The term "fast" indicates the general nature of the coincidence circuit; that is, input pulses are reshaped, and the actual coincidence determination is made on the leading edge, or leading portion, of the pulses. A dc-coupled anticoincidence input is provided to inhibit the coincidence output by a dc voltage or a pulse that overlaps the period of coincidence of the coincident pulses. The coincidence inputs are ac-coupled, and all four inputs are controlled by In/Out toggle switches.
The resolving time, 2τ, of the fast coincidence unit may be varied over a 10- to 110-ns range by a 10-turn control for accurate resetability of the resolving time. The resolving time of the anticoincidence circuit is set by the width of the input pulse.