JP2010109484A - Calibration method of internal reference signal source in frequency output apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calibration method of an internal reference signal in a frequency synthesizer, which performs accurate calibration by a simple technique. <P>SOLUTION: In the technique that calibrates an internal reference signal source 16 which outputs a reference clock signal in the frequency synthesizer 1 which outputs an established frequency signal, based on the reference clock signal and a frequency setting signal, it includes: a process to operate the frequency synthesizer 1 based on the frequency setting signal and to measure the output frequency by a frequency measuring apparatus 3; and a process to increase or decrease an instruction value memorized in a nonvolatile memory 17 of the frequency synthesizer 1 by an external control device 2 based on a frequency difference of the measured output frequency and the frequency setting value determined by the frequency setting signal, and to make the frequency as an optimal instruction value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for calibrating an internal reference signal source provided in a frequency output device such as a frequency synthesizer that outputs a set frequency signal.

  A frequency synthesizer that is a frequency output device, for example, used in a communication base station is required to have high accuracy and stability with respect to an output frequency. For example, in a base station that performs terrestrial digital broadcasting, if the output frequency deviates from the required frequency, the distribution image is disturbed. Therefore, the reference signal of the frequency synthesizer is extremely high precision and high stability obtained from a rubidium reference signal oscillator or the like In many cases, an external reference signal is captured and synchronized.

  However, since this type of reference signal source is expensive, it is advantageous in terms of cost to use a reference signal from an internal reference signal source provided in the frequency synthesizer. Even when the frequency synthesizer is operated by an external reference signal, if the external reference signal is interrupted due to cable degradation or maintenance, the frequency synthesizer must be driven by the internal reference signal.

  For this reason, naturally high frequency accuracy is required for the internal reference signal, and OCXO (Oven Controlled Crystal Oscillator) and TCXO (Temperature Compensated Crystal Oscillator) are used as the internal reference signal source. Or it is often composed of VCXO (Voltage Controlled Crystal Oscillator, hereinafter referred to as VCO). However, this type of signal source cannot avoid frequency fluctuations over the long term due to aging of the crystal oscillator and the frequency adjustment circuit.

  The internal reference signal source whose frequency has fluctuated needs to be calibrated periodically, for example, but such calibration is often performed manually using, for example, a trimmer potentiometer. Such calibration work can be done with large preparations such as opening the frequency synthesizer's housing or operating a trimmer potentiometer by inserting a screwdriver into the calibration hole provided in the housing. Time-consuming manual work was necessary.

  Patent Document 1 describes a crystal oscillation device including a first crystal oscillator for outputting a frequency signal and a second crystal oscillator for outputting a reference signal. According to this apparatus, the second crystal oscillator is intermittently started to suppress the aging deterioration of the second crystal oscillator, and the second crystal oscillator is not activated during the period when the second crystal oscillator is not started. The data relating to the frequency change of the first crystal oscillator obtained by comparing the signals output from the two crystal oscillators when starting the crystal oscillator is stored, and the frequency signal is calibrated based on this data. It is like that.

However, in general, a frequency synthesizer employs a mechanism that uses a PLL (Phase Locked Loop) that controls the output frequency by feeding back the phase difference between the reference signal and the output signal to the crystal oscillator. In order to suppress this, it is not practical to apply a technique of intermittently operating the internal reference signal source.
JP 2006-50025 A: Paragraphs 0012 to 0014

  The present invention has been made based on such circumstances, and an object of the present invention is to provide a method for calibrating an internal reference signal of a frequency output device capable of performing accurate calibration by a simple method. is there.

A method for calibrating an internal reference signal source of a frequency output apparatus according to the present invention includes an internal reference signal source and a control voltage for outputting a control voltage for controlling the frequency of a reference clock signal output from the internal reference signal source. And a method for calibrating an internal reference signal source of a frequency output device that outputs a set frequency signal based on the reference clock signal and the frequency setting signal.
A frequency output device comprising: a nonvolatile memory for storing a command value of the control voltage of the internal reference signal source; and a processor for reading the command value from the nonvolatile memory and supplying the command value to the control voltage output unit Use
Operating the frequency output device based on a frequency setting signal to calibrate the internal reference signal source, and measuring the output frequency of the frequency output device with a frequency measuring device;
Based on the frequency difference between the output frequency measured in this step and the frequency setting value determined by the frequency setting signal, it is stored in the nonvolatile memory by an external control device connected to the frequency output device. And a step of increasing / decreasing the command value to obtain an optimal command value.
Here, the frequency output device is preferably a frequency synthesizer, for example.

