CN101409543B - Multilevel Pulse Width Modulation Method - Google Patents

Abstract

The invention relates to a multilevel pulse width modulation method, which is used for sampling an input signal to generate a corresponding pulse width modulation signal, wherein the pulse width modulation signal comprises at least one modulation pulse, and the multilevel pulse width modulation method is characterized in that: the energy is gradually increased in the modulation pulse in a multi-step mode, so that the rising edge of the modulation pulse is approximately in a slope shape, and the instantaneous energy change is reduced. The invention makes the composing wave form of the pulse width modulation signal have gentle change, so the change of the instantaneous energy is more moderate than the prior art, and the degree of the instantaneous energy change can be effectively reduced. If the improved pulse width modulation signal is used to drive the loudspeaker, the noise generation condition can be greatly improved, and the method is very practical.

Description

Multilevel Pulse Width Modulation Method

technical field

The present invention relates to a pulse width modulation method, in particular to a multi-level pulse width modulation method (Multi-Level Pulse Width Modulation Method) which has a pulse wave with inclined edges and can effectively reduce the degree of instantaneous energy change.

Background technique

Pulse Width Modulation (PWM, hereinafter referred to as PWM) uses different duty cycles to represent various signals (signals are signals, which are referred to as signals in this article). Please refer to FIG. 1 , which is a waveform diagram of a PWM (Pulse Width Modulation) signal used in the prior art. In this technique, the waveform of the PWM signal is composed of square waves with different widths. A wider square wave represents higher energy, while a narrower square wave represents less energy. By using such a PWM signal to drive the speaker, an analog sound output can be generated from the speaker. This driving method has been adopted by many sound output devices.

Due to the limitation of the working frequency, the general PWM signal must strike a balance between sampling frequency and resolution, and cannot express the content of the original signal very accurately. This condition will cause distortion of the output analog signal. In order to solve this problem, many people have proposed various ways to increase resolution or sampling frequency at the same operating frequency. For example, Taiwan Patent No. 453045, titled "Multi-Level Pulse Width Modulation Device and Its Control Structure", proposes a technique for improving the resolution while maintaining the sampling rate.

In addition, please refer to FIG. 2 , which is a waveform diagram of another PWM signal used in the prior art. In this technique, in addition to the width, the amplitude of each square wave in the PWM signal is also used to represent the magnitude of the energy it represents.

However, whether it is a general PWM technology or a technology that has been improved later, a square wave is used as a reference waveform. In other words, there is a huge momentary energy boost at the rising edge of each wave. If such a PWM signal is used to drive the aforementioned speaker, then this instantaneous energy increase is likely to cause a sudden change in sound, which is commonly known as a pop.

Therefore, the signals generated by the currently used PWM technology still have their defects, and how to improve these signals has become an important issue.

It can be seen that the above-mentioned existing pulse width modulation method obviously still has inconvenience and defects in method and use, and needs to be further improved urgently. In order to solve the above-mentioned problems, the relevant manufacturers have tried their best to find a solution, but no suitable design has been developed for a long time, and the general method has no suitable method to solve the above-mentioned problems. This is obviously related The problem that the industry is eager to solve. Therefore, how to create a new multi-level pulse width modulation method is one of the current important research and development topics, and it has also become a goal that the industry needs to improve.

In view of the defects in the above-mentioned existing pulse width modulation method, the inventor actively researches and innovates based on years of rich practical experience and professional knowledge engaged in the design and manufacture of such products, and cooperates with the application of academic theory, in order to create a new The multi-level pulse width modulation method can improve the general existing pulse width modulation method and make it more practical. Through continuous research, design, and after repeated trials and improvements, the present invention with practical value is finally created.

Contents of the invention

The purpose of the present invention is to overcome the defects of the existing pulse width modulation method and provide a new multi-level pulse width modulation method. The technical problem to be solved is to reduce the degree of instantaneous energy change, which is very suitable for practical.

