A plurality of cross-point matrices each having a plurality of holding circuits respectively associated with a corresponding cross point are arranged in multiple stages, which are linked with each other to form a multi-stage switching network. Each switch matrix is provided with an associated NAND gate...http://www.google.de/patents/US4024352?utm_source=gb-gplus-sharePatent US4024352 - Cross-point switch matrix and multiswitching network using the same
