Carrier signal spectrum spreading method, class D amplifier and carrier signal generator

Abstract

The invention provides a carrier signal spectrum spreading method, a carrier signal generator, a medium and electronic equipment. The method comprises the following steps: determining the lowest frequency of a target signal; based on the lowest frequency of the target signal, determining a modulation frequency corresponding to the carrier signal, the modulation frequency being greater than 0, and the modulation frequency being less than or equal to a half of the lowest frequency of the target signal; presetting a frequency offset range corresponding to the carrier signal; based on the modulation frequency and the frequency offset range, spectrum spreading is carried out on the carrier signal, the carrier signal after spectrum spreading is used for modulating the target signal, the method remarkably improves the modulation coefficient, the energy of the fundamental wave of the carrier signal after spectrum spreading approaches 0, the spectrum spreading effect is good, the peak value of EMI can be reduced, the performance of the system can be optimized, and the performance of the system can be improved. Moreover, the carrier signal is prevented from entering the frequency range of the target signal during modulation, and the influence on the quality of the target signal is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, and in particular to a carrier signal spread spectrum method, a class D amplifier, a first carrier signal generator, a second carrier signal generator and an electronic device. Background Art

[0002] In recent years, spread spectrum technology (or "dithering") has been increasingly used in the field of radio and wired communications. For example, in a switching regulator or Class D amplifier environment, spread spectrum technology can work within the fixed operating frequency of the switching circuit and its n-fold frequency (harmonics), dispersing energy over multiple frequencies and reducing the electromagnetic interference (EMI) generated by fixed frequency switching.

[0003] However, the use of spread spectrum technology in class D amplifiers will encounter some limitations. In class D amplifiers, in order to reduce the output ripple of the switch output module in the audio circuit and avoid large changes in the inductor current ripple, the frequency deviation range corresponding to the carrier signal can only be set to a smaller range. In addition, in audio devices such as class D amplifiers, spread spectrum technology may bring additional audio distortion, reducing the sound quality of the device. This distortion is often manifested as an increase in noise level (Noise) or total harmonic distortion (THDN), affecting the user experience.

[0004] Therefore, how to significantly improve the EMI of the circuit without affecting the quality of the output signal has become a technical problem that the industry urgently needs to solve. Summary of the invention

[0005] The present invention provides a carrier signal spread spectrum method, a class D amplifier, a first carrier signal generator, a second carrier signal generator and an electronic device, which solve the technical problem of how to significantly improve the EMI of the circuit without affecting the quality of the output signal.

[0006] According to a first aspect of the present invention, an embodiment of the present invention provides a carrier signal spread spectrum method, the method comprising:

[0007] Determine the lowest frequency of the target signal;

[0008] Based on the lowest frequency of the target signal, determining a modulation frequency corresponding to the carrier signal, wherein the modulation frequency is greater than 0 and is less than or equal to half of the lowest frequency of the target signal;

[0009] Presetting a frequency deviation range corresponding to the carrier signal;

[0010] The carrier signal is spread spectrum-modulated based on the modulation frequency and the frequency deviation range, wherein the spread spectrum-modulated carrier signal is used to modulate the target signal.

[0011] Optionally, the modulation frequency is at least lower than one third of the lowest frequency of the target signal.

[0012] Optionally, the carrier signal is a triangle wave signal, a sawtooth wave signal, a sine wave signal or a square wave signal.

[0013] According to a second aspect of the present invention, an embodiment of the present invention provides a class D amplifier, comprising:

[0014] A pulse width modulation module, wherein a first input terminal receives a target signal, a second input terminal receives a carrier signal spread by the carrier signal spread method according to any one of the first aspects of the present invention, and an output terminal outputs a PWM control signal;

[0015] The switch output module is used to output a driving signal according to the PWM signal.

[0016] Optionally, the target signal is an audio signal, and the modulation frequency range corresponding to the carrier signal is greater than 0 and less than or equal to 10 Hz.

[0017] Optionally, the modulation frequency range corresponding to the carrier signal is greater than 0 and less than or equal to 20 / 3 Hz.

