CN203504532U - Phase-locked loop circuit for spreading spectrum control - Google Patents

Phase-locked loop circuit for spreading spectrum control Download PDF

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Publication number
CN203504532U
CN203504532U CN201320529544.8U CN201320529544U CN203504532U CN 203504532 U CN203504532 U CN 203504532U CN 201320529544 U CN201320529544 U CN 201320529544U CN 203504532 U CN203504532 U CN 203504532U
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China
Prior art keywords
phase
spread
locked loop
spectrum
circuit
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CN201320529544.8U
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Chinese (zh)
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麦日锋
刘明
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京微雅格(北京)科技有限公司
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Abstract

The utility model discloses a phase-locked loop circuit. In an embodiment, the phase-locked loop circuit comprises a switch capacitance circuit, the switch capacitance circuit generates modulation waveforms, and the modulation waveforms are injected to the phase-locked loop circuit in a current manner so that the output frequency of a phase-locked loop is modulated. Compared with the spectrum-spread phase-locked loop in the prior art, the spectrum-spread phase-locked loop is advantaged by simple structure, low power consumption, low cost of silicon, and flexibility in spectrum-spreading ratio and modulation frequency.

Description

The phase-locked loop circuit that a kind of spread-spectrum is controlled

Technical field

The utility model relates to phase-locked loop pll circuit, relates in particular to the phase-locked loop circuit that spread-spectrum is controlled.

Background technology

In recent years, along with SoC(system level chip) high speed, the problem of the electromagnetic interference of large scale integrated circuit and digital household appliances product is day by day serious.The phase-locked loop (SS-PLL) that spread-spectrum is controlled is a kind of effective means that reduces electromagnetic interference, and it is finely tuned by the frequency of the reference clock signal in integrated circuit, thereby the spread spectrum of clock signal is reduced to electromagnetic interference.

Fig. 1 is the block diagram of a kind of spread spectrum phase-locked loop SS-PLL of prior art.This spread spectrum phase-locked loop is except comprising phase-frequency detector (Phase-frequency detector, abbreviation PFD), the first current pump (charge pump, abbreviation CP), low pass filter (low pass filter, be called for short LPF) and voltage controlled oscillator (Voltage Controlled Oscillator, be called for short VCO) outside, also comprise the second current pump.This second current pump operating frequency is lower than the operating frequency of the first current pump.On the charging and discharging currents that the charging and discharging currents of the second current pump is added to from the first current pump by low pass filter, thereby modulate the voltage on the input that is applied to VCO, and then the frequency of modulation clock signal.Yet this scheme requires low pass filter to meet R1*C1=R2*C2.Particularly importantly, because one of input signal of PFD has also comprised the composition of modulation signal, the bandwidth of PLL under non-spread spectrum mode must enough little this feedback component being produced with filtering modulation signal.

Fig. 2 has illustrated the block diagram of spread spectrum phase-locked loop of another kind of prior art.This spread spectrum phase-locked loop (utilizes frequency divider is wherein modulated.Although this scheme obtains good effect, structure is comparatively complicated.

Summary of the invention

The utility model embodiment provides a kind of phase-locked loop circuit in first aspect.This phase-locked loop circuit comprises: switched-capacitor circuit, and switched-capacitor circuit produces modulation waveform, and this modulation waveform, with current forms injection phase-locking loop circuit, makes phase-lock-ring output frequency modulated.

Preferably, phase-locked loop circuit comprises spread-spectrum clock generator, described switched-capacitor circuit is arranged in spread-spectrum clock generator, spread-spectrum clock generator also has the first current source and the second current source, spread-spectrum clock generator with the frequency period alternate selection lower than feedback clock signal respectively with the first current source and the corresponding signal of the second current source, switched-capacitor circuit is made low-pass filtering to the signal of selecting, and the signal after described low-pass filtering is modulation waveform.

Preferably, phase-locked loop circuit comprises spread-spectrum clock generator, described switched-capacitor circuit is arranged in spread-spectrum clock generator, and spread-spectrum clock generator also has the first current source, the second current source and amplifier, and the second current source, amplifier and the 3rd electric capacity connect into integrator; Spread-spectrum clock generator with the frequency period alternate selection lower than feedback clock signal respectively with the first current source and the corresponding signal of the second current source, as the positive and negative input signal of integrator; The output signal of integrator is modulation waveform.

