WO2011157025A1

WO2011157025A1 - Method and device for controlling crystal oscillator output clock

Info

Publication number: WO2011157025A1
Application number: PCT/CN2010/078049
Authority: WO
Inventors: 马凤乾
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-06-17
Filing date: 2010-10-25
Publication date: 2011-12-22
Also published as: CN102291122A

Abstract

A method and a device for controlling a crystal oscillator output clock are provided, and the method includes: when the crystal oscillator is in a normal control state, the crystal oscillator voltage-controlled voltage for controlling the crystal oscillator is stored; when the external reference clock is lost, the stored crystal oscillator voltage-controlled voltage is used to control the crystal oscillator. Using the present solution, in the case of losing the reference clock of one second output by a Global Positioning System (GPS) receiver, the crystal oscillator can still control the crystal oscillator voltage-controlled voltage, so as to achieve the effect that the clock is output as stably as possible, and the reliability of the system is improved. The method of the present solution is simple and clear, it is easy to be implemented and without additional hardware and software resource requirements, it can be as a general method, which is used by the Oven Controlled Crystal Oscillator (OCXO) and the Temperature Compensate crystal Oscillator (TCXO) having the GPS reference to continue to output the clock stably when the reference is lost, and the method of the present solution is important for a system which is very strict to the clock, such as Worldwide Interoperability for Microwave Access (WIMAX), etc.

Description

Method and device for controlling crystal oscillator output clock

Technical field

The present invention relates to the field of clock control technologies, and in particular, to a method and apparatus for controlling a crystal oscillator output clock.

Background technique

A crystal oscillator (referred to as a crystal oscillator) is widely used as a local clock source in various communication products and equipment. The role of the crystal is to provide a clock source for the device. In the case of strict clock requirements, for example, Wimax (Worldwide Interoperability for Microwave Access), which uses time division multiplexing mode, the clock is very important in the whole protocol. If the clocks in the network element are not synchronized, the network cannot be implemented. Features such as meta-synchronization and switching base stations cause users to be unable to communicate.

The local crystal oscillator is affected by temperature, aging, etc., and is stable in a short time. There will be deviation after long-term operation. At present, GPS (Global Positioning System) receiver can be used to perform algorithm processing after searching for a sufficient number of satellites. The output is stable as a reference clock to correct the local clock to make the local clock as stable as possible.

The Is pulse output by the GPS receiver is synthesized from the atomic clock signals of a plurality of satellites received, and has long-term stability. Anywhere around the globe, you can usually find around 8 satellites when the weather is good. The satellite uses an atomic clock with high precision. The GPS receiver has a solidification algorithm inside, and it outputs a stable Is. However, because the search star is affected by the external environment such as weather and hardware conditions, it can be received once in 1 second. It can't completely replace the local clock, so use the local clock to count 10M times as the local Is, and use the Iss sent by the GPS receiver to synchronize the local clock every 1 second.

As shown in Fig. 1, in the prior art, the Iss issued by the GPS receiver is used as a standard, and the clock outputted by the local crystal oscillator is counted 10 times per time as a local output of 1 s, and compared with the standard 1 s, each control cycle ( That is, calculate the variation of the control voltage of the crystal oscillator and write the period of the digital-to-analog converter of the crystal oscillator.) The deviation obtained by comparing the two Is, perform the PID (proportional-integral-derivative) operation to obtain the crystal voltage control voltage, and set the analog value of the primary crystal. Converter to adjust the output frequency of the crystal, In a closed-loop control, the crystal output clock can continuously approach the 1S sent by the GPS receiver.

The Chinese Patent Application Publication No. CN200720069790.4 discloses a GPS/NTP dual input synchronous clock, which comprises a GPS receiving unit, a time reference unit, a time keeping unit OCXO oscillator, a real time clock, a bus, at least one output card and a display card board. One end of the GPS receiving unit is connected to the GPS antenna, and the other end is connected to the reference unit. The reference unit is respectively connected to the time keeping unit OCXO oscillator and the real-time clock, and is connected to at least one output card and the display card through the bus, and is characterized in that the reference is The unit and the bus are respectively connected to the NTP input card board, and the NTP input card board is connected to the RG45 cable.

