JP2002151956A - Piezoelectric oscillator with frequency calibration function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillator that is provided with a frequency calibration means that automatically starts frequency calibration when receiving an external calibration signal and completes calibration when the calibration signal is interrupted so as to simplify the calibration thereby suppressing a job cost. SOLUTION: The piezoelectric oscillator provided with a phase locked loop circuit including an input terminal for receiving a frequency calibration signal, a phase comparator 11, a low-pass filter 12 and a voltage controlled piezoelectric oscillator 2 and able to phase-lock the output of the voltage controlled piezoelectric oscillator 2 with the frequency calibration signal, is provided with a synchronizing voltage recording section 13 that digitizes the output signal of the low-pass filter 12 and stores the digitized signal when the frequency calibration signal is fed to the input terminal and the output signal of the voltage controlled piezoelectric oscillator 2 is phase-locked to the frequency calibration signal, and the oscillated frequency of the voltage controlled piezoelectric oscillator 2 is controlled on the basis of the information stored in the synchronizing voltage recording section 13 when the frequency calibration signal is not given to the input terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator having a frequency calibration function capable of maintaining frequency accuracy for a long time in a crystal oscillator which is a reference frequency source of a communication device, a measuring device and the like.

[0002]

2. Description of the Related Art As represented by portable telephones, communication technology has been remarkably developed in recent years. In addition to communication devices, measuring devices for developing and manufacturing them have advanced functions,
Performance is required. For this reason, a crystal oscillator used as a reference frequency source of these devices has also been required to have extremely high frequency stability. In general, the frequency accuracy of a crystal oscillator is high, but this may cause a problem because the resonance frequency of the crystal oscillator changes depending on the ambient temperature. For this reason, for example, in a mobile phone terminal,
A “temperature compensated crystal oscillator (TCXO)” that electrically compensates for the temperature characteristics of a crystal unit is used. For devices requiring extremely high frequency stability, such as wireless base stations, satellite communication base stations, and satellite communication devices, the frequency stability is improved by maintaining the quartz oscillator and oscillation circuit at a constant temperature. A crystal oscillator with a bath (OCXO) "is used.

On the other hand, there is a change with time called "aging" as a change in the resonance frequency of a crystal resonator. This is thought to be due to the fact that distortion is applied when the crystal resonator is attached to the crystal resonator package, and this distortion changes over time or the airtightness of the sealed crystal resonator package changes over time. Although the frequency change can be reduced by devising the design and manufacturing of the child,
Removing it completely is not possible with current technology. Further, when a large shock is applied to the crystal resonator due to vibration or impact, a frequency change occurs for the same reason. For this reason, the frequency changes due to aging, vibration, shock, or the like, and when this exceeds an allowable value, a calibration operation for adjusting the frequency of the crystal oscillator is required. In general, a crystal oscillator often cannot maintain required accuracy unless calibration is performed periodically.

By the way, when adjusting the frequency of a crystal oscillator mounted on a communication device or a measuring device, a crystal oscillator having higher frequency accuracy than the corresponding crystal oscillator or an atomic standard oscillator such as rubidium or cesium is usually used as a calibration signal source. In general, the frequency of the crystal oscillator is adjusted so that this difference becomes zero. FIG. 2 is a block diagram showing a conventional example of a high-precision crystal oscillator mounted on a communication device or a measuring device and a state in which measuring instruments necessary for the calibration thereof are connected.

[0005] The crystal oscillator shown in FIG. 2 is a crystal oscillator with an oven (OCXO) used as a high-precision frequency reference for a communication device, a measuring device, or the like. A constant temperature bath 2 for keeping the whole of the voltage controlled crystal oscillator 1 at a constant temperature, a temperature control circuit 3 for controlling the temperature in the constant temperature bath 2, and an oscillation resistor R for controlling the oscillation frequency of the crystal oscillator 1 And a control voltage generator 4 for generating a frequency control voltage. The output signal of the crystal oscillator 1 is output to the outside via the calibration terminal 5. Further, a phase meter 6 and a frequency calibration signal generator 7 are arranged for the purpose of calibrating the oscillation frequency of the voltage controlled crystal oscillator 1, and the output signal of the voltage controlled crystal oscillator 1 and the frequency calibration signal generation are generated in the phase meter 6. The phase difference from the output signal of the device 7 can be measured.

