JP2014107715A - Oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillator capable of shortening stabilization time independently of an ambient temperature.SOLUTION: An oscillator 10 includes a crystal vibration element 11 to be a piezoelectric element, a temperature sensor 12 for detecting an ambient temperature T, an oscillation part 20, and a frequency correction part 30. The oscillation part 20 generates an output signal Fout composed of a predetermined oscillation frequency f by using the crystal vibration element 11, inputs a correction voltage Vc and corrects the oscillation frequency f. The frequency correction part 30 outputs to the oscillation part 20, the correction voltage Vc for making a frequency deviation df/f close to a convergence value c at the time of starting on the basis of the ambient temperature T detected by the temperature sensor 12 and known relation of the ambient temperature T and the output signal Fout to the convergence value c of the frequency deviation df/f.

Description

  The present invention relates to an oscillator using a piezoelectric element.

  Conventionally, various oscillators have been developed, such as a temperature compensated crystal oscillator (TCXO). This temperature-compensated crystal oscillator has a temperature compensation circuit for compensating the frequency temperature characteristics of a crystal resonator used as a piezoelectric element, and is mounted on an electronic device such as a mobile phone or a personal navigation device (PND). used.

  FIG. 4 shows a configuration of an oscillator 100 disclosed in Patent Document 1 as an example of a conventional temperature compensated crystal oscillator. The oscillator 100 includes a crystal resonator 110 as a piezoelectric element and an IC chip 120 electrically connected to the crystal resonator 110, and generates an output signal Fout having a desired oscillation frequency.

  Inside the IC chip 120, a crystal oscillation circuit 130 connected to the crystal resonator 110 and a temperature compensation circuit 140 for compensating the frequency temperature characteristics of the crystal resonator 110 are formed.

  More specifically, one end of the crystal unit 110 is connected to one end of a resistance element 131 as a feedback resistor in the crystal oscillation circuit 130 and to an input terminal of the inverter 132. A variable capacitance element 134 is connected between one end of the crystal unit 110 and the ground GND.

  On the other hand, the other end of the crystal unit 110 is connected to the other end of the resistance element 131 in the crystal oscillation circuit 130 and to the output terminal of the inverter 132. A variable capacitance element 135 is connected between the other end of the crystal unit 110 and the ground GND.

  The output terminal of the inverter 132 is connected to the input terminal of the inverter 133 as a buffer, and an output signal Fout having a desired oscillation frequency is output from the output terminal of the inverter 132.

  The temperature compensation circuit 140 is a circuit for compensating the frequency temperature characteristic of the crystal unit 110 in order to output the output signal Fout having a constant oscillation frequency from the oscillator 100 regardless of the change in temperature.

  Specifically, the temperature compensation circuit 140 includes a temperature sensor for measuring the temperature around the crystal unit 110, and generates a predetermined temperature compensation voltage based on the temperature obtained by the temperature sensor. .

  The temperature compensation circuit 140 adjusts the oscillation frequency of the output signal Fout by applying the temperature compensation voltage to the variable capacitance elements 134 and 135 and changing the capacitance of the variable capacitance elements 134 and 135, thereby performing temperature compensation. Do.

  In this way, the oscillator 100 generates an output signal Fout having a desired oscillation frequency and outputs this to the outside. In other words, the oscillator 100 adjusts the operation so that a desired oscillation frequency can be obtained even if the ambient temperature changes by compensating the frequency temperature characteristic.

  By the way, from the viewpoint of an electronic device on which an oscillator is mounted, it is desirable that the time from startup to stabilization of the oscillation frequency (hereinafter referred to as “stabilization time”) is as short as possible. However, even with a temperature-compensated crystal resonator, a certain amount of time is required until the oscillation frequency is stabilized after startup. On the other hand, Patent Document 2 discloses a temperature-compensated crystal resonator that improves the temperature-compensating operation at startup and prevents frequency fluctuation. This temperature-compensated crystal resonator measures an error at the time of starting the temperature compensation voltage in advance, and applies a start-up correction voltage that cancels this error to the variable capacitance element.

Japanese Patent Laying-Open No. 2011-035482 (FIG. 3) JP 2008-271355 A (FIG. 1) Japanese Patent Laying-Open No. 2007-325033 (FIG. 3)

  However, in the technique of Patent Document 2, the stabilization time may be long. The reason will be described below.

