Continuous time analogue/digital converter

1. A continuous time analogue/digital converter, comprising:

a sigma delta modulator configured to receive an analogue input signal and including a quantization means having a sampling frequency; and

a high-pass filtering means having a chopping frequency that is equal to half of the sampling frequency of the quantization means.

2. The converter according to claim 1 , in which the sigma delta modulator comprises at least one summer and the high-pass filtering means comprises at least one unit including a resonator and a variable-gain amplifier coupled between an output of the quantization means and an input of the at least one summer, the gain of said variable-gain amplifier being fixed at a value for which a resonance frequency of the said resonator is equal to said chopping frequency.

3. The converter according to claim 2 , in which the at least one unit comprises at least one other variable-gain amplifier, the gains of all the amplifiers of said at least one unit being respectively fixed at values for which the resonance frequency of the said resonator is equal to said chopping frequency.

4. The converter according to claim 3 , in which the said sigma delta modulator also comprises a delay means coupled between the output of the quantization means and the input of one of the amplifiers of the at least one unit and configured to delay a digital output signal of the quantization means by a delay equal to half of a sampling period of the quantization means.

5. The converter according to claim 2 , in which the high-pass filtering means comprise at least one other unit.

6. The converter according to claim 1 , produced in integrated form within an integrated circuit.

7. The converter of claim 1 , wherein the sampling frequency is 4 GHz and the chopping frequency is 2 GHz.

8. A wireless communication device comprising:

a sigma delta modulator configured to receive an analogue input signal and including a quantization means having a sampling frequency; and

a high-pass filter having a chopping frequency that is equal to half of the sampling frequency of the quantization means.

9. The wireless communication device of claim 8 , in which the sigma delta modulator comprises a summer and the high-pass filter comprises a resonator and a gain amplifier coupled between an output of the quantization means and an input of the summer, the gain of the amplifier being at a value for which a resonance frequency of the resonator is equal to said chopping frequency.

10. The wireless communication device of claim 9 , in which the high-pass filter further comprises a second amplifier, the gain of the second amplifier being at a value for which the resonance frequency of the resonator is equal to said chopping frequency.

11. The wireless communication device of claim 10 , in which said sigma delta modulator further includes a delay means coupled between the output of the quantization means and an input of one of amplifier or second amplifier, the delay means being configured to delay a digital output signal of the quantization means by a delay equal to half of a sampling period of the quantization means.

12. The wireless communication device of claim 10 , in which the high-pass filter further includes a second resonator, a third amplifier and a fourth amplifier.

13. The wireless communication device of claim 9 , further comprising a receive chain and a transmit chain.

14. A method comprising:

receiving an analogue input signal;

adding to the analogue input signal a feedback signal to generate a modified analogue signal;

passing the modified analogue signal through a high-pass filter, filtering out a portion of the analogue signal having a frequency below a chopping frequency, the chopping frequency being approximately half a sampling frequency, to produce a filtered analogue signal;

quantizing the filtered analogue signal at the sampling frequency to produce a digital signal; and

converting the digital signal to an analogue signal to generate the feedback signal.

15. The method of claim 14 , further comprising amplifying the feedback signal with a gain, the gain being at a value to produce a resonance frequency equal to said chopping frequency.

16. The method of claim 15 , wherein the gain is between 300 and 400.

17. The method of claim 14 , further comprising:

converting the digital signal to an analogue signal to generate a first feedback signal;

delaying the digital signal and converting the delayed digital signal to a second analogue signal to generate a second feedback signal; and

amplifying both the first feedback signal and the second feedback signal before adding the first feedback signal and the second feedback signal to the analogue input signal.

18. The method of claim 17 , wherein delaying the digital signal comprises delaying the digital signal by one half a period of the sampling frequency.

19. The method of claim 14 , wherein the sampling frequency is 4 GHz and the chopping frequency is 2 GHz.

20. A continuous time analogue/digital converter, comprising:

a sigma delta modulator configured to receive an analogue input signal;

a quantizer having a sampling frequency; and

a high-pass filter having a chopping frequency, the chopping frequency being equal to half of the sampling frequency, wherein the high-pass filter comprises a resonator.