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US 4,731,827 AGranted
Interswitch line circuit
AssigneeDavid Systems, Inc.
InventorSamuel F. Wood
Life of this patent
Estimating the term…
Abstract
A tip-ring interface that utilizes a single detector to detect ringing, forward loop current, and reverse loop current. In one embodiment, forward or reverse battery state may be detected when on-hook.
Claims8
A method for determining the direction of loop current flow in a telephone loop circuit comprising the steps of:
- generating an input voltage with the polarity of said input voltage indicating the direction of said loop current;
- providing a bias voltage having a magnitude less than the magnitude of said input voltage;
- switching the polarity of said bias voltage according to a preselected time sequence;
- comparing said input voltage to said bias voltage to generate an output signal indicating whether said input voltage is of opposite polarity from said bias voltage;
- sampling said output signal at times t.sub.1 and t.sub.2 where the bias voltage is in a first polarity state at t.sub.1 and a second polarity state at t.sub.2 ;
- and
- comparing the sampled output signal to the first and second bias voltage polarity states to determine whether the input voltage is of opposite polarity from said first or said second bias voltage polarity state.
4 more elements
A tip-ring interface connecting a C.O. or PABX line circuit and a telephone set comprising:
- an A.C. resistive network for providing an A.C. input voltage state;
- a D.C. resistive network for providing a D.C. input voltage state;
- means for generating a bias voltage state of preselected magnitude, polarity, and duration;
- means for forming a sum of a selected one of said input voltage states and said bias voltage state;
- a comparator, adapted to receive said sum at its inputs, for producing an output signal that indicates whether said selected one of said input voltage states is of opposite polarity and greater magnitude than said bias voltage state;
- and
- means for switching the polarity of said bias voltage state according to a preselected time sequence.
4 more elements
An apparatus for determining the polarity of an externally supplied input voltage, V.sub.i, comprising:
- means for providing a reference voltage V.sub.b ;
- means for selectively switching the polarity of V.sub.b between the values positive V.sub.R and negative V.sub.R, where the absolute value of V.sub.R is less than the absolute value of V.sub.i ;
- means for algebraically adding V.sub.i to V.sub.b to form the algebraic sum of V.sub.i +V.sub.b ;
- a comparator, having inputs adapted to receive the sum of V.sub.i +V.sub.b, said comparator for producing an output signal, V.sub.O, representing a logic 1 when the algebraic sum of V.sub.i +V.sub.b is greater than 0 and for producing an output signal, V.sub.O, representing a logic 0 when the algebraic sum of V.sub.i +V.sub.b is less than 0;
- means for sampling V.sub.O at times t.sub.1 and t.sub.2 where V.sub.b is equal to positive V.sub.R at t.sub.1 and V.sub.b is equal to negative V.sub.R at t.sub.2 ;
- and
- means for comparing the sampled value of V.sub.O to the polarity of V.sub.b to determine the polarity of V.sub.i.
4 more elements
Dependencies are inferred from the claim text.