-converted in the mixer 11, amplified in the amplifier 12, frequency-converted in the mixer 13, demodulated in the demodulator 14, ), And output from the telephone receiver as voice.

The oscillation circuit 22 outputs a constant frequency, and the output frequency is supplied to the modulator 4 and the PLL 15. That is, the output frequency of the VCO 16 is controlled by the output of the PLL 15. The mixer 5 mixes the output signal of the modulator 4 and the output frequency of the VCO 16 together to convert the frequency of the output signal to a predetermined transmission frequency. The CPU 1 controls the PLL 15 to oscillate a predetermined frequency by the operation channel. The signal received from the amplifier 10 is also mixed with the output frequency of the VCO 16 in the mixer 11 to convert the frequency.

The oscillation circuit 22 also outputs a certain frequency to the PLL 17 to control the output frequency of the VCO 18. [ The mixer 13 mixes the received signal from the amplifier 12 and the output frequency of the VCO 18 together to convert the frequency of the received signal to a predetermined frequency. The CPU 1 controls the PLL 17 to control the VCO 18 to convert the frequency of the received signal to a predetermined frequency corresponding to the reception channel frequency.

Next, the temperature compensation control of the oscillation circuit 22 will be described below. The memory device 20 previously stores correction data (control voltage value) for correcting the drift of the output frequency at the antenna 9 caused by the temperature change. The temperature sensor 23 senses the temperature of the oscillation circuit 22. The sensed temperature is converted into a digital value in the A / D converter 24 and output to the CPU 1. [ The CPU 1 refers to the correction data stored in the storage device 20 and outputs a control voltage value (digital signal) corresponding to the sensed temperature to the D / A converter 21. The D / A converter 21 converts the control voltage, which is a digital signal, into an analog signal, and outputs the analog signal to the oscillation circuit 22 to control the frequency, thereby maintaining the output frequency at a predetermined constant level in the antenna 9.

Portable telephones are typically used under harsh ambient conditions. Therefore, in the past, a temperature sensor for temperature sensing was used to control the temperature of the portable telephone. The D / A converter 21 has also been conventionally used as a device for converting a signal to be input to the automatic output controller 19 or a digital audio signal into an analog signal. The A / D converter 24 has also been used as an apparatus for converting voice to a digital signal. Of course, the CPU 1 and the storage device 20 have also been used for control.

The portable telephone arranged as shown in FIG. 4 includes a temperature sensor 23, a D / A converter 21, an A / D converter 24, a CPU 1, And a temperature compensation function equivalent to that of the digital temperature compensated quartz crystal arranged as shown in FIG. 1 by using the storage device 20. [ That is, such a control element, which is installed in a conventional portable telephone, is used for temperature compensation of the oscillation circuit 22 like a portable telephone, thereby reducing the size and cost of the portable telephone.

In a portable telephone incorporating a conventional digital temperature-compensated crystal oscillator arranged as shown in Fig. 1, the controlled object is the output frequency of the oscillation circuit. Conversely, in the portable telephone shown in Fig. 4, And is the output frequency at the antenna 9. Therefore, the control can be realized more accurately than in the conventional system.

Further, in the above-mentioned conventional portable telephone, temperature compensation is made according to the temperature characteristic of the quartz crystal used therein. Therefore, when the quartz crystal oscillator, that is, the oscillation circuit 22 fails, not only the oscillation circuit but all of the digital temperature-compensated crystal oscillators arranged as shown in Fig. 1 should be replaced, Only the failed oscillation circuit 22 needs to be replaced.

As described above, the crystal oscillator is used in an oscillation circuit of a portable telephone. The crystal plate for use as a quartz crystal oscillator also has a temperature characteristic that the oscillation frequency changes with temperature change. The temperature characteristics of the crystal plate depend on the manner in which the crystal plate is cut, that is, the plate, the SC plate, and the CT plate. FIG. 5 shows the structure of an AT plate crystal plate. As shown in the figure, the quartz vibrator has electrodes provided on both sides thereof. The natural frequency of the quartz crystal is determined by the material, arrangement (c), cutting angle (b), and thickness (d).

FIG. 6 shows the frequency deviation-temperature characteristic of the crystal vibrator of the AT plate. As shown in the figure, the quartz crystal having the characteristic B exhibits very good characteristics in the range of -10 ° C to + 60 ° C, whereas the quartz crystal having the characteristic A has the characteristic in the range of -50 ° C to + 100 ° C It shows lower frequency deviation than the other two crystal oscillators. Therefore, a quartz oscillator having suitable characteristics is used depending on the practical application and the operating temperature range.

As shown in Fig. 6, the frequency deviation? F / f (ppm) of the AT plate quartz oscillator is generally given by the following polynomial.

? F / f = A ₀ + A ₁ T + A ₂ T ² + A ₃ T ³ + A ₄ T ⁴ + A ₅ T ⁵ + ‥‥‥ (One)

△ f is the frequency deviation, and f is the oscillation frequency, and A ₀ to A _n are constants, T is the temperature.

