Digital temperature compensation method and device for at-cut crystal oscillator fundamental frequency and third overtone difference frequency

Abstract

This application relates to a digital temperature compensation method and apparatus for the difference frequency between the fundamental frequency and the third overtone frequency of an AT-cut crystal oscillator. The method acquires the fundamental frequency signal and the third overtone signal of the same AT-cut crystal oscillator chip through a fundamental frequency oscillation circuit and a third overtone oscillation circuit. The difference frequency is taken as three times the frequency of the third overtone signal and the fundamental frequency. This difference frequency is used to cancel the second-order and third-order nonlinear terms in the frequency-temperature characteristics to linearly obtain the chip's operating temperature. Then, the output frequency is digitally corrected based on the operating temperature and the third-order temperature drift coefficient, achieving dynamic temperature compensation. This application eliminates the need for an external temperature sensor; the temperature is measured on the chip itself, which is beneficial for improving the accuracy of temperature measurement and compensation, as well as the consistency of batch products.

Description

Technical Field

[0001] This application relates to the field of temperature compensation for quartz crystal oscillators, and in particular to a digital temperature compensation method and apparatus for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator. Background Technology

[0002] AT-cut quartz crystals, with their excellent frequency-temperature characteristics, are the core resonant components of currently commercial high-precision crystal oscillators, and are widely used in high-precision quartz crystal oscillators, temperature-compensated crystal oscillators, isothermal crystal oscillators, as well as inertial navigation, satellite timing, precision measurement and control, and other scenarios. The frequency of AT-cut quartz crystals exhibits a third-order nonlinear drift with temperature, and its frequency-temperature characteristic is represented by a third-order curve that changes with temperature.

[0003] Without compensation, AT-cut crystal oscillators exhibit frequency drift exceeding ±10ppm over a wide temperature range of -40℃ to 85℃, which is insufficient to meet the frequency stability requirements of high-precision time synchronization, precision measurement and control, and navigation positioning applications. To ensure a stable output frequency across a wide temperature range, compensation for the crystal oscillator's frequency temperature drift is necessary.

[0004] Existing temperature-compensated crystal oscillator (TCC) compensation schemes are divided into two categories: analog temperature compensation and digital temperature compensation. The mainstream digital temperature compensation schemes all rely on external thermistors, diodes, or integrated temperature sensors to obtain the temperature. However, because the external temperature sensor and the quartz resonant crystal are physically separated, the temperature sensor measures the temperature at its location rather than the actual operating temperature of the crystal itself. This results in thermal hysteresis and differences in thermal gradients, causing the temperature measurement to deviate from the crystal's actual temperature from the source. Furthermore, the nonlinearity and temperature drift errors of the temperature sensor itself are amplified and superimposed in the signal chain, meaning that no matter how accurate the back-end compensation model is, the error introduced by the temperature measurement stage will be transmitted to the compensation result, limiting the compensation accuracy. Meanwhile, the large component dispersion and poor consistency of analog compensation circuits increase the difficulty and cost of batch calibration. Summary of the Invention

[0005] To address the problems of existing digital temperature compensation methods that rely on external temperature sensors, where the temperature measurement object and the compensated crystal are physically separated, resulting in temperature measurement distortion, limited compensation accuracy, and poor batch consistency, this application provides a digital temperature compensation method and apparatus for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator.

[0006] Firstly, this application provides a digital temperature compensation method for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator, which adopts the following technical solution: A digital temperature compensation method for the difference frequency between the fundamental frequency and the third overtone of an AT-cut crystal oscillator includes the following steps: S1. The fundamental frequency signal and the third overtone signal of the same AT-cut crystal oscillator are acquired through the fundamental frequency oscillation circuit and the third overtone oscillation circuit, respectively. S2. Perform multi-temperature point calibration on the AT-cut crystal oscillator wafer, and fit to obtain the difference frequency linear temperature measurement parameters and the third-order temperature drift coefficient; S3. Determine the difference between the frequency of the third overtone signal and three times the frequency of the fundamental frequency signal as the difference frequency, and determine the operating temperature of the AT-cut crystal oscillator wafer based on the difference frequency and the difference frequency linear temperature measurement parameters. S4. Determine the frequency drift of the AT-cut crystal oscillator chip based on the operating temperature and the third-order temperature drift coefficient, and digitally correct the output frequency of the AT-cut crystal oscillator chip based on the frequency drift to achieve dynamic temperature compensation.

[0007] By adopting the above technical solution, the fundamental frequency signal and the third overtone signal output simultaneously from the same AT-cut crystal oscillator chip are used. The difference frequency is obtained by subtracting three times the frequency of the third overtone signal from the fundamental frequency signal. This causes the second-order and third-order nonlinear terms in the temperature characteristics of the two frequencies to cancel each other out, leaving only the first-order linear term. Thus, the true operating temperature of the chip body is obtained linearly using the difference frequency. The temperature measurement object is the crystal itself being compensated, and it no longer relies on an external temperature sensor. The frequency drift is then calculated by combining the operating temperature with the third-order temperature drift coefficient, and the output frequency is corrected digitally. This allows the temperature measurement, drift calculation, and frequency correction to be iterated in a closed loop within the same digital process. This eliminates the thermal hysteresis error and thermal gradient error of the external temperature sensor, while achieving dynamic temperature compensation over a wide temperature range in a fully digital manner.

