CN114421977B - Device and method for quickly calibrating frequency of crystal oscillator for communication equipment - Google Patents
Device and method for quickly calibrating frequency of crystal oscillator for communication equipment Download PDFInfo
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- CN114421977B CN114421977B CN202111537966.5A CN202111537966A CN114421977B CN 114421977 B CN114421977 B CN 114421977B CN 202111537966 A CN202111537966 A CN 202111537966A CN 114421977 B CN114421977 B CN 114421977B
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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
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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
- H04B1/06—Receivers
- H04B1/16—Circuits
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- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- 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
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- 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
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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 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 the self-oscillating frequency signal to obtain an intermediate frequency signal; 3) The digital signal processor sequentially carries out analog-to-digital conversion, extraction and fast Fourier transform FFT on the intermediate frequency signal to obtain the actual frequency and the frequency offset, and realizes the 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 hardware circuit necessary in ultrashort wave communication equipment without additional instruments and special hardware circuits, and has short calibration time.
Description
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 a crystal oscillator is one of the important reasons that affects the frequency stability and accuracy of the crystal oscillator. With the development of wireless communication technology, the frequency accuracy requirements in the field of ultrashort wave communication are higher and higher. In some occasions with high requirements on the accuracy of the working frequency, the working frequency of the device needs to be calibrated frequently, and the calibration of the working frequency of the device is finally realized by adjusting the frequency of a crystal oscillator inside the device.
Currently, a common calibration method is to control the analog voltage of the voltage-controlled end of the crystal oscillator by a mechanical potentiometer to perform frequency adjustment. When the equipment needs frequency calibration, the equipment must be opened, the adjustment is completed by manually adjusting the resistance value of the potentiometer, and the potentiometer is also required to be coated and fixed after the adjustment.
The equipment calibrated by the common calibration method has poor anti-seismic performance and poor precision, and is difficult to realize high-precision frequency adjustment; particularly, under severe conditions such as high humidity, heat, vibration and the like of an airplane, a ship and the like, the resistance value is greatly changed, and the adaptability is poor; after multiple adjustments, the mechanical terminals are easy to wear and even damage, and the reliability of the equipment is affected.
Another method for calibrating the second pulse is to calibrate the crystal oscillator by using the second pulse 1PPS signal (1 PulsePerSecond signal) of the global positioning system, that is, acquire the second pulse 1PPS signal with higher precision (precision < 50 ns) by using the global positioning system time service. The local crystal oscillator is counted at the edge (rising edge or falling edge) of the pulse per second 1PPS signal, the oscillation frequency of the local crystal oscillator in the period of the pulse per second 1PPS signal is recorded, and after the frequency offset is acquired, calibration is carried out. The pulse per second calibration method has the defects of complex operation process, need of professional instruments and special calibration circuits, long calibration time, high cost, dependence on a global positioning system pulse per second 1PPS signal and the like.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention aims to provide a rapid calibration method of the frequency of a crystal oscillator for communication equipment, which only needs to be externally connected with a high-precision radio frequency source and a hardware circuit necessary in ultrashort wave communication equipment, can realize the frequency automatic calibration function of the crystal oscillator source without additional instruments and special hardware circuits, has short calibration time, and can overcome the defects of the prior frequency calibration method.
In order to achieve the aim of the invention, the invention is realized by adopting the following technical scheme.
