Low distortion switching amplifier circuits and methods
View Patent ↗Embodiments of the present invention include switching amplifier circuits and methods. In one embodiment, the present invention includes a low distortion method of driving a switching amplifier comprising modulating an audio input signal to produce a half-wave rectified pulse-width modulated signal and a complementary half-wave rectified pulse-width modulated signal. These signals may be amplified in a power amplifier and combined in a feedback circuit to generate a first feedback signal and a second feedback signal, which may be coupled the inputs of a modulator for controlling the output signal.
1. A method of controlling the output of a modulation circuit comprising:
modulating an audio input signal to produce a half-wave rectified pulse-width modulated signal and a complementary half-wave rectified pulse-width modulated signal;
amplifying the half-wave rectified pulse-width modulated signal to produce an amplified half-wave rectified pulse-width modulated signal;
amplifying the complementary half-wave rectified pulse-width modulated signal to produce an amplified complementary half-wave rectified pulse-width modulated signal;
combining the amplified half-wave rectified pulse-width modulated signal with an inverse of the amplified complementary half-wave rectified pulse-width modulated signal to generate a first feedback signal, and combining the amplified complementary half-wave rectified pulse-width modulated signal with an inverse of the amplified half-wave rectified pulse-width modulated signal to generate a second feedback signal;
coupling the first feedback signal to a first input of the modulator and coupling the second feedback signal to a second input of the modulator.
2. The method of claim 1 wherein the inverse of the amplified half-wave rectified pulse-width modulated signal is generated by inverting the half-wave rectified pulse-width modulated signal and the inverse of the amplified complimentary half-wave rectified pulse-width modulated signal is generated by inverting the complimentary half-wave rectified pulse-width modulated signal.
3. The method of claim 1 wherein the inverse of the amplified half-wave rectified pulse-width modulated signal is generated by inverting the amplified half-wave rectified pulse-width modulated signal and the inverse of the amplified complimentary half-wave rectified pulse-width modulated signal is generated by inverting the amplified complimentary half-wave rectified pulse-width modulated signal.
4. The method of claim 1 further comprising:
coupling the amplified half-wave rectified pulse-width modulated signal, through a first integrated circuit package terminal, to a first terminal of a speaker; and
coupling the amplified complementary half-wave rectified pulse-width modulated signal, through a second integrated circuit package terminal, to a second terminal of a speaker.
5. The method of claim 1 wherein the audio input signal is a differential signal.
6. An electronic circuit comprising:
a modulator having a first input for receiving an audio signal, a second input for receiving an audio signal, a first output for providing a half-wave rectified pulse-width modulated signal, and a second output for providing a complementary half-wave rectified pulse-width modulated signal;
a first amplifier having a first input coupled to the first output of the modulator and a first output for providing an amplified half-wave rectified pulse-width modulated signal;
a second amplifier having a first input coupled to the second output of the modulator and a first output for providing an amplified complementary half-wave rectified pulse-width modulated signal; and
a feedback circuit having at least one input coupled to the first output of the first amplifier and at least one other input coupled to the first output of the second amplifier, the feedback circuit combining the amplified half-wave rectified pulse-width modulated signal with an inverse of the amplified complementary half-wave rectified pulse-width modulated signal to generate a first feedback signal on a first output, and combining the amplified complementary half-wave rectified pulse-width modulated signal to with an inverse of the amplified half-wave rectified pulse-width modulated signal to generate a second feedback signal on a second output.
7. The circuit of claim 6 wherein the feedback circuit comprises:
a first resistor having a first terminal coupled to an intermediate node within the first amplifier which provides the inverse of the amplified half-wave rectified pulse-width modulated signal and having a second terminal coupled to the second input of the modulator;
a second resistor having a first terminal coupled to the first output of the second amplifier which provides the amplified complimentary half-wave rectified pulse-width modulated signal and having a second terminal coupled to the second input of the modulator;
a third resistor having a first terminal coupled to an intermediate node within the second amplifier which provides the inverse of the amplified complementary half-wave rectified pulse-width modulated signal and having a second terminal coupled to the first input of the modulator; and
a fourth resistor having a first terminal coupled to the first output of the first amplifier which provides the amplified half-wave rectified pulse-width modulated signal and having a second terminal coupled to the first input of the modulator.
