Class D switching amplifier and method of controlling a loudspeaker

1. A switching amplifier comprising:

a half-bridge first PWM modulator;

a half-bridge second PWM modulator;

at least one amplifier stage configured to receive input signals;

a PWM control stage coupled to the at least one amplifier stage and configured to control switching of the half-bridge first PWM modulator and of the half-bridge second PWM modulator as a function of the input signals by respective first PWM control signals and second PWM control signals;

a first output filter coupled to the half-bridge first PWM modulator;

a second output filter coupled to the half-bridge second PWM modulator;

an inner control loop coupled to outputs of the half-bridge first PWM modulator and of the half-bridge second PWM modulator and configured to pick up respective feedback signals at the outputs, upstream of the first output filter and of the second output filter, respectively; and

an outer control loop configured to pick up respective feedback signals downstream of the first output filter and of the second output filter;

the at least one amplifier stage and the PWM control stage each have a fully differential structure.

2. The switching amplifier according to claim 1 , wherein the inner and outer control loops define a common-mode feedback-control network configured to maintain a common-mode voltage of the PWM control stage constant.

3. The switching amplifier according to claim 2 , further comprising a first output terminal, and a second output terminal, wherein the PWM control stage has a first differential output coupled to the half-bridge first PWM modulator and configured to supply the first PWM control signals, and a second differential output coupled to the half-bridge second PWM modulator and configured to supply the second PWM control signals.

4. The switching amplifier according to claim 3 , wherein the inner control loop has a respective first branch between the first differential output of the half-bridge first PWM modulator and the PWM control stage, and a respective second branch between the second differential output of the half-bridge second PWM modulator and the PWM control stage.

5. The switching amplifier according to claim 4 , wherein the outer control loop has a respective first branch between the first output filter and the PWM control stage, and a respective second branch between the second output filter and the PWM control stage.

6. The switching amplifier according to claim 5 , wherein the common-mode feedback-control network comprises a clipping control loop configured to pick up respective feedback signals upstream of the half-bridge first PWM modulator and of the half-bridge second PWM modulator.

7. The switching amplifier according to claim 6 , wherein the clipping control loop has a respective first branch between the first differential output and a common-mode control terminal of the PWM control stage, and a respective second branch between the second differential output and the common-mode control terminal of the PWM control stage.

8. The switching amplifier according to claim 6 , further comprising a clipping-detector stage configured to detect conditions of clipping of at least one between the half-bridge first PWM modulator and the half-bridge second PWM modulator, and a selective-enabling stage configured to alternatively enable and disable the clipping control loop as a function of a response of the clipping-detector stage.

9. The switching amplifier according to claim 8 , wherein the selective-enabling stage configured to enable the clipping control loop when at least one between the half-bridge first PWM modulator and the half-bridge second PWM modulator is in clipping conditions and disabling the clipping control loop otherwise.

10. The switching amplifier according to claim 9 , wherein the half-bridge first PWM modulator and the half-bridge second PWM modulator are controlled as a function of a first reference signal and a second reference signal, which have a switching frequency, and comprising a low-pass filter configured to suppress oscillations on the switching frequency fed back from the common-mode feedback-control network to the PWM control stage.

11. The switching amplifier according to claim 10 , wherein the PWM control stage comprises a first control amplifier and a second control amplifier of the single-terminal type, coupled symmetrically between differential inputs and the first and second differential outputs of the PWM control stage to define the fully differential structure and the low-pass filter has an output coupled to respective inputs of the first control amplifier and of the second control amplifier.

12. The switching amplifier according to claim 1 , wherein the at least one amplifier stage has a positive output and a negative output, respectively, connected to a positive input and to a negative input of the PWM control stage.

13. The switching amplifier according to claim 1 , wherein the at least one amplifier stage further comprises a plurality of cascaded amplifier stages, wherein each amplifier stage comprises a positive output and a negative output, respectively, coupled to a positive input and a negative input of an adjacent amplifier stage of the plurality of cascaded amplifier stages.

14. The switching amplifier according to claim 13 , wherein the inner and outer control loops define a differential feedback-control network that defines a nested-loop feedback structure with the plurality of cascaded amplifier stages and the PWM control stage.

15. An electronic device comprising:

a signal source;

a loudspeaker; and

a switching amplifier coupled between the signal source and the loudspeaker, the switching amplifier comprising:

a half-bridge first PWM modulator;

a half-bridge second PWM modulator;

at least one amplifier stage configured to receive input signals;

a PWM control stage coupled to the at least one amplifier stage and configured to control switching of the half-bridge first PWM modulator and of the half-bridge second PWM modulator as a function of the input signals by respective first PWM control signals and second PWM control signals;

a first output filter coupled to the half-bridge first PWM modulator;

a second output filter coupled to the half-bridge second PWM modulator;

an inner control loop coupled to outputs of the half-bridge first PWM modulator and of the half-bridge second PWM modulator and configured to pick up respective feedback signals at the outputs, upstream of the first output filter and of the second output filter, respectively; and

an outer control loop configured to pick up respective feedback signals downstream of the first output filter and of the second output filter;

the at least one amplifier stage and the PWM control stage each have a fully differential structure.

16. The electronic device according to claim 15 , wherein the inner and outer control loops define a common-mode feedback-control network configured to maintain a common-mode voltage of the PWM control stage constant.

17. The electronic device according to claim 16 , further comprising a first output terminal, and a second output terminal, wherein the PWM control stage has a first differential output coupled to the half-bridge first PWM modulator and configured to supply the first PWM control signals, and a second differential output coupled to the half-bridge second PWM modulator and configured to supply the second PWM control signals.

18. A method of controlling a loudspeaker, comprising:

generating first PWM control signals and second PWM control signals by a switching amplifier as a function of input signals;

processing the input signals by at least one amplifier stage and one PWM control stage with a fully differential structure;

controlling switching of a first half-bridge PWM modulator and of a second half-bridge PWM modulator by the first PWM control signals and the second PWM control signals, respectively;

picking up respective feedback signals at outputs of the half-bridge first PWM modulator and of the half-bridge second PWM modulator, upstream of a first output filter coupled to the half-bridge first PWM modulator and of a second output filter coupled to the half-bridge second PWM modulator; and

picking up respective feedback signals downstream of the first output filter and of the second output filter.

19. The method according to claim 18 , further comprising controlling a common-mode voltage of the PWM control stage.

20. The method according to claim 18 , further comprising:

annulling one of the input signals;

carrying out a common-mode control on the PWM control stage through a first output or a second output of a switching amplifier, and through one of a first output and a second output of the amplifier stage; and

detecting a current supplied to a load present between the first output and the second output of the switching amplifier.