CN104836578A - Device and method for improving long-term stability of crystal oscillator - Google Patents

Abstract

The invention relates to a device and method for improving the long-term stability of a crystal oscillator, and the device comprises a constant temperature crystal oscillator, a frequency divider, a phase discriminator, a reference voltage source, and a comparator, wherein the constant temperature crystal oscillator is connected with the frequency divider. The input end of the phase discriminator is connected with the output end of the frequency divider. The inverted input end, in-phase input end and output end of the comparator are respectively connected with the output end of the phase discriminator, the reference voltage source, and the voltage-controlled voltage end of the constant temperature crystal oscillator. The method comprises the steps: carrying out pilot frequency discrimination of two frequency-dividing signals with different times through the phase discriminator; comparing a frequency discrimination voltage of the phase discriminator with a reference voltage through the comparator; generating an error signal voltage, and enabling the error signal voltage to act on the voltage-controlled voltage end of the constant temperature crystal oscillator for feedback adjustment, thereby completing the automatic adjustment of the output frequency of the constant temperature crystal oscillator, enabling the output frequency of the constant temperature crystal oscillator to be maintained at a fixed frequency so as to improve the long-time stability of frequency.

Description

A kind of apparatus and method improving crystal oscillator long-term stability

Technical field

The present invention relates to a kind of device improving crystal oscillator long-term stability, a kind of device applying the raising crystal oscillator long-term stability of microlock loop technique of special design.

Background technology

Modern society, in various fields such as satellite navigation, communication, broadcast, radar, precise guidance, electronic countermeasures, remote-control romote-sensings, crystal oscillator is all absolutely necessary parts, and requires more and more higher for the frequency accuracy of crystal oscillator.

Industry has utilized technique for temperature compensation to devise constant-temperature crystal oscillator (OCXO), and its frequency stability has had great improvement.But As time goes on, even constant-temperature crystal oscillator, its frequency accuracy also can run down, its main cause comprises the imbalance etc. of the change of aging, external environment, voltage-controlled voltage.The main cause that crystal oscillator is aging is mass effect and stress effect, is inevitable error term, and external environment changes, voltage-controlled voltage offsets, is equally also inevitable.Therefore, after crystal resonator uses a period of time, its frequency accuracy must worsen.But be no matter any factor in the imbalance of aging, external environment change, voltage-controlled voltage, or the frequency accuracy that acting in conjunction causes worsen, and can carry out its frequency shift (FS) of compensation for calibrating errors by the voltage-controlled terminal voltage adjusting crystal resonator.

Current crystal oscillator is in order to obtain higher long-term frequency stability, and the technical method of employing mainly contains:

(1) VCXO based on GPS and Beidou dual-mode time service is calibrated

The corrected signal of 1pps is obtained after utilizing 1pps (the Pulse Per Second) signal and crystal oscillator frequency division that in GPS or dipper system, stability is higher, corrected signal is carried out to the process such as frequency discrimination, filtering, EFC (Electrical Frequency Control), then the error voltage numerical value obtained is sent into D/A converter and be converted to magnitude of voltage, this magnitude of voltage is sent into the tuning end of crystal oscillator, revises the frequency shift (FS) of crystal oscillator.

Based on the calibration steps of the VCXO of GPS and Beidou dual-mode time service for very effective special crystal oscillator calibration system, but when the crystal oscillator be applied on the tester such as frequency counter, pulse modulation domain analysis instrument needs calibration.The method integrated level is limited, is unfavorable for being integrated in the printed board of limited space.

(2) digital frequency stabilization compensates

Output frequency during by working to crystal oscillator is measured for a long time, simulate the aging curve of crystal oscillator, graphical analysis processing method is utilized to generate one group of time to the array of frequency values according to ageing rate curve, calculate corresponding ageing rate DAC array by control system, thus digital frequency stabilization compensation is carried out to the frequency of crystal oscillator.