[0008] Optionally, the frequency changes of both the fundamental frequency signal and the third overtone signal with temperature conform to the characteristics of a third-order polynomial, and the second-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal, and the third-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal. The difference frequency cancels out the second-order and third-order nonlinear terms in the frequency-temperature characteristics of the fundamental frequency signal and the third overtone signal, retaining only the first-order linear temperature term, so that the difference frequency has a linear correspondence with the operating temperature of the AT-cut crystal oscillator wafer.

[0009] By adopting the above technical solution, the difference frequency cancels out the common-mode second-order and third-order nonlinear terms in the temperature characteristics of the two signals, retaining only the first-order linear term, so that the working temperature can be solved linearly by the difference frequency, avoiding the complexity and error in temperature measurement caused by the third-order nonlinearity of the single-channel frequency.

[0010] Optionally, the differential frequency linear temperature measurement parameters include temperature sensitivity and reference intercept. The temperature sensitivity is the difference between the first-order temperature coefficient of the third overtone signal and three times the first-order temperature coefficient of the fundamental frequency signal. The operating temperature is determined based on the difference between the differential frequency and the reference intercept, as well as the temperature sensitivity.

[0011] By adopting the above technical solution, the temperature sensitivity is defined as the difference of three times the first-order temperature coefficient between the two channels, so that the working temperature can be directly obtained from the difference frequency through a linear relationship, providing an accurate temperature input for subsequent temperature drift compensation.

[0012] Optionally, the operating temperature is the temperature of the AT-cut crystal oscillator chip, and the differential frequency is measured using the AT-cut crystal oscillator chip as the temperature measurement object, so as to eliminate the thermal hysteresis error and thermal gradient error introduced by the external temperature sensor without setting an external temperature sensor.

[0013] By adopting the above technical solution, the temperature measurement result reflects the true working temperature of the crystal by using the wafer itself as the temperature measurement object, thus eliminating the thermal hysteresis and thermal gradient error introduced by the physical separation of the external temperature sensor.

[0014] Optionally, multi-temperature point calibration includes sub-steps S21-S25: ​​S21. At multiple gradient temperature points, the AT-cut crystal oscillator wafer is brought to temperature stability, where temperature stability means the temperature fluctuation of the AT-cut crystal oscillator wafer is within a set range. S22. At each gradient temperature point, the fundamental frequency signal and the third overtone signal are simultaneously acquired, and the corresponding difference frequency is determined. S23. The difference frequency at each gradient temperature point is linearly fitted with the temperature to obtain the difference frequency linear temperature measurement parameters. S24. Based on the fundamental frequency signal at each gradient temperature point, the third-order temperature drift coefficient is fitted to obtain the third-order temperature drift coefficient. S25. The difference frequency linear temperature measurement parameters, the third-order temperature drift coefficient, the nominal frequency, and the reference temperature are stored in non-volatile memory.

[0015] By adopting the above technical solution, multiple temperature points are calibrated point by point, and temperature measurement parameters and temperature drift coefficients are obtained by linear fitting and third-order fitting respectively. The parameters can be solidified in one calibration and adapted to batch products.

[0016] Optionally, S3 includes sub-steps S31-S33: S31. Synchronously acquire the fundamental frequency signal and the third overtone signal with a fixed gating time. S32. Determine the difference frequency by finding that the frequency of the third overtone signal is three times the frequency of the fundamental frequency signal. S33. Determine the operating temperature of the AT-cut crystal oscillator wafer based on the difference frequency and the difference frequency linear temperature measurement parameters.

[0017] By adopting the above technical solution, two signals are acquired synchronously with a fixed gate time, and the difference frequency and operating temperature are calculated in real time, so that the acquisition of operating temperature and real-time compensation are carried out simultaneously.

[0018] Optionally, S4 includes sub-steps S41-S45: S41. Determine the temperature difference between the operating temperature and the reference temperature. S42. Determine the frequency drift of the AT-cut crystal oscillator chip based on the temperature difference and the third-order temperature drift coefficient. S43. Determine the compensated target frequency based on the nominal frequency and frequency drift of the AT-cut crystal oscillator chip. S44. Digitally correct the output frequency of the AT-cut crystal oscillator chip to the target frequency. S45. Cyclicly execute the acquisition of the fundamental frequency signal and the third overtone signal, the determination of the difference frequency, the determination of the operating temperature, and the correction of the output frequency to achieve dynamic temperature compensation.

[0019] By adopting the above technical solution, the compensated target frequency is calculated from the working temperature using temperature difference and third-order temperature drift, and then corrected digitally. Dynamic temperature compensation is achieved through iterative cycles.

