CN101316114B - Spread-spectrum modulation circuit, variable frequency triangular-wave generator and signal processing method - Google Patents

Abstract

The embodiment of the invention discloses a spread-spectrum modulation circuit, a variable frequency triangle generator and a signal processing method. The spread-spectrum modulation circuit comprises the variable frequency triangle generator, a first comparator and a second comparator; the variable frequency triangle generator is respectively connected with the first comparator and the second comparator; the first comparator and the second comparator realize the spread-spectrum of the pulse width modulation (PWM) according to the input signal and the variable frequency triangle waves input by the variable frequency triangle generator. In the embodiment of the invention, the random signal is used to control the changes of the so as to generate a triangle wave circuit with changed frequency, the spread-spectrum modulation circuit is realized, the structure realization is simple, and the high-frequency distribution is similar to the distribution of white noise, thus effectively reducing the electromagnetic interference in the existing circuit.

Description

Spread-spectrum modulation circuit, variable frequency triangular-wave generator and signal processing method

Technical field

The present invention relates to communication technical field, relate in particular to a kind of spread-spectrum modulation circuit, variable frequency triangular-wave generator and signal processing method.

Background technology

At present, the D genus audio power amplifier is widely used in driving loud speaker audio signal is carried out power transfer.The D power-like amplifier makes output stage be operated on off state, thereby reaches high efficiency purpose.The D power-like amplifier has high-efficiency characteristics, reduces even has removed the heat radiation cost, is used in to prolong battery service time in the handheld device greatly, reduces system cost, reduces volume.

Because PWM (Pulse Width Modulation; Pulse width modulation) still there be the carrier wave and the harmonic component thereof of high frequency in the output of the D power-like amplifier of the Filter less of modulation; The waveform of output is an impulse waveform; Therefore have very many high fdrequency components, EMI (Electro Magnetic Interference, electromagnetic interference) problem is very serious.

PWM modulator of the prior art mainly comprises two comparators and a triangular-wave generator (Ramp), and circuit is as shown in Figure 1.PWM be with input audio signal with compare with the triangular wave or the oblique wave of fixed carrier frequency, this produces pulse train under the carrier frequency condition.In each carrier cycle, the duty ratio of pwm pulse is proportional to the amplitude of audio signal.

One of Ramp realizes that circuit is as shown in Figure 2, is the circuit for generating triangular wave of a fixed frequency.Control SW through the Logic circuit module _SourceAnd SW _SinkTwo switches, two current source I _SourceAnd I _SinkUnder different state, respectively the integrated electric capacity in inside is charged and discharge, thereby obtain the RAMP ripple, because the frequency range of audio frequency is 20-20kHz, carrier frequency can be made as greater than 200kHz, just can meet the demands.

The inventor finds that there is following problem at least in prior art in realizing process of the present invention:

Prior art requirement end product must be through existing quasi-peak value detection limit to guarantee the EMI of minimum level.In quasi-peak value detected, the level of signal of being measured was to be weighed by the repetition rate of signal spectrum component.Repetition rate is low more, and the quasi-peak value reading is also just low more.Adopt the triangular modulation of FFM (Fixed Frequency Mode, fixed frequency modes), signal mainly concentrates at the energy on the frequency spectrum on the frequency of each harmonic component, and the repetition rate of signal spectrum component is high, will produce serious EMI problem like this.

Summary of the invention

Embodiments of the invention provide a kind of spread-spectrum modulation circuit, variable frequency triangular-wave generator and signal processing method, are used for reducing the electromagnetic interference of available circuit.

For achieving the above object; Embodiments of the invention provide a kind of spread-spectrum modulation circuit; Comprise variable frequency triangular-wave generator, first comparator and second comparator; Said variable frequency triangular-wave generator comprises the band spectrum modulation module, and said variable frequency triangular-wave generator is connected with said first comparator and second comparator respectively; Said first comparator and second comparator are realized the spread spectrum of pulse-width modulated PWM according to the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator; Specifically comprise in the wherein said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, said random signal generator are used for controlling said band spectrum modulation module changes in capacitance.

