CN102006021A - Frequency conversion class D amplifier and control method, and applied sawtooth wave generator and method - Google Patents

Abstract

A variable frequency class D amplifier, comprising: a sawtooth wave generator generating a sawtooth wave signal whose frequency varies with an input signal; and the modulator is used for converting the input signal into a variable-frequency pulse width modulation signal according to the sawtooth wave signal so as to drive a load. The frequency conversion D class amplifier, the control method thereof, the sawtooth wave generator applied to the frequency conversion D class amplifier and the method thereof have the advantages that the sawtooth wave signal frequency is determined by the audio input signal, no random generator is required to be additionally arranged, and the D class amplifier has better simulation effect.

Description

Frequency conversion class D amplifier and control method, and applied sawtooth wave generator and method

technical field

The invention relates to a class D amplifier, in particular to a frequency conversion class D amplifier for improving electromagnetic interference (Electro Magnetic Interference; EMI).

Background technique

With the development of light, thin, short, and small handheld electronic devices, such as mobile phones, MP3, PDA, IPOD, and LCD TV, high-efficiency class D amplifiers are gradually being valued. 1 shows a known class D amplifier 10, which includes a sawtooth generator 14, a modulator 16, and a drive circuit 18, wherein the sawtooth generator 14 is used to provide a sawtooth signal Vramp, and the modulator 16 is based on the sawtooth signal. Vramp converts the audio input signal Vaudio into a pulse width modulation signal PWM, and the driving circuit 18 drives the load 12 according to the pulse width modulation signal PWM. In the class D amplifier 10, EMI is a very important problem, and there are many ways to improve the EMI problem, and spread spectrum technology is one of them.

The current spread spectrum technology usually uses a random generator (random generator) to provide a random number to change the frequency of the sawtooth wave signal Vramp, so that the frequency of the pulse width modulation signal PWM is not fixed, as described in US Patent Publication No. 2004/0232978 No. 2007/0132509 and U.S. Patent No. 6,847257 all disclose class-D amplifiers using random generators. However, this method requires additional random generators to provide random numbers. In addition, in order to obtain a better simulation effect, when the amplitude of the audio input signal Vaudio is large, a sawtooth signal Vramp with a higher frequency is required. On the contrary, when the amplitude of the audio input signal Vaudio is smaller, a sawtooth signal with a lower frequency is required. The wave signal Vramp, but the random number provided by the random generator is unpredictable, so the low-frequency sawtooth signal Vramp may be generated when the amplitude of the audio input signal Vaudio is large, thereby causing distortion.

Therefore, the known spread spectrum technique using a random generator suffers from the above-mentioned inconveniences and problems.

Contents of the invention

The object of the present invention is to propose a variable frequency Class D amplifier that does not need a random generator and can reduce distortion and its control method.

Another object of the present invention is to provide a sawtooth wave generator and method applied to frequency conversion class D amplifiers.

For realizing the above object, technical solution of the present invention is:

A frequency conversion class D amplifier is characterized in that comprising:

A sawtooth wave generator that generates a sawtooth wave signal whose frequency varies with the input signal;

A modulator is configured to convert the input signal into a variable-frequency pulse-width modulated signal according to the sawtooth wave signal for driving a load.

The variable frequency class D amplifier of the present invention can also be further realized by adopting the following technical measures.

The aforementioned variable frequency class D amplifier, wherein the sawtooth wave generator includes:

capacitance;

A current supply circuit, connected to the capacitor, provides a variable charging current to charge the capacitor according to the input signal;

The charge and discharge controller is connected to the capacitor, and controls the charge and discharge of the capacitor to generate the sawtooth wave signal.

In the aforementioned variable frequency class D amplifier, the frequency of the sawtooth signal varies with the amplitude of the input signal.

The aforementioned variable frequency class D amplifier, wherein the current supply circuit includes:

A current source, coupled to the capacitor, supplies a first current to charge the capacitor;

A voltage-to-current converter, connected to the capacitor, provides a second current that varies with the amplitude of the input signal to charge the capacitor, wherein the sum of the first and second currents is equal to the charging current.

