Online calibration of Nyquist-rate analog-to-digital converters

Evolving methodologies for the Online Correction of the distortion at the output of a Nyquist-rate Analog-to-Digital (A/D) Converter is the goal of this study. The focus will be on the development of a generalized and cost-effective scheme wherein the calibration circuitry is shared among multiple Nyquist-rate A/D Converters with different internal architectures and processing different analog inputs. Both static and dynamic non-linearity errors that are responsible for signal distortion are considered. The well-known Code-density Test methodology is modified and applied to the problem of online calibration where the analog input is unknown. The online feature of such correction procedures intrinsically arms them with an ability to be trained, depending on the slowly varying characteristics of the A/D converter as well as the statistics of the analog signal being converted into digital representation.; The simpler task of static-error calibration is attempted first. Simulations performed employing the calibration techniques developed resulted in Spurious-free Dynamic Range (SFDR) improvements by around 20 dB for 12-bit A/D converters with uncorrected SFDR values of up to 80 dB, making the hardware overhead needed in the form of an additional A/D converter and some analog (attenuator, adder) and digital (memory, DSP) processing circuitry a good investment in modern Mixed-signal IC implementations.; Design-for-Testability (DFT) strategies are then introduced in order to efficiently extend the calibration procedure to the correction of dynamic errors.; A separate treatment is given for correcting mismatch-dependent errors exhibited by arrays of Nyquist-rate A/D converters such as time-interleaved A/D converters. A new methodology using orthogonal sequences, which focuses on the effective elimination of mismatch between the different parallel signal paths, is proposed. Simulation results showed improvements of over 50 dB in SFDR in 12-bit A/D converter arrays with uncorrected SFDR as low as 35 dB, when the orthogonal sequences' lengths were chosen equal to 4096. Longer sequences could result in higher improvement, at the cost of increased memory space, but limited by the individual A/D converter non-linearity. In the worst case, as in a time-interleaved A/D converter, online calibration would only need one additional A/D converter, at a fraction of the system's cost.