Abstract: A telephone paystation coin refund and collect circuit for operating a coin relay with power obtained from a two-wire business telephone line. The circuit employed utilizes charge storage capacitors and MOS-FET transistors for current pulsing of the relay coil with current flow in either direction as determined by a signal from an associated microprocessor controller.

Abstract: An amplifier having properties of natural side tone balancing based on the utilization of a bridge arrangement, high efficiency with resulting high gain, high AC impedance and compatibility with electret microphones and electret microphone amplifiers. A matched pair of differential transistors arranged as part of a bridge circuit form a detector of the receive signal at one input versus a transmit signal which appears at both inputs in the same phase and therefore is rejected as a common mode signal. The resultant balancing of side tone and high gain finds particular application in telephone networks where the characteristics dictate the need for higher than usual receive gain or for use by auditorially handicapped users over a normal telephone network.

Abstract: A method and system for detection of authorized connections to a telephone line where such connections are for the purposes of intercepting voice or data messages. The original or base line impedance would be measured by the system in response to the entry of a special code. The base line is stored in memory and used for subsequent impedance comparisons.

Abstract: An electronic telephone instrument circuit capable of dialing (address signaling) in either pulse or tone mode. The circuitry permits the placement of a call through a rotary dial only system into a second network that is of a tone only nature. The included circuitry has very high return loss and relatively high level of tone capability and is designed to function with a variety of types of dialer integrated circuits. The present circuitry provides part of its DC current supervision while in the voice mode through the included tone amplifiers circuit thereby minimizing components and reducing current load through the voice network.

Abstract: A transistorized current amplifier based on a cascode stage feeding into a composite transistorized output stage. The amplifier employs a constant current source, decoupling (isolation) from the power source and a signal limiting network to lower distortion on high signal input conditions. A two-wire device, the amplifier derives signal and power from a telephone line. Surge protection is provided by a signal limiting network and the inclusion of relatively high value resistors in the circuit.

Abstract: A circuit providing a message waiting indication using a light emitting diode and a constant current surge protected circuit for use with PABX extension telephone instruments. Recently developed light emitting diodes operated with current of one milliampere or less are effectively used in the present circuitry which limits current to the device in the operating mode and also as low leakage current while in the "off" mode.

Abstract: A temperature compensated voltage reference circuit adapted for on chip location with integrated bi-polar linear circuits, where a temperature stable reference voltage is required in the range of 1.2 to 2.0 volts DC. The circuitry requires only a low chip area and presents a high AC impedance, a low operating current drain, and requires no high value resistors or capacitors.

Abstract: An electrical circuit functioning as a temperature sensor which is fully compatible with silicon chip and similar integrated circuit technology. Four matched NPN bi-polar transistors provide a circuit that detects changes in temperature by monitoring the current throughput in operation. Environmental temperatures increase current approximately one order of magnitude for each 25 degrees centigrade of changing temperature. With a current gain of 100 for each transistor employed, the current increases from 0.1 microamp at 0 degrees centigrade to 11 microamps at 50 degrees centigrade.

Abstract: A snubber circuit for use with hold circuits employed in telecommunication applications that employ an SCR as the principle control device. The included circuit prevents false hold turn on in response to static discharge. Voice band impedance and ringing signals are not adversely affected by the addition of the circuit to a standard SCR type hold circuit.

Abstract: The present invention consists of a subcircuit which may be employed in integrated circuit technology to provide the necessary drop from a relatively high voltage source and to provide base current for biasing of associated transistorized circuitry. Each subcircuit employs four transistors and one resistor and provides an effective drop from approximately 1.1 volts when it is desired to provide at least 2 microamps of bias circuit. Additional subcircuits of similar configuration can be placed in series with the present circuitry to increase the amount of voltage drop in accordance with the requirements of the associated circuitry.

Abstract: A protective circuit for use in a subscriber's telephone circuit that includes a repertory memory and includes a battery which provides memory retention current. Circuitry permits the battery to be protected by a series current limiting resistor while maintaining sufficient voltage so that the memory maintains its integrity.

Abstract: A protective circuit consisting of two diodes which functions along with other external circuit elements to provide protection against transients for an integrated circuit utilized to generate dial pulses in an electronic telephone circuit. By means of included diodes, excessive transients are prevented from entering the integrated circuit internal circuitry and disturbing the memory included therein or other operational characteristics.

Abstract: A hold circuit for use with a single line telephone which may or may not be equipped with extension instruments. The circuitry in response to the momentary operation of a manual switch actuates a siliconcontrolled rectifier to place a resistive load across the telephone line thus allowing the subscriber at the basic telephone instrument to go "on hook". Subsequent removal of the basic instrument handset from the hookswitch or an extension phone going "OFF HOOK" will cause the resistive load to be removed. Also included is a hold release circuit which automatically disconnects the hold circuit after a predetermined period of time.

Abstract: An interface circuit for use with a telephone or PABX system or as a device applied to a subscriber's telephone line, that detects ringing voltage signals and either indicates the ringing condition visually or optically couples a detection signal to other annunciator or control devices such as microprocessors. The device conforms to the requirements and limitations for application of a device to the public telephone system. This device does not respond or interfere with voice or data signals nor address signaling.

Abstract: An amplifier combining the properties of high gain, wide band audio response with input signal conditioning, constant current output for use on two wire systems and compound negative feedback for resistance to oscillation in acoustic feedback environments. The direct coupled amplifier combines a modified cascode stage with a composite connected transistor output stage. It is intended primarily for use in two wire communication of voice transmission such as in telephone handsets or telephone instruments.

Abstract: An electret microphone gain regulation circuit employing an active load for use in high quality telephone instruments or handsets where two terminal electret microphones of the current source type are employed. The circuitry provides a heavier load on short loops and a lighter load on long loops to regulate the signal level at its output.

Abstract: A hold circuit for use with a single line telephone operable over long or short telephone loops. The included circuit during response to the momentary operation of a manual switch actuates a silicon controlled rectifier to place a resistive load across the telephone line thus allowing the subscriber at the telephone instrument to go "on-hook". Subsequent removal of the basic instrument handset from the hook-switch, or of a related extension telephone going "off-hook", will cause the resistive load to be removed.

Abstract: In a hold circuit including a relay normally latched and connecting the hold circuit to a subscriber telephone line, a first hold release circuit outputs a trigger signal to a silicon controlled rectifier turning on the rectifier responsive to a sensed drop in line potential, thereby providing an electrical path for the discharge of a capacitor. The capacitor discharges through the coil of the relay unlatching the relay and releasing the hold circuit from the line. The hold circuit is also arranged to be released by a second hold release circuit which outputs a trigger signal to the silicon controlled rectifier responsive to a pre-arranged timing interval.

Abstract: A telephone substation transmitter muting circuit used in a substation having a hold function wherein, a transistor turns on connecting a muting network across the handset transmitter whenever the hold circuit is activated.

Abstract: In a hold circuit including a silicon controlled rectifier (SCR) normally turned on and connecting the hold circuit to a subscriber line, a first hold release circuit outputs a trigger signal to a transistor turning off the transistor and disconnecting a line seizing network. A second hold release circuit outputs a trigger signal to a second transistor responsive to the line seizing network being disconnected. The second transistor connects a load resistor across the SCR dropping the holding current flowing through the SCR causing it to turn off. The second hold release circuit is also arranged to output its trigger signal to the second transistor responsive to a pre-arranged timing interval.