Background Calibration of Time-Interleaved ADCs with Polyphase Filters

This paper presents the utilization of polyphase finite impulse response (FIR) filters for timing skew mismatch calibration in time-interleaved ADCs (TI-ADCs). Comparison of the output cross-correlation of the sub-ADCs are used to establish the timing skew mismatch estimation. Time shifts generation is the main requirement in this concept. A polyphase FIR filter is chosen to generate the required time shifts. This polyphase implementation can better deal with the operating speed requirement than conventional filter banks. The proposed approach evaluates the output cross-correlation function of the sub-ADCs from which we drive timing skews in all the sub-ADCs. This technique also benefits from eliminating the need for any extra reference sub-ADC(s) for timing-mismatch calibration. The proposed calibration scheme was implemented and simulated with MATLAB/Simulink. With the proposed technique, the signal-to-noise-and-distortion ratio (SNDR) of a specific test was enhanced from 24.2 dB to more than 58 dB in a 10-bit TI-ADC.