The Chinese Patent Application Publication No. CN200510055360 discloses a digital phase locking method for a clock signal in a radio remote module, and relates to a digital phase locking method for a clock signal in a radio remote module of a wideband code division multiple access (WCDMA) system, the method The digital phase-locking technology of the clock signal is the core, and the digital phase-locking is realized by the field programmable gate array (FPGA), wherein the base station extracted by the GPS receiver is a 1-cycle/second ( Is ) square wave signal or an optical transmission physical interface module. The 1 cycle/second signal generated by the 30.7MHz square wave signal is used as a reference. The OCXO output frequency is dynamically adjusted by digital phase-locking technology to obtain a long-term stable high-precision clock signal, which is the other single in the RF remote module. The board provides a high precision synchronous clock.

In summary, the existing method uses the Is output of the GPS receiver as an external reference clock to calibrate the local clock. However, in the case of losing the GPS reference, the local clock will be in an uncontrollable state and will appear after a long time of operation. deviation.

Summary of the invention

The invention provides a method and a device for controlling a crystal oscillator output clock, which can realize a stable clock when the external reference clock is lost.

In order to solve the above technical problem, a method for controlling a crystal oscillator output clock of the present invention includes: saving a crystal voltage control voltage for controlling a crystal oscillator when a crystal oscillator is in a normal control state;

When the external reference clock is lost, the crystal is controlled by the saved crystal voltage control voltage. The step of controlling the crystal oscillator by using the saved crystal voltage control voltage may be: averaging a plurality of saved crystal voltage control voltages, and using the average value as a crystal voltage control voltage pair when the external reference clock is lost. The crystal oscillator is controlled; or, the crystal oscillator voltage control voltage is selected from the saved crystal voltage control voltage as the crystal oscillator voltage control voltage when the external reference clock is lost, and the crystal oscillator is controlled.

The method may further include: setting a data storage identifier; completing the saving of the crystal voltage control voltage for controlling the crystal oscillator when the crystal oscillator is in a normal control state, setting the data storage identifier to the mark data storage completion; The step of controlling the crystal oscillator voltage control voltage to control the crystal oscillator may further include: when the external reference clock is lost, switching the crystal oscillator to a holdover state according to the data storage identifier.

In the step of storing the crystal voltage control voltage for controlling the crystal oscillator, the crystal voltage control voltage may be saved once every control period; wherein, if a plurality of crystal voltage control voltages are generated in the control period, the plurality of crystal oscillators may be voltage-controlled The voltage is averaged and the average is saved.

The method may further include: if the crystal voltage control voltage that controls the crystal oscillator when the crystal oscillator is in a normal control state is not saved, setting the data storage identifier to the flag data storage is not completed; and, when the external reference clock is lost, according to the data The memory flag switches the crystal to a free-running state.

The crystal oscillator may be a thermostatically controlled crystal oscillator (OCXO); the method may further comprise: after consuming the saved crystal oscillator voltage control voltage to control the crystal oscillator: aging the OCXO by using the saved crystal oscillator voltage control voltage calculation The de-aging coefficient of the compensation, the de-aging coefficient is accumulated with the last crystal voltage control voltage that controls the OCXO when the external reference clock is lost, and the OCXO is controlled by the accumulation result. The step of calculating the de-aging coefficient for aging compensation of the OCXO may include: reading two sets of data xj ] and x ₂ [ ] from the saved crystal voltage control voltage, and respectively averaging the two sets of data, and calculating the first Two sub-coefficient, / ₂

Calculate the first holding coefficient ^= ^ / , calculate the second holding coefficient = , ^ calculate Μ = - ^ , calculate the de-aging coefficient Δν , Δν = ^ - ^ - ; where Α is a fixed coefficient, B > 0.

The present invention also provides an apparatus for controlling a crystal oscillator output clock, comprising: an interconnected data storage module and a crystal oscillator control module;

The data storage module is configured to save the crystal voltage control voltage for controlling the crystal oscillator when the crystal oscillator is in a normal control state; The crystal control module is configured to read the saved crystal voltage control voltage from the data storage module when the external reference clock is lost, and to control the crystal oscillator by using the read crystal voltage control voltage.

The crystal control module can be configured to control the crystal oscillator by using the read crystal voltage control voltage by: averaging the read voltages of the plurality of crystal oscillators, and using the average value as the external reference clock is lost. The crystal oscillator voltage control voltage controls the crystal oscillator; or, the crystal oscillator voltage control voltage is selected from the read crystal oscillator voltage control voltage as the crystal oscillator voltage control voltage when the external reference clock is lost, and the crystal oscillator is controlled.