Preferably, spread-spectrum clock generator comprises the 3rd current source, and spread-spectrum clock generator obtains difference signal by the current ratio of modulation waveform and the 3rd current source, and loop filter circuit is modulated to control voltage by this difference signal.Further preferably, spread-spectrum clock generator comprises transistor, and its grid receives the signal after low-pass filtering, and drain electrode receives the electric current of the 3rd current source.

Preferably, modulation waveform is triangular wave.

Preferably, spread spectrum phase-locked loop circuit comprises: charge pump circuit, release and the suction of according to the phase difference of the feedback clock signal of the clock signal of described phase-locked loop circuit and reference clock signal, switching charging and discharging currents; Loop filter circuit, has filter capacitor, and this filter capacitor is discharged and recharged and generated control voltage by charging and discharging currents; Voltage controlled oscillator, to vibrate with the corresponding frequency of described control voltage.

The utility model embodiment provides a kind of spectrum spreading method of phase-locked loop circuit in second aspect, the method comprises: switched-capacitor circuit produces modulation waveform; This modulation waveform, with current forms injection phase-locking loop circuit, makes phase-lock-ring output frequency modulated.

Compare with the spread spectrum phase-locked loop of prior art, the spread spectrum phase-locked loop structures of the utility model embodiment is simple, and power consumption is low, and silicon expense is low, and all has flexibility aspect spreading ratio and modulating frequency two.

Accompanying drawing explanation

Below by drawings and Examples, the technical solution of the utility model is described in further detail.

Fig. 1 is the block diagram of a kind of spread spectrum phase-locked loop SS-PLL of prior art;

Fig. 2 has illustrated the block diagram of spread spectrum phase-locked loop of another kind of prior art;

Fig. 3 has illustrated according to the spread spectrum phase-locked loop pll circuit of the utility model embodiment;

Fig. 4 has illustrated various voltages, the frequency oscillogram of phase-locked loop;

Fig. 5 is the schematic diagram that is related to of spread-spectrum and switching capacity modulation;

Fig. 6 has illustrated according to the spread spectrum phase-locked loop pll circuit of another embodiment of the utility model.

Embodiment

The utility model embodiment provides a kind of spread spectrum phase-locked loop circuit framework based on switched-capacitor circuit.This switched-capacitor circuit produces modulation waveform, and such as triangular wave, this modulation waveform, with current forms injection phase-locking loop circuit, makes phase-lock-ring output frequency modulated.Therefore, the frequency spectrum of phase-locked loop output clock is expanded.

Fig. 3 has illustrated according to the spread spectrum phase-locked loop pll circuit of the utility model embodiment.As shown in Figure 3, phase-locked loop is as closed-loop control system work, and it comprises phase detector 30, charge pump 31, loop filter 32 and voltage controlled oscillator (VCO) 33, loop divider 34 and spread-spectrum clock generator (SSCG) 35.In an example, can be by phase detector and charge pump combination in a functional block.

In phase detector 30, benchmark frequency Fclk and feedback frequency Ffb.In most systems, this phase detector is a phase place and frequency detector.This phase place-frequency detector generates the corresponding signal up of phase difference or a dn with reference frequency Fclk and feedback frequency Ffb.In an example, the clock signal Fout of 34 pairs of spread spectrum phase-locked loops of loop divider carries out frequency division and generates feedback clock signal Ffb.

Charge pump circuit (CP) 31 is according to release and the suction of the output switching charging current Icp of PFD30.When up is effective, discharge charging current; When dn is effective, suck discharging current.

Loop filter circuit (LPF) 32 makes charging current smoothing formation voltage Vc.In illustrated example, loop filter circuit comprises the low pass filter of 3 reinforced concrete structures, and the 1st grade comprises resistance R 2, resistance R 2 and capacitor C 1; The 2nd grade comprises capacitor C 2; 3rd level comprises resistance R 3 and capacitor C 3.Wherein, R3 and C3 can further eliminate spike (spike) problem of being brought by reference clock.This low pass filter carries out smoothly the electric current from charge pump circuit 12.Certainly, those of skill in the art recognize that the low pass filter that also can adopt other form, such as the low pass filter of 2 reinforced concrete structures, and do not depart from scope of the present utility model.