  The step of setting the optimum command value may be performed by an operator inputting an increase / decrease value of the command value via an external control device based on the frequency difference, or automatically performed by a program by the external control device. Also good. Further, a digital / analog converter or a PWM controller is suitable as the control voltage output unit.

  According to the present invention, the output frequency of the frequency output device is measured, and on the basis of the measurement result, the command value of the control voltage of the internal reference signal source is increased or decreased based on the difference between the measurement result and the frequency setting value. The internal reference signal source is calibrated by using the command value. As a result, for example, the internal reference signal source can be calibrated even under conditions where an external reference signal source cannot be prepared, and the flexibility of conditions under which calibration can be performed can be improved. . Further, since it is not necessary to use an expensive external reference signal source using, for example, rubidium or the like, the cost for calibration can be reduced.

  Furthermore, since the internal reference signal source is calibrated using software from the external control device, it is not necessary to perform hardware adjustment using a trimmer potentiometer, which has been conventionally performed. As a result, large-scale preparation and labor-intensive work such as opening the frequency output device housing or inserting a screwdriver into a calibration hole provided in this housing is eliminated, making it easy Calibration can be done with simple operations.

  The configuration of the system when the method of calibrating the internal reference signal source of the frequency output apparatus according to the present embodiment is applied to a frequency synthesizer will be described with reference to FIGS. As shown in FIG. 1, the system includes an internal reference signal source 16 to be calibrated by the system, a frequency synthesizer 1 that outputs a frequency signal having a desired output frequency to the signal line 4, and this The frequency measurement device 3 that measures the output frequency of the signal output from the frequency synthesizer 1 and the external control device 2 that adjusts the output frequency based on the measurement result of the output frequency by the frequency measurement device 3 include, for example, common data The configuration is connected to the bus 5. Here, the connection of the frequency synthesizer 1, the frequency measurement device 3, and the external control device 2 is not limited to the method of using the data bus 5, and the frequency synthesizer 1, the frequency measurement device 3, and the external control device 2 exchange information with each other. Any communication means or connection method may be used as long as it can be transmitted.

  The frequency synthesizer 1 constitutes a PLL (Phase Locked Loop) with a voltage controlled oscillator 13 (hereinafter referred to as a VCO), adjusts a control voltage supplied to the VCO 13, and has a desired output frequency from the VCO 13. A PLL control unit 12 that performs control to output a signal, an internal reference signal source 16 that supplies a reference clock signal (internal reference signal) to the PLL control unit 12, and a frequency adjustment of the internal reference signal source 16 A frequency adjustment unit 15 and a processor (Central Processing Unit: CPU) 11 that comprehensively controls each device in the frequency synthesizer 1 are provided.

  The PLL control unit 12 according to the present embodiment has a different principle from, for example, conventional PLL control, and is configured to execute new PLL control developed by the applicant. The configuration and operation of the PLL control unit 12 will be briefly described with reference to FIG. 2. The VCO 13 that constitutes the PLL in cooperation with the PLL control unit 12 is supplied from a coupler 127 (to be described later) forming a voltage output unit. An analog frequency signal which is a sine wave having a frequency corresponding to the supply voltage is output, and the frequency dividing means 121 divides the frequency signal by 1 / N (N is an integer).

The A / D converter 122 samples the frequency signal described above converted into a sine wave based on the sampling period (for example, 40 MHz) determined by the reference clock signal supplied from the internal reference signal source 16, The sampled signal is converted into a digital signal. The vector extracting unit 123 performs quadrature detection on the sine wave signal specified by the digital signal from the A / D conversion unit 122 using a sine wave signal having a frequency of ω ₀ t / 2π (angular velocity is ω ₀ t). Thus, a vector rotating at the frequency of the difference between the frequency of the frequency signal specified by the digital signal of the A / D converter 122 and the frequency of the sine wave signal used for detection is extracted.