[0020] Optionally, the third-order temperature drift coefficient includes a first coefficient, a second coefficient, and a third coefficient, and the frequency drift is the sum of the product of the first term of the temperature difference and the first coefficient, the product of the second term of the temperature difference and the second coefficient, and the product of the third term of the temperature difference and the third coefficient.

[0021] By adopting the above technical solution, the frequency drift is multiplied by the first, second, and third terms of the temperature difference and then summed, which matches the inherent third-order temperature drift characteristics of the AT-cut crystal oscillator and improves the compensation accuracy over a wide temperature range.

[0022] Optionally, the fundamental frequency oscillation circuit and the third overtone oscillation circuit operate independently of each other. The fundamental frequency signal and the third overtone signal are synchronously acquired within the same gate time, so that there is no phase deviation or timing error between the fundamental frequency signal and the third overtone signal.

[0023] By adopting the above technical solution, the two oscillation circuits are independent of each other and synchronously acquire data within the same gate time, eliminating phase deviation and timing error between the two signals and ensuring the accuracy of the difference frequency calculation.

[0024] Optionally, in multi-temperature point calibration, the least squares method is used to perform linear fitting of the difference frequency with temperature.

[0025] By adopting the above technical solution, the linear relationship between the difference frequency and temperature is fitted using the least squares method, thereby improving the fitting accuracy of the temperature measurement parameters.

[0026] Optionally, the digital method for correcting the output frequency can be any one of direct digital frequency synthesis, digital-to-analog conversion with voltage control tuning, and fractional frequency division.

[0027] By adopting the above technical solutions, digital frequency modulation can be implemented according to different hardware platforms by selecting direct digital frequency synthesis, digital-to-analog conversion voltage control tuning, or fractional frequency division, which is convenient for engineering adaptation.

[0028] Optionally, the AT-cut crystal oscillator chip can be either a temperature-compensated crystal oscillator or a temperature-controlled crystal oscillator.

[0029] By adopting the above technical solution, this method is compatible with both temperature-compensated crystal oscillators and temperature-controlled crystal oscillators, thus expanding its application range.

[0030] Secondly, the digital temperature compensation device for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator provided in this application adopts the following technical solution: A digital temperature compensation device for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator includes: The fundamental frequency oscillation circuit is configured to output the fundamental frequency signal of the AT-cut crystal oscillator chip; The third overtone oscillation circuit is configured to output the third overtone signal of the AT-cut crystal oscillator chip; A synchronous high-frequency counting module is connected to the fundamental frequency oscillation circuit and the third overtone oscillation circuit respectively, and is configured to synchronously acquire the fundamental frequency signal and the third overtone signal within the same gate time. The synchronous high-frequency counting module can be implemented by a high-frequency counter or a field-programmable gate array. The digital compensation control module, connected to the synchronous high-frequency counting module, is configured to determine the difference frequency as three times the frequency of the third overtone signal and the fundamental frequency signal. Based on the difference frequency and the pre-stored linear temperature measurement parameters of the difference frequency, the operating temperature of the AT-cut crystal oscillator chip is determined, and the frequency drift of the AT-cut crystal oscillator chip is determined according to the operating temperature and the pre-stored third-order temperature drift coefficient. The digital compensation control module can be implemented by a microcontroller, a field-programmable gate array, or a digital signal processor. The digital frequency modulation output module, connected to the digital compensation control module, is configured to digitally correct the output frequency of the AT-cut crystal oscillator chip based on the frequency drift.

[0031] By adopting the above technical solution, the device outputs the fundamental frequency signal and third overtone signal of the same wafer through two independent oscillation circuits. The synchronous high-frequency counting module collects them in parallel in the same gated window to eliminate phase and timing deviations. The digital compensation control module completes the wafer body temperature measurement and frequency drift calculation based on the difference frequency. The digital frequency modulation output module corrects the output frequency digitally, enabling the device to achieve fully digital dynamic temperature compensation without configuring an external temperature sensor.

[0032] In summary, this application includes at least one of the following beneficial technical effects: 1. By using differential frequency self-temperature measurement with the crystal body as the temperature measurement object, the thermal hysteresis error and thermal gradient error introduced by the physical separation of the external temperature sensor are eliminated, so that the temperature measurement result reflects the true working temperature of the crystal and improves the accuracy of temperature measurement.

[0033] 2. The difference frequency cancels the second-order and third-order nonlinear terms in the frequency temperature characteristics, and, together with the third-order temperature drift model, calculates the frequency drift, matching the inherent third-order temperature drift characteristics of the AT-cut crystal oscillator, thereby improving the frequency stability over a wide temperature range.

