Apparatus and method for determining the state of a telephone line

Assignee: Intertex Data AB

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Filing: 1990-10-02

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Granted: 1992-08-18

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Expires: 2010-10-02

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Abstract

Abstract A line state detector for a telephone line tests a voltage derived from the telephone line by closing a switch in series with a voltage sensing circuit in response to a polling signal. A modem testing the line state go Off-Hook immediately after it finds that the line was in On-Hook state, so it can use a low impedance voltage sensor directly on the telephone line. Monitoring equipment will need a line state detector with high impedance, which can be achieved by a high impedance in series with a capacitor. The capacitor voltage can then be tested by a low impedance sensing circuit.

Inventors

👤 Karl-Erik Stahl

Bibliographic Details

Application Number —

Jurisdiction US

Data Source google_patents

Last Synchronized 2026-10-26 21:48

CPC Classifications

H; H04; H04M; H04M3/00; H04M3/22; H04M3/2272; H04M1/00; H04M1/82

Claims Analysis

Total Claims: 7

Claim 1

Independent Claim 88 words

Apparatus for determining the state of a telephone line, comprising: (a) a voltage sensing device having a current sensing device in series with a zener diode; (b) a normally open switching device connected in series with said voltage sensing device, said series connected devices being connected to a voltage derived from said telephone line; (c) means for closing said switching device in response to a polling signal; and (d) a ring detector circuit connected to said telephone line, wherein said ring detector circuit includes said current sensing device.

Claim 2

Dependent Claim 88 words

Claim 3

Dependent Claim 22 words

Apparatus for determining the state of a telephone line as specified in claim 1, wherein said current sensing device comprises an opto-coupler.

Claim 4

Dependent Claim 81 words

Apparatus for determining the state of a telephone line, comprising: (a) a resistor, (b) a capacitor, (c) means for connecting said resistor in series with said capacitor across said telephone line, (d) a voltage sensing device including a current sensing device in series with a zener diode, (e) means for connecting said voltage sensing device to said capacitor in response to a polling signal, and (f) a ring detector circuit connected to said telephone line and including said current sensing device.

Claim 5

Dependent Claim 81 words

Claim 6

Dependent Claim 81 words

Apparatus for determining the state of a telephone line, comprising: (a) an inductance, (b) a capacitor, (c) means for connecting said inductance in series with said capacitor across said telephone line, (d) a voltage sensing device including a current sensing device in series with a zener diode, (e) means for connecting said voltage sensing device to said capacitor in response to a polling signal, and (f) a ring detector circuit connected to said telephone line and including said current sensing device.

Claim 7

Dependent Claim 81 words

References Cited (Backward Citations)

US4220825A Cited

US4224478A Cited

US4433212A Cited

US4679229A Cited

US4987586A Cited

US4958371A Cited

US4845741A Cited

USPTO Annuity & Maintenance Windows

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1995-08-18	1996-02-17	1996-08-18	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1999-08-18	2000-02-17	2000-08-18	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2003-08-18	2004-02-17	2004-08-18	$7700.00	Window Closed / Lapsed

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