It is that the matching carried out the aging curve of crystal oscillator compensates that digital frequency stabilization compensates, and the aging curve of every crystal oscillator under same process is also not quite similar, and the method for this compensation also can only be roughly be similar to, and is not suitable for the application that accuracy requirement is high.

(3) BVA crystal oscillator

Make BVA quartz resonator (electrodeless formula resonator) by tight technique, because BVA quartz resonator does not exist electrode film stress burn-in effects, its surface loss greatly reduces.Adopt the BVA quartz resonator that SC cutting is done, the frequency stability of its crystal oscillator reach 10-14/s, day frequency stability reach 5 × 10-12/d, the performance index of its performance index closely atomic clock.

But the process conditions made due to BVA oscillator require extremely harsh, and its cost of manufacture is expensive, and its technological process is complicated, is not suitable for batch production and uses widely.

Therefore there are the needs that a kind of structure of exploitation is simple, cost of manufacture is cheap and improve the device of crystal oscillator output frequency long-term stability.

Summary of the invention

For providing that a kind of structure is simple, cost of manufacture is cheap and improving the device of crystal oscillator output frequency long-term stability, the present invention by the following technical solutions.

The device of the raising crystal oscillator long-term stability in the present invention, it comprises constant-temperature crystal oscillator, frequency divider, phase discriminator, reference voltage source and comparator;

Described constant-temperature crystal oscillator is connected with described frequency divider, and described frequency divider carries out to the output frequency of described constant-temperature crystal oscillator the frequency division that two have different frequency dividing ratio;

The input of described phase discriminator is connected with the output of described frequency divider, and described phase discriminator carries out frequency discrimination to the first fractional frequency signal exported by described frequency divider and the second fractional frequency signal;

The reverse input end of described comparator is connected the output of described phase discriminator and described reference voltage source respectively with input in the same way, its output connects the voltage-controlled voltage end of described constant-temperature crystal oscillator, the reference voltage that the discriminating voltage of the more described phase discriminator of described comparator and described reference voltage source provide and output error signal voltage to the voltage-controlled voltage end of described constant-temperature crystal oscillator, to regulate the output frequency of described constant-temperature crystal oscillator.

According to one preferred embodiment, described device also comprises filter, and described filter is arranged between the output of described comparator and the voltage-controlled voltage end of described constant-temperature crystal oscillator.

According to one preferred embodiment, described device also comprises microprocessor, switch, ad/da converter;

Wherein, described microprocessor is connected with the output of described filter by the AD circuit of ad/da converter, is connected with an input of switch by the DA circuit of ad/da converter; The control end of described switch is connected with described microprocessor, and its another input is connected with the output of described filter, and its output is connected with the voltage-controlled voltage end of described constant-temperature crystal oscillator; Switch phase lock circuitry access to make described timing microprocessor ground control switch and withdraw from.

According to one preferred embodiment, the frequency discrimination interval of described phase discriminator comprises the frequency of the first fractional frequency signal and the second fractional frequency signal all the time, and the dead band of described phase discriminator is less than the difference in the equivalent phase demodulation cycle of described first fractional frequency signal and the second fractional frequency signal all the time.

A kind of method utilizing device of the present invention to improve crystal oscillator long-term stability, the method is frequency divider according to the different frequency dividing ratio of its two of arranging, two frequency divisions are carried out to the output frequency of constant-temperature crystal oscillator, and exports the first fractional frequency signal and the second fractional frequency signal to phase discriminator;

Described phase discriminator exports corresponding discriminating voltage to comparator according to described first fractional frequency signal to the frequency difference of the second fractional frequency signal;

Described comparator compares the in-phase input end voltage inputted by reference voltage source and the reverse input end voltage inputted by described phase discriminator, and exports the voltage-controlled voltage end of corresponding error voltage to described constant-temperature crystal oscillator;

Described error voltage regulates the output frequency of described constant-temperature crystal oscillator and the stability of described constant-temperature crystal oscillator is locked on the reference voltage of described reference voltage source.

According to one preferred embodiment, between the output and the voltage-controlled voltage end of described constant-temperature crystal oscillator of described comparator, filtering is carried out to error voltage, to reduce the alternating current component of the error voltage that described comparator exports.