In the actual calculation of equation (1), the terms of three or more are neglected because they are sufficiently small, and the frequency deviation can be calculated with sufficiently high accuracy as a representation of the following cubic equation about temperature.

? F / f = A ₀ + A ₁ T + A ₂ T ² + A ₃ T ³ (2)

Therefore, for the frequency control, the constant A ₀ of the crystal oscillator and the coefficients A ₁ , A ₂ , and A ₃ are obtained in advance. During the oscillation operation, the temperature of the quartz crystal is sensed, and equation (2) is calculated to obtain the frequency deviation? F / f. Then, the frequency deviation is corrected by a crystal oscillation circuit as shown in Fig. By doing so, a constant frequency can be maintained.

As described above, the quartz crystal vibrator 45 has a temperature characteristic in which the resonance frequency changes (about ± 10 ppm) due to the temperature change. The variable capacitance diode 42 is a device in which capacitance changes in accordance with a control voltage applied thereto. The characteristic curve showing the relationship between the control voltage applied to the variable capacitance diode 42 and the output frequency change is measured and obtained in advance. When the temperature of the quadrature electromotive force 45 changes during the oscillation operation of the oscillation circuit, the control device (not shown) calculates the frequency deviation according to equation (2) By controlling the voltage to correct the frequency deviation, the output frequency is controlled at a certain level.

Conventional oscillation frequency control should be performed by previously obtaining characteristics of the crystal oscillator constant A ₀ , the coefficients A ₁ , A ₂ , and A _3, and the variable capacitance diode 42. Therefore, conventionally, the coefficients A ₀ , A ₁ , A ₂ , and A ₃ of each crystal oscillator were obtained from data measured at four or more measurement points in advance. Is determined by the formula (2) (see FIG. 3), constant A ₀ is really (d) the thickness of the quartz plate in the coefficient A ₁ is determined for each (b) cutting, and the coefficient A ₂ and A ₃ are materials And array (c).

However, the aforementioned AT board crystal oscillator is different from the temperature characteristics according to the above-described conditions (constant A ₀ and the coefficients A _1, A _2, and A ₃ is different for each crystal oscillator.) In addition, the constant A ₀ and the coefficients A To obtain the four values for ₁ , A ₂ , and A ₃ , the measured data at four or more measurement points of each crystal oscillator should be prepared. The preparation of such measurement data requires complex operations and increases the number of insights and increases the cost. Furthermore, the operating efficiency is inferior and the frequency of the failure rate increases.

Thus, in this embodiment, an effective quadrature oscillator frequency calculation method provides a plurality of measurement points required to measure the temperature characteristic of the reduced quartz crystal.

The method of calculating the oscillation frequency of the quartz crystal will be described in detail below. The deviation of the values of the constants A ₀ , A ₁ , A ₂ , and A ₃ of the AT plate quartz oscillator made of the same material and manufactured by the same manufacturing process occurs within a relatively narrow range. For example, the deviation of the value of the coefficient A ₃ is within ± 8%. The deviation may be an error in production of the AT plate quartz crystal.

FIG. 7 is a characteristic curve obtained from the data measured at three measurement points by the oscillation frequency calculation method according to the present invention by using an average value as the coefficient A ₃ . FIG. 7 also shows the measured values. The characteristic curve shown in FIG. 7 can be obtained as follows. Fixing the coefficient A ₃ to the average value (-0.15 / 10 ⁵⁾ determined by calculation, and the frequency is -20 ℃ respectively, it is measured at 20 ℃, and three temperature points of 60 ℃, constant coefficients A ₀ and A _1, A ₂ , and A ₃ are obtained from the following equation (3), and a characteristic curve is calculated.

T ₁ : Measurement temperature of -20 ° C

T ₂ : Measurement temperature at 20 캜

T ₃ : measurement temperature at 60 캜

Y ₁ : Frequency deviation measured at -20 ° C

Y ₂ : Frequency deviation measured at 20 ° C

Y ₃ : When the measured frequency deviation is 60 ° C,

Y ₁ = A ₀ + A ₁ T ₁ + A ₂ T ₁ ² + A ₃ T ₁ ³

Y ₂ = A ₀ + A ₁ T ₂ + A ₂ T ₂ ² + A ₃ T ₂ ³ (3)

Y ₃ = A ₀ + A ₁ T ₃ + A ₂ T ₃ ² + A ₃ T ₃ ³

As understood from the seventh road, when an accurate value is selected as the coefficient A ₃ , the frequency deviation can be accurately calculated within 0.1 ppm.

The measurement temperature need not be limited to three points of -20 占 폚, 20 占 폚 and 60 占 폚. If an appropriate value is selected in the range of -20 DEG C to 75 DEG C, the frequency deviation can be accurately calculated within 0.1 ppm for the value (not shown) measured in the same manner as described above.

