Online calibration of a Nyquist-rate analog-to-digital converter using output code-density histograms

A scheme for the online correction of static nonlinearities in a Nyquist-rate analog-to-digital converter (ADC), using output code-density histograms, is presented. The estimation of the integral nonlinearity (INL) at each output level, followed by the creation of a corresponding entry in the look-up table for error correction, is analytically explained. The suitability of the scheme for calibrating high-end ADCs has been demonstrated. An extra ADC and the associated switching and postprocessing DSP circuitry along with some memory for storing the data to be processed, are the overhead in this scheme. An improvement of over 20 dB in the spurious-free dynamic range, from an uncalibrated value of over 80 dB, has been achieved.