Abstract: A time division switching system is disclosed having a plurality of telephone line circuits and common control circuits for switching calls over a time division communication bus. Ringing loop current detectors are shared by groups of the line circuits for detecting call answer signals during active ringing on a call and for controlling the line circuits to interrupt, or trip, the ringing upon a called party answer. Each group of the line circuits is permanently connected to a ringing current supply via an individual one of the loop current detectors. Each line circuit includes ringing control circuitry operated and released by the common control circuits for connecting ringing current to a called line during an active ringing interval and for disconnecting it during a silent interval of the ringing cycle. The circuitry is responsive to a detection of a called station answer signal by the shared loop current detector for immediately tripping ringing.

Abstract: This specification discloses transistor circuitry suitable for use as a switch or as a floating current driver to control the concurrent operation of a pair of utilization devices. The circuitry comprises an NPN and a PNP output transistor which are substantially simultaneously switchable to ON and OFF states by a bias control means. The output transistors each have a collector connectable to a utilization device and a voltage of a prescribed polarity. Emitters of the output transistors are connected together in a floating voltage arrangement via a resistor. The bias control means comprises a pair of NPN transistors and a diode connected PNP transistor illustrated for switching the NPN output transistor and then the PNP output transistor to ON and OFF states. A logic gate switches a constant current to the bias control transistors for controlling the switching operations.

Abstract: An electronic switch is disclosed comprising a transistor bridge having input and output signaling nodes and bias control nodes. A pair of matched current sources are selectively activated and deactivated in a series arrangement with symmetrical turn-on turn-off circuitry in response to a receipt of instruction signals. The instruction signals control the gating of a constant current to the turn-on/off circuitry for enabling the matched current sources to selectively apply and withdraw matched currents from bias control nodes. Switched turn-off circuitry is employed for reverse biasing the transistor bridge in response to a deactivation of the matched current sources. A pair of voltage reference and antisaturation circuits cooperate with bridge discharge circuits to effect the reverse biasing of the bridge and to discharge rapidly the effective electrical capacitance of that bridge shortly after the receipt of a bridge turn off instruction.

Abstract: An electronic switch is disclosed comprising a transistor bridge having input and output signaling nodes and bias control nodes. A pair of matched current sources are selectively activated and deactivated in a series arrangement with symmetrical turn-on turn-off circuitry in response to a receipt of instruction signals. The instruction signals control the gating of a constant current to the turn-on/off circuitry for enabling the matched current sources to selectively apply and withdraw matched currents from bias control nodes. Switched turn-off circuitry is employed for reverse biasing the transistor bridge in response to a deactivation of the matched current sources. A pair of voltage reference and antisaturation circuits cooperate with bridge discharge circuits to effect the reverse biasing of the bridge and to discharge rapidly the effective electrical capacitance of that bridge shortly after the receipt of a bridge turn-off instruction.

Abstract: A time division switching system is disclosed having a plurality of telephone line circuits and common control circuits for switching calls over a time division communication bus. Ringing loop current detectors are shared by groups of the line circuits for detecting call answer signals during active ringing on a call and for controlling the line circuits to interrupt, or trip, the ringing upon a called party answer. Each group of the line circuits is permanently connected to a ringing current supply via an individual one of the loop current detectors. Each line circuit includes ringing control circuitry operated and released by the common control circuits for connecting ringing current to a called line during an active ringing interval and for disconnecting it during a silent interval of the ringing cycle. The circuitry is responsive to a detection of a called station answer signal by the shared loop current detector for immediately tripping ringing.

Abstract: A digital computer arrangement is disclosed including a central processing unit, a plurality of peripheral units coupled to a peripheral bus, a memory access controller, a first memory bus, and a second memory bus. The first memory bus serves a first plurality of memory units and the second memory bus serves a second plurality of memory units. The memory access controller selects which of the peripheral units may use the peripheral bus to access a memory bus during a particular time interval. If use of a particular memory bus is requested by a peripheral unit for an interval in which that memory bus is required by the central processing unit, the memory access controller preempts the usage of that memory bus by the peripheral unit for the interval.

Abstract: In pulse amplitude modulated time division switching systems, noise and crosstalk often result because the time division switches used to connect individual channels to a common bus are not perfect open circuits when they are in the off-state. The switches in the off-state possess a small parasitic capacitance which couples energy on the common bus to the channel resulting in a noise signal during time slots which are not associated with the channel. A method is disclosed for substantially reducing crosstalk and noise induced by stray capacitances without increasing the complexity of the time division switch. Each pulse on the common bus is converted into a bipolar pulse in which positive and negative portions have equal average values. In addition, the timing of each of the time division switches is modified to extract the desired signal by sampling the first portion of the bipolar pulse in the appropriate time slot for that channel, and rejecting the second portion of the bipolar pulse.

Abstract: This specification discloses a time division communication system having a plurality of line circuits for coupling telephones over bidirectional lines to outgoing and incoming time division buses. Each of the line circuits comprises an active hybrid having separate transmit and receive operational amplifiers for connecting the outgoing and incoming buses to a telephone line via interface circuitry and during selected time slots of a time division frame. The interface circuitry comprises transformer and capacitor arrangements for coupling a bidirectional telephone line via a filter to an input of the hybrid transmit amplifier and an output of the receive amplifier. The filter together with a phase lead compensation network, a negative feedback resistor and a resistor-capacitor bias arrangement cooperate to control hybrid balance, stability and frequency response.