[0018] Optionally, the class D amplifier further includes a speaker and an LC filter module, and the LC filter module includes a filter inductor and a filter capacitor;

[0019] The first end of the filter inductor is coupled to the output end of the switch output module, the second end of the filter inductor is grounded through the filter capacitor, and the second end of the filter inductor is also coupled to the input end of the speaker.

[0020] According to a third aspect of the present invention, an embodiment of the present invention provides a first carrier signal generator, including:

[0021] A first oscillator integrated with a spread spectrum function is used to output the spread spectrum carrier signal based on the spread spectrum method described in any one of the first aspects of the present invention.

[0022] According to a fourth aspect of the present invention, an embodiment of the present invention provides a second carrier signal generator, including:

[0023] A second oscillator, used for outputting a high-frequency clock signal;

[0024] A frequency divider, configured to divide the high-frequency clock signal based on a spread spectrum pattern, and output a low-frequency clock signal with spread spectrum in a form preset by the spread spectrum pattern, wherein the spread spectrum pattern is used to implement the spread spectrum method according to any one of the first aspects of the present invention;

[0025] The carrier generation module is used to output the carrier signal after spectrum spreading based on the clock signal with spectrum spreading.

[0026] Optionally, the second carrier signal generator is a closed-loop structure or an open-loop structure.

[0027] According to a fifth aspect of the present invention, an embodiment of the present invention provides an electronic device, comprising the class D amplifier described in any one of the second aspect of the present invention.

[0028] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0029] In the carrier signal spread spectrum method, the first carrier signal generator, the second carrier signal generator and the electronic device of the technical solution of the present invention, the method determines the lowest frequency of the target signal; based on the lowest frequency of the target signal, determines the modulation frequency corresponding to the carrier signal, wherein the modulation frequency is greater than 0 and the modulation frequency is less than or equal to half of the lowest frequency of the target signal; presets the frequency deviation range corresponding to the carrier signal; based on the modulation frequency and the frequency deviation range, spreads the carrier signal, wherein the spread carrier signal is used to modulate the target signal. The method of the present invention significantly improves the modulation coefficient, and the energy of the fundamental wave of the spread carrier signal approaches 0, so that the spread spectrum effect is better, thereby reducing the peak value of EMI and optimizing the performance of the system. In addition, the present invention also avoids the carrier signal entering the frequency range of the target signal during modulation, thereby avoiding affecting the quality of the target signal.

[0030] The class D amplifier of the technical solution of the present invention includes a pulse width modulation module, a first input end of which receives a target signal, a second input end of which receives a carrier signal spread by the carrier signal spread method of the present invention, and an output end of which outputs a PWM control signal; and a switch output module, which is used to output a drive signal according to the PWM signal. Since the carrier signal received in the class D amplifier is the carrier signal of the present invention spread by the carrier signal spread method of the present invention, the carrier signal will not enter the frequency range of the target signal during modulation, thereby avoiding affecting the output signal of the class D amplifier, and the energy of the fundamental wave of the spread carrier signal approaches 0, and the energy of other orders approaches 0, so that the EMI energy of the power amplifier at these specific frequencies is low, which significantly improves the EMI problem of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 It is a flowchart of a carrier signal spreading method provided by an embodiment of the present invention;

[0033] Figure 2 is a waveform diagram of a first type Bessel function at different orders provided by an embodiment of the present invention;

[0034] Figure 3 is a structural schematic diagram of a class D amplifier provided by an embodiment of the present invention;

[0035] Figure 4 is a structural schematic diagram of a class D amplifier provided by another embodiment of the present invention;

[0036] Figure 5 This is an EMI spectrum diagram formed by a switch output module at different frequency points provided by an embodiment of the present invention;

[0037] Figure 6 It is a structural schematic diagram of a carrier signal generator provided in one embodiment of the present invention.