The cubic curve representing the temperature characteristics of the crystal plate of the AT plate is centered at about 25 ° C (inflection point). This is to make the characteristics as gentle as possible near room temperature. As a result, the frequency deviation is relatively large at high and low temperatures. Therefore, it is desirable to select the measured temperature at a higher or lower level in the operating temperature range (of the portable telephone). By doing so, the frequency deviation is uniformed as a whole, and good results are obtained.

If there is no manufacturing error, the crystal oscillator has the same value for the coefficient A ₃ . Furthermore, the measurement results of many existing AT quartz oscillators show that there is a manufacturing error of 占 8% even when the above-described conditions are the same. FIG. 8 shows measured values and calculated values obtained when the coefficient A ₃ changes from the average value to about -8%.

The values calculated in FIG. 8 are obtained by calculating the coefficients A ₀ , A ₁ and A ₂ from equation (3) and calculating the frequency deviation characteristic curve. As can be seen from the eighth road, the frequency deviation can be calculated with an error of 0.2 ppm in the measurement temperature range from -20 ° C to 60 ° C. For temperatures outside the temperature range, the frequency deviation can be calculated with an error of 0.35 ppm at -30 ° C, an error of 0.35 ppm at 70 ° C, and an error of 0.6 ppm at 75 ° C.

In another experiment, the + 8% increased coefficient A ₃ values from the average value, and the frequency is measured at three temperature points 20 ℃ away from the range of from -20 ℃ to 75 ℃, by calculating the frequency deviation coefficients A _0, A ₁ , and A ₂ are obtained. In this case also, the result is obtained similar to the above. These results fulfill the requirement that the frequency deviation should be within ± 1 ppm in the temperature range from -20 ° C to 60 ° C, as specified by RCR-STD (RCR Standards).

As described above, the frequency deviation can easily be calculated by obtaining the other coefficients A ₀ , A ₁ , A ₂ from the data measured at three measurement points using the average value as the value for the coefficient A ₃ of the quartz crystal. Although the mean value in the above description is used as the value for the coefficient A ₃ of the quartz crystal, it is also possible to use an average value as a value for the coefficient A, and from the data measured at three measurement points, other coefficients A ₀ , A ₁ , A ₃ . Alternatively, an average value may be used as a value for each of the coefficients A ₂ and A ₃ of the quartz crystal, and a constant A ₀ and a coefficient A ₁ may be obtained from the data measured at two measurement points.

Next, a special example of calculating the frequency deviation will be described. To obtain the control voltage (correction suppression), the frequency deviation is calculated and applied to the input terminal T _in of the crystal oscillation circuit shown in FIG. 2 (generally, it is calculated by the CPU). When the temperature of the crystal oscillator 45 is changed during the oscillating operation of the crystal oscillator circuit, the processing unit CPU receives the information from the temperature sensor and calculates a cubic equation (A ₀ + A ₁ T + A ₂ T ² + A ₃ T ³ ) to calculate the frequency deviation. To reduce the measurement time required for the calculation, each coefficient is multiplied by 10 ⁿ , and the result is rounded to the first decimal place to convert the coefficient to an integer value. This integer coefficient is stored in advance in the storage device. When the frequency deviation is calculated, the processing unit (CPU) divides the integer coefficient by 10 ⁿ to prevent an error in the calculation result. By doing so, the measurement time can be reduced to 1/15 in the case of floating point calculation, and the processing time can be reduced considerably.

In this embodiment, the constants of the measured data can be reduced using an average value for some of the n coefficients. For example, data measured at four measurement points are required to obtain the third order, second order, first order coefficients and constants, and thereby the oscillation frequency deviation values are calculated. However, when the mean value is used as the third order coefficient, It is possible to calculate the frequency deviation value by obtaining each coefficient from the data measured at three measurement points with sufficiently high accuracy.

When the mean value is used as the third and the second coefficient respectively, the frequency deviation value can be calculated with sufficiently high accuracy by obtaining each coefficient from the data measured at the two measurement points. Thus, the number and cost of the insights can be reduced as a result of the reduction of the number of data measurement points.

Next, a frequency correction method of the digital controlled oscillation circuit of the portable telephone according to the present invention will be described.

FIG. 9 shows the temperature characteristic of the quartz crystal. As can be understood from the drawings, the quartz vibrator is different in temperature characteristics. FIG. 9 is a graphical representation of a quartz crystal resonator in which the resonance frequency varies from -12 ppm to +7 ppm at the maximum value with respect to the reference frequency when the temperature varies between -30 ° C. and 75 ° C., Lt; / RTI > In order to correct the frequency deviation of the quartz oscillator, the control voltage applied to the variable capacitance diode 42 is regulated by the oscillation circuit in Fig.

