A Novel CDR-Based Low-Cost Time-Interleaved-ADC Timing Calibration

Digital signal processing (DSP)-based system is a common architecture for high-speed communication links. One of the most important components for DSP-based architectures is the analog-to-digital convertor (ADC). Most of the high-speed ADCs are implemented as time interleaved ADC (TI-ADC). One of the major challenges in TI-ADC is the timing mismatch between the parallel sub-ADCs. The calibration of this mismatch increases system cost and complexity. In this article we propose a new background calibration method based on existing clock and data recovery (CDR) circuits. The timing mismatch can be calibrated using a simple and unique CDR per sub-ADC. Using the existing phase error detector and pulse gain estimator of the regular CDR, the calibration circuit becomes very low-cost, requiring only a first order loop, and a slow numerically controlled oscillator (NCO). VCSEL-based lab experiments are performed, which demonstrate the proposed method efficiency, performance and robustness.