Embodiments of the invention also provide a kind of variable frequency triangular-wave generator; Comprise: band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity; Said random signal generator is used for controlling said band spectrum modulation module changes in capacitance, wherein:

There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; The voltage output of said band spectrum modulation module is connected respectively to the input of said first comparison module and second comparison module; The output of said first comparison module and second comparison module connects said application of logic circuit module; Said application of logic circuit module is controlled said first switch and second switch; Through controlling the state of said first switch and second switch; Make said first current source, second current source carry out charge or discharge at least one capacitor in the said band spectrum modulation module respectively, produce the triangular signal of changeable frequency.

Embodiments of the invention also provide the signal processing method in a kind of spread-spectrum modulation circuit, comprising:

Variable frequency triangular-wave generator produces at least one variable frequency triangular-wave signal; Said variable frequency triangular-wave generator comprises the band spectrum modulation module; Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity; Said random signal generator is controlled changes in capacitance in the said band spectrum modulation module, the voltage that obtains changing output;

Said variable frequency triangular-wave signal is input to first comparator and second comparator respectively; Make said first comparator and second comparator according to input signal and said variable frequency triangular-wave signal, realize the spread spectrum of pulse-width modulated PWM.

Embodiments of the invention also provide a kind of method for generation of variable frequency triangular-wave; Be applied to comprise in the circuit of band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; Said method comprises:

The voltage output of band spectrum modulation module is sent to the input of said first comparison module and second comparison module respectively;

The output of said first comparison module and second comparison module is sent to said application of logic circuit module;

Control the state of said first switch and second switch through said application of logic circuit module, make said first current source, second current source charge to a plurality of capacitors in the said band spectrum modulation module respectively and discharge, produce the triangular wave of changeable frequency;

Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, control changes in capacitance in the said band spectrum modulation module through said random signal generator, the voltage that obtains changing output.

Compared with prior art, embodiments of the invention have the following advantages:

Embodiments of the invention provide a kind of spread-spectrum modulation circuit; Variation through the random signal control capacitance is to produce the triangle wave circuit of a frequency change; And then realized spread-spectrum modulation circuit; Structure realizes simple, makes high fdrequency component be similar to the distribution of white noise, effectively reduces the electromagnetic interference in the available circuit.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art; To do one to the accompanying drawing of required use in embodiment or the description of the Prior Art below introduces simply; Obviously; Accompanying drawing in describing below only is some embodiments of the present invention, and adversary those of ordinary skills can also obtain other accompanying drawing according to these accompanying drawings under the prerequisite of not paying creative work property.

Fig. 1 is the sketch map of PWM modulator in the prior art;

Fig. 2 is the sketch map of prior art intermediate cam wave producer;

Fig. 3 is the structural representation of variable frequency triangular-wave generator in the embodiment of the invention;

Fig. 4 A and Fig. 4 B are the structural representations of spread-spectrum modulation circuit in the embodiment of the invention;

Fig. 5 A and Fig. 5 B are the sketch mapes that n electric capacity of random signal control is realized spread-spectrum modulation circuit in the embodiment of the invention;

Fig. 6 A and Fig. 6 B are the sketch mapes that is used in spread-spectrum modulation circuit in the DC-DC power management in the embodiment of the invention;

Fig. 7 A is the effect sketch map when not adopting spread spectrum scheme in the embodiment of the invention;

Fig. 7 B is the effect sketch map when adopting the PWM modulation system of Fig. 4 structure in the embodiment of the invention;

Fig. 8 is the flow chart of the signal processing method in the spread-spectrum modulation circuit in the embodiment of the invention;

Fig. 9 is the effect flow chart of the method for generation of variable frequency triangular-wave in the embodiment of the invention.

Embodiment

Embodiments of the invention also provide a kind of spread-spectrum modulation circuit, comprise variable frequency triangular-wave generator, first comparator and second comparator, and said variable frequency triangular-wave generator is connected with said first comparator and second comparator respectively; Said first comparator and second comparator are realized the spread spectrum of pulse-width modulated PWM according to the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator.

Wherein, said first comparator and second comparator realize that according to the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator the spread spectrum of pulse-width modulated PWM comprises:

Said first comparator and second comparator compare the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator respectively; Generate pwm signal; The duty ratio of said PMW signal is proportional to the amplitude of said input signal, has realized the spread spectrum to said PWM.

