WO2013075413A1

WO2013075413A1 - Pwm frequency control method and device for d-class power amplifier

Info

Publication number: WO2013075413A1
Application number: PCT/CN2012/071216
Authority: WO
Inventors: 李春雨; 虞培良; 李小建
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-11-21
Filing date: 2012-02-16
Publication date: 2013-05-30
Also published as: CN102510274A

Abstract

Disclosed is a PWM frequency control method for a D-class power amplifier, including: setting different PWM frequencies for a D-class power amplifier successively; acquiring the signal to noise ratios of a frequency modulation (FM) broadcast signal received by an FM receiving module successively under different PWM frequencies of the D-class power amplifier; and acquiring the PWM frequency value corresponding to the signal to noise ratio maximum value in the signal to noise ratios, taking the PWM frequency value as the best PWM frequency, and setting the best PWM frequency as the PWM frequency of the D-class power amplifier. Disclosed at the same time is a PWM frequency control device for a D-class power amplifier. The method and device in the present invention can be applied to effectively reduce the electromagnetic interference to the FM receiving module by the D-class power amplifier, so that the user can receive a distinct radio broadcast signal.

Description

PWM frequency control method and device for class D power amplifier

The invention relates to the field of mobile communication, in particular to a pulse width modulation (PWM, pulse width modulation) frequency control method and device for a class D power amplifier. Background technique

At present, with the maturity and development of mobile communication technologies, more and more functions of handheld devices such as mobile phones and MP3s have brought great convenience to people. At present, many handheld devices are equipped with a frequency modulation (FM, Frequency Modulation) receiving module, which has the function of receiving FM broadcast signals, which greatly facilitates users to listen to FM programs.

The FM receiving module can convert the FM broadcast signal into an audio signal, and then amplify the audio signal through the audio power amplifier and transmit it to the speaker for playback.

In China, the operating frequency range of the FM receiver module is generally set to 87.5MHz ~ 108.0MHz, and the step size is lOOKHz, which means that the FM broadcast frequency is limited. The FM receiver module must be equipped with an antenna to receive FM broadcast signals. The handheld terminal generally uses the lead wire in the earphone as the antenna of the FM receiving module, but when the user listens to the wireless broadcast, the earphone must be inserted, which brings inconvenience to the user. Some handheld terminals use a ceramic antenna as the antenna of the FM receiving module, but the price of the ceramic antenna is relatively expensive, which increases the cost of the handheld terminal. Here, the operating frequency of the FM receiving module can also be a frequency point; the step size is lOOKHz means: The frequency of each FM broadcast signal differs by at least 100KHz.

In the prior art, another technique is that the lead of the speaker of the handheld terminal is used as the antenna of the FM receiving module, which has the advantages of convenient use and low cost. FIG. 1 is a schematic diagram of a lead wire of a speaker using a handheld terminal in the prior art as an antenna of an FM receiving module. As shown in FIG. 1 , the microcontroller is connected to a class D power amplifier and an FM receiving module, and the FM receiving module is connected to the class D. Power amplifier.

Subjectively, the user usually evaluates the receiving effect of the FM receiving module from the sound played by the speaker. The clearer the sound and the smaller the noise, the better the playback effect of the FM receiving module. Objectively, the signal-to-noise ratio, or signal-to-noise ratio, is usually used to evaluate the reception effect of the FM receiver module. The larger the signal-to-noise ratio, the better the signal quality and the smaller the electronic noise, so that the sound of the speaker is clearer and the noise is smaller.

In the prior art, the FM receiving module utilizes the signal to noise ratio parameter to implement the function of automatic searching. That is: the FM receiving module starts from a certain operating frequency and increases the operating frequency by one step ( ΙΟΟΚΗζ ) to receive the FM broadcast signal. If the signal-to-noise ratio of the received FM broadcast signal exceeds a predetermined threshold, for example, 50 dB, at a certain operating frequency, it is regarded as a valid station, and the handheld terminal can set the FM receiver module to operate at this working frequency to receive the FM broadcast. signal.