  FIG. 5 is a graph showing a change in frequency deviation at the time of start-up in a conventional oscillator. The horizontal axis is the time t from power-on, the vertical axis is the frequency deviation df / f indicating the deviation from the desired oscillation frequency, and the measurement when the ambient temperature T is −30 ° C., + 25 ° C., + 85 ° C. Data is plotted. The frequency deviation df / f at each ambient temperature T approaches the convergence value c by temperature compensation as time t elapses from the time of startup. In general, the oscillator is designed so that the convergence value c has a frequency deviation df / f = 0 when the ambient temperature T is + 25 ° C. Therefore, the convergence value c when the ambient temperature T is −30 ° C. or + 85 ° C. does not necessarily become the frequency deviation df / f = 0. Since the convergence value c of the frequency deviation df / f only needs to be within the allowable range, the magnitude is not so important.

  On the other hand, as shown in FIG. 5, the frequency deviation df / f reaches the convergence value c at different times for each ambient temperature T. For example, when the ambient temperature T is + 85 ° C., it takes about three times longer to stabilize the oscillation frequency f than when the ambient temperature T is −30 ° C.

  In the technique of Patent Document 2, since the influence of the ambient temperature at the time of starting is not taken into consideration, the stabilization time becomes long depending on the ambient temperature.

  Therefore, an object of the present invention is to provide an oscillator that can shorten the stabilization time regardless of the ambient temperature.

The oscillator according to the present invention is
A piezoelectric element;
A temperature sensor for detecting the ambient temperature;
An oscillation unit that generates an output signal having a predetermined oscillation frequency using the piezoelectric element, and corrects the oscillation frequency by inputting a correction voltage;
Based on the ambient temperature detected by the temperature sensor and a known relationship between the ambient temperature and the convergence value of the frequency deviation of the output signal, the correction voltage that brings the frequency deviation closer to the convergence value at startup A frequency correction unit that outputs to the oscillation unit;
It is equipped with.

  According to the present invention, based on the ambient temperature detected by the temperature sensor and the known relationship between the ambient temperature and the convergence value of the frequency deviation of the output signal, the frequency deviation is made closer to the convergence value at startup. Since the frequency deviation can be quickly converged at any ambient temperature, the stabilization time can be shortened regardless of the ambient temperature.

FIG. 3 is a circuit diagram illustrating the oscillator according to the first embodiment. 6 is a graph showing a change in frequency deviation at startup in the oscillator according to the first embodiment. 6 is a circuit diagram illustrating an oscillator according to a second embodiment. FIG. It is a circuit diagram which shows the conventional oscillator. It is a graph which shows the change of the frequency deviation at the time of starting in the conventional oscillator.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components.

  FIG. 1 is a circuit diagram illustrating the oscillator according to the first embodiment. Hereinafter, description will be given based on this drawing.

  The oscillator 10 according to the first embodiment includes a crystal resonator element 11 as a piezoelectric element, a temperature sensor 12 that detects an ambient temperature T, an oscillation unit 20, and a frequency correction unit 30. The oscillation unit 20 generates an output signal Fout having a predetermined oscillation frequency f using the crystal resonator element 11 and inputs the correction voltage Vc to correct the oscillation frequency f. The frequency correction unit 30 is based on the ambient temperature T detected by the temperature sensor 12 and the known relationship between the ambient temperature T and the convergence value c of the frequency deviation df / f of the output signal Fout. A correction voltage Vc that approximates f to the convergence value c is output to the oscillation unit 20.

  The frequency correction unit 30 includes a correction voltage output circuit 31 and a memory 32. The memory 32 stores data related to the correction voltage Vc for each ambient temperature T in advance. The correction voltage output circuit 31 receives the data of the ambient temperature T detected by the temperature sensor 12, generates a correction voltage Vc corresponding to the ambient temperature T based on this data and the data of the memory 32, and generates the correction voltage Vc. Output to the oscillator 20. The data regarding the correction voltage Vc for each ambient temperature T in the first embodiment is the gain of the operational amplifier as will be described later.

  The oscillation unit 20 includes a temperature compensation circuit 21 that generates the temperature compensation voltage Va, an addition circuit 22 that adds the temperature compensation voltage Va generated by the temperature compensation circuit 21 to the correction voltage Vc output from the correction voltage output circuit 31, and And variable capacitance elements 26 and 27 that are provided in an oscillation loop including the crystal oscillation element 11 and correct the oscillation frequency f by the correction voltage Vc to which the temperature compensation voltage Va is added.

  The frequency correction unit 30 further includes a correction voltage stop circuit 33 that detects the amplitude of the output signal Fout and stops the output of the correction voltage Vc when the amplitude is greater than or equal to a certain value.

  Next, each component will be described in more detail.

