Switching amplifier system and method for suppressing signal distortion thereof
The invention further provides a switching amplifier system. In one embodiment, the switching amplifier system comprises a noise shaper, a corrector, and a pulse width logic. The noise shaper receives a first signal, performs a noise shaping process to process the first signal according to a feedback signal to generate a second signal sliced into a plurality of frames. The corrector adds a plurality of correction pulses respectively to the frames of the second signal to obtain a third signal in such a way that the correction pulse added to the second signal in a target frame selected from the frames has a polarity inverse to that of an original waveform of the second signal in the target frame. The pulse width logic then converts the third signal to a pulse width modulation (PWM) signal.
1. A switching amplifier system, comprising:
a noise shaper, receiving a first signal, performing a noise shaping process to process the first signal according to a feedback signal to generate a second signal sliced into a plurality of frames;
a corrector, adding a plurality of correction pulses respectively to the frames of the second signal to obtain a third signal in such a way that the correction pulse added to the second signal in a target frame selected from the frames has a polarity inverse to that of an original waveform of the second signal in the target frame;
a pulse width logic, converting the third signal from a pulse code modulation (PCM) format to a pulse width modulation (PWM) signal; and
a PWM-to-PCM converter, converting the PWM signal to a fourth signal with the PCM format, and sending the fourth signal back to the noise shaper as the feedback signal.
2. The switching amplifier system as claimed in claim 1 , wherein the corrector adds the correction pulse with a negative polarity to the second signal in the target frame when the original waveform of the second signal in the target frame has a positive polarity, and adds the correction pulse with a positive polarity to the second signal in the target frame when the original waveform of the second signal in the target frame has a negative polarity.
3. The switching amplifier system as claimed in claim 1 , wherein the noise shaper comprises:
a first summation circuit, adding a filtered error signal to the first signal to obtain a fifth signal;
a quantizer, reducing a word length of the fifth signal to obtain the second signal;
a second summation circuit, subtracting the fifth signal from the feedback signal to obtain an error signal; and
an error filter, filtering the error signal to obtain the filtered error signal.
4. The switching amplifier system as claimed in claim 1 , wherein the feedback signal is the third signal.
5. The switching amplifier system as claimed in claim 1 , wherein the switching amplifier system further comprises:
a digital signal processor, processing an input signal to generate the first signal.
6. The switching amplifier system as claimed in claim 1 , wherein the switching amplifier system further comprises:
an H bridge, coupled to a loudspeaker, amplifying the PWM signal to obtain a driving signal, and driving the loudspeaker according to the driving signal.
7. The switching amplifier system as claimed in claim 3 , wherein the transfer functions of the quantizer, the corrector, and the pulse width logic are determined according to the following equation:
∂
Y
∂
E
=
∂
Y
∂
C
=
∂
Y
∂
D
=
(
1
+
H
)
;
wherein Y is the PWM signal, H is the transfer function of the error filter, E is quantization noise E added by the quantizer to the fifth signal, C is correction error added by the corrector to the second signal, and D is distortion added by the pulse width logic to the third signal.
8. A switching amplifier system, comprising:
a digital signal processor, processing an input signal to generate a first signal;
a noise shaper, performing a noise shaping process to process the first signal according to a feedback signal to generate a second signal sliced into a plurality of frames;
a corrector, adding a plurality of correction pulses respectively to the frames of the second signal to obtain a third signal in such a way that the correction pulse added to the second signal in a target frame selected from the frames has a polarity inverse to that of an original waveform of the second signal in the target frame;
a pulse width logic, converting the third signal from a pulse code modulation (PCM) format to a pulse width modulation (PWM) signal;
an H bridge, coupled to a loudspeaker, amplifying the PWM signal to obtain a driving signal, and driving the loudspeaker according to the driving signal; and,
a PWM-to-PCM converter, converting the PWM signal to a fourth signal with the PCM format, and sending the fourth signal back to the noise shaper as the feedback signal.
9. The switching amplifier system as claimed in claim 8 , wherein the corrector adds the correction pulse with a negative polarity to the second signal in the target frame when the original waveform of the second signal in the target frame has a positive polarity, and adds the correction pulse with a positive polarity to the second signal in the target frame when the original waveform of the second signal in the target frame has a negative polarity.
10. The switching amplifier system as claimed in claim 8 , wherein the noise shaper comprises:
a first summation circuit, adding a filtered error signal to the first signal to obtain a fifth signal;
a quantizer, reducing a word length of the fifth signal to obtain the second signal;
a second summation circuit, subtracting the fifth signal from the feedback signal to obtain an error signal; and
an error filter, filtering the error signal to obtain the filtered error signal.
11. The switching amplifier system as claimed in claim 8 , wherein the feedback signal is the third signal.
12. The switching amplifier system as claimed in claim 10 , wherein the transfer functions of the quantizer, the corrector, and the pulse width logic are determined according to the following equation:
∂
Y
∂
E
=
∂
Y
∂
C
=
∂
Y
∂
D
=
(
1
+
H
)
;
wherein Y is the PWM signal, H is the transfer function of the error filter, E is quantization noise E added by the quantizer to the fifth signal, C is correction error added by the corrector to the second signal, and D is distortion added by the pulse width logic to the third signal.