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TELEPHONE INTERFACE CIRCUIT

  • US 20080181391A1
  • Filed: 01/31/2007
  • Published: 07/31/2008
  • Est. Priority Date: 01/31/2007
  • Status: Active Grant
First Claim
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1. A telephone interface circuit comprising:

  • a speech circuit;

    a transistor which turns on, in an off-hook state, to connect the speech circuit to telephone lines and which turns off, in an on-hook state, to disconnect the speech circuit from the telephone lines;

    a capacitor for storing an electric charge to turn on the transistor;

    a charging circuit for charging the capacitor with electric power supplied by the telephone lines;

    a hook switch for turning on the transistor by connecting a positive electrode terminal of the capacitor to an electric current control terminal of the transistor in an off-hook state, and for turning off the transistor by disconnecting the positive electrode terminal from the electric current control terminal in an on-hook state in order to; and

    a holding circuit for holding a voltage at the positive electrode terminal at a substantially fixed value by charging the capacitor with the electric power supplied from the telephone lines in an off-hook state.

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