According to one preferred embodiment, phase lock circuitry is periodically accessed or removes, to reduce mutually the make an uproar impact of described phase lock circuitry on constant-temperature crystal oscillator.

According to one preferred embodiment, under the condition that the dead band of the output frequency of described constant-temperature crystal oscillator and its Stability index and phase discriminator is certain, the ratio range between two different frequency dividing ratios of described frequency divider is determined.

Beneficial effect of the present invention is: the present invention completes the self-control to constant-temperature crystal oscillator frequency accuracy by the negative feedback of alien frequencies phase lock circuitry and phase-locked loop thereof, and the stability of its output frequency is locked on reference voltage source, substantially increase the long-term stability of constant-temperature crystal oscillator, and structure is simple, with low cost, the application demand in many fields can be met.

Accompanying drawing explanation

Fig. 1 is the schematic diagram that the present invention improves crystal oscillator long-term stability device;

Fig. 2 is apparatus of the present invention first embodiment schematic diagram;

Fig. 3 is the transfer function block diagram of apparatus of the present invention first embodiment;

Fig. 4 is apparatus of the present invention second embodiment schematic diagram;

Fig. 5 is the waveform schematic diagram of fractional frequency signal in the present invention;

Fig. 6 is the waveform schematic diagram of discriminating voltage in the present invention;

Fig. 7 is the waveform schematic diagram of medial error signal voltage of the present invention.

Reference numerals list

1: constant-temperature crystal oscillator 2: frequency divider 3: phase discriminator

4: reference voltage source 5: comparator 6: filter

7: microprocessor 8: switch 9:AD/DA transducer

Embodiment

Be described in detail below in conjunction with accompanying drawing.

Fig. 1 is the schematic diagram that the present invention improves crystal oscillator long-term stability device, and it comprises constant-temperature crystal oscillator 1, frequency divider 2, phase discriminator 3, reference voltage source 4 and comparator 5; Constant-temperature crystal oscillator 1 is connected with the input of frequency divider 2, and the input of phase discriminator 3 is connected with the output of frequency divider 2, and phase discriminator 3 receives the fractional frequency signal that frequency divider 2 transmits; The reverse input end of comparator 5 is connected output and the reference voltage source 4 of phase discriminator 3 respectively with input in the same way, and the output of comparator 5 connects the voltage-controlled voltage end of constant-temperature crystal oscillator 1.

The operation principle of raising crystal oscillator long-term stability device of the present invention: frequency divider 2 pairs of constant-temperature crystal oscillator 1 output frequencies have the frequency division of different frequency dividing ratio, and export the first fractional frequency signal and the second fractional frequency signal to phase discriminator 3; Phase discriminator 3 exports corresponding discriminating voltage to comparator 5 according to the first fractional frequency signal to the difference on the frequency of the second fractional frequency signal; The discriminating voltage that the reference voltage of comparator 5 benchmark voltage source 4 and phase discriminator 3 export also exports the voltage-controlled voltage end of corresponding error voltage to constant-temperature crystal oscillator 1, to regulate the output frequency of described constant-temperature crystal oscillator.

Fig. 2 is the schematic diagram of apparatus of the present invention first embodiment, the present embodiment increases filter 6 in the foundation structure of apparatus of the present invention, filter 6 is arranged between the output of comparator 5 and the voltage-controlled voltage end of constant-temperature crystal oscillator 1, the error voltage exported by filter 6 pairs of comparators 5 carries out filtering, the alternating current component of error voltage can be reduced, contribute to the accuracy improving error voltage.

Fig. 3 is the transfer function block diagram of apparatus of the present invention first embodiment, wherein, and V_reffor the reference voltage that reference voltage source 4 provides, V_dfor the discriminating voltage that phase discriminator 3 exports, V_efor the error voltage that comparator 5 exports, V_tfor tuning voltage relevant to error voltage after filter 6 filtering, K is the gain amplifier of comparator 5, the transfer function that F (S) is filter 6, f_outfor the output frequency of constant-temperature crystal oscillator 1, θ₀for the output phase place of constant-temperature crystal oscillator 1, θ₁and θ₂the frequency dividing ratio being respectively frequency divider 2 output is the phase place of the fractional frequency signal of M and N.

