Reference circuits for sampled-data circuits

1. A switched capacitor circuit, comprising:

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a voltage reference level;

a waveform generator to generate a predetermined waveform;

a switched capacitance circuit operatively connected to said level-crossing detector;

a switch operatively coupled to said level-crossing detector; and

a voltage reference circuit operatively coupled to said switched capacitance circuit to provide a voltage reference level;

said switch turning OFF when said level-crossing detection signal indicates said input signal crossed said voltage reference level.

2. The analog-to-digital converter as claimed in claim 1 , wherein said voltage reference means includes an operational amplifier.

3. The analog-to-digital converter as claimed in claim 2 , wherein said operational amplifier includes a pre-amplifier.

4. The analog-to-digital converter as claimed in claim 2 , wherein said operational amplifier includes a current mirror with gain.

5. The analog-to-digital converter as claimed in claim 1 , further comprising:

a second level-crossing detector to generate a second level-crossing detection signal when a second input signal crosses a second predetermined level;

a second sampling switch, operatively coupled to said second level-crossing detector; and

a second switched capacitance circuit, operatively connected to said first sampling switch;

said second sampling switch turning OFF when said second level-crossing detection signal indicates said second input signal crossed said second predetermined level.

6. The analog-to-digital converter as claimed in claim 1 , wherein said level-crossing detector is a zero-crossing detector.

7. The analog-to-digital converter as claimed in claim 1 , wherein said level-crossing detector is a comparator.

8. The analog-to-digital converter as claimed in claim 1 , wherein said waveform generator produces a plurality of predetermined waveforms.

9. A switched capacitor circuit, comprising:

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a voltage reference level;

a waveform generator, operatively connected to said level-crossing detector, to generate a predetermined waveform;

a switched capacitance circuit operatively connected to said level-crossing detector;

a switch operatively coupled to said level-crossing detector; and

a voltage reference circuit operatively coupled to said switched capacitance circuit to provide a voltage reference level;

said switch turning OFF when said level-crossing detection signal indicates said input signal crossed said voltage reference level.

10. The switched-capacitor circuit as claimed in claim 9 , wherein said voltage reference means includes an operational amplifier.

11. The switched-capacitor circuit as claimed in claim 10 , wherein said operational amplifier includes a pre-amplifier.

12. The switched-capacitor circuit as claimed in claim 10 , wherein said operational amplifier includes a current mirror with gain.

13. The switched capacitor circuit as claimed in claim 1 , further comprising:

a second waveform generator to generate a second predetermined waveform;

a second level-crossing detector, operatively connected to said second waveform generator, to generate a second level-crossing detection signal when a second input signal crosses the voltage reference level; and

a second switch operatively coupled to said second level-crossing detector;

said second switch turning OFF when said second level-crossing detection signal indicates said second input signal crossed the voltage reference level.

14. The switched capacitor circuit as claimed in claim 9 , wherein said level-crossing detector is a comparator.

15. The switched capacitor circuit as claimed in claim 9 , wherein said level-crossing detectors is a zero-crossing detector.

16. The switched capacitor circuit as claimed in claim 13 , wherein said second waveform generator produces a plurality of predetermined waveforms.

17. The switched capacitor circuit as claimed in claim 9 , wherein said waveform generator produces a plurality of predetermined waveforms.

18. The switched capacitor circuit as claimed in claim 13 , further comprising:

a third switch operatively coupled to said second level-crossing detector; and

a sampling capacitor operatively connected to said first level-crossing detector;

said third switch turning OFF when said second level-crossing detection signal indicates said second input signal crossed said voltage reference.

19. The switched capacitor circuit as claimed in claim 18 , further comprising:

a fourth switch operatively coupled to said second level-crossing detector; and

a second sampling capacitor operatively connected to said first level-crossing detector;

said fourth switch turning OFF when said second level-crossing detection signal indicates said second input signal crossed said voltage reference level a second time.

20. A switched capacitor circuit, comprising:

a first waveform generator to generate a first predetermined waveform;

a first level-crossing detector to generate a first level-crossing detection signal when an input signal crosses a first voltage reference;

a first switch operatively coupled to said first level-crossing detector;

a first sampling capacitor operatively connected to said first level-crossing detector;

a second waveform generator to generate a second predetermined waveform;

a second level-crossing detector to generate a second level-crossing detection signal when a second input signal crosses a second voltage reference level;

a second switch operatively coupled to said second level-crossing detector;

a second sampling capacitor operatively connected to said first level-crossing detector; and

a third level-crossing detector differentially coupled to said first and second sampling capacitors;

said first switch turning OFF when said first level-crossing detection signal indicates said input signal crossed said first voltage reference;

said second switch turning OFF when said second level-crossing detection signal indicates said second predetermined waveform crossed said second voltage reference level.

