Telephone-signal receiver for switching exchanges having centralized

Abstract

Switching criteria are transmitted over a plurality of trunk lines to a central office of a telecommunication system in the form of a set of binary signals modulated on three carriers for each trunk line, the triads of carriers being cyclically sampled and demodulated. During each sampling interval t.sub.i allocated to a particular trunk G.sub.i within a cycle, a locally generated identification code of that trunk is transmitted to each of three sections of a read-only memory MS, each memory section permanently storing four different threshold values for the length of 'on' signals (1) and 'off' signals (0). Integrators IN, rejecting spurious changeovers from one type of signal to the other, feed respective counters CT via respective coincidence circuits CFR which receive from a register MG the bits of the preceding cycle and reset arithmetic units .sigma. in these counters whenever there is a definite change in the type of signal received; each counter CT, emitting a count which increases by 1 in each new cycle, is maintained at its maximum count (unless previously reset) as long as no change occurs. The count of each counter is compared with the several threshold values, stored in the associated memory section, in a corresponding section of a comparator CMP whose output is delivered to a processor AC.