Correction of the Timing Mismatch Error in Four-Channel Time-Interleaved DACs

The digital-to-analog converters (DACs) used in modern RF communication systems are required to synthesize broadband signals at high frequency bands with high spectral purity. Time-interleaving (TI) is one of the promising techniques for extending the synthesizable frequency and bandwidth of the DACs. However, timing mismatch errors in the sub-DAC clocks introduce spurious images in the TIDAC's Nyquist band, thus degrading the TIDAC's spurious-free-dynamic-range (SFDR) performance. Nonetheless, correction of the spurious images in TIDACs with more than 2 channels have been little studied. In this paper, we consider a 4-channel TIDAC and investigate its image generation mechanism. A pre-correction filter bank structure to correct for the images in the TIDAC's Nyquist band is presented and a weighted least squares (WLS) approach for optimizing the coefficients is introduced. Simulation examples demonstrate that our technique is able to achieve 40 dB in-band SFDR improvement with 55-tap finite impulse response (FIR) filters.