CN104092459A - Fast locking frequency locking ring with automatic frequency control circuit - Google Patents
Fast locking frequency locking ring with automatic frequency control circuit Download PDFInfo
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- CN104092459A CN104092459A CN201410359897.7A CN201410359897A CN104092459A CN 104092459 A CN104092459 A CN 104092459A CN 201410359897 A CN201410359897 A CN 201410359897A CN 104092459 A CN104092459 A CN 104092459A
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Abstract
A fast locking frequency locking ring with an automatic frequency control circuit comprises the automatic frequency control circuit and a frequency locking loop. The frequency locking loop comprises an amplifier, a first switch, a second switch, a voltage-controlled oscillator, a buffer, a frequency divider N and a frequency and voltage converter. The automatic frequency control circuit comprises a voltage comparator and a logic control circuit. At the beginning, the logic control circuit outputs an enabling signal to control the first switch to be turned off and the second switch to be turned on, the circuit is in the open loop state, the frequency locking ring carries out rough frequency selecting, increase and decrease of the number of logic output control words are controlled according to the output m of the voltage comparator to select an appropriate sub-band, the frequency locking ring carries out fine frequency selecting, the logical control circuit outputs the enabling signal to control the first switch to be turned on and the second switch to be turned off, the circuit is in the closed loop state, the frequency locking loop finishes the target frequency locking according to a signal input into the amplifier, and the fast locking frequency locking ring has the advantage of being fast in locking due to the work mode.
Description
Technical field
The present invention relates to a kind of FLL, relate in particular to a kind of quick lock in FLL with automatic frequency control circuit.
Background technology
FLL FLL, for phase-locked loop pll, has fast feature locking time, is generally applied in there being the occasion of strict demand locking time, and the output area of FLL is determined by the tuning range of voltage controlled oscillator VCO.For wideband voltage controlled oscillator, its tuning range generally will reach more than 50%, if adopt single tuning curve to realize so wide tuning range, its tuning gain Kvco is too large, bring serious AM-PM conversion, worsen phase noise performance.Therefore wide-band oscillator generally adopts the method that switch is selected, and a wide-band tuning scope is divided into several arrowbands tuning range, and guarantees that adjacent voltage-controlled curve has certain overlapping region.In practical application, adopt switched tuning electric capacity to realize the method for wide-band oscillator in the majority.Adopt the method, Digital and analog tuning circuit has been realized very wide tuning range, has kept very little VCO gain simultaneously, has guaranteed the application requirements of low phase noise.But for the VCO of use switched capacitor array, additionally need a circuit to carry out the switching of control switch capacitor array.When requiring FLL to export certain frequency of oscillation, control circuit must produce one group of control word, and the operating state of control switch pipe, from 2
nin individual frequency sideband, find the frequency sideband of a coverage goal frequency.So the work of this control circuit is very important to the work of whole frequency-locked loop.
Automatic frequency control circuit can automatic transfer switch capacitor array, adjust digital control word, more current frequency sideband and target frequency, until find can coverage goal frequency frequency tuning sideband, and can overcome the skew of the frequency tuning range that process deviation brings.For automatic frequency control circuit AFC, should consider its performance from two aspects: precision and speed.So-called precision, AFC must guarantee to produce correct switched capacitor array control word, and its frequency sideband of selecting must coverage goal frequency, otherwise FLL disabler, so the precision of AFC realizes most important for the function of whole FLL.So-called speed, refers to AFC and completes under the prerequisite of function, should the operating time as far as possible short.From this two aspect, can obtain figure place n, AFC T locking time of three performance index: AFC
aFCwith frequency ratio compared with precision f
res.At certain f
resunder condition, larger tuning bandwidth has brought the increase of AFC figure place n, and the locking time of AFC also can be elongated; Tuning bandwidth is certain, and n diminishes, and makes f
reschange is large and Kvco change is large, worsens phase noise performance.In the design of AFC, f
res, T
aFC, exist very complicated tradeoff between the performance such as the parameter such as n, Kvco and tuning range and phase noise.