8. The circuit of claim 6 wherein the feedback circuit comprises:
a first inverter having an input terminal coupled to the first output of the first amplifier which provides the amplified half-wave rectified pulse-width modulated signal and having an output terminal which provides the inverse of the amplified half-wave rectified pulse-width modulated signal;
a second inverter having an input terminal coupled to the first output of the second amplifier which provides the amplified complimentary half-wave rectified pulse-width modulated signal and having an output terminal which provides the inverse of the amplified complimentary half-wave rectified pulse-width modulated signal;
a first resistor having a first terminal coupled to the output of a first inverter and having the second terminal coupled to the second input of the modulator;
a second resistor having a first terminal coupled to the first output of the second amplifier and having the second terminal coupled to the second input of the modulator;
a third resistor having a first terminal coupled to the output of the second inverter and having the second terminal coupled to the first input of the modulator; and
a fourth resistor having a first terminal coupled to the first output of the first amplifier and having the second terminal is coupled to the first input of the modulator.
9. The circuit of claim 6 wherein the feedback circuit comprises:
a first current inverter having an input terminal and an output terminal;
a second current inverter having an input terminal and an output terminal;
a first resistor network having a first terminal coupled to the first output of the first amplifier which provides the amplified half-wave rectified pulse-width modulated signal and having a second terminal coupled to the input terminal of the first current inverter;
a second resistor network having a first terminal coupled to the first output of the second amplifier which provides the amplified complementary half-wave rectified pulse-width modulated signal and having a second terminal coupled to the second input of the modulator and to the output terminal of the first current inverter;
a third resistor network having a first terminal coupled to the first output of the second amplifier which provides the amplified complementary half-wave rectified pulse-width modulated signal and having a second terminal coupled to the input terminal of the second current inverter; and
a fourth resistor network having a first terminal coupled to the first output of the first amplifier which provides the amplified complementary half-wave rectified pulse width modulated signal and having a second terminal coupled to the first input of the modulator and to the output terminal of the second current inverter.
10. The circuit of claim 9 wherein the first resistor network comprises:
a first resistor having a first terminal coupled to the first output of the first amplifier which provides the amplified half-wave rectified pulse-width modulated signal and having a second terminal;
a second resistor having a first terminal coupled to the second terminal of the first resistor and having the second terminal coupled to a first reference voltage; and
a third resistor having a first terminal coupled to the first terminal of the second resistor and the second terminal of the first resistor and having a second terminal coupled to the input terminal of the first current inverter.
11. The circuit of claim 9 wherein the second resistor network comprises:
a first resistor having a first terminal coupled to the first output of the second amplifier which provides the amplified complimentary half-wave rectified pulse-width modulated signal and having a second terminal coupled to the second input of the modulator; and
a second resistor having a first terminal coupled to the second terminal of the first resistor and to the second input of the modulator, and having a second terminal coupled to a first reference voltage.
12. The circuit of claim 9 wherein the third resistor network comprises:
a first resistor having a first terminal coupled to the first output of the second amplifier which provides the amplified complementary half-wave rectified pulse-width modulated signal and having a second terminal;
a second resistor having a first terminal coupled to the second terminal of the first resistor and having a second terminal coupled to a first reference voltage; and
a third resistor having a first terminal coupled to the first terminal of the second resistor and the second terminal of the first resistor and having a second terminal coupled to the input of the second current inverter.
13. The circuit of claim 9 wherein the fourth resistor network comprises:
a first resistor having a first terminal coupled to the first output of the first amplifier which provides the amplified half-wave rectified pulse-width modulated signal and having a second terminal coupled to the first input of the modulator; and
a second resistor having a first terminal coupled to the second terminal of the first resistor and to the first input of the modulator and having a second terminal coupled to a first reference voltage.
14. The circuit of claim 9 wherein the first current inverter comprises:
a first transistor having a first terminal coupled to the second terminal of the first resistor network and having a control terminal coupled to the second terminal of the first resistor network, and having a second terminal coupled to ground;
a second transistor having a first terminal, having a control terminal coupled to the control terminal of the first transistor, and having a second terminal coupled to ground; and
a first resistor having a first terminal coupled to the first terminal of the second transistor and having a second terminal coupled to the second input of the modulator.
15. The circuit of claim 9 wherein the second current inverter comprises:
a first transistor having a first terminal coupled to the second terminal of the third resistor network and having a control terminal coupled to the second terminal of the third resistor network, and having a second terminal coupled to ground; and
a second transistor having a first terminal, having a control terminal coupled to the control terminal of the first transistor, and having a second terminal coupled to ground; and
a first resistor having a first terminal coupled to the first terminal of the second transistor and having a second terminal coupled to the first input of the modulator.
16. The circuit of claim 6 wherein the first output terminal is coupled to a first integrated circuit package terminal and the second output terminal is coupled to a second integrated circuit package terminal.