Abstract: An improved solid state isolation device that uses opto-isolators to provide an electrical barrier between a telephone network and user telephone equipment includes a load and current control circuit, and an adjustable termination circuit to eliminate or reduce signal distortion and insensitivity to low signal levels resulting from low loop current, and lack of complex impedance compensation/termination for diverse telephone system parameters. An improved trans-hybrid return loss circuit reduces internal losses; while loop termination losses are reduced by the use of Shottky diodes in the line coupler circuit. A high pass filter improves common mode rejection ratios in the transmit and receive paths, and adjustable compensation is provided to account for manufacturing variances in the opto-isolators. An additional connection is also provided to adapt the opto-isolator circuit for use with 3-wire ring circuitry.

Abstract: An isolation circuit (20) that is devoid of coupling transformers and yet suitable for use as a telephone line interface. The circuit is characterized by very wide bandwidth, low noise, and high linearity. Opto-isolators couple analog transmit and receive channels in a user device (12) across an isolation barrier (57) to a line pair for full duplex communication on the line pair. The interface circuit, which also includes a hybrid (55), includes first and second oppositely directed linear optocouplers (50,52). The first is disposed between the transmit channel and the hybrid; the second between the receive channel and the hybrid.

Abstract: A device having a universal receiver transmitter, a modem, and a mode selector switch. The mode selector switch is used to switch the serial data side of the universal receiver transmitter between the modem and the host terminal whereby the universal modem receiver transmitter can be substituted into a host terminal where a universal receiver transmitter had been located, and the universal modem receiver transmitter can perform the function of the universal receiver transmitter or can perform as a universal receiver transmitter and modem, facilitating data format conversion between formats appropriate to the host terminals parallel data bus and a format appropriate for telephone line data transmission.

Abstract: A remote-telemetry unit for monitoring and reporting to a remote location over a telephone line the condition of an associated piece of equipment at predetermined times, when polled and when the equipment condition dictates, the unit including a direct access arrangement, a switched-frequency Friend Biquad type filter and a detector, the combination for detecting tone signals developed on the line, and a digital-to-analog converter and a controller, in combination with the direct access arrangement for developing on the line tone signals for dialing and for condition reporting.

Abstract: An improved solid state isolation device that uses opto-isolators to provide an electrical barrier between a telephone network and user telephone equipment includes a load and current control circuit, and an adjustable termination circuit to eliminate or reduce signal distortion and insensitivity to low signal levels resulting from low loop current, and lack of complex impedance compensation/termination for diverse telephone system parameters. An improved trans-hybrid return loss circuit reduces internal losses; while loop termination losses are reduced by the use of Shottky diodes in the line coupler circuit. A high pass filter improves common mode rejection ratios in the transmit and receive paths, and adjustable compensation is provided to account for manufacturing variances in the opto-isolators. An additional connection is also provided to adapt the opto-isolator circuit for use with 3-wire ring circuitry.