Correction static errors in a/d-converter

A method of correcting static errors in an analog-to-digital converter receiving analog values successively sampled from an analog signal and providing uncorrected digital values representing the sampled analog values, the method comprising the steps of:

• during a predetermined time period or for a predetermined number of sampled analog values, counting occurrences of at least some of the uncorrected digital values,
• after having counted the occurrences:
• calculating from the counted occurrences a model distribution of the occurrences of the uncorrected digital values to provide model occurrences of the uncorrected digital values, and
• comparing the counted occurrences to the model occurrences,
• for each of the analog values sampled after having made the comparing, using the result of the comparing to correct the uncorrected digital value to provide a corrected digital value more accurately representing the sampled analog value than the uncorrected digital value.

A method of determining digital values from analog values successively sampled from an analog signal, the method comprising the steps of:

• providing a first sequence of coarse reference values and a second sequence of fine reference values, each of the course reference values having an order number and each of the course reference values having an order number,
• for each of the sampled analog values:
• comparing the sampled analog value to the coarse reference values of the first sequence and to the fine reference value of the second sequence,
• determining that one of the coarse reference values and that one of the fine reference values which when added to each other give a value having the smallest deviation from the sampled analog value, and
• combining or adding the order number of the determined coarse reference value and the order number of the determined fine reference value to give a digital value representing the sampled analog signal,
• storing, for a plurality of successively sampled analog values, counts of occurrences of each pair of a coarse reference value and a fine reference value determined from the successively sampled analog values,
• determining from the stored counts a model distribution of the counts,
• comparing the counts of the pairs of a first one of the coarse reference levels and the fine reference levels at an upper boundary of the sequence of fine reference levels and the counts of the pairs of a second one of the coarse reference levels located directly above said first one of the coarse reference levels and the fine reference levels at the lower boundary of the sequence of fine reference levels to counts for the same pairs calculated from the model distribution,
• determining from the result of the comparing correction terms, and
• for each analog value sampled after having determined the correction terms, combining or adding a respective one of the determined correction terms and the combined or added digital value representing the sampled analog value to give a corrected digital value representing the sampled analog signal.

A converter for determining digital values from analog values successively sampled from an analog signal, the converter comprising:

• a reference level generator providing a sequence of reference values, each of the reference values having an order number,
• a comparator for comparing each sampled analog value to reference values obtained from the reference level generator to determine a reference value best agreeing with the sampled analog value,
• first calculation means for determining, from the order number of the reference value determined for each one of the sampled analog values, an uncorrected digital value representing the sampled analog value,
• memory means connected for storing counts of the occurrences of at least some of the uncorrected digital values,
• means connected to the calculation means for incrementing, when receiving an uncorrected digital value for which a count is stored in the memory means, the stored count of the occurrence of the uncorrected digital value,
• second calculation means connected to the memory means for calculating from the stored counts of occurrences a model distribution of occurrences of the uncorrected digital values to provide model occurrences of the uncorrected digital values,
• comparing means connected to the memory means and the second calculation means for comparing the stored counts of occurrences to the model occurrences,
• the first calculation means connected to the comparing means and arranged to use, for each one of the sampled analog values, both the order number of the reference value determined for the sampled analog value and the result of the comparing of the counted and model occurrences made by the comparing means to determine a corrected digital value representing the sampled analog value more accurately than the uncorrected digital value.

A device for correcting static errors in an analog-to-digital converter, the device comprising:

• memory means for storing counts of the occurrences of at least some of uncorrected digital values which are output from the analog-to-digital converter and represent analog values sampled from an input signal,
• means connected to the memory means and to an output of the analog-to-digital converter for incrementing, during a predetermined time period, at each time when the analog-to-digital converter outputs an uncorrected digital value for which a count is stored in the memory means, the count of the uncorrected digital value,
• calculation means for calculating from the stored counts of occurrences an expected distribution of occurrences of the uncorrected digital values to provide model occurrences of the digital values,
• comparing means connected to the memory means and the calculation means for comparing the stored counts of occurrences to the model occurrences,
• a correction unit connected to the comparing means and using, after the time period, the result of the comparing made by the comparing to correct uncorrected digital values output from the converter to provide corrected digital values which more accurately represent the sampled analog values than the uncorrected digital values.

A device for determining digital values from analog values successively sampled from an analog signal, the device comprising:

• a reference level generator to provide a first sequence of coarse reference values and a second sequence of fine reference values,
• a comparator for comparing a sampled analog value to the coarse reference values of the first sequence and to the fine reference values of the second sequence,
• means for determining that one of the coarse reference values and that one of the fine reference values which when added to each other give a value having the smallest deviation from the sampled analog value,
• calculation means for combining or adding order numbers of the determined coarse reference value and fine reference value as placed in the first and second sequences respectively to give a digital value representing the analog signal,
• memory and counting means for storing, for a plurality of successively analog values, the number of occurrences of the order numbers of the determined coarse reference value and fine reference value to give counts for each pair of the order number of a coarse reference value and of the order number of fine reference value,
• means for determining from the stored counts a model distribution of counts,
• comparing means for comparing the counts of the pairs of a first coarse reference level and fine reference levels at the upper boundary of the sequence of fine reference levels and the counts of the pairs of the coarse reference level directly above the first coarse reference level and fine reference levels at the lower boundary of the sequence of fine reference levels to counts for the same pairs calculated from the model distribution,
• means connected to the comparing means for determining from the result of the comparing a correction term to be added, after determining the order numbers for a sampled analog value, to the sum of the order numbers of a determined coarse reference value and a determined fine reference value to give a digital value representing the sampled analog signal, from which the values were determined.

A parallel converter device comprising a plurality of element converter devices working in parallel for determining digital values from analog values successively sampled from an analog signal, each element device arranged to provide uncorrected digital values representing sampled analog values, the parallel converter device further comprising:

• first calculation means connected to receive the uncorrected digital values and arranged to calculate a center measure and a width measure of the distribution of the uncorrected digital values for each element device and for all the uncorrected digital values, and
• in each element device:
• comparing means connected to the first calculation means for comparing the center and width measures to the center and width measures for all values,
• a correction table for storing corrections,
• second calculation means connected to the comparing means and the correction table for calculating, based on the result of the comparing, in particular on the difference of the measures, corrections stored in the correction table,
• correction means connected to the correction table and connected to receive the uncorrected digital values and determining from the uncorrected digital values and the corrections corrected digital values which represent the sampled analog values more accurately than the uncorrected digital values.