CN114421977A - Quick calibration device and method for frequency of crystal oscillator for communication equipment - Google Patents

Quick calibration device and method for frequency of crystal oscillator for communication equipment Download PDF

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Publication number
CN114421977A
CN114421977A CN202111537966.5A CN202111537966A CN114421977A CN 114421977 A CN114421977 A CN 114421977A CN 202111537966 A CN202111537966 A CN 202111537966A CN 114421977 A CN114421977 A CN 114421977A
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frequency
signal
digital
crystal oscillator
voltage
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CN114421977B (en
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王君方
王博一
樊俊畅
唐宏震
张凡
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Shaanxi Fenghuo Communication Group Co Ltd
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Shaanxi Fenghuo Communication Group Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/20—Monitoring; Testing of receivers
    • H04B17/21—Monitoring; Testing of receivers for calibration; for correcting measurements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The invention relates to the field of communication equipment, and discloses a device and a method for quickly calibrating the frequency of a crystal oscillator for communication equipment. The device comprises a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source; the method comprises the following steps: 1) constructing a hardware architecture; 2) mixing the high-precision radio frequency signal with a local oscillation frequency signal to obtain an intermediate frequency signal; 3) and the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal to acquire actual frequency and frequency offset, so as to realize frequency calibration of the voltage-controlled crystal oscillator to be calibrated. The invention can realize the frequency calibration function of the crystal oscillator only by externally connecting a high-precision radio frequency source and a necessary hardware circuit in the ultrashort wave communication equipment without additional instruments and special hardware circuits, and has short calibration time.

Description

Quick calibration device and method for frequency of crystal oscillator for communication equipment
Technical Field
The invention relates to the field of communication equipment, in particular to a device and a method for quickly calibrating the frequency of a crystal oscillator for communication equipment.
Background
Aging drift of the crystal oscillator is one of the important reasons for influencing the frequency stability and accuracy of the crystal oscillator. With the development of wireless communication technology, the requirement of the ultra-short wave communication field on frequency accuracy is higher and higher. In some occasions with high requirements on the accuracy of the working frequency, the working frequency of the equipment needs to be calibrated frequently, and the calibration of the working frequency of the equipment is finally realized by adjusting the frequency of a crystal oscillator inside the equipment.
At present, the common calibration method is to adjust the frequency by controlling the analog voltage at the voltage control end of the crystal oscillator through a mechanical potentiometer. When the device needs frequency calibration, the device must be opened, and the resistance value of the potentiometer is manually adjusted to complete the calibration, and the potentiometer is coated and fixed after the adjustment.
The equipment calibrated by the common calibration method has poor anti-seismic performance and poor precision, and high-precision frequency adjustment is difficult to realize; particularly under the severe conditions of high humidity, heat, vibration and the like of airplanes, ships and the like, the resistance value is greatly changed, and the adaptability is poor; after multiple times of adjustment, the mechanical terminal is easy to wear and even damage, and the reliability of the equipment is affected.
The other pulse per second calibration method is to calibrate a crystal oscillator through a pulse per second 1PPS signal (1pulsePerSecond signal) of a global positioning system, namely to obtain a pulse per second 1PPS signal with higher precision (precision < 50ns) through time service of the global positioning system. Counting the number of the oscillation times of the local crystal oscillator in the period of the pulse per second 1PPS signal when the local crystal oscillator starts to count the edge (rising edge or falling edge) of the pulse per second 1PPS signal, and calibrating after acquiring the frequency offset. The pulse per second calibration method is complex in operation process, needs a professional instrument and a special calibration circuit, and has the defects of long calibration time, high cost, dependence on a Pulse Per Second (PPS) signal of a global positioning system and the like.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a method for quickly calibrating the frequency of a crystal oscillator for communication equipment, which can realize the frequency automatic calibration function of a crystal oscillator source only by externally connecting a high-precision radio frequency source and a hardware circuit required in ultrashort wave communication equipment without additional instruments and special hardware circuits, has short calibration time and can overcome the defects of the existing frequency calibration method.
In order to achieve the above purpose, the present invention is realized by the following technical scheme.