[0038] Reference numerals:

[0039] 51- Pulse width modulation module;

[0040] 52- switch output module;

[0041] 53-LC filter module;

[0042] 54-speaker;

[0043] L-filter inductor;

[0044] C-filter capacitor;

[0045] 61 - second oscillator;

[0046] 62-divider;

[0047] 63-carrier generation module;

[0048] 631-Frequency and phase detector;

[0049] 632-charge pump;

[0050] 634-Voltage Controlled Oscillator;

[0051] 633-reference voltage generation module;

[0052] 635-loop filter;

[0053] 636 - Second divider. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0056] The technical solution of the present invention is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0057] As described in the background art, the problem of how to significantly improve the EMI of the circuit without affecting the quality of the output signal is described in detail below.

[0058] When optimizing spread spectrum technology, the most important factor is the modulation index Among them, f C is the center frequency of the unmodulated oscillator (carrier signal), f m is the modulation frequency, Δf C It is the frequency deviation range, which can be understood as the range in which the switching frequency deviates from the unmodulated oscillator (carrier) frequency;

[0059] Among them, the larger the modulation coefficient, the higher the fundamental frequency f of the carrier signal. C The lower the energy, the better the spectrum spreading effect, which can significantly reduce the EMI problem in the circuit. For example, by increasing the frequency deviation range Δf C, increasing the energy dispersed at other frequencies, and also reducing the modulation frequency f m , so that the spectrum distribution of the spread spectrum signal is wider, thereby converting the original concentration at the center frequency f C The energy on the surface is dispersed into a wider bandwidth, that is, dispersed into the bandwidth defined by the Casson formula (2Δf C )Inside.

[0060] However, in practical applications, for the frequency deviation range Δf C and the modulation frequency f m There are limits to changes.

[0061] Specifically, for the frequency deviation range Δf C , in the time domain, increase the frequency deviation range Δf C It will increase the output ripple of the circuit. In the frequency domain, it may cause f C + / -Δf C Entering the frequency range where electromagnetic compatibility (EMC) limitations occur.

[0062] For the modulation frequency f m , theoretically the modulation frequency f m The lower the modulation frequency is, the lower the attenuation of the base frequency is. However, in some special applications, such as audio circuits (such as Class D amplifiers), if the modulation frequency f m If it falls into the audio frequency range (i.e. 20Hz ~ 20kHz), the two key performance indicators of the audio circuit (such as Class D amplifier), the noise level (Noise) and total harmonic distortion (THDN), will be significantly deteriorated, and the output audio quality will be reduced;

[0063] If the modulation frequency f m The frequency falls within the range of 20k~40kHz, the performance of the noise level (Noise) in the audio band will not be affected, but when there is an audio signal f in When the audio circuit (such as a Class D amplifier) ​​is input, the audio signal will follow the modulation frequency f m Intermodulation is generated, producing f in -n×f m , or f in +n×f m The additional frequency components of , where n is a natural number, will also lead to a degradation of the total harmonic distortion (THDN) performance.

[0064] Therefore, for a Class D amplifier, the modulation frequency f corresponding to the carrier signal is m The minimum frequency cannot be lower than 40kHz, and the frequency deviation range is Δf CIt is usually set within the range of + / -10% of the fundamental frequency, which makes the modulation coefficient smaller, and thus the reduction of the energy of the fundamental frequency and harmonics is very limited.

[0065] To solve the above problems, please refer to Figure 1 , an embodiment of the present invention provides a carrier signal spread spectrum method, the method comprising:

[0066] S1: Determine the lowest frequency of the target signal;

[0067] It should be understood that the lowest frequency of the target signal is preset in step S1.

[0068] S2: determining a modulation frequency corresponding to the carrier signal based on the lowest frequency of the target signal, wherein the modulation frequency is greater than 0 and is less than or equal to half of the lowest frequency of the target signal;

[0069] S3: Preset the frequency deviation range corresponding to the carrier signal;

[0070] S4: Based on the modulation frequency and the frequency deviation range, the carrier signal is spread spectrum, wherein the carrier signal after the spread spectrum is used to modulate the target signal.

