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Channel unit interface circuit

  • US 4,993,063 A
  • Filed: 12/27/1988
  • Issued: 02/12/1991
  • Est. Priority Date: 03/03/1987
  • Status: Expired due to Term
First Claim
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1. In a communication system including a channel unit interface circuit for interconnecting a two-wire, bidirectional signal transmitting means and a four-wire digital signal transmitting means, and a two-wire port having tip and ring terminals adapted for connection to the two-wire means, the improvement comprising:

  • tip terminal transconductance amplifier driver means having a first input coupled to receive incoming tip terminal "DC band" frequency signals from said four-wire means, a second input coupled to receive incoming tip terminal "voice band" frequency signals from said four-wire means, a third input coupled to the tip terminal of said two-wire port, and an output connected to the tip terminal;

    first feedback impedance means coupled between the tip terminal and the third input of said tip terminal transconductance amplifier driver means and being responsive to incoming tip terminal "DC band" frequency signals from said two-wire means for generating a simulated tip terminal impedance;

    ring terminal transconductance amplifier driver means having a first input coupled to receive the incoming ring terminal "DC band" frequency signals from said four-wire means, a second input coupled to receive the incoming ring terminal "voice band" frequency signals from said four-wire means, a third input coupled to the ring terminal of said two-wire port, and an output connected to the ring terminal;

    second feedback impedance means coupled between the ring terminal and the third input of said ring terminal transconductance amplifier driver means and being responsive to incoming ring terminal "DC band" frequency signals from said two-wire means for generating a simulated ring terminal impedance;

    said tip terminal transconductance driver means being formed of a first switching operational amplifier having a non-inverting input, an inverting input, and an output, said tip driver means further including a first input resistor coupled between its first input and the non-inverting input of said first switching operational amplifier to receive the tip terminal "DC band" frequency signals from said four-wire means, a second input resistor coupled between its third input and the inverting input of said first switching operational amplifier, an output sense resistor coupled between the output of said first switching operational amplifier and the output of said tip driver means, a negative feedback resistor coupled between the output of said first switching operational amplifier and the inverting input of said first switching operational amplifier, and a positive feedback resistor coupled between the output of said tip driver means and the non-inverting input of said first switching operational amplifier;

    said ring terminal transconductance driver means being formed of a second switching operational amplifier having a non-inverting input, an inverting input, and an output, said ring driver means further including a first input resistor coupled between its first input and the non-inverting input of said second switching operational amplifier to receive the ring terminal "DC band" frequency signals from said four-wire means, a second input resistor coupled between its third input and the inverting input of said second switching operational amplifier, an output sense resistor coupled between the output of said second switching operational amplifier and the output of said ring driver means, a negative feedback resistor coupled between the output of said second switching operational amplifier and the inverting input of said second switching operational amplifier, and a positive feedback resistor coupled between the output of said ring driver means and the non-inverting input of said second switching operational amplifier;

    each of said first and second switching operational amplifiers including of a low voltage transconductance amplifier, high voltage comparator means, a filter network having an input and an output, and feed forward compensation amplifier means;

    said low voltage transconductance amplifier having a non-inverting input defining the non-inverting input of said switching operational amplifier, an inverting input defining the inverting input of said switching operational amplifier, and an output for generating a slowly varying control signal;

    said high voltage comparator means having a first input, a second input, and an output, the first input of said high voltage comparator means being coupled to the output of said low voltage transconductance amplifier;

    the input and output of said filter network being coupled between the output of said high voltage comparator means and the output of said switching operational amplifier; and

    said feed forward compensation amplifier means being coupled between the output of said low voltage transconductance amplifier and the output of said filter network.

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