Wherein, said variable frequency triangular-wave generator specifically comprises: band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module, wherein:

There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; The voltage output of said band spectrum modulation module is connected respectively to the input of said first comparison module and second comparison module; The output of said first comparison module and second comparison module connects said application of logic circuit module; Said application of logic circuit module is controlled said first switch and second switch; Through controlling the state of said first switch and second switch; Make said first current source, second current source carry out charge or discharge at least one capacitor in the said band spectrum modulation module respectively, produce the triangular signal of changeable frequency.

Wherein, specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, said random signal generator are used for controlling said band spectrum modulation module changes in capacitance.

Volume embodiment of the present invention is year a kind of variable frequency triangular-wave generator also, comprising: band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module, wherein:

There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; The voltage output of said band spectrum modulation module is connected respectively to the input of said first comparison module and second comparison module; The output of said first comparison module and second comparison module connects said application of logic circuit module; Said application of logic circuit module is controlled said first switch and second switch; Through controlling the state of said first switch and second switch; Make said first current source, second current source carry out charge or discharge at least one capacitor in the said band spectrum modulation module respectively, produce the triangular signal of changeable frequency.

Wherein, specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, said random signal generator are used for controlling said band spectrum modulation module changes in capacitance.

In the embodiments of the invention; Variation through the random signal control capacitance to be producing the triangle wave circuit of a frequency change, and then realized spread-spectrum modulation circuit, and structure realizes simple; Make high fdrequency component be similar to the distribution of white noise, effectively reduce the electromagnetic interference in the available circuit.

Below in conjunction with accompanying drawing and embodiment, specific embodiments of the invention is done further explain.

Embodiments of the invention provide a kind of variable frequency triangular-wave generator, are used to produce the triangular wave of a changeable frequency, and its structure is as shown in Figure 3, comprising: band spectrum modulation module 10, application of logic circuit module 20, the first current source I _Source30, the second current source I _Sink40, first comparison module 70 and second comparison module 80, wherein: have first switch SW between the band spectrum modulation module 10 and first current source 30 _Source50, there is second switch SW between the band spectrum modulation module 10 and second current source 40 _Sink60; The voltage output of band spectrum modulation module 10 is connected respectively to the input of first comparison module 70 and second comparison module 80; Another input of first comparison module 70 and reference voltage Vref+be connected, another input of second comparison module 80 and reference voltage Vref-be connected.

The output of first comparison module 70 and second comparison module 80 connects application of logic circuit module 20; Application of logic circuit module 20 control first switch 50 and second switches 60; Through controlling the state of first switch 50 and second switch 60; Win current source 30, second current source 40 are charged to a plurality of capacitors in the band spectrum modulation module 10 respectively and discharge, produce the triangular wave of changeable frequency.

Concrete, specifically comprise in the band spectrum modulation module 10: random signal generator 11, at least one first capacitor C _Ramp12 and one second capacitor C _x13, random signal generator 11 is used for controlling band spectrum modulation module 10 changes in capacitance.The variation of this band spectrum modulation module 10 through random signal (Random Signal) control capacitance is to produce the triangular wave of a frequency change; Circuit is realized simple; Realize SSM (Spread Spectrum Mode, spread spectrum mode) function, produced the triangular wave that has spread performance; Promptly realize spread spectrum, reduce circuit EMI through changing the triangle wave frequency.The random signal generator that random signal generator 11 among Fig. 3 is made up of d type flip flop can change the size of electric capacity, realizes the change of frequency.

For the performance to this circuit is analyzed explanation in more detail, the following spread spectrum RAMP parameter of existing definition: the rate of spread, spread spectrum type, modulation rate and modulation waveform.The rate of spread is frequency jitter (or expansion) scope and former RAMP frequency (f _C) ratio.The spread spectrum type is pointed to spread spectrum, center spread spectrum or the spread spectrum that makes progress down.Suppose that the spread spectrum scope is Δ f, then rate of spread δ is defined as:

Downward spread spectrum: $\mathrm{\δ}=-\frac{\mathrm{\Δ\; f}}{f_C}\×100\%---\left(1\right)$

The center spread spectrum: $\mathrm{\δ}=\±\frac{\mathrm{\Δ\; f}}{2f_C}\×100\%---\left(2\right)$

Spread spectrum makes progress: $\mathrm{\δ}=\frac{\mathrm{\Δ\; f}}{f_C}\×100\%---\left(3\right)$

Modulation rate f _m, be used for confirming RAMP frequency expansion cycle rate, RAMP frequency change Δ f and turn back to original frequency in this cycle.Modulation waveform is represented RAMP frequency curve over time, is generally sawtooth waveforms.

