JP2012060583A - Clock generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and inexpensive clock generator capable of outputting a highly accurate clock signal over a wide temperature range.SOLUTION: A clock generator includes a reference clock generating part 11 which generates a reference clock signal, a first oscillator 12 which generates a first clock signal, a first accuracy guaranteeing part 13 which generates a second clock signal in which the first clock signal is corrected to have the same frequency and the same phase as the reference clock signal, a temperature detection part 15, a second oscillator 17 which generates a third clock signal, a second accuracy guaranteeing part 18 which generates a fourth clock signal in which the third clock signal is corrected to have the same frequency and the same phase as the reference clock signal, and a clock switching part 20 which outputs the second clock signal when a temperature is within a guaranteed temperature range of the first oscillator 12 and outputs the fourth clock signal when the temperature is not within the guaranteed temperature range of the first oscillator 12.

Description

  The present invention relates to a clock generator that switches and outputs a clock signal according to temperature.

  In a conventional radio base station, in order to reduce interference with an adjacent radio base station during data communication, each base station includes a clock generator and synchronizes data transmission timing between the base stations. Since high synchronization accuracy is required as the data communication speed increases, an OCXO (Oven Controlled Crystal Oscillator) capable of supplying a high-accuracy clock signal is mounted on the clock generator.

  OCXO is known that can shorten the time required to stabilize the temperature in the thermostatic chamber at a target temperature (see, for example, Patent Document 1). There is also known a clock signal output device that uses a high-precision oscillator such as a reference oscillator and OCXO and increases the accuracy of the output clock signal based on the high-precision oscillator (see, for example, Patent Document 2).

JP 2007-259345 A Table 2006/090831

  However, in order to reliably generate a highly accurate clock signal even in a low temperature environment or a high temperature environment, it is necessary to use an OCXO having a wide temperature range in which operation is guaranteed (hereinafter referred to as a guaranteed temperature range). OCXO has a problem that it is very expensive.

  Even if the OCXO described in Patent Document 1 or the clock signal output device described in Patent Document 2 is mounted, it is difficult to widen the guaranteed temperature range, and the ambient temperature inside the base station is the guaranteed temperature range of OCXO. The base station had to be designed not to exceed. For example, in order to reduce the influence of the OCXO from the ambient temperature as much as possible, the oven part is doubled, or the high heat part is separated and housed in a separate casing to isolate the OCXO. For this reason, there is a problem in that the structure of the entire base station becomes complicated and the cost and size increase.

  In order to solve the above problems, an object of the present invention is to provide an inexpensive and compact clock generator capable of outputting a highly accurate clock signal in a wide temperature range.

  In order to solve the above-described problem, a clock generator according to the present invention includes a reference clock generator that generates a reference clock signal, and a first clock signal that generates a first clock signal that is guaranteed to operate in a first guaranteed temperature range. 1 oscillator (OCXO) and a first accuracy assurance unit that generates a second clock signal (OCXO_clk signal) obtained by correcting the first clock signal so as to have the same frequency and the same phase as the reference clock signal (OCXO accuracy assurance unit), a temperature detection unit for detecting the temperature in the vicinity of the clock generator, and a third clock whose operation is guaranteed in a second guaranteed temperature range wider than the first guaranteed temperature range. A second oscillator (TCXO) that generates a signal, and a fourth clock in which the third clock signal is corrected to have the same frequency and the same phase as the reference clock signal. A second accuracy guarantee unit (TCXO accuracy guarantee unit) that generates a lock signal (TCXO_clk signal) and the temperature acquired by the temperature detection unit are within the first guarantee temperature range, the second A clock switching unit that outputs a clock signal and outputs the fourth clock signal when the temperature is outside the first guaranteed temperature range.