The purpose of the present invention and the solution to its technical problems are achieved by adopting the following technical solutions. A multi-level pulse width modulation method proposed according to the present invention is used to sample an input signal to generate a corresponding pulse width modulation signal, the pulse width modulation signal includes at least one modulation pulse, and the multi-level pulse The characteristic of the width modulation method is that: in the modulation pulse, the energy is gradually increased in a multi-stage manner, so that the rising edge of the modulation pulse is generally inclined, so as to reduce the instantaneous energy change.

The purpose of the present invention and its technical problems can also be further realized by adopting the following technical measures.

In the aforementioned multi-level pulse width modulation method, wherein the duty cycle of the modulated pulse spans multiple unit times, and within two adjacent unit times only increases by one unit energy at most.

The aforementioned multi-level pulse width modulation method includes the following steps: gradually increasing a pulse width modulation count value from zero to generate a plurality of different pulse width modulation count values, and the pulse width modulation count value is an integer; and before the pulse width modulation count value reaches the maximum amount of unit time that the modulation pulse can span, for each of the pulse width modulation count values, determining a pulse width modulation output value, wherein: when the pulse width modulation count value When the value is not less than 0 and less than a first preset value, the determined PWM output value is at most one unit energy more than the previously determined PWM output value.

In the aforementioned multi-level pulse width modulation method, the step of making the determined output value of the pulse width modulation more than the previous determined output value of the pulse width modulation by at most one unit of energy includes: using A base count value indicates a corresponding unit time in the modulation pulse: initialize the base count value to zero; set an increment count value to represent a maximum energy value per unit time of the rising edge in the modulation pulse and gradually increasing the base count value to the first preset value and gradually decreasing the increment count value to zero, and before the base count value reaches the first preset value and the increment count value reaches zero, causing The PWM output value is one plus one to the reference count value.

In the aforementioned multi-level pulse width modulation method, the first preset value is 2n-1, where n is the number of bits representing the amplitude resolution.

The aforementioned multi-level pulse width modulation method further includes when determining the pulse width modulation output value: when the pulse width modulation count value is not less than the first preset value and is not greater than the duty cycle minus the first When the preset value is used, the pulse width modulation output value is the maximum amplitude.

The aforementioned multi-level pulse width modulation method, wherein when determining the pulse width modulation output value further includes: when the pulse width modulation count value is greater than the duty cycle minus the first preset value, and not less than the duty cycle , the determined output value of the pulse width modulation is reduced by at most one energy unit from the output value of the pulse width modulation determined last time.

The aforementioned multi-level pulse width modulation method further includes: gradually reducing the energy in the modulated pulse in a multi-stage manner, so that the falling edge of the modulated pulse is generally inclined to reduce the instantaneous energy change.

The aforementioned multi-level pulse width modulation method further includes: using a reference count value to indicate a corresponding unit time in the modulation pulse: initializing the reference count value to zero; setting an increment count value to the modulation pulse A maximum energy value to be represented per unit time of the rising edge in the middle; and gradually increase the base count value to a second preset value and gradually decrease the increment count value to zero, and when the base count value reaches the first before the incremental count value reaches zero, the unit of energy output per unit time corresponding to the reference count value in the modulated pulse is the base count value plus 1.

In the aforementioned multi-level pulse width modulation method, the second preset value is 2n-1, where n is the number of bits representing the amplitude resolution.

Compared with the prior art, the present invention has obvious advantages and beneficial effects. As can be seen from the above, in order to achieve the above object, the present invention proposes a multi-level pulse width modulation method, which is used to sample an input signal to generate a corresponding pulse width modulation signal, wherein the pulse width modulation signal includes at least one modulation pulse. The feature of the multi-level pulse width modulation method is that the energy is gradually increased in a multi-stage manner, so that the edge of the modulated pulse is generally inclined to reduce the instantaneous energy change.

In one embodiment of the present invention, firstly, the PWM count value is gradually increased from zero to generate a plurality of different PWM count values. Before the pulse width modulation count value reaches the duty cycle of the modulation pulse, a corresponding pulse width modulation output value is determined for each pulse width modulation count value, wherein when the pulse width modulation count value is not less than 0 and less than a first preset When setting the value, the determined output value of the pulse width modulation is at most one unit energy more than the output value of the previously determined pulse width modulation.

