D-class audio power amplifier and method thereof
A D-class audio power amplifier including a microprocessor, a power amplifier, and a low pass filter is provided. The microprocessor is used to sample an input audio signal and output a pulse width modulation (PWM) clock signal. The power amplifier is used to amplify the power of the PWM clock signal and output a power-amplified signal. The low-pass filter is used to filter the high-frequency signal portion off the power-amplified signal and output an output audio signal. The method includes sampling the input audio signal to obtain a number of digital sampling values; obtaining corresponding duty cycles according to the digital sampling values and a reference voltage level and generating the PWM clock signal accordingly; power-amplifying the PWM clock signal to obtain the power-amplified signal; and filtering the high-frequency signal portion off the power-amplified signal to obtain the output audio signal.
1. A D-class audio power amplifier, for amplifying an input audio signal and outputting an output audio signal, comprising:
a micro-processor, including
an analog/digital converter for sampling the input audio signal and outputting a plurality of digital sampling values, and
a calculating unit for calculating a plurality of corresponding duty cycles according to calculation of the digital sampling values and a reference voltage level and outputting a pulse width modulation (PWM) clock signal accordingly;
a power amplifier for power-amplifying the PWM clock signal to obtain a power-amplified signal;
a low-pass filter for filtering out a high-frequency signal portion of the power-amplified signal and outputting the output audio signal; and
wherein the calculating unit calculates the corresponding duty cycles according to the absolute difference between the digital sampling values and the reference voltage level.
2. The D-class audio power amplifier according to claim 1 , wherein the calculating unit determines the level of the PWM clock signal by comparing the digital sampling values and the reference voltage level.
3. The D-class audio power amplifier according to claim 1 , wherein the micro-processor pre-sets a parameter reference table via firmware and the parameter reference table comprises a column of sampling comparison values and a column of corresponding duty cycles.
4. The D-class audio power amplifier according to claim 3 , wherein the calculating unit calculates the absolute differences between the digital sampling values and the reference voltage level and obtain appropriate corresponding duty cycles with reference to the column of sampling comparison values of the parameter reference table.
5. The D-class audio power amplifier according to claim 1 , wherein the D-class audio power amplifier is adapted for use in an LCD device, while the micro-processor is a power-saving CPU operated when the LCD device is in a power-saving mode.
6. The D-class audio power amplifier according to claim 5 , wherein the power amplifier has a first operating voltage and a second operating voltage, provided by system voltages of the LCD device.
7. The D-class audio power amplifier according to claim 5 , wherein the LCD device is an LCD TV, while the power-saving CPU is an 8051 processor.
8. The D-class audio power amplifier according to claim 1 , wherein the sampling frequency of the analog/digital converter is larger than 100 kHz.
9. A method of power-amplifying a D-class audio signal, for amplifying an input audio signal to obtain an output audio signal, the method comprising:
sampling the input audio signal to obtain a plurality of digital sampling values;
calculating a plurality of corresponding duty cycles according to the digital sampling values and a reference voltage level and accordingly generating a PWM clock signal;
power-amplifying the PWM clock signal to obtain a power-amplified signal;
filtering out the high-frequency signal portion of the power-amplified signal to obtain the output audio signal; and
wherein the step of generating the PWM clock signal comprises:
obtaining the corresponding duty cycle values according to the absolute differences between the digital sampling values and the reference voltage level; and
determining the level of the PWM clock signal by comparing the digital sampling values and the reference voltage level.
10. The method according to claim 9 , using an analog/digital converter to sample the input audio signal.
11. The method according to claim 9 , pre-setting a parameter reference table via firmware, wherein the parameter reference table comprises a column of sampling comparison values and a column of corresponding duty cycles.
12. The method according to claim 11 , wherein the step of obtaining the corresponding duty cycles comprises calculating the absolute differences between the digital sampling values and the reference voltage level and obtaining appropriate corresponding duty cycles with reference to the column of sampling comparison values of the parameter reference table.
13. The method according to claim 9 , wherein the frequency of sampling the input audio signal is larger than 100 kHz.