The operation of the conventional embodiment shown in the drawings and its calibration method will be described below. First, the entire crystal oscillator 1 is housed in a thermostat 2, and the internal temperature of the thermostat 2 is controlled by a temperature control circuit 3 so that the oscillation frequency is always constant without being affected by the ambient temperature. . Here, the voltage controlled crystal oscillator 1 is internally provided with a voltage variable capacitance element such as a variable capacitance diode so that the oscillation frequency can be adjusted by the frequency control voltage supplied from the control voltage generator 4. When the adjustment resistor R is adjusted, the frequency control voltage changes and the oscillation frequency of the voltage controlled crystal oscillator 1 changes. However, the adjustment resistor R adjusts the oscillation frequency of the voltage control crystal oscillator 1 to a specified value. Is adjusted to a predetermined position and fixed.

[0007] The oscillation frequency of the above-mentioned voltage-controlled crystal oscillator 1 gradually changes due to aging after shipment, and it becomes impossible to maintain a predetermined frequency accuracy over a long period of time. For this reason, calibration will be performed as needed every predetermined period. In order to perform the calibration, first, the output of the voltage controlled crystal oscillator 1 is pulled out from the calibration terminal 5 and connected to the phase meter 6. A phase calibration signal is input from the frequency calibration signal generator 7 to the phase meter 6, and the phase of the output signal of the voltage controlled crystal oscillator 1 is compared with the phase of the output signal of the voltage controlled crystal oscillator 1 and measured. . In this state, the adjustment resistance R is adjusted while referring to the indicated value of the phase meter 6 so that the indicated value of the phase meter 6 becomes 0 °. Then, the adjustment position of the resistor R is fixed in a state where the indicated value becomes 0 °, and the calibration is completed.

[Problems to be solved by the invention]

However, the above-mentioned conventional calibration of the crystal oscillator has the following problems. That is, in order to perform the calibration, it is necessary to draw the output of the crystal oscillator to the outside of the mounting device. In addition, in calibration, an on-board device must be designed in advance so that the adjustment resistor R can be adjusted from the outside. Further, when performing "calibration", the function of the corresponding device must be temporarily stopped, and there is a disadvantage that a great deal of cost is generated in actually calibrating the crystal oscillator. Furthermore, when a device equipped with a crystal oscillator is a general-purpose measuring device such as a frequency counter, there are many occasions where the device is taken out and used outdoors.

In general, when a high-precision frequency counter is used in a factory, a high-precision frequency signal is input from the outside, and the frequency can be accurately measured based on the input signal. However, when used outdoors, it is necessary to calibrate beforehand so that the frequency of the oscillator with a built-in frequency counter does not shift. That is, calibration must be performed so that accurate measurement can be performed without a high-precision frequency signal.
For this reason, the calibration must be performed frequently every time the measuring instrument is taken out, and the cost of the calibration cannot be ignored.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a crystal oscillator that can be incorporated into a communication device or a measuring instrument, can simplify a frequency calibration operation, and can reduce calibration costs. Aim.

[0011]

In order to solve the above-mentioned object, a piezoelectric oscillator having a frequency calibration function according to the present invention is provided with an input terminal for a frequency calibration signal, a phase comparator and a low-frequency signal. A piezoelectric oscillator comprising a filter and a phase-locked loop including a voltage-controlled piezoelectric oscillator, wherein the output signal of the voltage-controlled piezoelectric oscillator can be phase-locked to the frequency-calibration signal, wherein the frequency-calibration signal is supplied to an input terminal. When the output signal of the voltage-controlled piezoelectric oscillator is phase-synchronized with the storage means for digitizing and storing the output signal of the low-pass filter, and the storage means is not provided when the frequency calibration signal is not supplied. The oscillation frequency of the piezoelectric oscillator is controlled based on the stored information.

