JP2010068065A - Reference signal generating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate highly accurate reference frequency signals by suppressing the influence of various kinds of frequency variation elements related to temperature. <P>SOLUTION: A control part 10 observes the level of a synchronizing type control voltage signal with time, while 1PPS is inputted, and estimates and stores a control voltage signal for free-running. The control part 10 observes and stores the temperature of a voltage-controlled oscillator 14, on the basis of a temperature detection signal from a temperature sensor 16. When hold-over is detected, the control part 10 detects the temperature at the point of time (S101) and also calculates the time change rate of the temperature including the stored past temperature (S102). The control part 10: reads a coefficient for control correction value calculating set beforehand (S103); substitutes the detected temperature and the calculated time change rate of the temperature in an operation expression set by the coefficient; and calculates a control correction value (S104). The control part 10 corrects the control voltage signal for free-running, on the basis of the control correction value, and supplies it to the voltage-controlled oscillator 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reference signal generator for use in wireless communication equipment such as digital communication.

  When a wireless system is provided in a wide area such as a cellular phone or terrestrial digital broadcasting, a plurality of base stations are required to transmit data to a terminal device. In these base stations, a high-accuracy reference frequency signal is required due to specifications. As a reference signal generator for obtaining such a high-accuracy reference frequency signal, an apparatus using a very expensive Rb oscillator is also used, but generally includes a crystal oscillator, such as a GPS 1PPS. What generates a reference frequency signal while synchronizing with a highly accurate external reference signal is used.

  However, a reference signal generator using a crystal oscillator generates a reference frequency signal having a different frequency when a voltage signal of the same level is applied in a situation where the temperature is different due to the frequency temperature characteristics of the crystal resonator.

In order to solve this problem, in the invention described in Patent Document 1, a control voltage signal level correction value is set in advance for each temperature, and the control voltage signal is corrected according to the detected temperature and applied to the crystal oscillator. ing.
Japanese Patent No. 405618

  Incidentally, it is generally known that a crystal resonator has frequency temperature characteristics having hysteresis.

  However, the inventor of the present application views the problem that even if the correction value is set according to the frequency temperature characteristic having hysteresis, the frequency of the output reference frequency signal is slightly shifted from the set value. The crystal resonator was experimentally found to have the following frequency temperature characteristics.

  FIG. 5 is a graph showing frequency temperature characteristics of a general AT-cut quartz crystal resonator, (A) shows the overall temperature characteristics, and (B) shows the temperature characteristics Hy around 40 ° C. In the figure, Hy (ΔT1U), Hy (ΔT2U), Hy (ΔT3U) indicate temperature characteristics for each time change rate of the temperature in the temperature rising process, and Hy (ΔT1D), Hy (ΔT2D), Hy (ΔT3D). Indicates the temperature characteristics for each time change rate of the temperature in the temperature lowering process. Here, the time change rate of the temperature is in the order of ΔT1 <ΔT2 <ΔT3.

  As shown in FIG. 5, the crystal resonator generates reference frequency signals of different frequencies even in a situation where a voltage signal of the same voltage level is applied at the same temperature during the temperature rising process and the temperature falling process. End up. Furthermore, the quartz resonator generates a reference frequency signal having a different frequency even if the time change rate of the temperature is different.

  That is, a higher-accuracy reference frequency signal cannot be generated unless three elements including the temperature, the temperature transition direction of the temperature rising process or the temperature lowering process, and the time change rate of temperature are taken into consideration.

  Accordingly, an object of the present invention is to realize a reference signal generator capable of generating a highly accurate reference frequency signal while suppressing the influence of various frequency fluctuation elements related to temperature.

  The reference signal generator according to the present invention includes a crystal oscillator that generates a reference frequency signal when a voltage signal is applied to a crystal resonator, a control unit that generates a voltage signal, and a temperature control unit that detects the temperature of the crystal oscillator. Temperature detecting means for outputting to the means. Then, the control means of the reference signal generator calculates the time change state of the temperature from the time-series temperatures sequentially acquired and stored, and the voltage signal signal based on the time change state of the temperature and the temperature. The level is corrected and given to the crystal oscillator.