The control voltage ( _Vcont ) versus the frequency deviation characteristic of the variable capacitance diode is represented by a linear equation as an approximation to the control voltage as shown in FIG. The slope of the control voltage versus the frequency deviation characteristic of the variable capacitance diode 42 can be estimated as K. [

Thus, the frequency deviation is a control voltage when V ₀ is a frequency deviation of 0,? F _i is a frequency deviation at each temperature, V _i is a control voltage applied at a specific temperature, and K is a variable capacitance diode ) ≪ / RTI >

V _i = V ₀ -? F _i K (4)

Can be corrected by applying a control voltage (correction voltage) V _{i given} by?

The conventional frequency correction method has been performed as follows. 1 and 2, the memory device 67 stores the temperature characteristic of the crystal oscillator 45 (temperature difference between the temperature change and the frequency deviation? F _i ) with the slope K value of the variable capacitance diode 42 Or a reference table related to temperature characteristics) can be stored in advance. The CPU 64 calculates the control voltage (correction voltage) V _i by a linear form based on the temperature sensed by the temperature sensor 62 and applies the calculated control voltage V _i to the variable capacitance diode 42, Correct the deviation of the output frequency.

Moreover, as shown in FIG. 3, the slope K of the variable capacitance diode 42 is different from the other. The conventional practice is to select a variable capacitance diode having a slope close to the predetermined slope K and to store the value in the storage device 67 as slope K of the variable capacitance diode 42 in advance. Thus, the conventional implementation has the problem that a variable capacitance diode other than having a slope K can not be used. In addition, since the slope of the control voltage vs. frequency deviation characteristic is not accurate, an error occurs in the control voltage (correction voltage) V _i . As in the example shown in FIG. 22, the change in slope K causes the control voltage to have a maximum error of about 0.15 V, that is, a maximum error of about 5 ppm for the frequency deviation.

As shown in FIG. 3, the linear slope K representing the control voltage versus frequency deviation characteristic of the variable capacitance diodes is not constant over the entire control voltage range, and the control voltage vs. frequency deviation characteristic of each variable capacitance diode is approximate Given by a straight line. Therefore, if correction is not performed using the control voltage (correction suppressing voltage) V _i given by the linear equation having the slope K obtained in an appropriate control voltage range, an error will occur. These errors, which are considered together with other error factors of the quartz crystal vibrator 45, exceed 1 ppm and the variation in the number of parking is within ± 1 ppm within a temperature range of -20 ° C to 60 ° C, as embodied by RCR-STD It does not satisfy the requirement to be.

Therefore, in the present invention, a linear equation representing the relationship between the frequency deviation and the control voltage is obtained for each variable capacitance diode and used for temperature compensation, thereby improving the accuracy of the frequency.

The arrangement and oscillation circuit of the digital temperature compensated crystal oscillator to which the frequency correction method according to the present invention is applied are the same as those shown in FIG. 1 and FIG. 2, and description thereof is omitted.

FIG. 10 shows characteristics of a variable capacitance diode used in the frequency correction method according to the present invention. As shown by the graph of measured values in the figure, the characteristic of the variable capacitance diode 42 is nonlinear by increasing the distance from the center. However, in this embodiment, the slope K of the variable capacitance diode 42 is estimated as a straight line b including a point where the frequency deviation is zero. The slope K is a control voltage when V ₀ is a frequency deviation of 0, and? F _i is a frequency deviation of the control voltage V,

K = (VV ₀ ) /? F (5)

.

The control voltage (correction voltage) to be applied to the variable capacitor diode 42 is calculated by the equation (4) (V _i = V ₀ - Δf _i · K), and the calculated control voltage is applied to the variable capacitor diode 42 .

The quartz oscillator 45 exhibits a temperature characteristic as shown in Fig. 9 and is generally given as a cubic expression relating to temperature. The slope K of the variable capacitor diode 42 and the temperature characteristic (cubic) of the crystal oscillator 45 are stored in the storage device 67 in advance. The CPU 64 calculates the frequency deviation from the temperature sensed by the temperature sensor and the temperature characteristic of the quartz crystal. Then, the CPU 64 calculates the control voltage by the equation (4) using the slope K of the variable capacitance diode 42, and applies the calculated control voltage to the variable capacitance diode 42. [

FIG. 11 shows a method of varying the control voltage _V.sub.cont according to the temperature by the frequency correction method according to the present invention. In the case of using a variable capacitance diode having a nearly linear control voltage versus frequency deviation characteristic as shown in FIG. 3 and a crystal oscillator having a temperature characteristic as shown by MIN in FIG. 9, the frequency deviation (error) Can be maintained within 0.6 ppm by changing the control voltage according to the temperature as shown in FIG. 11.

FIG. 12 also shows a method of varying the control voltage with respect to temperature with the frequency correction method according to the present invention. In the case of using a variable capacitance diode with nearly linear control voltage versus frequency deviation characteristic as shown in FIG. 3 and a quartz crystal with temperature characteristic as shown in MAX in FIG. 9, the frequency deviation May be maintained within 0.5 ppm by varying the control voltage with respect to temperature, as shown in FIGS. 11 and 12.