For FLL, be an extremely important parameter locking time.And the operating time T of automatic frequency control circuit
aFCdirectly affect the locking time of whole FLL FLL.For FLL, conventional method is to adopt closed loop AFC to carry out FREQUENCY CONTROL at present, as shown in Figure 2.After treating loop stability, amplifier output voltage Vctrl will compare with predetermined voltage range Vmax and Vmin, if within this voltage range, show that current frequency tuning sideband can coverage goal frequency, otherwise will not cover.Logic control circuit, by according to the value of Vctrl, produces new control word, by switching capacity, chooses next frequency sideband, and FLL will lock again afterwards, and voltage Vctrl will relatively judge whether coverage goal frequency of new frequency band with Vmax and Vmin again.FLL will repeat above-mentioned calibration process, until Vctrl between Vmax and Vmin, shows that VCO has chosen the sub-band of coverage goal frequency.The AFC of this closed loop work need to FLL complete expendable locked after, could produce a new control word, the locking time of whole loop is longer.
Summary of the invention
Goal of the invention: for above-mentioned prior art, provide a kind of quick lock in FLL with automatic frequency control circuit, can solve long problem of whole loop-locking time in FLL.
Technical scheme: a kind of quick lock in FLL with automatic frequency control circuit, comprise automatic frequency control circuit and frequency-locked loop, described frequency-locked loop comprises amplifier, the first switch, second switch, voltage controlled oscillator, buffer, Fractional-N frequency device, FV convertor; Described automatic frequency control circuit comprises voltage comparator and logic control circuit; The output of described amplifier connects the input of voltage controlled oscillator through the first switch, outside direct voltage is through the input of second switch access voltage controlled oscillator simultaneously, described voltage controlled oscillator output connects the input of buffer, the output of buffer connects the input of Fractional-N frequency device, the input of the output rate of connections electric pressure converter of described Fractional-N frequency device, the output of FV convertor connects respectively an input of amplifier and voltage comparator, and external reference voltage connects respectively another input of described amplifier and voltage comparator; The output signal of described voltage comparator is received the input of logic control circuit, logic control circuit output enable signal controlling the first switch and second switch, and output frequency control word is brought in the sub-band of adjusting in voltage controlled oscillator to the control inputs of voltage controlled oscillator;
Wherein, described FLL comprises frequency and the thin frequency-selecting process of roughly selecting; When initial, described logic control circuit output enable letter is controlled the first switch disconnection, second switch is closed, and original frequency control word is set to the control input end of described voltage controlled oscillator; First FLL roughly selects frequently, and described automatic frequency control circuit can coverage goal frequency according to the sub-band of the signal controlling voltage controlled oscillator of input; Then FLL is carried out thin frequency-selecting, and described logic control circuit output enable signal controlling the first switch is closed, second switch disconnects, and described frequency-locked loop completes target frequency locking according to the signal of the described amplifier of input.
Further, described voltage controlled oscillator adopts the ring oscillator of switched capacitor array.
The control magnitude of voltage at the optimum place of tuning curve Linear degree that further, described outside direct voltage is voltage controlled oscillator.