The technical scheme is as follows: the device 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, a signal output end of the 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, a signal output end of the frequency synthesizer is connected with one signal input end of the mixer, and the other signal input end of the mixer is connected with a signal output end of a high-precision radio frequency signal source;
performing down-conversion mixing processing on the high-precision radio frequency signal provided by the high-precision radio frequency signal source and the self-oscillation frequency signal provided by the frequency synthesizer to obtain an intermediate frequency signal; the intermediate frequency signal is input into a digital signal processor after analog-to-digital conversion;
the digital signal processor sequentially carries out analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains the actual frequency through the FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated, thereby realizing the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
The second technical scheme is as follows: a method for rapid calibration of a crystal oscillator frequency 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, a signal output end of the 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, a signal output end of the frequency synthesizer is connected with one signal input end of the mixer, and the other signal input end of the mixer is connected with a signal output end of a high-precision radio frequency signal source;
step two, performing down-conversion mixing processing on the high-precision radio frequency signal provided by the high-precision radio frequency signal source and the self-oscillation frequency signal provided by the frequency synthesizer to obtain an intermediate frequency signal; the intermediate frequency signal is input into a digital signal processor after analog-to-digital conversion;
step three, the digital signal processor sequentially carries out analog-to-digital conversion, extraction and fast Fourier transform FFT on the intermediate frequency signal, and obtains the actual frequency through the fast Fourier transform FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled oscillator to be calibrated, thereby realizing 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) The frequency offset is difficult to calibrate to the expected value by one time most of the time, the frequency calibration accuracy can be enabled to be close to the expected value rapidly by the iteration calibration method, and the frequency offset can be corrected by the iteration frequency of the method generally not exceeding 2 times;
(2) The frequency offset estimation method based on the fast Fourier transform FFT rapidly identifies the accurate frequency of the signal, the frequency resolution of the scheme is 8000/2048= 3.90625Hz, the frequency resolution can reach 3.90625/10= 0.390625Hz after being calculated back to the crystal oscillator, namely the final calibration result precision is 0.390625Hz, and the use requirement of ultrashort wave communication equipment is met;
(3) The crystal oscillator frequency push-back algorithm is used for pushing back a specific frequency offset range and direction of the crystal oscillator according to a Fast Fourier Transform (FFT) result, directly calculating a tuning voltage control value of the digital potentiometer, writing the tuning voltage control value into EEMEM of the digital potentiometer, directly reading the EEMEM value for the next startup, and initializing the digital potentiometer to obtain the high-precision local crystal oscillator frequency;
(4) The invention can directly calibrate the frequency without disassembling the ultrashort wave equipment, and can complete the calibration by inputting the standard radio frequency from the radio frequency interface of the equipment.
Drawings
The invention will now be described in further detail with reference to the drawings and to specific examples.
FIG. 1 is a hardware architecture building diagram for calibration of the present invention;
fig. 2 is a block diagram of a frequency synthesizer of the present invention;
FIG. 3 is a schematic diagram of the connection of a digital potentiometer to a voltage controlled crystal oscillator in the present invention;
fig. 4 is a flow chart of a fast calibration of the frequency of a voltage controlled crystal oscillator for a 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 for illustrating the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, a hardware architecture for calibration of the present invention is constructed, and the hardware architecture 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 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 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 mixer, and the other signal input end of the 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 self-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 analog-to-digital conversion.
The channel receiver unit of the present embodiment uses a channel receiver unit in a communication device, which has a frequency synthesizer and a mixer, and functions to perform down-conversion mixing processing on a standard radio frequency correction signal with a frequency of 260.002MHz of a received high-precision radio frequency signal source and a local oscillation frequency signal with a frequency of 260MHz generated by the frequency synthesizer in the mixer, down-convert the frequency into an intermediate frequency signal with a frequency of 2KHz, and then send the intermediate frequency signal with the frequency of 2KHz to a digital signal processing unit.
As shown in fig. 2, a frequency synthesizer according to the present invention is constructed. 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 the parts are mutually connected to form a negative feedback closed loop system.
Input reference signal F at the left end of the loop ref (i.e. the frequency output signal of the voltage-controlled crystal oscillator to be calibrated), and the feedback signal F after being divided by the frequency divider div And meanwhile, the output voltage is input into a phase discriminator to carry out phase comparison, and the output voltage is output in the form of voltage after the phase difference value is compared. The phase difference is in direct proportion to the output voltage (digital voltage), the charge pump converts the digital voltage output by the phase detector into charge-discharge current of the post loop filter, and the charge-discharge current is in direct proportion to the digital voltage output by the phase detector.
The charge pump charges and discharges the capacitor in the loop filter to make the loop filter output voltage V ctr The bandwidth of the loop filter performs high-frequency part inhibition on the voltage output by the charge pump, and filters out voltage ripples to enable the loop filter to output voltage V ctr Keep better DC characteristic, and finally send into the voltage-controlled oscillator of the frequency synthesizer.