  The clock generation device according to the present invention further includes a correction table generation unit, wherein the first accuracy assurance unit detects a first frequency deviation of the first clock signal with respect to the reference clock signal, and The second accuracy assurance unit detects a second frequency deviation of the third clock signal with respect to the reference clock signal, and the correction table generation unit detects the temperature acquired from the temperature detection unit, the first accuracy Generating a correction table in which the first frequency deviation obtained from the guarantee unit and the second frequency deviation obtained from the second accuracy guarantee unit are associated with each other, and the first accuracy guarantee unit includes a holdover When the temperature acquired by the temperature detection unit at the time of occurrence is within the first guaranteed temperature range, the first frequency deviation corresponding to the acquired temperature is referred to with reference to the correction table. The second clock signal is generated by performing correction for compensating for the first frequency deviation, and the second accuracy assurance unit detects the temperature acquired by the temperature detection unit when a holdover occurs. If the temperature is outside the guaranteed temperature range of 1, the second frequency deviation corresponding to the acquired temperature is obtained by referring to the correction table, and the fourth frequency deviation is corrected to compensate for the second frequency deviation. The clock signal is generated.

  Further, in the clock generator according to the present invention, the first accuracy assurance unit may associate the first frequency deviation with a frequency stored in the correction table and closest to the acquired temperature. The second accuracy guaranteeing unit sets the second frequency deviation as a frequency deviation stored in the correction table and associated with a temperature closest to the acquired temperature. .

  Further, in the clock generator according to the present invention, the first accuracy assurance unit obtains the first frequency deviation by interpolation calculation of a plurality of frequency deviations stored in the correction table, and the second accuracy is obtained. The guarantee unit obtains the second frequency deviation by interpolation of a plurality of frequency deviations stored in the correction table.

  According to the present invention, an inexpensive oscillator with a wide guaranteed temperature range is used, and when the ambient temperature is outside the guaranteed temperature range of the oscillator, switching to an oscillator with a wide guaranteed temperature range enables a wide temperature range. An inexpensive and compact clock generator capable of outputting a highly accurate clock signal can be provided.

It is a block diagram which shows the structure of the clock generator of one Embodiment by this invention. It is a flowchart which shows the production | generation operation | movement of the correction table of the clock generator of one Embodiment by this invention. It is a flowchart which shows the switching operation | movement of the clock of the clock generator of one Embodiment by this invention. It is a flowchart which shows the operation | movement at the time of the holdover generation | occurrence | production of the clock generator of one Embodiment by this invention.

  Hereinafter, an embodiment of a clock generator according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a clock generator according to an embodiment of the present invention. The clock generator 1 according to the present embodiment includes a reference clock generator 11, an OCXO 12, an OCXO accuracy guarantee unit 13, a time acquisition unit 14, a temperature detection unit 15, a correction table generation unit 16, and a TCXO (temperature guarantee). A crystal oscillator (Temperature Compensated Crystal Oscillator) 17, a TCXO accuracy guarantee unit 18, a switching timing generation unit 19, and a clock switching unit 20 are provided. The correction table generation unit 16 includes an OCXO correction table 161 and a TCXO correction table 162.

  The reference clock generation unit 11 receives a radio wave of a GPS (Global Positioning System) satellite, generates a reference clock signal (for example, a 1 pps signal), and outputs the reference clock signal to the OCXO accuracy assurance unit 13 and the TCXO accuracy assurance unit 18. The reference clock signal may be generated by network control such as IEEE 1588.

  The OCXO 12 is a constant-temperature bath crystal oscillator that outputs a highly accurate clock signal within the guaranteed temperature range, although the guaranteed temperature range is not wide (for example, 0 ° C. to 70 ° C.). The clock generator 1 uses the clock generated by the OCXO 12 so that a clock signal can be provided even when a state in which a signal from a GPS satellite cannot be captured (this state is referred to as holdover) occurs. In this embodiment, OCXO is adopted, but the present invention is not limited to this, and any oscillator that satisfies the performance in the average operating temperature range in a steady state may be used.

  The OCXO accuracy assurance unit 13 divides the clock signal input from the OCXO 12, and the OCXO_clk signal is corrected in frequency and phase so that the frequency and phase are the same as those of the reference clock signal input from the reference clock generation unit 11. And the OCXO_clk signal is output to the clock switching unit 20. The OCXO accuracy assurance unit 13 detects a frequency deviation (frequency error) in the guaranteed temperature range of the OCXO 12 and outputs the frequency deviation to the correction table generation unit 16.

  The time acquisition unit 14 acquires time from, for example, a built-in clock, time data (UTC time) included in a GPS signal transmitted from a GPS satellite, and outputs the acquired time to the correction table generation unit 16.