[0034] 3. The all-digital compensation architecture does not contain analog compensation devices, so it is less affected by the discreteness of devices. It can be adapted to batch products with a one-time calibration at the factory, which improves the consistency of batch products and reduces calibration costs. Attached Figure Description

[0035] Figure 1 A schematic flowchart illustrating the digital temperature compensation method for the fundamental frequency and third overtone difference frequency of an AT-cut crystal oscillator provided in an embodiment of this application.

[0036] Figure 2 This is a schematic diagram of the structure of the digital temperature compensation device for the fundamental frequency and third overtone difference frequency of the AT-cut crystal oscillator provided in the embodiments of this application.

[0037] Figure 3 This is a schematic diagram illustrating the linear relationship between the difference frequency and the operating temperature, as provided in an embodiment of this application. Detailed Implementation

[0038] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application.

[0039] This application discloses a digital temperature compensation method for the difference frequency between the fundamental frequency and the third overtone of an AT-cut crystal oscillator. This method acquires the fundamental frequency signal and the third overtone signal of the same AT-cut crystal oscillator chip, linearly obtaining the chip's operating temperature by offsetting the nonlinear term in the frequency-temperature characteristic using their difference frequency. Then, it combines this with a third-order temperature drift model to digitally correct the output frequency. First, the fundamental frequency signal and the third overtone signal of the same chip are acquired through two oscillation circuits. Then, multi-temperature point calibration is performed on the chip to obtain the difference frequency linear temperature measurement parameters and the third-order temperature drift coefficient. Next, the difference frequency is calculated in real time and used to linearly solve for the chip's operating temperature. Finally, the frequency drift is calculated based on the operating temperature and the third-order temperature drift coefficient, and the output frequency is digitally corrected. Therefore, it can reflect the true operating temperature of the crystal without the need for an external temperature sensor and achieve dynamic temperature compensation over a wide temperature range in a fully digital manner. The following provides a detailed description of the terminology, main method flow, specific implementation of the difference frequency linear temperature measurement, digital compensation process, and device mapping.

[0040] For ease of understanding, the following will first explain some of the technical terms involved in the embodiments of this application.

[0041] AT-cut crystal oscillator wafers are quartz resonator wafers processed according to the AT-cut type. The fundamental frequency and the frequency of the third overtone both exhibit third-order nonlinear characteristics as the temperature changes. This method utilizes the inherent coefficient relationship between the fundamental frequency and the third overtone of the same wafer to achieve self-temperature measurement.

[0042] The fundamental frequency signal and the third overtone signal are the signals output from the fundamental frequency resonance and the third overtone resonance of the same AT-cut crystal oscillator chip, respectively. Their frequencies are denoted as F1 and F3, respectively. They are taken from the same chip and are subjected to the same operating temperature.

[0043] The difference frequency, denoted as ΔF, is the difference between the frequency of the third overtone signal and three times the frequency of the fundamental frequency signal. It is used as a variable in linear temperature measurement, and its relationship with temperature is linear.

[0044] The differential frequency linear temperature measurement parameters are parameters that characterize the linear relationship between the differential frequency and the operating temperature. They include temperature sensitivity and reference intercept, and are obtained by multi-temperature point calibration fitting.

[0045] The third-order temperature drift coefficient is the first, second, and third-order coefficient of a third-order polynomial that characterizes the relative frequency drift of a wafer as a function of temperature. It is used to calculate the relative frequency drift based on the operating temperature.

[0046] Reference Figure 1 This method first acquires the fundamental frequency signal and third overtone signal from the same AT-cut crystal oscillator wafer. In the specific implementation, the same AT-cut crystal oscillator wafer is excited by a fundamental frequency oscillation circuit and a third overtone oscillation circuit, respectively. The fundamental frequency oscillation circuit outputs the fundamental frequency signal F1, and the third overtone oscillation circuit outputs the third overtone signal F3. The two signals are acquired by a synchronous high-frequency counting module. Since the two signals are taken from the same wafer and are subjected to the same operating temperature, a physical prerequisite is provided for subsequent nonlinearity cancellation using difference frequency.

[0047] The fundamental frequency oscillation circuit and the third overtone oscillation circuit operate independently. The fundamental frequency signal and the third overtone signal are synchronously acquired within the same gate time, ensuring no phase deviation or timing error between them. Since the difference frequency is obtained by subtracting the two frequencies, any phase or timing deviation in the two acquisitions will directly introduce difference frequency error. Therefore, synchronous acquisition within the same gate window guarantees the accuracy of the difference frequency calculation. The AT-cut crystal oscillator can be either a temperature-compensated crystal oscillator or a temperature-controlled crystal oscillator; this method is applicable to both types of crystal oscillators.

[0048] Based on the data acquisition, multi-temperature point calibration is performed on the AT-cut crystal oscillator wafers to obtain the difference frequency linear temperature measurement parameters and the third-order temperature drift coefficient. The multi-temperature point calibration is a one-time calibration and batch adaptation. It acquires the fundamental frequency and third overtone at multiple gradient temperature points and fits them accordingly. After the obtained parameters are solidified, they can be used for real-time temperature measurement and compensation of this batch of crystal oscillators.

