Background Calibration Techniques for Low-Power and High-Speed Data Conversion

Progress of roles and schemes of calibration techniques in data converters are reviewed. Correction techniques of matching error and nonlinearity in analog circuits have been developed by digital assist using high-density and low-power digital circuits. The roles of the calibration are not only to improve accuracy but also to reduce power dissipation and chip area. Among various calibration schemes, the background calibration has significant advantages to achieve robustness to fast ambient change. Firstly the nonlinearity calibrations for pipeline ADCs are reviewed. They have required new solutions for redundancy of the circuits, an error estimation algorithm and reference signals. Currently utilizing the calibration techniques, the performance of 100 Msps and 12 bit has been achieved with 10 mW power dissipation. Secondly the background calibrations of matching error in flash ADC and DAC with error feedback to the analog circuits are described. The flash ADC utilizes the comparator offset correction with successive approximation algorithm. The DAC adopts a self current matching scheme with an analog memory. Measured dissipation power of the ADC is 0.38 mW at 300 MHz clock. Effects of the background calibration to suppress crosstalk noise are also discussed. key words: digital assist analog circuit, flash ADC, comparator, current summing DAC, substrate noise