  In this configuration, the correction data to the voltage signal applied to the crystal resonator is based on the temperature and the time change state of the temperature, that is, the temperature transition direction identified by the temperature rising process or the temperature falling process and the time change rate of the temperature. It is determined. Thereby, the correction data is set not only based on the temperature alone but also including the temperature transition direction and the time change rate of the temperature reflecting a more detailed temperature change.

  The reference signal generator of the present invention is a voltage-controlled oscillator in which the crystal oscillator can control the frequency of the reference frequency signal generated according to the signal level of the applied voltage signal. Further, the reference signal generator includes a phase comparator that obtains a phase difference between an external reference signal and a reference frequency signal and outputs a phase difference signal, a loop filter that generates a synchronous control voltage signal from the phase difference signal, . The control means of the reference signal generator switches the voltage signal applied to the crystal oscillator depending on whether or not a reference signal is input. Specifically, during the synchronization period in which the input of the reference signal is detected, the synchronous control voltage signal is supplied to the crystal oscillator as a voltage signal. On the other hand, the corrected voltage signal is applied to the crystal oscillator during the free-running period during which the reference signal input interruption is detected.

  In this configuration, by synchronizing with the reference signal during the synchronization period, it is possible to generate a highly accurate reference frequency regardless of the various elements related to temperature, and during the free-running period, the above-mentioned various elements related to temperature are taken into account. A highly accurate reference frequency can be generated from the corrected data. That is, in the synchronous reference signal generator, even if a holdover in which the reference signal is not input occurs, a highly accurate reference frequency signal can be continuously generated.

  Further, the control means of the reference signal generator according to the present invention acquires the synchronous control voltage signal during the synchronization period in which the reference signal is input, and performs the synchronous control with the temperature and the time change state of the temperature at the acquisition time. Based on the voltage signal, a correction element used for correction is learned and updated and stored.

  In this configuration, the above-described correction data is optimized during the synchronization period according to the installation state of the reference signal generator. Thereby, a reference frequency signal with higher accuracy can be generated during the free-running period.

  According to the present invention, even in a situation where the reference signal for synchronization cannot be obtained and the temperature environment for the crystal unit fluctuates, the influence of various frequency fluctuation factors related to temperature And a highly accurate reference frequency signal can be output.

  A reference signal generator according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram showing a reference signal generating device of this embodiment and a circuit for supplying a reference signal to this device. In the following description, an example in which a reference signal is acquired using GPS is shown, but another GNSS may be used, and further, another reference signal may be acquired from an external device.

  The reference signal generator 1 of this embodiment includes a control unit 10, a phase comparator 11, a loop filter 12, a switch circuit 13, a voltage controlled oscillator 14, a frequency divider 15, and a temperature sensor 16.

  A GPS receiver 2 is connected to the reference signal generator 1, and a GPS antenna 3 is connected to the GPS receiver 2. The GPS receiver 2 acquires positioning-related information such as a navigation message based on the positioning signal received by the GPS antenna 3, generates 1 PPS which is a reference signal, and supplies it to the phase comparator 11.

  The phase comparator 11 detects a phase difference between 1 PPS and an adjustment timing signal obtained by dividing the reference frequency signal output from the voltage controlled oscillator 14 by the frequency divider 15, and a voltage level based on the phase difference. The phase difference signal is generated and output. The loop filter 12 is configured by a low-pass filter or the like, and generates a synchronous control voltage signal by averaging the voltage level of the phase difference signal on the time axis, and outputs it to the control unit 10 and the switch circuit 13.

  The switch circuit 13 is a circuit that can be switched to connect either the loop filter 12 or the control unit 10 to the control signal input terminal of the voltage controlled oscillator 14. This switching is performed according to a switching control signal from the control unit 10.

  For example, the temperature sensor 16 is installed in contact with the voltage controlled oscillator 14 or is installed near the mounting position of the substrate on which the voltage controlled oscillator 14 is mounted. A temperature detection signal corresponding to the signal is generated and output to the control unit 10.