[0071] For example, the carrier signal is a triangular wave signal, a sawtooth wave signal, a sine wave signal or a square wave signal. Of course, the present invention is not limited to this, and those skilled in the art can select a suitable signal shape as needed.

[0072] In actual use, the modulated target signal can be used to drive a switch tube. The use of the spread spectrum carrier signal provided by the present invention can significantly reduce the EMI impact generated by a fixed frequency switch.

[0073] Now combined Figure 2 The specific principle and effect of this method are explained. Figure 2 The waveforms of the first kind of Bessel function at different orders are shown.

[0074] A periodic signal f(t) with a period of T can be expanded by Fourier series. At the same time, according to the spread spectrum theory, the first-kind Bessel function can be used to represent the energy of the fundamental wave and harmonics after spread spectrum, and the following formula can be obtained:

[0075]

[0076] Among them, cos(2πf C t+βsin(2πf m t)) can be understood as the carrier signal after spread spectrum, where 2πf Ct is used to represent the phase of the carrier signal, βsin(2πf m t) is used to indicate the modulation of the carrier signal by the modulating signal, f C is the fundamental frequency of the carrier signal, f m is the modulation frequency of the spread spectrum, β is the spread spectrum factor, where

[0077] We can understand the performance of the carrier signal after spreading in the frequency domain, where J k (β) is the k-th order Bessel function of the first kind, representing the amplitude coefficient of the k-th order sideband component, cos(2π(f C +kf m )t) represents the harmonic components in the frequency domain.

[0078] In a specific implementation, the target signal frequency range is 20 Hz to 20 kHz, and the fundamental frequency of the carrier signal is 400 kHz;

[0079] In this case, if the frequency deviation range Δf is set C is 40kHz, the modulation frequency f m is 40kHz, then the calculated spreading factor is

[0080] Please continue to refer to Figure 2 , showing the first kind Bessel functions J from order 0 to 4 k (β) waveform diagram, where:

[0081] J0 can be understood as the unmodulated fundamental frequency component of the carrier signal;

[0082] J1 can be understood as the first-order sideband component of the carrier signal after modulation;

[0083] J2 can be understood as the second-order sideband component of the carrier signal after modulation;

[0084] J3 can be understood as the third-order sideband component of the carrier signal that appears after modulation;

[0085] J4 can be understood as the fourth-order sideband component of the carrier signal that appears after modulation.

[0086] It can be seen that when the spread spectrum factor is 1, the component of the fundamental frequency J0 is still strong, and the weakening of the fundamental frequency is not obvious. The component of J1 is also large, indicating that the main energy after modulation is concentrated in the fundamental frequency and the first-order sideband, and the second-order and higher sideband components are small, indicating that the modulation does not effectively disperse the energy to the high-order sidebands, and the spread spectrum effect is limited. As a result, the reduction of the energy of the fundamental frequency and harmonics is very limited.

[0087] In this case, if the frequency deviation range Δf is set C is 40kHz, the modulation frequency f m is 10Hz, then the calculated spreading factor is It can be seen that the present invention greatly increases the spread spectrum factor, so that the energy of the baseband component and the sideband component can both approach 0, so that the spread spectrum effect is better, thereby reducing the peak value of EMI in the circuit and optimizing the performance of the system. Not only that, the present invention also avoids the carrier signal entering the frequency range of the target signal during modulation, avoiding affecting the quality of the target signal.

[0088] In actual implementation, the carrier signal is not a single-frequency sine wave. There are also higher harmonics such as the 2nd and 3rd harmonics of the carrier center frequency. The carrier after spread spectrum, the spread frequency fm, and its higher harmonics, such as the second harmonic (2nd frequency), third harmonic (3rd frequency) and other high-frequency components, will also appear on the carrier signal. Therefore, in a preferred embodiment, the modulation frequency can be set to be at least one-third lower than the lowest frequency of the target signal, so that the third harmonic will also be lower than the target signal frequency, and the energy of the 5th and above harmonics is often small enough to be drowned by noise;

[0089] In this way, it can be ensured that when the carrier after spread spectrum modulates the input signal, the quality of the output signal can be further improved and the EMI of the circuit can be significantly improved.