In order to obtain the relation between EMI inhibition and the spread spectrum RAMP parameter, need at first calculate the frequency spectrum of spread spectrum RAMP.According to above-mentioned definition, signal spectrum is the power density with frequency dependence.In order to simplify analysis, only consider the primary harmonic of RAMP signal.

For RAMP, can be expressed as: Asin2 π f without spread spectrum _CT (4)

For the RAMP of spread spectrum, can be expressed as: Asin2 π (f _C+ ω (t)) t (5)

In the formula (5), ω (t) is a modulation waveform.For the RAMP frequency spectrum without spread spectrum, it is to be positioned at f _CA spectral line, amplitude does

Because this frequency spectrum is a spectral line, the resolution bandwidth B of its amplitude and spectrum analyzer is irrelevant.For the spectrum amplitude of the RAMP of spread spectrum, it depends on resolution bandwidth B.Because the power of spread spectrum RAMP distributes quite even in Δ f frequency band; Utilize resolution bandwidth to be approximately:

for the power that the test of the spectrum analyzer of B obtains like this, can obtain EMI inhibiting rate S (dB) and be:

$S=10\log \left(\frac{1}{2}{A}^2\right)\left(\frac{1}{2}{A}^2\frac{B}{\mathrm{\Δf}}\right)=10\log \frac{\mathrm{\Δf}}{B}---\left(6\right)$

In conjunction with above-mentioned spread spectrum RAMP parameter: rate of spread δ, RAMP frequency f _CAnd modulation type, can use following method to calculate S:

Spread spectrum downward or upward: $S=10\mathrm{Log}\frac{\left|\mathrm{\δ}\right|\×f_C}{B}---\left(7\right)$

The center spread spectrum $S=10\mathrm{Log}\frac{2\left|\mathrm{\δ}\right|\×f_C}{B}---\left(8\right)$

It should be noted that and work as f _SW＜＜f _m＜＜f _CThe time, EMI inhibiting rate S and modulation rate f _mIrrelevant, wherein, f _SWIt is the sweep speed of spectrum analyzer.Suppose δ and f _CBe respectively 15% and 1MHz, resolution bandwidth is 10kHz, and scanning frequency is 10Hz, adopts the mode of center spread spectrum to calculate the EMI inhibiting rate according to formula (8):

$S=10\log \frac{2\&times;0.15\&times;1\mathrm{<figure-callout\; id="10"\; label="MHz"\; filenames="S2008101279007E00021.png,S2008101279007E00032.png"\; state="\{\{state\}\}">MHz</figure-callout>}}{10\mathrm{kHz}}=14.77\mathrm{dB}.$

Usually, when the EMI between the estimation peak value suppressed, because the fluctuation of spread frequency spectrum, the possibility of result that is obtained by formula (6) can exceed 1dB to 2dB.Suppress with average EMI for peak value, calculated value is very near measured value.The simple computation formula that utilizes EMI to suppress can be according to desirable EMI inhibiting rate, RAMP frequency and the desired resolution bandwidth of the Electro Magnetic Compatibility rate that is expanded.

Embodiments of the invention are modes of employing center spread spectrum, and under the band spectrum modulation pattern, the Cycle by Cycle in its cycle changes can reduce (f under the fundamental frequency ₀± (10%～20%)) spectrum energy is expanded specific bandwidth (nf simultaneously ₀± (10%～20%) %, n is a positive integer) interior harmonic component.At this moment a large amount of spectrum energies is not each the frequency multiplication place that concentrates on switching frequency, but in a bandwidth that increases with frequency broadening.Behind the frequency exceedance megahertz, broader frequency spectrum seems similarly to be white noise, thereby reaches the purpose that reduces EMI.Energy is included in the frequency band of broad, and peak energy also is minimized.