  The control unit 10 performs various controls for operating the reference signal generator 1. Further, the control unit 10 stores the temperature detection signal from the temperature sensor 16 in time series.

  Further, the control unit 10 detects and stores the level value (DAC value) of the synchronous control voltage signal output from the loop filter 12, and is used for self-running based on the stored time-series DAC value group. Estimate the control voltage signal.

  In addition, the control unit 10 performs switching control of the switch circuit 13 according to whether or not 1 PPS is received from the GPS receiver 2. Specifically, the control unit 10 gives a switching control signal to the switch circuit 13 so as to connect the loop filter 12 and the voltage controlled oscillator 14 if 1 PPS can be acquired from the GPS receiver 2. Thus, the synchronous voltage control signal from the loop filter 12 is given to the voltage controlled oscillator 14 while 1 PPS is acquired. The switch switching control is not limited to the determination of the presence or absence of 1PPS, but can also be executed based on whether or not 1PPS is normal, a command from the GPS receiver 2, and the like.

  On the other hand, if the control unit 10 cannot acquire 1 PPS from the GPS receiver 2, that is, if a holdover is detected, the control unit 10 sends a switching control signal to connect the voltage control oscillator 14 to itself (the control unit 10). Give to 13. Then, the control unit 10 outputs the estimated self-running control voltage signal when the holdover is detected. Thus, in the holdover state, the free-running control voltage signal is given to the voltage controlled oscillator 14 via the switch circuit 13. At this time, the control unit 10 corrects the level value of the self-running control voltage signal using the following method.

  FIG. 2 is a flowchart showing a processing flow of level value correction of the control voltage signal for self-running, and shows a case where calculation for calculating the control correction value is performed.

  The control unit 10 detects the temperature Tr when it is time to calculate the correction value (for example, when a holdover occurs) (S101). Further, the control unit 10 reads the temperature Tr ′ in the past predetermined section set in advance with respect to the detected temperature Tr, and calculates the time change rate of the temperature, that is, the temperature gradient ΔTr (S102). At this time, the control unit 10 detects the temperature transition direction based on the temperature gradient ΔTr.

  In accordance with the temperature transition direction, the control unit 10 reads the correction frequency calculation formula shown below, and calculates the correction frequency fco by substituting the temperature Tr and the temperature gradient ΔTr into the calculation formula.

fco = a · Tr ³ + b · Tr ² + c · Tr + d − (1)
a to d are represented by the following formulas (2A) to (2D).

a = (K _A (ΔTr) ³ + L _A (ΔTr) ² + M _A (ΔTr) + N _A ) − (2A)
b = (K _B (ΔTr) ³ + L _B (ΔTr) ² + M _B (ΔTr) + N _B ) − (2B)
c = (K _C (ΔTr) ³ + L _C (ΔTr) ² + M _C (ΔTr) + N _C ) − (2C)
d = (K _D (ΔTr) ³ + L _D (ΔTr) ² + M _D (ΔTr) + N _D ) − (2D)
Here, K _{A to} K _D , L _{A to} L _D , M _{A to} M _D , and N _{A to} N _D are constants set in advance by experiments according to the voltage controlled oscillator 14.

  By performing such calculation, the difference between the frequency actually output according to the temperature environment of the reference signal generator by the estimated and calculated self-running control voltage signal and the frequency to be output from the voltage controlled oscillator 14 is obtained. A certain correction frequency fco can be calculated.

  The control unit 10 converts the correction frequency fco into the same unit as the DAC value, and calculates a control correction value (S104). Note that this conversion is preliminarily stored in the control unit 10 in advance according to the voltage controlled oscillator 14 and the temperature Tr, and is easily calculated by using the conversion equation. In this conversion, if the influence of the temperature gradient ΔTr is also taken into consideration, a more accurate control correction value can be calculated.

  The control unit 10 corrects and outputs the self-running control voltage signal with the calculated control correction value. Specifically, the control unit 10 outputs a control voltage signal having a signal level corresponding to the corrected DAC value obtained by adding the DAC value corresponding to the control correction value to the DAC value before correction (S105).

