Apparatus for transmitting and/or receiving balanced signals on a two-wire telecommunication line
Patent 4485277 Issued on November 27, 1984. Estimated Expiration Date: 
February 18, 2002. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
February 18, 2002. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3855430 Wide-band hybrid network Transmission networks for telephone system Two to four wire hybrid circuit Hybrid circuit Patent #: 4380690 InventorsAssigneeApplicationNo. 06/350028 filed on 02/18/1982US Classes:379/345, Including two-to-four wire conversion or hybrid circuit379/402Hybrid circuitExaminersPrimary: Rubinson, Gene Z.Assistant: Myers, Randall P. Attorney, Agent or FirmInternational ClassesH04B 1/54 (20060101)H04B 1/58 (20060101) AbstractA transformerless hybrid circuit arrangement for a subscriber line interface circuit of a telecommunications exchange is disclosed. A preferred embodiment of the hybrid arrangement comprises a first and a second operational amplifier plus a differential amplifier connected together in the following manner: The non-inverting input of the first operational amplifier is connected to a first reference voltage and the output of this amplifier is connected (1) via a first resistor to one wire of the two-wire subscriber line, and (2) via a third resistor to the inverting input of the amplifier. The non-inverting input of the second operational amplifier is connected to a second reference voltage and to the receiving branch of the four-wire line of the telecommunications exchange. The output of this second operational amplifier is connected via a second resistor to the other wire of the two-wire subscriber line, via a fourth resistor to the inverting input thereof and via a fifth resistor to the inverting input of the first operational amplifier. Each of the two inputs of the differential amplifier are connected, via respective resistors, to one wire of the two-wire subscriber line and to the output of that operational amplifier which is connected to the other wire of the two-wire subscriber line. The output of the differential amplifier is connected to the transmitting branch of the four-wire line of the exchange.Other References
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