A kind of spread-spectrum modulation circuit is provided in the embodiments of the invention.Shown in Fig. 4 A and 4B, use existing Ramp (triangular-wave generator) among the replacement of the variable frequency triangular-wave generation circuit in the embodiment of the invention shown in Fig. 4 B Fig. 4 A.Comprise: frequency conversion rate triangle wave generating circuit 100, first comparator 200 and second comparator 300; Variable frequency triangular-wave generator 100 is connected with first comparator 200 and second comparator 300 respectively; First comparator 200 and second comparator 300 are realized the spread spectrum of pulse-width modulated PWM according to the variable frequency triangular-wave of input signal and variable frequency triangular-wave generator 100 inputs.In the present embodiment, the PWM modulation circuit of the band spread spectrum shown in Fig. 4 B adopts frequency conversion rate triangle wave generating circuit, and input audio signal and triangular wave or oblique wave with variable carrier frequency work are compared, and this produces pulse train under the carrier frequency condition.In each carrier cycle, the duty ratio of pwm pulse is proportional to the amplitude of audio signal.Can solve the EMI problem like this, and circuit is realized simple.The detailed structure of this frequency conversion rate triangle wave generating circuit please refer to the description among above-mentioned Fig. 3, does not do being repeated in this description at this.

A kind of spread-spectrum modulation circuit also is provided in the embodiments of the invention.Shown in Fig. 5 A and 5B, use existing Ramp (triangular-wave generator) among the replacement of the variable frequency triangular-wave generation circuit in the embodiment of the invention shown in Fig. 5 B Fig. 5 A.In the present embodiment, control a plurality of electric capacity with random signal, the PWM modulation circuit of this belt transect spread spectrum is the triangular-wave generator that adopts variable frequency, can solve the EMI problem very effectively like this, and circuit is realized simple.The detailed structure of this frequency conversion rate triangle wave generating circuit please refer to the description among above-mentioned Fig. 3, and difference only is to have used with random signal controls a plurality of electric capacity, does not do being repeated in this description at this.

In power management chip, carry out the PWM modulation through triangular wave generator and comparator, there is the EMI problem equally.Also be provided at the method for Using P WM band spectrum modulation in the DC-DC power management in the embodiments of the invention.Shown in Fig. 6 A and 6B, the triangular-wave generator of Ramp in the prior art can reduce the EMI problem effectively among the frequency conversion rate triangle wave generating circuit replacement Fig. 6 A shown in use Fig. 6 B in the embodiment of the invention, has improved the overall performance of DC-DC circuit.The detailed structure of this frequency conversion rate triangle wave generating circuit please refer to the description among above-mentioned Fig. 3, does not do being repeated in this description at this.

When using the spread-spectrum modulation circuit that the embodiment of the invention provides, the EMI that carries out with prior art relatively sketch map shown in Fig. 7 A and Fig. 7 B.Wherein, Fig. 7 A is not for adopting the effect of spread spectrum scheme, and Fig. 7 B is for adopting the effect of the PWM modulation system of structure shown in Fig. 4 A.δ and f _CBe respectively 15% and 1MHz, resolution bandwidth is 10kHz, and scanning frequency is 10Hz, adopts the mode of center spread spectrum to calculate the EMI inhibiting rate: $\text{S=10log}\frac{2\&times;0.15\&times;1\mathrm{<figure-callout\; id="10"\; label="MHz"\; filenames="S2008101279007E00021.png,S2008101279007E00032.png"\; state="\{\{state\}\}">MHz</figure-callout>}}{10\mathrm{KHz}}=14.77\mathrm{DB}.$ Shown in Fig. 7 B, for the spread-spectrum modulation circuit in the embodiment of the invention, weigh the EMI problem with 30MHz with upper frequency usually, the 15dB that descended, so Fig. 7 B compares than Fig. 7 A, obviously reduced the problem of EMI effectively, reduced the cost of whole system.Usually, when the EMI between the estimation peak value suppressed, because the fluctuation of spread frequency spectrum, the possibility of result that is calculated by formula (1) can exceed 1dB to 2dB.Suppress with average EMI for peak value, calculated value is very near measured value.Adopt the present invention, the Cycle by Cycle in its cycle changes can reduce (f under the fundamental frequency ₀± (10%～20%)) spectrum energy is expanded specific bandwidth (nf simultaneously ₀± (10%～20%), n are positive integer) interior harmonic component.At this moment a large amount of spectrum energies is not each the frequency multiplication place that concentrates on switching frequency, but in a bandwidth that increases with frequency broadening.Behind the frequency exceedance megahertz, broader frequency spectrum seems similarly to be white noise, thereby reaches the purpose that reduces EMI.