Output frequency F of frequency synthesizer out And loop filter output voltage V ctr The magnitude is proportional and the relationship is determined by formula 1.
F out ＝F 0 +K VC0 ×V ctr (equation 1)
F 0 For free-running frequency of voltage-controlled oscillator in frequency synthesizer, i.e. loop filter output voltage V ctr Output frequency at=0, K VC0 Is the gain factor 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 F div Then with the input reference signal F ref Comparing corresponding to the input reference signal F ref After M frequency multiplication, the frequency is multiplied by the output frequency F of the frequency synthesizer out Comparing, thus realizing the input reference signal F ref Is a frequency multiplication of (a) to (b).
Output frequency F of the frequency synthesizer when the loop filter is locked out With the input reference signal frequency F ref Has the relationship of equation 2.
F out ＝M×F ref (equation 2)
In the present embodiment, the output frequency F of the frequency synthesizer out I.e. the local oscillation signal of the mixer, the frequency value F thereof out =260 MHz; input reference signal F of frequency synthesizer ref Namely the frequency output signal of the voltage-controlled crystal oscillator to be calibrated of the digital signal processing unit, the frequency value F thereof ref =26 MHz, and therefore the frequency multiplication value m=10 is obtained from equation 2.
The digital signal processor has two parts of functions, namely a control part which is responsible for a physical layer protocol stack and mainly controls the functions of a channel machine receiving and transmitting channels, including working frequency switching, automatic gain control of a receiving channel, dormancy wakeup control, power amplifier power control and the like; secondly, a wireless communication baseband algorithm is realized, and the frequency offset is calculated mainly through a fast Fourier transform algorithm in the invention.
The digital signal processor sequentially carries out analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains the actual frequency through the FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated, thereby realizing 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 an 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 sending the digital signal with the 1MSPS sampling rate into a digital signal processor, setting the extraction multiple to 125 times, extracting 125 times, reducing the sampling rate to 8KSPS, and performing 2048-point fast Fourier transform FFT on the extracted 8KSPS digital signal to obtain the actual frequency.
Specifically, the actual frequency is obtained by the fast fourier transform FFT, and the actual frequency is obtained 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 containing N points. Each point corresponds to a frequency point and each complex value contains information about 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 value at this point is the amplitude characteristic at this frequency value. The larger the modulus, the larger the signal amplitude at that frequency point, and the frequency value corresponding to the point at which the modulus is largest is the fundamental frequency (i.e., the actual frequency).
After knowing the sampling frequency Fs, the actual frequency corresponding to the xth complex value (x starts from 0) after the FFT is
f(x)＝x*(Fs/N)
In this embodiment, the analog signal with the frequency f=2khz is sampled at the sampling rate of 1MHz and extracted at the sampling frequency of fs=8khz to obtain a corresponding digital signal, and the digital signal is subjected to a fast fourier transform FFT analysis with the frequency n=2048 points, where the range of the subscript N of the sampling point is 0,1,2,3, …,2047. Then the analog signal frequency at frequency f=2 KHz is divided into 2048 parts and the frequency resolution f0=fs/n=8000/2048= 3.90625Hz.
Thus, in the abscissa of the frequency chart:
the frequency f corresponding to n=1 is 1 (8000/2048) = 3.90625Hz
The frequency f corresponding to n=2 is 2×8000/2048= 7.8125Hz
…
The frequency f corresponding to n=2047 is 2047 (8000/2048) = 7996.09375Hz
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 ± Δ. After the frequencies corresponding to the points are determined, the fundamental wave frequency (actual frequency) is obtained by only traversing the modulus values of the 0 th to 1023 rd points of the FFT result and searching the point corresponding to the maximum modulus value.
According to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency deviation +/-delta, judging the frequency deviation direction, controlling the digital potentiometer through the synchronous serial bus, and outputting the 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, a schematic diagram of connection between a digital potentiometer and a voltage controlled crystal oscillator in the present invention is shown; 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 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 digital control circuit based on the nonvolatile memory can be programmed through a standard three-wire serial interface, has various working and adjusting modes, comprises scratch pad programming and memory storage and recovery, and additionally provides EEMEM for storing user-defined information, such as memory data of other devices, a lookup table or system identification information and the like. In the scratch-pad programming mode, certain settings may be written directly to 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 upon system power up. EEMEM content may be restored dynamically or by an external pin strobe; the write function may then protect the EEMEM content.