  The frequency difference extracting means 124 extracts the difference between the vector frequency and the vector frequency when the output frequency of the VCO 13 becomes the set frequency. The frequency of the vector when the output frequency reaches the set frequency is calculated, for example, in the frequency synthesizer 1 based on, for example, an externally input frequency setting signal. The integrating means 125 constitutes a part of the feedback means of the PLL, integrates the frequency difference extracted by the frequency difference extracting means 124, and corresponds to the frequency difference via a D / A converter not shown. A voltage is supplied to the input side of the VCO 13. By providing these configurations, the loop composed of the PLL control unit 12 and the VCO 13 forms a PLL. When the frequency difference extracted by the frequency difference extracting means 124 becomes zero, the PLL is locked and the output of the VCO 13 The frequency will be locked to the set frequency.

  The frequency pull-in means 126 serves to supply a start control voltage to the VCO 13. When the external control device 2 is started, the frequency pull-in means 126 receives the control voltage from the frequency pull-in means 126 via the coupler 127, for example, based on an instruction from the CPU 11. The control voltage is gradually increased. Along with this, the output frequency of the VCO 13 rises, the output frequency becomes a predetermined frequency that falls within the control range of the vector extracting means 123 and the frequency difference extracting means 124 described above, and these means 123 and 124 start to function. Then, the increase of the control voltage from the frequency pull-in means 126 is stopped to obtain a fixed value. Then, the output of the integrating means 125 from the PLL side is added to the fixed value by the coupler 127 and added to the VCO 13 as a control voltage. The detailed configuration and operation principle of the novel PLL described above are disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-295537.

  Returning to the description of the entire frequency synthesizer 1 shown in FIG. 1, the amplifier 14 amplifies the frequency signal locked to the set frequency output from the VCO 13 and outputs the amplified signal to the signal line 4, and the output terminal 19. The frequency signal can also be output to the frequency measuring device 3 connected to the frequency synthesizer 1 via the.

  The internal reference signal source 16 serves to supply a reference clock signal to the A / D converter 122 of the PLL controller 12, and is configured by a voltage controlled oscillator including a crystal resonator, for example. The control voltage supplied to the internal reference signal source 16 is adjusted by a frequency adjusting unit 15 that forms a control voltage output unit. As shown in FIG. 3, the frequency adjustment unit 15 has a configuration in which an analog low-pass filter 152 is connected to a subsequent stage of a PWM (Pulse Width Modulation) controller 151, for example. The PWM controller 151 plays a role of outputting a pulse train controlled to a predetermined duty ratio based on a command value acquired from the CPU 11 to the analog low-pass filter 152, and the analog low-pass filter 152 is a pulse train from the PWM controller 151. Is integrated and smoothed into a DC voltage, and this is output as a control voltage to the internal reference signal source 16.

  The duty ratio of the pulse train output from the PWM controller 151 is controlled so that the oscillation frequency of the internal reference signal source 16 becomes the frequency of the above-described reference clock signal (for example, 40 MHz), and a command value for determining this duty ratio. (Hereinafter referred to as duty ratio information) is stored in, for example, the nonvolatile memory 17 shown in FIG. For example, the duty ratio information is read from the nonvolatile memory 17 and output to the PWM controller 151 at the start of the operation of the frequency synthesizer 1, and the nonvolatile memory 17 is rewritable. For example, when the frequency of the reference clock signal is deviated from 40 MHz due to a change in physical properties of the crystal in the internal reference signal source 16 over time, the output frequency of the frequency synthesizer 1 is also deviated from the set frequency. From this, the duty ratio information is rewritten to a new value, and the frequency of the reference clock signal is set to 40 MHz again, so that the frequency adjustment for matching the output frequency from the frequency synthesizer 1 with the set frequency is performed. The work memory 18 serves to temporarily store duty ratio information when performing frequency adjustment of the frequency synthesizer 1, and may be a memory built in the CPU 11.

  In the frequency synthesizer 1 according to the present embodiment, instead of using an expensive external reference signal source such as rubidium, the external control device 2 and the frequency measurement device 3 are used, so that the frequency synthesizer 1 The internal reference signal source 16 can be calibrated.