[0090] In addition, please refer to Figure 3 , an embodiment of the present invention further provides a class D amplifier, comprising:

[0091] A pulse width modulation module 51, whose first input terminal receives a target signal, whose second input terminal receives a carrier signal spread by any of the above-mentioned carrier signal spread spectrum methods, and whose output terminal outputs a PWM control signal;

[0092] The switch output module 52 is used to output a driving signal according to the PWM signal.

[0093] It should be understood that Figure 3 An example of a single-ended Class D amplifier is Figure 3 Only the circuit structure related to the carrier signal is shown. In actual implementation, the class D amplifier can also be implemented in a differential manner. The class D amplifier also includes other modules, such as an integrator, a feedback module, etc. Of course, the present invention does not limit the specific structure of the class D amplifier. As long as the carrier signal is spread by the carrier signal spread spectrum method described in the present invention, it is within the protection scope of the present invention.

[0094] It can be seen that since the carrier signal received in the class D amplifier is a carrier signal spread by the carrier signal spreading method of the present invention, the carrier signal will not enter the frequency range of the target signal during modulation, thereby avoiding affecting the output signal of the class D amplifier. In addition, the energy of the fundamental wave of the spread carrier signal approaches 0, and the energy of other orders approaches 0, so that the EMI energy of the power amplifier at these specific frequencies is lower, which significantly improves the EMI problem of the circuit.

[0095] In a specific implementation, the target signal is an audio signal. Since the frequency range of the audio signal is 20 Hz to 20 kHz, the modulation frequency range corresponding to the carrier signal can be set to be greater than 0 and less than or equal to 10 Hz.

[0096] In audio signal processing, in order to further avoid harmonic interference, the second harmonic or third harmonic is generally prevented from falling into the frequency band of the target signal. Therefore, in a preferred embodiment, the modulation frequency range corresponding to the carrier signal is greater than 0 and less than or equal to 20 / 3 Hz.

[0097] In actual design, please refer to Figure 4 , the class D amplifier further includes a speaker 54 and an LC filter module 53, the LC filter module 53 includes a filter inductor L and a filter capacitor C;

[0098] The first end of the filter inductor L is coupled to the output end of the switch output module 52 , the second end of the filter inductor L is grounded through the filter capacitor C, and the second end of the filter inductor L is also coupled to the input end of the speaker 54 .

[0099] In this case, as an example, the switch output module 52 may include an H-bridge circuit, the on-off of the upper tube and the lower tube in the H-bridge circuit is controlled by the PWM signal, and the output end of the H-bridge circuit outputs the speaker 54 drive signal (i.e., the drive signal).

[0100] Now combined Figure 3 and Figure 5 The effect of improving EMI of the present invention is described.

[0101] Please refer to Figure 5 , showing Figure 3 The EMI spectrum diagram formed by the switch output module 52 at different frequency points shown in the figure, the EMI test frequency range corresponding to the EMI spectrum diagram is 150kHz~30MHz, and the frequency range corresponds to the standard conducted interference (Conducted Emission) test range; wherein:

[0102] The purple curve can be understood as a scanning curve of EMI caused by the switching frequency inside the switch output module 52 after the carrier signal is directly input into the pulse width modulation module 51;

[0103] The orange curve can be understood as the EMI scanning curve caused by the switching frequency inside the switch output module 52 after the carrier signal spread by any of the above-mentioned carrier signal spread methods is input into the pulse width modulation module 51;

[0104] The red straight line can be understood as the limit standard of EMI test, that is, the maximum allowable value during the test;

[0105] Since the switching frequency inside the switch output module 52 is the same as the frequency of the carrier signal, then:

[0106] ① can be understood as the frequency of the carrier signal, that is, f C ;

[0107] ②It can be understood as the second harmonic, which is twice the frequency of the carrier signal, that is, 2f C ;

[0108] ③ You can understand the third harmonic, which is three times the frequency of the carrier signal, that is, 3f C .

