Mobile device

1. A method of operation of a mobile device

having a first mode of operation and a further mode of operation,

the mobile device comprising a loudspeaker,

wherein the loudspeaker is configured to generate an electrical signal in response to an acoustic stimulus received from a non-stationary sound source;

the method comprising:

in the first mode of operation

detecting the electrical signal generated by the loudspeaker in response to the acoustic stimulus,

generating an activation signal in response to the detected electrical signal,

enabling the further mode of operation in response to the activation signal.

2. The method of claim 1

wherein the mobile device comprises a system processor and

wherein enabling the further mode of operation comprises activating the system processor in response to the activation signal.

3. The method of claim 1

wherein the mobile device comprises a digital signal processor and

wherein enabling the further mode of operation comprises activating the digital processor in response to the activation signal.

4. The method of claim 1

wherein the mobile device further comprises a microphone and

wherein enabling the further mode of operation comprises enabling the microphone in response to the activation signal.

5. The method of claim 4

wherein enabling the further mode of operation comprises detecting an electrical signal generated by the microphone in response to a further acoustic stimulus.

6. The method of claim 1

wherein the first mode of operation has a lower power consumption than the further mode of operation.

7. The method of claim 1

wherein the first mode of operation is a standby mode and

wherein the power consumption of the standby mode is less than 1 mW.

8. A method of voice activation of a mobile device comprising the method of claim 1 .

9. The method of claim 1 :

wherein the non-stationary sound source is voice activity.

10. A mobile device having a first mode of operation and a further mode of operation, the mobile device comprising:

a loudspeaker configured to generate an electrical signal in response to an acoustic input signal received from a non-stationary sound source;

a controller having an input coupled to the loudspeaker;

wherein the controller is operable in a first mode of operation

to detect the electrical signal generated by the loudspeaker in response to the acoustic input signal, and

to generate an activation signal in response to the detected electrical signal; and

wherein the mobile device is operable to enable the further mode of operation in response to the activation signal.

11. The mobile device of claim 10 further comprising

an audio amplifier switchably coupled to the loudspeaker and

wherein the controller is switchably coupled to the loudspeaker,

wherein the controller is coupled to the loudspeaker in the first mode of operation and the audio amplifier is coupled to the loud speaker in the further mode of operation.

12. The mobile device of claim 11 further comprising

a codec coupled to the microphone and the controller and

wherein the controller is operable to enable the codec in response to the activation signal and

wherein the codec is operable to generate a further activation signal in response to the activation signal.

13. The mobile device of claim 10

wherein the controller further comprises a first level detector having a first response time and a second level detector having a second different response time;

wherein

inputs of the first level detector and the second level detector are coupled to the loudspeaker in the first mode of operation,

respective outputs of the first level detector and the second level detector are coupled to respective inputs of a comparator,

the comparator output is coupled to an output of the controller.

14. The mobile device of claim 10 further comprising

a microphone switchably coupled to a power supply and

wherein the controller is configured to enable the microphone in response to the activation signal.

15. The mobile device of any of claim 10 further comprising

a system processor and

wherein the controller is operable to enable the system processor in response to the further activation signal.

16. The mobile device of claim 10 comprising at least one of a mobile phone, a laptop computer, and a tablet computer.

17. The mobile device of claim 10 :

wherein the non-stationary sound source is voice activity.