Logic circuit for analog channel of digital telephone appts. - has three shift register cell and logic gate circuits in which NOR=gate produces digital output

摘要

The digital telephone apparatus can be of single- or multichannel type. The logic circuit has three shift register cells (12, 14, 16) a logic XOR-gate circuit (18), and a logic NOR -gate circuit (20). These components are connected in such manner that the NOR-gate circuit can generate a digital output which indicates the presence of a train of at least three identical bits at the logic circuit input. If the circuit is used in the transmission part of the apparatus it contains a selective connector (24, 26) for the input of the first register to the telephone channel (22), or with the third register output, which has not been negated. The connection depends on the presence or absence of a call signal. Thus the circuit forms also a generator of a pseudo-random signal trains.