[0109] It can be seen that when the frequency of the carrier signal is fixed, the EMI spectrum will show a peak at the frequency point corresponding to the fundamental wave of the carrier signal and its harmonics. It can be seen that the fixed switching frequency will produce significant peak interference at the fundamental frequency and harmonic frequency;

[0110] The spread spectrum carrier signal provided by the present invention can make the switching frequency inside the switch output module 52 vary within a range, which disperses the fundamental and harmonic energy into a wider frequency band. It can be seen from the EMI spectrum diagram that the peak of the orange curve is reduced and the spectrum is smoother, thereby effectively reducing EMI noise and improving the electromagnetic compatibility (EMC) of the system.

[0111] It can be seen that the spread spectrum carrier signal provided by the present invention can reduce the EMI impact caused by the fixed frequency switch. It should be understood that the EMI test frequency range shown in the present invention is only an example, and does not mean that the effect of the present invention is only effective when the EMI test frequency range is in the standard conducted interference test range of 150kHz to 30MHz, and it can also be effective when the frequency range corresponds to the standard radiated interference test range.

[0112] In addition, the present invention also provides a first carrier signal generator, comprising:

[0113] The first oscillator integrated with a spread spectrum function is used to output the carrier signal after spread spectrum based on any of the spread spectrum methods described above.

[0114] It should be understood that this oscillator can directly output the carrier signal required by the circuit;

[0115] In another embodiment, the carrier signal generator may also be an oscillator without a spread spectrum function. Figure 6 The present invention also provides a second carrier signal generator, comprising:

[0116] A second oscillator 61, configured to output a high-frequency clock signal;

[0117] A frequency divider 62, configured to divide the high-frequency clock signal based on a spread spectrum pattern, and output a low-frequency clock signal with spread spectrum in a form preset by the spread spectrum pattern, wherein the spread spectrum pattern is used to implement any of the above-mentioned spread spectrum methods;

[0118] The carrier generation module 63 is used to output the carrier signal after spectrum spreading based on the clock signal with spectrum spreading.

[0119] In actual implementation, the second carrier signal generator may be a closed-loop structure or an open-loop structure.

[0120] As an example, please refer to Figure 6 ,exist Figure 6 In the example, the carrier generation module 63 is a closed-loop phase-locked loop system, including a frequency detector 631, a charge pump 632, a voltage-controlled oscillator 634, a reference voltage generation module 633, a loop filter 635 and a second frequency divider 636 connected in sequence;

[0121] The phase frequency detector 631 is connected to the second frequency divider 636, the external input terminal and the charge pump 632 respectively, the external input terminal is used to receive the clock signal with spread spectrum, the phase frequency detector 631 is used to compare the phase difference between the clock signal with spread spectrum and the feedback signal output by the second frequency divider 636, and generate a control signal according to the comparison result;

[0122] The charge pump 632 is connected to the low-pass filter and the voltage-controlled oscillator 634. The charge pump 632 charges or discharges the filter capacitor in the low-pass filter under the control of the control signal.

[0123] The low-pass filter is connected between the charge pump 632 and the voltage-controlled oscillator 634 to filter out high-frequency jitter of the output voltage of the charge pump 632;

[0124] The voltage controlled oscillator 634 is coupled to the reference voltage generating module 633 and is used to generate a corresponding output signal under the control of the voltage output by the reference voltage generating module 633;

[0125] The second frequency divider 636 is also connected to the voltage-controlled oscillator 634 . The second frequency divider 636 is used to divide the output signal generated by the voltage-controlled oscillator 634 to obtain a feedback signal, and input the feedback signal to the frequency detector 631 .

[0126] Among them, after the frequency detector and phase detector 631 receives the clock signal with spread spectrum, the voltage-controlled oscillator 634 immediately generates a clock and a carrier that follow the input spread spectrum signal. The clock can be understood as the output signal generated by the voltage-controlled oscillator 634 received by the second frequency divider 636, and the carrier can be understood as the carrier signal after the above-mentioned spread spectrum.