Width, according to the method of the present invention, the frequency deviation characteristic for the control voltage is such that the frequency deviation is zero for each variable capacitance diode 42 to be used, and the slope K is set based on the measured value. Lt; / RTI > Therefore, there is no error due to the deviation as in the conventional execution, and accurate frequency control becomes possible.

In addition, since the control voltage vs. frequency deviation characteristic is displayed as a linear signal in the entire control range, the measurement becomes easy and the operation required in the past can be omitted. The best optimum voltage range for obtaining the slope K is 1.8 V to 3.5 V.

Further, by the method of the present invention, frequency correction can easily perform frequency correction by storing necessary coefficients in a storage device using conventional hardware. Therefore, no additional cost is required. Further, since the feedback control is not used, the control operation is quickly stabilized. Therefore, the present invention is most suitable for use as a frequency correction method of a portable telephone.

Next, another frequency correction method of the digital controlled oscillation circuit of the portable telephone according to the present invention will be described.

As described above, the quartz crystal resonator has a temperature characteristic in which the resonance frequency varies with temperature change (about 10 ppm), and the variable capacitance diode 42 is a device in which capacitance changes in accordance with a control voltage applied thereto. Therefore, when the temperature of the crystal oscillator 45 changes, the CPU 64 (see FIG. 1) controls the voltage applied to the variable capacitance diode 42 of the oscillation circuit 61 (see FIG. 2) Thereby controlling the capacitance of the variable capacitance diode 42. By doing so, it is possible to control the output frequency (oscillation frequency) at a certain level.

FIG. 13 shows an example of resonance frequency characteristics of a quartz crystal resonator. And the vertical axis represents the deviation of the resonance frequency from the reference frequency. In general, the resonant frequency versus temperature characteristics can be approximated by a cubic equation. FIG. 14 shows a correction curve for correcting the frequency deviation caused by the temperature change. The abscissa represents the temperature and the ordinate represents the deviation of the control voltage applied to the variable capacitor diode 42 from the reference control voltage. The graph of FIG. 14 shows that the control voltage corresponding to the temperature is input to the input terminal T _in (see FIG. 2) to maintain the output frequency at a certain level by correcting the output frequency at the output terminal T _out .

In FIG. 2, the quartz oscillator which can be used as the quartz oscillator 45 is different for each of the temperature characteristics. Therefore, the frequency deviation must be corrected for each crystal oscillator. FIG. 15 shows an example of a cubic calibration curve determined by obtaining an estimated value from the measured values at three points. The frequency correction method is described below with reference to FIG.

(1) An input terminal voltage (control voltage applied to the variable capacitance diode 42) from which a predetermined output frequency is obtained is measured at a point measuring each temperature of -20 占 폚, room temperature (10 占 폚 to 35 占 폚), and 60 占 폚 . The measured input terminal voltages are estimated to be V- ₂₀ , V _NT , and V ₆₀ , respectively. Subsequently, steps (2) to (4) are carried out. For these steps (2) to (4), three different methods are useful and are shown in the following paragraphs A, B,

A. (2) Determine the difference between V _-20-NT and V _60-NT .

V _-20-NT = V _-20 -V _NT

V _60-NT = V ₆₀ -V _NT?

3 equations ① and ②, the value of the difference between V and V _-20-NT using the _NT-60 in accordance with the linear polynomial regression model V _-30-NT and _NT-75 V is estimated from the resultant.

(4) V _NT is added to V _{- 30-NT} and V _75-NT estimated in (3) to obtain values for V- ₃₀ and V ₇₅ (see the estimates shown in FIG. 15).

V _-30 = V _-30-NT + V _NT?

V ₇₅ = V _75-NT + V _NT ④

B. (2) Determine the ratio of V- _{20 / NT} to V _{60 / NT} .

V _{-20 / NT} = V _-20 / V _NT ‥‥‥

V _{60 / NT} = V ₆₀ / V _NT?

(3) Estimate the values of V- _{30 / NT} and V _{75 / NT} according to the linear polynomial regression model using the ratio of V- _{20 / NT} to V _{60 / NT} obtained from equations (1) and (2).

(4) The values of V- _{30 / NT} and V _{75 / NT} estimated in (3) are multiplied by V _NT to obtain values of V _-30 and V ₇₅ (see the estimated values shown in FIG. 15).

_{V -30 = V -30 / NT ×} V NT ‥‥‥ ③

V ₇₅ = V _{75 / NT} × V _NT ④

C. (2) Determine the values of V- _{30 / NT} and V _{75 / NT} according to the linear polynomial regression model using V- ₂₀ , V _NT and V ₆₀ as variables.

There are no steps (3) and (4).