The device may further include an identifier setting module; the data storage module may be further configured to notify the identifier setting module that the data storage is completed after the crystal voltage control voltage for controlling the crystal oscillator is completed when the crystal oscillator is in a normal control state; It may be set to set a data storage identifier to be marked data storage completion according to the notification of the data storage module; the crystal vibration control module may be configured to switch the crystal oscillator to a holdover state according to the data storage identifier when the external reference clock is lost.对 Control the crystal with the saved crystal voltage control voltage.

In summary, the present invention enables the crystal oscillator to control the crystal voltage control voltage in the case of losing the 1-second reference clock output from the GPS receiver, thereby achieving the effect of stabilizing the output clock as much as possible, and improving the reliability of the system. . The method provided by the invention is simple and clear, easy to implement and has no additional hardware and software resource requirements, and can be used as a GPS reference thermostat controlled crystal oscillator (OCXO), temperature compensated crystal oscillator (TCXO) crystal oscillator to continue stable output when the reference is lost. A general method under the clock is important for systems such as wimax that have very strict clock requirements.

BRIEF abstract

1 is a schematic diagram of controlling a crystal oscillator by using an Is clock outputted by a GPS receiver as a reference in the prior art;

2 is a flowchart of a method for controlling a crystal oscillator output clock according to an embodiment of the present invention;

3 is a flow chart of a method for controlling an OCXO crystal oscillator according to an embodiment of the present invention;

FIG. 4 is a structural diagram of an apparatus for controlling a crystal oscillator output clock according to an embodiment of the present invention.

Preferred embodiment of the invention

In the embodiment, when the Is output of the GPS receiver is lost as the reference clock, The crystal oscillator continues to output the clock steadily to overcome the influence of the crystal oscillator when the reference clock is lost, which can increase the reliability of the device.

At present, when the Is output of the GPS receiver is used as the reference clock, the state of the crystal oscillator can be divided into: preheating, coarse tuning, fine tuning 1, fine tuning 2, and free oscillation.

Preheating means: When the board starts to power on, the GPS receiver and the CPU of the board perform the preparation process of the message response. This process does not perform phase discrimination and voltage control of the crystal oscillator.

In the case that the GPS receiver completes initialization, receives satellite signal normal, continuous 10s state is 3D FIX or TIME mode, and Is error-free, the crystal preheating phase is terminated. If there is an external reference clock, the crystal oscillator is controllable, and the crystal oscillator may enter. The status is: coarse, fine 1 and fine 2.

Coarse adjustment refers to the first stage of the normal crystal oscillator control process after the GPS receiver has completed initialization. After the crystal control enters the coarse adjustment state, the crystal oscillator constantly adjusts the local Is, and constantly moves closer to the GPS standard Is. According to the range of the crystal voltage control voltage average obtained in one control cycle, and the change trend between adjacent control cycles, the crystal state is switched between coarse adjustment, fine adjustment 1 and fine adjustment 2 correspondingly. , Fine tuning 2 has the highest clock accuracy.

Free oscillation means that the crystal oscillator cannot be controlled, and the crystal oscillator is free to run. At this moment, the clock output of the crystal oscillator is unusable. For the wimax base station, all the terminals are off-grid at the moment, and all access and handover fail. In the prior art, the crystal oscillator enters a free oscillation state in the event that the external reference clock is lost.

In the case that the crystal oscillator loses the external reference clock, if the clock is to be kept as stable as possible, it is necessary to continue to control the crystal voltage control voltage, and the crystal voltage control voltage should be as close as possible to the voltage data of the crystal oscillator during normal control, from the Is state. That is, when the external reference clock is lost, the crystal oscillator still tries not to deviate from Is to maintain the stability of the clock.

Therefore, this embodiment considers adding a state to the crystal oscillator: the holdover state, which is a state in which the crystal oscillator can stably output the clock when the crystal oscillator loses the reference clock, and can compensate for the aging of the crystal oscillator to stabilize the output clock of the crystal oscillator.

In order to enable the crystal to enter the holdover state, the precondition is that when there is a GPS external reference and the crystal oscillator is in the fine adjustment 2 state, the crystal voltage control voltage data is stored, and the data is called holdover data. When Is without the GPS receiver output is used as an external reference, if the required holdover data is stored, it enters the holdover state; if it is not stored, it enters the free-running state. The present embodiment will be described in detail below with reference to the accompanying drawings.

