A system and method for improving the temperature characteristics of crystal oscillator output frequency

Abstract

This invention relates to a system and method for improving the temperature characteristics of the output frequency of a crystal oscillator. The high-stability crystal oscillator simultaneously generates two frequency signals with different temperature characteristics: a B-mode signal and a C-mode signal. The temperature sensitivity of the B-mode signal's output frequency is higher than that of the C-mode signal. The system includes a mixer-divider, a frequency-to-voltage conversion circuit, and an adder. The mixer-divider mixes the C-mode and B-mode signals and then divides them to obtain a temperature sensing signal, which is then sent to the frequency-to-voltage conversion circuit. The frequency-to-voltage conversion circuit performs frequency-to-voltage conversion on the temperature sensing signal to obtain a feedback regulation voltage. The adder superimposes the feedback regulation voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain a temperature control voltage signal V. c Temperature control voltage signal V c The temperature control bath in the high-stability crystal oscillator is controlled to keep the crystal temperature in the bath stable.

Description

Technical Field

[0001] This invention belongs to the technical field of OCXO (high-stability crystal oscillator), and specifically relates to a system and method for improving the temperature characteristics of the output frequency of a crystal oscillator. Background Technology

[0002] High-stability crystal oscillators (OCXOs) will experience frequency variations with changes in ambient temperature during operation. This is primarily due to the temperature-sensitive nature of the crystal itself. OCXOs will deviate in output frequency during temperature changes, with a deviation of ±1E-8 to 1E-7. Aerospace applications typically require OCXOs with output frequency accuracy on the order of ±5E-8 to 1E-7. Therefore, frequency accuracy deviations or loss of lock-up may occur during high and low temperature changes in system applications.

[0003] Existing technologies generally improve this indicator by enhancing the temperature control accuracy and capability of the temperature control system. However, since the actual temperature measurement point is near the crystal shell, it is impossible to accurately measure the true temperature of the wafer inside the crystal. Therefore, the crystal does not truly operate at the inflection point temperature. There is a temperature gradient deviation between the wafer temperature at high and low temperatures and the actual control temperature, causing the wafer temperature to change at high and low temperatures, and thus the output frequency to change. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a system and method for improving the output frequency temperature characteristics of a crystal oscillator, thus solving the problem of accurate temperature measurement of crystals without deviation.

[0005] The solution of this invention is: a system for improving the output frequency temperature characteristics of a high-stability crystal oscillator, wherein the high-stability crystal oscillator simultaneously generates two frequency signals with different frequency temperature characteristics: a B-mode signal and a C-mode signal, with the B-mode signal having a higher temperature sensitivity at its output frequency than the C-mode signal; the system includes a mixer-divider, a frequency-to-voltage conversion circuit, and an adder; wherein:

[0006] The mixer-divider mixes the C-mode signal and the B-mode signal and then divides the frequency to obtain the temperature sensing signal, which is then sent to the frequency-to-voltage conversion circuit.

[0007] The frequency-to-voltage conversion circuit converts the temperature sensing signal into a frequency-to-voltage conversion circuit to obtain a feedback regulation voltage.

[0008] The adder superimposes the feedback adjustment voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain the temperature control voltage signal V. c Temperature control voltage signal V c The temperature control bath in the high-stability crystal oscillator is controlled to keep the crystal temperature in the bath stable.

[0009] Preferably, the temperature sensitivity of the output frequency of the B-mode signal is at least two orders of magnitude higher than that of the C-mode signal.

[0010] Preferably, the mixer-divider uses the C-mode signal as the clock reference signal to perform mixing and division sequentially.

[0011] Preferably, the mixer-divider and frequency-voltage conversion circuit are implemented using an FPGA.

[0012] Preferably, the temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50Hz.

[0013] Preferably, in the frequency-to-voltage conversion circuit, the frequency of the temperature sensing signal at different temperatures and the feedback adjustment voltage V are... t The correspondence is obtained through the following method:

[0014] S1.1 Disconnect the connection between the frequency-to-voltage conversion circuit and the adder;

[0015] S1.2 Connect the output signal of the external power supply as the feedback adjustment voltage to the adder, calibrate the feedback adjustment voltage corresponding to keeping the frequency of the temperature sensing signal constant at different temperatures within the preset temperature range, and thus obtain the frequency of the temperature sensing signal and the feedback adjustment voltage V at different temperatures. t The correspondence.