(5) The input terminal voltages V- ₃₀ and V (obtained by estimation using the measured input terminal voltage V- ₂₀ , V _NT , and V ₆₀₎ and the linear polynomial model with the control voltage applied to the variable capacitance diode 42 ₇₅ , a calibration curve that is expressed in cubic form is created using the method of least squares. The vertical axis of the graph shown in FIG. 15 shows the control voltage deviation. In addition, when the measured values at four or more measurement points are used, the step of obtaining the estimated values is omitted.

The respective coefficients (temperature coefficients) of the cubic calibration curve obtained by the above method are stored in advance in the storage circuit 67 shown in Fig. The CPU 64 calculates a cubic equation based on the temperature sensed by the temperature sensor 62, inputs it through the A / D converter 63 to obtain a control voltage deviation, and outputs the calculated control voltage deviation as an output signal to provide. The output signal is converted into an analog value by the D / A converter 65, and is input to the oscillation circuit 61. The input voltage is applied to the variable capacitor diode 42 in the oscillator circuit 61 to control the output frequency (see FIG. 2).

FIG. 16 shows frequency vs. temperature characteristics before and after correction made by the control method according to the present invention. In the figure, the curve A (continuous line) represents the frequency-to-temperature characteristic after correction, and the curve B (dotted line) represents the frequency vs. temperature characteristic before correction. As apparent from the figure, the control method according to the present embodiment can control the output frequency at a substantially constant level in a wide temperature range.

As described above, in the control method according to the present embodiment, the calibration curve can be obtained simply by measuring data at a plurality of points, particularly three points, with respect to each oscillation circuit 61, The coefficient (temperature coefficient) is obtained and stored in the memory circuit. Therefore, the required storage capacity is minimized, and the number of insights is also reduced. Therefore, accurate temperature compensation can be realized at a reduced cost.

In this embodiment, the data is measured at three loads of -20 DEG C, room temperature (10 DEG C to 35 DEG C), and 60 DEG C, but other temperatures may be selected. Moreover, it is preferable that the two points are selected within a temperature range of -30 캜 to -10 캜 and 50 캜 - 75 캜, in particular, in which large deviations are observed.

In the control method according to the present embodiment, a frequency deviation curve (correction curve) is calculated from data calculated at a plurality of points, particularly three points, and the coefficient (temperature coefficient) of the correction curve is stored in the memory circuit. Therefore, the required storage capacity is minimized, and the number of inches also decreases. Therefore, it is possible to make an oscillation circuit capable of accurate temperature compensation at a reduced cost.

In addition, in the prior art, it has been difficult to use a quartz crystal having a frequency-to-temperature characteristic which is significantly different from the reference characteristic. However, since a calibration curve for each quartz crystal is directly obtained, So that a quartz crystal having temperature characteristics can be easily used. That is, the frequency control method is excellent in flexibility from the prior art.

Even if only the crystal oscillator is replaced with another, the calibration curve can be easily corrected.

Next, a digital control type frequency correction method of another portable telephone according to the present invention will be described.

As shown in FIG. 3, the variable capacitance diode changes at slope K, and the conventional practice allows the variable capacitance diode 42 having a slope approaching the predetermined slope K to be selected, K is stored. Thus, it takes a lot of time to select an appropriate variable capacitance diode. Further, since the slope of the control voltage versus frequency characteristic variation not to correct the errors of the control voltage (correction voltage) V _i is causing.

Also, the slope K of the straight line shown in FIG. 3 is not uniform over the entire control voltage range. That is, the control voltage vs. frequency deviation characteristic of each variable capacitance diode is given by an approximate linear expression. Therefore, when the correction uses the control voltage (correction voltage) V _i given by the linear equation (1) having the slope K different from the nonlinear voltage value portion, the error increases. For example, in the case of a crystal oscillator having a temperature characteristic as shown by MIN in FIG. 9, results as shown in FIG. 17 are obtained according to the frequency correction. That is, the maximum error e ₁ is 0.6 ppm with respect to the output frequency. In the case of a quartz crystal having a temperature characteristic as shown by MAX in FIG. 9, the frequency correction is as shown in FIG. 18. That is, the maximum error e ₃ is 0.5 ppm with respect to the output frequency. These errors, taking into account the different error factors of the quartz oscillator, exceeded 1 ppm and the frequency deviation, as specified by RCR-STD (RCR standard), was 1 ppm in the temperature range of -20 캜 to 60 캜 It does not satisfy the requirement to be within.

Therefore, in the present embodiment, the control voltage applied to the variable capacitance diodes used for temperature compensation is controlled by the control voltage vs. frequency deviation characteristic of the diodes divided into a plurality of control regions, thereby improving the frequency accuracy.

The block arrangement and the oscillation circuit of the digital temperature-compensated quartz oscillator to which the frequency correction method according to the present embodiment is applied are the same as those shown in Figs. 1 and 2, and the description thereof is omitted.