  The voltage controlled oscillator 14 generates a reference frequency signal based on a synchronous control voltage signal given via the switch circuit 13 or a corrected self-running control voltage signal. More specifically, the voltage controlled oscillator 14 generates a reference frequency signal based on the synchronous control voltage signal in a period in which 1 PPS is input and is synchronized, and is corrected by the temperature and the temperature gradient in the holdover state. A reference frequency signal is generated based on the self-running control voltage signal.

  By adopting such a configuration, even if it becomes a holdover state and a high-accuracy reference signal cannot be acquired, a high-accuracy reference frequency signal can be generated without being affected by the temperature or temperature gradient. .

  In addition, when a highly accurate reference signal such as 1 PPS is obtained, a highly accurate reference frequency signal can be generated in synchronization therewith, so that it is constantly high without being affected by temperature or temperature gradient. An accurate reference frequency signal can be generated.

  In the above-described method, the control correction value is performed using only mathematical calculation. However, a temperature correction table may be created in advance and the control correction value may be calculated using the table.

  FIG. 3 is a flowchart showing a process flow of level value correction of the self-running control voltage signal, and shows a case where a temperature correction table is used.

  As described above, the control unit 10 detects the temperature Tr and calculates the time change rate (temperature gradient) ΔTr of the temperature (S201 → S202).

  The control unit 10 sets a plurality of temperatures Tn (n is a preset constant) and a plurality of temperature gradients ΔTm (m is a preset positive integer) at each temperature Tn within the operating temperature range of the reference signal generator. Are stored as temperature correction tables in which control correction values Xmn obtained experimentally are respectively set.

  The controller 10 reads this temperature correction table, and if the detected temperature Tr and temperature gradient ΔTr match the combination of the temperature Tn and the temperature gradient ΔTm stored in the table, the control correction corresponding to these combinations is performed. The value Xmn is read and used. If the detected temperature Tr and the temperature gradient ΔTr do not match the combination of the temperature Tn and the temperature gradient ΔTm stored in the table, the control unit 10 stores the detected temperature Tr and the temperature gradient ΔTr in the table. At least two combinations of the stored temperature Tn and temperature gradient ΔTm are extracted. At this time, the control unit 10 also reads out the control correction value Xmn corresponding to the combination of the extracted temperature Tn and the temperature gradient ΔTm. And the control part 10 calculates the hysteresis correction value Hm from following Formula based on each temperature gradient (DELTA) Tm.

Hm = Am (ΔTm) ³ + Bm (ΔTm) ² + Cm (ΔTm) + Dm − (3)
Am, Bm, Cm, and Dm are constant coefficients obtained experimentally according to the voltage controlled oscillator 14 and the temperature gradient ΔTm.

  Then, the control unit 10 uses the temperature Tn, the hysteresis correction value Hm that depends on the temperature gradient ΔTm, and the control correction value Xmn to calculate the control correction value for the detected temperature Tr and temperature gradient ΔTr from the following equation using linear interpolation. Xr is calculated (S204). In the following equation, the extracted temperature, the hysteresis correction value based on the temperature gradient, and the control correction value are represented as (Tn, Hm, Xmn) and (Tn ′, Hm ′, Hmn ′).

Xr = {Tn ′ (Xmn + Hm) −Tn (Xmn ′ + Hm ′)} / (Tn′−Tn)
-(4)
The control unit 10 corrects and outputs the self-running control voltage signal with the calculated control correction value. Specifically, the control unit 10 outputs a control voltage signal having a signal level corresponding to the corrected DAC value obtained by adding the DAC value corresponding to the control correction value to the DAC value before correction (S205).

  As described above, even with the method using the temperature correction table, it is possible to generate a highly accurate reference frequency signal as in the case where the control correction value is calculated only with the above-described arithmetic expression.

  In each of the above methods, the control correction value remains set at the time of shipment from the factory. However, if the following method is used, a more optimal control correction value can be obtained according to the installation environment of the reference signal generator. Can do.

  FIG. 4 is a flowchart showing a process flow for correcting the level value of the control voltage signal for self-running, including the process of optimizing the control correction value according to the installation environment.