Beneficial effect: a kind of quick lock in FLL with automatic frequency control circuit of the present invention, comprises automatic frequency control circuit and frequency-locked loop.In frequency-locked loop, be provided with the first switch and second switch, in frequency-locked loop, the output of amplifier connects the input of voltage controlled oscillator through the first switch; Meanwhile, outside direct voltage V0 is through the input of second switch access voltage controlled oscillator; The first switch and second switch are controlled by logic control circuit output logic control signal.FLL comprises roughly selects frequently and thin frequency-selecting process.When initial, logic control circuit output enable letter is controlled the first switch disconnection, second switch is closed, and output original frequency control word Q is to voltage controlled oscillator.First FLL roughly selects frequently, now frequency-locked loop is in open loop situations, automatic frequency control circuit is according to the adjust frequency increase and decrease of control word Q of the magnitude of voltage that is input to voltage comparator: if the voltage comparator in AFC is output as 0, make frequency control word Q subtract 1, if be output as 1, control word adds 1; And then constantly according to the result m of voltage comparator output, readjust the increase and decrease of frequency control word Q at next, until m changes polarity, now make frequency control word Q remain unchanged, thereby select suitable sub-band in voltage controlled oscillator VCO, make this sub-band can coverage goal frequency.After loop is roughly selected and frequently finished, then FLL is carried out thin frequency-selecting, and logic control circuit output enable signal controlling the first switch is closed, second switch disconnects, and frequency-locked loop is now in closed loop state.Because amplifier has higher open-loop gain, after circuit is stable, the output Vfvc of FV convertor FVC is approximately equal to reference voltage Vref, and the frequency of oscillation of final VCO depends on the size of reference voltage Vref.Suppose to reduce because environmental factor makes the output frequency of VCO under former control voltage, now the output Vfvc of FVC circuit starts to increase, and Vref is substantially constant, so the output voltage of amplifier raises, impel the operating frequency of VCO to raise, until the output Vfvc of FVC circuit is reduced to reference voltage Vref; Otherwise also can there is similar negative feedback adjustment process in circuit.So far, this frequency-locked loop completes target frequency locking according to the signal of input amplifier, thereby the locking process that does not need to repeat to experience FLL while making automatic control circuit at every turn change the control word of VCO switched capacitor array, has shortened locking time of FLL, reaches the object of quick lock in.
Voltage controlled oscillator adopts the ring oscillator of switched capacitor array, is of value to when keeping voltage controlled oscillator output signal less reference frequency output larger.
Direct voltage V0 is the control magnitude of voltage at the optimum place of tuning curve Linear degree of voltage controlled oscillator VCO, its beneficial effect is: the tuning gain Kvco at the optimum place of the linearity of tuning curve changes minimum, the phase noise of FLL can be improved on the one hand, the loop stability of FLL can be improved on the other hand.
In sum, the open loop AFC that is applicable to FLL FLL that the present invention proposes, the control word that this automatic frequency control circuit changes VCO switched capacitor array at every turn does not need to repeat to experience the locking process of FLL, only need to guarantee FV convertor steady operation, this will shorten the locking time of FLL greatly, the implementation of the AFC that the present invention proposes is in addition simple, can't increase the complexity of circuit when guaranteeing FLL superperformance.
Accompanying drawing explanation
Fig. 1 is the structured flowchart of the quick lock in FLL with automatic frequency control circuit of the present invention;
Fig. 2 is the structured flowchart of the FLL of tradition based on closed loop automatic control circuit AFC;
Fig. 3 is the workflow diagram of automatic frequency control circuit in the present invention;
Fig. 4 is the simulation waveform figure that controls voltage Vctrl in the present invention;
Fig. 5 is the simulation waveform figure of the output Vfvc of reference voltage Vref and FV convertor FVC in the present invention;
Fig. 6 is the simulation waveform figure of logic control circuit output enable signal En in the present invention;
Fig. 7 is the final output frequency Fout simulation waveform figure of buffer stage in the present invention;
Embodiment
Below in conjunction with accompanying drawing, the present invention will be further described.
As shown in Figure 1, a kind of quick lock in FLL with automatic frequency control circuit, comprise automatic frequency control circuit and frequency-locked loop, frequency-locked loop comprises amplifier, the first switch S 0, second switch S1, voltage controlled oscillator VCO, buffer buffer, Fractional-N frequency device, FV convertor FVC.Automatic frequency control circuit AFC comprises voltage comparator and logic control circuit.The output of amplifier connects the input of voltage controlled oscillator VCO through the first switch S 0, outside direct voltage V0 is through the input of second switch S1 access voltage controlled oscillator VCO, voltage controlled oscillator VCO output connects the input of buffer buffer, the output of buffer buffer connects the input of Fractional-N frequency device, the input of the output rate of connections electric pressure converter FVC of Fractional-N frequency device.Reference input voltage Vref connects respectively the in-phase input end of voltage comparator of automatic frequency control circuit and the inverting input of the voltage amplifier of frequency-locked loop; The output Vfvc of FV convertor connects respectively the in-phase input end of voltage amplifier of frequency-locked loop and the inverting input of the voltage comparator of automatic frequency control circuit.The output signal of voltage comparator is received the input of logic control circuit, logic control circuit output enable signal controlling the first switch S 0 and second switch S1, and output frequency control word is to the control input end of voltage controlled oscillator, according to the increase and decrease of control word, selects sub-band suitable in voltage controlled oscillator.Its peripheral direct voltage V0 is the control magnitude of voltage at the optimum place of tuning curve Linear degree of voltage controlled oscillator.