FIG. 19 shows characteristics of a variable capacitance diode used in the frequency correction method according to the present invention. As illustrated in the figure, the slope K of the variable capacitance diode 42 is slightly different at both ends than at the center. For example, in the control region b where the frequency deviation is from 0 to 4 ppm, K is 0.057, while K in the control regions a and c is 0.06. The slope K is expressed by equation (5). The control voltage (correction voltage) applied to the variable capacitance diode 42 is calculated by the above equation (4) (V _i = V ₀ -? F _i · K), and the calculated control voltage is applied to the variable capacitance diode 42 .

The quartz oscillator 45 generally exhibits a temperature characteristic as shown in Fig. 9 given by a cubic equation for temperature. The slope K of the variable capacitance diode 42 and the temperature characteristic (cubic) of the crystal oscillator are stored in advance in the storage device 67. [ The CPU 64 calculates the control voltage according to the equation (1) using the slope K of the variable capacitance diode 42 in the corresponding control region among the three control regions a, b and c, and outputs the control voltage to the variable capacitance diode 42 And the calculated control voltage is applied.

20 shows how the control voltage V _cont varies in proportion to the temperature by the frequency correction method according to the present invention. In this case, a crystal oscillator having a temperature characteristic as shown by MIN in FIG. 9 is used. That is, the temperature deviation (error) can be kept within 0.1 ppm by changing the control voltage with respect to temperature as shown in FIG. 20. FIG. 21 also shows how the control voltage _Vcont is varied with respect to temperature by the frequency correction method according to the invention. In this case, a crystal oscillator having a temperature characteristic as shown in MAX in FIG. 9 is used. That is, the frequency deviation (error) can also be kept within 0.1 ppm by varying the control voltage in relation to the temperature, as shown in FIGS. 20 and 21.

In the above embodiment, the control voltage applied to the variable capacitance diode 42 is controlled according to the control voltage versus frequency deviation characteristic of the diode 42 divided into three control regions. If the number of control regions increases, It is correct.

As described above, the control voltage versus frequency deviation characteristic of the variable capacitance diode 42 is divided into three control regions a, b, and c as shown in FIG. 19, and the slope K of the variable capacitance diode 42 (K = (VV ₀ ) /? F); (See equation (5) above) is set for each control area based on the measured value. Therefore, the frequency deviation (error) is reduced in all the control regions, and more accurate frequency control becomes possible in the conventional execution.

That is, by the frequency correction method, the control voltage versus frequency deviation characteristic of the variable capacitance diodes used for temperature compensation is divided into a plurality of control areas, and the slope K of the variable capacitance diodes is divided into control areas . Therefore, the frequency deviation (error) is reduced in all the control regions, and more accurate frequency control is possible than in the prior art.

Further, by the method of the present invention, frequency correction can be easily performed by storing coefficients necessary for a storage device using conventional hardware. Therefore, no additional cost is required. In addition, since the fetish back control is not used, the control operation is quickly stabilized. Therefore, the present invention is very suitable for use in a portable telephone.

FIG. 1 is a layout diagram of a conventional digital temperature compensated crystal oscillator; FIG.

FIG. 2 is a layout diagram of an oscillation circuit using a crystal oscillator. FIG.

Figure 3 also shows control voltage versus frequency deviation characteristics of various variable capacitance diodes.

FIG. 4 is a layout diagram of a portable telephone using a digital controlled oscillation circuit according to the present invention; FIG.

Figure 5 is a structural view of an AT plate quartz plate.

FIG. 6 is a frequency deviation versus temperature characteristic curve of a crystal vibrator of an AT plate according to the present invention.

7 shows the characteristic curves obtained from the data measured at three measuring points with fixed coefficients A ₃ , together with the measured values.

FIG. 8 shows the calculated values and measured value curves obtained when the coefficient A ₃ changes by -8%.

9 is a temperature characteristic curve of the quartz crystal.

10 is a characteristic curve of a variable capacitance diode used in the frequency correction method according to the present invention.

FIG. 11 is a curve showing the relationship between the temperature and the control voltage obtained by the frequency correction method according to the present invention; FIG.

12 is a curve showing the relationship between the temperature and the control voltage obtained by the frequency correction method according to the present invention;

13 is a temperature characteristic curve of the quartz crystal.

14 is a calibration curve for correcting a frequency deviation caused by a temperature change;

FIG. 15 is an example of an example in which an estimated value is obtained from measured values at three measurement points, and a cubic calibration curve is obtained from these values. FIG.

FIG. 16 is a frequency vs. temperature characteristic diagram before and after frequency correction made by the control method according to the present invention; FIG.

FIG. 17 is a curve showing the relationship between the control voltage and the temperature obtained by the conventional frequency correction method; FIG.

FIG. 18 is a curve showing the relationship between control voltage and temperature obtained by the conventional frequency correction method; FIG.