  The oscillating unit 20 also includes a resistance element 23 for feedback, an inverter 24 for oscillation, and an inverter 25 for buffering. One end of the crystal element 11 is connected to one end of the resistance element 23, the input end of the inverter 24, and one end of the variable capacitance element 26. The other end of the crystal oscillator 11 is connected to the other end of the resistance element 23 and the output of the inverter 24. One end of the variable capacitor 26 and one end of the variable capacitor 26 are connected, and the ground GND is connected to the other ends of the variable capacitors 26 and 27. The crystal oscillator 11, the resistance element 23, the inverter 24, and the variable capacitance elements 26 and 27 constitute an oscillation loop.

  The variable capacitance elements 26 and 27 are, for example, variable capacitance diodes. In that case, the cathode of the variable capacitance diode corresponds to one end of the variable capacitance elements 26 and 27, the anode of the variable capacitance diode corresponds to the other end of the variable capacitance elements 26 and 27, and the correction voltage Vc and the cathode of the variable capacitance diode are applied. A temperature compensation voltage Va is applied. As the reverse voltage applied to the variable capacitance diode increases, the capacitance value of the variable capacitance diode increases, so the oscillation frequency f decreases.

  The temperature compensation circuit 21 is a general circuit incorporating a temperature sensor for measuring the ambient temperature, for example. When the crystal unit 11 uses an AT-cut crystal piece, the frequency-temperature characteristic is, for example, a cubic function. At this time, the frequency deviation becomes a positive cubic curve with respect to the ambient temperature. Therefore, the temperature compensation circuit 21 generates a temperature compensation voltage Va that becomes a negative cubic curve with respect to the ambient temperature so as to cancel out a frequency deviation that becomes a positive cubic curve with respect to the ambient temperature. Such a temperature-compensated voltage Va having a cubic curve can be generated as a temperature-compensated voltage Va that approximates a polygonal line by combining straight lines for each temperature region, for example (see Patent Document 3, for example). The adder circuit 22 is an arithmetic circuit centered on an operational amplifier, for example.

  The temperature sensor 12 is a semiconductor temperature sensor that outputs a detection voltage Vt corresponding to the ambient temperature T as data of the ambient temperature T, for example, suitable for IC chip formation. As the semiconductor temperature sensor, one utilizing the temperature dependence of the resistance value of the semiconductor or the temperature dependence of the forward voltage of the pn junction is known. For example, in the case of a silicon pn junction, its forward voltage changes at -2 mV / ° C. Further, the temperature sensor 12 may include a circuit that converts temperature information (ambient temperature T) of the resistance value and the forward voltage into an analog voltage (detection voltage Vt) having a magnitude that is easy to use.

  The correction voltage output circuit 31 is composed of, for example, an operational amplifier. When the detection voltage Vt is input, the correction voltage output circuit 31 outputs a correction voltage Vc corresponding thereto. The memory 32 is, for example, a digital potentiometer with a nonvolatile semiconductor memory, and has a write terminal for writing the gain of an operational amplifier constituting the correction voltage output circuit 31. In the memory 32, the gain of the operational amplifier corresponding to the data related to the correction voltage Vc for each ambient temperature T is written. For example, when a certain value of the ambient temperature T is T1, T2, T3 (T1 <T2 <T3), the gain is α, that is, the correction voltage Vc = αVt, and T2 ≦ T ≦ T3 when T1 ≦ T <T2. Then, the gain is β, that is, the correction voltage Vc = βVt. In this way, the specific configuration of the correction voltage output circuit 31 having different gains for each temperature region can be obtained in accordance with the configuration of the temperature compensation circuit 21 described above.

  Here, a method for determining the gain will be described. First, the relationship between the ambient temperature T and the convergence value c of the frequency deviation df / f is measured without the frequency correction unit 30 or without operating the frequency correction unit 30 to obtain a graph as shown in FIG. . Specifically, the frequency deviation df / f is measured at every ambient temperature T and every time t until the frequency deviation df / f changes to the convergence value c at startup. Then, when what correction voltage Vc is output and when, the frequency deviation df / f can be brought to the convergence value c earliest at the time of startup, or the time until the frequency deviation df / f reaches the convergence value c at the time of startup is constant. The optimum correction voltage Vc is determined by repeating calculation and experiment. For example, when the ambient temperature T is + 85 ° C., the time t until reaching the convergence value c is long, and therefore, the overshoot-like frequency deviation df / The correction voltage Vc is set to f. Finally, the gain corresponding to the determined optimum correction voltage Vc is written in the memory 32. It should be noted that this gain may be the same value as long as the types are the same for the plurality of oscillators 10, or may be a different value for each oscillator 10.

