Audio amplifier with duty cycle control

Abstract

An audio amplifier with duty cycle control is presented. The audio amplifier includes a pulse width modulator, a power stage, and a voltage converter. The pulse width modulator is configured to receive an input signal to generate a pulse width modulated signal. The power stage is configured to output an output signal according to a supply voltage and the pulse width modulated signal. The voltage converter is configured to adjust a voltage level of the supply voltage according to the pulse width modulated signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when a duty cycle of the pulse width modulated signal is greater than a duty cycle threshold.

Description

Technical Field

[0001] This application relates to an audio amplifier, and more particularly to an audio amplifier that can adaptively adjust the supply voltage PVDD to operate at an optimal operating point. Background Technology

[0002] Audio amplifiers are commonly used in electronic circuits that reproduce input audio signals at the sound output. Therefore, these amplifiers must meet requirements such as volume control, low harmonic distortion, and high efficiency. Furthermore, compared to other amplifiers, Class D amplifiers are currently the best choice for meeting the demands of optimal efficiency, low power consumption, and lightweight design. Generally, pulse width modulation (PWM) is used to precisely control the output of Class D amplifier systems.

[0003] To improve efficiency, Class H amplifiers were developed, which are variations of Class A / B amplifiers operating at the power supply voltage level. Class H amplifiers utilize the low rail voltage to effectively reduce power consumption at low voltage conditions, and the system dynamically controls the low rail voltage to drive high-amplitude transients at high voltage conditions.

[0004] Please refer to Figure 1A, which is a schematic diagram of a typical Class D amplifier circuit. As shown in Figure 1A, a typical Class D amplifier includes an audio pulse width modulation (PWM) modulator 110, a pre-driver 120, and a voltage converter 130.

[0005] The audio pulse width modulation (PWM) modulator 110 receives an audio signal (IN) as its input. The output of the PWM modulator is electrically connected to the input of the pre-driver 120. The pre-driver 120 amplifies the audio signal and outputs the amplified audio signal to power switches 140 and 150.

[0006] The voltage converter 130 receives the 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.

[0007] One end of inductor 160 is connected between upper power switch 140 and lower power switch 150. The other end of inductor 160 is connected to speaker 180 so that the audio is output by speaker. Capacitor 170 is connected in parallel with speaker.

[0008] Please refer to Figure 1B, which is a schematic diagram of an independent Class H amplifier based on a general Class D amplifier.

[0009] The Class H amplifier circuit 200 shown in Figure 1B has some of the same components as that shown in Figure 1A. The difference between the Class H amplifier circuit 200 and the Class D amplifier circuit 100, as shown in Figure 1B, is that the audio signal (IN) is fed into the voltage converter 131 via an envelope detector 190, so the envelope of the audio signal can be tracked. Furthermore, the voltage converter 131 is configured to dynamically output a supply voltage PVDD based on the output of the envelope detector 190.

[0010] Please refer to Figure 1C, which is a schematic diagram of the supply voltage PVDD signal and the audio signal of the circuits in Figures 1A and 1B.

[0011] As shown in Figure 1C, the supply voltage PVDD of the Class D amplifier is a fixed voltage, as indicated by the dashed line.

[0012] Conversely, the supply voltage PVDD of the Class H amplifier (as shown by the solid curve) is the voltage that tracks the envelope of the audio signal (IN) as shown by the gray curve.

[0013] Please refer to Figure 2, which is a schematic diagram comparing the efficiency of Class H amplifiers and Class D amplifiers.

[0014] As shown in Figure 2, in this example, the Class H amplifier improves power conversion efficiency by approximately 15% compared to the Class D amplifier designed for a fixed voltage. Therefore, Class H amplifier technology is an excellent design choice for applications with limited battery voltage. The Class H amplifier utilizes typical audio tracking to adjust the supply voltage PVDD, reducing power switching losses due to higher cross-voltage and providing better power conversion efficiency compared to Class D amplifiers.

[0015] Therefore, compared to the fixed supply voltage used in Figure 1A, the amplifier circuit 200 of Figure 1B has multiple switchable or variable supply voltages PVDD. The Class H amplifier has higher power efficiency compared to the Class D amplifier. Summary of the Invention

[0016] One 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 according to a pulse width modulation signal. The audio amplifier can operate at an optimal operating point and control the duty cycle of the pulse width modulation signal.