Currently, D-class amplifiers are commonly used in audio amplifiers in which handheld terminals are used to drive speakers. The so-called Class D power amplifier refers to: Class D audio power amplifier, which can convert the input analog audio signal into a PWM pulse signal, and then the PWM pulse signal controls the conduction or disconnection of the high power switching device to drive the speaker. Here, Class D audio power amplifiers are sometimes referred to as digital amplifiers. In general, the Class D power amplifier's PWM frequency is between 300KHz and 1200KHz. The micro controller can set the frequency value of the PWM of the class D amplifier through the communication interface.

Compared with general linear class AB power amplifier circuits, Class D power amplifiers have the characteristics of high efficiency and small size. However, Class D power amplifiers also have disadvantages. Specifically, since the output signal of the class D power amplifier is a large current and a high speed pulse width modulation switching signal, electromagnetic interference is generated, and the electromagnetic interference has a broad spectrum and directly affects The reception performance of the FM receiving module connected to it causes the reception quality to deteriorate, so that the sound played by the speaker contains more noise.

Therefore, there is a need for a method of controlling the PWM frequency of a Class D power amplifier to minimize the electromagnetic interference of the Class D power amplifier to the FM receiving module, thereby enabling the user to receive a clear wireless broadcast signal. Summary of the invention

The invention provides a PWM frequency control method and device for a class D power amplifier, so as to solve the problem that the class D power amplifier generates electromagnetic interference to the FM receiving module in the prior art, so that the user cannot receive the clear wireless broadcast signal.

The invention provides a PWM frequency control method for a class D power amplifier, comprising:

Set different PWM frequencies for the Class D power amplifiers in turn;

Obtaining the signal-to-noise ratio of the FM broadcast signal received by the FM receiving module in sequence under different PWM frequencies of the class D power amplifier;

Obtain the PWM frequency value corresponding to the maximum SNR of the signal-to-noise ratio, use the PWM frequency value as the optimal PWM frequency, and set the optimal PWM frequency to the PWM frequency of the Class D amplifier.

The invention also provides a PWM frequency control device for a class D power amplifier, comprising: a signal to noise ratio acquisition module, an optimal PWM frequency acquisition module, and a PWM frequency setting module; wherein, a signal to noise ratio acquisition module is used for the class D The power amplifier sequentially sets different PWM frequencies, and sequentially acquires the signal-to-noise ratio of the FM broadcast signal received by the frequency modulation FM receiving module under different PWM frequencies of the class D power amplifier;

The optimal PWM frequency acquisition module is configured to obtain the PWM frequency value corresponding to the maximum signal to noise ratio in the signal to noise ratio, and use the PWM frequency value as the optimal PWM frequency;

The PWM frequency setting module is used to set the optimal PWM frequency to the PWM frequency of the Class D amplifier.

The beneficial effects of the present invention are as follows:

By sequentially setting the PWM frequency of the class D power amplifier, the signal-to-noise ratio of the FM broadcast signal received by the FM receiving module is obtained under different PWM frequencies of the class D power amplifier, and the class D power amplifier corresponding to the maximum signal to noise ratio is selected. The PWM frequency value is used as the PWM frequency value of the best Class D amplifier. The invention solves the problem that the class D power amplifier generates electromagnetic interference to the FM receiving module in the prior art, so that the user cannot receive the clear wireless broadcast signal, and the FM receiving signal will be the FM broadcast signal. When converting to a sound signal, the microcontroller finds the PWM frequency value of the best class D power amplifier for sound playback according to the current working frequency of the FM receiving module, thereby minimizing the electromagnetic interference of the class D power amplifier to the FM receiving module, so that the user Able to receive clear radio broadcast signals. DRAWINGS

1 is a schematic diagram of a lead wire of a speaker using a handheld terminal in the prior art as an antenna of an FM receiving module;

2 is a flowchart of a PWM frequency control method for a class D power amplifier according to an embodiment of the present invention; FIG. 3 is a flowchart of detailed processing of a PWM frequency control method for a class D power amplifier according to an embodiment of the present invention;

4 is a schematic structural diagram of a PWM frequency control apparatus for a class D power amplifier according to an embodiment of the present invention. detailed description

In order to solve the problem that the class D power amplifier generates electromagnetic interference to the FM receiving module in the prior art, so that the user cannot receive the clear wireless broadcast signal, the present invention provides a PWM frequency control method and device for the class D power amplifier, and the D Class amps have minimal electromagnetic interference to the FM receiver module. The present invention will be further described in detail below in conjunction with the drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Method embodiment

