A Digital Technique for Calibrating and Correcting Nonlinearities in Current-Steering DACs

One of the key limiting factors in the performance of modern high speed digital-to-analog converters' (DACs') is nonlinearities. Nonlinearities introduce unwanted spurs which are observable in the generated signal's spectrum and limit the DAC's spurious free dynamic range (SFDR). As the generated signal's frequency becomes higher, the effect of the nonlinearities becomes more prominent. In this paper, we propose a digital pre-distortion method which corrects for the nonlinearities and improves the overall SFDR of the DAC. The method includes a calibration stage to identify a nonlinearity error matrix. We have tested the method on a commercial off-the-shelf (COTS) DAC unit with 4 GHz clock rate and shown that more than 10 dB improvement of the nonlinearity spurs can be achieved.

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