The first technical scheme is as follows: a quick calibration device of crystal oscillator frequency for communication equipment is characterized by comprising a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source, wherein a high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency correction signal;
the digital signal processing unit in the communication equipment is provided with an analog-to-digital converter, a digital signal processor, a digital potentiometer and a voltage-controlled crystal oscillator to be calibrated; a channel receiver unit in a communication device has a frequency synthesizer and a mixer;
specifically, the signal output end of the frequency mixer is sequentially connected with an analog-to-digital converter, a digital signal processor, a digital potentiometer, a voltage-controlled crystal oscillator to be calibrated and a frequency synthesizer, the signal output end of the frequency synthesizer is connected with one signal input end of the frequency mixer, and the other signal input end of the frequency mixer is connected with the signal output end of a high-precision radio frequency signal source;
performing down-conversion frequency mixing processing on a high-precision radio-frequency signal provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion;
the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains an actual frequency through the FFT; and calculating frequency deviation according to the frequency values of the actual frequency and the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated so as to realize the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
The second technical scheme is as follows: a method for rapidly calibrating the frequency of a crystal oscillator for a communication device, comprising the steps of:
step one, constructing a hardware architecture; the hardware architecture comprises a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source, wherein a high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency correction signal;
the digital signal processing unit in the communication equipment is provided with an analog-to-digital converter, a digital signal processor, a digital potentiometer and a voltage-controlled crystal oscillator to be calibrated; a channel receiver unit in a communication device has a frequency synthesizer and a mixer;
specifically, the signal output end of the frequency mixer is sequentially connected with an analog-to-digital converter, a digital signal processor, a digital potentiometer, a voltage-controlled crystal oscillator to be calibrated and a frequency synthesizer, the signal output end of the frequency synthesizer is connected with one signal input end of the frequency mixer, and the other signal input end of the frequency mixer is connected with the signal output end of a high-precision radio frequency signal source;
step two, performing down-conversion mixing processing on a high-precision radio-frequency signal provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion;
thirdly, the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and actual frequency is obtained through the FFT; and calculating frequency deviation according to the actual frequency and the frequency value of the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled oscillator to be calibrated so as to realize the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
Compared with the prior art, the invention has the beneficial effects that:
(1) most of the time, the frequency deviation can not be calibrated to a desired value through one time, the iterative calibration method can enable the frequency calibration precision to quickly approach the desired value, and the frequency deviation can be corrected when the iteration frequency of the method generally does not exceed 2 times;
(2) the frequency deviation estimation method based on the fast Fourier transform FFT is used for rapidly identifying the accurate frequency of a signal, the frequency resolution of the scheme is 8000/2048-3.90625 Hz, the frequency resolution is calculated back to a crystal oscillator, the resolution can reach 3.90625/10-0.390625 Hz, namely the final calibration result precision is 0.390625Hz, and the use requirement of ultra-short wave communication equipment is met;
(3) the crystal oscillator frequency back-pushing algorithm calculates the specific frequency offset range and direction of the crystal oscillator according to the back-pushing of a Fast Fourier Transform (FFT) result, directly calculates the tuning voltage control value of the digital potentiometer and writes the tuning voltage control value into EEMEM of the digital potentiometer, and the digital potentiometer is initialized by directly reading the EEMEM value when the crystal oscillator is started next time so as to obtain the high-precision local crystal oscillator frequency;
(4) the invention can directly carry out frequency calibration without disassembling ultrashort wave equipment, and can finish calibration by inputting standard radio frequency from the radio frequency interface of the equipment.
Drawings
The invention is described in further detail below with reference to the figures and specific embodiments.
FIG. 1 is a diagram of the hardware architecture for calibration of the present invention;
fig. 2 is a block diagram of the frequency synthesizer of the present invention;
FIG. 3 is a schematic diagram of the connection between a digital potentiometer and a VCO in accordance with the present invention;
fig. 4 is a flow chart of the fast calibration of the frequency of the voltage controlled crystal oscillator for the communication device of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, a hardware architecture building diagram for calibration of the present invention includes a digital signal processing unit in a communication device, a channel receiver unit in the communication device, and a high-precision radio frequency signal source, where the high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency calibration signal.