Loop filter circuit can also comprise the bleeder circuit consisting of R1, R2, on the electric current that this bleeder circuit is added to the electric current from spread-spectrum clock generator 35 from charge pump circuit 12.

Voltage controlled oscillator (VCO) 33 is to vibrate with the corresponding frequency of Vc, and output has the clock signal of frequency Fout.

The phase-locked loop that phase detector 30, charge pump circuit 31, loop filter circuit 32 and voltage controlled oscillator 33 form under non-spread spectrum mode, those skilled in the art will recognize that, this phase-locked loop also can adopt the circuit of other configuration to form, and does not depart from scope of the present utility model.

Spread-spectrum clock generator (SSCG) has switched-capacitor circuit, the first current source Iss1 and the second current source Iss2.Spread-spectrum clock generator is with the frequency Fmod lower than feedback clock signal Ffb periodically alternately on-off switch φ 1 and φ 1b, thus alternate selection respectively with the first current source Iss1 and the corresponding signal Iss1*R of the second current source Iss2 m1, Iss2*R m2flow into switched-capacitor circuit 352.R m1, R m2respectively the resistance that transistor M1 and M2 present.

Switch in switched-capacitor circuit 352 is with the frequency f c work higher than flowing into voltage signal frequency, and switched-capacitor circuit is equivalent to the resistance that resistance is 1/ (fc*Css1), the capacitance that wherein Css1 is switching capacity.This resistance and capacitor C ss2 form a low pass filter.Thus, the grid voltage of transistor M3 is that frequency is class triangular wave 40(Fig. 4 of Fmod), the rising edge of such triangular wave or the time constant of trailing edge are

T=R*Css2=1/F*Css2/Css1。

Due to F, Css1 and Css2 all with power, voltage and temperature in any one factor irrelevant, so this time constant and power, voltage and temperature all irrelevant.Therefore, not being subject to above-mentioned factor disturbs.

Transistor M3 is converted to current signal by the signal after low-pass filtering, and obtain difference signal with the current ratio of the 3rd current source Iss3, this difference signal is specially the charging and discharging currents of frequency Fmod, and a part for complete cycle is charging current, and another part is discharging current.Loop filter circuit 32 is modulated to this difference signal to control on voltage Vc.

In an example, the On The Current Value of the 3rd current source Iss3 is I0, and the electric current of the first current source Iss1 and the second current source Iss2 respectively value is 2I0 and 0.5I0.Thus, the class triangular wave charging and discharging currents that spread-spectrum clock generator produces and the output cycle is Fmod.Certainly, also can, by configuration transistor M1, M2 and M3, make to produce equally spaced charging and discharging electric current in the drain electrode of M3.

In operation, when phase-locked loop starts, the clock signal of voltage controlled oscillator 33 does not also reach the frequency of expection, and feedback clock signal and reference clock signal exist phase difference, therefore can produce up or dn signal.Under the effect of up or dn signal, charge pump 31 produces corresponding charging and discharging currents.Now, electric current loop filter 32 being discharged and recharged is mainly from charge pump 31.Loop filter 32 discharges and recharges rear generation voltage Vc, is applied to the input of phase-locked loop 33, thereby adjusts the output frequency of phase-locked loop 33.

When feedback clock signal and reference clock signal do not exist phase difference or approach same phase, up and dn signal narrow down or disappear, so Vcp approaches or equals 0.Now, the charging and discharging currents that acts on loop filter circuit 32 is mainly the spill current relevant with Iss3 to Iss1, Iss2 that spread-spectrum clock generator produces, this spill current modulation voltage Vc, and then the frequency of the clock signal of modulation phase-locked loop.