  The temperature detection unit 15 detects the temperature near the clock generator 1, preferably the temperature near the OCXO 12 and the TCXO 17, and outputs the detected temperature to the correction table generation unit 16 and the switching timing generation unit 19. The temperature detector 15 is configured by, for example, a contact type platinum resistance temperature detector, a thermistor, a thermocouple, or a non-contact type radiation thermometer.

  The TCXO 17 is a temperature-guaranteed crystal oscillator having a guaranteed temperature range wider than that of the OCXO 12 (for example, −40 ° C. to 85 ° C.), but having a larger frequency deviation than the OCXO 12. In the present embodiment, TCXO is adopted, but the present invention is not limited to this, and any oscillator having a wider guaranteed temperature range than OCXO12 that is a commonly used oscillator may be used.

  The TCXO accuracy assurance unit 18 divides the clock signal input from the TCXO 17 and corrects the frequency and phase so that the frequency and phase are the same as the reference clock signal input from the reference clock generation unit 11. And outputs the TCXO_clk signal to the clock switching unit 20. Further, a frequency deviation (frequency error) in the guaranteed temperature range of the TCXO 17 is detected, and the frequency deviation is output to the correction table generation unit 16.

  The correction table generation unit 16 generates an OCXO correction table 161 that associates the time input from the time acquisition unit 14, the temperature input from the temperature detection unit 15, and the frequency deviation input from the OCXO accuracy assurance unit 13. ,Remember. Similarly, a TCXO correction table 162 in which the time input from the time acquisition unit 14, the temperature input from the temperature detection unit 15, and the frequency deviation input from the TCXO accuracy assurance unit 18 are generated and stored.

  The switching timing generation unit 19 determines whether the temperature acquired from the temperature detection unit 15 is within the guaranteed temperature range of the OCXO 12 and outputs a switching signal indicating the determination result to the clock switching unit 20.

  In addition, when the switching timing generation unit 19 determines that the temperature acquired from the temperature detection unit 15 is within the guaranteed temperature range of the OCXO 12, the switching timing generation unit 19 stops the oscillation of the TCXO 17 in order to suppress power consumption and radiation noise. The TCXO 17 may be controlled to oscillate only when it is determined that the temperature acquired from the detection unit 15 is outside the guaranteed temperature range of the OCXO 12.

  The clock switching unit 20 receives the OCXO_clk signal input from the OCXO accuracy assurance unit 13 and the TCXO accuracy assurance unit 18 without causing an instantaneous interruption of the clock signal in accordance with the switching signal input from the switching timing generation unit 19. The TCXO_clk signal is switched, and one of them is output as a clock signal. That is, the clock switching unit 20 outputs the OCXO_clk signal when the switching signal indicates that the temperature acquired from the temperature detection unit 15 is within the guaranteed temperature range of the OCXO 12, and is outside the guaranteed temperature range of the OCXO 12. If it indicates that there is, a TCXO_clk signal is output. When switching the signal, the clock switching unit 20 outputs the signal after aligning the phases of the OCXO_clk signal and the TCXO_clk signal by a phase shift circuit (not shown).

  The OCXO correction table 161 and the TCXO correction table 162 may be combined into one correction table. In that case, the “OCXO correction table 161” in the following description will be referred to as “table related to the OCXO 12 in the correction table” and “ It is assumed that “TCXO correction table 162” is read as “table related to TCXO 17 in the correction table”.

  FIG. 2 is a flowchart showing the correction table generation operation of the clock generator 1. The clock generator 1 acquires the temperature from the temperature detection unit 15 by the correction table generation unit 16 (step S101), acquires the time from the time acquisition unit 14 (step S102), and the frequency of the OCXO 12 from the OCXO accuracy assurance unit 13 The deviation is acquired (step S103), and the OCXO correction table 161 in which these are associated is generated (step S104). Similarly, the clock generator 1 acquires the time from the time acquisition unit 14 by the correction table generation unit 16 (step S101), acquires the temperature from the temperature detection unit 15 (step S102), and from the TCXO accuracy assurance unit 18 The frequency deviation of the TCXO 17 is acquired (step S103), and the TCXO correction table 162 in which these are associated is generated (step S104). The clock generator 1 performs such correction table generation processing at predetermined intervals.

