Methods and apparatus for a class-D amplifier
Various embodiments of the present technology comprise a method and apparatus for a class-D amplifier. In various embodiments, the class-D amplifier operates to control an output signal during a start-up state to suppress a pop noise (start-up noise) without the need for a mute switch. The class-D amplifier may utilize a transition signal during the start-up state to prime or otherwise stabilize the output signal to suppress the pop noise.
1. An amplifier circuit configured to receive an input signal, comprising:
an interpolator circuit configured to receive the input signal;
a noise-shaper circuit connected in series with the interpolator;
a pulse-width modulation (PWM) generator circuit connected in series with the noise shaper; and
a driver circuit connected in series with the pulse-width modulation generator circuit and configured to receive:
an output signal of the PWM generator circuit at a first input terminal; and
a control signal at a second input terminal, wherein the control signal controls an output impedance of the driver circuit.
2. The amplifier circuit according to claim 1 , wherein the noise-shaper circuit comprises a delta sigma modulator.
3. The amplifier circuit according to claim 1 , wherein the PWM generator generates an output signal having a varying duty cycle and a varying amplitude.
4. The amplifier circuit according to claim 3 , wherein the input signal controls the duty cycle of the output signal.
5. The amplifier circuit according to claim 4 , wherein the duty cycle increases gradually from a starting percentage up to fifty percent as the input signal increases.
6. The amplifier circuit according to claim 1 , wherein a starting value of the input signal is less than zero.
7. The amplifier circuit according to claim 1 , wherein increasing the control signal increases a drive capability of the driver circuit.
8. The amplifier circuit according to claim 1 , wherein, when the output impedance of the driver reaches a predetermined value, the input signal is increased to zero.
9. The amplifier circuit according to claim 1 , further comprising a low pass filter connected to an output terminal of the driver circuit and comprises an inductor connected to a capacitor.
10. A method for suppressing noise in an audio system, comprising:
generating a transition signal;
controlling a duty cycle of an output signal of a PWM generator circuit according to the transition signal;
controlling an output impedance of a driver circuit according to a control signal; and
increasing the transition signal from a minimum value to a zero value after the output impedance reaches a predetermined value.
11. The method according to claim 10 , wherein:
as the transition signal increases, the duty cycle of the output signal increases; and
as the control signal increases, the output impedance decreases.
12. The method according to claim 10 , wherein the duty cycle increases gradually from a starting percentage up to 50%.
13. The method according to claim 10 , wherein an output voltage of the audio system is substantially constant during a first period when the control signal is increasing and a second period when the transition signal is increasing.
14. An audio system configured to generate audio input signal and a transition input signal, comprising:
a class-D amplifier circuit comprising:
a selector circuit configured to selectively transmit one of the audio signal and the transition signal to an input terminal of an interpolator circuit;
a noise-shaper circuit connected to an output terminal of the interpolator;
a pulse-width modulation (PWM) generator circuit connected to an output terminal of the noise-shaper circuit, wherein the PWM generator circuit generates a first output signal having a variable duty cycle controlled according to the transition input signal; and
a driver circuit connected to an output terminal of the pulse-width modulation generator circuit and configured to generate a second output signal according to:
the first output signal; and
a control signal; and
a speaker connected to the class-D amplifier circuit, wherein the class-D amplifier circuit transmits a substantially constant third output voltage to the speaker during a start-up state.
15. The audio system according to claim 14 , wherein the noise-shaper circuit comprises a delta sigma modulator.
16. The audio system according to claim 14 , wherein, during the start-up state, the transition input signal is set to a minimum value less than zero, and the control signal increases.
17. The audio system according to claim 14 , wherein the control signal controls an output impedance of the driver circuit.
18. The audio system according to claim 17 , wherein, when an output impedance of the driver circuit reaches a predetermined value, the transition input signal is increased to zero.
19. The audio system according to claim 14 , wherein:
the duty cycle of the first output signal increases gradually from a starting percentage up to 50% as the input signal increases; and
an amplitude of the first output signal increases as the duty cycle increases.