Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
  • H04B1/40—Circuits
  • H04B1/54—Circuits using the same frequency for two directions of communication
  • H04B1/58—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M19/00—Current supply arrangements for telephone systems
  • H04M19/001—Current supply source at the exchanger providing current to substations
  • H04M19/005—Feeding arrangements without the use of line transformers

Definitions

• hybrid transformers are utilized to provide signal conversion from the balanced, bidirectional subscriber end loop signal path to a pair of unidirectional signal paths.
• These trans ⁇ formers must be well matched with the hybrid transformers located at the telephone central office equipment to insure good AC impedance matching between the termination signal paths and the bidirectional transmission path in order to reduce and/or eliminate signal echo returns.
• These transformers are generally very bulky and expensive.
• impedance matching is not easily adjusted using conventional transformers. Therefore, commun cations systems utilizing such transformers utilized in a modem application may have degraded performance.
• FIG. 2 illustrates the electronic terminator circuit of the present invention which comprises the SLIC of FIG. 1. Detailed Description of the Invention
• SLIC 10 is typically located at the telephone central office and is adapted to be coupled at Tip and Ring terminals 12 and 14 via telephone lines to a subscriber loop.
• the subscriber loop generally comprises a telephone for providing bidirectional signal transmission.
• incoming signals appearing at VRX for example, signals transmitted through the central exchange from a calling party
• SLIC 10 is received by SLIC 10 and converted to proportional differential signals at terminals 12 and 14. Therefore, transhybrid reception is realized by converting the AC coupled received signals through capacitor 16 through resistor 18 to a current which is processed via SLIC 10 to drive the two-wire output line coupled at terminals 12 and 14 via PNP and NPN Darlington transistors 20, 22 and resistors 24, 26 with a balanced AC current proportional to the receive input voltage.
• the line i.e., a current is sourced through transistor 20, and resistor 24. This current is returned through the subscriber loop to SLIC 10 via resistor 26 and transistor 22. Additionally, the DC current flowing through the subscriber loop produces a voltage across Tip and Ring terminals 12 and 14 which is sensed and converted to a current flow through resistor 36, the TSI input, and resistor 38 through the RSI input.
• Terminator circuit 100 can be used in many modem applications. For example, a speaker-phone could be coupled to terminals 106 and 108 such that the speaker would be coupled to terminal 108. The speaker-phone microphone would then be coupled to terminal 106 whereby two-way voice communication could be conducted through terminator 100 and the telephone system. Teletype equipment could be coupled at terminals 106 and 108 as another example of an application of terminator 100.
• a DC current would be sourced to Tip terminal 102 to resistor 38 and transistor 22 of terminator 100 and terminator 100 would source a DC current to Ring terminal 104 to the SLIC at the central office.
• the current sourced from the central office to terminator 100 would be equal to the current sourced from terminator 100 to the central office equipment with the DC voltage across Tip and Ring terminals being substantially equal to (VQC-VEE)/ .
• VQC-VEE DC voltage across Tip and Ring terminals
• the DC feedback path has been changed to prevent the aforementioned offset problem from occurring.
• the emitter of transistor 22 is now coupled through current sensing resistor 120 to the EN terminal of SLIC 10 whereas before, as shown in FIG. 1, the emitter was directly returned to the EN terminal.
• the DC current sourced from the central office equipment to Tip terminal 102 is sourced through transistor 22 through resistor 120.
• the current through resistor 120 establishes a voltage at the emitter of transistor 122.
• Transistor 122 the current flow therethrough being determined by resistor 124, has its collector returned to its base through resistor 126 and functions as a diode of a well known current mirror circuit such that the voltage appearing at node 128 is a function of the current through resistor 120.
• Resistor 130 coupled between node 128 and the base of transistor 132 (transistor 132 being matched to transistor 122) being of equal value as resistor 126 causes the voltage at the emitter of transistor 132 to be equal to the voltage at the emitter of transistor 122.
• the current through transistor 132 is made a function of the value of resistor 134 which is coupled between the emitter of transistor 132 and EN.
• the collector current sourced through transistor 132 is made proportional to the current sourced to Tip terminal 102. This forms a current source at the TSI terminal of SLIC 10.
• a high gain internal C-circuit of SLIC 10 is coupled to the RSI and TSI terminals which causes the bias on transistors 20 and 22 to be varied if the TSI and RSI sensed currents are not equal.
• the current sourced by transistor 132 causes the transistors 20 and 22 to adjust to an equili ⁇ brium wherein the currents through resistors 124 and 136 are equal; these resistors being of equal value with resistor 136 being coupled between ground and the RSI input of SLIC 10 of terminator 100.
• the gain of the internal C-circuit thereof is approximately 95 wherein resistor 134 is made 95 times greater than resistor 120.
• an electronic terminator circuit as described above has been built and tested utilizing an MC3419 subscriber loop interface circuit having the following component values: Transistor 20 MJE271 Transistor 22 MJE270 Resistor 36 17.4 ohms Resistor 38 17.4 ohms Resistor 120 20 ohms Resistor 124 180K ohms Resistor 126 20K ohms Resistor 130 20K ohms Resistor 134 1.9 ohms
• Resistor 136 180K ohms Capacitor 116 1.0 yF Capacitor 118 1.0 yF Capacitor 138 2.0 yF

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Power Engineering (AREA)
• Computer Networks & Wireless Communication (AREA)
• Interface Circuits In Exchanges (AREA)
• Devices For Supply Of Signal Current (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

Country Status (4)

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Citations (2)

Family Cites Families (5)

• 1982
  • 1982-08-03 CA CA000408607A patent/CA1177985A/fr not_active Expired
  • 1982-08-06 EP EP19820902779 patent/EP0089350A4/fr not_active Withdrawn
  • 1982-08-06 JP JP50274782A patent/JPS58501529A/ja active Pending
  • 1982-08-06 WO PCT/US1982/001068 patent/WO1983001162A1/fr not_active Application Discontinuation

Patent Citations (2)

Non-Patent Citations (2)

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