[0049] Specifically, multi-temperature point calibration includes sub-steps S21 to S25.

[0050] S21. At multiple gradient temperature points, the AT-cut crystal oscillator wafer is brought to temperature stability. Temperature stability means that the temperature fluctuation of the AT-cut crystal oscillator wafer is within a set range, so that the frequency collected at each temperature point corresponds to the wafer temperature that has reached thermal equilibrium, avoiding measurement deviations introduced by thermal transition states. For example, the crystal oscillator sample is placed in a programmable temperature chamber, and multiple gradient temperature points covering -40℃, 0℃, 25℃, 50℃, and 85℃ are set, and each temperature point is held at the same temperature for 30 minutes.

[0051] S22. At each gradient temperature point, the fundamental frequency signal and the third overtone signal are collected synchronously, and the corresponding difference frequency is determined. That is, the difference frequency at that temperature point is obtained by subtracting three times the fundamental frequency from the third overtone frequency at that temperature point, and is used as sample data for fitting the temperature measurement parameters.

[0052] S23. Perform linear fitting between the difference frequency and temperature at each gradient temperature point to obtain the difference frequency linear temperature measurement parameters, thereby characterizing the linear change of the difference frequency with temperature using the difference frequency temperature sensitivity and the reference intercept, and establishing a mapping from the difference frequency to the working temperature.

[0053] S24. Based on the fundamental frequency signal at each gradient temperature point, the third-order temperature drift coefficient is obtained by fitting, which is used for subsequent calculation of the relative frequency drift at the operating temperature.

[0054] S25. Store the differential frequency linear temperature measurement parameters, third-order temperature drift coefficient, nominal frequency, and reference temperature in a non-volatile memory so that the parameters obtained from the above calibration can still be saved after power failure and can be directly called by the real-time compensation process.

[0055] In some embodiments, the least squares method is used to perform linear fitting of the difference frequency with temperature.

[0056] After calibration, the real-time temperature measurement phase begins. The difference frequency is defined as three times the frequency of the fundamental frequency and the frequency of the third overtone signal. Based on this difference frequency and the linear temperature measurement parameters, the operating temperature of the AT-cut crystal oscillator wafer is determined. In the specific implementation, the fundamental frequency signal and the third overtone signal are acquired in real time, and the real-time difference frequency is calculated. Then, the real-time operating temperature of the crystal is calculated using the differential frequency linear temperature measurement parameters obtained from calibration. Taking a crystal oscillator with a nominal fundamental frequency of 10MHz, a nominal third overtone of 30MHz, and a reference temperature of 25℃ as an example, the differential frequency temperature sensitivity K = 6.5Hz / ℃ and the reference intercept B = 0Hz are obtained from calibration. For example, if the real-time sampling yields a fundamental frequency F1 = 9999985Hz and a third overtone F3 = 29999962.5Hz, then the differential frequency... Hz, substituting into the temperature measurement model, yields the operating temperature. ℃ (All calculation results in this example are rounded approximations). It should be noted that the fundamental frequency and third overtone sampling values ​​in this real-time temperature measurement example are independent schematic values ​​used to illustrate the calculation process of difference frequency linear temperature measurement and third-order drift compensation, respectively, and do not represent the actual measurement correspondence of the same wafer under the same operating conditions.

[0057] The frequency variations of both the fundamental frequency signal and the third overtone signal with temperature conform to the characteristics of a third-order polynomial. Specifically, the frequency-temperature characteristics of the fundamental frequency F1 and the third overtone F3 satisfy... and ,in The difference between the operating temperature and the reference temperature. The reference temperature is 25℃. , These are the fundamental frequency and the nominal frequency of the third overtone at the reference temperature, respectively. , , and , , These are the absolute frequency temperature coefficients of the fundamental frequency, the first order, the second order, and the third order overtone, respectively, with dimensions of Hz / ℃ and Hz / ℃. 2 Hz / ℃ 3 For the same AT-cut resonant crystal, its inherent characteristics satisfy... , , Only the first-order temperature coefficient has an inherent difference, i.e. In other words, the second-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal, and the third-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal. (Define difference frequency) Substituting into the above third-order polynomial, the second-order nonlinear terms cancel each other out, leaving only the first-order linear temperature term, i.e. In the formula, K represents the difference frequency temperature sensitivity, and is a fixed constant. Thus, the difference frequency cancels out the second and third-order nonlinear terms in the frequency-temperature characteristics of the fundamental frequency signal and the third overtone signal, retaining only the first-order linear temperature term, making the difference frequency strictly linearly correlated with the operating temperature of the AT-cut crystal oscillator. In some embodiments, when the above three-fold relationship is only approximately true, the residual constant deviation and slight nonlinearity can be absorbed by the reference intercept and calibration process, thereby maintaining the linear correspondence between the difference frequency and the operating temperature in engineering applications.

