The term time-to-digital converter is used when talking about time interval measurements in the range of 1 nanosecond down to the picosecond range. The first TDCs have been developed for scientific and research purposes. They have been realized as a combination of time-to-analog (TAC) and analog-to-digital (ADC) converter. A sophisticated design of the TAC together with limitations to update rate or multihit capability make these solutions inattractive for industrial applications.
Integrated digital TDCs
Thanks to modern CMOS-technology it is possible to integrate fully digital time-to-digital converters into a single chip. The high precision of the time measurement - down to 14 ps - in combination with the large dynamic range (up to 30 Bit), the high stability over temperature and supply voltage and the possibilty of a low cost production thanks to the CMOS technology make them the first choice for industrial applications.