US 4,815,124 A · DX circuit

Abstract

An improved DX circuit may be connected to signaling and reference leads of a DX signaling link, without need to balance the internal impedance of the DX circuit against that of the external DX signaling link. The DX circuit senses the magnitude and direction of current flow on the leads, and operates on the principle that when a near end signaling circuit is on-hook, a positive current flow indicates that a far end signaling circuit is off-hook and a current flow of zero indicates that it is on-hook, while if the near end signaling circuit is off-hook, a negative current flow indicates that the far end signaling circuit is on-hook and a current flow of zero indicates that it is off-hook. The arrangement allows the DX circuit to properly function irrespective of the resistive load presented by the DX signaling link. To enable the DX circuit to function with various capacitive loads, it also detects the rate of change of current on the leads and, in the absence of a change in status of the near end signaling circuit, provides an output representative of a change in the on-hook/off-hook status of the far end signaling circuit, immediately upon detecting a sufficient rate of change.

Claims19

Dependent claims

A DX circuit for connection between E and M leads of a signaling circuit and a pair of leads at one end of a DX signaling link, to convert E and M signaling to DX signaling, and vice versa, wherein DX signals are introduced onto a distant end of the signaling link in response to E and M signaling at the distant end, said DX circuit comprising status detector means for sensing the value of a signal on one of the E and M leads of the one end signaling circuit and for generating and applying a status voltage, across the signaling link leads, having a value in accordance with the signal on the one of the E and M leads of the one end signaling circuit indicating an off-hook or an on-hook status of the one end signaling circuit;

current detector means for sensing the magnitudes and polarities of current flows on the signaling link leads and for generating a control voltage having a value in accordance with the difference between the current flows;
and output circuit means, coupled with said status detector means and said current detector means, for generating and applying onto the other of the E and M leads of the one end signaling circuit an output signal having a value in accordance with the values of said control and status voltages, to indicate an off-hook or an on-hook status of a signaling circuit at the distant end of the signaling link.

A DX circuit for connection between E and M leads of a signaling circuit and a pair of leads at one end of a DX signaling link, to convert E and M signaling to DX signaling, and vice versa, wherein DX signals are introduced onto a distant end of the signaling link in response to E and M signaling at the distant end, said DX circuit comprising status detector means for connection with one of the E and M leads of the one end signaling circuit for sensing the on-hook/off-hook status of the one end signaling circuit and for generating and applying a first or a second voltage across the pair of signaling link leads in accordance with the status being off-hook or on-hook, respectively;

a current-to-voltage converter for sensing the current flows on the pair of signaling link leads and for generating a control voltage having a value in accordance with the difference between the current flows;
and output circuit means, coupled with said current-to-voltage converter and said status detector means, for applying onto the other of the E and M leads of the one end signaling circuit a signal having a first state when the value of said control voltage and the voltage being generated by said status detector means indicate that a signaling circuit at the distant end of the signaling link is off-hook, and a signal having a second state when the value of said control voltage and the voltage being generated by said status detector means indicate that the distant end signaling circuit is on-hook.

A method of converting E and M signaling on E and M leads of a signaling circuit to DX signaling on a pair of leads at one end of a DX signaling link, and vice versa, wherein DX signals are introduced onto a distant end of the DX signaling link in response to E and M signaling at the distant end, said method comprising the steps of detecting the on-hook/off-hook status of the one end signaling circuit as indicated by the status of a signal on one of the E and M leads of the one end signaling circuit;

applying a first or a second voltage across the pair of signaling link leads in accordance with the status of the signal indicating off-hook or on-hook, respectively;
sensing the magnitudes and polarities of current flows on the pair of signaling link leads;
generating a control voltage, having a value of V, greater than V (>V) or less than V (<V) in accordance with the difference between the sensed current flows;
determining, in accordance with the status of the signal and the value of the control voltage, the on-hook/off-hook status of a signaling circuit at the distant end;
and applying onto the other of the E and M leads of the one end signaling circuit a signal having a first or second state in accordance with the determined status of the distant end signaling circuit being off-hook or on-hook, respectively.

2 more elements

Dependencies are inferred from the claim text.

DX circuit

Life of this patent

DX circuit

Life of this patent

Abstract

Claims19