In the aforementioned variable frequency class D amplifier, wherein the voltage-to-current converter includes a transconductance amplifier.

The aforementioned variable frequency class D amplifier further includes a switch connected between the current source and the capacitor, which is turned off when the input signal ends.

The aforementioned variable frequency class D amplifier, wherein the charge and discharge controller includes:

a switch connected in parallel with the capacitor;

a first comparator, connected to the capacitor, and sending a first comparison signal when the sawtooth signal is greater than a first critical value;

a second comparator connected to the capacitor, and sends a second comparison signal when the sawtooth signal is smaller than a second critical value;

The flip-flop generates a control signal according to the first and second comparison signals to switch the switch so as to control the charging and discharging of the capacitor.

A sawtooth wave generator applied to a frequency conversion class D amplifier, the frequency conversion class D amplifier includes a modulator to convert an input signal into a pulse width modulation signal according to a sawtooth wave signal for driving a load, characterized in that The sawtooth generator includes:

capacitance;

A current supply circuit, connected to the capacitor, provides a charging current that changes with the audio input signal to charge the capacitor;

The charge and discharge controller is connected to the capacitor, and controls the charge and discharge of the capacitor to generate the sawtooth wave signal.

The sawtooth wave generator applied to the variable frequency class D amplifier of the present invention can be further realized by adopting the following technical measures.

In the aforementioned sawtooth wave generator, the frequency of the sawtooth wave signal varies with the amplitude of the audio input signal.

The aforementioned sawtooth wave generator, wherein the current supply circuit includes:

A current source, coupled to the capacitor, supplies a first current to charge the capacitor;

A voltage-to-current converter, connected to the capacitor, provides a second current that varies with the amplitude of the input signal to charge the capacitor, wherein the sum of the first and second currents is equal to the charging current.

In the aforementioned sawtooth wave generator, wherein the voltage-to-current converter includes a transconductance amplifier.

The aforementioned sawtooth wave generator further includes a switch connected between the current source and the capacitor, which is turned off when the input signal ends.

The aforementioned sawtooth wave generator, wherein the charge and discharge controller includes:

a switch connected in parallel with the capacitor;

a first comparator, connected to the capacitor, and sending a first comparison signal when the sawtooth signal is greater than a first critical value;

a second comparator connected to the capacitor, and sends a second comparison signal when the sawtooth signal is smaller than a second critical value;

The flip-flop generates a control signal according to the first and second comparison signals to switch the switch so as to control the charging and discharging of the capacitor.

A kind of control method of frequency conversion class D amplifier is characterized in that comprising the following steps:

(A) providing a sawtooth wave signal whose frequency varies with the input signal;

(B) converting the input signal into a frequency-variable pulse-width modulated signal according to the sawtooth wave signal for driving a load.

The control method of the variable frequency class D amplifier of the present invention can also be further realized by adopting the following technical measures.

The aforementioned control method, wherein said step A includes providing said sawtooth wave signal whose frequency varies with the amplitude of said input signal.

Aforesaid control method, wherein said A step comprises:

providing a variable charging current according to the input signal to charge a capacitor to generate the sawtooth wave signal;

The charging and discharging of the capacitor is controlled to generate the sawtooth wave signal.

The aforementioned control method, wherein the step of providing the variable charging current includes:

providing a fixed first current;

Providing a second current that varies with the amplitude of the input signal combines with the first current to generate the charging current.

The aforementioned control method, wherein the step of controlling the charging and discharging of the capacitor comprises:

controlling the capacitor to discharge when the sawtooth signal is greater than a first critical value;

When the sawtooth wave signal is smaller than a second critical value, the capacitor is controlled to be charged.

The aforementioned control method further includes stopping providing the sawtooth signal when the input signal ends.

