Multi-bit sigma-delta TDC architecture with self-calibration

This paper describes the architecture and principles of operation of sigma-delta (ΣΔ) time-to-digital converters (TDC) for high-speed I/O interface circuit test applications; they offer good accuracy with short test times. In particular, we describe a multi-bit ΣΔ TDC architecture for fast testing. However, mismatches among delay cells in delay lines degrade the linearity there. Then we propose a self-calibration method that measures delay values using an improved ring oscillator circuit to improve the overall TDC linearity. Our MATLAB simulation results demonstrate the effectiveness of the proposed approach.