Asynchronous self-timed analog-to-digital converter

1. An analog-to-digital converter comprising:

two or more comparators configured to receive an analog input signal;

a digital-to-analog converter communicatively coupled to said comparators, wherein said digital-to-analog converter is configured to produce a reference signal for said comparators; and

asynchronous logic configured to sample an output signal from said comparators and to adjust a digital output signal based on said comparator output signal, wherein said asynchronous logic also outputs a data valid indicator;

wherein a digital output signal from said asynchronous logic is fed through said digital-to-analog converter to produce said reference signal;

wherein said analog-to-digital converter does not use an external clock signal to adjust said digital output signal based on said analog input signal.

2. The analog-to-digital converter of claim 1 , wherein said two or more comparators comprises:

a first comparator configured to receive both said analog input signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is lower than said analog input signal; and

a second comparator configured to receive both said analog input signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is greater than said analog input signal.

3. The analog-to-digital converter of claim 2 , wherein said first and second comparators are designed with a measured hysteresis, said hysteresis defining a least significant bit.

4. The analog-to-digital converter of claim 1 , further comprising:

multiple pairs of comparators, wherein each pair of comparators includes a different hysteresis design to increase a conversion reaction speed of said analog-to-digital converter.

5. The analog-to-digital converter of claim 1 , wherein if said analog input signal is not a least significant bit above or below said output from said digital-to-analog converter, said asynchronous logic remains in an inactive state.

6. The analog-to-digital converter of claim 1 , wherein said asynchronous logic remains inactive for a designated settling period of time after an adjustment of said digital output in response to said comparator signals.

7. An apparatus comprising:

an analog-to-digital converter including an analog-to-digital conversion circuit configured to receive an analog input signal, sample said analog input signal, and output a representative digital signal based on said sampling of said analog input signal, wherein said analog-to-digital conversion circuit does not receive or use a clock signal and outputs a data valid indicator; and

a host device communicatively coupled to said analog-to-digital converter, wherein said host device is configured to receive said representative digital signal and said data valid indicator, said data valid indicator indicating to said host device when said analog input signal is changing.

8. The apparatus of claim 7 , wherein said analog-to-digital converter further comprises:

a plurality of comparators;

a digital-to-analog converter communicatively coupled to said plurality of comparators; and

asynchronous digital logic communicatively coupled to both said plurality of comparators and said digital to analog converter, wherein said asynchronous digital logic is configured to receive a signal from said plurality of comparators and adjust a digital output based on said signal.

9. The apparatus of claim 8 , wherein said comparators are configured to:

receive an analog input signal;

compare said analog input signal to an output signal from said digital-to-analog converter; and

transmit a signal to said asynchronous digital logic requesting a change in said digital output based on said comparison.

10. The apparatus of claim 9 , wherein said comparators are designed with a measured hysteresis, said hysteresis defining a least significant bit.

11. The apparatus of claim 10 , wherein said asynchronous digital logic further comprises an output signal indicator configured to transmit a signal to said host device when said analog-to-digital converter changes said digital output.

12. The apparatus of claim 11 , wherein said output signal indicator is further configured to transmit signal accuracy information to said host device.

13. An asynchronous analog-to-digital converter comprising:

an analog-to-digital conversion circuit which receives an analog input signal and outputs a digital signal based on sampling of the analog input signal; wherein said conversion circuit changes state only when the input analog signal changes by more than a least significant bit (LSB), said conversion circuit comprising:

a plurality of comparator pairs, wherein each comparator pair is designed with a different hysteresis value;

a digital-to-analog converter communicatively coupled to said plurality of comparators configured to produce and transmit a digital reference signal to said comparators: and

asynchronous digital logic communicatively coupled to both said plurality of comparators and said digital-to-analog converter;

wherein said asynchronous digital logic is configured to receive a signal from said plurality of comparators and to adjust a digital output based on said signal.

