An On-Chip Self-Characterization of a Digital-to-Time Converter by Embedding it in a First-Order $\Delta\Sigma$ Loop

To characterize an on-chip programmable delay in a low-cost and high-resolution manner, a built-in self-test based on a first-order $\Delta \Sigma $ time-to-digital converter with self-calibration is proposed and implemented in TSMC 28-nm CMOS. The system is self-contained, and only one digital clock is needed for the measurements. A system self-calibration algorithm is proposed to calibrate nonlinearities of the analog circuitry. The operation is robust over PVT variations since the delay information is normalized to the input clock period. To verify the proposed idea, two different digital-to-time converters performing the on-chip delay are measured and analyzed at 50-MHz clocking frequency with 0.65-ps standard time deviation per measurement.