Battery switching subscriber loop interface circuit

Details Battery switching subscriber loop interface circuit Battery switching subscriber loop interface circuit

1998-05-15

2001-05-15

{haeck over (S)}mits, T{overscore (a)}livaldis I. (Department: 2741)

Telephonic communications

Subscriber line or transmission line interface

Power supply

C379S399010

Reexamination Certificate

active

06233335

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to semiconductor subscriber loop interface circuits (SLIC's) and, more specifically, the invention relates to power management of subscriber loop interface circuits.
Telecommunication systems employ access products (e.g., remote terminals or subscriber interface units) for interfacing with each individual subscriber unit. An access product may include a SLIC for performing two to four wire conversion, battery feed, line supervision, and common-mode rejection. Together the SLIC, subscriber unit, and interface lines (e.g., TIP and RING lines) form a subscriber loop.
In a subscriber loop, the subscriber unit is generally powered from the SLIC through the interface lines. Typically, the SLIC must deliver 3 to 5 volts DC to a subscriber unit (e.g., a telephone) for off-hook states and deliver −42.5 to −56 volts DC (i.e., open circuit voltage levels) for on-hook states. SLIC's are generally powered with a −48 V power supply and are backed up with a power supply of the same magnitude.
A SLIC may be of the type that applies a voltage signal to the TIP and RING lines in an asymmetrical manner as illustrated in FIG.
1
. For example, The SLIC may hold the voltage signal on the TIP line essentially constant (e.g., −4 Volts) while varying the voltage signal on the RING line (e.g., −4 to −44 Volts) according to a predetermined relationship between loop current and the load resistance (i.e., resistance across TIP and RING). The predetermined relationship may be constant current or constant voltage through an internal source resistance, either physically defined or simulated via feedback.
When installed, SLIC's are coupled to loads of variable resistance. The resistance being primarily a function of loop length. For short loop lengths (i.e., small resistance), the SLIC requires less than a conventional SLIC power supply to drive the subscriber loop. Excess power is dissipated in the output stages of line interface amplifiers on-board the SLIC. The power dissipation increases the SLIC operating temperature and decreases line interface reliability. Accordingly, the power management of SLIC's for widely variable loop lengths is a problem which has not been effectively solved since the inception of SLIC's over fifteen years ago.
Today, there is even a greater need for better power management and power reduction of SLIC's. In emerging telecommunication technologies, SLIC's are often installed in equipment that is located at a remote site not having access to a continuous power source. It is imperative for these technologies to have efficient and reliable SLIC operation.
In one known technique for power management, a SLIC is directly coupled to a conventional SLIC battery supply and coupled to second battery of the same magnitude through a discrete switch. To activate the discrete switch, a circuit detects loop voltage signals and compares loop voltage signals to an internal or external reference voltage. The circuit implementing this technique includes a loop voltage detect circuit, a comparator with hysteresis, two series high current bipolar devices (for switching), and an associated level shifter to operate the switches. In another known technique, the conventional SLIC power supply is replaced with a variable voltage power supply and complex switched mode power supply circuitry. In both techniques, the additional circuitry increases circuit complexity, size, density, operational temperature, and/or cost.
Accordingly, it is an object of the present invention to provide a novel method for efficiently powering a SLIC with a primary and a secondary voltage source.
It is another object of the present invention to provide a novel SLIC having a circuit for reducing the power consumption of the SLIC.
It is yet another object of the present invention to provide a novel SLIC having a circuit for automatically powering a subscriber loop by steering current to a secondary power supply.
It is still another object of the present invention to provide a novel SLIC having a circuit for varying the voltage of a secondary power supply as a function of the loop signals.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.


REFERENCES:
patent: 5511118 (1996-04-01), Gores et al.
patent: 5659608 (1997-08-01), Stiefel
patent: 5721774 (1998-02-01), Stiefel
patent: 5737411 (1998-04-01), Apfel et al.
patent: 5854839 (1998-12-01), Chen et al.
patent: 5881129 (1999-03-01), Chen et al.

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