  The frequency measuring device 3 is a portable device configured to be detachable from the frequency synthesizer 1 through, for example, an output terminal 19, and receives an instruction from the external control device 2 or an instruction from an operator at the site. Thus, it plays the role of measuring the output frequency of the frequency synthesizer 1 and outputting the measurement result to the external control device 2.

  The external control device 2 has a configuration in which a calibration program 22 for the internal reference signal source 16 is installed in a computer having a processor (CPU) 21, for example, a personal computer, and the operation control of the frequency synthesizer 1 during calibration work A function of outputting the measurement result of the output frequency of the frequency synthesizer 1 in the frequency measuring device 3 is provided.

  Reference numeral 23 in FIG. 1 denotes an interface unit including a monitor, a keyboard, a mouse, and the like. For example, various instructions relating to frequency adjustment can be received from an operator via a GUI (Graphical User Interface). For example, the calibration work start switch 231 illustrated in the interface unit 23 of FIG. 1 serves to instruct the frequency synthesizer 1 to start the calibration work of the internal reference signal source 16, and the frequency confirmation switch 232 is set for calibration. It plays the role of switching the frequency setting value of the frequency synthesizer 1 between the maximum output (for example, 900 MHz), the minimum output (for 700 MHz), and the center output (for the same frequency 800 MHz) of the frequency synthesizer 1.

  The coarse / fine adjustment switch 233 plays a role of switching the adjustment unit of the frequency at the time of calibration between fine adjustment and coarse adjustment. The frequency adjustment switch 234 is read into the frequency adjustment amount, that is, the work memory 18. It serves to indicate the adjustment amount of the duty ratio information. The frequency adjustment switch 234 includes, for example, four switches “−2, −1, +1, +2” corresponding to the adjustment direction and adjustment amount of the output frequency. On the other hand, information (hereinafter referred to as adjustment information 24) indicating the adjustment amount of the duty ratio necessary to increase the output of the internal reference signal source 16 by, for example, 1 Hz is stored in the nonvolatile memory 20 of the external control device 2, for example. Thus, the adjustment amount of the duty ratio according to the setting of the interface unit 23 and the selection result of the frequency adjustment switch 234 is output to the frequency synthesizer 1.

  For example, when the coarse adjustment switch of the coarse adjustment / fine adjustment switch 233 is set to output the selection result of the frequency adjustment switch 234 by 10 times, the frequency adjustment is performed with the coarse adjustment switch being selected. When the switch “+2” of the switch 234 is pressed, information for instructing the adjustment by adjusting the adjustment information 24 by +20 times (× (+2) × 10) is output to the frequency synthesizer 1. The adjustment amount is added to the duty ratio information read out to the memory 18.

  If the fine adjustment switch of the coarse / fine adjustment switch 233 is set to output the selection result of the frequency adjustment switch 234 at the same magnification, for example, the frequency adjustment switch 234 is in a state where the fine adjustment switch is selected. When the switch of “−1” is pressed, information for instructing the adjustment of the amount of adjustment information 24 multiplied by −1 is output to the frequency synthesizer 1, for example, in the work memory 18 adjusted by the coarse adjustment described above. The adjustment amount is further added to the duty ratio information.

  The write switch 235 rewrites the duty ratio information (control voltage command value) already stored in the nonvolatile memory 17 to the value after calibration when the calibration work by the external control device 2 is finished. Is output to the frequency synthesizer 1.

  The frequency display unit 236 is an area in which the output frequency of the frequency synthesizer 1 measured by the frequency measuring device 3 is displayed. The operator checks each output frequency displayed on the frequency display unit 236 and switches each of the switches 232 to 235. Can be used to perform calibration work. The content of the operation | work which calibrates the internal reference signal source 16 of the frequency synthesizer 1 using the system demonstrated above is demonstrated.

