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Self-calibration in approximately 10 000 conversions is demonstrated in a 16-bit, 1-MS/s algorithmic analog-to-digital converter (ADC). Continuous digital background calibration is enabled by introduction of a "split ADC" architecture, in which the die area of a single ADC design is split into two independent converters, each converting the same input signal. The two independent outputs are averaged to produce the ADC output code. The difference of the two outputs provides information for the background calibration process. Since both ADCs convert the same input, when correctly calibrated their outputs should be equal and the difference should be zero. Any nonzero difference provides information to an error estimation process which adjust calibration parameters in each ADC. For the specific realization of an algorithmic ADC described in this paper, a multiple residue mode amplifier is used to ensure different decision trajectories and provide valid calibration information. The analog sub-system of the ADC is implemented in 0.25-μm CMOS, consumes 105 mW, and has a die size of 1.2 mm × 1.4 mm.