[0017] According to one embodiment of this application, an audio amplifier with duty cycle control is provided. The audio amplifier includes a pulse width modulator, a power stage, and a voltage converter. The pulse width modulator is configured to receive an input signal to generate a pulse width modulated signal. The power stage is configured to output an output signal based on a supply voltage and the pulse width modulated signal. The voltage converter is configured to adjust the voltage level of the supply voltage based on the pulse width modulated signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulated signal is greater than a duty cycle threshold.

[0018] According to one embodiment of this application, an audio amplifier with duty cycle control is provided. The audio amplifier with duty cycle control includes a pulse width modulator, a power stage, and a voltage converter. The pulse width modulator is used to generate a pulse width modulated signal. The power stage is connected to the pulse width modulator. The voltage converter is connected to the power stage and configured to output a supply voltage to the power stage, wherein the voltage converter is configured to adjust the voltage level of the supply voltage according to the duty cycle of the pulse width modulated signal.

[0019] In some embodiments of the audio amplifier, the audio amplifier further includes a pulse width modulation detector electrically connected between the power stage and the voltage converter, and used 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 the duty cycle threshold, and the voltage converter is configured to adjust the voltage level of the supply voltage according to the indication signal.

[0020] In some embodiments of the audio amplifier, the pulse width modulation detector is configured to output the indication signal based on the pulse width modulation signal and the duty cycle threshold.

[0021] 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.

[0022] 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.

[0023] In some embodiments of the audio amplifier, a closed loop is formed between the power stage and the voltage converter. Attached Figure Description

[0024] Figure 1A (Background Art) is a schematic diagram of a typical Class D amplifier circuit with a boost converter but without a Class H amplifier.

[0025] Figure 1B (Background Art) is a schematic diagram of a typical Class D amplifier circuit with a boost converter and a Class H amplifier.

[0026] Figure 1C (Background Art) is a schematic diagram of the power supply VDD (PVDD) signal and audio signal (IN) of the circuits in Figures 1A and 1B.

[0027] Figure 2 (Background Art) is a schematic diagram comparing the efficiency of Class H amplifiers and Class D amplifiers.

[0028] Figure 3 This is a schematic diagram of a closed-loop control of a Class H audio amplifier according to an embodiment of this application.

[0029] Figure 4 This is a schematic diagram of a pulse width modulation detector according to an embodiment of this application.

[0030] Figure 5 for Figure 4 A waveform diagram of a circuit with pulse width modulation (PWM) control according to an embodiment of this application is shown.

[0031] Figure 6 This is a schematic diagram of a voltage converter according to an embodiment of this application.

[0032] Figure 7A This is a schematic diagram of a closed-loop control of a Class H audio amplifier according to an embodiment of this application.

[0033] Figure 7B This is a schematic diagram of a closed-loop control of a Class H audio amplifier according to an embodiment of this application.

[0034] Figure 7C This is a schematic diagram of a closed-loop control of a Class H audio amplifier according to an embodiment of this application.

[0035] Figure label:

[0036] 100 Class D amplifier circuit

[0037] 110 Audio Pulse Width Modulator (PWM)