[0127] For example, the carrier wave may be a sine wave, a sawtooth wave, a triangle wave, etc.

[0128] Of course, the present invention does not limit the specific structure of the carrier signal generator, and it can also be implemented by clock jitter injection (Clock Jitter Injection) and other methods. Those skilled in the art can select a suitable implementation method according to needs.

[0129] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions.

[0130] In summary, the present invention determines the lowest frequency of the target signal; based on the lowest frequency of the target signal, determines the modulation frequency corresponding to the carrier signal, wherein the modulation frequency is greater than 0 and is less than or equal to half of the lowest frequency of the target signal; presets the frequency deviation range corresponding to the carrier signal; based on the modulation frequency and the frequency deviation range, performs spectrum spreading on the carrier signal, wherein the spread carrier signal is used to modulate the target signal. The method of the present invention significantly improves the modulation coefficient, and the energy of the fundamental wave of the spread carrier signal approaches 0, so that the spectrum spreading effect is better, thereby reducing the peak value of EMI and optimizing the performance of the system. Not only that, the present invention also avoids the carrier signal entering the frequency range of the target signal during modulation, thereby avoiding affecting the quality of the target signal.

[0131] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A carrier signal spreading method, characterized in that: The method comprises: Determine the lowest frequency of the target signal; Based on the lowest frequency of the target signal, determining a modulation frequency corresponding to the carrier signal, wherein the modulation frequency is greater than 0 and is less than or equal to half of the lowest frequency of the target signal; Presetting a frequency deviation range corresponding to the carrier signal; The carrier signal is spread spectrum-modulated based on the modulation frequency and the frequency deviation range, wherein the spread spectrum-modulated carrier signal is used to modulate the target signal.

2. The carrier signal spreading method according to claim 1, characterized in that: The modulation frequency is at least one third lower than the lowest frequency of the target signal.

3. The carrier signal spreading method according to claim 1, characterized in that: The carrier signal is a triangle wave signal, a sawtooth wave signal, a sine wave signal or a square wave signal.

4. A class D amplifier, characterized in that: include: A pulse width modulation module, wherein a first input terminal receives a target signal, a second input terminal receives a carrier signal spread by the carrier signal spread method according to any one of claims 1 to 3, and an output terminal outputs a PWM control signal; The switch output module is used to output a driving signal according to the PWM signal.

5. The class D amplifier according to claim 4, wherein: If the target signal is an audio signal, the modulation frequency range corresponding to the carrier signal is greater than 0 and less than or equal to 10 Hz.

6. The class D amplifier according to claim 4, wherein: The modulation frequency range corresponding to the carrier signal is greater than 0 and less than or equal to 7. The class D amplifier according to any one of claims 5 to 6, characterized in that: The class D amplifier also includes a speaker and an LC filter module, and the LC filter module includes a filter inductor and a filter capacitor; The first end of the filter inductor is coupled to the output end of the switch output module, the second end of the filter inductor is grounded through the filter capacitor, and the second end of the filter inductor is also coupled to the input end of the speaker.

8. A first carrier signal generator, characterized in that: include: A first oscillator integrated with a spread spectrum function is used to output the spread spectrum carrier signal based on the spread spectrum method according to any one of claims 1 to 3.

9. A second carrier signal generator, characterized in that: include: A second oscillator, used for outputting a high-frequency clock signal; A frequency divider, used to divide the high-frequency clock signal based on a spread spectrum pattern, and output a low-frequency clock signal with spread spectrum in a form preset by the spread spectrum pattern, wherein the spread spectrum pattern is used to implement the spread spectrum method according to any one of claims 1 to 3; The carrier generation module is used to output the carrier signal after spectrum spreading based on the clock signal with spectrum spreading.

10. The second carrier signal generator as claimed in claim 9, characterized in that: The second carrier signal generator is a closed-loop structure or an open-loop structure.

11. An electronic device, characterized in that: It comprises a class D amplifier as claimed in any one of claims 4 to 7.

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