According to an embodiment of the present invention, a PWM frequency control method for a class D power amplifier is provided. FIG. 2 is a flowchart of a PWM frequency control method for a class D power amplifier according to an embodiment of the present invention. As shown in FIG. 2, the embodiment of the present invention The PWM frequency control method of the class D power amplifier includes the following processing: Step 201, sequentially setting different PWM frequencies for the class D power amplifier;

Preferably, before the step 201 is performed, the variable may be preset and the variable is initialized, wherein the set variable includes four, respectively: a first variable storing an optimal PWM frequency, and a second variable storing a maximum signal to noise ratio , storing the third variable of the current signal to noise ratio, and storing the current The fourth variable of the PWM frequency.

Step 202: sequentially acquire the signal to noise ratio of the FM broadcast signal received by the FM receiving module under different PWM frequencies of the class D power amplifier.

Preferably, in the actual application, step 201 and step 202 specifically perform the following processing: Step 1: Set the value of the fourth variable to the current PWM frequency value;

Step 2: Control the FM receiving module to receive the FM signal broadcast;

Step 3: Obtain a signal-to-noise ratio value at the current PWM frequency from the FM receiving module. Step 4: Store the signal-to-noise ratio value into the third variable.

Step 203: Acquire a PWM frequency value corresponding to a maximum signal to noise ratio in a signal to noise ratio, use a PWM frequency value as an optimal PWM frequency, and set an optimal PWM frequency to a PWM frequency of the class D power amplifier.

Preferably, in an actual application, step 203 specifically includes the following processing:

Step 5: Compare the value of the third variable with the value of the second variable. If the value of the third variable is greater than the value of the second variable, store the value of the third variable to the second variable, and set the value of the fourth variable. Store to the first variable; if the value of the third variable is less than the second variable, keep the value of the first variable and the value of the second variable unchanged;

Step 6, the value of the fourth variable = the current PWM frequency value + the predetermined step value, and determine whether the value of the fourth variable is greater than a preset maximum power value. If the determination is yes, the PWM frequency in the first variable is obtained. Value, set the PWM frequency of the class D amplifier to the value of the first variable. If the determination is no, perform step 1.

The above technical solutions of the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

In this example, it is assumed that the PWM frequency range of the Class D power amplifier used by the handheld terminal is

500KHz ~ 600KHz, step size is 10KHz.

FIG. 3 is a flowchart of detailed processing of a PWM frequency control method for a class D power amplifier according to an embodiment of the present invention. As shown in FIG. 3, the following processing is included: Step 1. Set four variables and initialize them: Among them, the four variables are specifically:

D PWM B = 500 KHz, this variable is used to store the PWM frequency value of the best Class D amplifier;

FM SN B = 0 dB, this variable is used to store the maximum value of the signal-to-noise ratio of the received FM broadcast signal;

D PWM = 500 KHz, this variable is used to store the PWM frequency value of the current Class D amplifier;

FM—SN = 0 dB, this variable is used to store the signal-to-noise ratio of the current FM broadcast signal.

Step 2: The microcontroller sets the Class D power amplifier PWM frequency value to D-PWM, and sends and receives a command to the FM receiving module to receive the FM broadcast signal, and then sends a signal-to-noise ratio query command to the FM receiving module. After receiving the signal-to-noise ratio value returned by the FM receiving module, the microcontroller stores the signal-to-noise ratio value in the FM-SN variable;

Step 3: Compare the size of FM-SN and FM-SN-B, if FM-SN is greater than or equal to

FM SN B, then D - PWM - B = D - PWM, FM_SN_B = FM SN, if FM - SN is greater than or equal to FM - SN - B, then step 4;

Step 4, D PWM = D PWM +10K, if D-PWM is less than or equal to 600KHz, repeat steps 2, 3, and 4, if D-PWM is greater than 600KHz, perform step 5;

Step 5: The microcontroller sets the PWM frequency value of the Class D amplifier to D—PWM—B, and ends. According to the above steps, you can get the data as shown in Table 1:

