TWI824457B - Audio amplifier with duty ratio control - Google Patents

Abstract

An audio amplifier with duty ratio control is provided. The audio amplifier comprises a pulse width modulation modulator, a power stage, and a voltage converter. The pulse width modulation modulator is configured to receive an input signal for generating a pulse width modulation signal. The power stage is configured to output an output signal according to a supply voltage and the pulse width modulation signal. The voltage converter is configured to adjust voltage level of the supply voltage according to the pulse width modulation signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when duty ratio of the pulse width modulation signal is greater than a duty ratio threshold.

Description

Audio amplifier with duty cycle control

The present application relates to an audio amplifier, particularly an audio amplifier that can adaptively adjust the supply voltage PVDD to operate at an optimal operating point.

Audio amplifiers are often used in electronic circuits that reproduce input audio signals at the sound output end. Therefore, the amplifier must meet the requirements of volume control, low harmonic distortion, and high performance. In addition, compared with other amplifiers, Class D amplifiers are currently the best choice to meet the needs of better efficiency, low power consumption and lightweight. Generally, pulse width modulation is used to tightly control the output devices in Class D amplifier systems.

In order to improve efficiency, Class H amplifiers were derived, which were modified from Class A/B amplifiers operating at the power supply voltage level. Class H amplifiers utilize low rail voltage to effectively reduce power consumption at low voltages, and the system dynamically controls the rail voltage to drive high-amplitude transients at high voltages.

Please refer to Figure 1A, which is a schematic diagram of a general Class D amplifier circuit. As shown in FIG. 1A , a typical class D amplifier includes an audio pulse width modulation (PWM) modulator 110 , a pre-driver 120 and a voltage converter 130 .

The audio pulse width modulation (PWM) modulator 110 receives an audio signal (IN) as its input. The output terminal of the audio pulse width modulation (PWM) modulator is electrically connected to the input terminal of the pre-driver 120 catch. The pre-driver 120 amplifies the audio signal and outputs the amplified audio signal to the power switch pair 140, 150.

The voltage converter 130 receives an input voltage VIN and outputs a fixed supply voltage PVDD. The output terminal of the voltage converter 130 is connected to the upper power switch 140 .

One end of an inductor 160 is connected between the upper power switch 140 and the lower power switch 150 . The other end of the inductor 160 is connected to a speaker 180 so that the audio is output by the speaker. A capacitor 170 is connected in parallel with the speaker.

Please refer to Figure 1B, which is a schematic diagram of an independent class H amplifier based on a general class D amplifier.

Some components of the class H amplifier circuit 200 shown in FIG. 1B are the same as those shown in FIG. 1A . The difference between the class H amplifier circuit 200 and the class D amplifier circuit 100 is as shown in Figure 1B. The audio signal (IN) is fed into a voltage converter 131 through an envelope detector 190. Therefore, The envelope of the audio signal can be traced. In addition, the voltage converter 131 is configured to dynamically output a supply voltage PVDD according to the output of the envelope detector 190 .

Please refer to FIG. 1C , which is a schematic diagram of the supply voltage PVDD signal and the audio signal of the circuit of FIG. 1A and FIG. 1B .

As shown in Figure 1C, the supply voltage PVDD of the class D amplifier is a fixed voltage, as shown by the dotted line.

In contrast, the voltage of the supply voltage PVDD of the class H amplifier (as shown by the solid curve) tracks the envelope of the audio signal (IN) as shown by the gray curve.

Please refer to Figure 2, which is a schematic diagram comparing the efficiency of Class H amplifiers and Class D amplifiers.

As shown in Figure 2, in this example, the Class H amplifier improves the power conversion efficiency by about 15% compared to the Class D amplifier designed for a fixed voltage. Therefore, Class H amplifier technology is an excellent design choice for limited battery voltage applications. The Class H amplifier uses typical audio tracking to adjust the supply voltage PVDD, which can reduce power switching losses caused by higher cross-voltage and improve power conversion efficiency compared to Class D amplifiers.