21. The switched capacitor circuit as claimed in claim 20 , wherein said first, second, and third level-crossing detectors are zero-crossing detectors.

22. The switched capacitor circuit as claimed in claim 20 , wherein said first, second, and third level-crossing detectors are comparators.

23. The switched capacitor circuit as claimed in claim 20 , wherein said first and second waveform generators produce a plurality of predetermined waveforms.

24. A switched capacitor circuit, comprising:

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a first predetermined level;

a waveform generator, operatively connected to said level-crossing detector, to generate a first predetermined waveform;

a switched capacitance circuit operatively connected to said level-crossing detector;

a voltage reference circuit operatively coupled to said switched capacitance circuit to provide a voltage reference level;

a switch operatively coupled to said level-crossing detector; and

a sampling capacitor operatively connected to said level-crossing detector;

said switch turning OFF when said level-crossing detection signal indicates said input signal crossed said first predetermined level.

25. The switched-capacitor circuit as claimed in claim 24 , wherein said voltage reference means includes an operational amplifier.

26. The switched-capacitor circuit as claimed in claim 25 , wherein said operational amplifier includes a pre-amplifier.

27. The switched-capacitor circuit as claimed in claim 25 , wherein said operational amplifier includes a current mirror with gain.

28. The switched capacitor circuit as claimed in claim 24 , further comprising:

a second waveform generator to generate a second predetermined waveform;

a second level-crossing detector, operatively connected to said second waveform generator, to generate a second level-crossing detection signal when a second input signal crosses the voltage reference level;

a second switch operatively coupled to said second level-crossing detector; and

a second sampling capacitor operatively connected to said level-crossing detector;

said second switch turning OFF when said second level-crossing detection signal indicates said second input signal crossed said voltage reference level.

29. The switched capacitor circuit as claimed in claim 28 , further comprising:

a third switch operatively coupled to said first level-crossing detector;

said third switch turning OFF when said first level-crossing detection signal indicates said input signal crossed said first predetermined level.

30. The switched capacitor circuit as claimed in claim 28 , wherein said first and second level-crossing detectors are comparators.

31. The switched capacitor circuit as claimed in claim 28 , wherein said first and second level-crossing detectors are zero-crossing detectors.

32. The switched capacitor circuit as claimed in claim 28 , wherein said second switch is operatively connected between said voltage reference and said second sampling capacitor.

33. The switched capacitor circuit as claimed in claim 28 , wherein said second waveform generator produces a plurality of predetermined waveforms.

34. A reference voltage source, comprising:

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a predetermined level;

a waveform generator to generate a first predetermined waveform;

a switch operatively coupled to said level-crossing detector;

a sampling capacitor operatively connected to said level-crossing detector;

a first bias voltage source operatively connected to an input terminal of the level-crossing detector; and

a second bias voltage source operatively connected to said input terminal of the level-crossing detector;

said switch turning OFF when said level-crossing detection signal indicates said input signal crossed said predetermined level.

35. The reference voltage source as claimed in claim 34 , wherein said level-crossing detector is a comparator.

36. The reference voltage source as claimed in claim 34 , wherein said level-crossing detector is a zero-crossing detector.

37. The reference voltage source as claimed in claim 34 , wherein said waveform generator is a variable current source.

38. A reference voltage source, comprising:

a waveform generator to generate a predetermined waveform;

a first transistor operatively connected to said waveform generator;

a second transistor operatively connected to said waveform generator;

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a predetermined level;

a switch operatively coupled to said level-crossing detector; and

a sampling capacitor operatively connected to said level-crossing detector;

said first switch turning OFF when said level-crossing detection signal indicates said input signal crossed said predetermined level.

39. The reference voltage source as claimed in claim 38 , wherein said level-crossing detector is a comparator.

40. The reference voltage source as claimed in claim 38 , wherein said level-crossing detector is a zero-crossing detector.

41. The reference voltage source as claimed in claim 38 , wherein said waveform generator is a variable current source.

42. A reference voltage source, comprising:

a waveform generator to generate a predetermined waveform;

an amplifier operatively connected to said waveform generator;

a first bias voltage source operatively connected to said amplifier;

a second bias voltage source operatively connected to said amplifier; and

a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a predetermined level;

said waveform generator turning OFF when said level-crossing detection signal indicates said input voltage crossed said predetermined level.

43. The reference voltage source as claimed in claim 42 , wherein said level-crossing detector is a comparator.

44. The reference voltage source as claimed in claim 42 , wherein said level-crossing detector is a zero-crossing detector.

45. The reference voltage source as claimed in claim 42 wherein said waveform generator is a variable current source.