[0016] Another solution of the present invention is: a method for improving the temperature characteristics of the output frequency of a high-stability crystal oscillator, the method comprising the following steps:

[0017] S1. Control the high-stability crystal oscillator to simultaneously generate two frequency signals with different frequency temperature characteristics: B-mode signal and C-mode signal, wherein the temperature sensitivity of the output frequency of the B-mode signal is higher than that of the C-mode signal.

[0018] S2. Mix the C-mode signal and the B-mode signal and then divide the frequency to obtain the temperature sensing signal. Perform frequency-voltage conversion on the temperature sensing signal to obtain the feedback regulation voltage.

[0019] S3. Superimpose the feedback adjustment voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain the temperature control voltage signal V. c ;

[0020] S4, using temperature control voltage signal V c The temperature control of the thermostat bath in the high-stability crystal oscillator is used to keep the crystal temperature in the thermostat bath stable.

[0021] Preferably, the temperature sensitivity of the output frequency of the B-mode signal is at least two orders of magnitude higher than that of the C-mode signal.

[0022] Preferably, step S2 uses the C-mode signal as the clock reference signal to sequentially perform frequency mixing and frequency division.

[0023] Preferably, the temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50Hz.

[0024] The advantages of this invention compared to the prior art are:

[0025] (1) This invention enables the crystal in the OCXO to work under dual-mode conditions and uses a combination of analog and digital circuits to achieve stable output frequency by extracting temperature and frequency information to form feedback control when the ambient temperature of the OCXO product changes.

[0026] (2) The present invention converts the frequency change of the B-mode signal carrying temperature change information into voltage change, and improves the frequency and temperature stability by using a feedback control temperature control loop.

[0027] (3) Since the frequency sensitivity of the B-mode signal is two orders of magnitude higher than that of the C-mode signal, the B-mode frequency is used to measure the temperature of the crystal body, which solves the problem of deviation-free temperature measurement of crystals in high-stability crystal oscillators.

[0028] (4) This invention can significantly improve the frequency stability of OCXO at high and low temperatures without changing the power consumption. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating the principle of the deviation-free temperature measurement and control system according to an embodiment of the present invention. Detailed Implementation

[0030] To more clearly illustrate the embodiments of the present invention, comparisons will be made below. Figure 1 The specific embodiments of the present invention are described below. Obviously, the accompanying drawings described below are merely some embodiments of the present invention. Those skilled in the art can obtain other drawings and other embodiments based on these drawings without any creative effort.

[0031] Example 1:

[0032] The OCXO is used to generate a stable reference signal. To improve the frequency and temperature stability of the product, an analog-to-digital temperature control technology based on a dual-mode oscillator circuit is adopted. When the OCXO product experiences temperature changes in high and low temperature environments, the B-mode frequency is more sensitive to temperature changes and exhibits a linear relationship with them. Therefore, the B-mode frequency can be used as a temperature sensing signal to compensate the temperature control circuit.

[0033] This embodiment provides a system for improving the temperature characteristics of the output frequency of a crystal oscillator. The high-stability crystal oscillator simultaneously generates two frequency signals with different temperature characteristics: a B-mode signal and a C-mode signal. In this embodiment, the nominal frequency of the B-mode signal is 108.8 MHz, and the nominal frequency of the C-mode signal is 100 MHz. The temperature sensitivity of the B-mode signal output frequency is higher than that of the C-mode signal, and the B-mode frequency accurately and without deviation reflects the inflection point temperature of the crystal.

[0034] like Figure 1 As shown, the system described above for improving the output frequency temperature characteristics of a crystal oscillator includes a mixer-divider, a frequency-to-voltage conversion circuit, and an adder; wherein:

[0035] The mixer-divider mixes the C-mode signal and the B-mode signal and then divides the frequency to obtain the temperature sensing signal, which is then sent to the frequency-to-voltage conversion circuit.

[0036] The frequency-to-voltage conversion circuit converts the temperature sensing signal into a frequency-to-voltage conversion circuit to obtain a feedback regulation voltage.

[0037] The adder superimposes the feedback adjustment voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain the temperature control voltage signal V. c Temperature control voltage signal V c The temperature control bath in the high-stability crystal oscillator is controlled to keep the crystal temperature in the bath stable.

[0038] The temperature sensitivity of the output frequency of the B-mode signal is at least two orders of magnitude higher than that of the C-mode signal.

[0039] The mixer-divider uses the C-mode signal as the clock reference signal to perform mixing and division in sequence.

