Joint sampling-time error and channel skew calibration of time-interleaved ADC in multichannel fiber optic receivers

A joint sampling-time error and channel skew background calibration technique for time interleaved analog to digital converters (TI-ADC) is presented. The technique is aimed at applications in dual-polarization QPSK/QAM receivers for coherent optical communications at high data rates (e.g., 40Gb/s and beyond). Unlike previous proposals, the calibration algorithm introduced here is used to jointly compensate for sampling-time and channel skew errors. Estimates of the gradient of the mean squared error (MSE) or the bit error rate (BER) with respect to the sampling phases of the different signal lanes and interleaves are computed and used to iteratively minimize a cost function (i.e., MSE or BER). Computer simulations demonstrate the excellent behavior of the proposed compensation technique. The calibration algorithm can be implemented with minimal hardware requirements and with a slow clock. This allows power dissipation in a CMOS VLSI implementation to be minimized.