A nonlinear background technique for pipelined ADCs is proposed. By dividing the raw output of the pipeline core into different segments addressed by the digital codes defined by the outputs of the first several stages, a code-by-code gain error and offset calibration by using least mean square (LMS) adaptive algorithm is introduced to eliminate the conversion nonlinearity due to circuit nonidealities including nonlinear opamp gain. Behavioral simulation results confirm its effectiveness in significantly improving the conversion accuracy in the presence of various circuit nonidealities, and its advantage over the typical previously reported technique in correcting nonlinear interstage gain errors. And comparing to existing techniques, it has less limitation on the nonlinear pattern and requires a smaller hardware overhead.