A method for generating a sawtooth signal applied to a variable frequency class D amplifier, the variable frequency class D amplifier includes a modulator that converts an input signal into a pulse width modulated signal according to a sawtooth signal for driving a load, its features The method for generating the sawtooth signal comprises the following steps:

(A) providing a variable charging current to charge a capacitor according to the input signal;

(B) controlling the charging and discharging of the capacitor to generate the sawtooth wave signal.

The method for generating a sawtooth wave signal applied to a frequency-variable class D amplifier of the present invention can be further realized by adopting the following technical measures.

In the aforementioned control method, the step A includes generating the sawtooth signal whose frequency varies with the amplitude of the input signal.

Aforesaid control method, wherein said A step comprises:

providing a fixed first current;

Providing a second current that varies with the amplitude of the input signal combines with the first current to generate the charging current.

Aforesaid control method, wherein said B step comprises

controlling the capacitor to discharge when the sawtooth signal is greater than a first critical value;

When the sawtooth wave signal is smaller than a second critical value, the capacitor is controlled to be charged.

The aforementioned control method further includes stopping providing the sawtooth signal when the input signal ends.

After adopting the above technical scheme, the frequency conversion class D amplifier and its control method of the present invention and the sawtooth wave generator and method applied to the frequency conversion class D amplifier have the following advantages:

1. The frequency of the sawtooth wave signal is determined by the audio input signal, without additional random generators.

2. Class D amplifier has better simulation effect.

Description of drawings

FIG. 1 is a schematic diagram of a known class D amplifier;

Fig. 2 is the schematic diagram of frequency conversion class D amplifier of the present invention;

FIG. 3 is a schematic diagram of an embodiment of the sawtooth wave generator in FIG. 2 .

In the figure, 10, class D amplifier 12, load 14, sawtooth wave generator 16, modulator 18, drive circuit 20, class D amplifier 22, load 24, sawtooth wave generator 26, modulator 28, drive circuit 30 , a current supply circuit 32, a charge-discharge controller 34, a voltage-to-current converter 36, a transconductance amplifier 38, a current source 40, a comparator 42, a comparator 44, and a flip-flop.

Detailed ways

The present invention will be further described below in conjunction with embodiment and accompanying drawing.

In fact, the sound itself is a random number in both frequency and amplitude, so the random number can be obtained by using the audio input signal input to the class D amplifier to achieve spread spectrum.

Please refer to FIG. 2 now. FIG. 2 is a schematic diagram of the variable frequency class D amplifier of the present invention. As shown in the figure, the variable frequency class D amplifier 20 of the present invention includes a sawtooth wave generator 24 , a modulator 26 and a driving circuit 28 . The sawtooth wave generator 24 generates a sawtooth wave signal Vramp according to the audio input signal Vaudio, and the frequency of the sawtooth wave signal Vramp varies with the audio input signal Vaudio. The modulator 26 converts the audio input signal Vaudio into a pulse width modulation signal PWM according to the sawtooth signal Vramp, and the frequency of the pulse width modulation signal PWM will vary with the frequency of the sawtooth signal Vramp. The driving circuit 28 drives the load 22 according to the pulse width modulation signal PWM.