Theoretical according to the Laplace transform of classical phase-locked loop, there is following relation.

θ₀＝K₀*V_t(s)/s (1)

V_t(s)＝K*F(s)*V_e(s) (2)

V_e(s)＝V_ref(s)-V_d(s) (3)

V_d(s)＝K_d*(θ₁(s)-θ₂(s))＝K_d*θ₀(s)*(1/M-1/N) (4)

Wherein, K₀for the gain factor of constant-temperature crystal oscillator, K_dfor the gain of phase discriminator frequency discrimination.

Therefore, open-loop transfer function G (s) obtained at the input of comparator 5 is:

G(s)＝V_d(s)/V_e(s)＝[K_d*(1/M-1/N)*K₀*K*F(s)]/s (5)

According to above-mentioned equation, qualitative analysis is carried out to the closed loop transfer function, of phase lock circuitry, wherein, work as f_outduring increase, be the integration of frequency according to mathematical relationship phase place, then θ₀increase; Due to θ₀increase, according to equation 4, V_dincrease; Due to V_dincrease, according to equation 3, V_ereduce; Due to V_ereduce, according to equation 2, V_treduce; Due to V_treduce, according to the voltage-controlled voltage end voltage of constant-temperature crystal oscillator 1 and the positive correlation of its output frequency, f_outreduce.

In like manner, f is worked as_outduring reduction, the result after closed loop transfer function, transmission is f_outincrease.So the phase-locked loop of alien frequencies phase lock circuitry of the present invention has negative feedback, simultaneously due to the negative feedback of phase-locked loop, the output frequency of constant-temperature crystal oscillator 1 just only and V_refrelevant, thus reach f_outthe object of Selfstabilizing.

When the element in alien frequencies phase lock circuitry of the present invention is determined, i.e. K₀, K_d, the value of K is all determined, only needs the value selecting M and N, can provide the long-term stability of constant-temperature crystal oscillator 1.Therefore, alien frequencies phase lock circuitry structure of the present invention is simple, selects suitable element as required, can reduce costs to a certain extent.

Fig. 4 is the schematic diagram of apparatus of the present invention second embodiment, and the present embodiment increases microprocessor 7, switch 8, ad/da converter 9 on the basis of the first embodiment, to realize the timing access of phase lock circuitry and to remove.

Wherein, the I/O port of microprocessor 7 is corresponding with the FPDP of ad/da converter 9 to be connected, the I/O port of the D11 ~ D15 of microprocessor 7 is connected with the output of filter 6 by the AD circuit of ad/da converter 9, and the I/O port of the D21 ~ D25 of microprocessor 7 is connected with an input of switch 8 by the DA circuit of ad/da converter 9; The control end of switch 8 is connected with microprocessor 7, and another input of switch 8 is connected with the output of filter 6, and the output of switch 8 is connected with the voltage-controlled voltage end of constant-temperature crystal oscillator 1; With make microprocessor 7 periodically control switch 8 switch phase lock circuitry access and withdraw from.Thus reduce alien frequencies phase lock circuitry to the impact of making an uproar mutually of constant-temperature crystal oscillator 1.

Concrete, microprocessor 7 starts according to setting-up time timing, and phase lock circuitry is access state, and the output of filter 6 is connected with the voltage-controlled voltage end of constant-temperature crystal oscillator 1, realizes the regulation and control of error voltage to the output frequency of constant-temperature crystal oscillator 1.After self-control completes, microprocessor 7 reads this tuning voltage V by the AD circuit of ad/da converter 9_tand store, then export V by the DA circuit of ad/da converter 9_o(V_o=V_t) keep the voltage-controlled voltage end of constant-temperature crystal oscillator 1 to be in calibration after state, when microprocessor 7 reach setting-up time time, microprocessor 7 exports the control end that controls signal to switch 8, switch 8 state switches, the DA circuit of ad/da converter 9 is connected with the voltage-controlled voltage end of constant-temperature crystal oscillator 1, removes by phase-locked loop circuit.Microprocessor 7 in the present embodiment can adopt ARM9 series microprocessor.

