GB1447693A - Time division communication systems - Google Patents

Abstract

1447693 Automatic exchange system WESTERN ELECTRIC CO Inc 12 March 1974 [22 March 1973 (2)] 10915/74 Heading H4K In a TDM system in which each subscriber's line circuit comprises an outgoing 115 and an incoming 109 amplifier which are connectible simultaneously via respective gates 119, 105 to outgoing and incoming highway 160, 150, the latter are linked by a summing circuit 170 which sums all the signal samples occurring on the outgoing highway during a particular time slot while the outgoing and incoming amplifiers of each pair are so interconnected as to eliminate sidetone and echo effects. Considering line circuit 103, the store 107, e.g. a capacitor, contains a signal sample during the frame interval between successive time slots, where e 1 is the signal originating from this line circuit and e 2 is the total of the signals originating from all the other line circuits partaking in a considered, e.g. conference connection. (The signal e 1 is adjusted throughout the frame by a leakage signal via impedance 108 from the output of the Go amplifier). The incoming amplifier 109 is an operational or similar differential amplifier which performs the operation on the signals appearing at its upper and lower inputs so as to produce an output e 2 . The outgoing amplifier performs the operation {¢.(e 1 +e 2 )-¢(e 2 )} on the signals (e 1 +e 2 ) and e 2 appearing at its lower and upper inputs respectively so as to produce an output It will be appreciated therefore that a speaker on line 101 will only hear signals incoming to his line circuit from the incoming highway while the outgoing highway 160 will only receive signals which originated on the lines, i.e. 101, during a single time slot. The impedances 111 and 117 match the amplifier to the subscriber's line and the highway respectively.