14. An analog-to-digital converter comprising:

two or more signal comparison means for receiving and comparing an analog input signal to a reference signal;

a digital-to-analog conversion means for generating said reference signal; and

asynchronous logic configured to sample output signals from said signal comparison means and output a digital signal and a data valid indicator;

wherein a digital output from said asynchronous logic is fed through said digital-to-analog conversion means for generating said reference signal;

wherein said analog-to-digital converter does not use an external clock signal to convert an incoming analog input signal into a digital output signal.

15. The analog-to-digital converter of claim 14 , wherein said two or more signal comparison means comprises:

a first comparator configured to receive both said input analog signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is lower than said input analog signal; and

a second comparator configured to receive both said input analog signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is greater than said input analog signal;

wherein said asynchronous logic adjusts said digital output in response to said comparator signals.

16. The analog-to-digital converter of claim 14 , wherein said comparison means comprise a least significant bit value determined by the application of hysteresis.

17. A method for analog-to-digital conversion comprising:

receiving an analog input signal in a plurality of comparators;

receiving a reference signal in said plurality of comparators;

comparing said analog input signal and said reference signal using said plurality of comparators;

signaling a change of a digital output based on said signal comparisons without the use of a clock signal;

changing said digital output and said reference signal based on said signaled change; and

using multiple pairs of comparators with differing least significant bit values to enhance the responsiveness of said method to varying signal rates.

18. The method of claim 17 , further comprising pausing said method for a predetermined settling period after changing a digital output based on said signal comparison.

19. An analog-to-digital converter comprising:

a single comparator configured to receive an analog input signal;

a digital-to-analog converter communicatively coupled to said comparator, wherein said digital-to-analog converter is configured to produce a reference signal for said comparator; and

asynchronous logic configured to sample an output signal from said comparator and to adjust a digital output signal based solely on said comparator output signal, wherein said asynchronous logic also outputs a data valid indicator;

wherein a digital output signal from said asynchronous logic is fed through said digital-to-analog converter to produce said reference signal.

20. The converter of claim 19 , wherein said analog-to-digital converter; does not use an external clock signal to adjust said digital output signal based on said analog input signal.

21. An analog-to-digital converter comprising:

multiple pairs of comparators, wherein each pair of comparators includes a different hysteresis design to increase a conversion reaction speed of said analog-to-digital converter;

a digital-to-analog converter communicatively coupled to said comparators, wherein said digital-to-analog converter is configured to produce a reference signal for said comparators; and

asynchronous logic configured to sample output signals from said comparators and output a digital output signal based on said comparator output signals;

wherein a digital output signal from said asynchronous logic is fed through said digital-to-analog converter to produce said reference signal.

22. The converter of claim 21 , wherein said asynchronous logic also outputs a data valid indicator.

23. The converter of claim 21 , wherein said analog-to-digital converter does not use an external clock signal to adjust said digital output signal based on said analog input signal.

24. The converter of claim 21 , further comprising an additional digital-to-analog converter, wherein each digital to analog converter provides said reference signal for a different pair of comparators.

25. The converter of claim 21 , wherein said pairs of comparators comprise:

a first comparator configured to receive both said analog input signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is lower than said analog input signal; and

a second comparator configured to receive both said analog input signal and said output from said digital-to-analog converter, compare said input analog signal to said output from said digital-to-analog converter, and produce a signal if said output from said digital-to-analog converter is greater than said analog input signal.

26. The converter of claim 25 , wherein said first and second comparators are designed with a measured hysteresis, said hysteresis defining a least significant bit.

27. The converter of claim 21 , wherein said asynchronous logic further comprises an output signal indicator configured to produce a signal when said asynchronous logic changes said digital output in response to a change in said analog input signal.

28. The converter of claim 21 , wherein if said analog input signal is not a least significant bit above or below said output from said digital-to-analog converter, said asynchronous logic remains in an inactive state.

29. The converter of claim 21 , wherein said asynchronous logic remains inactive for a designated settling period of time after an adjustment of said digital output in response to said comparator signals.