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This paper presents a short review of time-to-digital and digital-to-time converters (TDCs and DTCs, respectively) adopting a time-mode signal-processing perspective. The primary definitions, operating principles, and basic building blocks are presented. The discussion applies to most, if not all, DTCs and TDCs. A series of voltage-controlled delay units are used as the primary building block of these converter circuits. When configured in a servo-loop manner, a very short time resolution is achievable with excellent manufacturing robustness. Such designs can be synthesized in field-programmable gate arrays (FPGAs) or constructed in custom silicon. TDCs and DTCs are not new, as they have extensively been used for making very accurate and repeatable time measurements in both the physics-related and semiconductor industry. Today, TDCs and DTCs are finding new applications in phase-locked loops and frequency synthesizers.