ABSTRACT
All evolutions related to high-resolution analog-to-digital converter (ADC) techniques. Historically, ADC resolution or linearity has been improved by trimming, and it will continue in production. The resolution of all multistage ADCs such as pipeline and cascadedb is fundamentally limited by the residue accuracy. In the pipelined ADC, such inaccuracy results from the capacitor mismatch, operational amplifier (opamp) finite direct current gain, and opamp nonlinearity. Some inherently linear analog techniques were introduced to overcome analog imperfections, but worked only in specific ADC configurations. The capacitor-error averaging concept makes the residue inherently linear both in integral nonlinearity and differential nonlinearity but requires one additional clock phase and one additional averaging amplifier. The gain nonlinearity calibration is based on the fact that the nonlinear residue transfer function can be approximated with a high-order polynomial. Calibrating gain mismatch and sample-time errors in the two-path system is already a challenging task that requires precise group delay filtering with very fine time steps.