The digital signal processing unit in the communication equipment is provided with an analog-to-digital converter, a digital signal processor, a digital potentiometer and a voltage-controlled crystal oscillator to be calibrated; a channel receiver unit in a communication device has a frequency synthesizer and a mixer.
Specifically, the signal output end of the frequency mixer is sequentially connected with an analog-to-digital converter, a digital signal processor, a digital potentiometer, a voltage-controlled crystal oscillator to be calibrated and a frequency synthesizer, the signal output end of the frequency synthesizer is connected with one signal input end of the frequency mixer, and the other signal input end of the frequency mixer is connected with the signal output end of a high-precision radio frequency signal source.
Performing down-conversion mixing processing on a high-precision radio-frequency signal (a standard radio-frequency correction signal) provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion.
The channel receiver unit of this embodiment utilizes a channel receiver unit in a communication device, where the channel receiver unit in the communication device has a frequency synthesizer and a mixer, and functions to down-convert and mix a received standard radio frequency correction signal with a frequency of 260.002MHz from a high-precision radio frequency signal source in the mixer with a local oscillation frequency signal with a frequency of 260MHz generated by the frequency synthesizer to a 2KHz intermediate frequency signal, and then send the 2KHz intermediate frequency signal to a digital signal processing unit.
As shown in fig. 2, a configuration diagram of the frequency synthesizer of the present invention is shown. The frequency synthesizer of the embodiment adopts a phase-locked loop type, and is composed of a phase discriminator, a charge pump, a loop filter, a voltage-controlled oscillator and a frequency divider, and all parts of the frequency synthesizer are mutually connected to form a negative feedback closed-loop system.
At the left end of the loopInput reference signal Fref(i.e., the frequency output signal of the VCO to be calibrated) and the feedback signal F divided by the frequency dividerdivMeanwhile, the voltage is input into a phase discriminator to carry out phase comparison, and after a phase difference value is compared, the voltage is output in a voltage form, and the output voltage is a digital signal. The phase difference is in direct proportion to the output voltage (digital voltage), the charge pump converts the digital voltage output by the phase discriminator into the charge-discharge current of the post-stage loop filter, and the magnitude of the charge-discharge current is in direct proportion to the digital voltage output by the phase discriminator.
The charge pump charges and discharges a capacitor in the loop filter to enable the loop filter to output a voltage VctrThe size of the filter changes, the bandwidth of the loop filter restrains the high-frequency part of the voltage output by the charge pump, and the voltage ripple is filtered out, so that the loop filter outputs the voltage VctrMaintaining good DC characteristic, and finally sending the signal to a voltage-controlled oscillator of a frequency synthesizer.
Output frequency F of frequency synthesizeroutAnd loop filter output voltage VctrThe sizes are proportional and the relationship is determined by equation 1.
Fout＝F0+KVC0×Vctr(formula 1)
F0Being free-running frequency of voltage-controlled oscillator in frequency synthesizer, i.e. loop filter output voltage VctrOutput frequency when equal to 0, KVC0Is the gain coefficient of the voltage-controlled oscillator frequency and the loop filter output voltage in the frequency synthesizer.
The frequency divider divides the output frequency of the voltage controlled oscillator in the frequency synthesizer by M to obtain a feedback signal FdivIs then compared with the input reference signal FrefMaking a comparison, equivalent to inputting a reference signal FrefAfter M frequency multiplication, the frequency is compared with the output frequency F of the frequency synthesizeroutAre compared, thus realizing the comparison of the input reference signal FrefFrequency doubling.
The output frequency F of the frequency synthesizer being locked in the loop filteroutAnd the frequency F of the input reference signalrefHaving the relationship of equation 2.
Fout＝M×Fref(formula 2)
In this embodiment, the output frequency F of the frequency synthesizeroutI.e. the local oscillator signal of the mixer, with a frequency value Fout260 MHz; input reference signal F of frequency synthesizerrefI.e. the frequency output signal of the voltage controlled crystal oscillator to be calibrated, which is the digital signal processing unit, the frequency value Fref26MHz, the frequency multiplier M is 10 from equation 2.