  The clock generator 1 generates only the OCXO correction table 161 when the temperature acquired in step S101 is within the guaranteed temperature range of the OCXO 12, and the TCXO correction table when it is outside the guaranteed temperature range of the OCXO 12. Only 162 may be generated. Table 1 below shows an example of the OCXO correction table 161.

  When the clock generator 1 has acquired data at a temperature close to the past, the clock generator 1 may be configured not to acquire the time and frequency deviation, but the frequency deviation depends on the usage time and usage environment of the OCXO 12 and TCXO 17. Therefore, it is preferable to always update the latest frequency deviation. When the frequency deviation of the TCXO 17 is large, the clock generator 1 may acquire the frequency deviation a plurality of times for the same temperature and store the average value in the TCXO correction table 162.

  FIG. 3 is a flowchart showing the clock switching operation of the clock generator 1. The clock generation device 1 acquires the temperature by the temperature detection unit 15 (step S201). Then, the switching timing generation unit 19 determines whether or not the temperature acquired in step S201 is within the guaranteed temperature range of the OCXO 12 (step S202).

  When it is determined that the temperature acquired in step S202 is not within the guaranteed temperature range of the OCXO 12, the clock generator 1 generates a TCXO_clk signal by the TCXO accuracy assurance unit 18 (step S203), and the clock switching unit 20 generates the TCXO_clk. A signal is output (step S204).

  On the other hand, when it is determined that the temperature acquired in step S202 is within the guaranteed temperature range of the OCXO 12, the clock generator 1 outputs an OCXO_clk signal by the clock switching unit 20 (step S205). The clock generator 1 performs such clock switching processing at predetermined intervals.

  FIG. 4 is a flowchart showing the operation of the clock generator 1 when a holdover occurs. In the clock generator 1, the reference clock generator 11 detects whether or not a holdover has occurred (step S301). If a holdover has occurred, the temperature is acquired by the temperature detector 15 (step S302).

  When the temperature acquired in step S302 is within the guaranteed temperature range of the OCXO 12, the clock generator 1 refers to the OCXO correction table 161 by the OCXO accuracy assurance unit 13 and obtains a frequency deviation corresponding to the acquired temperature. (Step S303). Similarly, when the temperature acquired in step S302 is outside the guaranteed temperature range of the OCXO 12, the clock generator 1 uses the TCXO accuracy assurance unit 18 to refer to the TCXO correction table 162 and use the frequency corresponding to the acquired temperature. A deviation is obtained (step S303).

  If the OCXO_clk signal cannot be synchronized with the reference clock signal from the reference clock generation unit 11, it is considered that an error has occurred by the frequency deviation acquired in step S303. Therefore, when the temperature acquired in step S302 is within the guaranteed temperature range of the OCXO 12, the clock generator 1 uses the OCXO accuracy assurance unit 13 to perform OCXO_clk that has been corrected to compensate for the frequency deviation acquired in step S303. A signal is generated and output as a clock signal by the clock switching unit 20 (step S304). Similarly, when the temperature acquired in step S302 is outside the guaranteed temperature range of the OCXO 12, the clock generator 1 performs correction for compensating for the frequency deviation acquired in step S303 by the TCXO accuracy assurance unit 18. A TCXO_clk signal is generated and output as a clock signal by the clock switching unit 20 (step S304).

  In step S303, several methods for obtaining the frequency deviation are conceivable. In the first method, the clock generator 1 refers to the OCXO correction table 161 or the TCXO correction table 162 by the OCXO accuracy assurance unit 13 or the TCXO accuracy assurance unit 18, and selects the temperature closest to the temperature acquired in step S302. The frequency deviation associated with the temperature is obtained by searching. When a plurality of temperatures approximate to the searched temperature are stored, the frequency deviation with the latest time (date) associated with the temperature is set.

  In the second method, the clock generator 1 refers to the OCXO correction table 161 or the TCXO correction table 162 by the OCXO accuracy guarantee unit 13 or the TCXO accuracy guarantee unit 18, and a plurality of temperatures near the temperature acquired in step S302. To obtain a plurality of frequency deviations associated with the temperature, and an interpolation operation of the obtained plurality of frequency deviations (for example, a linear interpolation or a calculation by nonlinear interpolation such as Lagrange interpolation, spline interpolation, Newton interpolation) To obtain the frequency deviation.

