Bilateral current source for a multi-terminal intercom
AssigneeRTS Systems, Inc.
InventorStanley L. Hubler
Life of this patent
Estimating the term…
Abstract
A bilateral current source operates as a two-wire to four-wire converter circuit for an intercom system. The circuit provides a high impedance current driver for putting a local voice signal on the common line connecting the intercom stations. The same circuit acts as a buffer amplifier for connecting voice signals received on the same line to a listening device such as a speaker. The circuit suppresses any sidetones by preventing the local voice signal from being coupled to the listening device.
Claims9
In a system having a plurality of stations for either transmitting or receiving signals over a single line pair, a two-wire to four-wire converter circuit, comprising:
- a differential amplifier having first and second input terminals and an output terminal, a signal source, means including a first resistor connecting the first input terminal of the differential amplifier to said source, asecond resistor connecting the second input terminal to a reference voltage, a first feedback resistor connecting the first input terminal to the output terminal of the amplifier, second and third feedback resistors in series connecting the second input terminal to the output terminal of the amplifier, impedance means including a potentiometer connected in shunt across the amplifier and first resistor between the source and the output terminal of the amplifier, an output load connected to the tap of the potentiometer for preventing signals from said signal source from appearing at said output load, and means connecting one wire of said line to the series junction of said second and third feedback resistors.
A circuit for transmitting an audio signal from a local source to a communication line and for coupling an audio signal received on the line to a local load, said circuit comprising:
- a differential type operational amplifier having a negative input terminal, a positive input terminal and an output terminal, means including a first resistor connecting the audio signal from said local source to the negative input terminal, a second resistor connecting a reference voltage to the positive input terminal, a third resistor connecting the output terminal to the negative input terminal, fourth and fifth series resistors connecting the output terminal to the positive input terminal, first impedance means connecting the input to the first resistor from the local source to said output terminal, means connecting the local load to the output terminal through a portion of the first impedance means for preventing signals from said local source from appearing at said local load, and second impedance means connecting the communication line to the series junction between the fourth and fifth resistors.
Dependencies are inferred from the claim text.