Controlled current source; in particular for digital/analogue converters in continuous-time sigma/delta modulators

1. A controlled current source having a control input, in particular for digital/analogue converters in continuous-time sigma/delta modulators, which generates an output current dependent on a control voltage applied to said control input, and having a controller for converting a clock signal into a voltage signal, with said controller being connected to said current source in such a manner that said voltage signal is applied as a control voltage to said control input of said current source, wherein said controller is designed to convert said clock signal into a voltage signal which has within a clock duration a reproducible curve ending with a falling flank.

2. A controlled current source according to claim 1 , wherein said controller comprises a capacitor and a resistance, which are connected in such a manner that said capacitor is discharged over said resistance to ground, with the voltage over said resistance corresponding to said voltage signal.

3. A controlled current source according to claim 1 , wherein said controller comprises a slope converter.

4. A controlled current source according to claim 1 , wherein said current source is formed by at least one transistor whose gate forms said control input.

5. A digital/analogue converter, in particular for continuous-time sigma/delta modulators, having a current source according to claim 1 for converting a digital signal into a current signal, with said digital signal being connected to said current source or said controller.

6. A digital/analogue converter according to claim 5 which is disposed in a feedback branch of a continuous-time sigma/delta modulator.

7. A sigma/delta analogue/digital converter having a sigma/delta modulator which receives a feedback signal via a feedback branch, wherein in said feedback branch, a digital/analogue converter according to claim 5 is disposed, whose output current forms said feedback signal.

8. A sigma/delta analogue/digital converter according to claim 7 , wherein said sigma/delta modulator is a continuous-time sigma/delta modulator.

9. A sigma/delta analogue/digital converter according to claim 7 , wherein said digital/analogue converter is connected to said sigma/delta modulator in such a manner that said feedback signal is applied to one integrator or a multiplicity of integrators of said sigma/delta modulator.

10. A sigma/delta analogue/digital converter according to claim 7 , wherein said sigma/delta modulator is provided with a Gm-C integrator and said digital/analogue converter is connected to said sigma/delta modulator in such a manner that said feedback signal is directly applied to a capacitor of said Gm-C integrator.

11. A method of operating a sigma/delta analogue/digital converter having a continuous time sigma/delta modulator, in which a feedback signal is generated for said sigma/delta modulator by switching on and off dependent on a clock signal of said sigma/delta modulator a current source, which supplies an output current dependent on a control voltage, wherein said control voltage of said current source is selected in such a manner that it has within each clock duration a reproducible curve which ends with a falling flank.

12. A method according to claim 11 , wherein said output current is directly applied to an input of an integrator of said sigma/delta modulator.

13. A method according to claim 11 , wherein if utilizing a Gm-C integrator in said sigma/delta modulator, said output current is directly applied to a capacitor of said Gm-C integrator.

14. A method according to claim 11 , wherein a transistor circuit is utilized as said current source.

15. A method according to claim 11 , wherein said control voltage of said current source is generated via a resistance-capacitance module.

16. A method according to claim 11 , wherein said control voltage of said current source is generated via a slope converter.