A method for use in testing an analog-to-digital converter. The method includes providing a set of bins, varying a voltage, taking samples of the voltage, providing a selection flag, associating each sample with one bin of the set of bins, and observing a number of samples associated with the bins. An apparatus includes an analog-to-digital converter configured to convert a voltage at an input node to a digital representation provided at an output node. The input node is configured to be coupled to a voltage generator. A sample select unit is configured to determine if a voltage at the input node at least equals a first threshold level and does not exceed a second threshold level. The apparatus is configured, based on the determining, to selectively associate the digital representation with a bin of a set of bins.