Digital amplifier

1. A digital amplifier comprising:

a first modulation stage arranged to receive a digital data signal and to generate a corresponding modulated reference signal;

a comparator arranged to receive a feedback signal and the modulated reference signal and generate a corresponding error signal indicative of a difference between the modulated reference signal and the feedback signal;

an integration stage arranged to integrate the error signal from the comparator to generate an integrated digital error signal;

a summer arranged to receive the integrated digital error signal and the digital data signal and generate an adjusted digital data signal indicative of their sum;

an output stage comprising a second modulation stage, the output stage being arranged to receive the adjusted digital data signal and to generate a corresponding modulated output signal for driving a load; and

a feedback circuit arranged to provide said feedback signal to the comparator, the feedback signal being indicative of the modulated output signal.

2. A digital amplifier according to claim 1 , wherein the integration stage comprises at least three integrators arranged to provide at least third order integration of the error signal.

3. A digital amplifier according to claim 1 , wherein the second modulation stage operates at a switching frequency within the range 0 Hz-4 MHz.

4. A digital amplifier according to claim 1 , further comprising a digital noise shaper adapted to receive a digital input signal and to noise-shape said digital input signal and provide the noise-shaped signal to the first modulation stage as said digital data signal.

5. A digital amplifier according to claim 1 , wherein the first modulation stage comprises a pulse width modulator and the modulated reference signal is a pulse width modulated signal.

6. A digital amplifier according to claim 1 , wherein the second modulation stage comprises a pulse width modulator and the modulated output signal is a pulse width modulated signal.

7. A digital amplifier according to claim 1 , wherein the first modulation stage comprises a modulator, arranged to receive the digital data signal, and an inverter arranged to invert the modulator output.

8. A digital amplifier according to claim 1 , wherein said second modulation stage is arranged to generate a modulated control signal corresponding to the adjusted digital data signal, and the output stage further comprises a switching circuit arranged so as to be controlled by the modulated control signal.

9. A digital amplifier according to claim 1 , wherein said modulated output signal is a modulated output voltage for application to one side of a load.

10. A digital amplifier according to claim 1 , wherein the integration stage comprises a first analogue integrator arranged to integrate the error signal, an analogue to digital converter (ADC) arranged to convert an analogue output of the first analogue integrator to a digital signal, and two digital integrators arranged in series to integrate the digital signal from the ADC.

11. A digital amplifier according to claim 1 , wherein the integration stage comprises at least three digital integrators.

12. A digital amplifier according to claim 1 , wherein the integration stage comprises at least one analogue integrator, an analogue to digital converter, and at least one digital integrator.

13. A digital amplifier according to claim 12 , wherein the integration stage comprises at least two digital integrators.

14. A digital amplifier according to claim 10 , wherein the analogue to digital converter provides at least 10 bit resolution.

15. A digital amplifier according to claim 14 , wherein the analogue to digital converter provides at least 14 bit resolution.

16. A digital amplifier according to claim 1 , wherein the modulated output signal is a modulated voltage, and the feedback circuit comprises a voltage divider, arranged such that the feedback signal is a voltage signal proportional to said output voltage.

17. A digital amplifier according to claim 1 , wherein the modulated output signal is a modulated output voltage for application to one side of a load, the amplifier further comprising:

an inverter arranged to invert the digital data signal

a third modulation stage arranged to receive the inverted digital data signal and to generate a corresponding second modulated reference signal;

a second comparator arranged to receive a second feedback signal and the second modulated reference signal and generate a corresponding second error signal indicative of a difference between the second modulated reference signal and the second feedback signal;

a second integration stage arranged to integrate the second error signal from the second comparator to generate a second integrated digital error signal;

a second summer arranged to receive the second integrated digital error signal and the inverted digital data signal and generate a second adjusted digital data signal indicative of their sum;

a second output stage comprising a fourth modulation stage, the second output stage being arranged to receive the second adjusted digital data signal and to generate a corresponding second modulated output signal for driving a load; and

a second feedback circuit arranged to provide said second feedback signal to the second comparator, wherein the second modulated output signal is a second modulated voltage for application to a second side of the load, and the second feedback signal is indicative of the second modulated voltage.

18. A digital amplifier according to claim 17 , wherein the first and second output stages comprise an H-bridge circuit for driving an output load.