2 is a method for controlling a crystal oscillator output clock according to an embodiment of the present invention, including:

201 : Stores the holdover data when the crystal oscillator is in a normal control state (such as fine tuning 2); in the case of the GPS receiver stable output Is, according to the result of the GPS output Is and the local Is phase, according to the PID (proportional-integral The -differential algorithm calculates the crystal voltage control voltage in each control cycle, and sends the calculated crystal voltage control voltage to the digital-to-analog converter of the crystal oscillator, and the output frequency of the crystal oscillator is adjusted by the digital-to-analog converter to control the output clock of the crystal oscillator . When the crystal is in fine state 2, the crystal oscillator is in the state of stable output clock. Therefore, the crystal voltage control voltage at fine tuning 2 is stored as holdover data.

The holdover data can be stored once per control cycle, and each second of each control cycle is phase-detected. If the control period is 5 seconds, five crystal voltage-controlled voltages are generated, and the average of the five voltages is obtained. A holdover data, the crystal voltage control voltage as holdover data can be stored in an array of memory.

202: After completing the data storage, setting a data storage identifier, marking the holdover data storage is completed;

203: When the crystal oscillator loses the external reference clock, judge whether the holdover data is stored according to the data storage identifier, and if the required holdover data has been stored, switch the crystal oscillator to the holdover state;

When the GPS receiver is affected by the outside world, if there are less than 4 search stars or abnormal antenna feeds, it may cause the Is output of the GPS receiver to disappear, that is, the external reference clock is lost.

The crystal can be switched to the holdover state when the external reference clock is lost for a specified period of time, such as 10 seconds, to maintain the local clock without interruption, and maintain the normal output of the clock.

If the required holdover data is not stored, the crystal oscillator is switched to the free-running state.

204: Use the stored holdover data to control the crystal.

In this embodiment, a plurality of stored holdover data may be averaged, and the obtained average value is used as a crystal oscillator voltage control voltage to control the crystal oscillator, and data may be selected from the stored holdover data as crystal oscillator voltage control. Voltage, control of the crystal.

The current indicator is that within 1 hour, the local Is deviation is within 800ns, making The NE clock can be kept in sync.

Application example 1 :

The method of this embodiment will be described below by taking an example of controlling the OCXO crystal.

The OCXO crystal oscillator is large in size and has a temperature compensation circuit inside, which can be used as the source of the clock module. As a high-precision frequency source, OCXO is applied to the clock reference of various devices and the hold mode of the base station. Base stations, time servers, high-precision instrumentation, and military communication equipment such as GSM, CDMA2000, TD-SCDMA, and WCDMA.

According to the characteristics of the crystal oscillator, the crystal voltage control voltage can be calculated to the maximum extent that the crystal oscillator output clock deviates from the standard Is by no more than 1575 ns. After the crystal oscillator loses the reference, it can still be locked for a long period of time, ensuring stable and reliable clock. Output.

The OCXO crystal oscillator is characterized by different curves at different time periods, but the aging trend is always the same. In the holdover state, the aging trend is compensated and the aging compensation is returned. According to the results of the experimental study, by storing 442 holdover data, the crystal voltage control voltage that compensates for the aging of the crystal oscillator can be calculated, so that the crystal oscillator can be controlled with the most precise control, so that a stable clock can still be output. 442 holdover data is stored. When the control period is 10 seconds, it takes 4420 seconds to store the required holdover data. If it is full, it will be re-stored from the lowest space to prepare for the application after the OCXO crystal enters the holdover state.

For the OCXO crystal oscillator, after losing the reference clock and entering the holdover state, a timer can be started, which is incremented every 1 second to facilitate the phased operation of the holdover data. As shown in Figure 3, the method for controlling the crystal output clock includes:

301: Read multiple holdover data (such as 10) from the holdover data stored before entering the holdover state, and store them in the holdover array 1;

The readover data read is preferably the most recently stored data.

302: From the holdover data stored before entering the holdover state, the same amount of holdover data that is not repeated in the holdover array 1 is read and stored in the holdover array 2;

303: Find the accumulated sum of the data in the holdover array 1 and the holdover array 2, respectively;

304 : For the two accumulated sums divided by the number of data stored in the array, the holdover mean 1 ( χ _λ ) and the holdover mean 2 ( x ₂ ) are obtained; 305: Enable a counter, the initial count value is 0, subtract the first data of the holdover array 1 to obtain the difference 1, and subtract the fixed coefficient A (for example, 108.5) from the counter value to obtain the difference 2, and obtain the difference. 1 is the product of the difference 2, added to the first sub-coefficient ( ^ ) (the initial value is 0); 求 Use the same method to find the second sub-coefficient ( ) for the holdover array 2; subtract the fixed coefficient from the count value A, square the difference, add the result to the parent coefficient ( ^ ) (the initial value of ^ is 0), and add 1 to the counter, repeat the above operation;

For example, divide 442 holdover data into two groups [221] and x ₂ [221], where χ ₂ [221] is the most recent data, and Β is used to indicate the number of repeated executions, Β>0, in this example Β= 117.