Therefore, compared to the fixed supply voltage used in FIG. 1A , the amplifier circuit 200 of FIG. 1B has multiple switchable or variable supply voltages PVDD. The class H amplifier has higher power efficiency than the class D amplifier.

An object of this application is to provide an audio amplifier with duty cycle control. The audio amplifier may be implemented based on a class H amplifier with closed loop control to adjust the supply voltage of the audio amplifier based on the pulse width modulation signal of the audio amplifier. The audio amplifier can operate at an optimal operating point and control the duty cycle of the pulse width modulation signal.

According to an embodiment of the present application, an audio amplifier with duty cycle control is provided. The audio amplifier includes a pulse width modulation modulator, a power stage and a voltage converter. The PWM modulator is configured to receive an input signal to generate a PWM signal. The power stage is configured to output an output signal based on a supply voltage and the pulse width modulation signal. The voltage converter is configured to adjust the voltage level of the supply voltage according to the pulse width modulation signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulation signal is greater than a duty cycle threshold.

According to an embodiment of the present application, an audio amplifier with duty cycle control is provided. A duty cycle controlled audio amplifier includes a pulse width modulation modulator, a power stage and a voltage converter. The pulse width modulation modulator is used to generate a pulse width modulation signal. The power stage is coupled to the pulse width modulation modulator. The voltage converter is coupled to the power stage and configured to output a supply voltage to the power stage, wherein the voltage converter is configured to adjust a voltage level of the supply voltage according to a duty cycle of the pulse width modulation signal. .

In some embodiments of the audio amplifier, the audio amplifier further includes a pulse width modulation detector electrically coupled between the power stage and the voltage converter and used to output an indication signal to the voltage A converter, wherein the indication signal indicates whether the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold, and the voltage converter is configured to adjust the voltage level of the supply voltage according to the indication signal.

In some embodiments of the audio amplifier, the PWM detector is configured to output the indication signal according to the PWM signal and the duty cycle threshold.

In some embodiments of the audio amplifier, the voltage converter is configured to adjust the voltage level of the supply voltage when the indication signal indicates that the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold.

In some embodiments of the audio amplifier, the audio amplifier is configured to limit the duty cycle of the pulse width modulation signal to a percentage based on the duty cycle threshold.

In some embodiments of the audio amplifier, a closed loop is formed between the power stage and the voltage converter.

100: Class D amplifier circuit

110: Audio pulse width modulation (PWM) modulator

120:Predriver

130, 131: Voltage converter

140: Turn on the power switch

150: Lower the power switch

160:Inductor

170: Capacitor

180: Speaker

190:Envelope Detector

200:Amplifier circuit

400, 400A, 400B, 400C: closed loop control class H audio amplifier

410:Voltage converter

415:PWM detector

420: Audio pulse width modulation modulator

425: Class D amplifier

430:Predriver

440: Second switch

450: first switch

460: Load inductance

470: Capacitor

480: Speaker

510: filter

520: Error amplifier

530:Output stage

610: Adding circuit

620: Error amplifier

630:Output stage

A(t): Instruction signal

D(t): duty cycle

Dref: reference duty cycle

FB: feedback signal

IN, IN(t): audio signal

PVDD, PVDD(t): supply voltage

pwm(t): pulse width modulation signal

Ron: Resistor

VIN, VIN(t): input voltage

Vref: reference signal

Figure 1A (prior art) is a schematic diagram of a general class D amplifier circuit with a boost converter and no class H amplifier.

FIG. 1B (prior art) is a schematic diagram of a general class D amplifier circuit with a boost converter and a class H amplifier.

FIG. 1C (prior art) is a schematic diagram of the power VDD (PVDD) signal and the audio signal (IN) of the circuit in FIGS. 1A and 1B.

Figure 2 (prior art) is a schematic diagram comparing the efficiency of a class H amplifier and a class D amplifier.