According to a second aspect of the present invention, there is provided a piezoelectric oscillator having a frequency calibration function, comprising: an input terminal for a frequency calibration signal; a phase locked loop including a phase comparator, a low-pass filter, and a voltage controlled piezoelectric oscillator. In the oscillator, wherein the output signal of the voltage-controlled piezoelectric oscillator can be phase-locked to the frequency calibration signal, a changeover switch inserted between the low-pass filter and the piezoelectric oscillator, and an output signal of the low-pass filter Storage means for storing information; synchronous voltage generation means for generating a frequency control signal for controlling the oscillation frequency of the voltage-controlled piezoelectric oscillator based on the information stored in the storage means; and Signal detection means for detecting that a signal has been input, and when the frequency calibration signal is not supplied, the synchronization is performed via the changeover switch. The synchronous voltage generated by the pressure generating means is supplied to the voltage-controlled piezoelectric oscillator, and when the frequency calibration signal is supplied, the output signal of the low-pass filter is supplied to the voltage-controlled piezoelectric oscillator via the changeover switch. In addition, the output signal of the low-pass filter is stored in a synchronous voltage recording unit.

According to a second aspect of the present invention, there is provided a piezoelectric oscillator having a frequency calibration function according to the first or second aspect, wherein the voltage-controlled piezoelectric oscillator is a crystal oscillator housed in a thermostat. . The invention according to claim 3 of the piezoelectric oscillator with the frequency calibration function according to the present invention is based on claim 1,
In the second or third aspect, the frequency calibration signal input to the input terminal is automatically detected, and the phase synchronization circuit is caused to function. According to a fourth aspect of the present invention, there is provided a piezoelectric oscillator having a frequency calibration function according to the first, second, third or fourth aspect, wherein a frequency divider is inserted in a required part of the phase locked loop circuit. It is a thing.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments shown in the drawings. FIG. 1 is a block diagram of a crystal oscillator (OCXO) with a thermostat showing an embodiment of the present invention.
A constant temperature bath 2 for keeping the whole of the voltage controlled crystal oscillator 1 at a constant temperature, a temperature control circuit 3 for controlling the temperature in the constant temperature bath 2, and supplying a frequency calibration voltage to the voltage controlled crystal oscillator 1 A frequency calibrator 8 for calibrating the oscillation frequency of the control crystal oscillator 1.

The frequency calibrating unit 8 comprises a first frequency divider 9 for dividing the frequency calibration signal supplied from the frequency calibration signal generator 7 by a predetermined number, and the first frequency divider 9 A phase comparator 11 for outputting a phase difference signal in accordance with a phase difference between a first frequency-divided signal output by a second frequency divider 9 and a second frequency-divided signal output by a second frequency divider 10 to be described later; LPF 12 (low-pass filter) that filters the phase difference signal output from comparator 11 at a predetermined cutoff frequency to generate a phase difference DC voltage
A synchronization voltage recording unit 13 (storage means) for digitizing the phase difference voltage output from the LPF 12 and storing the same as a synchronization signal; reading out the synchronization signal from the synchronization voltage recording unit 13 and converting it into an analog signal to synchronize Synchronous voltage generator 14 (synchronous voltage generating means) for outputting as a voltage
A changeover switch 15 for selectively outputting the phase difference voltage output from the LPF 12 and the synchronization voltage output from the synchronization voltage generator 14 and supplying the same as a frequency calibration voltage to the voltage controlled crystal oscillator 1, and an output of the voltage controlled crystal oscillator 1 A second frequency divider 10 that divides the signal by a predetermined number and feeds back a second frequency-divided signal to the phase comparator 11 and a first frequency-divided signal output from the first frequency divider 9 are detected. A signal detection unit 16 that supplies a switch switching signal to the changeover switch 15 and supplies a recording control signal to the synchronization voltage recording unit 13.

