A/D converter calibration

1. A method of improving accuracy of an A/D converter structure including a set of comparators with associated calibrating D/A converters for providing individual offset voltages and a range D/A converter for providing a common gain control voltage, comprising the steps of:

providing each comparator with a predefined reference voltage;

providing each calibrating D/A converter with a common calibration value;

determining a minimum calibration range value for said range D/A converter to cover a gain control common to all comparators; and

adjusting the individual offset of each comparator by adjusting the associated calibrating D/A converter.

2. The method of claim 1 , comprising the step of distributing said dynamic range symmetrically around zero output.

3. The method of claim 1 , comprising the step of distributing said dynamic range asymmetrically around zero output.

4. The method of claim 1 , wherein the step of providing each comparator with a predefined reference voltage includes the step of providing each input of a comparator with the same reference voltage.

5. A D/A converter range calibration system in an A/D converter structure, comprising:

a plurality of comparators each comprising a calibration input coupled with an associated calibrating D/A converter;

a plurality of calibration registers each coupled with an associated calibrating D/A converter;

a range D/A converter coupled with said associated calibrating D/A converters;

a range register coupled with said range D/A converter;

control means for determining a range gain control value to be stored in said range register for the entire set of comparators.

6. The system of claim 5 , wherein each calibrating D/A converter is a differential calibrating D/A converter.

7. The system of claim 6 , wherein the range D/A converter comprises positive range D/A converter and a negative range D/A converter.

8. The system of claim 6 , wherein each calibration register can be forced to output a maximum or minimum value.

9. A D/A converter range calibration system in an A/D converter structure comprising:

a set of comparators with associated calibrating D/A converters,

a control unit for determining an gain control value common to the entire set of comparators; and

a range D/A converter for adjusting each calibrating D/A converter by the determined gain control value.

10. The system of claim 9 , wherein each calibrating D/A converter is a differential calibrating D/A converter.

11. The system of claim 10 , wherein the range D/A converter comprises positive range D/A converter and a negative range D/A converter.

12. The system of claim 9 , comprising said control unit adjusts the dynamic range of each comparator symmetrically around zero output by adjusting said associated calibrating D/A converters.

13. A method of improving accuracy of an A/D converter structure including a set of comparators with associated differential calibrating D/A converters for providing individual differential offset voltages and a differential range D/A converter for providing a common differential gain control voltage, comprising the steps of:

providing each comparator with a predefined reference voltage;

providing each calibrating D/A converter with a first calibration value;

determining a first calibration range value for said range D/A converter to cover a first gain control common to all comparators;

providing each calibrating D/A converter with a second calibration value;

determining a second calibration range value for said range D/A converter to cover a second gain control common to all comparators; and

adjusting the individual offset of each comparator by adjusting the differential associated calibrating D/A converter.

14. The method according to claim 13 , wherein the first calibration value is a minimum value and the second calibration value is a maximum value.

15. The method according to claim 13 , wherein first calibration range offset is provided by a negative range D/A converter and the second calibration range offset is provided by a positive range D/A converter.

16. The method according to claim 13 , wherein the step of providing each comparator with a predefined reference value includes the step of providing each input of a comparator with the same reference value.