Craig & Antonelli
Speech path system
 A speech path system for a telephone exchange having crosspoint switches of a speech path network comprising semiconductor switching devices of four or more layers, including a memory circuit for storing the operating conditions of said switching devices, a drive circuit of a high A.C. impedance for actuating said switching devices in response to output signals from said memory circuit, a subscriber D.C. loop detection circuit of a high impedance provided at a subscriber terminal of said speech path network, and a speech current supply circuit with speech current switching means and a supply current detection circuit provided at a trunk terminal of said speech path network. 
Hitachi, Ltd.
H
H04Q
inventional
Takafumi Tatsuru Tetsuo Takuji
Kojima Miyoshi Takeshita Mukaemachi