FIG. 3 is a schematic diagram of a closed loop control class H audio amplifier according to an embodiment of the present application.

FIG. 4 is a schematic diagram of a pulse width modulation detector according to an embodiment of the present application.

FIG. 5 is a schematic waveform diagram of the circuit with pulse width modulation (PWM) control in FIG. 4 according to an embodiment of the present application.

FIG. 6 is a schematic diagram of a voltage converter according to an embodiment of the present application.

FIG. 7A is a schematic diagram of a closed loop control class H audio amplifier according to an embodiment of the present application.

7B is a schematic diagram of a closed loop control class H audio amplifier according to an embodiment of the present application.

FIG. 7C is a schematic diagram of a closed loop control class H audio amplifier according to an embodiment of the present application.

In order to facilitate understanding of the purpose, features, and effects of the present application, the present application provides multiple embodiments and drawings to explain the disclosure content of the present application in detail.

Supply voltage PVDD adjustment (rise/fall slope, gain) of Class H amplifiers is important for total harmonic distortion (THD) and power conversion efficiency. Get a D Voltage modulation using a pulse width modulation (PWM) signal of a class amplifier allows the supply voltage PVDD to be adaptively adjusted so that the audio amplifier can operate at an optimal point.

Please refer to FIG. 3 , which is a schematic diagram of a closed-loop control class H audio amplifier according to an embodiment of the present application.

As shown in Figure 3, the closed loop control class H audio amplifier 400 includes an audio pulse width modulation (PWM) modulator 420 and a pre-driver 430. The audio pulse width modulation (PWM) modulator 420 and the The pre-driver 430 together forms the basis of a class D amplifier. The audio pulse width modulation (PWM) modulator 420 receives an input signal, such as an audio signal (IN). The audio pulse width modulation (PWM) modulator 420 converts the audio signal (IN) into a pulse width modulation signal. The PWM signal is output by the audio PWM modulator 420 and input to the pre-driver 430 . The pre-driver 430 amplifies the pulse width modulation (PWM) signal and outputs the amplified pulse width modulation (PWM) signal to a power stage. The power stage includes a first switch 450 and a second switch 440 . The pre-driver 430 includes two output terminals. One output terminal of the pre-driver 430 is electrically connected to the first switch 450 , and the other output terminal of the pre-driver 430 is electrically connected to the second switch 440 . For example, the audio pulse width modulation (PWM) modulator 420 and the pre-driver 430 can be implemented based on using a comparator to compare the input signal with a triangle wave. A low-pass filter includes an inductor 460 and a capacitor 470. One end of the inductor 460 is electrically coupled between the first switch 450 and the second switch 440. A speaker 480 is connected in parallel with the capacitor 470 of the low pass filter.

One end of the first switch 450 is connected to the output end of a voltage converter 410 . The voltage converter 410 receives an input voltage VIN and outputs a supply voltage PVDD according to a control signal. For example, the voltage converter 410 may utilize a boost converter, a buck converter, or a low dropout regulator. It is implemented by a voltage converter, which can dynamically output a supply voltage according to a control signal. The control signal can be obtained, for example, according to the pulse width modulation signal.

The closed loop control class H audio amplifier 400 further includes a PWM detector 415 . An input terminal of the PWM detector 415 is electrically connected to the output terminal of the pre-driver 430 , and the output terminal of the pre-driver 430 is electrically connected to the first switch 450 . The output terminal of the PWM detector 415 is connected to the feedback input terminal of the voltage converter 410 .

As shown in FIG. 3 , a closed loop is formed through the output terminal of the voltage converter 410 , through the first switch 450 , and through the input terminal of the PWM detector 415 and the feedback input terminal of the voltage converter 410 Formed between the voltage converter 410, the PWM detector 415, and the first switch 450.

