Improving the linearity in high-speed analog-to-digital converters

Future telecommunication systems will require A/D converters with resolution as high as 12 bit and very high linearity (>90 to dB) at more than 40 MHz sampling rate. These specifications make essential the use of digital calibration for attenuating the errors due to analog components inaccuracies. In this paper we propose a correction technique suitable for off-line and on-line operation. For the first approach we use statistical methods and digital look-up tables. For the second one we suggest a system where the input signal is doubly converted: at the required speed and at a reduced rate but with a higher precision. The slow representation updates the calibration digital look-up table while the data of the fast one are corrected by the look-up table itself. Simulations using Matlab on acquired data and extensive system studies indicated more than 15 dB of improvement in the converter linearity.