The operation of the oven controlled crystal oscillator (OCXO) shown in FIG. 1 will be described below. First, a calibration signal is input from the reference frequency generator 7 to the minute divider 9 when performing calibration. The frequency divider 9 divides the calibration signal by a predetermined number and supplies a first frequency-divided signal to the phase comparator 11 and the signal detector 16 respectively. A phase comparator 11 compares a phase difference between the first frequency-divided signal and a second frequency-divided signal supplied from a second frequency divider 10 described later, and converts a phase difference signal corresponding to the phase difference into an LPF 12. Output to The LPF 12 filters this at a predetermined cutoff frequency and supplies a phase difference voltage to the changeover switch 15.

On the other hand, the signal detecting section 16 detects the first frequency-divided signal supplied from the first frequency divider 9 and outputs a switch switching signal to the change-over switch 15. The changeover switch 15 selectively outputs the phase difference DC voltage supplied from the LPF 12 according to the switch changeover signal, and supplies it to the voltage controlled crystal oscillator 1. The oscillation frequency of the voltage-controlled crystal oscillator 1 changes according to the phase difference DC voltage.
Is divided by a predetermined number, and is fed back to the phase comparator 11 as a second frequency-divided signal.

Accordingly, as a result of feedback control of the phase of the output signal of the voltage controlled crystal oscillator 1, the phase comparator 1
Control is performed so that the phase difference between the first frequency-divided signal and the second frequency-divided signal input to 1 is 0 °, that is, the first frequency-divided signal and the second frequency-divided signal are phase-synchronized. As a result, the oscillation frequency of the crystal oscillator 1 is calibrated to the frequency accuracy of the first frequency-divided signal, that is, the frequency accuracy equivalent to the frequency accuracy of the frequency calibration signal.

Here, the signal detector 16 is provided with the first frequency divider 9
And outputs a recording control signal to the synchronous voltage recording unit 13. Synchronous voltage recording unit 13
Converts the phase difference DC voltage supplied from the LPF 12 into a digital signal in accordance with the recording control signal, stores and stores the digital signal as digital data, and updates its value every moment. The synchronous voltage generator 14 reads out the digital data momentarily, converts it into an analog signal, and supplies it to the switch 15 as a synchronous voltage. That is, the synchronous voltage is the same as the phase difference DC voltage.

Therefore, if the frequency calibration signal supplied from the frequency calibration signal generator 7 is cut off, the signal detector 1
The first frequency-divided signal supplied to 6 is turned off. At this time, the signal detecting section detects a state in which the first frequency-divided signal is cut off, supplies a switch switching signal to the changeover switch 15, and supplies a recording control signal to the synchronous voltage recording section 13. Then, the synchronization voltage recording unit 13 suspends updating of the digital data according to the recording control signal, and the digital data is fixed at a predetermined value immediately before the interruption. The synchronous voltage generator 14 converts this into an analog signal and continues to supply a synchronous voltage corresponding to a predetermined value immediately before the interruption to the changeover switch 15. At the same time, the changeover switch 15 selectively outputs the synchronous voltage according to the switch changeover signal and supplies the synchronous voltage to the voltage controlled crystal oscillator 1.

Therefore, the output signal of the voltage controlled crystal oscillator 1 can be obtained as a signal which is phase-locked to the frequency calibration signal once the calibration signal is input, and is synchronized with the frequency calibration signal even if the frequency calibration signal is cut off. , The predetermined frequency accuracy can be maintained.
As described above, once the frequency calibration signal is supplied from the frequency calibration signal generator 7 and then cut off, the calibration of the oscillation frequency of the voltage controlled crystal oscillator 1 can be automatically started and ended.

The frequency calibrator 8 itself must have an input terminal for inputting a frequency calibration signal. However, unlike the conventional calibration, it is necessary to draw the output of the oscillator to the outside and connect it directly to the measuring instrument. Therefore, there is no need for a calibration terminal for extracting the output signal of the oscillator in a device equipped with the oscillator. Furthermore, since the high-frequency signal output from the oscillator is not routed to the outside, it is not easy to pick up noise from the output of the oscillator, which is advantageous in terms of high frequency.