Phase discriminator 3 in the present invention can adopt ADF4002, and frequency divider 2 can be integer frequency divider, also can be decimal frequency divider or DDS (direct digital synthesis technique) device etc.Comparator 5 can adopt OP184.Filter 6 can adopt second-order low-pass filter.

Wherein, usually because phase discriminator 3 can exist dead band, namely when the difference in the equivalent phase demodulation cycle of two input signals is less than dead band, phase discriminator 3 will lose the output of this part phase discriminating pulse, causes frequency difference or the difference information that intactly can not react input signal.

As shown in Figure 5, in alien frequencies phase demodulation process, the frequency of the first fractional frequency signal and the second fractional frequency signal is f₁and f₂, and f₁≠ f₂, f₁=A*f_c, f₂=B*f_c, f_cfor f₁and f₂greatest common factor (G.C.F.) frequency, f₀=A*B*f_c, T₀=1/A*B*f_c, f₀for equivalent phase demodulation frequency, T₀for the equivalent phase demodulation cycle.

The process that apparatus of the present invention lock at alien frequencies can make f₁* B=f₂* A equation is set up, i.e. f₁and f₂the equivalent phase demodulation cycle equal and equal T₀, the phase demodulation voltage V that phase discriminator 3 exports_dbe a fixing AC wave shape, after device 6, obtain a fixing tuning voltage V after filtering_t.

If in locking process, f₁* B=f₂* A equation is false, equivalent phase demodulation frequency f₀aC wave shape can change, tuning voltage V_tsize also correspondingly change the output frequency size of regulating thermostatic crystal oscillator 1, make f₁* B=f₂* A equation is set up, and completes alien frequencies locking; And when phase demodulation, due to the equivalent phase demodulation cycle T of the first fractional frequency signal and the second fractional frequency signal₀₁and T₀₂closely, situation that rising edge arrives simultaneously can be there is and make phase discriminator 3 in the time range in dead band, there is no the output of phase demodulation voltage, causing the output frequency error of constant-temperature crystal oscillator 1.

Therefore, for ensureing that phase discriminator 3 can react the minor variations of the difference on the frequency of the first fractional frequency signal and the second fractional frequency signal, the dead band of phase discriminator 3 should be less than the difference in the equivalent phase demodulation cycle of the first fractional frequency signal and the second fractional frequency signal all the time.Thus ensure the accuracy of the discriminating voltage that phase discriminator 3 exports.

Based on the inventive concept identical with device of the present invention, the present invention also provides a kind of method utilizing apparatus of the present invention to improve crystal oscillator long-term stability, and embodiment see the embodiment of device of the present invention, can repeat no more herein.

In composition graphs 1, the present invention improves the general principle figure of crystal oscillator long-term stability device, the invention provides a kind of method utilizing apparatus of the present invention to improve crystal oscillator long-term stability to be:

By frequency divider 2 according to the different frequency dividing ratio of its two of arranging, two frequency divisions are carried out to the output frequency of constant-temperature crystal oscillator 1, and export the first fractional frequency signal and the second fractional frequency signal to phase discriminator 3.

Corresponding discriminating voltage is exported to comparator 5 according to the first fractional frequency signal to the frequency difference of the second fractional frequency signal by phase discriminator 3; Compare the in-phase input end voltage inputted by reference voltage source 4 and the reverse input end voltage inputted by phase discriminator 3 by comparator 5 again, and export the voltage-controlled voltage end of corresponding error voltage to constant-temperature crystal oscillator 1; Carry out the output frequency of regulating thermostatic crystal oscillator 1 by error voltage and the stability of constant-temperature crystal oscillator 1 be locked on the reference voltage of reference voltage source 4.

