P-N-P-N Interface-to-Interface Switching for Telephony and Broad-Band Communication

To be economically attractive, all-electronic spacedivision multiplex (SDM) networks must have a minimum of wiring and interconnection joints, take maximum advantage of IC-type matrix modules, offer inexpensive control (including checking, fault location and traffic supervision) and still satisfy transmission requirements. A means to meet all these demands is presented. It is based on a special p-n-p-n triode crosspoint featuring negligible crosstalk and signal current losses and a very low level of switching noise. Spurious triggering (rate effect) can be eliminated without any special requirements regarding the slope of any signal or the properties of the p-n-p-n device. When such crosspoints are used in unbalanced networks with single-wire through-switching and common return, the added application of the "high-low" principle ensures effective suppression of wiring crosstalk and noise pickup. The resultant signal transfer properties depend practically solely on the interfaces of the network as if these interfaces were directly interconnected. Wiring is minimized by suitable integration of control circuitry into the matrix module and by using the transmission wiring additionally for control without disturbing transmission paths in use. IC modules with
n \times m
crosspoints can be made with only
n + m + 1
terminals for transmission and control in addition to supply terminals.