Pipelined analog-to-digital converters

1. A pipelined analog to digital converter (ADC), comprising:

a first ADC stage that receives an input voltage, that receives a first voltage reference, and that generates a first digital signal and a first residue voltage;

a second ADC stage that receives said first residue voltage and a second voltage reference and that generates a second digital signal; and

a digital voltage supply that generates said second voltage reference,

wherein said second voltage reference is lower than said first voltage reference, and wherein at least one of said first voltage reference and said second voltage reference is a digital reference.

2. A system comprising the pipelined analog to digital converter of claim 1 and further comprising:

a first voltage source that supplies said first voltage reference; and

a second voltage source that supplies said second voltage reference.

3. The system of claim 2 further comprising:

an analog circuit that receives said first voltage reference; and

a digital circuit that receives said second voltage reference.

4. An integrated circuit comprising the pipelined analog to digital converter of claim 1 and further comprising:

a first voltage source that supplies said first voltage reference; and

a second voltage source that supplies said second voltage reference.

5. The integrated circuit of claim 4 further comprising:

an analog circuit that receives said first voltage reference; and

a digital circuit that receives said second voltage reference.

6. The integrated circuit of claim 4 wherein said first voltage source and said second voltage source include voltage regulators.

7. The integrated circuit of claim 6 wherein said first voltage source and said second voltage source receive power from a common power supply.

8. The integrated circuit of claim 4 wherein said first voltage source is independent of said second voltage source.

9. The pipelined analog to digital converter of claim 1 wherein said first ADC stage further comprises:

a sample and hold module that samples and holds said one of said input voltage and said first residue voltage;

an analog to digital converter that converts an output of said sample and hold module to a digital signal; and

a digital to analog converter that converts said digital signal to an analog signal.

10. The pipelined analog to digital converter of claim 6 wherein said first ADC stage further comprises:

a difference module that generates a difference between said output of said sample and hold module and said analog signal; and

an amplifier module that amplifies said difference.

11. An integrated circuit comprising the pipelined analog to digital converter of claim 1 and further comprising:

an analog voltage supply that generates said first voltage reference, wherein said first voltage reference is an analog voltage reference; and

a digital voltage supply that generates said second voltage reference, wherein said second voltage reference is a digital voltage reference.

12. A system comprising the pipelined analog to digital converter of claim 1 and further comprising an analog voltage supply that generates said first voltage reference, wherein said first voltage reference is an analog voltage reference.

13. The pipelined ADC of claim 1 further comprising at least one additional ADC stage that receives a third voltage reference that is one of an analog reference or a digital reference.

14. A pipelined analog to digital converter (ADC), comprising:

first ADC stage means for receiving an input voltage, for receiving a first voltage reference, and for generating a first digital signal and a first residue voltage;

second ADC stage means for receiving said first residue voltage and a second voltage reference and for generating a second digital signal; and

digital supply means for generating said second voltage reference,

wherein said second voltage reference is lower than said first voltage reference, and wherein said second voltage reference is independent of said first voltage reference.

15. A system comprising the pipelined analog to digital converter of claim 14 and further comprising:

first voltage means for supplying said first voltage reference; and

second voltage means for supplying said second voltage reference.

16. The system of claim 15 further comprising:

analog means for receiving said first voltage reference; and

digital means for receiving said second voltage reference.

17. The system of claim 15 wherein said first voltage means and said second voltage means receive power from a common power supply means.

18. An integrated circuit comprising the pipelined analog to digital converter of claim 14 and further comprising:

first voltage means for supplying said first voltage reference; and

second voltage means for supplying said second voltage reference.

19. The integrated circuit of claim 18 further comprising:

analog means for receiving said first voltage reference; and

digital means for receiving said second voltage reference.

20. The pipelined analog to digital converter of claim 14 wherein said first ADC stage further comprises:

sample and hold means for sampling and holding said one of said input voltage and said first residue voltage;

analog to digital converting means for converting an output of said sample and hold means to a digital signal; and

digital to analog converting means for converting said digital signal to an analog signal.

21. The pipelined analog to digital converter of claim 20 wherein said first ADC stage means further comprises:

difference means for generating a difference between said output of said sample and hold means and said analog signal; and

amplifying means for amplifying said difference.

22. An integrated circuit comprising the pipelined analog to digital converter of claim 14 and further comprising:

analog supply means for generating said first voltage reference, wherein said first voltage reference is an analog voltage reference; and

digital supply means for generates said second voltage reference, wherein said second voltage reference is a digital voltage reference.

23. A system comprising the pipelined analog to digital converter of claim 14 and further comprising analog supply means for generating said first voltage reference, wherein said first voltage reference is an analog voltage reference.

24. The pipelined ADC of claim 14 further comprising at least one additional ADC means that receives a third voltage reference that is independent of at least one of said first voltage reference and said second voltage reference.

25. A method for operating a pipelined analog to digital converter, comprising:

receiving one of an input voltage and a first residue voltage at a first ADC stage;

receiving a first voltage reference at said first ADC stage;

generating a first digital signal and a second residue voltage;

receiving said second residue voltage from said first ADC stage and a second voltage reference at a second ADC stage;

generating a second digital signal, wherein said second voltage reference is lower than said first voltage reference; and

receiving a third voltage reference at a third ADC stage that is lower than said second voltage reference.

26. The method of claim 25 further comprising:

generating said first voltage reference using a first voltage source; and

generating said second voltage reference using a second voltage source.

27. The method of claim 26 further comprising:

supplying said first voltage reference to an analog circuit; and

supplying said second voltage reference to a digital circuit.

28. The method of claim 25 further comprising:

sampling and holding said one of said input voltage and said first residue voltage;

converting an output of said sample and hold module to a digital signal; and

converting said digital signal to an analog signal.

29. The method of claim 28 further comprising:

generating a difference between an output of said sampling and holding and said analog signal; and

amplifying said difference.

30. The method of claim 25 further comprising:

using an analog voltage supply to generate said first voltage reference, wherein said first voltage reference is an analog voltage reference; and

using a digital voltage supply to generate said second voltage reference, wherein said second voltage reference is a digital voltage reference.

31. A pipelined analog to digital converter (ADC), comprising:

an ADO stage that receives a residue voltage, that receives a voltage reference, and that generates a digital signal and another residue voltage;

another ADO stage that receives said another residue voltage and another voltage reference and that generates another digital signal; and

a digital voltage supply that generates said another voltage reference,

wherein said another voltage reference is lower than said voltage reference, and wherein at least one of said voltage reference and said another voltage reference is a digital reference.

32. A pipelined analog to digital converter (ADO), comprising:

ADC stage means for receiving a residue voltage, for receiving a voltage reference, and for generating a digital signal and another residue voltage;

another ADO stage means for receiving said another residue voltage and another voltage reference and for generating another digital signal; and

digital supply means for generating said another voltage reference,

wherein said another voltage reference is lower than said voltage reference, and wherein said another voltage reference is independent of said voltage reference.