FLL comprises roughly selects frequently and thin frequency-selecting process, as shown in Figure 3, when initial, logic control circuit output enable letter is controlled the first switch disconnection, second switch is closed, and original frequency control word Q < 3:0>=1000 is set to the control input end of voltage controlled oscillator.First FLL roughly selects frequently, judges whether voltage comparator output m is 0: if m is 0, control word Q < 3:0> subtracts 1, otherwise control word adds 1; And then constantly according to the result m of voltage comparator output, readjust the increase and decrease of frequency control word Q<3:0> at next, until m changes, now make frequency control word Q<3:0> remain unchanged, thereby select suitable sub-band in voltage controlled oscillator VCO.After loop is roughly selected and frequently finished, then FLL is carried out thin frequency-selecting, and logic control circuit output enable signal controlling the first switch is closed, second switch disconnects, and frequency-locked loop completes target frequency locking according to the signal of input amplifier.The dichotomy equifrequent search algorithm that wherein logic control circuit can adopt sequential search method, dichotomy search and code to estimate completes the calculating that outputs to VCO control word.
For feasibility of the present invention is described, make reference voltage Vref=176mV, outside direct voltage V0=850mV while frequently saving for roughly selecting, the original frequency control word Q<3:0>=1000 of logic control circuit, can obtain result as Figure 4-Figure 7.Fig. 4 is the simulation waveform figure that controls voltage Vctrl in the present invention, as can be seen from the figure controls voltage Vctrl and tends towards stability at 2.6us place, illustrate that now circuit has completed frequency locking process, and locking time is very fast; Under worst case, suppose that it is on 0000 or 1111 sub-tuning curve that required target frequency is positioned at frequency control word, and while adopting sequential search method, loop just can complete locking through 8 frequency locking cycles at most, the time in one of them frequency locking cycle equals the stable output time of FV convertor FVC, its value is less than 600ns, is now about 4.8us locking time, is also the locking time under worst case.If the dichotomy that logic control circuit adopts dichotomy or code to estimate, will be less than 2.5us the longest locking time; Fig. 5 is the simulation waveform figure of the output Vfvc of reference input voltage Vref and FV convertor FVC in the present invention, can find out that, when circuit is finally realized frequency locking function, the output Vfvc of FV convertor equals reference input voltage Vref substantially; Fig. 6 is the simulation waveform figure of logic control circuit output enable signal En in the present invention, and as can be seen from the figure, when automatic frequency control circuit AFC completes thick frequency locking, enable signal becomes high level from low level; Fig. 7 is the final output frequency Fout simulation waveform figure of buffer stage in the present invention, wherein the transverse and longitudinal coordinate figure of M0 equals the difference of the transverse and longitudinal coordinate of selected two points, its abscissa is the now cycle of output waveform, from figure, can calculate, and now output frequency equals 426.62MHz.
The foregoing is only better embodiment of the present invention; protection scope of the present invention is not limited with above-mentioned execution mode; in every case the equivalence that those of ordinary skills do according to disclosed content is modified or is changed, and all should include in the protection range of recording in claims.