[0040] The mixer-divider and frequency-to-voltage conversion circuit are implemented using FPGA. The mixer-divider is implemented using DDS, and the frequency-to-voltage conversion circuit is implemented using a digital-to-analog converter.

[0041] The temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50Hz.

[0042] The implementation method of this embodiment is as follows: The oscillation circuit in the high-stability crystal oscillator simultaneously generates B-mode and C-mode signals. The C-mode signal is output as a clock signal, and the output B-mode signal is input into the FPGA. The C-mode signal and the B-mode signal are mixed and processed to output a 20kHz sine wave signal, which is the temperature sensing signal. After being processed by the FPGA, the 20kHz sine wave signal (temperature sensing signal) undergoes frequency-voltage conversion and is added to the control voltage output by the temperature control circuit. This controls the heating tube to keep the crystal temperature in the constant temperature bath stable, achieving the purpose of precise temperature control and stable frequency, thus improving the product's performance and environmental adaptability.

[0043] The frequency and feedback adjustment voltage V of the temperature sensing signal at different temperatures in the frequency-to-voltage conversion circuit t The correspondence is obtained through the following method:

[0044] S1.1 Disconnect the connection between the frequency-to-voltage conversion circuit and the adder;

[0045] S1.2 Connect the output signal of the external power supply as the feedback adjustment voltage to the adder, calibrate the feedback adjustment voltage corresponding to keeping the frequency of the temperature sensing signal constant at different temperatures within the preset temperature range, and thus obtain the frequency of the temperature sensing signal and the feedback adjustment voltage V at different temperatures. t The correspondence.

[0046] In this embodiment, under high and low temperatures, the adjustment voltage V is changed. t To stabilize the 20kHz signal at different temperatures, the voltage V was recorded with and without feedback adjustment. t The frequency value at 20kHz was obtained, and finally the 20kHz frequency and feedback regulation voltage V at different temperatures were obtained. t The correspondence.

[0047] Based on the above system, the present invention also provides a method for improving the temperature characteristics of the output frequency of a crystal oscillator. This method is a temperature control solution combining analog and digital circuits, employing an adaptive frequency difference reduction method for precise temperature control. The method includes the following steps:

[0048] S1. Control the high-stability crystal oscillator to simultaneously generate two frequency signals with different frequency temperature characteristics: B-mode signal and C-mode signal, wherein the temperature sensitivity of the output frequency of the B-mode signal is higher than that of the C-mode signal.

[0049] S2. Mix the C-mode signal and the B-mode signal and then divide the frequency to obtain the temperature sensing signal. Perform frequency-voltage conversion on the temperature sensing signal to obtain the feedback regulation voltage.

[0050] S3. Superimpose the feedback adjustment voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain the temperature control voltage signal V. c ;

[0051] S4, using temperature control voltage signal V c The temperature control of the thermostat bath in the high-stability crystal oscillator is used to keep the crystal temperature in the thermostat bath stable.

[0052] The temperature sensitivity of the output frequency of the B-mode signal is at least two orders of magnitude higher than that of the C-mode signal.

[0053] Step S2 uses the C-mode signal as the clock reference signal to sequentially perform frequency mixing and frequency division.

[0054] The temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50Hz.

[0055] The above method tests the frequency difference between the B-mode and C-mode outputs, and converts the frequency change into a voltage change through F / V conversion (or direct output), thereby stabilizing the OCXO output frequency and improving the product's performance and environmental adaptability.

[0056] The test data for this embodiment, including the high and low temperature frequency data of the 100MHz crystal oscillator, are as follows:

[0057] temperature B-mode signal frequency C-mode signal frequency 50℃ 108.842 340 791 100.000 116 248 25℃ 108.847 007 135 100.000 133 523 -23℃ 108.856 140 633 100.000 152 358

[0058] The total variation of the B-mode signal between high and low temperatures is 13799.842 Hz (-189.0389315 / ℃), while the total variation of the C-mode signal is 36.11 Hz (-0.494657534 / ℃), with a variation ratio of 382.1612. Using the C-mode frequency as a reference clock frequency, the variation over the entire temperature range relative to the B-mode frequency variation is 36.11 / 13799.842 = 0.26% (less than 1%).