Step 304 can be expressed as:

Step 305 can be expressed as:

^ =∑(X [i]-^)(i -108.5)

i=0

k ₂ =∑(x ₂ [i]-Y ₂ )(i-\0S.5)

i=0 i=0

306: Calculate the mean value of the latest plurality of data in all the retained data, and obtain the crystal voltage control voltage V after rounding off, write a digital analog controller of the crystal oscillator to control the primary crystal;

For example, the operation can be performed at a time of 160 seconds, etc., and the plurality of data used can be the latest 36 data of all the stored holdover data.

307: Divide by ^ to obtain the first holdover coefficient ( ), divide by to obtain the second holdover coefficient ( ), and subtract to obtain M;

Step 307 can be expressed as:

= I ^m^i = k ₂ 1 k _m , /k = k ₂ -k _x ,

308: The de-aging coefficient Δν will be obtained, and Δν will be accumulated with the previous crystal voltage control voltage V. After rounding off, the digital analog controller will be used to write the crystal oscillator as the crystal voltage control voltage to control the crystal oscillator.

Step 308 can be performed at 4400 seconds. Application example 2:

The TCXO uses an additional temperature compensation circuit to reduce the amount of oscillation frequency variation caused by ambient temperature changes to achieve a crystal oscillator that satisfies the stability requirements over a wide temperature range. TCXO has the advantages of high stability, small size, low power consumption, etc. It is mainly used in wireless small base stations, navigation equipment and wireless terminals.

For 60 data stored in the TCXO crystal, the crystal voltage control voltage that compensates for the aging of the crystal can be calculated. If the control period is 5 seconds, it takes 300 seconds to store the required holdover data.

Since the TCXO crystal oscillator can only be stabilized for a short period of time, the aging tendency of the crystal oscillator is not fixed. Therefore, after losing the reference to enter the holdover state, only the average value of the stored holdover data needs to be averaged, and the obtained mean value is rounded off. As the crystal oscillator voltage-controlled voltage is written into the crystal oscillator DAC, the primary crystal oscillator is controlled. According to the measured results, the average value of 60 data can be kept within 1 Hz within one hour. If the holding time is controlled, The number of holdover data for which the mean is averaged can be selected as needed.

As shown in FIG. 4, the embodiment further discloses an apparatus for controlling a crystal oscillator output clock, comprising: a data storage module connected to each other, a crystal oscillator control module, and an identifier setting module;

The data storage module is configured to save the crystal voltage control voltage for controlling the crystal oscillator when the crystal oscillator is in a normal control state; after the storage of the crystal oscillator voltage control voltage is completed, the notification flag setting module data is saved.

The identification setting module is configured to set a data storage identifier to mark data storage completion according to the notification of the data storage module.

The crystal oscillator control module is configured to switch the crystal oscillator to the holdover state according to the data storage identifier when the external reference clock is lost, read the saved crystal oscillator voltage control voltage from the data storage module, and use the read crystal oscillator voltage control voltage to the crystal oscillator. Take control. The crystal control module uses the read crystal oscillator voltage control voltage to control the crystal oscillator by: averaging the read voltage voltages of the plurality of crystal oscillators, and using the average value as the crystal oscillator voltage control when the external reference clock is lost. The voltage controls the crystal oscillator; or selects the crystal voltage control voltage from the read crystal voltage control voltage as the crystal oscillator voltage control voltage when the external reference clock is lost. One of ordinary skill in the art will appreciate that all or a portion of the above steps may be performed by a program to instruct the associated hardware, such as a read only memory, a magnetic disk, or an optical disk. Alternatively, all or part of the steps of the above embodiments may also be implemented using one or more integrated circuits. Correspondingly, each module/unit in the foregoing embodiment may be implemented in the form of hardware, or may be implemented in the form of a software function module. The invention is not limited to any specific form of combination of hardware and software.

Industrial applicability

Compared with the prior art, the invention enables the crystal oscillator to control the crystal voltage control voltage in the case of losing the 1-second reference clock outputted by the GPS receiver, thereby achieving the effect of stabilizing the output clock as much as possible, and improving the system. reliability.