In the above-described embodiment, a crystal oscillator having a constant temperature bath is used. However, the present invention is not limited to this, and a temperature compensated crystal oscillator (TCXO) having a temperature compensation circuit is provided. A frequency control function may be added. As described above, by incorporating the frequency calibration function into the crystal oscillator, the calibration operation itself is simplified as compared with the related art, so that the cost associated with the calibration can be reduced and the effect is large.

[0024]

As described above, according to the present invention, when the oscillation frequency of the crystal oscillator changes due to aging or the like,
Solving the problem that caused enormous cost because each time complicated calibration work was performed, providing a frequency calibration means in the crystal oscillator and automatically inputting a frequency calibration signal from the outside, automatically starts the frequency calibration, Since the calibration is completed if the frequency calibration signal is cut off, the calibration operation can be simplified, and this is extremely effective in providing a crystal oscillator with reduced operation costs associated with the calibration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a crystal oscillator with a thermostat according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a conventional crystal oscillator with a thermostat.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Voltage control crystal oscillator 2 ... Constant temperature chamber 3 ... Temperature control circuit 4 ... Control voltage generation part 5 ... Calibration terminal 6 ... Phase meter 7 ... Frequency calibration signal generation 8: Frequency calibrator 9: First frequency divider 10: Second frequency divider 11: Phase comparator 12: LPF 13: Synchronous voltage recording unit 14. ..Synchronous voltage generator 15 ... Changeover switch 16 ... Signal detector X ... Crystal oscillator R ... Adjustment resistor

Claims (5)

[Claims] An input terminal for a frequency calibration signal, a phase locked loop including a phase comparator, a low-pass filter, and a voltage controlled piezoelectric oscillator, wherein the frequency calibration signal includes an output signal of the voltage controlled piezoelectric oscillator. In the piezoelectric oscillator capable of synchronizing the phase, when the frequency calibration signal is supplied to an input terminal and the output signal of the voltage controlled piezoelectric oscillator is phase-synchronized with the input terminal, the output signal of the low-pass filter is digitized and stored. Means for controlling the oscillation frequency of the piezoelectric oscillator based on information stored in the storage means when the frequency calibration signal is not supplied. 2. An input terminal for a frequency calibration signal, a phase synchronization circuit including a phase comparator, a low-pass filter, and a voltage controlled piezoelectric oscillator, wherein the frequency calibration signal includes an output signal of the voltage controlled piezoelectric oscillator. An oscillator capable of phase synchronization, a changeover switch inserted between the low-pass filter and the voltage-controlled piezoelectric oscillator, storage means for storing information of an output signal of the low-pass filter, and storage means for storing the information. Synchronous voltage generation means for generating a frequency control signal for controlling the oscillation frequency of the piezoelectric oscillator based on information, and signal detection means for detecting that the frequency calibration signal has been input to the input terminal, When the frequency calibration signal is not supplied, the synchronous voltage generated by the synchronous voltage generating means is supplied to the voltage-controlled piezoelectric oscillator via the changeover switch, When the frequency calibration signal is supplied, the output signal of the low-pass filter is supplied to the voltage-controlled piezoelectric oscillator via the changeover switch, and the output signal of the low-pass filter is stored in the synchronous voltage recording unit. A piezoelectric oscillator with a frequency calibration function, characterized in that: 3. The piezoelectric oscillator according to claim 1, wherein the piezoelectric oscillator is a crystal oscillator housed in a thermostat. 4. The phase synchronization circuit according to claim 1, wherein said frequency calibration signal input to said input terminal is automatically detected to cause said phase synchronization circuit to function. Piezoelectric oscillator with frequency calibration function. 5. A piezoelectric device with a frequency calibration function according to claim 1, wherein a frequency divider is inserted in a required portion of said phase locked loop circuit. Oscillator.