[0058] The differential frequency linear temperature measurement parameters include temperature sensitivity and reference intercept. Temperature sensitivity is the difference between the first-order temperature coefficient of the third overtone signal and three times the first-order temperature coefficient of the fundamental frequency signal, i.e. The operating temperature is determined based on the difference between the differential frequency and the reference intercept, as well as the temperature sensitivity, i.e., by the temperature measurement model. The formula is derived, where B is the reference intercept, representing the intercept of the difference frequency-temperature fitting line. Since the difference frequency has already canceled out the second and third order nonlinear terms, such as... Figure 3 As shown, the difference frequency exhibits a linear relationship with the operating temperature, with a temperature measurement linearity better than 99.9% and a temperature measurement accuracy of ±0.1℃. In some embodiments, the temperature sensitivity and reference intercept can be calibrated either batch-wise or individually for each wafer. Individual wafer calibration can further compensate for individual differences between wafers.

[0059] The operating temperature is the temperature of the AT-cut crystal oscillator itself. The differential frequency measurement uses the AT-cut crystal oscillator itself as the temperature measurement object, thereby eliminating the thermal hysteresis error and thermal gradient error introduced by the external temperature sensor without the need for an external temperature sensor. Since the differential frequency is taken from two frequencies of the crystal itself, it reflects the real-time temperature of the crystal itself, rather than the temperature at the location of the external temperature sensor. Therefore, there is no temperature hysteresis or thermal gradient difference between the external temperature sensor and the crystal, nor is it introduced into the nonlinear error or temperature drift error of the temperature sensor itself.

[0060] In the specific implementation of real-time temperature measurement, S3 includes sub-steps S31 to S33.

[0061] S31. The fundamental frequency signal and the third overtone signal are synchronously acquired with a fixed gating time to provide two frequency data at the same time and under the same gating window for difference frequency calculation. For example, the high-frequency counting module synchronously acquires the real-time fundamental frequency F1 and the third overtone F3 with a fixed gating time of 1 second.

[0062] S32. Determine the difference between the frequency of the third overtone signal and three times the frequency of the fundamental frequency signal to obtain the difference frequency, that is, subtract three times the fundamental frequency from the frequency of the third overtone signal collected this time, and output the real-time difference frequency for solving the working temperature.

[0063] S33. Based on the difference frequency and the difference frequency linear temperature measurement parameters, determine the operating temperature of the AT-cut crystal oscillator wafer, that is, substitute the real-time difference frequency into the temperature measurement model to obtain the current operating temperature of the wafer, which is used as the temperature input for subsequent calculation of frequency drift.

[0064] After determining the operating temperature, the frequency drift of the AT-cut crystal oscillator is determined based on the operating temperature and the third-order temperature drift coefficient. The output frequency of the AT-cut crystal oscillator is then digitally corrected based on the frequency drift to achieve dynamic temperature compensation. In the specific implementation, the target frequency after compensation is calculated by subtracting the real-time temperature drift error from the nominal frequency. In the formula For nominal frequency, This represents the relative frequency drift. Continuing with the previous example, at an operating temperature of 26.15℃, the calculated relative frequency drift is approximately -0.0470ppm. Therefore, the target frequency... The output frequency is corrected in real time based on the Hz value. With this compensation, for this example crystal oscillator, the frequency temperature stability is improved from the original ±12ppm to within ±0.1ppm in the full temperature range of -40℃ to 85℃, with no temperature hysteresis error, and the consistency error of batch devices is less than 0.05ppm.

[0065] In the specific implementation of digital compensation, S4 includes sub-steps S41 to S45.

[0066] S41. Determine the temperature difference between the operating temperature and the reference temperature, i.e., subtract the reference temperature from the obtained operating temperature to get the temperature difference. , as the independent variable for the third-order temperature drift calculation.

[0067] S42. Based on the temperature difference and the third-order temperature drift coefficient, determine the frequency drift of the AT-cut crystal oscillator chip, that is, substitute the temperature difference into the third-order temperature drift model to calculate the relative frequency drift at the current temperature, which is used to calculate the target compensation frequency.

[0068] S43. Based on the nominal frequency and frequency drift of the AT-cut crystal oscillator wafer, determine the compensated target frequency, that is, subtract the frequency error corresponding to the frequency drift from the nominal frequency to obtain the target frequency.

[0069] S44. The output frequency of the AT-cut crystal oscillator is digitally corrected to the target frequency, that is, the digital compensation control module drives the digital frequency modulation output module to digitally adjust the output frequency to the target frequency.

[0070] S45. It continuously performs the acquisition of fundamental frequency signal and third overtone signal, determination of difference frequency, determination of operating temperature and correction of output frequency to achieve dynamic temperature compensation. This allows the operating temperature and compensation amount to be updated in real time as the temperature changes, so that the output frequency is kept near the target frequency after compensation.