FIG. 3 shows a schematic diagram of an embodiment of the sawtooth generator 24 in FIG. 2 , which includes a capacitor Cm, a current supply circuit 30 and a charge-discharge controller 32 . The current supply circuit 30 is used to supply a charging current Ich to charge the capacitor Cm. In the current supply circuit 30, the current source 38 supplies the current I1. The switch SW2 is connected between the current source 38 and the capacitor Cm, controlled by the signal S1, the voltage current The converter 34 generates the current I2 and the signal S1 according to the audio input signal Vaudio. The voltage-to-current converter 34 includes a transconductance amplifier 36 to determine the magnitude of the current I2 according to the amplitude of the audio input signal Vaudio. Since the current I2 changes with the audio input signal Vaudio, it charges Current Ich=I1+I2, so the charging current Ich also changes with the audio input signal Vaudio, when there is no audio input signal Vaudio, the transconductance amplifier 36 will close (turn off) switch SW2 to close the sawtooth wave generator 24, thereby reducing static The current (quiescent current) is consumed, and the modulator 26 will also stop working at this time. The charge and discharge controller 32 controls the charge and discharge of the capacitor Cm to generate a sawtooth wave signal Vramp. In the charge and discharge controller 32, the switch SW1 is connected in parallel with the capacitor Cm, and the resistors R1, R2 and R3 divide the voltage supply VCC to generate critical values Vth1 and Vth2. The comparator 40 compares the sawtooth signal Vramp and the critical value Vth1 to generate a comparison signal Sc1, the comparator 42 compares the sawtooth signal Vramp and the critical value Vth2 to generate a comparison signal Sc2, and the flip-flop 44 generates a control signal Sq to switch the switch according to the comparison signals Sc1 and Sc2 SW1 controls the charging and discharging of the capacitor Cm. When the sawtooth signal Vramp is greater than the critical value Vth1, the flip-flop 44 turns on (turn on) the switch SW1 to discharge the capacitor Cm. When the sawtooth signal Vramp is smaller than the critical value Vth2, the positive and negative The switch 44 turns off the switch SW1 to charge the capacitor Cm.

Since the class D amplifier 20 uses the audio input signal Vaudio as a random number source to implement spread spectrum, no additional random generator is needed. In addition, in the sawtooth wave generator 24, when the amplitude of the audio input signal Vaudio is larger, the current I2 is also larger so that the frequency of the sawtooth wave signal Vramp increases; on the contrary, when the amplitude of the audio input signal Vaudio is smaller, the current I2 The smaller the value is, the lower the frequency of the sawtooth wave signal Vramp is, so the class D amplifier 20 also has a better simulation effect.

The above embodiments are only for illustrating the present invention, rather than limiting the present invention. Those skilled in the relevant technical field can also make various transformations or changes without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also belong to the category of the present invention and should be defined by each claim.

Claims (24)