Fig. 4 has illustrated various voltages, the frequency oscillogram of phase-locked loop.The waveform of waveform 42 before corresponding to input switched capacitor circuit, is square wave substantially; This is a square wave that frequency is Fmod, and high level is Iss1*R m1, low level is Iss2*R m2.Waveform 40 is processed waveform afterwards corresponding to switched-capacitor circuit; Label 44 has been illustrated to modulate the situation of change of the frequency of the output signal of VCO afterwards, and this frequency presents the variation tendency of approximate triangular wave.

In an example, Ffb is 10MHz; Fc can equal Ffb, can be also the frequency division of Ffb, such as 2MHz.Fmod can be set as the further frequency division of Fc, for example, be 100kHz.Thus, can form Fmod/Ffb(in this example, 1%) spread spectrum effect.

Compare with the spread spectrum phase-locked loop of prior art, the spread spectrum phase-locked loop structures of the utility model embodiment is simple.The spread spectrum phase-locked loop of the utility model embodiment and only having any different of non-spread spectrum phase-locked loop are switched-capacitor circuit, and this switched-capacitor circuit is controlled the sub-fraction in charge pump current source.This has guaranteed the extremely low and lower power consumption of silicon expense.

The spread spectrum phase-locked loop of the utility model embodiment all has flexibility aspect spreading ratio and modulating frequency two.The capacity ratio changing in switched-capacitor circuit will change spreading ratio.Modulating frequency also can be regulated by changing switching capacity switching frequency.Therefore, the spread spectrum phase-locked loop of the utility model embodiment is specially adapted to SOC application and other embedded system.

Switched-capacitor circuit also can be implemented dissimilar modulation waveform, such as trapezoidal.In an example, change electric capacity and recently change modulation waveform.Fig. 5 is the schematic diagram that is related to of spread-spectrum and switching capacity modulation.As shown in Figure 5, the waveform of switch φ 1 and φ 1b is complementary.The voltage that appears at Css2 end changes along with the variation of RC, and wherein, R is switching capacity equivalent resistance, R=T/C, and T is the switching frequency of switched-capacitor circuit, C=Css1.When RC is larger, the voltage of Css2 end is close to triangle; And RC is less time, the voltage of Css2 end is close to rectangle.

Fig. 6 has illustrated according to the spread spectrum phase-locked loop pll circuit of another embodiment of the utility model.The place that Fig. 6 is different from Fig. 3 is, with an amplifier Op, has substituted a switching capacity filter in the switched-capacitor circuit of connecting.Specifically, the negative input end of amplifier Op is connected with a switched-capacitor circuit.Under the control of the signal psi 2 that switching capacity filter is fc at switching frequency, alternately switch on and off electric capacity, play low pass filter, it is equivalent to the resistance R that resistance is 1/fcCss1, the capacitance that wherein Css1 is switching capacity.Between the output of amplifier Op and negative input end, be connected with capacitor C ss3.Therefore, amplifier Op plays integrator.The integrating function of integrator is as shown in the formula expression:

Vo ( t ) = - 1 RCss 3 ∫ t 0 t Vi ( t ) dt + Vo ( t 0 )

Wherein, the output that Vo is integrator, Vi is the input voltage at the integrator of switched-capacitor circuit one side; R is the resistance of switched-capacitor circuit.

Electric current I ss1 and Iss2 be the switch under controlling at frequency pulse φ 1 complimentary to one another and φ 1b respectively, then periodically by gating alternately, is connected to respectively the positive input terminal of switching capacity filter (being then connected to the negative input end of amplifier Op) and amplifier Op.Specifically, when φ 1 is effective, electric current I ss1 is coupled to the negative input end of amplifier through switched-capacitor circuit, and electric current I ss2 is coupled to the positive input terminal of amplifier; When φ 1b is effective, electric current I ss2 is coupled to the negative input end of amplifier through switched-capacitor circuit, and electric current I ss1 is coupled to the positive input terminal of amplifier.Therefore, integrator within the different time periods respectively to voltage Iss1*R m1and Iss2*R m2difference and voltage Iss2*R m2and Iss1*R m1difference carry out integration.

Transistor M3 is converted to current signal by the signal after integration, and obtains difference signal with the current ratio of the 3rd current source Iss3.Loop filter 32 is modulated to this signal to control on voltage Vc.