[0071] The third-order temperature drift coefficient includes a first coefficient, a second coefficient, and a third coefficient. The frequency drift is the sum of the product of the first term of the temperature difference and the first coefficient, the product of the second term of the temperature difference and the second coefficient, and the product of the third term of the temperature difference and the third coefficient. In the formula , , These are the first, second, and third coefficients, representing the relative temperature drift coefficients of the fundamental frequency relative to the nominal frequency, with dimensions of ppm / ℃, ppm / ℃, and ppm / ℃, respectively. 2 ppm / ℃ 3 , and the aforementioned , absolute frequency temperature coefficient , , The two are distinguished by their nominal frequency conversion, i.e. ( , (And so on). This third-order polynomial matches the inherent third-order temperature drift characteristics of AT-cut crystal oscillators, and compared to linear compensation and second-order compensation, it can improve the compensation accuracy across the entire temperature range. For example, taking... ppm / ℃ ppm / ℃ 2 , ppm / ℃ 3 When temperature difference At ℃, relative frequency shift ppm.

[0072] Digital frequency correction can be implemented using various known methods. One possible implementation is through direct digital frequency synthesis, where a phase accumulator, in conjunction with a waveform lookup table, generates and adjusts the output frequency. In other embodiments, the output frequency is corrected using a digital-to-analog converter (DAC) with controlled voltage tuning, where a DAC outputs a control voltage to drive a varactor element to adjust the oscillation frequency. Still other embodiments use a fractional frequency division method, where a programmable frequency divider is used to divide a reference frequency to obtain the target frequency. The above digital frequency modulation implementations can be chosen based on the hardware platform.

[0073] The following describes the digital temperature compensation device for the fundamental frequency and third overtone difference frequency of the AT-cut crystal oscillator corresponding to the above method. (Refer to...) Figure 2 The device includes a fundamental frequency oscillation circuit, a three-overtone oscillation circuit, a synchronous high-frequency counting module, a digital compensation control module, and a digital frequency modulation output module.

[0074] The fundamental frequency oscillation circuit is configured to output the fundamental frequency signal of the AT-cut crystal oscillator chip.

[0075] The third overtone oscillation circuit is configured to output the third overtone signal of the AT-cut crystal oscillator.

[0076] The synchronous high-frequency counting module is connected to the fundamental frequency oscillation circuit and the third overtone oscillation circuit respectively, and is configured to synchronously acquire the fundamental frequency signal and the third overtone signal within the same gate time. The synchronous high-frequency counting module can be implemented by a high-frequency counter or a field-programmable gate array.

[0077] The digital compensation control module is connected to the synchronous high-frequency counting module and is configured to determine the difference frequency as three times the difference between the frequency of the third overtone signal and the frequency of the fundamental frequency signal. Based on the difference frequency and the pre-stored linear temperature measurement parameters of the difference frequency, the operating temperature of the AT-cut crystal oscillator chip is determined, and the frequency drift of the AT-cut crystal oscillator chip is determined according to the operating temperature and the pre-stored third-order temperature drift coefficient. The digital compensation control module can be implemented by a microcontroller, a field-programmable gate array, or a digital signal processor.

[0078] The digital frequency modulation output module is connected to the digital compensation control module and is configured to digitally correct the output frequency of the AT-cut crystal oscillator chip based on the frequency drift.

[0079] The aforementioned modules are responsible for acquiring the fundamental frequency and third overtone signals, determining the difference frequency and detecting the temperature of the wafer itself, calculating the frequency drift, and digitally correcting the output frequency, respectively. These correspond one-to-one with the acquisition, temperature measurement, and compensation steps of the aforementioned method. This device completes the compensation in a fully digital manner, without analog compensation devices, is less affected by device discreteness, has high consistency in mass production, and is simple and low-cost to calibrate.

[0080] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0081] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A digital temperature compensation method for the difference frequency between the fundamental frequency and the third overtone of an AT-cut crystal oscillator, characterized in that, Includes the following steps: S1. The fundamental frequency signal and the third overtone signal of the same AT-cut crystal oscillator are acquired through the fundamental frequency oscillation circuit and the third overtone oscillation circuit, respectively. S2. Perform multi-temperature point calibration on the AT-cut crystal oscillator wafer, and fit to obtain the difference frequency linear temperature measurement parameters and the third-order temperature drift coefficient; S3. Determine the difference between the frequency of the third overtone signal and three times the frequency of the fundamental frequency signal as the difference frequency, and determine the operating temperature of the AT-cut crystal oscillator wafer based on the difference frequency and the linear temperature measurement parameters of the difference frequency; S4. Determine the frequency drift of the AT-cut crystal oscillator chip based on the operating temperature and the third-order temperature drift coefficient, and digitally correct the output frequency of the AT-cut crystal oscillator chip based on the frequency drift to achieve dynamic temperature compensation.

2. The digital temperature compensation method according to claim 1, characterized in that, The frequency changes of the fundamental frequency signal and the third overtone signal with temperature both conform to the characteristics of a third-order polynomial. The second-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal, and the third-order temperature coefficient of the third overtone signal is three times that of the fundamental frequency signal. The difference frequency cancels out the second-order and third-order nonlinear terms in the frequency-temperature characteristics of the fundamental frequency signal and the third overtone signal, retaining only the first-order linear temperature term, so that the difference frequency has a linear correspondence with the operating temperature of the AT-cut crystal oscillator wafer.

