Speaker driver

1. A speaker driver comprising

an amplifier comprising an amplifier output terminal and an amplifier input terminal, wherein the amplifier is configured to:

receive a test signal at the amplifier input terminal, wherein the test signal comprises a series of a plurality of equivalent test-blocks; and

provide measurement-signalling for a speaker at the amplifier output, the measurement-signalling comprising a series of a plurality of measurement-blocks, wherein each of the measurement-blocks corresponds to the output of the amplifier for one of the plurality of test-blocks;

an output-current-sensor configured to:

measure a current level of the measurement-signalling, and

provide sensed-signalling as an output, wherein the sensed-signalling comprises a plurality of sensed-blocks, wherein each of the plurality of sensed-blocks corresponds to one of the plurality of measurement-blocks of the measurement-signalling; and

a processor configured to either:

combine the plurality of sensed-blocks to provide a time-averaged-block; and determine a frequency-spectrum of the time-averaged-block to provide a time-averaged-frequency-spectrum-block; or

determine a frequency-spectrum of each of the plurality of sensed-blocks to provide a plurality of frequency-spectrum-sensed-blocks; and

combine the plurality of frequency-spectrum-sensed-blocks to provide a time-averaged-frequency-spectrum-block.

2. The speaker driver of claim 1 , wherein the amplifier is a class-D amplifier.

3. The speaker driver of claim 1 , wherein each of the plurality of test-blocks is a portion of a periodic function of time.

4. The speaker driver of claim 3 , wherein each of the plurality of test-blocks consists of an integer number of periods of the periodic function of time.

5. The speaker driver of claim 4 , wherein the integer number is a prime number.

6. The speaker driver of claim 1 , wherein the processor is configured to perform a Fast Fourier Transform in order to determine the frequency-spectrum.

7. The speaker driver of claim 1 , further comprising a signal generator configured to provide the test signal to the amplifier input terminal.

8. The speaker driver of claim 1 , wherein:

the amplifier comprises an amplifier output stage, and wherein the amplifier output stage comprises one or more output-stage-FETS; and

the output-current-sensor comprises a measurement terminal that is selectively connectable to the amplifier output stage, such that the output-current-sensor is configured to measure a current level of current flowing through the output-stage-FET.

9. The speaker driver of claim 8 , wherein the measurement terminal is configured to be connected to the amplifier output stage when an output-stage-FET is conducting, and disconnected from the amplifier output stage when the associated output-stage-FET is not conducting.

10. The speaker driver of claim 1 , wherein the amplifier-output is coupled to a first output terminal and a second output terminal and the amplifier comprises:

a positive voltage terminal and a negative voltage terminal

a first high-side switch coupled between the positive voltage terminal and the first output terminal;

a second high-side switch coupled between the positive voltage terminal and the second output terminal;

a first low-side switch coupled between the negative voltage terminal and the second output terminal; and

a second low-side switch coupled between the negative voltage terminal and the first output terminal;

wherein the first high-side switch, the first low-side switch, the second high-side switch and the second low-side switch are configurable to provide for:

a first conduction pathway between the positive voltage terminal and the negative voltage terminal through the first high-side switch and the first low-side switch; or

a second conduction pathway between the positive voltage terminal and the negative voltage terminal through the second high-side switch and the second low-side switch; and wherein:

when the first conduction pathway is provided for, the output-current-sensor is configured to measure the current flowing between the second-output terminal and the negative voltage terminal; and

when the second conduction pathway is provided for, the output-current-sensor is configured to measure the current flowing between the first-output terminal and the negative voltage terminal.

11. The speaker driver of claim 10 , the first low-side switch comprising a first segmented Field Effect Transistor and the second low-side switch comprising a second segmented Field Effect Transistor, wherein:

when the first conduction pathway is provided for, only a subset of the segments of the first segmented Field Effect Transistor are configured to conduct; and

when the second conduction pathway is provided for, only a subset of the segments of the second segmented Field Effect Transistor are configured to conduct.

12. The speaker driver of claim 1 , further comprising:

a low-pass-filter connected to the amplifier output; and

a selector-switch configured to selectively connect the ADC to either the output-current sensor or the low-pass-filter;

wherein when the low-pass-filter is connected to the ADC, the ADC is configured to provide a digitized-voltage-representation of an ADC-characterising-output-voltage-signal to the processor, and the processor is configured to determine an ADC-distortion-spectrum based on a difference between (i) the digitized-voltage-representation of the ADC-characterising-output-voltage-signal; and (ii) an ADC-characterising-input-signal supplied to the amplifier to generate the ADC-characterising-output-voltage-signal.

13. The speaker driver of claim 12 , wherein the processor is configured to determine the time-averaged-frequency-spectrum-block based on the ADC-distortion-spectrum.

14. An electronic device or an integrated circuit comprising the speaker driver of claim 1 .

15. A method of testing a speaker comprising:

receiving a test signal at an amplifier input terminal of an amplifier, wherein the test signal comprises a series of a plurality of equivalent test-blocks; and

providing measurement-signalling, for a speaker, at an amplifier output of the amplifier, the measurement-signalling comprising a series of a plurality of measurement-blocks, wherein each of the measurement-blocks corresponds to an output of the amplifier for one of the plurality of test-blocks;

measuring a current level of the measurement-signalling in order to provide sensed-signalling, wherein the sensed-signalling comprises a plurality of sensed-blocks, wherein each of the plurality of sensed-blocks corresponds to one of the plurality of measurement-blocks of the measurement-signalling; and either:

combining the plurality of sensed-blocks to provide a time-averaged-block; and

determining a frequency-spectrum of the time-averaged-block to provide a time-averaged-frequency-spectrum-block; or

determining a frequency-spectrum of each of the plurality of sensed-blocks to provide a plurality of frequency-spectrum-sensed-blocks; and

combining the plurality of frequency-spectrum-sensed-blocks to provide a time-averaged-frequency-spectrum-block.