In one embodiment of the present invention, when determining the pulse width modulation output value, the pulse width modulation count value is not less than the aforementioned first preset value and is not greater than the aforementioned duty cycle minus the first preset value , so that the pulse width modulation output value is the maximum amplitude.

In one embodiment of the present invention, when determining the pulse width modulation output value, when the pulse width modulation count value is greater than the aforementioned duty cycle minus the first preset value and not less than the duty cycle, the determined The pulse width modulation output value is reduced by at most one energy unit from the previous determined pulse width modulation output value.

By means of the above-mentioned technical solution, the multi-level pulse width modulation method of the present invention has at least the following advantages and beneficial effects: the present invention makes the composition waveform of the pulse width modulation signal have a relatively gentle change, so the instantaneous energy change is faster than the existing Known technology comes with ease. If this improved pulse width modulation signal is used to drive the speaker, then the situation of noise generation will be greatly improved.

To sum up, the multi-level pulse width modulation method of the present invention can effectively reduce the degree of instantaneous energy change. The present invention slows down the rising speed of the rising edge in the PWM waveform, thereby reducing the degree of energy change, improving the smoothness of subsequent analog output, and reducing electromagnetic interference caused by strong energy changes. The present invention has the above-mentioned many advantages and practical value, and it has great improvement no matter in method or function, has significant progress in technology, and has produced easy-to-use and practical effects, and compared with the existing pulse width modulation The method has the outstanding effect of promotion, thereby is more suitable for practical use, and is a novel, progressive and practical new design.

The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable , the following preferred embodiments are specifically cited below, and are described in detail as follows in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is a waveform diagram of a PWM signal used in the prior art.

FIG. 2 is a waveform diagram of another PWM signal used in the prior art.

FIG. 3 is a waveform diagram of a PWM signal generated according to an embodiment of the invention.

FIG. 4 is a flowchart of a method for generating a PWM signal according to an embodiment of the invention.

FIG. 5 is a diagram of a modulated pulse in a PWM signal generated according to an embodiment of the present invention.

FIG. 6 is a flowchart of a method used in generating a rising edge according to an embodiment of the invention.

FIG. 7 is a block diagram of a circuit used for generating a slowly rising edge according to an embodiment of the present invention.

FIG. 8 is a detailed circuit block diagram of the back-end driving circuit shown in FIG. 7 according to an embodiment of the present invention.

S400～S460: Implementation steps of an embodiment of the present invention

S600-S660: implementation steps of another embodiment of the present invention

700: Control unit 702: Clock generation unit

704: Counter 706: Latch

708: Inverter 710: Calculator

712: Comparator 714, 716: Pulse width drive circuit

718, 718a: current control logic circuit 72, 72a: back-end drive circuit

800, 810, 830: Multiplexer 802: Incremental register

804: Subtractor 812: Reference register

814: Adder

Detailed ways

In order to further explain the technical means and effects of the present invention to achieve the intended purpose of the invention, the specific implementation methods, methods and steps of the multi-level pulse width modulation method proposed according to the present invention will be described below in conjunction with the accompanying drawings and preferred embodiments. , features and their effects are described in detail below.

Please refer to FIG. 3 , which is a waveform diagram of a pulse width modulation signal generated according to an embodiment of the present invention. In order to reduce the instantaneous energy change, for each modulated pulse wave (hereinafter referred to as the modulated pulse) contained in the pulse width modulation (PWM) signal, the rising edge and falling edge should be made to rise slowly. Or the state of slow descent is better. But relatively speaking, users generally pay more attention to the noise effect caused by sudden energy increase (because it will cause popping sound). In addition, if multiple PWMs operate at the same time and the operation mode is aligned to the left (Left- aligned), the rising edge has more impact because each PWM (Pulse Width Modulation) rises at the same time, but does not fall at the same time. Therefore, it is also possible to only make the rising edge a slow rise, while the falling edge is a general square wave rapid decline.