  FIG. 4 shows the entire system of the frequency synthesizer 1, the external control device 2, and the frequency measurement device 3, and the operation and flow of the operator. The internal reference signal source 16 is calibrated periodically, for example, every several months. For example, it is performed in accordance with the maintenance timing of the frequency synthesizer 1. When starting calibration (start), first, the operator connects the external control device 2 and the frequency measuring device 3 to the frequency synthesizer 1 (step S1), and then presses the calibration work start switch 231 (step S2). A frequency setting signal corresponding to one of the maximum output, center output, and minimum output preselected at 232, for example, 800 MHz as the center output is read from the nonvolatile memory 20 and sent to the frequency synthesizer 1. And the frequency synthesizer 1 is operated based on the frequency setting signal (step S3).

  In the frequency synthesizer 1, the frequency synthesizer 1 is operated based on the frequency setting signal from the external control device 2 and the duty ratio information read to the work memory 18, and the frequency measuring device 3 connected to the output terminal 19 The output frequency is measured (step S4). The measurement result of the frequency measuring device 3 is displayed on the frequency display unit 236 of the external control device 2, and the operator outputs the output frequency measured based on this display result and the frequency setting value for calibration (for example, the above-described 800 MHz). (Step S5).

  As shown in the frequency display section 236 in FIG. 1, for example, when the measurement result is 800.000003 MHz (800000003 Hz), the output frequency of the frequency synthesizer 1 exceeds the maintenance frequency by 3 Hz. It is determined that the value is not zero, for example, zero (step S6; N). The operator selects the coarse / fine adjustment switch 233 and the frequency adjustment switch 234 so that the frequency difference approaches zero, and outputs information instructing adjustment according to the selection result to the frequency synthesizer 1 (step S7). ). In this example, for example, since it is desired to adjust the output frequency by 3 Hz, an instruction to select the “fine adjustment” of the coarse / fine adjustment switch 233 and “−2” of the frequency adjustment switch 234 to bring the frequency difference closer to zero I do.

  In the frequency synthesizer 1, the duty ratio information in the work memory 18 is increased / decreased based on an instruction from the external control device 2, the frequency synthesizer 1 is operated based on the duty ratio information thus adjusted, and the output frequency is changed. Let Then, the operations from step S4 to step S7 are repeated until the frequency difference becomes zero. When the frequency difference becomes zero (step S6; Y), the write switch 235 is pressed, and then the work memory 18 is stored. The duty ratio information after a certain calibration is rewritten to the duty ratio information in the nonvolatile memory 17 (step S8), and a series of calibration work is finished (end).

  The frequency synthesizer 1 in which the internal reference signal source 16 has been calibrated by the operations and operations described above is disconnected from the external control device 2 and the frequency measurement device 3 and operates independently during normal operation. That is, the frequency synthesizer 1 reads the calibrated duty ratio information (control voltage command value) from the non-volatile memory 17, operates the internal reference signal source 16 based on this information, generates a reference clock signal, and operates the frequency synthesizer. I will let you.

  The present embodiment has the following effects. Measure the output frequency of the frequency synthesizer 1, and adjust the duty ratio information, which is the command value of the control voltage of the internal reference signal source 16, so that the difference between the measurement result and the frequency setting value becomes zero based on the measurement result Therefore, calibration work can be performed without the need for an external reference signal. As a result, for example, the internal reference signal source 16 can be calibrated even under conditions where an external reference signal source cannot be prepared, and the flexibility of conditions under which calibration can be performed can be improved. it can. Further, since it is not necessary to use an expensive external reference signal source using, for example, rubidium or the like, the cost for calibration can be reduced.

  Further, since the internal reference signal source 16 is calibrated by using software from the external control device 2, it is not necessary to perform hardware adjustment using, for example, a trimmer potentiometer, which has been conventionally performed. As a result, large-scale preparations and laborious operations such as opening the housing of the frequency synthesizer 1 and inserting a screwdriver into a calibration hole provided in the housing for adjustment are simplified and simplified. Calibration can be done with simple operations.

  The method for calibrating the internal reference signal source 16 is as follows. The operator confirms the measurement result of the output frequency of the frequency synthesizer 1 with the external control device 2 as described with reference to FIGS. It is not limited to adjusting by operation. For example, the calibration operation may be automatically executed by the external control device 2. In this case, for example, the operations from step S5 to step S7 performed by the operator in FIG. The instructions of the program 22 may be assembled so as to be executed by the second CPU 21.