  The correction voltage stop circuit 33 includes an amplitude comparison circuit 34 and an electronic switch 35. The amplitude comparison circuit 34 detects the DC voltage Vdc corresponding to the amplitude of the output signal Fout by rectifying the output signal Fout, for example, compares the DC voltage Vdc with the reference voltage Vref, and if Vdc ≦ Vref, A switch control signal Vs1 for closing the contact of the switch 35 is output. If Vdc> Vref, a switch control signal Vs0 for opening the contact of the electronic switch 35 is output. The electronic switch 35 is made of, for example, a transistor, and allows the output of the correction voltage Vc when the contact is closed, and cuts off the output of the correction voltage Vc when the contact is open. The correction voltage stop circuit 33 can be omitted by providing the correction voltage output circuit 31 with a function of outputting the correction voltage Vc for a predetermined time.

  Next, the operation of the oscillator 10 will be described.

  When the power supply voltage is turned on, the oscillator 10 is started. That is, the oscillation unit 20 starts to output the output signal Fout, the temperature compensation circuit 21 starts to output the temperature compensation voltage Va, the temperature sensor 12 starts to output the detection voltage Vt, and the correction voltage output circuit 31 outputs the correction voltage Vc. Start outputting. The correction voltage Vc is added to the temperature compensation voltage Va by the adding circuit 22 to be Vc + Va and applied to the variable capacitance elements 26 and 27. Then, the oscillation frequency f of the output signal Fout is corrected by changing the impedance of the oscillation loop including the crystal resonator 11. Subsequently, when the amplitude of the output signal Fout exceeds a certain level, the switch control signal Vs0 is output from the amplitude comparison circuit 34, whereby the contact of the electronic switch 35 is opened and the correction voltage Vc is cut off.

  If the correction voltage output circuit 31 does not operate, the frequency deviation df / f takes a long time depending on the ambient temperature T and reaches the convergence value c as shown in FIG. The time required to reach different temperatures for each ambient temperature T. On the other hand, in the first embodiment, as the correction voltage output circuit 31 operates, as shown in FIG. 2, the frequency deviation df / f is a convergence value in a short time and the same time regardless of the ambient temperature T. c. In the example shown in FIG. 2, when the ambient temperature T is + 85 ° C. and + 25 ° C., the time t until the convergence value c is long, so that the correction voltage is such that the overshoot frequency deviation df / f is obtained. When the ambient temperature T is −30 ° C., the correction voltage Vc is almost zero because the time t until the convergence value c is short. For example, the overshoot-like frequency deviation df / f is a pulse width or a predetermined pulse that is cut off when the amplitude becomes a certain value or higher than the correction voltage Vc having a frequency deviation df / f larger than the convergence value c. By width, it can be obtained by instantaneous output.

  Next, the effect of the oscillator 10 will be described.

  (1) Based on the known relationship between the ambient temperature T detected by the temperature sensor 12 and the convergence value c of the ambient temperature T and the frequency deviation df / f of the output signal Fout, the frequency deviation df / f is converged at startup. Since the frequency deviation df / f can be quickly converged at any ambient temperature T by approaching the value c, the stabilization time can be shortened regardless of the ambient temperature T. Further, since the stabilization time can be shortened regardless of the ambient temperature T, the stabilization time can be made constant regardless of the ambient temperature T.

  (2) Since the frequency correction unit 30 is configured by an analog arithmetic circuit that converts the detection voltage Vt into the correction voltage Vc, a quick response is possible.

  (3) By correcting the oscillation frequency f using the existing temperature compensation circuit 21 and the variable capacitance elements 26 and 27, many parts of the existing oscillation unit can be used, so that the configuration can be simplified.

  (4) By having the correction voltage stop circuit 33 that stops the output of the correction voltage Vc when the amplitude of the output signal Fout becomes a certain level or more, useless correction operation of the oscillation frequency f can be prevented.

  FIG. 3 is a circuit diagram illustrating the oscillator according to the second embodiment. Hereinafter, description will be given based on this drawing.

  The oscillator 40 of the second embodiment is different from the first embodiment in part of the oscillation unit 50. That is, the oscillating unit 50 supplies an oscillation inverter 51 connected in parallel to the crystal resonator 11 and a constant current Ic to the inverter 51, and changes the value of the constant current Ic by the correction voltage Vc to thereby oscillate the frequency f. And a variable constant current source 52 for correcting.