Concrete, as Fig. 5, wherein, the frequency of the first fractional frequency signal that frequency divider 2 exports and the second fractional frequency signal is respectively f₁and f₂.Because phase discriminator 3 carries out error output by the rising edge comparison of f1 and f2, phase discriminator 3 is when the rising edge of the first fractional frequency signal, and phase detector output signal puts 1, when the rising edge of the second fractional frequency signal, phase detector output signal sets to 0, and finally obtains equivalent frequency discrimination frequency f₀.

As Fig. 6, wherein, U_mfor the minimum voltage of discriminating voltage, V_ppfor the crest voltage of discriminating voltage.No matter phase discriminator 3 adopts the method for average pulse or the method for pulse sampling, the discriminating voltage V that phase discriminator 3 exports_dit will be an one group of sawtooth waveform presenting mechanical periodicity.

As Fig. 7, wherein, at comparator 5 by comparing discriminating voltage V_dand reference voltage V_refafter, and correspondingly output error signal voltage V_e, its process is for passing through reference voltage V_refby discriminating voltage V_dsawtooth waveform move down U_mvoltage, and the error voltage V obtained_etake no-voltage as the periodically variable sawtooth waveform of minimum voltage, i.e. V_e=V_d-V_ref=V_d-U_m; Therefore, error voltage V_ealso be one group of sawtooth waveform in mechanical periodicity.

In conjunction with the first embodiment of the present invention, to error voltage V between the output and the voltage-controlled voltage end of constant-temperature crystal oscillator 1 of comparator 5_ecarry out filtering, error voltage V_etuning voltage V is obtained after filtering after device 6_t, wherein, tuning voltage V_tfor error voltage V_ethe more level and smooth direct voltage obtained after filtering radio-frequency component and error component, the size of this voltage and V_ecycle is relevant with peak value, is the equal of error voltage V_ethe effect of effective value voltage.

Further, when phase lock circuitry does not lock completely, f₁and f₂not the proportionate relationship in strict accordance with setting, small phase deviation can be there is, then can make error voltage V_ecycle and peak value change, thus pass through V_tthe output frequency controlling constant-temperature crystal oscillator is tending towards locking; And when after phase lock circuitry locking, system just forms negative feedback loop, f₁and f₂strict satisfied set proportionate relationship, the output frequency of constant-temperature crystal oscillator 1 is by error voltage V_tstable control, is equivalent to the Frequency Locking of the output of constant-temperature crystal oscillator 1 in reference voltage V_refon, therefore, can select to have reference voltage source 4 compared with high stability to ensure the long-term stability of constant-temperature crystal oscillator 1.

The long-term stability of accurate reference voltage source is generally tens to hundreds of PPM/, can accomplish several PPM/ preferably, for the common reference voltage source of 50PPM/, suppose reference voltage V_reffor 2V, its annual aging fluctuation voltage is: 2*50*10^-6* 10³=0.1V, wherein 10³for the gain amplifier of comparator 5; Constant-temperature crystal oscillator 1 is in the tuning range of 12V, and its frequency tuning range is 2PPM; Due to reference voltage V_refthe constant-temperature crystal oscillator 1 output frequency drift brought is 2*0.1/12=0.02PPM/, reaches 10^-8/ year (10^-11/ sky) long-term stability of magnitude.

Improve in the present invention in the method for crystal oscillator long-term stability, if select have compared with high stability reference voltage source 4 and select suitable loop parameter, just can improve the long-term stability of constant-temperature crystal oscillator 1.

In conjunction with the second embodiment of the present invention, the present invention improves in the method for crystal oscillator long-term stability, by the switching of microprocessor 7 periodically control switch 8, realizes the access of phase-locked loop or removes, when removing phase-locked loop, keep the tuning voltage V removing phase-locked loop eve_t, make the output frequency of constant-temperature crystal oscillator 1 keep short-term stability, reduce alien frequencies phase lock circuitry to the impact of making an uproar mutually of constant-temperature crystal oscillator 1 simultaneously; When accessing phase-locked loop, then again produce tuning voltage V accordingly_tcarry out the output frequency of regulating thermostatic crystal oscillator 1.

