Interpolator

1. A signal interpolator comprising:

a fractional interpolator; and

a numeric controlled oscillator for generating a control signal for controlling said fractional interpolator, said numeric controlled oscillator comprising:

a register for holding a count value;

a modulo-M device for applying a modulo-M function to said count value stored in said register, and generating said control signal therefrom; and

an adder for adding an increment value to said control signal from said modulo-M device, for updating said count value in said register.

2. The signal interpolator according to claim 1 , wherein said adder is configured to add a value STEP to said signal from said modulo-M device, said value STEP being an integer greater than zero.

3. The signal interpolator according to claim 1 , wherein said modulo-M device comprises an overflow signal generator configured to generate an overflow signal when said count value inputted to said modulo-M device overflows said modulo-M function.

4. The signal interpolator according to claim 1 , wherein a value M of said modulo-M device is an integer other than an integer power of two.

5. The signal interpolator according to claim 4 , wherein said value M is an odd number.

6. The signal interpolator according to claim 1 , wherein said signal interpolator is implemented in digital form in an integrated circuit.

7. A digital signal interpolator for converting a first signal comprising digital samples synchronised to a first clock frequency, to a second signal synchronised to a second clock frequency, said signal interpolator comprising:

a fractional interpolator for receiving said digital samples of said first signal synchronised to said first clock frequency; and

a numeric controlled oscillator for generating a control signal for controlling said fractional interpolator, said numeric controlled oscillator comprising:

a modulo-M counter driven by a counter clock frequency being one of said first and said second clock frequencies, said modulo-M counter being configured to (i) repeatedly count through a sequence of count values in a count range of modulus M, where the value M is an integer other than a power of 2, and (ii) generate a modulo-M signal as said control signal for controlling said fractional interpolator.

8. The digital signal interpolator according to claim 7 , wherein the numeric controlled oscillator further comprises:

a period signal generator configured to generate a period signal each time said count value overflows said value M periodically, said period signal being synchronised to one of said first and said second clock frequencies other than said counter clock frequency.

9. The digital signal interpolator according to claim 7 , wherein said counter clock frequency for said modulo-M counter is said first clock frequency to which said first signal is synchronised.

10. The digital signal interpolator according to claim 9 , wherein said numeric controlled oscillator further comprises:

a period signal generator configured to generate a period signal each time said count value overflows said value M periodically, said period signal being synchronised to said second clock frequency.

11. The digital signal interpolator according to claim 7 , wherein said counter clock frequency for said modulo-M counter is said second clock frequency.

12. The digital signal interpolator according to claim 11 , wherein said numeric controlled oscillator further comprises:

a period signal generator configured to generate a period signal each time said count value overflows said value M periodically, said period signal being synchronised to said first clock frequency.

13. The digital signal interpolator according to claim 7 , wherein said modulo-M counter comprises:

a register for holding a count value;

a modulo-M device for applying a modulo-M function to said count value stored in said register; and

an adder for adding an increment value to an output from said modulo-M device, for updating said count value in said register.

14. The digital signal interpolator according to claim 13 , wherein said increment value is a value greater than zero.

15. The digital signal interpolator according to claim 7 , wherein one of said first and said second frequencies is k×13 MHz, where k is an integer between 1 and 10 inclusive.

16. The digital signal interpolator according to claim 7 , wherein one of said first and said second clock frequencies is n×10.24 MHz, where n is an integer between 1 and 10 inclusive.

17. The digital signal interpolator according to claim 7 , wherein said interpolator is incorporated in a quadrature amplitude modulation circuit for adjusting an output timing of said quadrature amplitude modulation circuit.

18. The digital signal interpolator according to claim 7 , wherein said digital signal interpolator is implemented in an integrated circuit.

19. A signal interpolator comprising:

means for performing fractional interpolator in response to a control signal;

means for applying a modulo-M function to a count value for generating said control signal therefrom; and

means for adding an increment value to said control signal for updating said count value.

20. A digital signal interpolator for converting a first signal comprising digital samples synchronised to a first clock frequency, to a second signal synchronised to a second clock frequency, said signal interpolator comprising:

means for receiving said digital samples of said first signal synchronised to said first frequency and for performing fractional interpolation thereon according to a control signal; and

means for counting driven by a counter clock frequency being one of said first and said second clock frequencies, and configured to (i) repeatedly count through a sequence of count values in a count range of modulus M, where the value M is an integer other than a power of 2, and (ii) generate a modulo-M signal as said control signal.

21. A method of interpolating a signal comprising the steps of:

(A) holding a count value;

(B) generating a control signal in response to applying a modulo-M function to said count value;

(C) generating a second signal in response to adding an increment value to said control signal;

(D) updating said count value with said second signal; and

(E) fractional interpolating said signal in response to said control signal.