  The inverter 51 is, for example, a CMOS inverter. The variable constant current source 52 uses, for example, a saturation region of a transistor, and has a function of controlling the current supplied from the power supply voltage Vdd to the inverter 51 by the correction voltage Vc. When a CMOS inverter is used as an oscillator, the oscillation frequency can be changed by limiting the operating current of the CMOS inverter. In the second embodiment, the constant current Ic is the operating current of the inverter 51. That is, if the constant current Ic is decreased, the operation of the inverter 51 is delayed and the oscillation frequency f is decreased, and if the constant current Ic is increased, the operation of the inverter 51 is accelerated and the oscillation frequency f is increased.

  Next, the operation of the oscillator 40 will be described.

  When the power supply voltage is turned on, the oscillator 40 is started. That is, the oscillation unit 50 starts to output the output signal Fout, the temperature compensation circuit 21 starts to output the temperature compensation voltage Va, the temperature sensor 12 starts to output the detection voltage Vt, and the correction voltage output circuit 31 outputs the correction voltage Vc. Start outputting. The correction voltage Vc is applied to the variable constant current source 52. Then, the constant current Ic corresponding to the correction voltage Vc is supplied as the operating current from the variable constant current source 52 to the inverter 51, whereby the oscillation frequency f of the output signal Fout is corrected. For example, if the correction voltage Vc is increased, the constant current Ic is decreased and the oscillation frequency f is decreased, and if the correction voltage Vc is decreased, the constant current Ic is increased and the oscillation frequency f is increased. Subsequently, when the amplitude of the output signal Fout exceeds a certain level, the switch control signal Vs0 is output from the amplitude comparison circuit 34, whereby the contact of the electronic switch 35 is opened and the correction voltage Vc is cut off.

  Other configurations, operations, and effects of the second embodiment are the same as those of the first embodiment.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. Further, the present invention includes a combination of some or all of the configurations of the above-described embodiments as appropriate.

  The present invention can be used for an oscillator using a piezoelectric element made of, for example, quartz or ceramics.

DESCRIPTION OF SYMBOLS 10 Oscillator 11 Crystal oscillator 12 Temperature sensor 20 Oscillator 21 Temperature compensation circuit 22 Adder circuit 23 Resistor element 24, 25 Inverter 26, 27 Variable capacity element 30 Frequency correction part 31 Correction voltage output circuit 32 Memory 33 Correction voltage stop circuit 34 Amplitude Comparison circuit 35 Electronic switch T Ambient temperature t Time Va Temperature compensation voltage Vc Correction voltage Fout Output signal f Oscillation frequency df / f Frequency deviation c Convergence value GND Ground Vt Detection voltage Vdc DC voltage Vref Reference voltage Vs0, Vs1 Switch control signal

40 Oscillator 50 Oscillator 51 Inverter 52 Variable constant current source Ic Constant current Vdd Power supply voltage

DESCRIPTION OF SYMBOLS 100 Oscillator 110 Crystal oscillator 120 IC chip 130 Crystal oscillation circuit 140 Temperature compensation circuit 131 Resistance element 132,133 Inverter 134,135 Variable capacitance element

Claims (5)

A piezoelectric element;
A temperature sensor for detecting the ambient temperature;
An oscillation unit that generates an output signal having a predetermined oscillation frequency using the piezoelectric element, and corrects the oscillation frequency by inputting a correction voltage;
Based on the ambient temperature detected by the temperature sensor and a known relationship between the ambient temperature and the convergence value of the frequency deviation of the output signal, the correction voltage that brings the frequency deviation closer to the convergence value at startup A frequency correction unit that outputs to the oscillation unit;
With an oscillator. The frequency correction unit is
A memory for storing in advance data relating to the correction voltage for each ambient temperature;
Data on the ambient temperature detected by the temperature sensor is input, the correction voltage corresponding to the ambient temperature is generated based on the data and data on the correction voltage, and the correction voltage is output to the oscillation unit. A correction voltage output circuit,
The oscillator according to claim 1. The oscillation unit is
A temperature compensation circuit for generating a temperature compensation voltage;
An addition circuit for adding the temperature compensation voltage generated by the temperature compensation circuit to the correction voltage output from the correction voltage output circuit;
A variable capacitance element provided in an oscillation loop including the piezoelectric element and correcting the oscillation frequency by the correction voltage to which the temperature compensation voltage is added;
The oscillator according to claim 2. The oscillation unit is
An inverter for oscillation connected in parallel to the piezoelectric element;
A constant current source for supplying a constant current to the inverter, and a variable constant current source for correcting the oscillation frequency by changing a value of the constant current according to the correction voltage;
The oscillator according to claim 2. The frequency correction unit is
A correction voltage stop circuit that detects the amplitude of the output signal and stops the output of the correction voltage when the amplitude is equal to or greater than a certain value;
The oscillator according to any one of claims 2 to 4.

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