  The control unit 10 detects the input of 1 PPS, and if there is an input (S301: Yes), continuously acquires the level (DAC value) of the control voltage signal output from the loop filter 12 (S302). At this time, the control unit 10 detects the temperature at the acquisition timing of each DAC value (S303).

  The control unit 10 calculates the change amount of the DAC value according to the time change rate of the temperature from the combination of each DAC value and the temperature detected continuously in this way. Here, the PLL circuit including the phase comparator 11, the loop filter 12, the voltage controlled oscillator 14, and the frequency divider 15 was controlled so that each DAC value was synchronized with 1PPS and a reference frequency signal having a constant frequency was output. Therefore, if the voltage-controlled oscillator is provided with a sufficient energization time, the amount of change due to the aging characteristic is almost eliminated, so that the difference between continuously detected DAC values is that of temperature and the amount of change in temperature. Is determined by Therefore, the above control correction value can be obtained by calculating the difference between the DAC values (S304).

  The control unit 10 continuously performs and stores such control correction value calculation processing while 1 PPS is input. Thereby, the optimal control correction value according to the installation operation environment can be stored.

  Then, when detecting the holdover, the control unit 10 refers to the stored optimal control correction value, detects the temperature and the time change rate of the temperature at that time, and sets the control correction value corresponding to these. decide. The control unit 10 corrects the self-running control voltage signal using the determined control correction value and supplies the corrected voltage to the voltage controlled oscillator 14.

  By using such processing, it is possible to correct with the optimal control correction value according to the installation environment of the reference signal generator instead of the control correction value set at the time of shipment from the factory. A signal can be generated.

  Although the cubic equation is used in the above-described arithmetic expression, another n-order equation (for example, a sixth-order equation) or the like may be used.

1 is a schematic block diagram illustrating a reference signal generating device according to an embodiment of the present invention and a circuit for supplying a reference signal to the device. It is a flowchart which shows the processing flow of level value correction | amendment of the self-propelled control voltage signal using only a computing equation. It is a flowchart which shows the processing flow of level value correction | amendment of the self-propelled control voltage signal using the temperature correction table. It is a flowchart which shows the processing flow of level value correction | amendment of the control voltage signal for self-propelled including the process which optimizes a control correction value according to an installation environment. It is a graph which shows the frequency temperature characteristic of a general AT cut crystal resonator.

Explanation of symbols

1-reference frequency signal generator, 10-control unit, 11-phase comparator, 12-loop filter, 13-switch circuit, 14-voltage controlled oscillator, 15-frequency divider, 16-temperature sensor, 2-GPS reception Machine, 3-GPS antenna

Claims (3)

A reference signal generator comprising: a crystal oscillator that generates a reference frequency signal when a voltage signal is applied to a crystal resonator; and a control unit that generates the voltage signal,
Temperature detecting means for detecting the temperature of the crystal oscillator and outputting the detected temperature to the control means;
The control means calculates a time change state of the temperature from the time series of temperatures sequentially obtained and stored, and corrects the signal level of the voltage signal based on the time change state of the temperature and the temperature. A reference signal generator for supplying to the crystal oscillator. The crystal oscillator is a voltage controlled oscillator capable of controlling the frequency of a reference frequency signal generated according to the signal level of an applied voltage signal,
A phase comparator that obtains a phase difference between an external reference signal and the reference frequency signal and outputs a phase difference signal;
A loop filter that generates a synchronous control voltage signal from the phase difference signal,
The control means includes
In the synchronization period in which the input of the reference signal is detected, the synchronous control voltage signal is supplied to the crystal oscillator as the voltage signal,
The reference signal generator according to claim 1, wherein the voltage signal subjected to the correction is supplied to the crystal oscillator during a free-running period in which an input interruption of the reference signal is detected.   The control means acquires the synchronous control voltage signal during the synchronization period, and uses the correction control voltage signal based on the temperature at the time of acquisition, the time variation state of the temperature, and the synchronous control voltage signal. The reference signal generation device according to claim 2, wherein the correction element to be learned is learned and updated and stored.

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