Analog-to-digital converter (ADC) with background calibration

A mobile terminal comprising:

• a transceiver circuit comprising an analog-to-digital converter (ADC), comprising:
• a reference ladder configured to output a plurality of voltage reference levels at a corresponding number of reference outputs;
• an input voltage ladder configured to provide an input voltage value at a plurality of nodes equal to the corresponding number of reference outputs;
• a plurality of comparators, each coupled to the reference ladder and the input voltage ladder and configured to output a thermometer code value based on signals received from the reference ladder and the input voltage ladder;
• a thermometer decoder coupled to the plurality of comparators and configured to assemble the thermometer code values from the plurality of comparators and determine an output value based on how many comparators report a 1 or 0 as the respective thermometer code value;
• and
• a calibration control circuit configured to:
• while in normal operation, randomly take one of the plurality of comparators off-line without providing a substitute comparator;
• and
• assemble the thermometer code values from remaining ones of the plurality of comparators and provide the thermometer code value from the off-line comparator by:
• when comparators above and below the off-line comparator are 1, assign the thermometer code value from the off-line comparator to 1;
• when the comparators above and below the off-line comparator are 0, assign the thermometer code value from the off-line comparator to 0;
• and
• when the comparators above and below the off-line comparator are different, assign the thermometer code value from the off-line comparator randomly to 1 or 0.

A method of calibrating an analog-to-digital converter (ADC), comprising:

• taking one of a plurality of comparators off-line without providing a substitute comparator;
• assembling thermometer code values from remaining ones of the plurality of comparators;
• and
• providing a value from the off-line comparator by:
• when comparators above and below the off-line comparator are 1, assigning the value from the off-line comparator to 1;
• when the comparators above and below the off-line comparator are 0, assigning the value from the off-line comparator to 0;
• and
• when the comparators above and below the off-line comparator are different, assigning the value from the off-line comparator randomly.