Sometimes users ask us to provide them with a ‘modern’ (but) TDC based TCSPC system. Of course, we do also show them our TDC based systems, but after comparison the users are usually more interested in our high-end TAC based systems which are more than one order of magnitude higher in time resolution when compared to the fastest available TDC based system worldwide. Please compare the performance of our fastest module SPC-150NXX with a time channel width of 200 fs, and a real electronic time resolution of about 0.8 ps RMS with any other board available. The confusion seems to originate in the word ‘modern’ which someone has used in some text.
Fact is, the first direct predecessor of a TDC was invented in the year 1942 by Bruno Rossi for the measurement of muon lifetimes . TAC and TDC based systems are being developed in parallel for decades. To us there is no reason to call one more modern than the other, by that causing confusion. Both concepts have strengths, TDC is cheaper to produce, especially with several/many channels in parallel – therefore, this is our low budget solution (see DPC-230). TDC based TCSPC electronics are sufficient for e.g. FCS or FCCS experiments. TAC is much higher in performance, usually necessary in FLIM applications like e.g. FLIM FRET where high precision, stability and reproducibility is essential.
 Bruno Benedetto Rossi, George W. Clark, National Academic Press, Washington D.C. 1998, S. 13