The PWM detector 415 senses the duty cycle of the pulse width modulation (PWM) signal at the input end of the PWM sensor. By using the PWM detector 415, the percentage of the duty cycle of the pulse width modulation (PWM) signal can be limited based on an operating threshold. Since larger audio volumes have larger duty cycles, the pulse width modulation (PWM) signal can be limited to ensure that the audio signal is not reduced or distorted.

In an embodiment of the present application, the duty cycle threshold is preset in hardware or firmware.

In an embodiment of the present application, the duty cycle threshold can be controlled or changed by a user of hardware or firmware.

The PWM detector 415 outputs a feedback control signal to the feedback input terminal of the voltage converter. The voltage converter 410 uses the received feedback control signal to continuously or adaptively adjust the supply voltage. In this way, the adaptive supply voltage PVDD can ensure that the audio amplifier operates at the optimal point.

Please refer to FIG. 4 , which is a schematic diagram of a PWM detector 415 according to an embodiment. In FIG. 4 , an embodiment of the PWM detector 415 includes a filter 510 , an error amplifier 520 and an output stage 530 . The filter 510 receives the pulse width modulation signal (as indicated by pwm(t)) and outputs a filtered signal indicating the duty cycle D(t) of the pulse width modulation signal. The error amplifier 520 is used to compare the filtered signal indicating the duty cycle D(t) with a reference duty cycle Dref. The output stage 530 outputs an indication signal A(t) according to the output of the error amplifier 520 . When the duty cycle D(t) is equal to or greater than the reference duty cycle Dref, the error amplifier 520 outputs an output through the output stage 530, so that the PWM detector 415 outputs the indication signal A(t), and the indication The signal A(t) is used to indicate that the duty cycle of the pulse width modulation signal will be equal to or greater than the reference duty cycle Dref.

Please refer to FIG. 5 , which is a schematic waveform diagram of the circuit with pulse width modulation (PWM) control in FIG. 4 according to an embodiment of the present application.

Please refer to Figure 5. When the audio signal IN(t) is modulated internally, the duty cycle D(t) of the PWM signal will change. When the duty cycle D(t) is equal to or about to be greater than the reference duty cycle Dref, the voltage converter 410 adjusts the voltage level of the supply voltage PVDD(t) according to the indication signal A(t) output by the PWM detector 415. Bit. For example, the voltage converter 410 increases the voltage level of the supply voltage PVDD(t). The audio amplifier 400 has the characteristic that when the voltage level of the supply voltage PVDD(t) increases, the duty cycle of the PWM signal decreases. Through this characteristic, the duty cycle of the PWM signal can be controlled, for example, to be locked to the reference duty cycle Dref. Therefore, the circuit of this implementation can operate at the optimal operating point to obtain optimal system efficiency.

In addition, as shown in FIG. 5 , the duty cycle of the PWM signal is limited by a duty cycle threshold, for example, the reference duty cycle Dref corresponds to a percentage of the duty cycle (such as 80%, 85% or other suitable percentages). When the duty cycle of the PWM signal is less than the duty cycle threshold, the PWM The signal changes according to the audio signal IN(t), and the supply voltage PVDD(t) remains at a specific voltage level. When the duty cycle of the PWM signal is equal to or about to be higher than the duty cycle threshold, based on the characteristics of the audio amplifier 400, the supply voltage PVDD(t) increases while the duty cycle of the PWM signal decreases. In this way, overall, the duty cycle of the PWM signal is limited by the duty cycle threshold.

In some embodiments, the voltage converter may be implemented such that the duty cycle threshold may be controlled or changed by hardware, firmware, or software.

In some embodiments, the PWM detector 415 may be implemented by or based on a phase locked loop or a feedback control module.

