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Harmonic Distortion Correction (HDC) is one of two published digital background calibration techniques that compensate for residue amplifier nonlinearity in pipelined ADCs. The techniques make it possible to reduce the gains and bandwidths, and therefore the power dissipations, of the op-amps that make up the residue amplifiers without sacrificing pipelined ADC accuracy. Unfortunately, the previously published techniques fail to operate properly when they measure residue amplifier distortion for certain pipelined ADC input signals, most notably input signals with small peak-to-peak variations about certain constant values. This paper identifies the cause of the problem, quantifies its effects, and provides an all-digital solution applicable to the HDC technique.