Abstract: The subject array structure provides a large current mirror array which generates a plurality of substantially equal output currents from high impedance sources in response to at least one input control current. This array structure reduces the control current deviation problem of prior art current mirror circuits.

Abstract: The subject channel interface circuit functions to provide a high speed interface between a processor and a data link, which link carries data messages having virtual addresses. The message handler is programmable and serves to translate the header portion of the data message from a virtual address into a hardware memory address, which is used to activate a specific location in the processor memory. The data portion of the data message is then directly inputted to this memory location (i.e., DMA) and the appropriate file pointers are reset. When a complete file is received and stored in memory, the message handler generates a processor interrupt.Thus, the subject message handler performs all the data receiving tasks, including file storage and linking, without requiring the involvement of the associated processor.

Abstract: The subject precision isolation amplifier adds error correction circuitry to a basic isolation amplifier circuit to thereby produce an error-free output signal comprising only the metallic component of the monitored voltages. The error correction circuit consists of a pair of up/down emitter followers and a current mirror circuit which function to eliminate both the longitudinal components of the monitored voltage signals and the voltage offset generated by the basic isolation amplifier. A second error-free ouput signal comprising only the longitudinal component of the monitored voltage signals is also provided.

Abstract: The loop switching system of this invention overcomes the problems of prior art loop switching systems by providing dynamic rearrangeability of loop switching systems. In particular, the subject loop switching system is comprised of a number of port circuits or nodes serially connected together to form one or more loops. The interconnection of these various ports into one or more loops is implemented on a dynamic basis by means of a central switching matrix.

Abstract: Electronic battery feed circuits are connected across the communication pair, in parallel with the voice transformer, and serve as a dc path for loop current. These electronic battery feed circuits must provide both a low dc impedance to sink loop current and a high ac impedance so as not to shunt the ac signal away from the transformer. Prior art electronic battery feed circuits draw their bias current directly from the communication pair and this configuration tends to unbalance the line, provide too low an ac impedance, and provide too high a dc impedance. The subject electronic battery feed circuit obtains a low level bias current from the voice transformer and presents a low dc impedance to loop current. This particular circuit configuration eliminates hybrid balance problems and ac shunting of the voice transformer.

Abstract: The subject circuit is a converter/isolation circuit which employs only a few components yet functions to monitor a particular signal and produce an output signal which is identical to or proportional to (to a high degree of accuracy) to the monitored input signal. The subject circuit monitors a voltage and generates both a current and a voltage as output signals.

Abstract: The subject sampling filter employs fractional period displacement of samples to force additional nulls in the filter characteristic response. This sampling method and cascading antialiasing filters provides a filter structure which minimizes the complexity of the circuit yet which provides great flexibility to implement a desired filter characteristic.

Abstract: The disclosed four-wire to two-wire converter employs a pair of dual detector opto-isolator circuits to both linearize the converter transfer characteristic and eliminate signal feedback between ports. This is accomplished by feeding back the signals transmitted by the transmit portion of the four-wire port through the auxiliary detector of the opto-isolator circuit connected across the two-wire port to prevent signal feedback to the receive portion of the four-wire port. This opto-isolator feedback arrangement eliminates the need for complex feedback and impedance matching circuitry thereby enabling direct connection of the opto-isolator circuits to the communication paths while also rendering the converter circuit transparent to signals appearing thereon.

Abstract: The disclosed signal multiplexing circuit (110) makes use of a single pair of wires (T, R) to interface a data and voice communication circuit such as an electronic key telephone (EKT) station set (100) with a central data and voice communication system such as a communication system (BCS). The signal multiplexing circuit transmits outgoing standard voice signals, outgoing auxiliary signals and outgoing data and, in turn, simultaneously receives incoming standard voice signals, incoming data and incoming auxiliary signals on the single pair of wires. Both time division and frequency separation techniques are concurrently employed to achieve multiple use of the single pair of wires without crosstalk between the plurality of signals. The data signals are transmitted as bipolar bit pairs preceded by a data start pulse pair. The outgoing data bipolar bit pairs are delayed until the center transition of the incoming data bipolar pulse pair is detected.