DIGITAL CONFERENCE CIRCUIT

摘要

A conference circuit is of a type in which a digital matrix switch (20) under control of a central processing unit (21) responds to a conference request by connecting three or more parties through the digital switch to a digital conference connection processor (28). In a preferred embodiment of the digital processor (28), the voice signal arrives as PCM signals which are on a data line (CIP), and which are successively communicated into various temporary storage means (110, 130, 150 and 160) while undergoing processing in the nature of summarizing signals of all the parties to the requested conference connection and successively subtracting therefrom the signal of each respective party to form the signal sent back to that respective party. This processing is performed under control of a sign bit processor (180) and an arithmetic logic unit (140). In accordance with the invention, sign bit processor (180) effects inversion of alternate sign bits to cancel parasitic echo signals which tend to create oscillating or ringing, thereby creating greater stability in voice transmissions. The resultant signal which is sent back to each party is provided to a gain control register (190). Gain control in 6 db increments is provided by a gain control processor (220) which selectively shifts the word in register (190) according to the size of the requested conference to provide for flexibility of conference sizes.