Table 1

Class D power amplifier PWM frequency value Signal to noise ratio of FM broadcast signal

500 KHz 60dB

510 KHz 58dB

520 KHz 58dB

530 KHz 59dB

540 KHz 59dB 550 KHz 60dB

560 KHz 61dB

570 KHz 60dB

580 KHz 59dB

590 KHz 58dB

600 KHz 58dB In the case of Class D power amplifier PWM frequency range from 500KHz to 600KHz, the step size is ΙΟΚΗζ, as can be seen from Table 1, the microcontroller sets the Class D power amplifier PWM frequency value: 500KHz, 510KHz, 520KHz , 530KHz, 540KHz, 550KHz, 560KHz, 570KHz, 580KHz, 590KHz, 600KHz.

When the FM receiver module has different PWM frequency values of the Class D amplifier, the signal-to-noise ratio of the received FM broadcast signals is: 60dB, 58dB, 58dB, 59dB, 59dB, 60dB, 61dB, 60dB, 59dB, 58dB, 58dB. .

It can be seen that the received signal FM signal has a maximum signal-to-noise ratio (FM) SNR of 61 dB, and the corresponding Class D power amplifier PWM frequency value D-PWM-B is 560 kHz.

Through the above processing, the microcontroller sets the PWM frequency value of the optimal class D power amplifier according to the frequency of the FM receiving module, thereby minimizing the electromagnetic interference of the class D power amplifier to the FM receiving module, thereby enabling the user to receive clear Wireless broadcast signal.

Device embodiment

According to an embodiment of the present invention, a PWM frequency control device for a class D power amplifier is provided. FIG. 4 is a schematic structural diagram of a PWM frequency control device for a class D power amplifier according to an embodiment of the present invention. As shown in FIG. The PWM frequency control device of the class D power amplifier includes: a signal to noise ratio acquisition module 40, an optimal PWM frequency acquisition module 42, and a PWM frequency setting module 44. The respective modules of the embodiments of the present invention are described in detail below.

Specifically, the signal to noise ratio acquisition module 40 is configured to sequentially set different PWMs for the class D power amplifiers. Frequency, in a different PWM frequency of the class D power amplifier, sequentially acquiring the signal to noise ratio of the FM broadcast signal received by the frequency modulation FM receiving module;

The optimal PWM frequency acquisition module 42 is configured to obtain the PWM frequency value corresponding to the maximum signal to noise ratio in the signal to noise ratio, and use the PWM frequency value as the optimal PWM frequency;

The PWM frequency setting module 44 is configured to set the optimal PWM frequency to the PWM frequency of the class D amplifier.

Preferably, the PWM frequency control device of the class D power amplifier of the embodiment of the invention further includes: a variable setting module, configured to set a variable and initialize a variable, wherein the variable comprises: a first variable storing an optimal PWM frequency, and storing a signal noise A second variable that is greater than the maximum value, a third variable that stores the current signal to noise ratio, and a fourth variable that stores the current PWM frequency.

The signal-to-noise ratio acquisition module 40 is specifically configured to: set a value of the fourth variable to a current PWM frequency value; control an FM receiving module to receive an FM signal broadcast; obtain a signal-to-noise ratio value at a current PWM frequency from the FM receiving module; The noise ratio value is stored in the third variable.

The optimal PWM frequency acquisition module 42 is specifically configured to: compare the size of the third variable and the second variable, and if the value of the third variable is greater than the second variable, store the value of the third variable to the second variable, and the fourth variable The value of the third variable is stored in the first variable; if the value of the third variable is smaller than the second variable, the value of the first variable and the value of the second variable are kept unchanged; let the fourth variable = current PWM frequency value + predetermined step value, And determining whether the value of the fourth variable is greater than a preset power maximum value. If the determination is yes, the PWM frequency value in the first variable is obtained, and if the determination is no, the signal to noise ratio acquisition module is invoked.

The PWM frequency setting module 44 is specifically configured to: set the PWM frequency of the class D power amplifier to the value in the first variable.