The spread spectrum phase-locked loop pll circuit of Fig. 6 has been guaranteed the extremely low and lower power consumption of silicon expense equally.In addition, by the capacity ratio changing in switched-capacitor circuit, will change spreading ratio.Modulating frequency also can be regulated by changing switching capacity switching frequency.

In the present embodiment, the dc point of transistor M3 grid is determined by the output DC level of amplifier, therefore, more flexible to the control of transistor M3.

In addition, by changing the frequency of φ 2, can change resistance R, and then change the bandwidth of integrator, so that control better.

Above-described embodiment; the purpose of this utility model, technical scheme and beneficial effect are further described; institute is understood that; the foregoing is only embodiment of the present utility model; and be not used in and limit protection range of the present utility model; all within spirit of the present utility model and principle, any modification of making, be equal to replacement, improvement etc., within all should being included in protection range of the present utility model.

Claims (7)

1. the phase-locked loop circuit that spread-spectrum is controlled, comprising:
Switched-capacitor circuit, switched-capacitor circuit produces modulation waveform, and this modulation waveform, with current forms injection phase-locking loop circuit, makes phase-lock-ring output frequency modulated.
2. the phase-locked loop circuit that spread-spectrum as claimed in claim 1 is controlled, wherein phase-locked loop circuit comprises spread-spectrum clock generator, described switched-capacitor circuit is arranged in spread-spectrum clock generator, spread-spectrum clock generator also has the first current source and the second current source, spread-spectrum clock generator with the frequency period alternate selection lower than feedback clock signal respectively with the first current source and the corresponding signal of the second current source, switched-capacitor circuit is made low-pass filtering to the signal of selecting, and the signal after described low-pass filtering is modulation waveform.
3. the phase-locked loop circuit that spread-spectrum as claimed in claim 1 is controlled, wherein phase-locked loop circuit comprises spread-spectrum clock generator, described switched-capacitor circuit is arranged in spread-spectrum clock generator, spread-spectrum clock generator also has the first current source, the second current source and amplifier, and the second current source, amplifier and the 3rd electric capacity connect into integrator; Spread-spectrum clock generator with the frequency period alternate selection lower than feedback clock signal respectively with the first current source and the corresponding signal of the second current source, as the positive and negative input signal of integrator; The output signal of integrator is modulation waveform.
4. the phase-locked loop circuit that spread-spectrum as claimed in claim 1 is controlled, wherein spread-spectrum clock generator comprises the 3rd current source, spread-spectrum clock generator obtains difference signal by the current ratio of modulation waveform and the 3rd current source, and loop filter circuit is modulated to control voltage by this difference signal.
5. the phase-locked loop circuit that spread-spectrum as claimed in claim 4 is controlled, wherein spread-spectrum clock generator comprises transistor, and its grid receives the signal after low-pass filtering, and drain electrode receives the electric current of the 3rd current source.
6. the phase-locked loop circuit that spread-spectrum as claimed in claim 1 is controlled, wherein modulation waveform is triangular wave.
7. the phase-locked loop circuit that spread-spectrum as claimed in claim 1 is controlled, comprising:
Charge pump circuit (CP), release and the suction of according to the phase difference of the feedback clock signal of the clock signal of described phase-locked loop circuit and reference clock signal, switching charging and discharging currents;
Loop filter circuit (LPF), has filter capacitor, and this filter capacitor is discharged and recharged and generated control voltage by charging and discharging currents;
Voltage controlled oscillator (VCO), to vibrate with the corresponding frequency of described control voltage.
CN201320529544.8U 2013-08-28 2013-08-28 Phase-locked loop circuit for spreading spectrum control CN203504532U (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104426541A (en) * 2013-08-28 2015-03-18 京微雅格(北京)科技有限公司 Phase-locked loop circuit for spreading spectrum control, and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104426541A (en) * 2013-08-28 2015-03-18 京微雅格(北京)科技有限公司 Phase-locked loop circuit for spreading spectrum control, and method
CN104426541B (en) * 2013-08-28 2018-03-30 京微雅格(北京)科技有限公司 A kind of phase-locked loop circuit and method of spread-spectrum control

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