US 5,636,273 A · Integrated ring detection circuit and power cross detection circuit with persistence timers

Abstract

An apparatus for determining a power cross condition during a ringing state of a telephone. The apparatus also is capable of distinguishing a true power cross condition from a short loop ringing condition, by including a first path for receiving a signal indicative of a voltage across a ring feed resistor exceeding a predetermined value, and determining if that voltage is in an active state for a predetermined amount of time (i.e., 14 milliseconds). The apparatus also includes a second path for receiving a first and second current that flow respectively across a first and second sense resistor connected to opposite ends of the ring feed resistor. On the second path, the first and second currents are subtracted, converted to a digital value, filtered, and compared to a threshold value to determine if a ring trip has occurred. If so, the potential ring trip is sent to a persistence timer circuit, for checking if it is in an active state for a predetermined amount of time (i.e., 104 milliseconds). If either of the first and second paths indicate a ring trip, then the apparatus outputs a ring trip detection signal. The apparatus also is configured to work with a power cross validation circuit, which may be connected on a third path for switching ring relays quickly to save components on the telephone lines during a power cross occurrence.

Claims20

Dependent claims

An apparatus for detecting the presence of an off-hook condition of a telephone connected by a first and a second ring relay being in a first state to a ring line and a tip line when said telephone is in a ringing state and for connecting said telephone to a surge protection circuit by switching said first and second ring relays to a second state when said telephone is in both said off-hook condition and in said ringing state, said ring line including a ring feed resistor connected thereto, comprising:

a ringing current sensor circuit connected to said ring line and configured to output a first voltage signal when a voltage measured across said ring feed resistor exceeds a predetermined voltage value and to output a second voltage signal indicative of a ringing current;
a first persistence timer circuit connected to receive said first voltage signal over a first path from said ringing current sensor circuit and to output a first timer signal when said first voltage signal is active for at least a first predetermined amount of time;
a digital signal processor connected to receive said second voltage signal over a second path from said ringing current sensor circuit and to output a digital signal indicative of said ringing current;
a second persistence timer circuit connected to receive said digital signal from said digital signal processor and to output a second timer signal when said digital signal is active for at least a second predetermined amount of time;
and
a logic circuit connected to receive said first and second timer signals and to output a ring trip bit indicative of a ring trip condition when either one of said first and second timer signals are active,
wherein said apparatus detects both a short loop ring trip condition and a long loop ring trip condition.

4 more elements

An apparatus for detecting the presence of an off-hook condition of a telephone connected to a ring line and a tip line when said telephone is in a ringing state and for connecting said telephone to a surge protection circuit when said telephone is in both said off-hook condition and in said ringing state, said ring line including a ring feed resistor connected thereto, comprising:

means for determining when a voltage measured across said ring feed resistor exceeds a first predetermined voltage value and outputting a first signal indicative thereof;
means for measuring a loop current flowing across said ring and tip lines and outputting a second signal indicative thereof;
means for determining if said first signal is in an active state for at least a first predetermined amount of time and outputting a fourth signal indicative thereof;
digital signal processing means for processing said second signal and comparing said processed second signal to a second predetermined voltage value, and for outputting a third signal when said processed signal exceed said second predetermined voltage value;
means for determining if said second signal is in an active state for at least a second predetermined amount of time and outputting a fifth signal indicative thereof;
and
means for outputting a ring trip detection signal when either one of said fourth and fifth signals are in an active state.

4 more elements

A method for detecting the presence an off-hook condition of a telephone connected to a ring line and a tip line when said telephone is in a ringing state and for connecting said telephone to a surge protection circuit when said telephone is in both said off-hook condition and in said ringing state, said ring line including a ring feed resistor connected thereto, and having a first and second sense resistor connected to opposite ends of said ring feed resistor, the method comprising the steps of:

a) determining if a voltage across said ring feed resistor exceeds a first threshold value and outputting a first signal indicative thereof;
b) receiving a first current flowing across said first sense resistor and a second current flowing across said second sense resistor and outputting a second signal indicative of a difference between said first and second currents;
c) determining if said first signal is continuously output for at least a first amount of time and outputting a third signal indicative thereof;
d) filtering said second signal to remove any high frequency components from said second signal;
e) comparing said filtered second signal to a second threshold value and outputting a fourth signal indicative thereof;
f) determining if said fourth signal is continuously output for at least a second amount of time and outputting a fifth signal indicative thereof;
and
g) determining if either one of said fourth and fifth signals are being output, and outputting a ring trip detection signal indicative thereof,
wherein said ring trip detection signal is indicative of said off-hook condition during said ringing state of said telephone.

6 more elements

Dependencies are inferred from the claim text.

Integrated ring detection circuit and power cross detection circuit with persistence timers

Life of this patent

Integrated ring detection circuit and power cross detection circuit with persistence timers

Life of this patent

Abstract

Claims20