  Further, the frequency adjusting unit 15 (control voltage output unit) for adjusting the control voltage of the internal reference signal source 16 is not limited to the case of being configured by the PWM controller illustrated in FIG. A digital / analog converter that outputs a control voltage may be used.

  In addition, the frequency synthesizer to which the calibration method according to this embodiment can be applied is not limited to the frequency synthesizer 1 employing the novel PLL control described with reference to FIG. For example, a normal type frequency synthesizer, that is, a signal indicating the comparison result by comparing the phase of the frequency obtained by dividing the output of the VCO with the frequency obtained by dividing the output of the internal reference signal source (for example, another VCO). May be applied to a frequency synthesizer that is fed back to the output VCO through a loop filter. In this case, the internal reference signal source may be calibrated so as to adjust the oscillation frequency of the internal reference signal based on the measurement result of the oscillation frequency of the output VCO.

  In addition to these, in the above-described embodiment, the measured output frequency and the frequency setting for calibration are used as the optimum values of the command value (duty ratio information) for determining the duty ratio of the pulse train output from the PWM controller 151. The case where the values coincide with each other and these frequency differences are set to zero is exemplified, but the optimum command value is not limited to this. For example, when the required precision is low and the frequency setting value for calibration is adjusted in units of 5 Hz, for example, the frequency difference is not limited to zero, and the measured output frequency is 5 Hz centered on the set frequency. The duty ratio information corresponding to the output frequency may be set as the optimum command value when the error width is within the range.

  The frequency output device is not limited to the example of the frequency synthesizer described above, and any device that outputs a preset frequency may be used. For example, a reference frequency output device provided in a measuring instrument may be calibrated. The present invention is applicable.

It is a block diagram which shows the structure of the system which implements the method of calibrating the internal reference signal source of this invention. It is a block diagram which shows the basic composition of the frequency synthesizer provided with the said internal reference signal source. It is a block diagram which shows the basic composition of the frequency adjustment part which outputs the control voltage of the said internal reference signal source. 4 is a flowchart showing an operation and a work flow of frequency adjustment of an internal reference signal source using the system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frequency synthesizer 2 External control device 3 Frequency measuring device 4 Signal line 5 Data bus 11 Processor (CPU)
12 PLL control unit 13 VCO
14 Amplifier 15 Frequency adjuster 16 Internal reference signal source 17 Non-volatile memory 18 Work memory 19 Output terminal 20 Non-volatile memory 21 Central processing unit (CPU)
22 Program 23 Interface section 24 Adjustment information

Claims (5)

An internal reference signal source, and a control voltage output unit that outputs a control voltage for controlling the frequency of the reference clock signal output from the internal reference signal source, based on the reference clock signal and the frequency setting signal In the method of calibrating the internal reference signal source of the frequency output device that outputs the set frequency signal,
A frequency output device comprising: a nonvolatile memory for storing a command value of the control voltage of the internal reference signal source; and a processor for reading the command value from the nonvolatile memory and supplying the command value to the control voltage output unit Use
Operating the frequency output device based on a frequency setting signal to calibrate the internal reference signal source, and measuring the output frequency of the frequency output device with a frequency measuring device;
Based on the frequency difference between the output frequency measured in this step and the frequency setting value determined by the frequency setting signal, it is stored in the nonvolatile memory by an external control device connected to the frequency output device. A method of calibrating the internal reference signal source of the frequency output apparatus, comprising the step of increasing or decreasing the command value to obtain an optimum command value.   2. The method of calibrating an internal reference signal source of the frequency output device according to claim 1, wherein the frequency output device is a frequency synthesizer.   The frequency according to claim 1 or 2, wherein the step of setting the optimum command value is performed by an operator inputting an increase / decrease value of the command value via an external control device based on the frequency difference. A method for calibrating an internal reference signal source of an output device.   The method of calibrating the internal reference signal source of the frequency output apparatus according to claim 1, wherein the step of setting the optimum command value is automatically performed by an external control device by a program.   5. The method of calibrating the internal reference signal source of the frequency output device according to claim 1, wherein the control voltage output unit is a digital / analog converter or a PWM controller.

Images