Claims (3)
1. the quick lock in FLL with automatic frequency control circuit, it is characterized in that: comprise automatic frequency control circuit and frequency-locked loop, described frequency-locked loop comprises amplifier, the first switch, second switch, voltage controlled oscillator, buffer, Fractional-N frequency device, FV convertor; Described automatic frequency control circuit comprises voltage comparator and logic control circuit; The output of described amplifier connects the input of voltage controlled oscillator through the first switch, outside direct voltage is through the input of second switch access voltage controlled oscillator simultaneously, described voltage controlled oscillator output connects the input of buffer, the output of buffer connects the input of Fractional-N frequency device, the input of the output rate of connections electric pressure converter of described Fractional-N frequency device, the output of FV convertor connects respectively an input of amplifier and voltage comparator, and external reference voltage connects respectively another input of described amplifier and voltage comparator; The output signal of described voltage comparator is received the input of logic control circuit, logic control circuit output enable signal controlling the first switch and second switch, and output frequency control word is brought in the sub-band of adjusting in voltage controlled oscillator to the control inputs of voltage controlled oscillator;
Wherein, described FLL comprises frequency and the thin frequency-selecting process of roughly selecting; When initial, described logic control circuit output enable letter is controlled the first switch disconnection, second switch is closed, and original frequency control word is set to the control input end of described voltage controlled oscillator; First FLL roughly selects frequently, and described automatic frequency control circuit can coverage goal frequency according to the sub-band of the signal controlling voltage controlled oscillator of input; Then FLL is carried out thin frequency-selecting, and described logic control circuit output enable signal controlling the first switch is closed, second switch disconnects, and described frequency-locked loop completes target frequency locking according to the signal of the described amplifier of input.
2. a kind of quick lock in FLL with automatic frequency control circuit according to claim 1, is characterized in that: described voltage controlled oscillator adopts the ring oscillator of switched capacitor array.
3. a kind of quick lock in FLL with automatic frequency control circuit according to claim 1, is characterized in that: the control magnitude of voltage at the optimum place of tuning curve Linear degree that described outside direct voltage is voltage controlled oscillator.
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| CN201410359897.7A CN104092459A (en) | 2014-07-25 | 2014-07-25 | Fast locking frequency locking ring with automatic frequency control circuit |
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| CN201410359897.7A CN104092459A (en) | 2014-07-25 | 2014-07-25 | Fast locking frequency locking ring with automatic frequency control circuit |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105119600A (en) * | 2015-09-18 | 2015-12-02 | 东南大学 | AFC (Automatic Frequency Calibration) method for realizing rapid locking of a phase-locked loop system |
| CN105245222A (en) * | 2015-11-30 | 2016-01-13 | 成都西科微波通讯有限公司 | Novel help lock circuit in broadband phase-locked loop |
| CN105610436A (en) * | 2015-12-22 | 2016-05-25 | 西安电子科技大学 | Charge pump phase-locked loop with adaptive acceleration locking structure |
| CN112039652A (en) * | 2020-09-14 | 2020-12-04 | 华北水利水电大学 | Communication signal frequency error calibration circuit |
| WO2022126894A1 (en) * | 2020-12-16 | 2022-06-23 | 深圳市紫光同创电子有限公司 | Frequency selection circuit |
-
2014
- 2014-07-25 CN CN201410359897.7A patent/CN104092459A/en active Pending
Non-Patent Citations (1)
| Title |
|---|
| XUELOU: "《中国电子顶级开发网论坛》", 22 February 2014 * |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105119600A (en) * | 2015-09-18 | 2015-12-02 | 东南大学 | AFC (Automatic Frequency Calibration) method for realizing rapid locking of a phase-locked loop system |
| CN105119600B (en) * | 2015-09-18 | 2017-11-17 | 东南大学 | A kind of automatic band calibration method for making phase-locked loop systems quick lock in |
| CN105245222A (en) * | 2015-11-30 | 2016-01-13 | 成都西科微波通讯有限公司 | Novel help lock circuit in broadband phase-locked loop |
| CN105610436A (en) * | 2015-12-22 | 2016-05-25 | 西安电子科技大学 | Charge pump phase-locked loop with adaptive acceleration locking structure |
| CN105610436B (en) * | 2015-12-22 | 2018-10-02 | 西安电子科技大学 | It is a kind of to have the adaptive charge pump phase lock loop for accelerating locking structure |
| CN112039652A (en) * | 2020-09-14 | 2020-12-04 | 华北水利水电大学 | Communication signal frequency error calibration circuit |
| WO2022126894A1 (en) * | 2020-12-16 | 2022-06-23 | 深圳市紫光同创电子有限公司 | Frequency selection circuit |
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