The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings. In this example, it is assumed that the PWM frequency value of the class D power amplifier used in the handheld terminal ranges from 500 kHz to 600 kHz, and the step size is 10 kHz. FIG. 3 is a flowchart of detailed processing of a PWM frequency control method for a class D power amplifier according to an embodiment of the present invention. As shown in FIG. 3, the following processing is included:

Step 1. The variable setting module sets 4 variables and initializes them: Among them, 4 variables are specifically:

D PWM = 500 KHz, this variable is used to store the PWM frequency value of the current Class D amplifier; FM_SN = 0 dB, this variable is used to store the signal-to-noise ratio of the current FM broadcast signal.

Step 2: The signal-to-noise ratio acquisition module of the microcontroller sets the PWM frequency value of the Class D power amplifier to D PWM, and sends a receiving command to the FM receiving module to receive the FM broadcast signal, and then sends a signal to noise ratio query command to the FM receiving module. After receiving the signal to noise ratio value returned by the FM receiving module, the signal to noise ratio obtaining module of the microcontroller stores the signal to noise ratio value in the FM_SN variable;

Step 3: The optimal PWM frequency acquisition module compares the size of FM_SN and FM_SN-B. If FM_SN is greater than or equal to FM_SN-B, then D-PWM-B = D PWM, FM SN B = FM — SN;

Step 4: The optimal PWM frequency acquisition module calculates D—PWM = D—PWM +10K. If D PWM is less than or equal to 600KHz, repeat steps 2, 3, and 4. If D—PWM is greater than 600KHz, go to step 5. ;

Step 5: The PWM frequency setting module of the microcontroller sets the PWM frequency value of the Class D power amplifier to D—PWM—B, and ends.

According to the above steps, the data as shown in Table 1 can be obtained.

In the case that the PWM frequency value of the Class D power amplifier ranges from 500KHz to 600KHz, and the step size is ΙΟΚΗζ, it can be seen from Table 1 that the microcontroller sets the PWM frequency value of the Class D power amplifier in turn: 500KHz, 510KHz, 520KHz, 530KHz, 540KHz, 550KHz, 560KHz, 570KHz, 580KHz, 590KHz, 600KHz.

It can be seen that the received signal FM signal has a maximum signal-to-noise ratio FM SN B of 61 dB, and the corresponding Class D power amplifier PWM frequency value D PWM B is 560 KHz.

In summary, in the embodiment of the present invention, the PWM frequency of the class D power amplifier is sequentially set, and the signal to noise ratio of the FM broadcast signal received by the FM receiving module is obtained under different PWM frequencies of the class D power amplifier, and the signal to noise ratio is selected. The PWM frequency value of the Class D power amplifier corresponding to the maximum value is used as the PWM frequency value of the best Class D power amplifier. The invention solves the problem that the class D power amplifier generates electromagnetic interference to the FM receiving module in the prior art, so that the user cannot receive the clear wireless broadcast signal. When the FM receiving module converts the FM broadcast signal into a sound signal, the microcontroller according to the FM Receiving the current working frequency of the module, finding the PWM frequency value of the best class D power amplifier for sound playback, thereby minimizing the electromagnetic interference of the class D power amplifier to the FM receiving module, so that the user can receive a clear wireless broadcast signal.

While the preferred embodiments of the present invention have been disclosed for purposes of illustration, those skilled in the art will recognize that various modifications, additions and substitutions are possible, and the scope of the invention should not be limited to the embodiments described above.

Claims

Claim

A pulse width modulation PWM frequency control method for a class D power amplifier, characterized in that the method comprises:

Set different PWM frequencies for the Class D power amplifiers in turn;

Obtaining a signal to noise ratio of the FM broadcast signal received by the frequency modulation FM receiving module in sequence under different PWM frequencies of the class D power amplifier;

Obtaining a PWM frequency value corresponding to a maximum signal to noise ratio in the signal to noise ratio, using the PWM frequency value as an optimal PWM frequency, and setting the optimal PWM frequency to a PWM frequency of the class D power amplifier .

2. The method according to claim 1, wherein before the setting of different PWM frequencies for the class D power amplifiers, the method further comprises:

Setting a variable and initializing the variable, wherein the variable comprises: a first variable storing the optimal PWM frequency, a second variable storing the maximum signal to noise ratio, and a third variable storing a current signal to noise ratio And a fourth variable that stores the current PWM frequency.

