Digital mean timers for the straw tube tracking system at SDC

Application-specific integrated circuits are being developed for use with the straw tube tracking system at SDC. These are called digital mean timers, and can be used to accept or reject tracks based on the transverse momentum P_t of the particle. They can also be used to determine whether a pair of hits left in two tubes or sets of tubes was caused by the same particle, by summing the drift times. These devices use chains of slowed digital buffers whose propagation delay is variable through one or two control voltages. A clock lock circuit on the chip uses an external-crystal-controlled oscillator to develop the correct control voltage(s) for a given delay per stage. Results from the first two chip designs are presented