In order to generate the two-sided ramp-down waveform shown in FIG. 3 , a possible implementation is shown in FIG. 4 . Please refer to FIG. 4 , which is a flowchart of a method for generating a PWM (Pulse Width Modulation) signal according to an embodiment of the present invention. In this embodiment, the method for generating a PWM (Pulse Width Modulation) signal adopts a multi-stage method to gradually increase the energy of each modulation pulse. The method for generating a PWM signal comprises the following steps:

First, before outputting any modulated pulse, confirm that its pulse width modulated output value is 0 (step S400).

Next, set the pulse width modulation count value X (which is an integer) to 0 to start the operation (X can be regarded as representing the value on the horizontal axis) (step S410).

When the pulse width modulation count value X is between 0 and 2 ⁿ -1 (n is the number of bits of the amplitude resolution) (0≤X<2 ⁿ -1), the pulse width modulation output value is gradually increased, That is, make the output value of the pulse width modulation to be output more than the previous pulse width modulation output value in the same modulation pulse by at most one unit energy (step S420 ).

Furthermore, when the pulse width modulation count value X is between 2 ⁿ -1 and the duty cycle (duty cycle) PWMD of the modulation pulse minus 2 ⁿ -1 (2 ⁿ -1≤X≤PWMD-( 2 ⁿ -1)), just make the pulse width modulation output value the maximum square wave amplitude (step S430);

When the pulse width modulation count value X is greater than the duty cycle PWMD minus 2 ⁿ -1 and not greater than the duty cycle PWMD (PWMP-(2 ⁿ -1)<X≤PWMD), the pulse width modulation output value will be gradually reduced ( Step S440).

After each time the above operation is performed on a PWM count value X, the PWM count value X will be incremented by 1 (step S450).

Before the pulse width modulation count value X has been incremented to the duty cycle PWMD of the modulation pulse, repeat the aforementioned steps S420-S450 to output the signal, and after the pulse width modulation count value X reaches the duty cycle PWMD (step S460), The foregoing operations are ended and the output is reset to 0 (step S470).

A practical example is given next, so that those skilled in the art can more easily understand the technology provided by the present invention. Please refer to FIG. 5 , which is a modulation pulse diagram of a PWM signal generated according to an embodiment of the present invention. In this embodiment, the number of resolution bits of the amplitude is 2, so there are four kinds of changes in the amplitude, which are respectively the values 0 to 3 on the vertical axis as shown in Figure 5, and the interval between two adjacent numbers It represents a unit of energy; moreover, the duty cycle (PWMD) of the modulation pulse in this embodiment is 7 (0-7), and the time width (PWMP) is 9 (0-9).

According to the execution steps shown in FIG. 4 , when the pulse width modulation count value X is 0, it starts incrementing and its output is 1. Next, as the pulse width modulation count value X is incremented to 1 and 2 (less than 2 ² −1=3), the PWM output value (amplitude) is incremented to 2 and 3 units of energy (step S420).

Next, when the pulse width modulation count value X is 3 and 4 (3=2 ² −1≤X≤7−3=4), the PWM output value is set to the maximum square wave amplitude of 3 (step S430 ).

Finally, when the PWM count value X is 5˜7 (7−(2 ² −1)=4<X≦7), the PWM output value will be decremented to 0 one by one (step S440 ). And when X is 8-9, the PWM output value is 0 (or terminated output).

It should be noted that although the example mentioned here is the case where the duty cycle PWMD of the modulating pulse is different from the overall period PWMP, this method is also applicable to the case where the duty cycle PWMD is the same as the overall period PWMP to generate the modulating pulse. Furthermore, although the rise sources of the waveforms generated in the aforementioned two embodiments are all absolute increments, those skilled in the art will know that they can also be relatively incremental rises (that is, the two adjacent unit times may show same energy).

Next, please refer to FIG. 6 , which is a flowchart of a method used when generating a rising edge according to an embodiment of the present invention. In this embodiment, first, initialize a base count value (BAS) (step S600), the base count value is equal to the pulse width modulation count value X in the previous embodiment, and can be used to indicate the corresponding a unit of time.

Next, the maximum energy value to be present in each unit time of the rising edge is set as an increment count value (INC) (step S610).