The digital signal processor has two functions, one is responsible for the control part of the physical layer protocol stack, mainly carry on the control of the channel machine receiving and transmitting channel function, including working frequency switch, receiving channel automatic gain control, dormancy awaken control, power amplifier power control, etc., mainly play the control to the tuning voltage of the digital potentiometer in the invention; secondly, a wireless communication baseband algorithm is realized, and in the invention, the frequency offset is mainly calculated by a fast Fourier transform algorithm.
The digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains an actual frequency through the FFT; and calculating frequency deviation according to the frequency values of the actual frequency and the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated so as to realize the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
Specifically, the digital signal processing unit converts the received 2KHz intermediate frequency signal into a digital signal with a sampling rate of 1MSPS through the analog-to-digital converter. The analog-to-digital converter adopts 12 bits, has a spurious-free dynamic range of about 72dB, and meets the requirements of wireless communication equipment.
And then sending the digital signal with the sampling rate of 1MSPS into a digital signal processor, setting the extraction multiple to be 125 times, extracting the 125 times, reducing the sampling rate to 8KSPS, and then performing 2048-point Fast Fourier Transform (FFT) on the extracted 8KSPS digital signal to obtain the actual frequency.
Specifically, the actual frequency is acquired by fast fourier transform FFT, and the actual frequency is acquired as follows.
And performing Fast Fourier Transform (FFT) on the extracted digital signals to obtain N complex numbers. The result of the fast fourier transform FFT is a complex number comprising N points. Each point corresponds to a frequency point, and each complex value contains information of a specific frequency. From these N complex numbers, the respective frequencies and corresponding amplitudes obtained by splitting the original signal can be known. The modulus of this point is the amplitude characteristic at that frequency value. The larger the modulus value is, the larger the signal amplitude at the frequency point is, and the frequency value corresponding to the point with the largest modulus value is the fundamental frequency (i.e., the actual frequency).
Knowing the sampling frequency Fs, the x-th (x starting from 0) complex value after FFT corresponds to the actual frequency of
f(x)＝x*(Fs/N)
In this embodiment, an analog signal with a frequency f of 2KHz and a sampling rate of 1MHz are extracted by 125 times, and then the sampling frequency Fs of 8KHz is obtained, and a corresponding digital signal is obtained, and a FFT analysis with N2048 points is performed on the digital signal, where the range of the sampling point index N is 0, 1, 2, 3, …, and 2047. The frequency of the analog signal with the frequency F2 KHz is divided into 2048 parts, and the frequency resolution F0 Fs/N8000/2048 Hz 3.90625 Hz.
Thus, in the abscissa of the frequency diagram:
the frequency f corresponding to 1-n is 1-x (8000/2048) -3.90625 Hz
The frequency f corresponding to n-2 is 2 × 7.8125Hz (8000/2048) — 7.8125Hz
…
The frequency f corresponding to 2047 is 2047 × 7996.09375Hz (8000/2048) ═ 2047
The spectrum is symmetric about n 1024, so only the spectrum of n 0-1023 needs to be calculated. Because, the highest frequency of the original signal is 2KHz + -delta. After the frequency corresponding to each point is determined, the fundamental frequency (actual frequency) is obtained only by traversing the modulus values of the 0 th to 1023 th points of the Fast Fourier Transform (FFT) result and searching the point corresponding to the maximum modulus value.
And calculating the frequency deviation +/-delta according to the frequency values of the actual frequency and the intermediate frequency signal, judging the frequency deviation direction, controlling the digital potentiometer through a synchronous serial bus, and outputting an analog tuning voltage to control the 26MHz frequency precision output by the voltage-controlled crystal oscillator to be corrected.
Specifically, as shown in fig. 3, it is a schematic diagram of the connection between the digital potentiometer and the voltage controlled crystal oscillator according to the present invention; the reference voltage end of the voltage-controlled crystal oscillator is electrically connected with the positive electrode of the voltage input end of the digital potentiometer, the negative electrode of the voltage input end of the digital potentiometer is grounded, and the voltage output end of the digital potentiometer is connected with the tuning voltage input end of the voltage-controlled crystal oscillator.