3. The digital temperature compensation method according to claim 2, characterized in that, The differential frequency linear temperature measurement parameters include temperature sensitivity and reference intercept. The temperature sensitivity is the difference between the first-order temperature coefficient of the third overtone signal and three times the first-order temperature coefficient of the fundamental frequency signal. The operating temperature is determined based on the difference between the differential frequency and the reference intercept, as well as the temperature sensitivity.

4. The digital temperature compensation method according to claim 1, characterized in that, The operating temperature is the temperature of the AT-cut crystal oscillator wafer, and the differential frequency uses the AT-cut crystal oscillator wafer as the temperature measurement object to eliminate the thermal hysteresis error and thermal gradient error introduced by the external temperature sensor without setting an external temperature sensor.

5. The digital temperature compensation method according to claim 1, characterized in that, The multi-temperature point calibration includes the following sub-steps: S21. At multiple gradient temperature points, the AT-cut crystal oscillator wafer is made to reach temperature stability, wherein the temperature stability means that the temperature fluctuation of the AT-cut crystal oscillator wafer is within a set range; S22. At each gradient temperature point, the fundamental frequency signal and the third overtone signal are simultaneously acquired, and the corresponding difference frequency is determined; S23. Perform linear fitting between the difference frequency and temperature at each gradient temperature point to obtain the difference frequency linear temperature measurement parameters; S24. The third-order temperature drift coefficient is obtained by fitting the fundamental frequency signal at each of the gradient temperature points; S25. Store the difference frequency linear temperature measurement parameters, the third-order temperature drift coefficient, the nominal frequency, and the reference temperature in a non-volatile memory.

6. The digital temperature compensation method according to claim 1, characterized in that, S3 includes the following sub-steps: S31. Synchronously acquire the fundamental frequency signal and the third overtone signal with a fixed gating time; S32. Determine the difference between the frequency of the third overtone signal and three times the frequency of the fundamental frequency signal to obtain the difference frequency; S33. Determine the operating temperature of the AT-cut crystal oscillator wafer based on the difference frequency and the difference frequency linear temperature measurement parameters.

7. The digital temperature compensation method according to claim 1, characterized in that, S4 includes the following sub-steps: S41. Determine the temperature difference between the operating temperature and the reference temperature; S42. Determine the frequency drift of the AT-cut crystal oscillator wafer based on the temperature difference and the third-order temperature drift coefficient; S43. Based on the nominal frequency of the AT-cut crystal oscillator wafer and the frequency drift, determine the compensated target frequency; S44. Digitally correct the output frequency of the AT-cut crystal oscillator chip to the target frequency; S45. The acquisition of the fundamental frequency signal and the third overtone signal, the determination of the difference frequency, the determination of the operating temperature, and the correction of the output frequency are performed cyclically to achieve dynamic temperature compensation.

8. The digital temperature compensation method according to claim 7, characterized in that, The third-order temperature drift coefficient includes a first coefficient, a second coefficient, and a third coefficient. The frequency drift is the sum of the product of the first term of the temperature difference and the first coefficient, the product of the second term of the temperature difference and the second coefficient, and the product of the third term of the temperature difference and the third coefficient.

9. The digital temperature compensation method according to claim 1, characterized in that, The fundamental frequency oscillation circuit and the third overtone oscillation circuit operate independently of each other. The fundamental frequency signal and the third overtone signal are synchronously acquired within the same gate time, so that there is no phase deviation or timing error between the fundamental frequency signal and the third overtone signal.

10. A digital temperature compensation device for the difference frequency between the fundamental frequency and the third overtone of an AT-cut crystal oscillator, characterized in that, include: The fundamental frequency oscillation circuit is configured to output the fundamental frequency signal of the AT-cut crystal oscillator chip; The third overtone oscillation circuit is configured to output the third overtone signal of the AT-cut crystal oscillator chip; A synchronous high-frequency counting module is connected to the fundamental frequency oscillation circuit and the third overtone oscillation circuit respectively, and is configured to synchronously acquire the fundamental frequency signal and the third overtone signal within the same gate time. The digital compensation control module, connected to the synchronous high-frequency counting module, is configured to determine the difference frequency as three times the frequency of the third overtone signal and the fundamental frequency signal, and to determine the operating temperature of the AT-cut crystal oscillator chip based on the difference frequency and the pre-stored difference frequency linear temperature measurement parameters, and to determine the frequency drift of the AT-cut crystal oscillator chip according to the operating temperature and the pre-stored third-order temperature drift coefficient. A digital frequency modulation output module, connected to the digital compensation control module, is configured to digitally correct the output frequency of the AT-cut crystal oscillator wafer based on the frequency drift.

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