[0038] 120 Pre-drive

[0039] 130, 131 voltage converter

[0040] 140 Power switch

[0041] 150 power switch

[0042] 160 Inductor

[0043] 170 capacitor

[0044] 180 loudspeakers

[0045] 190 Envelope Detector

[0046] 200 Amplifier Circuit

[0047] 400, 400A, 400B, 400C Closed-Loop Controlled Class H Audio Amplifiers

[0048] 410 Voltage Converter

[0049] 415 PWM detector

[0050] 420 audio pulse width modulator

[0051] 425 Class D amplifier

[0052] 430 Pre-Driver

[0053] 440 Second Switch

[0054] 450 First Switch

[0055] 460 load inductance

[0056] 470 capacitor

[0057] 480 loudspeakers

[0058] 510 filter

[0059] 520 Error Amplifier

[0060] 530 Output Stage

[0061] 610 Adder Circuit

[0062] 620 Error Amplifier

[0063] 630 Output Stage

[0064] A(t) indicator signal

[0065] D(t) working cycle

[0066] Dref Reference Working Cycle

[0067] FB feedback signal

[0068] IN, IN(t) audio signals

[0069] PVDD, PVDD(t) supply voltage

[0070] Pwm(t) pulse width modulation signal

[0071] Ron resistor

[0072] VIN, VIN(t) Input voltage

[0073] Vref reference signal Detailed Implementation

[0074] To facilitate understanding of the purpose, features, and effects of this application, this application provides several embodiments and accompanying drawings to illustrate the disclosure of this application in detail.

[0075] Adjusting the supply voltage PVDD (rise / fall slope, gain) of a Class H amplifier is crucial for total harmonic distortion (THD) and power conversion efficiency. Using a pulse width modulation (PWM) signal from a Class D amplifier for voltage modulation allows the supply voltage PVDD to be adaptively adjusted, enabling the audio amplifier to operate at its optimal point.

[0076] Please refer to Figure 3 , Figure 3 This is a schematic diagram of a closed-loop control of a Class H audio amplifier according to an embodiment of this application.

[0077] like Figure 3As shown, the closed-loop controlled Class H audio amplifier 400 includes an audio pulse width modulation (PWM) modulator 420 and a pre-driver 430, which together form the basis of a Class D amplifier. The PWM modulator 420 receives an input signal, such as an audio signal (IN). The PWM modulator 420 converts the audio signal (IN) into a pulse width modulated signal. The PWM signal is output from the PWM modulator 420 and input to the pre-driver 430. The pre-driver 430 amplifies the PWM signal and outputs the amplified 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 outputs. One output of the pre-driver 430 is electrically connected to the first switch 450, and the other output 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 comparing the input signal with a triangular wave using a comparator. The low-pass filter includes an inductor 460 and a capacitor 470, with one end of the inductor 460 electrically connected between the first switch 450 and the second switch 440. The speaker 480 is connected in parallel with the capacitor 470 of the low-pass filter.

[0078] One end of the first switch 450 is connected to the output of the 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 can be implemented using a boost converter, a buck converter, or a low-dropout regulator, which can dynamically output the supply voltage according to the control signal. The control signal can be, for example, derived from the pulse width modulation signal.

[0079] The closed-loop controlled Class H audio amplifier 400 further includes a PWM detector 415. The input of the PWM detector 415 is electrically connected to the output of the pre-driver 430, and the output of the pre-driver 430 is electrically connected to the first switch 450. The output of the PWM detector 415 is connected to the feedback input of the voltage converter 410.

[0080] like Figure 3 As shown, a closed loop is formed between the voltage converter 410, the PWM detector 415, and the first switch 450 via the output terminal of the voltage converter 410, the first switch 450, and the input terminal of the PWM detector 415 and the feedback input terminal of the voltage converter 410.

[0081] The PWM detector 415 senses the duty cycle of the pulse width modulation (PWM) signal at the input of the PWM sensor. By using the PWM detector 415, the percentage of the duty cycle of the PWM signal can be limited based on a working threshold. Since larger audio volumes have larger duty cycles, the PWM signal can be limited to ensure that the audio signal is not attenuated or distorted.

[0082] In one embodiment of this application, the working cycle threshold is preset in the hardware or firmware.

[0083] In one embodiment of this application, the duty cycle threshold may be controlled or changed by the user of the hardware or firmware.

[0084] The PWM detector 415 outputs a feedback control signal to the feedback input of the voltage converter. The voltage converter 410 uses the received feedback control signal to continuously or adaptively adjust the supply voltage. This adaptively adjusted supply voltage PVDD ensures that the audio amplifier operates at its optimal point.

[0085] Please refer to Figure 4 , Figure 4 This is a schematic diagram of one embodiment of the PWM detector 415. Figure 4 In this embodiment, 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 compares 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) based on 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, causing the PWM detector 415 to output the indication signal A(t), which indicates that the duty cycle of the pulse width modulation signal will be equal to or greater than the reference duty cycle Dref.

[0086] Please refer to Figure 5 , Figure 5 for Figure 4 A waveform diagram of a circuit with pulse width modulation (PWM) control according to an embodiment of this application is shown.