The preferred digital potentiometer of the invention adopts a digital control circuit based on a nonvolatile memory, can provide 1024-order resolution, can realize the same electronic adjustment function as a mechanical potentiometer, and has enhanced resolution, solid-state reliability and remote control capability. The non-volatile memory based digital control circuit can be programmed through a standard three-wire serial interface, has multiple operating and adjustment modes including scratch pad programming and memory storage and recovery, and additionally provides EEMEM for storing user-defined information such as memory data, look-up tables or system identification information of other devices. In the scratch pad programming mode, a particular setting may be written directly into the RDAC register to set the resistance between terminals W-A and W-B. This setting may be stored in EEMEM and automatically transferred to the RDAC register when the system is powered up. The EEMEM content may be restored dynamically or by external pin strobing; the write function may then protect the EEMEM contents.
The core specifications of the preferred voltage controlled crystal oscillator of the present invention are shown in table 1.
Core index of 126 MHz voltage-controlled crystal oscillator
Index (I) Minimum value Typical value Maximum value Unit of
Frequency of operation 26 MHz
1 annual aging rate ±1 ppm
10-year aging rate ±3 ppm
Voltage control range 0 2.7 V
Frequency tuning range ±5 ±10 ppm
Tuning frequency and voltage slope 5 ppm/V
It can be seen from table 1 that the minimum value of the tuning range of the crystal oscillator frequency of the voltage controlled crystal oscillator is 5ppm, i.e., +/-130 Hz, and according to the frequency multiplication relationship, the maximum frequency offset of 260MHz can be calibrated when the maximum frequency offset is + -1300 Hz.
Finally, 2048-point fast fourier transform FFT (fast fourier transform) is adopted, the sampling rate is 8KSPS, the calculated frequency resolution is 8000/2048-3.90625 Hz, and the frequency offset of the 26MHz digital signal provided by the voltage-controlled crystal oscillator to be calibrated can be calculated back by the frequency resolution and the frequency multiplication (in this embodiment, the frequency multiplication is 10), which can be accurate to 3.90625/10-0.390625 Hz.
Referring to fig. 4, it is a flow chart of fast calibration of the frequency of the voltage controlled crystal oscillator for communication equipment according to the present invention, based on the hardware architecture.
The invention relates to a method for quickly calibrating the frequency of a crystal oscillator for communication equipment, which comprises the following steps:
firstly, constructing a hardware architecture; the hardware architecture comprises a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source, wherein a high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency correction signal.
Secondly, performing down-conversion mixing processing by using a high-precision radio-frequency signal provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion.
Finally, the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains the actual frequency through the FFT; and calculating frequency deviation according to the actual frequency and the frequency value of the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled oscillator to be corrected so as to realize the frequency correction of the voltage-controlled crystal oscillator to be corrected.
Specifically, the fast calibration process of the crystal oscillator frequency for the communication device comprises the following steps:
(1) the standard radio frequency correction signal (260.002MHz) and the local oscillation frequency (frequency deviation may exist) of the locally generated 260MHz are subjected to down-conversion mixing to generate an intermediate frequency single tone signal F of 2KHz +/-delta1Wherein, delta is more than or equal to 0 and less than or equal to 1300, if delta is more than 1300, the frequency deviation is too large and the calibration cannot be carried out, and the calibration is quit;
(2) to the intermediate frequency single tone signal F obtained after mixing1Performing 125 times of extraction, and reducing the sampling rate to 8 KHz;
(3) for intermediate frequency single tone signal F reduced to 8KSPS sampling rate1Performing 2048-point Fast Fourier Transform (FFT) and back-calculating the current frequency F2；
(4) If | F2-F1If the | is less than or equal to 4Hz, the frequency deviation of the crystal oscillator for controlling the frequency of the crystal oscillator meets the use requirement, the calibration is finished, and the calibration process is exited; otherwise, entering the step (5);
(5) if F2＞F1If the actual frequency of the crystal oscillator is smaller, the adjusting direction D is 1, and the frequency of the crystal oscillator is adjusted to be larger; otherwise, adjusting the direction D to-1, and adjusting the frequency of the crystal oscillator to be small;
(6) and (3) a push-back process: the RDAC register value R of the current digital potentiometer AD5231 is read and recorded, and the adjustment quantity A ═ F is calculated2-F1D/10 (2.7/1024) 5 26/1000 (multiplication in the calculation formula), rewriting the RDAC register value of AD5231 to R + a, and proceeding to step (1) and thenAnd continuing to circulate until the frequency calibration meets the requirement.
