Sigma-delta converter with noise suppression

1. A sigma-delta converter for converting a digital input signal into an analog output signal with noise suppression within a useful band, comprising:

a principal path including

at least one principal path sigma-delta modulator having a transmission function including a filter and having an output producing a digital output signal, and

at least one principal path digital-to-analog converter respectively coupled to the output of the at least one principal path sigma-delta modulator;

at least one parallel path connected in parallel with the principal path, each parallel path including

at least one parallel path sigma-delta modulator receiving a differential signal filtered to exclude at least noise components outside the useful band and obtained from the digital output signal of the principal path sigma-delta modulator and the input signal after spectral shaping by the filter according to the transmission function of the sigma-delta modulator in the principal path, and having an output, and

a parallel path digital-to-analog converter coupled to the output of the at least one parallel path sigma-delta modulator; and

an analog signal totaler, coupled to the principal path and the at least one parallel path, producing an analog output signal of the sigma-delta converter from analog output signals of the principal and parallel paths.

2. A sigma-delta converter as claimed in claim 1 , wherein the at least one parallel path further includes an amplifier of the differential signal immediately before the at least one parallel path sigma-delta modulator.

3. A sigma-delta converter as claimed in claim 1 , wherein the at least one parallel path further includes an attenuator attenuating the analog output signal between the parallel path digital-to-analog converter and before the analog signal totaler.

4. A sigma-delta converter as claimed in claim 3 , wherein the at least one parallel path further includes a temporal delay of the input signal balancing out propagation time differences with respect to the principal path.

5. A sigma-delta converter as claimed in claim 4 , wherein the principal path further includes compensation filtering after the input signal is branched to the parallel path and before the principal path digital-to-analog converter.

6. A sigma-delta converter as claimed in claim 5 , wherein the principal path sigma-delta converter is a multi-stage sigma-delta converter.

7. A sigma-delta converter as claimed in claim 6 , wherein the multi-stage sigma-delta converter in the principal path includes a direct path and at least one cascade stage in parallel to the direct path.

8. A sigma-delta converter as claimed in claim 7 ,

wherein the multi-stage sigma-delta converter in the principal path includes n cascade stages, where n>1, and for each cascade stage i for 2≦i≦n, an immediately prior cascade stage i−1 provides a principal stage path,

wherein each cascade stage i for 2≦i≦n in the multi-stage sigma-delta converter includes a cascade stage sigma-delta modulator and an adder adding the input signal after the temporal delay to a noise-filtered signal of each prior cascade stage to produce an input for the cascade stage sigma-delta modulator, and

wherein said sigma-delta converter further comprises a digital signal totaler producing the digital output signal of the principal path by summing output signals of each cascade stage sigma-delta modulator in the multi-stage sigma-delta modulator.

9. A sigma-delta converter as claimed in claim 5 , wherein each cascade stage sigma-delta modulators in the multi-stage sigma-delta converter in the principal path has a linear-phase frequency response with an absolute frequency response of 1.

10. A sigma-delta converter as claimed in claim 9 , wherein the cascade stage sigma-delta modulator in cascade stage n has an input receiving the differential signal from the input signal and a noise-filtered and n-normalized total signal of the output signals of the cascade stage sigma-delta modulators in cascade stages i for 1<i<n−1.

11. A sigma-delta converter is claimed in claim 10 , wherein the input of the cascade stage sigma-delta modulator of cascade stage n is multiplied by n.

12. A sigma-delta converter as claimed in claim 11 , wherein the sigma-delta converter is a 1-bit sigma-delta converter.

13. A sigma-delta converter as claimed in claim 12 , wherein the sigma-delta converter further comprises a 1-bit digital to analog converter possessing unequal output powers.

14. A sigma-delta converter as claimed in claim 13 , wherein the cascade stage sigma-delta modulators of the multi-stage sigma-delta modulator have uncorrelated noise signals.

15. A sigma-delta converter as claimed in claim 14 , further comprising at least one adder to add uncorrelated stochastic signals to the input of the cascade stage sigma-delta modulators of the multi-stage sigma-delta modulator.

16. A sigma-delta converter as claimed in claim 15 , wherein the sigma-delta converter is manufactured in CMOS technology.

17. A radio communication reception device, comprising:

a sigma-delta converter for converting a digital input signal into an analog output signal with noise suppression within a useful band, including

a principal path including

at least one principal path sigma-delta modulator having a transmission function including a filter and having an output producing a digital output signal, and

at least one principal path digital-to-analog converter respectively coupled to the output of the at least one principal path sigma-delta modulator;

at least one parallel path connected in parallel with the principal path, each parallel path including

at least one parallel path sigma-delta modulator receiving a differential signal filtered to exclude at least noise components outside the useful band and obtained from the digital output signal of the principal path sigma-delta modulator and the input signal after spectral shaping by the filter according to the transmission function of the sigma-delta modulator in the principal path, and having an output, and

a parallel path digital-to-analog converter respectively coupled to the output of the at least one parallel path sigma-delta modulator; and

a signal totaler, coupled to the principal path and the at least one parallel path, producing an analog output signal of the sigma-delta converter from analog output signals of the principal and parallel paths.