[0087] Please refer to Figure 5When the audio signal IN(t) is internally modulated, the duty cycle D(t) of the PWM signal changes. 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. For example, the voltage converter 410 increases the voltage level of the supply voltage PVDD(t). The audio amplifier 400 has the characteristic that the duty cycle of the PWM signal decreases as the voltage level of the supply voltage PVDD(t) increases. By virtue of this characteristic, the duty cycle of the PWM signal can be controlled to, for example, lock to the reference duty cycle Dref. Therefore, the circuit of this embodiment can operate at an optimal operating point to obtain optimal system efficiency.

[0088] In addition, such as Figure 5 As shown, 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 (e.g., 80%, 85%, or other suitable percentage). When the duty cycle of the PWM signal is less than the duty cycle threshold, the PWM 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 exceed the duty cycle threshold, based on the characteristics of the audio amplifier 400, the duty cycle of the PWM signal decreases as the supply voltage PVDD(t) increases. In this way, overall, the duty cycle of the PWM signal is limited by the duty cycle threshold.

[0089] In some embodiments, the voltage converter may be implemented such that the duty cycle threshold can be controlled or changed by hardware, firmware, or software.

[0090] In some embodiments, the PWM detector 415 may be implemented by means of or based on a phase-locked loop or a feedback control module.

[0091] Please refer to Figure 6 , Figure 6 This is a schematic diagram of a voltage converter according to one embodiment of this application. Figure 6In one embodiment, the voltage converter 410 may be implemented as including an adder circuit 610 (e.g., indicated by the symbol ∑), an error amplifier 620, and an output stage 630. The adder circuit 610 outputs an addition signal based on the indication signal A(t) from the PWM detector 145 and the feedback signal FB from the voltage converter 410 (e.g., 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) based on 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.

[0092] Please refer to Figure 7A , Figure 7B as well as Figure 7C , Figure 7A , Figure 7B as well as Figure 7C This is a schematic diagram of a closed-loop controlled Class H audio amplifier (such as 400A, 400B, 400C) according to several embodiments of this application.

[0093] Figure 7A , Figure 7B as well as Figure 7C The operation method of the closed-loop control of the Class H audio amplifier shown is similar to... Figure 3 Similar to a closed-loop controlled Class H audio amplifier.

[0094] However, in these embodiments, the input of the PWM detector 415 is electrically connected to an alternative node in the circuit. For example, in Figure 7B In this configuration, the input terminal of the PWM detector 415 is electrically connected to a node connected to the load inductor (L) 460. Figure 7C In this configuration, the input terminal of the PWM detector 415 is electrically connected to the node located between the resistor Ron and the second switch 440. Figure 7A In one embodiment, the input terminal of the PWM detector 415 is electrically connected to the feedback output terminal of the Class D amplifier, but is not connected between the pre-driver 430 and the first switch 450.

[0095] exist Figure 7A , Figure 7B as well as Figure 7C In one embodiment, the Class D amplifier 425 is formed by a combination of the audio pulse width modulation (PWM) modulator 420 and the pre-driver 430.

[0096] According to some embodiments of this application, an audio amplifier with duty cycle control is provided. The audio amplifier (e.g.) Figure 3 , Figure 7A , Figure 7B or Figure 7C The 400, 400A, 400B, or 440C shown include a pulse width modulator (such as...). Figure 3 , Figure 7A , Figure 7B or Figure 7C The 420 shown), power stage (such as Figure 3 , Figure 7A , Figure 7B or Figure 7C The 440 and 450 shown, or Figure 3 , Figure 7A , Figure 7B or Figure 7C (as shown in 430, 440, and 450) and voltage converters (such as Figure 3 , Figure 7A , Figure 7B or Figure 7C (As shown in 410). The pulse width modulator is configured to receive an input signal to generate a pulse width modulated signal. The power stage is configured to output an output signal based on the supply voltage and the pulse width modulated signal. The voltage converter is configured to adjust the voltage level of the supply voltage based on the pulse width modulated signal. The audio amplifier is configured to adjust the voltage level of the supply voltage when the duty cycle of the pulse width modulated signal is greater than a duty cycle threshold.