In this embodiment, the digital signal processor obtains the frequency offset of the 2KHz intermediate frequency single tone signal through fast fourier transform FFT, calculates the frequency offset of the voltage-controlled crystal oscillator to be calibrated with a frequency of 26MHz by back-and-forth extrapolation of the frequency offset of the intermediate frequency single tone signal, and adjusts the frequency of the crystal oscillator to be calibrated with a frequency of 26MHz, so that the accuracy of the frequency of the local oscillation signal with a frequency of 260MHz, which is mixed with the standard radio frequency correction signal with a frequency of 260.002MHz, is improved, and the frequency accuracy of the voltage-controlled crystal oscillator to be calibrated with a frequency of 26MHz meets the requirement. The parameters for controlling the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated are stored in an on-chip storage unit of the digital potentiometer, and when the equipment is powered on next time, the parameters of the tuning voltage calibrated last time can be automatically read, so that the precision of the voltage-controlled crystal oscillator to be calibrated with the frequency of 26MHz is ensured. The frequency calibration process is an iterative process.
Although the present invention has been described in detail in this specification with reference to specific embodiments and illustrative embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made thereto based on the present invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (3)

1. A quick calibration device of crystal oscillator frequency for communication equipment is characterized by comprising a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source, wherein a high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency correction signal;
the digital signal processing unit in the communication equipment is provided with an analog-to-digital converter, a digital signal processor, a digital potentiometer and a voltage-controlled crystal oscillator to be calibrated; a channel receiver unit in a communication device has a frequency synthesizer and a mixer;
specifically, the signal output end of the frequency mixer is sequentially connected with an analog-to-digital converter, a digital signal processor, a digital potentiometer, a voltage-controlled crystal oscillator to be calibrated and a frequency synthesizer, the signal output end of the frequency synthesizer is connected with one signal input end of the frequency mixer, and the other signal input end of the frequency mixer is connected with the signal output end of a high-precision radio frequency signal source;
performing down-conversion frequency mixing processing on a high-precision radio-frequency signal provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion;
the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains an actual frequency through the FFT; and calculating frequency deviation according to the frequency values of the actual frequency and the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated so as to realize the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
2. A method for rapidly calibrating the frequency of a crystal oscillator for a communication device, comprising the steps of:
step one, constructing a hardware architecture; the hardware architecture comprises a digital signal processing unit in the communication equipment, a channel receiver unit in the communication equipment and a high-precision radio frequency signal source, wherein a high-precision radio frequency signal of the high-precision radio frequency signal source is used as a standard radio frequency correction signal;
the digital signal processing unit in the communication equipment is provided with an analog-to-digital converter, a digital signal processor, a digital potentiometer and a voltage-controlled crystal oscillator to be calibrated; a channel receiver unit in a communication device has a frequency synthesizer and a mixer;
specifically, the signal output end of the frequency mixer is sequentially connected with an analog-to-digital converter, a digital signal processor, a digital potentiometer, a voltage-controlled crystal oscillator to be calibrated and a frequency synthesizer, the signal output end of the frequency synthesizer is connected with one signal input end of the frequency mixer, and the other signal input end of the frequency mixer is connected with the signal output end of a high-precision radio frequency signal source;
step two, performing down-conversion mixing processing on a high-precision radio-frequency signal provided by a high-precision radio-frequency signal source and a local oscillation frequency signal provided by a frequency synthesizer to obtain an intermediate-frequency signal; the intermediate frequency signal is input into a digital signal processor after being subjected to analog-to-digital conversion;
thirdly, the digital signal processor sequentially performs analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and actual frequency is obtained through the FFT; and calculating frequency deviation according to the frequency values of the actual frequency and the intermediate frequency signal, and controlling the digital potentiometer according to the frequency deviation direction to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated so as to realize the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
3. The method according to claim 2, wherein the actual frequency is obtained by fast fourier transform FFT, and the actual frequency is obtained by:
and performing Fast Fourier Transform (FFT) on the extracted digital signal to obtain N complex numbers, wherein N is a natural number, and the frequency value corresponding to the complex number with the maximum modulus value in the N complex numbers is the fundamental frequency, namely the actual frequency.
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