1. A variable frequency class D amplifier, characterized in that it comprises: A sawtooth wave generator that generates a sawtooth wave signal whose frequency varies with the input signal; A modulator is configured to convert the input signal into a variable-frequency pulse-width modulated signal according to the sawtooth wave signal for driving a load. 2. frequency conversion class D amplifier as claimed in claim 1, is characterized in that, described sawtooth generator comprises: capacitance; A current supply circuit, connected to the capacitor, provides a variable charging current to charge the capacitor according to the input signal; The charge and discharge controller is connected to the capacitor, and controls the charge and discharge of the capacitor to generate the sawtooth wave signal. 3. The variable frequency class-D amplifier according to claim 1, wherein the frequency of the sawtooth signal varies with the amplitude of the input signal. 4. frequency conversion class D amplifier as claimed in claim 2, is characterized in that, described current supply circuit comprises: A current source, coupled to the capacitor, supplies a first current to charge the capacitor; A voltage-to-current converter, connected to the capacitor, provides a second current that varies with the amplitude of the input signal to charge the capacitor, wherein the sum of the first and second currents is equal to the charging current. 5. The variable frequency class-D amplifier of claim 4, wherein the voltage-to-current converter comprises a transconductance amplifier. 6. The variable frequency class D amplifier as claimed in claim 4, further comprising a switch connected between the current source and the capacitor, which is turned off when the input signal ends. 7. The frequency conversion class D amplifier as claimed in claim 2, wherein the charge and discharge controller comprises: a switch connected in parallel with the capacitor; a first comparator, connected to the capacitor, and sending a first comparison signal when the sawtooth signal is greater than a first critical value; a second comparator connected to the capacitor, and sends a second comparison signal when the sawtooth signal is smaller than a second critical value; The flip-flop generates a control signal according to the first and second comparison signals to switch the switch so as to control the charging and discharging of the capacitor. 8. A sawtooth wave generator applied to a variable frequency class D amplifier, the frequency variable class D amplifier includes a modulator to convert an input signal into a pulse width modulated signal according to a sawtooth wave signal for driving a load, its It is characterized in that the sawtooth wave generator comprises: capacitance; A current supply circuit, connected to the capacitor, provides a charging current that changes with the audio input signal to charge the capacitor; The charge and discharge controller is connected to the capacitor, and controls the charge and discharge of the capacitor to generate the sawtooth wave signal. 9. The sawtooth wave generator as claimed in claim 8, wherein the frequency of the sawtooth wave signal varies with the amplitude of the audio input signal. 10. The sawtooth wave generator according to claim 8, wherein the current supply circuit comprises: A current source, coupled to the capacitor, supplies a first current to charge the capacitor; A voltage-to-current converter, connected to the capacitor, provides a second current that varies with the amplitude of the input signal to charge the capacitor, wherein the sum of the first and second currents is equal to the charging current. 11. The sawtooth wave generator as claimed in claim 10, wherein the voltage-to-current converter comprises a transconductance amplifier. 12. The sawtooth wave generator as claimed in claim 10, further comprising a switch connected between the current source and the capacitor, which is closed when the input signal ends. 13. The sawtooth wave generator according to claim 8, wherein the charge and discharge controller comprises: a switch connected in parallel with the capacitor; a first comparator, connected to the capacitor, and sending a first comparison signal when the sawtooth signal is greater than a first critical value; a second comparator connected to the capacitor, and sends a second comparison signal when the sawtooth signal is smaller than a second critical value; The flip-flop generates a control signal according to the first and second comparison signals to switch the switch so as to control the charging and discharging of the capacitor. 14. A control method for a variable frequency class D amplifier, characterized in that it comprises the following steps: (A) providing a sawtooth wave signal whose frequency varies with the input signal; (B) converting the input signal into a frequency-variable pulse-width modulated signal according to the sawtooth wave signal for driving a load. 15. The control method according to claim 14, wherein said step A comprises providing said sawtooth signal whose frequency varies with the amplitude of said input signal. 16. control method as claimed in claim 14, is characterized in that, described A step comprises: providing a variable charging current according to the input signal to charge a capacitor to generate the sawtooth wave signal; The charging and discharging of the capacitor is controlled to generate the sawtooth wave signal. 17. The control method according to claim 16, wherein the step of providing the variable charging current comprises: providing a fixed first current; Providing a second current that varies with the amplitude of the input signal combines with the first current to generate the charging current. 18. The control method according to claim 16, wherein the step of controlling the charging and discharging of the capacitor comprises: controlling the capacitor to discharge when the sawtooth signal is greater than a first critical value; When the sawtooth wave signal is smaller than a second critical value, the capacitor is controlled to be charged. 19. The control method as claimed in claim 14, further comprising stopping providing the sawtooth signal when the input signal ends. 20. A method for generating a sawtooth signal applied to a variable frequency class D amplifier, the variable frequency class D amplifier comprising a modulator converting an input signal into a pulse width modulated signal according to a sawtooth signal for driving a load, It is characterized in that the sawtooth wave signal generation method comprises the following steps: (A) providing a variable charging current to charge a capacitor according to the input signal; (B) controlling the charging and discharging of the capacitor to generate the sawtooth wave signal. 21. The method for generating a sawtooth signal according to claim 20, wherein the step A comprises generating the sawtooth signal whose frequency varies with the amplitude of the input signal. 22. The sawtooth wave signal generating method as claimed in claim 20, wherein said A step comprises: providing a fixed first current; Providing a second current that varies with the amplitude of the input signal combines with the first current to generate the charging current. 23. The sawtooth wave signal generating method as claimed in claim 20, wherein said B step comprises controlling the capacitor to discharge when the sawtooth signal is greater than a first critical value; When the sawtooth wave signal is smaller than a second critical value, the capacitor is controlled to be charged. 24. The method for generating a sawtooth signal as claimed in claim 20, further comprising stopping providing the sawtooth signal when the input signal ends.

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