[0097] According to other embodiments of this application, an audio amplifier with duty cycle control is provided. The audio amplifier (such as...) Figure 3 , Figure 7A , Figure 7B or Figure 7C The 400, 400A, 400B, or 440C shown include a pulse width modulator (such as...). Figure 3 , Figure 7A , Figure 7B or Figure 7C The 420 shown), power stage (such as Figure 3 , Figure 7A , Figure 7B or Figure 7C The 440 and 450 shown, or Figure 3 , Figure 7A , Figure 7B or Figure 7C (as shown in 430, 440, and 450) and voltage converters (such as Figure 3 , Figure 7A , Figure 7B or Figure 7C(As shown in 410). The pulse width modulator is used to generate a pulse width modulated signal. The power stage is connected to the pulse width modulator. The voltage converter is connected to the power stage and configured to output a supply voltage to the power stage, wherein the voltage converter is configured to adjust the voltage level of the supply voltage according to the duty cycle of the pulse width modulated signal.

[0098] In some embodiments of the audio amplifier, the audio amplifier further includes a pulse width modulation detector (such as...). Figure 3 , Figure 7A , Figure 7B or Figure 7C 415), which is electrically connected between the power stage and the voltage converter, and is used to output an indication signal (such as... Figure 3 , Figure 7A , Figure 7B or Figure 7C The signal A(t) is sent to the voltage 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.

[0099] In some embodiments of the audio amplifier, the pulse width modulation detector is configured to output the indication signal (e.g., based on the pulse width modulation signal (e.g., pwm(t)) and the duty cycle threshold (e.g., Dref)). Figure 3 , Figure 7A , Figure 7B or Figure 7C A(t)), such as Figure 4 As shown.

[0100] In some embodiments of the audio amplifier, the voltage converter is configured to respond to the indication signal (such as...) Figure 3 , Figure 7A , Figure 7B or Figure 7C When the duty cycle of the pulse width modulation signal is greater than the duty cycle threshold, the voltage level of the supply voltage is adjusted.

[0101] 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, such as... Figure 5 As shown.

[0102] In some embodiments of the audio amplifier, a closed loop is formed between the power stage and the voltage converter (e.g. Figure 3 , Figure 7A , Figure 7B or Figure 7C (As shown).

[0103] 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 scope and spirit of the contents disclosed in this application as set forth in the claims.

Claims

1. An audio amplifier with duty cycle control, characterized in that, include: A pulse width modulator is configured to receive an input signal to generate a pulse width modulated signal. The power stage is configured to output a signal based on the supply voltage and the pulse width modulation signal; A voltage converter is configured to adjust the voltage level of the supply voltage according to the pulse width modulation signal; as well as A pulse width modulation detector is electrically connected between the power 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 the duty cycle threshold, and the voltage converter is configured to adjust the voltage level of the supply voltage according to the indication 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 the duty cycle threshold, and the duty cycle of the pulse width modulation signal is limited by the duty cycle threshold.

2. The audio amplifier according to claim 1, characterized in that, The pulse width modulation detector is configured to output the indication signal based on the pulse width modulation signal and the duty cycle threshold.

3. The audio amplifier according to claim 1, characterized in that, 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.

4. The audio amplifier according to claim 1, characterized in that, 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.

5. The audio amplifier according to claim 1, characterized in that, A closed loop is formed between the power stage and the voltage converter.

6. An audio amplifier with duty cycle control, characterized in that, include: A pulse width modulator is used to generate pulse width modulated signals. A power stage, connected to the pulse width modulator; A voltage converter, connected to the power stage, is configured to output a supply voltage to the power stage; as well as A pulse width modulation detector is electrically connected 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; 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, wherein the duty cycle of the pulse width modulation signal is limited by the duty cycle threshold.

7. The audio amplifier according to claim 6, characterized in that, The pulse width modulation detector is configured to output the indication signal based on the pulse width modulation signal and the duty cycle threshold.

8. The audio amplifier according to claim 6, characterized in that, 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.

9. The audio amplifier according to claim 6, characterized in that, 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.

10. The audio amplifier according to claim 6, characterized in that, A closed loop is formed between the power stage and the voltage converter.

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