Next, the method gradually increases the base count value BAS to ²ⁿ -1, and gradually decreases the incremental count value INC to zero, and before the base count value BAS reaches ²ⁿ -1 and the incremental count value INC reaches zero, the The pulse width modulation output value adds 1 to the reference count value BAS (steps S620-S660).

Taking the waveform shown in Figure 5 as an example, the rising edge will rise to the maximum amplitude because the modulation pulse needs to present a large amount of energy. In other words, the maximum energy value to be presented per unit time in the rising edge is 3. Therefore, in addition to initializing the base count value BAS to 0 (step S600), the increment count value INC is also set to 3 (step S610).

Next, in the first round of the process, in step S620 , since the incremental count value INC is not 0, the output at time 0 (because the base count value BAS is currently 0) will be 1 (0+1). Since the increment count value INC is not 0 in step S630, the increment count value INC is decremented to 2 (step S640). And because it is judged in step S650 that the base count value BAS is not 3 (22-1=3), the base count value BAS will be incremented to 1 (step S660), and the process returns to step S620 to continue.

In the second round of the process, since the incremental count value INC is not 0, the output at time point 1 (BAS is 1) will be 2 (BAS+1=2). Similarly, the increment count value INC is decremented to 1, and the base count value BAS is incremented to 2. Next, in the process of the third round, since the incremental count value INC is still not 0, the output at time point 2 (BAS is 2) will be 3 (BAS+1=3), and the incremental count value INC will be decremented to 0 and the base count value BAS will be incremented to 3.

In the fourth round of the process, since the incremental count value INC has become 0, the output at time point 3 will be 3 (that is, the value of BAS), and because the incremental count value INC is 0 and the base count value BAS is 3, so step S650 judges that it meets the regulations, and this program will be ended.

By means of the method shown in FIG. 6 , an adjustment pulse with a rising edge slope can be easily made. Of course, the method shown in FIG. 6 can also be combined in step S420 of FIG. 4 to generate the rising edge of the adjustment pulse.

Please refer to FIG. 7 , which is a block diagram of a circuit used for generating a slow rising edge according to an embodiment of the present invention. In this circuit, a control unit 700, a clock generating unit (clock generator) 702, a counter 704, a latch 706, an inverter 708, an arithmetic unit 710, a comparator 712, and pulse width driving circuits 714 and 716 are The operation of the pulse width modulation circuit used in the prior art is basically that the control unit 700 controls the output frequency of the clock generation unit (clock generator) 702, the output mode of the latch 706 and the comparator 712 compare mode. The latch 706 outputs the received audio data DA, which will generate a value of the current pulse width after being calculated by the inverter 708 and the arithmetic unit 710, and the value is input to an input end of the comparator 712; The other input terminal of the comparator 712 receives the output value of the counter 704 , and the output value is a value of a predetermined pulse width. After the two values are compared by the comparator 712, they are used to determine whether to enable the pulse width driving circuits 714 and 716 to generate the pulse width modulation signals PWM0 and PWM1 respectively.

The main difference between this embodiment shown in FIG. 7 and the prior art is that a current control logic circuit 718 is newly added. The current control logic circuit 718 receives the output of the comparator 712 to generate the pulse width modulation signal CUR that changes based on the current change.

Please refer to FIG. 8 , which is a detailed circuit block diagram of the back-end driving circuit 72 shown in FIG. 7 according to an embodiment of the present invention. In FIG. 8 , the comparator 712 in the rear driving circuit 72a transmits the generated signal to the current control logic circuit 718a. The incremental register 802 is used to store the incremental count value INC, which is combined with the subtractor 804 to form an incremental counter; the reference register 812 is used to store the reference count value BAS, which is combined with the adder 814 to form a reference counter. The multiplexer 800 decides according to the output value of the comparator 712 whether to store the output of the subtractor 804 into the incremental register 802, or to store the energy value (inc_value) to be represented into the incremental register In 802 (such as step S610 in FIG. 6 ). Similarly, the multiplexer 810 decides according to the output value of the comparator 712 whether to store the output of the adder 814 into the reference register 812, or to initialize the reference register to 0 (that is, to 0 Stored in the reference register 812, as shown in step S600 of FIG. 6).

