Digital sample rate conversion

1. An apparatus for sample rate conversion, comprising:

an interpolator configured to interpolate a digital input data stream having a first sample rate using values of an interpolation phase shift control quantity to generate a digital output data stream having a second sample rate;

a computing stage configured to compute values of the interpolation phase shift control quantity; and

an enabling/disabling stage configured to selectively disable the interpolator while keeping the computing stage enabled.

2. The apparatus of claim 1 , wherein the interpolator comprises a Farrow filter.

3. The apparatus of claim 2 , wherein the Farrow filter comprises a third order filter.

4. The apparatus of claim 1 , wherein the interpolator comprises a polyphase filter.

5. The apparatus of claim 1 , wherein the computing stage comprises a phase accumulator.

6. The apparatus of claim 5 , wherein the phase accumulator is clocked at the first sample rate.

7. The apparatus of claim 5 , wherein the computing stage further comprises a modulo stage coupled to an output of the phase accumulator.

8. The apparatus of claim 5 , wherein the computing stage further comprises an overflow stage coupled to an output of the phase accumulator.

9. The apparatus of claim 1 , wherein the computing stage comprises an input for variably setting a quantity representative of the first or second sample rate, or both.

10. A receiver, comprising:

an apparatus for sample rate conversion, comprising:

an interpolator configured to interpolate a digital input data stream having a first sample rate using values of an interpolation phase shift control quantity to generate a digital output data stream having a second sample rate;

a computing stage configured to compute values of the interpolation phase shift control quantity; and

an enabling/disabling stage configured to selectively disable the interpolator while keeping the computing stage enabled.

11. A receiver of claim 10 , further comprising:

a mode determining unit configured to determine whether the receiver is operating in a first receive mode associated with a first data rate of the received data stream or in a second receive mode associated with a second data rate of the received data stream, wherein

the enabling/disabling stage is controlled by the mode determining unit.

12. The receiver of claim 11 , wherein:

the receiver comprises a mobile phone receiver, and

the first mode is a receive mode for signals stipulated in a first mobile communications system standard and the second mode is a receive mode for signals stipulated in a second mobile communications system standard different from the first mobile communications system standard.

13. The receiver of claim 10 , further comprising:

a mode determining unit configured to dictate whether the receiver is operating in a first receive mode associated with an active state of the receiver or in a second receive mode associated with an idle state of the receiver, wherein

the enabling/disabling stage is controlled by the mode determining unit.

14. The receiver of claim 10 , further comprising:

a baseband processing unit having an input, and

a selector configured to feed the input of the baseband processing unit either with the digital output data stream having a second sample rate or the digital input data stream having a first sample rate.

15. A transmitter, comprising:

an apparatus for sample rate conversion, comprising:

an interpolator configured to interpolate a digital input data stream having a first sample rate using values of an interpolation phase shift control quantity to generate a digital output data stream having a second sample rate;

a computing stage configured to compute values of the interpolation phase shift control quantity, and

an enabling/disabling stage configured to selectively disable the interpolator while keeping the computing stage enabled.

16. The transmitter of claim 15 , further comprising:

a mode determining unit configured to dictate whether the transmitter is operating in a first transmit mode associated with a first data rate of the transmitted data stream or in a second transmit mode associated with a second data rate, wherein

the enabling/disabling stage is controlled by the mode determining unit.

17. The transmitter of claim 16 , wherein:

the transmitter is a mobile phone transmitter, and

the first mode is a transmit mode for signals stipulated in a first mobile communications system standard and the second mode is a transmit mode for signals stipulated in a second mobile communications system standard different from the first mobile communications system standard.

18. The transmitter of claim 15 , further comprising:

a mode determining unit configured to dictate whether the receiver is operating in a first transmit mode associated with an active state of the transmitter or in a second transmit mode associated with an idle state of the transmitter, wherein

the enabling/disabling stage is controlled by the mode determining unit.

19. The transmitter of claim 15 , further comprising:

an RF processing unit having an input; and

a selector configured to feed the input of the RF processing unit either with the digital output data stream having a second sample rate or the digital input data stream having a first sample rate.

20. A method for sample rate conversion, comprising:

receiving a digital input data stream having a first sample rate;

computing values of an interpolation phase shift control quantity;

generating a digital output data stream having a second sample rate by interpolating the digital input data stream using the values of the interpolation phase shift control quantity;

disabling the generation of the digital output data stream while continuing to compute updated values of the phase shift control quantity; and

enabling the disabled generation of the digital output data stream using the updated values of the interpolation phase shift control quantity.

21. The method of claim 20 , further comprising de-jittering the digital output data stream.

22. The method of claim 20 , wherein interpolating the digital input data stream comprises filtering the digital input data stream using a Farrow filter.

23. The method of claim 20 , wherein interpolating the digital input data stream comprises filtering the digital input data stream using a polyphase filter.

24. A method for processing an input data stream in a receiver or transmitter, comprising:

receiving a digital input data stream having a first sample rate;

computing values of an interpolation phase shift control quantity;

generating a digital output data stream having a second sample rate by interpolating the digital input data stream using the values of the interpolation phase shift control quantity;

disabling the generation of the digital output data stream while continuing to compute values of phase shift control quantity; and thereafter

enabling the generation of the digital output data stream using the updated values of the interpolation phase shift control quantity.

25. The method of claim 24 , further comprising;

while the generation of the digital output data stream is enabled, feeding the generated digital output data stream having a second sample rate to a baseband processing unit of the receiver; and

while the generation of the digital output data stream is disabled, feeding the digital input data stream having a first sample rate to the baseband processing unit of the receiver.

26. The method of claim 24 , further comprising;

while the generation of the digital output data stream is enabled, feeding the generated digital output data stream having a second sample rate to a RF processing unit of the transmitter; and

while the generation of the digital output data stream is disabled, feeding the digital input data stream having a first sample rate to the RF processing unit of the transmitter.