Embodiments of the invention also provide the signal processing method in a kind of spread-spectrum modulation circuit, comprising:

Step 800: produce at least one variable frequency triangular-wave signal;

Step 801: said variable frequency triangular-wave signal is input to first comparator and second comparator respectively; Make said first comparator and second comparator according to input signal and said variable frequency triangular-wave signal, realize the spread spectrum of pulse-width modulated PWM.

Wherein, said first comparator and second comparator realize that according to input signal and said variable frequency triangular-wave signal the spread spectrum of pulse-width modulated PWM comprises:

Said first comparator and second comparator compare the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator respectively; Generate pwm signal; The duty ratio of said PMW signal is proportional to the amplitude of said input signal, has realized the spread spectrum to said PWM.

Wherein, The step of at least one variable frequency triangular-wave signal of said generation is implemented by variable frequency triangular-wave generator; Said variable frequency triangular-wave generator specifically comprises: band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source;

At least one variable frequency triangular-wave signal of said generation comprises:

The voltage output of band spectrum modulation module is sent to the input of said first comparison module and second comparison module respectively;

Said application of logic circuit module is sent in the output of said first comparison module and second comparison module;

Control the state of said first switch and second switch through said application of logic circuit module, make said first current source, second current source charge to a plurality of capacitors in the said band spectrum modulation module respectively and discharge, produce the triangular wave of changeable frequency.

Wherein, specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, the voltage output of said band spectrum modulation module comprises:

Control changes in capacitance in the said band spectrum modulation module through said random signal generator, the voltage that obtains changing output.

Embodiments of the invention also provide a kind of method for generation of variable frequency triangular-wave; Be applied to comprise in the circuit of band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; Said method comprises:

Step 900: the input that the voltage output of band spectrum modulation module is sent to said first comparison module and second comparison module respectively;

Step 901: the output of said first comparison module and second comparison module is sent to said application of logic circuit module;

Step 902: the state of controlling said first switch and second switch through said application of logic circuit module; Make said first current source, second current source charge to a plurality of capacitors in the said band spectrum modulation module respectively and discharge, produce the triangular wave of changeable frequency.

Wherein, specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, control changes in capacitance in the said band spectrum modulation module through said random signal generator, the voltage that obtains changing output.

The embodiment of the application of the invention; The variation of using the random signal control capacitance has realized spread-spectrum modulation circuit to produce the triangle wave circuit of a frequency change, and structure realizes simple; Make high fdrequency component be similar to the distribution of white noise, effectively reduced the EMI problem; The output of spread-spectrum modulation circuit can directly come filtering through the stray inductance of loud speaker in addition, need not add inductance capacitance and come filtering, has significantly reduced system cost.

More than disclosedly be merely several specific embodiment of the present invention, still, the present invention is not limited thereto, any those skilled in the art can think variation all should fall into protection scope of the present invention.

Claims (8)

1. spread-spectrum modulation circuit; It is characterized in that; Comprise variable frequency triangular-wave generator, first comparator and second comparator; Said variable frequency triangular-wave generator comprises the band spectrum modulation module, and said variable frequency triangular-wave generator is connected with said first comparator and second comparator respectively; Said first comparator and second comparator are realized the spread spectrum of pulse-width modulated PWM according to the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator;

Specifically comprise in the wherein said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, said random signal generator are used for controlling said band spectrum modulation module changes in capacitance.

