Diagnosing ADC nonlinearity at the bit level

Two methods for identifying analog-to-digital converter (ADC) nonlinearity at the bit level are discussed. The integral nonlinearity (INL) is analyzed in the frequency domain using both DFT and Walsh transforms to determine which ADC bit is responsible for which harmonic or bin. It is shown that the effects of different bits on the outputs of either transform are separable. A 5-bit ADC example is investigated using both transforms to illustrate the implementation of the techniques.>