Please refer to FIG. 6 , which is a schematic diagram of a voltage converter according to an embodiment of the present application. In the embodiment of FIG. 6 , the voltage converter 410 may be implemented to include an adder circuit 610 (as indicated by the symbol Σ), an error amplifier 620 and an output stage 630 . The adding circuit 610 outputs an adding signal according to the instruction signal A(t) from the PWM detector 145 and the feedback signal FB of the voltage converter 410 (eg, the supply voltage PVDD(t)). The error amplifier 620 outputs a comparison signal based on the addition signal and a reference signal (indicated by Vref). The output stage 630 outputs the supply voltage PVDD(t) according to the input voltage VIN(t) and the comparison signal. For example, the input voltage VIN(t) is a DC voltage signal, and the output stage 630 of the voltage converter 410 adjusts the supply voltage PVDD(t) in response to the comparison signal.

Please refer to FIGS. 7A, 7B and 7C. FIGS. 7A, 7B and 7C are schematic diagrams of closed loop control class H audio amplifiers (such as 400A, 400B and 400C) according to various embodiments of the present application.

The operation method of the closed-loop controlled class H audio amplifier shown in FIGS. 7A , 7B and 7C is similar to that of the closed-loop controlled class H audio amplifier of FIG. 3 .

However, in these embodiments, the input of the PWM detector 415 is electrically connected to an alternative node in the circuit. For example, in FIG. 7B , the input terminal of the PWM detector 415 is electrically connected to the node connected to the load inductor (L) 460 . In FIG. 7C , the input end of the PWM detector 415 is electrically connected to a node between a resistor Ron and the second switch 440 . In the embodiment of FIG. 7A , the input terminal of the PWM detector 415 is electrically connected to the feedback output terminal of the class D amplifier, and is not connected between the pre-driver 430 and the first switch 450 .

In the embodiments of FIGS. 7A , 7B and 7C , the class D amplifier 425 is formed by a combination of the audio pulse width modulation (PWM) modulator 420 and the pre-driver 430 .

According to some embodiments of the present application, an audio amplifier with duty cycle control is provided. The audio amplifier (400, 400A, 400B or 440C shown in Figure 3, Figure 7A, Figure 7B or Figure 7C) includes a pulse width modulation modulator (shown in Figure 3, Figure 7A, Figure 7B or Figure 7C 420), a power stage (440 and 450 as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C, or 430, 440 and 450 as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C) and a Voltage converter (410 shown in Figure 3, Figure 7A, Figure 7B or Figure 7C). The PWM modulator is configured to receive an input signal to generate a PWM signal. The power stage is configured to output an output signal based on a supply voltage and the pulse width modulation signal. The voltage converter is configured to adjust the voltage level of the supply voltage according to the pulse width modulation signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulation signal is greater than a duty cycle threshold.

According to other embodiments of the present application, an audio amplifier with duty cycle control is provided. The audio amplifier (400, 400A, 400B or 440C shown in Figure 3, Figure 7A, Figure 7B or Figure 7C) includes a pulse width modulation modulator (shown in Figure 3, Figure 7A, Figure 7B or Figure 7C 420), a power stage (440 and 450 as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C, or as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C 430, 440 and 450) and a voltage converter (410 as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C). The pulse width modulation modulator is used to generate a pulse width modulation signal. The power stage is coupled to the pulse width modulation modulator. The voltage converter is coupled to the power stage and configured to output a supply voltage to the power stage, wherein the voltage converter is configured to adjust a voltage level of the supply voltage according to a duty cycle of the pulse width modulation signal. .

In some embodiments of the audio amplifier, the audio amplifier further includes a pulse width modulation detector (415 in Figure 3, Figure 7A, Figure 7B or Figure 7C), which is electrically coupled to the power stage and between the voltage converter and used to output an indication signal (A(t) in Figure 3, Figure 7A, Figure 7B or Figure 7C) to the voltage converter, wherein the indication signal indicates the pulse width modulation signal Whether the duty cycle is greater than the duty cycle threshold, and the voltage converter is configured to adjust the voltage level of the supply voltage according to the indication signal.

