Wireless cellular telephone with audio codec

1. An audio codec chip comprising a digital-to-analog converter, first, second and third digital duplex audio bus interfaces, and a connection for an analog transducer,

the first, second and third digital duplex audio bus interfaces each enabling the audio codec to be coupled to a respective one of first, second and third further chips via a respective bidirectional digital audio bus or bus section,

and the digital-to-analog converter being connectable to receive a digital audio signal in a path from one of the first to third digital duplex audio bus interfaces, convert the signal to an analog audio signal and output the analog audio signal in a path to said connection.

2. An audio codec chip according to claim 1 in which the first and second digital duplex audio bus interfaces share a common clock pin.

3. An audio codec chip according to claim 1 in which the first and second digital duplex audio bus interfaces have separate clock pins.

4. An audio codec chip according to claim 1 in which there is a digital-only signal path between the first and second digital duplex audio bus interfaces usable to transmit digital audio signals from one of the first and second digital duplex audio bus interfaces to the other without analog processing of the transmitted digital audio signals in the digital-only path.

5. An audio codec chip according to claim 4 in which the digital-only signal path is usable to transmit digital audio signals from one of the first and second digital duplex audio bus interfaces to the other without digital processing of the transmitted digital audio signals in the digital-only path.

6. An audio codec chip according to claim 1 further comprising a digital sample-rate converter arranged to convert the sample rate of digital data received from one of the first, second and third digital duplex audio bus interfaces.

7. An audio codec chip according to claim 1 further comprising a digital signal adder operable to add together a digital audio signal received from the first digital duplex audio bus interface with a digital audio signal received from the second digital duplex audio bus interface to form a combined audio signal,

the audio codec being operable to transmit the combined signal from one of the first, second and third digital duplex audio bus interfaces.

8. An audio codec chip according to claim 7 which is operable to transmit the combined signal from the second digital duplex audio bus interface.

9. An audio codec chip according to claim 7 which is operable to transmit the combined signal from the third digital duplex audio bus interface.

10. An audio codec chip according to claim 7 further comprising a digital multiplier arranged to scale one of the said digital audio signals relative to the other before they are added together by said digital signal adder.

11. An audio codec chip comprising:

a digital-to-analog converter;

first, second and third digital duplex audio bus interfaces for connection to respective first, second and third further chips via a respective bidirectional digital audio bus; and

a connection for an analog transducer,

wherein in use the digital-to-analog converter is connectable to receive a digital audio signal in a path from one of said audio bus interfaces for converting said digital audio signal to an analog audio signal and output the analog audio signal in a path to said connection.

12. An audio codec chip comprising an analog-to-digital converter, first, second and third digital duplex audio bus interfaces, and a connection for an analog transducer,

the first, second and third digital duplex audio bus interfaces each enabling the audio codec to be coupled to a respective one of first, second and third further chips via a respective bidirectional digital audio bus or bus section,

and the analog-to-digital converter being connectable to receive an analog audio signal in a path from said connection, convert the signal to digital form and output the signal in a path to one of the first to third digital duplex audio bus interfaces.

13. An audio codec chip according to claim 12 in which the first and second digital duplex audio bus interfaces share a common clock pin.

14. An audio codec chip according to claim 12 in which the first and second digital duplex audio bus interfaces have separate clock pins.

15. An audio codec chip according to claim 12 in which there is a digital-only signal path between the first and second digital duplex audio bus interfaces usable to transmit digital audio signals from one of the first and second digital duplex audio bus interfaces to the other without analog processing of the transmitted digital audio signals in the digital-only path.

16. An audio codec chip according to claim 15 in which the digital-only signal path is usable to transmit digital audio signals from one of the first and second digital duplex audio bus interfaces to the other without digital processing of the transmitted digital audio signals in the digital-only path.

17. An audio codec chip according to claim 12 further comprising a digital sample-rate converter arranged to convert the sample rate of digital data received from one of the first, second and third digital duplex audio bus interfaces.

18. An audio codec chip according to claim 12 further comprising a digital signal adder operable to add together a digital audio signal received from the first digital duplex audio bus interface with a digital audio signal received from the second digital duplex audio bus interface to form a combined audio signal, the audio codec being operable to transmit the combined signal from one of the first, second and third digital duplex audio bus interfaces.

19. An audio codec chip according to claim 18 which is operable to transmit the combined signal from the second digital duplex audio bus interface.

20. An audio codec chip according to claim 18 which is operable to transmit the combined signal from the third digital duplex audio bus interface.

21. An audio codec chip according to claim 18 further comprising a digital multiplier arranged to scale one of the said digital audio signals relative to the other before they are added together by said digital signal adder.

22. An audio codec chip comprising: an analog-to-digital converter; first, second and third digital duplex audio bus interfaces for connection to respective first, second and third further chips via a respective bidirectional digital audio bus; and a connection for an analog transducer, wherein in use the analog-digital converter is connectable to receive an analog audio signal in a path from said connection for converting said analog audio signal to a digital form and output the converted signal in a path to one of said audio bus interfaces.

23. An audio codec chip comprising:

an analog-to-digital and/or digital-to analog converter;

first, second and third bidirectional digital audio bus interfaces usable to connect the audio codec chip to respective further chips via respective bidirectional digital audio buses or bus sections; and

a connection for an analog transducer,

said converter being connectable for conversion, between analog and digital form, of an audio signal passing between said connection and one of said interfaces.