The method according to claim 2, wherein, in the different PWM frequencies of the class D power amplifier, sequentially acquiring a signal to noise ratio of the FM broadcast signal received by the frequency modulation FM receiving module, including:

Setting the value of the fourth variable to a current PWM frequency value;

Controlling the FM receiving module to receive an FM signal broadcast;

Obtaining a signal to noise ratio value at a current PWM frequency from the FM receiving module;

The signal to noise ratio value is stored into the third variable.

The method according to claim 3, wherein the acquiring a PWM frequency value corresponding to a maximum signal to noise ratio in the signal to noise ratio, and using the PWM frequency value as an optimal PWM frequency, includes :

Comparing the value of the third variable with the magnitude of the value of the second variable, if the third variable If the value of the quantity is greater than the value of the second variable, storing the value of the third variable to the second variable, storing the value of the fourth variable to the first variable; If the value of the variable is smaller than the second variable, the value of the first variable and the value of the second variable are kept unchanged; the value of the fourth variable is equal to the current PWM frequency value plus a predetermined step value, and the Whether the value of the fourth variable is greater than a preset power maximum value, and if the value of the fourth variable is greater than a preset power maximum value, acquiring a PWM frequency value in the first variable.

The method according to claim 4, wherein the setting the optimal PWM frequency to the PWM frequency of the class D power amplifier comprises:

The PWM frequency of the class D power amplifier is set to the value of the first variable.

The method according to claim 4 or 5, wherein the method further comprises: if the value of the fourth variable is less than or equal to a preset power maximum value, setting the value of the fourth variable to The current PWM frequency value controls the FM receiving module to receive the FM signal broadcast in such a loop to sequentially acquire the signal to noise ratio of the FM broadcast signal received by the FM receiving module under different PWM frequencies of the class D power amplifier.

7. A pulse width modulation PWM frequency control device for a class D power amplifier, characterized in that: the device comprises: a signal to noise ratio acquisition module, an optimal PWM frequency acquisition module, and a PWM frequency setting module; wherein

a signal-to-noise ratio acquisition module is configured to sequentially set different PWM frequencies for the class D power amplifier, and sequentially obtain a signal to noise ratio of the FM broadcast signal received by the frequency modulation FM receiving module under different PWM frequencies of the class D power amplifier;

An optimal PWM frequency acquisition module is configured to obtain a PWM frequency value corresponding to a maximum signal to noise ratio in the signal to noise ratio, and use the PWM frequency value as an optimal PWM frequency;

The PWM frequency setting module is configured to set the optimal PWM frequency to the PWM frequency of the class D power amplifier.

8. The device according to claim 7, wherein the device further comprises: a variable setting module, configured to set a variable and initialize the variable, wherein the variable includes: a first variable storing the optimal PWM frequency, a second variable storing the maximum signal to noise ratio, and storing a current letter The third variable of the noise ratio, and the fourth variable that stores the current PWM frequency.

The apparatus according to claim 8, wherein the signal to noise ratio acquisition module is configured to: set a value of the fourth variable to a current PWM frequency value; and control the FM receiving module to receive an FM signal. Broadcasting; acquiring a signal to noise ratio value at a current PWM frequency from the FM receiving module; storing the signal to noise ratio value in the third variable.

The device according to claim 9, wherein the optimal PWM frequency acquisition module is specifically configured to: compare a value of the third variable with a value of a value of the second variable, if the The value of the third variable is greater than the value of the second variable, then the value of the third variable is stored to the second variable, and the value of the fourth variable is stored to the first variable; The value of the third variable is smaller than the second variable, and the value of the first variable and the value of the second variable are kept unchanged; the value of the fourth variable is equal to the current PWM frequency value plus a predetermined step value, and is determined. Whether the value of the fourth variable is greater than a preset power maximum value, and if the value of the fourth variable is greater than a preset power maximum value, acquiring a PWM frequency value in the first variable.

The device according to claim 10, wherein the PWM frequency setting module is specifically configured to: set a PWM frequency of the class D power amplifier to a value of the first variable.

The device according to claim 10 or 11, wherein the optimal PWM frequency acquisition module is further configured to invoke the letter when the value of the fourth variable is less than or equal to a preset power maximum value. Noise ratio acquisition module.