19 is a characteristic diagram of a variable capacitance diode used in the frequency correction method according to the present invention.

20 is a curve showing the relationship between control voltage and temperature obtained by the frequency correction method according to the present invention.

FIG. 21 is a curve showing the relationship between control voltage and temperature obtained by the frequency correction method according to the present invention; FIG.

FIG. 22 is a temperature characteristic diagram obtained by a conventional frequency correction method; FIG.

Description of the Related Art [0002]

1: CPU 2: Data signal processing device

3: Baseband unit for transmission and reception processing

4: Modulator 5, 11, 13: Mixer

6, 10, 12: amplifier 7: output control section

8: Antenna multiplexer 9: Antenna

14: Demodulator 15, 17: PLL

16, 18: VCO 19: Automatic output controller

20: memory device 21: D / A converter

22: oscillation circuit 23: temperature sensor

24: A / D converter 30: Display device

31: Keypad 32: Interface

33: telephone transmitter 34: telephone receiver

Claims (4)

There is provided an oscillation circuit having an oscillation circuit including a CPU, a storage device, a temperature sensor, a quartz oscillator, and a variable capacitance diode, wherein a change in the resonant frequency of the quartz oscillator caused by a temperature change is controlled by a control voltage to be applied to the variable capacitance diode A frequency correction method for a digital control type oscillation circuit which is calibrated and outputs a predetermined frequency, Expresses in advance a frequency deviation characteristic of the variable capacitance diode with respect to a control voltage in the form of a linear equation with respect to a linear region including a point having a frequency deviation of 0, Lt; RTI ID = 0.0 > Calculating a frequency deviation from the temperature characteristic of the quartz crystal according to the temperature sensed by the temperature sensor under control of the CPU and calculating a control voltage to be applied to the variable capacitance diode from the linear equation represented by the first coefficient And controlling the output frequency to a predetermined level by applying the control voltage to the variable capacitance diode. An oscillation circuit comprising: an oscillation circuit including a quartz oscillator and a variable capacitance element; a temperature sensor for sensing a temperature change of the quartz oscillator; a resonance sensor for detecting a temperature change of the quartz crystal by the temperature sensor, A method of controlling an oscillation frequency for a digital controlled oscillation circuit having a control unit for correcting frequency drift and controlling a control voltage to be applied to the variable capacitance element to control an oscillation frequency of the oscillation circuit to a predetermined level, A storage device is provided in the control section, Determining at least three suitable temperature points, measuring a control voltage for correcting the frequency deviation of the quartz oscillator at the temperature point, determining a calibration curve represented by a cubic equation from the measured value at the temperature point, Storing a coefficient of the correction curve in a storage device, Calculating a control voltage corresponding to the temperature measured by the temperature sensor from the cubic calibration curve and controlling the capacitance of the variable capacitance element by applying the control voltage to the variable capacitance element, Is maintained at a predetermined level. ≪ RTI ID = 0.0 > 11. < / RTI > An oscillation circuit comprising: an oscillation circuit including a quartz oscillator and a variable capacitance element; a temperature sensor for sensing a temperature change of the quartz oscillator; a resonance sensor for detecting a temperature change of the quartz crystal by the temperature sensor, A method of controlling an oscillation frequency for a digital control oscillation circuit having a control unit for correcting frequency drift and controlling an oscillation frequency of the oscillation circuit to a predetermined level by controlling a control voltage to be applied to the variable capacitance element, A storage device is provided in the control section, Three suitable temperature points are selected in advance, a control voltage for correcting the frequency deviation of the quartz oscillator at the three temperature points is measured, and a calibration curve indicated by a cubic expression is determined from the measured values at the three temperature points And stores coefficients of the cubic calibration curve in the storage device, Calculating a control voltage corresponding to the temperature measured by the temperature sensor from the third calibration curve and controlling the capacitance of the variable capacitance element by applying the control voltage to the variable capacitance element, Wherein the oscillation frequency of the digital control oscillation circuit is maintained at a predetermined level. There is provided an oscillation circuit having an oscillation circuit including a CPU, a storage device, a temperature sensor, a quartz oscillator, and a variable capacitance diode, wherein a change in the resonant frequency of the quartz oscillator caused by a temperature change is controlled by a control voltage to be applied to the variable capacitance diode A frequency correction method for a digital controlled oscillation circuit that outputs a predetermined frequency, Wherein a control voltage versus frequency deviation characteristic of the variable capacitance diode is preliminarily divided into a plurality of suitable control regions and a frequency deviation of each control region is expressed in a linear form with respect to a control voltage, And stores the linear coefficient of each linear form in the storage device, Calculating a frequency deviation from a temperature characteristic of the quartz crystal according to a temperature detected by the temperature sensor under the control of the CPU and obtaining a control voltage to be applied to the variable capacitance diode by using a first coefficient for the control region, And controlling the output frequency to a predetermined level by applying the control voltage to the variable capacitance diode.