[0059] Through experimental verification and data analysis, this embodiment shows that the frequency sensitivity of the B mode is at least two orders of magnitude higher than that of the C mode. At the same time, due to the high frequency acquisition accuracy of DDS (0.029Hz), theoretically, the control frequency (100MHz) can achieve an accuracy of 0.029 / 100 = 2.9E-4Hz, that is, the frequency accuracy of 100MHz can reach 2.9E-12 (the best aging rate is currently in the E-10 range), achieving deviation-free control.

[0060] The core of this invention is based on a crystal oscillator circuit that simultaneously generates two frequency signals with different frequency-temperature characteristics: C-mode and B-mode (frequency changes linearly with temperature). The C-mode signal with better frequency-temperature characteristics is used as the clock reference signal for the FPGA. The B-mode frequency is mixed and divided to generate a 20kHz frequency. The frequency-temperature change is converted into a temperature-voltage change by an F / V circuit. This voltage can adjust the temperature control accuracy to keep the output frequency stable when the temperature changes.

[0061] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A system for improving the temperature characteristics of the output frequency of a crystal oscillator, a high-stability crystal oscillator simultaneously generating two frequency signals with different temperature characteristics: a B-mode signal and a C-mode signal, the temperature sensitivity of the output frequency of the B-mode signal being higher than that of the C-mode signal; characterized in that The mixer-frequency divider, the frequency-voltage conversion circuit, and the adder are included. The mixer-frequency divider mixes the C-mode signal with the B-mode signal and then divides the frequency to obtain a temperature sensing signal, and sends the temperature sensing signal to the frequency-voltage conversion circuit. The frequency-voltage conversion circuit performs frequency-voltage conversion processing on the temperature sensing signal to obtain a feedback adjustment voltage. The adder superimposes the feedback adjustment voltage with the control voltage output from the temperature control circuit in the high-stability crystal oscillator to obtain the temperature control voltage signal V. c Temperature control voltage signal V c The temperature control bath in the high-stability crystal oscillator is controlled to keep the crystal temperature in the temperature control bath stable; The temperature sensitivity of the B-mode signal output frequency is at least two orders of magnitude higher than that of the C-mode signal. The mixer-frequency divider uses the C-mode signal as a clock reference signal to sequentially complete mixing and frequency division.

2. The system for improving the temperature characteristics of the output frequency of a crystal oscillator according to claim 1, characterized in that, The mixer-frequency divider and the frequency-voltage conversion circuit are implemented by using an FPGA.

3. The system for improving the temperature characteristics of the output frequency of a crystal oscillator according to claim 1, wherein The temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50 Hz.

4. The system for improving the temperature characteristics of the output frequency of a crystal oscillator according to claim 1, characterized in that The frequency and feedback adjustment voltage V of the temperature sensing signal at different temperatures in the frequency-to-voltage conversion circuit t The correspondence is obtained through the following method: S1.1, disconnect the connection node between the frequency-voltage conversion circuit and the adder. S1.2, connect the output signal of the external power supply to the adder as the feedback adjustment voltage, and calibrate the feedback adjustment voltage corresponding to the temperature sensing signal with a constant frequency at different temperatures in the preset temperature range, thereby obtaining the corresponding relationship between the frequency of the temperature sensing signal and the feedback adjustment voltage Vt at different temperatures.

5. A method of improving the temperature characteristics of the output frequency of a crystal oscillator, characterized in that, The method includes the following steps: S1, control the high-stability crystal oscillator to simultaneously generate two frequency signals with different temperature characteristics: a B-mode signal and a C-mode signal, wherein the temperature sensitivity of the B-mode signal output frequency is higher than that of the C-mode signal. S2, mix the C-mode signal with the B-mode signal and then divide the frequency to obtain a temperature sensing signal, and perform frequency-voltage conversion on the temperature sensing signal to obtain a feedback adjustment voltage. S3, superimpose the feedback adjustment voltage and the control voltage outputted by the temperature control circuit in the high-stability crystal oscillator to obtain a temperature control voltage signal V c ; S4, adopt temperature control voltage signal V c The constant-temperature groove in the high-stability crystal oscillator is controlled, so that the crystal temperature in the constant-temperature groove of the high-stability crystal oscillator is kept stable. The temperature sensitivity of the B-mode signal output frequency is at least two orders of magnitude higher than that of the C-mode signal. The step S2 uses the C-mode signal as a clock reference signal to sequentially complete mixing and frequency division.

6. The method of claim 5, wherein the temperature-compensated crystal oscillator is a temperature-compensated microelectromechanical system (MEMS) crystal oscillator. The temperature sensing signal is a sinusoidal signal with a frequency not exceeding 50 Hz.

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