In some embodiments of the audio amplifier, the pulse width modulation detector is configured to output the indication signal (such as A(t) in Figure 3, Figure 7A, Figure 7B or Figure 7C), as shown in Figure 4.

In some embodiments of the audio amplifier, the voltage converter is configured to indicate the duty cycle of the pulse width modulation signal when the indication signal (A(t) in FIG. 3, FIG. 7A, FIG. 7B or FIG. 7C) indicates When it is greater than the duty cycle threshold, the voltage level of the supply voltage is adjusted.

In some embodiments of the audio amplifier, the audio amplifier is configured to limit the duty cycle of the pulse width modulation signal to a percentage based on the duty cycle threshold, as shown in FIG. 5 .

In some embodiments of the audio amplifier, a closed loop is formed between the power stage and the voltage converter (as shown in Figure 3, Figure 7A, Figure 7B or Figure 7C).

Although the contents disclosed in this application have been described with reference to specific embodiments, those skilled in the art may make numerous modifications and variations without departing from the contents disclosed in this application as set forth within the scope of the patent application. Category and spirit.

400: Closed loop control Class H audio amplifier

410:Voltage converter

415:PWM detector

420: Audio pulse width modulation modulator

430:Predriver

440: Second switch

450: first switch

460: Load inductance

470: Capacitor

480: Speaker

A(t): Instruction signal

IN(t): audio signal

PVDD(t): supply voltage

pwm(t): pulse width modulation signal

VIN(t): input voltage

Claims (10)

An audio amplifier with duty cycle control, which includes: a pulse width modulation modulator configured to receive an input signal to generate a pulse width modulation signal; a power stage configured to respond to a supply voltage and the pulse The wide modulation signal outputs an output signal; a voltage converter is configured to adjust the voltage level of the supply voltage according to the pulse width modulation signal; and a pulse width modulation detector is electrically coupled to the power between the stage and the voltage converter to output an indication signal to the voltage converter, wherein the indication signal is used to indicate whether the duty cycle of the pulse width modulation signal is greater than a duty cycle threshold, and the voltage converter is configured To adjust the voltage level of the supply voltage according to the instruction signal; wherein the audio amplifier is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold, and the The duty cycle of the pulse width modulation signal is limited by the duty cycle threshold. The audio amplifier of claim 1, wherein the pulse width modulation detector is configured to output the indication signal according to the pulse width modulation signal and the duty cycle threshold. The audio amplifier of claim 1, wherein the voltage converter is configured to adjust the voltage level of the supply voltage when the indication signal indicates that the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold. The audio amplifier of claim 1, wherein the audio amplifier is configured to limit the duty cycle of the pulse width modulation signal to a percentage based on the duty cycle threshold. The audio amplifier of claim 1, wherein a closed loop is formed between the power stage and the voltage converter. An audio amplifier with duty cycle control, which includes: a pulse width modulation modulator for generating a pulse width modulation signal; a power stage coupled to the pulse width modulation modulator; a voltage converter, coupled to the power stage and configured to output a supply voltage to the power stage; and a pulse width modulation detector electrically coupled between the power stage and the voltage converter to output an indication signal to the voltage converter, wherein the indication signal indicates whether the duty cycle of the pulse width modulation signal is greater than a duty cycle threshold, and the voltage converter adjusts the voltage level of the supply voltage according to the indication signal; wherein, the The voltage converter is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold, and the duty cycle of the pulse width modulation signal is limited by the duty cycle threshold. The audio amplifier of claim 6, wherein the pulse width modulation detector is configured to output the indication signal according to the pulse width modulation signal and the duty cycle threshold. The audio amplifier of claim 6, wherein the voltage converter is configured to adjust the voltage level of the supply voltage when the indication signal indicates that the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold. The audio amplifier of claim 6, wherein the audio amplifier is configured to limit the duty cycle of the pulse width modulation signal to a percentage based on the duty cycle threshold. The audio amplifier of claim 6, wherein a closed loop is formed between the power stage and the voltage converter.