Improve in the method for crystal oscillator long-term stability in the present invention, export two different signals of frequency by two of setting on frequency divider 2 different frequency dividing ratios, the stability of the frequency dividing ratio of two signals and the output frequency of constant-temperature crystal oscillator and stability, reference voltage source is set, the dead band of phase discriminator is all relevant, if the frequency dividing ratio of the first fractional frequency signal is M, the frequency dividing ratio of the second fractional frequency signal is that the defining method of N, M and N value is as follows:

Suppose that the frequency of the first fractional frequency signal and the second fractional frequency signal is respectively f₁and f₂, the corresponding cycle is t₁and t₂, according to the definition in phase discriminator 3 dead band, if dead band is 1ps, so exist | t₁-t₂| during≤1ps, phase discriminator will can not respond frequency difference or difference change less than reaction.

Because minimum detected frequency difference is determined by phase discriminator dead band, so have:

$\mathrm{\Δ}f=f_1-f_2=\frac{1}{t_1}-\frac{1}{t_2}=\frac{t_2-t_1}{t_1*t_2}---\left(6\right)$

△f＝f₁*f₂*1*10^-12≈f₁*f₁*1*10^-12(7)

Wherein, 1ps=1*10^-12s; f₁=f_out/ N, f_outthe output frequency of constant-temperature crystal oscillator 1, according to equation 7:

△f＝f1²*10^-12＝(f_out/N)²*10^-12(8)

△f/(f_out/N)＝(f_out/N)*10^-12(9)

Wherein △ f/ (f_out/ N) be the frequency stability of constant-temperature crystal oscillator 1, the method of crystal oscillator long-term stability is improved according to the present invention, in phase lock circuitry, the stability of constant-temperature crystal oscillator 1 is locked on reference voltage source 4, when the type selecting of reference voltage source 4 is determined, the stability of constant-temperature crystal oscillator 1 should be not less than the stability of reference voltage 4, supposes that constant-temperature crystal oscillator 1 requires that the stability reached is 10 in the present invention^-8/ year, according to equation 9:

10^-8＝(f_out/N)*10^-12(10)

According to equation 10, as the output frequency f of constant-temperature crystal oscillator 1_outwhen determining, the minimum value of frequency dividing ratio N is confirmable.The constant-temperature crystal oscillator 1 output frequency f that the present invention selects_outfor 100MHz, then N>=10⁴.

If the output frequency f of constant-temperature crystal oscillator 1_outduring change 1Hz, now frequency discrimination signal f₀frequency be:

(f_out+1)*(1/N-1/M)＝f_out*(1/N-1/M)+(1N-1/M) (11)

Wherein, f_out* (1/N-1/M) is initial frequency discrimination frequency difference, the minimum frequency difference that (1/N-1/M) can have frequency discrimination to export for phase discriminator 3.If N=10⁴, i.e. f₁=10KHz.According to equation (6):

1/N-1/M≥10^-4(12)

If M=X*N, then X-1>=1; I.e. X>=2; Get the minimum value of X, then M=2*10⁴.

Namely input different first fractional frequency signal of phase discriminator 3 and the frequency of the second fractional frequency signal are respectively 10KHz and 5KHz.Therefore, the present invention is meeting the span determining M and N under specific output frequency, the long-term stability of particular requirement and specific phase discriminator dead band condition.

It should be noted that; above-mentioned specific embodiment is exemplary; those skilled in the art can find out various solution under the inspiration of the disclosure of invention, and these solutions also all belong to open scope of the present invention and fall within protection scope of the present invention.It will be understood by those skilled in the art that specification of the present invention and accompanying drawing thereof are illustrative and not form limitations on claims.Protection scope of the present invention is by claim and equivalents thereof.

