Telephonic communications – Supervisory or control line signaling – Using line or loop condition detection
Reexamination Certificate
2000-03-17
2004-08-17
Barnie, Rexford (Department: 2643)
Telephonic communications
Supervisory or control line signaling
Using line or loop condition detection
C379S399010, C379S413000
Reexamination Certificate
active
06778663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to telecommunications, and, more particularly, to a method and apparatus for sensing current in a subscriber line card.
2. Description of the Related Art
In communications systems, particularly telephony, it is a common practice to transmit signals between a subscriber station and a central switching office via a two-wire bi-directional communication channel. A line card generally connects the subscriber station to the central switching office through a subscriber line. At the subscriber end, a telephonic device may be employed to establish communication with a remote user using the subscriber line. The combination of the telephonic device and the subscriber line is commonly referred to as a subscriber loop.
A line card generally includes at least one subscriber line interface circuit (SLIC) as well as a subscriber line audio-processing circuit (SLAC). The primary functions of the line card may include supplying talk battery, performing impedance matching, determining whether telephonic equipment is on-hook or off-hook, and handling ringing signals, voice signals, and testing signals.
Typically, a line card senses voice currents on the subscriber line by amplifying the voltage drops across resistors (commonly referred to as “sense resistors”) in series with the line driver. This technique, however, has at least one shortcoming in that the sense resistors create an excessive voltage drop in the subscriber loop, especially if large sense resistors are employed. Furthermore, handling these large voltage drops across sensing resistors requires use of voltage amplifiers, which require larger current draw from a battery supply or other such circuitry. One way to avoid the large voltage drops is to utilize smaller sense resistors. However, when smaller sense resistors are employed, the available signal is also small, thereby making the available signal more susceptible to noise.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method is provided for sensing current in a subscriber line. The method includes receiving a current signal from a driver capable of driving the current signal on the subscriber line, and generating a second signal in response to receiving the current signal, wherein the second signal is proportional to the current signal. The method includes receiving at least a portion of the current signal from a driver capable of sinking the portion of the current signal from the subscriber line, and generating a third signal in response to receiving at least the portion of the current signal, wherein the third signal is proportional to the portion of the current signal. The method further includes adding the second signal and the third signal to generate an output signal.
In another aspect of the present invention, a circuit is provided for sensing current in a subscriber line. The apparatus includes an output driver adapted to drive a current signal on the subscriber line, and first circuitry coupled to the output driver and adapted to generate a second signal in response to receiving the current signal, wherein the second signal is proportional to the current signal. The circuit includes second circuitry adapted for receiving at least a portion of the current signal, and third circuitry coupled to the second circuitry and adapted to generate a third signal in response to receiving at least the portion of the current signal, wherein the third signal is proportional to the portion of the current signal. The circuit further includes fourth circuitry capable of adding the second signal and the third signal to generate an output signal.
REFERENCES:
patent: 4406929 (1983-09-01), Pace et al.
patent: 5289359 (1994-02-01), Ziermann
patent: 5424662 (1995-06-01), Bonaccio
patent: 6226696 (2001-05-01), Lin et al.
patent: 6636116 (2003-10-01), Cameron
International Search Report dated Jun. 6, 2002 for International application No. PCT/US01/07995 Filed Mar. 3, 2001.
Barnie Rexford
Legerity Inc.
Williams Morgan & Amerson P.C.
LandOfFree
Method and apparatus for sensing current does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for sensing current, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for sensing current will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3304407