2. spread-spectrum modulation circuit according to claim 1; It is characterized in that; Said first comparator and second comparator realize that according to the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator the spread spectrum of pulse-width modulated PWM comprises:

Said first comparator and second comparator compare the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator respectively; Generate pwm signal; The duty ratio of said PMW signal is proportional to the amplitude of said input signal, has realized the spread spectrum to said PWM.

3. spread-spectrum modulation circuit according to claim 1 is characterized in that said variable frequency triangular-wave generator also comprises application of logic circuit module, first current source, second current source, first comparison module and second comparison module, wherein:

There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; The voltage output of said band spectrum modulation module is connected respectively to the input of said first comparison module and second comparison module; The output of said first comparison module and second comparison module connects said application of logic circuit module; Said application of logic circuit module is controlled said first switch and second switch; Through controlling the state of said first switch and second switch; Make said first current source, second current source carry out charge or discharge at least one capacitor in the said band spectrum modulation module respectively, produce the triangular signal of changeable frequency.

4. variable frequency triangular-wave generator; It is characterized in that; Comprise: band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, said random signal generator are used for controlling said band spectrum modulation module changes in capacitance, wherein:

There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; The voltage output of said band spectrum modulation module is connected respectively to the input of said first comparison module and second comparison module; The output of said first comparison module and second comparison module connects said application of logic circuit module; Said application of logic circuit module is controlled said first switch and second switch; Through controlling the state of said first switch and second switch; Make said first current source, second current source carry out charge or discharge at least one capacitor in the said band spectrum modulation module respectively, produce the triangular signal of changeable frequency.

5. the signal processing method in the spread-spectrum modulation circuit is characterized in that, comprising:

Variable frequency triangular-wave generator produces at least one variable frequency triangular-wave signal; Said variable frequency triangular-wave generator comprises the band spectrum modulation module; Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity; Said random signal generator is controlled changes in capacitance in the said band spectrum modulation module, the voltage that obtains changing output;

Said variable frequency triangular-wave signal is input to first comparator and second comparator respectively; Make said first comparator and second comparator according to input signal and said variable frequency triangular-wave signal, realize the spread spectrum of pulse-width modulated PWM.

6. the signal processing method in the spread-spectrum modulation circuit as claimed in claim 5; It is characterized in that; Said first comparator and second comparator realize that according to input signal and said variable frequency triangular-wave signal the spread spectrum of pulse-width modulated PWM comprises:

Said first comparator and second comparator compare the variable frequency triangular-wave signal of input signal and the input of said variable frequency triangular-wave generator respectively; Generate pwm signal; The duty ratio of said PMW signal is proportional to the amplitude of said input signal, has realized the spread spectrum to said PWM.

7. like the signal processing method in the said spread-spectrum modulation circuit of claim 5; It is characterized in that; Said variable frequency triangular-wave generator also comprises: application of logic circuit module, first current source, second current source, first comparison module and second comparison module; There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source;

At least one variable frequency triangular-wave signal of said generation comprises:

The voltage output of band spectrum modulation module is sent to the input of said first comparison module and second comparison module respectively;

Said application of logic circuit module is sent in the output of said first comparison module and second comparison module;

Control the state of said first switch and second switch through said application of logic circuit module, make said first current source, second current source charge to a plurality of capacitors in the said band spectrum modulation module respectively and discharge, produce the triangular wave of changeable frequency.

8. the method for generation of a variable frequency triangular-wave; It is characterized in that; Be applied to comprise in the circuit of band spectrum modulation module, application of logic circuit module, first current source, second current source, first comparison module and second comparison module; There is first switch between said band spectrum modulation module and said first current source, has second switch between said band spectrum modulation module and said second current source; Said method comprises:

The voltage output of band spectrum modulation module is sent to the input of said first comparison module and second comparison module respectively;

The output of said first comparison module and second comparison module is sent to said application of logic circuit module;

Control the state of said first switch and second switch through said application of logic circuit module, make said first current source, second current source charge to a plurality of capacitors in the said band spectrum modulation module respectively and discharge, produce the triangular wave of changeable frequency;

Specifically comprise in the said band spectrum modulation module: random signal generator, at least one first electric capacity and one second electric capacity, control changes in capacitance in the said band spectrum modulation module through said random signal generator, the voltage that obtains changing output.

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