The core index of the preferred voltage controlled crystal oscillator of the present invention is shown in table 1.
Table 1 core index for 26mhz voltage controlled crystal oscillator
| Index (I) | Minimum value | Typical value | Maximum value | Unit (B) |
| Operating frequency | 26 | MHz | ||
| Aging rate of 1 year | ±1 | ppm | ||
| Aging rate of 10 years | ±3 | ppm | ||
| |
0 | 2.7 | V | |
| Frequency tuning range | ±5 | ±10 | ppm | |
| Tuning frequency and voltage slope | 5 | ppm/V |
As can be seen from Table 1, the tuning range of the crystal oscillator frequency of the voltage controlled crystal oscillator has a minimum value of 5ppm, namely + -130 Hz, and the maximum frequency deviation of 260MHz can be calibrated at + -1300 Hz according to the frequency multiplication relation.
Finally, through 2048-point fast fourier transform FFT, the sampling rate is 8KSPS, the calculated frequency resolution is 8000/2048= 3.90625Hz, the frequency offset of the 26MHz digital signal provided by the voltage controlled crystal oscillator to be calibrated can be back calculated through the frequency resolution and frequency multiplication (the frequency multiplication of the embodiment is 10), and the frequency offset can be accurate to 3.90625/10= 0.390625Hz.
Referring to fig. 4, a flow chart of the fast calibration of the frequency of the voltage controlled crystal oscillator for the communication device according to the present invention is based on the construction of a hardware architecture.
The invention relates to a rapid calibration method of crystal oscillator frequency 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 device, a channel receiver unit in the communication device 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 utilizing a high-precision radio frequency signal provided by a high-precision radio frequency signal source and a self-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 analog-to-digital conversion.
Finally, the digital signal processor sequentially carries out analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains the actual frequency through the FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled oscillator to be corrected, thereby realizing the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
Specifically, the rapid calibration procedure of the crystal oscillator frequency for the communication device includes the following steps:
(1) The standard radio frequency correction signal (260.002 MHz) is subjected to down-conversion mixing with the locally generated 260MHz local oscillation frequency (possibly with frequency offset) to generate an intermediate frequency single tone signal F of 2KHz + -delta 1 Wherein 0.ltoreq.delta.ltoreq.1300, ifDelta is larger than 1300, the frequency offset is too large to calibrate, and the calibration is stopped;
(2) For the intermediate frequency single-tone signal F obtained after mixing 1 Extracting 125 times, and downsampling to 8KHz sampling rate;
(3) For intermediate frequency single-tone signal F reduced to 8KSPS sampling rate 1 Performing 2048-point fast Fourier transform FFT, and back-calculating the current frequency F 2 ；
(4) If |F 2 -F 1 If the frequency deviation of the crystal oscillator of the voltage-controlled crystal oscillator is less than or equal to 4Hz, the frequency deviation of the crystal oscillator meets the use requirement, the calibration is completed, and the calibration process is exited; otherwise, entering the step (5);
(5) If F 2 ＞F 1 The actual frequency of the crystal oscillator is smaller, the adjusting direction D=1, and the frequency of the crystal oscillator is adjusted to be larger; otherwise, the adjusting direction d= -1, the crystal oscillator frequency is adjusted to be small;
(6) And (3) a push-back process: reading the RDAC register value R of the current digital potentiometer AD5231, recording, and calculating the adjustment quantity A= |F 2 -F 1 D/10 (2.7/1024) 5×26/1000 (representing the multiplication in this formula), the RDAC register value of AD5231 is rewritten to r+a, and the process jumps to step (1) to continue the loop 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 the fast fourier transform FFT, and calculates the frequency offset of the voltage controlled crystal oscillator to be calibrated with the frequency of 26MHz by pushing back the frequency offset of the intermediate frequency single tone signal, and adjusts the frequency of the crystal oscillator to be calibrated with the frequency of 26MHz, so that the frequency accuracy of the local oscillation signal with the frequency of 260MHz mixed with the standard radio frequency correction signal with the frequency of 260.002MHz is improved, and the frequency accuracy of the voltage controlled crystal oscillator to be calibrated with the frequency of 26MHz meets the requirement. 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 the tuning voltage parameters after the last calibration can be automatically read when the next device is powered on, 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.