Claims (8)

1. one kind is improved the device of crystal oscillator long-term stability, it is characterized in that, described device comprises constant-temperature crystal oscillator (1), frequency divider (2), phase discriminator (3), reference voltage source (4) and comparator (5);

Described constant-temperature crystal oscillator (1) is connected with described frequency divider (2), and the output frequency of described frequency divider (2) to described constant-temperature crystal oscillator (1) carries out the frequency division that two have different frequency dividing ratio;

The input of described phase discriminator (3) is connected with the output of described frequency divider (2), and described phase discriminator (3) carries out frequency discrimination to the first fractional frequency signal exported by described frequency divider (2) and the second fractional frequency signal;

The reverse input end of described comparator (5) is connected output and the described reference voltage source (4) of described phase discriminator (3) respectively with input in the same way, its output connects the voltage-controlled voltage end of described constant-temperature crystal oscillator (1), the reference voltage that the discriminating voltage of described comparator (5) more described phase discriminator (3) and described reference voltage source (4) provide and output error signal voltage to the voltage-controlled voltage end of described constant-temperature crystal oscillator (1), to regulate the output frequency of described constant-temperature crystal oscillator (1).

2. the device of raising crystal oscillator long-term stability according to claim 1, it is characterized in that, described device also comprises filter (6), and described filter (6) is arranged between the output of described comparator (5) and the voltage-controlled voltage end of described constant-temperature crystal oscillator (1).

3. the device of raising crystal oscillator long-term stability according to claim 2, is characterized in that, described device also comprises microprocessor (7), switch (8), ad/da converter (9);

Wherein, described microprocessor (7) is connected with the output of described filter (6) by the AD circuit of ad/da converter (9), is connected with an input of switch (8) by the DA circuit of ad/da converter (9); The control end of described switch (8) is connected with described microprocessor (7), its another input is connected with the output of described filter (6), and its output is connected with the voltage-controlled voltage end of described constant-temperature crystal oscillator (1); With make described microprocessor (7) periodically control switch (8) switch phase lock circuitry access and withdraw from.

4. the device of raising crystal oscillator long-term stability according to claim 1, it is characterized in that, the frequency discrimination interval of described phase discriminator (3) comprises the frequency of the first fractional frequency signal and the second fractional frequency signal all the time, and the dead band of described phase discriminator (3) is less than the difference in the equivalent phase demodulation cycle of described first fractional frequency signal and the second fractional frequency signal all the time.

5. the method utilizing device described in claim 1 to improve crystal oscillator long-term stability, it is characterized in that, frequency divider (2) is according to the different frequency dividing ratio of its two of arranging, two frequency divisions are carried out to the output frequency of constant-temperature crystal oscillator (1), and exports the first fractional frequency signal and the second fractional frequency signal to phase discriminator (3);

Described phase discriminator (3) exports corresponding discriminating voltage to comparator (5) according to described first fractional frequency signal to the frequency difference of the second fractional frequency signal;

Described comparator (5) compares the in-phase input end voltage inputted by reference voltage source (4) and the reverse input end voltage inputted by described phase discriminator (3), and exports the voltage-controlled voltage end of corresponding error voltage to described constant-temperature crystal oscillator (1);

Described error voltage regulates the output frequency of described constant-temperature crystal oscillator (1) and the stability of described constant-temperature crystal oscillator (1) is locked on the reference voltage of described reference voltage source (4).

6. the method for raising crystal oscillator long-term stability according to claim 5, it is characterized in that, between the output and the voltage-controlled voltage end of described constant-temperature crystal oscillator (1) of described comparator (5), filtering is carried out to error voltage, to reduce the error component of described error voltage.

7. the method for raising crystal oscillator long-term stability according to claim 6, is characterized in that, periodically accessed by phase lock circuitry or remove, to reduce the effect of phase noise of described phase lock circuitry to constant-temperature crystal oscillator (1).

8. the method for raising crystal oscillator long-term stability according to claim 5, it is characterized in that, under the condition that the dead band of the output frequency of described constant-temperature crystal oscillator (1) and its Stability index and phase discriminator (3) is certain, the ratio range between two different frequency dividing ratios of described frequency divider is determined.