Claims

Claim

1. A method of controlling a crystal oscillator output clock, comprising:

Saving a crystal pressure control voltage that controls the crystal oscillator while the crystal oscillator is in a normal control state;

When the external reference clock is lost, the crystal is controlled by the saved crystal voltage control voltage.

2. The method of claim 1, wherein the step of controlling the crystal with the saved crystal voltage control voltage comprises:

A plurality of saved crystal voltage control voltages are averaged, and the obtained average value is controlled as a crystal voltage control voltage when the external reference clock is lost; or

The crystal oscillator is controlled by selecting a crystal voltage control voltage from the stored crystal voltage control voltage as a crystal voltage control voltage when the external reference clock is lost.

3. The method according to claim 1 or 2, further comprising: setting a data storage identifier; completing the saving of the crystal voltage control voltage for controlling the crystal oscillator when the crystal oscillator is in a normal control state, storing the data The identity is set to mark the data storage completion;

The method further includes: before the step of controlling the crystal oscillator by using the saved crystal oscillator voltage control voltage, when the external reference clock is lost, switching the crystal oscillator to a hold holdover state according to the data storage identifier.

4. The method according to claim 1 or 2, wherein

In the step of storing the crystal voltage control voltage for controlling the crystal oscillator, the crystal voltage control voltage is saved once for each control period; wherein, if a plurality of crystal voltage control voltages are generated in the control period, the plurality of crystal oscillators are voltage-controlled The voltage is averaged and the average value obtained is saved.

5. The method of claim 3, further comprising:

If the crystal oscillator voltage control voltage for controlling the crystal oscillator is not saved when the crystal oscillator is in a normal control state, setting the data storage identifier to the mark data storage is not completed; When the external reference clock is lost, the crystal oscillator is switched to a free oscillation state according to the data storage identifier.

6. The method of claim 2, wherein

The crystal oscillator is a thermostatically controlled crystal oscillator OCXO;

After the step of controlling the crystal oscillator by using the saved crystal oscillator voltage control voltage, the method further includes: calculating a de-aging coefficient for aging compensation of the OCXO by using the saved crystal oscillator voltage control voltage, and de-aging the OCXO The coefficient is summed with the last crystal voltage control voltage that controls the OCXO when the external reference clock is lost, and the OCXO is controlled by the accumulated result.

7. The method of claim 6, wherein the step of calculating a de-aging coefficient for aging compensation of the OCXO comprises:

Two sets of data xj ] and χ ₂ [ ] are read from the saved crystal voltage control voltage, and the two sets of data are respectively averaged ^ and ^, and the first sub-coefficient is calculated ^ = ∑(^[ ] -^) ( -^ , calculate the second sub-coefficient ^ , Λ ₂

² ) Calculate the first holding coefficient, I^kk^ calculate the second holding coefficient = k ₂ ik _m ,

Where Α is a fixed coefficient and B > 0.

8. A device for controlling a crystal oscillator output clock, comprising: an interconnected data storage module and a crystal control module; wherein

The data storage module is configured to save a crystal voltage control voltage for controlling the crystal when the crystal oscillator is in a normal control state;

The crystal oscillator control module is configured to read the saved crystal oscillator voltage control voltage from the data storage module when the external reference clock is lost, and to control the crystal oscillator by using the read crystal oscillator voltage control voltage.

9. The apparatus of claim 8, wherein the crystal oscillator control module is configured to control the crystal oscillator by using the read crystal oscillator voltage control voltage in the following manner:

Average the voltage control voltages of the multiple crystals read, and take the average value as the loss of the external reference The crystal oscillator is controlled by the crystal voltage control voltage when the clock is tested; or

The crystal oscillator is controlled by selecting a crystal voltage control voltage from the read crystal voltage control voltage as a crystal voltage control voltage when the external reference clock is lost.

10. The apparatus of claim 8 or 9, further comprising an identification setting module;

The data storage module is further configured to: after saving the crystal oscillator voltage control voltage that controls the crystal oscillator when the crystal oscillator is in a normal control state, notify the identifier setting module that data storage is completed; and the identifier setting module is configured to be configured according to The notification of the data storage module sets a data storage identifier to be completed for marking data storage;

The crystal oscillator control module is configured to control the crystal oscillator by using the saved crystal oscillator voltage control voltage after switching the crystal oscillator to a hold holdover state according to the data storage identifier when the external reference clock is lost.