  As described above, according to the clock generator 1 of this embodiment, when the inexpensive OCXO 12 having a wide guaranteed temperature range is used and the ambient temperature is outside the guaranteed temperature range of the OCXO 12, the TCXO accuracy guarantee unit 18 By switching to an output clock signal, a highly accurate clock signal can be output over a wide temperature range. Such a clock generator 1 can be provided at a low cost and in a compact size.

  Further, when a holdover occurs, the accuracy of the clock signal can be guaranteed by obtaining the frequency deviation with reference to the OCXO correction table 161 or the TCXO correction table 162. Even when the frequency deviation at the temperature acquired by the temperature detector 15 is not stored in the correction table, an approximate value of the frequency deviation can be used. In particular, a highly accurate frequency deviation value can be calculated by performing an interpolation calculation of a plurality of frequency deviations stored in the correction table.

  Although the above embodiments have been described as representative examples, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims. For example, the correction table generation unit 16 may not be provided, and only the OCXO_clk signal and the TCXO_clk signal may be switched according to the temperature. Further, the TCXO accuracy assurance unit 18 may continuously output the TCXO_clk signal regardless of whether or not the ambient temperature is within the guaranteed temperature range of the OCXO 12.

1 Clock generator 11 Reference clock generator 12 OCXO
13 OCXO accuracy guarantee unit 14 Time acquisition unit 15 Temperature detection unit 16 Correction table generation unit 161 OCXO correction table 162 TCXO correction table 17 TCXO
18 TCXO Accuracy Assurance Unit 19 Switching Timing Generation Unit 20 Clock Switching Unit

Claims (4)

A reference clock generator for generating a reference clock signal;
A first oscillator that generates a first clock signal that is guaranteed to operate in a first guaranteed temperature range;
A first accuracy assurance unit that generates a second clock signal obtained by correcting the first clock signal so as to have the same frequency and phase as the reference clock signal;
A temperature detector for detecting the temperature in the vicinity of the clock generator;
A second oscillator that generates a third clock signal that is guaranteed to operate in a second guaranteed temperature range that is wider than the first guaranteed temperature range;
A second accuracy assurance unit that generates a fourth clock signal obtained by correcting the third clock signal so as to have the same frequency and the same phase as the reference clock signal;
When the temperature acquired by the temperature detector is within the first guaranteed temperature range, the second clock signal is output, and when the temperature is out of the first guaranteed temperature range, the fourth clock signal is output. A clock switching unit for outputting a clock signal;
A clock generator comprising: A correction table generator;
The first accuracy assurance unit detects a first frequency deviation of the first clock signal with respect to the reference clock signal;
The second accuracy assurance unit detects a second frequency deviation of the third clock signal from the reference clock signal;
The correction table generation unit includes the temperature acquired from the temperature detection unit, the first frequency deviation acquired from the first accuracy assurance unit, and the second frequency deviation acquired from the second accuracy assurance unit. A correction table that associates
The first accuracy assurance unit refers to the correction table and corresponds to the acquired temperature when the temperature acquired by the temperature detection unit when the holdover occurs is within the first guaranteed temperature range. Obtaining a first frequency deviation, performing a correction to compensate for the first frequency deviation, and generating the second clock signal;
When the temperature acquired by the temperature detection unit when a holdover occurs is outside the first guaranteed temperature range, the second accuracy assurance unit refers to the correction table and corresponds to the acquired temperature. 2. The clock generator according to claim 1, wherein a second frequency deviation is obtained, and the fourth clock signal is generated by performing correction for compensating for the second frequency deviation. 3. The first accuracy assurance unit sets the first frequency deviation as a frequency deviation stored in the correction table and associated with a temperature closest to the acquired temperature,
The second accuracy assurance unit is characterized in that the second frequency deviation is a frequency deviation stored in the correction table and associated with a temperature closest to the acquired temperature. 3. The clock generator according to 2. The first accuracy assurance unit obtains the first frequency deviation by interpolation calculation of a plurality of frequency deviations stored in the correction table,
The clock generator according to claim 2, wherein the second accuracy assurance unit obtains the second frequency deviation by interpolation calculation of a plurality of frequency deviations stored in the correction table.

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