DISPOSITIF DE COUPLAGE ENTRE UN CENTRAL TELEPHONIQUE A PARTAGE DE TEMPS PAM ET UN SYSTEME DE TRANSMISSION A PARTAGE DE TEMPS PCM

At a central office communicating with a remote exchange via a PCM link carrying recurrent frames of 32 channels each, a coupler comprises 30 parallel circuit branches for exchanging analog-voltage samples between as many local lines and a PCM terminal. Each branch includes a tuned circuit for resonant transfer of voltage samples between a storage capacitor, individual to a local line, and the PCM link which contains an A/D converter or coder in an outgoing path and a D/A converter or decoder in an incoming path. The tuned circuit of each branch comprises two filter sections in cascade, each with a shunt condenser, separated by a normally open circuit breaker which closes once per scanning cycle, i.e. in a time slot (No. 0) immediately preceding a series of 15 time slots in the first half of this 32-slot cycle for the first 15 branches and in another time slot (No. 16) immediately preceding another series of 15 time slots in the second half thereof for the second 15 branches. A transmit switch individual to each branch discharges the terminal-side shunt condenser thereof into a common storage capacitor for delivery of its sample to the coder; an associated receive switch closes less than half a cycle thereafter to charge that condenser from the output of the decoder. As the operating frequencies of the groups of transmit and receive switches are not exactly identical, a delay circuit in the incoming path with a delay time of half a cycle is cut either in or out and the closure times of the receive switches are retarded or advanced to the same extent by a monitoring unit whenever the deviation between corresponding switch-closing phases reaches a predetermined limit. Binary supervisory signals, registered in circulating caller and responder memories, are exchanged in the 16th time slot between a processor and the PCM terminal over paths bypassing the coupler.