Reference circuits for sampled-data circuits
A switched capacitor circuit includes a first level-crossing detector to generate a level-crossing detection signal when an input signal crosses a first predetermined level. A first waveform generator generates a first predetermined waveform and a second waveform generator generates a second predetermined waveform. A second level-crossing detector generates a second level-crossing detection signal when said second predetermined waveform crosses a voltage reference level a second time. A second switch is coupled to the second level-crossing detector, and a third switch is coupled to the first level-crossing detector. The second switch turns OFF when the second level-crossing detection signal indicates the second predetermined waveform crossed the voltage reference level a second time. The third switch turns OFF when the first level-crossing detection signal indicates the input signal crossed the first predetermined level.
1. An analog-to-digital converter, 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 predetermined waveform;
a switched capacitance circuit;
a sampling 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 sampling switch turning OFF when said level-crossing detection signal indicates said input signal crossed said predetermined 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 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.
10. The reference voltage source as claimed in claim 9 , wherein said level-crossing detector is a comparator.
11. The reference voltage source as claimed in claim 9 , wherein said level-crossing detector is a zero-crossing detector.
12. The reference voltage source as claimed in claim 9 , wherein said waveform generator is a variable current source.
13. 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.
14. The reference voltage source as claimed in claim 13 , wherein said level-crossing detector is a comparator.
15. The reference voltage source as claimed in claim 13 , wherein said level-crossing detector is a zero-crossing detector.
16. The reference voltage source as claimed in claim 13 , wherein said waveform generator is a variable current source.
17. 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.
18. The reference voltage source as claimed in claim 17 , wherein said level-crossing detector is a comparator.
19. The reference voltage source as claimed in claim 17 , wherein said level-crossing detector is a zero-crossing detector.
20. The reference voltage source as claimed in claim 17 wherein said waveform generator is a variable current source.