Methods and apparatus to calibrate a dual-residue pipeline analog to digital converter

An analog to digital converter (ADC) comprising:

• a plurality of open-loop amplifiers, each of the plurality of open-loop amplifiers configured to amplify one of a plurality of reference inputs by an amplifier gain and provide such amplified reference input at an output of each of such open-loop amplifiers;
• a plurality of comparators, each coupled to the output of one of the plurality of the open-loop amplifiers, the plurality of comparators configured to determine a sign of the outputs of the plurality of open-loop amplifiers;
• a first residue output coupled to a first portion of the outputs of the plurality of the open-loop amplifiers;
• a second residue output coupled to a second portion of the outputs of the plurality of open-loop amplifiers, the second portion is different than the first portion;
• and
• a controller coupled to each of the plurality of comparators and operable to:
• determine approximately a mean of a difference between the first residue output and the second residue output;
• increment the reference inputs;
• and
• increment the amplifier gain of the open-loop amplifiers.

A method comprising:

• configuring an amplifier gain to be a gain reference;
• configuring a plurality of DAC ladder outputs to be reference DAC values;
• determining a zone between a plurality of reference DAC values in response to an analog input;
• determining a plurality of residues in response to determining the zone;
• determining a mean of a difference between the plurality of residues in response to determining the plurality of residues;
• determining a difference between the mean of the difference between the plurality of residues and a reference mean difference in response to determining the mean of the difference between the plurality of residues;
• incrementing the reference DAC values in response to determining the difference between the mean of the difference between the plurality of residues and the reference mean difference;
• and
• incrementing the amplifier gains in response to:
• determining the plurality of residues;
• and
• determining a variance of each residue.