While the invention has been described in detail in this specification with reference to the general description and the specific embodiments thereof, it will be apparent to one skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (3)
1. The device 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, a signal output end of the 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, a signal output end of the frequency synthesizer is connected with one signal input end of the mixer, and the other signal input end of the mixer is connected with a signal output end of a high-precision radio frequency signal source;
performing down-conversion mixing processing on the high-precision radio frequency signal provided by the high-precision radio frequency signal source and the self-oscillation frequency signal provided by the frequency synthesizer to obtain an intermediate frequency signal; the intermediate frequency signal is input into a digital signal processor after analog-to-digital conversion;
the digital signal processor sequentially carries out analog-to-digital conversion, extraction and Fast Fourier Transform (FFT) on the intermediate frequency signal, and obtains the actual frequency through the FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated, thereby realizing the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
2. A method for rapid calibration of a crystal oscillator frequency 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, a signal output end of the 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, a signal output end of the frequency synthesizer is connected with one signal input end of the mixer, and the other signal input end of the mixer is connected with a signal output end of a high-precision radio frequency signal source;
step two, performing down-conversion mixing processing on the high-precision radio frequency signal provided by the high-precision radio frequency signal source and the self-oscillation frequency signal provided by the frequency synthesizer to obtain an intermediate frequency signal; the intermediate frequency signal is input into a digital signal processor after analog-to-digital conversion;
step three, the digital signal processor sequentially carries out analog-to-digital conversion, extraction and fast Fourier transform FFT on the intermediate frequency signal, and obtains the actual frequency through the fast Fourier transform FFT; according to the actual frequency and the frequency value of the intermediate frequency signal, calculating the frequency offset, and controlling the digital potentiometer according to the direction of the frequency offset to adjust the analog tuning voltage of the voltage-controlled crystal oscillator to be calibrated, thereby realizing the frequency calibration of the voltage-controlled crystal oscillator to be calibrated.
3. The method for rapidly calibrating a frequency of a crystal oscillator for a communication device according to claim 2, wherein the actual frequency is obtained by a fast fourier transform FFT, and the actual frequency is obtained by:
and performing fast Fourier transform FFT on the extracted digital signals to obtain N complex numbers, wherein N is a natural number, and the frequency value corresponding to the maximum complex number of the modulus values in the N complex numbers is fundamental frequency, namely actual frequency.
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| EP1032173A2 (en) * | 1999-02-24 | 2000-08-30 | Matsushita Electric Industrial Co., Ltd. | Frequency offset correction in multicarrier receivers |
| JP2005026891A (en) * | 2003-06-30 | 2005-01-27 | Sharp Corp | Frequency synthesizer, tuner, and receiver |
| CN104639161A (en) * | 2014-12-31 | 2015-05-20 | 陕西烽火电子股份有限公司 | Automatic calibration method for frequency of crystal oscillator |
| CN112003655A (en) * | 2020-09-11 | 2020-11-27 | 中国电子科技集团公司第五十四研究所 | Digital-analog hybrid phased array antenna system calibration method |
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| US20140004887A1 (en) * | 2012-06-29 | 2014-01-02 | Qualcomm Incorporated | Crystal oscillator calibration |
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| EP1032173A2 (en) * | 1999-02-24 | 2000-08-30 | Matsushita Electric Industrial Co., Ltd. | Frequency offset correction in multicarrier receivers |
| JP2005026891A (en) * | 2003-06-30 | 2005-01-27 | Sharp Corp | Frequency synthesizer, tuner, and receiver |
| CN104639161A (en) * | 2014-12-31 | 2015-05-20 | 陕西烽火电子股份有限公司 | Automatic calibration method for frequency of crystal oscillator |
| CN112003655A (en) * | 2020-09-11 | 2020-11-27 | 中国电子科技集团公司第五十四研究所 | Digital-analog hybrid phased array antenna system calibration method |
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