The value output by the increment register 802 is used to control the multiplexer 830 . In this way, the multiplexer 830 can determine the output according to the process shown in FIG. One of them is the pulse width modulation signal CUR.

To sum up, the present invention slows down the rising speed of the rising edge in the PWM waveform, thereby reducing the degree of energy variation and improving the smoothness of the subsequent analog output, reducing the electromagnetic interference caused by strong energy variation. Of course, this approach can also be used on the falling edge of the PWM waveform, and it also has considerable efficacy.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, may use the technical content disclosed above to make some changes or modify them into equivalent embodiments with equivalent changes, but as long as they do not depart from the technical solution of the present invention, the Technical Essence Any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the technical solution of the present invention.

Claims (7)

1. A multilevel pulse width modulation method for sampling an input signal to generate a corresponding pulse width modulation signal, the pulse width modulation signal comprising at least one modulation pulse, the multilevel pulse width modulation method is characterized by: gradually increasing a pulse width modulation count value from zero to generate a plurality of different pulse width modulation count values, and the pulse width modulation count value is an integer; and The duty cycle of the modulated pulse spans a plurality of unit times, and for each of the pulse width modulated count values, a pulse Width modulated output value, where: When the pulse width modulation count value is not less than 0 and less than a first preset value, wherein the first preset value is ²ⁿ -1, n is the number of bits representing the amplitude resolution, so that the determined pulse The output value of the width modulation is greater than the output value of the pulse width modulation determined last time, so that the rising edge of the modulation pulse rises in steps, so as to gradually increase the energy and reduce the instantaneous energy change. 2. The multi-level pulse width modulation method according to claim 1, wherein when the pulse width modulation count value is not less than 0 and less than the first preset value, the determined output value of the pulse width modulation The pulse width modulation output value is at most one unit energy more than the previous determined value. 3. The multi-level pulse width modulation method as claimed in claim 2, wherein the determined output value of the pulse width modulation is at most only more than the output value of the pulse width modulation determined last time A unit energy step which includes: Using a reference count value to indicate a corresponding unit time in the modulation pulse: Initialize the base count value to zero; Setting an increment count value as a maximum energy value to be expressed per unit time of the rising edge in the modulation pulse; and gradually increasing the base count value to the first preset value and gradually decreasing the increment count value to zero, and before the base count value reaches the first preset value and the increment count value reaches zero, the pulse The width modulated output value is this base count value plus 1. 4. The multi-level pulse width modulation method as claimed in claim 2, wherein when determining the pulse width modulation output value, further comprising: When the pulse width modulation count value is not less than the first preset value and not greater than the duty cycle minus the first preset value, the pulse width modulation output value is made to have a maximum amplitude. 5. The multi-level pulse width modulation method as claimed in claim 2, wherein when determining the pulse width modulation output value, further comprising: When the pulse width modulation count value is greater than the duty cycle minus the first preset value and not less than the duty cycle, the determined pulse width modulation output value is greater than the previously determined pulse width modulation output The value is reduced by at most one unit of energy. 6. The multi-level pulse width modulation method as claimed in claim 1, further comprising: gradually reducing the energy in the modulated pulse in a multi-stage manner, so that the falling edge of the modulated pulse is stepped down to reduce Instant energy change. 7. A multilevel pulse width modulation method for sampling an input signal to generate a corresponding pulse width modulation signal, the pulse width modulation signal comprising at least one modulation pulse, the multilevel pulse width modulation method is characterized by: Using a reference count value to indicate a corresponding unit time in the modulation pulse: Initialize the base count value to zero; Setting an increment count value as a maximum energy value to be expressed per unit time of the rising edge in the modulation pulse; and gradually increasing the base count value to a second preset value and gradually reducing the increment count value to zero, wherein the second preset value is ²ⁿ -1, n is the number of bits representing the amplitude resolution, and Before the base count value reaches the second preset value and the incremental count value reaches zero, the unit of energy output by the unit time corresponding to the base count value in the modulated pulse is the base count value plus 1.

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